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Opamps stage design questions

Discussion in 'Cases, Modding & Electronics' started by trodas, Jun 10, 2008.

  1. trodas

    trodas

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    Altrough I'm reasonably skilled moder of mainbords and GFX cards and all electronics stuff, I did not play into the audio field much.

    So I think I better ask these who know about my ideas how to modify a existing design.

    This one:

    [​IMG]

    Complete scheme:
    [​IMG]

    Input swichboard:
    [​IMG]

    As soon as the signal hit the switching part of the amplifier, it is shorted to ground with C99 cap, a 0.1nF one. I think this is completely unnecessary blurring of the sound, as capacitor in general act to prevent voltage changes, so it has to "blur" a little the amplitude to prevent fast and rapid changes of it.
    Do I get it right?

    Later the signal go thru a 0.9 resistor divider, witch is probably used to put some small load (11k to ground) on the audio source. Is this value optimal for the X-Fi equiped with LM4562 opamps...?

    What about keeping just ONE of these dividers and adjust it to the 0.68 as the result of two dividers (0.9 and 0.76) after themselves are in the end.
    The aim is less distortion in resistors - or even using a audio grade resistors such as Vishay Audio Resistors:
    diyAudio Forums - Vishay Audio Resistors

    I also fear that the combination of R and C components can create a slight RC filter that in the end make the "blur" effect of the C99 stronger a little. Right?

    After it pass thru the switch, here come another ground-shorting cap, a C1. Now with 0.33nF capacity.
    Why?

    Then come another resistor divider, this time 0.76 and directly after him a first decoupling cap, a C3 - 10uF 25V.
    As far as I understand audio, the blocking caps is necessary for the filtering of the DC offset. What if my X-Fi has very low DC offset? Is not no cap better for audio that ANY cap, even quality audio one?

    I think the C3 is entirely unnecessary one. I think only one decoupling cap in the whole spekers (or none) is best solution - and placed directly before the output amplifier.
    Right?

    And it get worse. Just after the opamp, there is another decoupling cap! A C9 - again 10uF 25V for all except CENTER and SW channels. First thing I did not like is that the capacity on the output is same as on input - should not be bigger? Maybe is the level of signal not that high still, but... it just did not feel right.
    Second thing I did not like at all is the fact that we already removed the DC offset before the opamp, so, why now? Sure, a badly balanced of sucking opamp could produce some DC voltage at the output, but... why not balance it better or remove it and use quality one instead that does not need second decoupling?

    I think with the LM4562 or perhaps better AD8599 I can remove these.
    Right?

    And right after the potentiometer we have another decoupling cap - a C13! In fact, he is in serial circuit with the C9, witch bring the ending capacity down to half... not to mention that with the huge resistance between then the impact on the signal can be high.
    I hope I'm wrong on this one, but... IIRC the most clean voltage filering is a RC way. Only with the problem that it's output voltage differ with different current - so current has to be always the same and stable...

    I think the designer of this speakers just put together the recommended way of the used circuits and then these double-triple decoupling caps are the result.

    Suggestions?
  2. lemonadesoda

    lemonadesoda

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    Ah trodas. You are *king* of power supply management capacitor mods :)

    I'm surprised you are asking these questions, esp. here. I would imagine very few TPU members are electrical engineers, but you never know. I'll watch this thread closely.

    Capacitors are used for purposes OTHER than being a "reservoir" to hold charge in a "DC circuit". Audio amp circuits are an interesting opposite, since here capacitors are being used in an AC circuit.

    I'm an amateur so here is my understanding of what is going on, but it is very possible I am not 100% correct:

    • C1/C2: a snubber (protection), you never know what residual charges might exist on the input jacks when you connect.
    • C3/C4: to decouple the input from the opamps or you will blow them.
    • OpAmp 4558D has been set up as an inverting circuit. http://webpages.ursinus.edu/lriley/ref/circuits/node5.html
    • C9/C10 are obvious. This is an audio circuit. The output should be AC. If its not, or it is biased, you dont want to amplify that bias or fixed DC in the output stage or you will saturate or blow the second stage.
    • C13/C14 are not so obvious on your zoom, but obvious if you go to the full schema. You need to decouple from the MIXED, SUBWOOFER take-out from the MULTIPLE inputs. And yes, this gives a second reason for C9/C10... you dont want to send a bias to the subwoofer circuit.
  3. trodas

    trodas

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    Heh, thanks. In fact, these are fairly easy and intuitive. The audio stuff is proving to be difficult to me :rolleyes:

    Exactly. A chance is a chance. Maybe I got some answers... maybe not.

    True. A DC offset removal is the case there.

    I tend to agree. Protection of RFI noise and stuff. Could be. But I prefer my shielded cables and not messing with stuff over blurring of my audio. I vote for removal. C99 and C1 are the case for left channel, please stick to the left channel only, when labeling caps ;)

    Yes, C3 is decoupling the left channel input. But what for? Opamps can't be blown with even like 200mV of DC offset. That is like 2V on the end, witch is not even going to clip my signal, as the opamps are powered from +/-12V = 24V (and 15.8V in other case) ...
    I vote to keep only ONE decoupling cap in whole amplifier and my vote is for C9. Just to protect the pot from amplified DC offset. That would create more noise too, but basicaly any pot create noise, so...
    Just not more :)

    True. Notice that there is excessive number of caps around him. C7 and C117 I mean. C7 is used to lower the opamp gain in higher frequency, so basicaly to prevent oscilation. Hi-Fists will vote to remove it for sure. Me too.
    C117 purpose is not clear for me now. I did not yet seen opamps scheme with cap equivalent to C117 ...

    But look. You already killed the DC offset before the opamp. If opamp produce one (in perfect world it should not), then it is crappy and should be replaced with better one, right?
    And okay, we do not live in perfect world and opamps produce SOME DC offset. But then you filter out with C9. Why again C13, just after pot...?
    This is IMHO engineering mistake done by connecting two recommended schemes w/o looking at the whole picture.

    I see no reason to C13 exist at all.
    You need to decouple what? The already decoupled signal? You gotta be kidding me :p
    What misex signal? In AC3 (and we are in AC3 only) we have just what we should have in those channels already. I did not quite understand why you taking subwoofer signal into considertion, when we are talking about LEFT signal only.
    I take that as attempt to defend a faulty scheme, unless you explain better. This is just does not make sense. Sorry.


    The problem

    Plaing with the amp, like tracing the signal, is very hard to do, almost extremly. It is even hard to diassemble, and can't really run in such state... that just added to the trouble...

    Nevermind, how to stop the opamps from oscilating is the question. I did not have any other opamps to do replacement ATM and for like weeks, till I can recieve the new/different opamps :(

    That is not good. Not to mention the aim was to improve the quality, so, use new opamps is the goal. Possibly AD8599 later, however it looks like the samples will took like a month (!) to get there, and I need 2 shipments - only 2 pcs per one... (likely 4 shipments, if I use AD8599 on X-Fi too...)

    So the question is, how to change the circuit to stop the oscilation from happening?

    ;)

    Shorting to ground? Not need. Unplugging the X-Fi is enought and there is silence then :D
    Suddently. Obviously the opamps are oscilating, why then hell I did not figure that out myself... :(

    X-Fi output DC offset measuring:
    --------------------------------------
    L: -190mV DC, 10mV AC
    R: -174mV DC, 10.2mV AC
    RL: -210.2mV DC, 10.1mV AC
    RR: -204.7mV DC, 10mV AC
    CENTER: -209.5mV DC, 10mV AC
    SW: -231.9mV DC, 10.2mV AC

    Good? Bad? Terrible? Usable?

    What does worry me is the constant output signal noise... I cant hear it, but around 5.2 to 5.6kHz signal is there... Even the X-Fi is not playing anything ATM. I used the X-Fi control panned to check on the signals, when mesuring AC voltage, then letting the card say "left, right, center..." is clearly visible on the scope :)

    PS. come to think, you are right. No capacitor removal (and certainly not AFTER the opamps) could trigger such noisy oscilations as I experiencing. Well, what about the C117 then? It is this a part of the "to be removed" stuff from the amp too?
  4. trodas

    trodas

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    Hoooray! I figured what I did wrong! :)

    It is very embarrassing, but these 10uF SMD ceramics I added to the opamps legs, well... I added them to the legs 1 and 5, not 8 and 4 ... :eek:

    No wonder the amplifier did not play well...

    So, when I figured this silly mistake made, I fixed it and - hoooray - it now play MUCH better. There is only one catch - it is still very noisy. There is, as soon as the amplifier is powered on (w/o connecting to my X-Fi), still noise in all channels :thumbdn:

    Much less that before, but there it is. So I put all my changes back. I give back all the ceramic blocking caps, even these for the opamps feedback (witch should not be there IMHO), and no change.
    So as last desperate attempt I even removed my voltage filtering caps, but quess what - no change at all. It is not these caps...

    Just instead of the original C9, C10, C35, C36, C61, C62, C52, C64, C3, C4, C29, C30, C55 and C56 10uF 25V CapXon crap caps I used Elna RFS 22uF 25V audio caps. (true, C52 is 1uF and C64 is 0.1uF by original design, but all these caps are used only for the DC offset filtering, so they can be bigger... at least C64 does not limit the bass line now..)

    And of course, instead of JRC4558 opamps are there now a LM4562 ones...

    So, can anyone tell me, how to get rid of this little (3x hoooray!) oscilation ... ? What about the C117? I never seen that capacitor in any design... and the C7 might also trigger the oscilation, right? :confused:

    I read some there:
    http://tangentsoft.net/audio/hs-opamp.html
    ...but I did not yet come to any practical solution. Help?

    A good example of opamp circuit:
    [​IMG]

    See? No C117 from my amplifier...
  5. lemonadesoda

    lemonadesoda

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    1./ I also dont know about C117 (other than it is 10pF). My guess is it is there to kill off hi-frequency stuff. Remember that if the op-amp is busy (not even saturated) amplifying stuff out of the audible range, it will create significant harmonic distortions within the audible range. Theres a lot of HF noise in a PC case or picked up through cables. Who knows, maybe even the "4558D" is a noisey opamp and needs help. I can understand the need to "crimp" what the op-amp will work on.

    2./ C9/10, there's a lot of LF noise created by a potentiometer (master vol). Perhaps this protects the op-amp from the feedback-stage being contaminated by this noise. (old amplifiers tend to crackle when turning the volume up or down... suggesting that perhaps these very caps have gone).

    3./ There's a subwoofer OUT that is fed WITHOUT sub IN, by MIXING left and right channels of front and rear inputs. There is a potential bias on the mix. C13/14 and C20/21 make sense due to this reason in addition to point 2.

    Interested to know more.
  6. lemonadesoda

    lemonadesoda

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  7. Oliver_FF

    Oliver_FF New Member

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    I'm no expert and i'm no electrician, but i've tinkered guitar amplifiers several times and made some effects pedals...

    Those JRC4558's.... they're legendary chips in their own right - they give a very warm noise close to that of valve amplifiers. I don't think the audio properties looked that good for them on paper, but something about them made them sound amazing. The first section of your circuit, leading up to the master volume control has a gain of 0 - i think it's there solely to give this warmer tone to the audio. It might be noisy or sounds poor, but it'll give it an amazing warm tone - sadly you might need to be a guitarist to notice it (I haven't had the honor of hearing one :()
    http://www.diyaudio.com/forums/showthread/t-67906.html

    My theory on C13... Pots tend to wear away fairly quickly as they get swiveled, to the point where the metal tracks start to wear away and you get places where you lose contact. This gives a horrible clicking/clacking noise when you pass over them. I'd say C13 is there to lessen the effect.
  8. trodas

    trodas

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    It is 100pF. 10pF is in the Chu Moy's example only.

    Good point. And indeed, it probably limit the HF noise... I come to no other conclusion also.

    Possible. I wonder if the 4558D is able to work at zero gain just thanks to these caps or not...

    Can't be, but C9 is IMHO for decoupling of the otuput. All opamps have some DC offset on output, so... this is only one cap I would like to keep.

    This amp does crackle too, when the pot is dirty in some anges...

    Can be, but not with the 5.1 AC3 output, where the bellow 120Hz noises is run to the SUB channel and hence are separated well before the signal reach DAC - much less anything else.
    Hence no reason for C13 at all.

    But this is IMHO not a case of AC3, hence C13 it not need. And consequently all the other caps in his position - look bellow, CENTER channel has a C5 there... with dangerously low capacity either...

    Thanks for the informative links, tough. I was not aware that the input resistor should be taken into the gain calculation. I wonder if this is still true, if the resistor is separated by the decouplig cap, C3 in our case... Probably not, hence the gain of the circuit is ZERO :twitch:

    Could be. Others seems to dislike the 4558 opamps:
    :rolleyes: I don't know. Given the noisy oscilations I can't judge much now... :eek:

    This is interesting... because the gain zero is what might cause all these oscilations! :twitch:
    And well, I would prefer the sound the way it should be. So, driving the end amplifiers directly from the X-Fi opamps perhaps? :D

    It still sounds terrible when the pot is starting to wear-out... so if C13 should prevent that, it is not doing it's job. Regardless, the pot noise is a AC spikes, mostly. That means they go easily (just as the audio signal already!) thru any cap.
    I still think it is more like puting the recommended schemes together and forgetting about the double-decoupling... :p


    Votage filtering for IC6, IC7 and IC8 - all channels input opamps in short, powered from +/-12V, now this is filtered:
    [​IMG]
    by 2x Panny FM 1000uF 16V ( P12366-ND ) caps.

    Voltage filtering on the opamps pins
    [​IMG]
    Done by 10uF 16V Murata X7R 1206 caps, ( 490-3911-1-ND ) 7x of them.

    No change in behaviour. Still the damn noise is there. Side note - upon powering the amplifier on, the noise seems to none, then sharply the amp become very noisy and then the noise get lowered to what it is for the rest of the time. That happen in like 0.3 sec.

    Is this significant?

    Another question - the opamp gain is determined by the R9 / R7 size ratio, right? In the Chu Moy's example this is 3.91 ...
    In the Genius case it is 1.
    Does that mean the opamps gain is ZERO?
    Should not that pose a problem for the majority of opamps?
    What is the minimal gain to keep the amp stable?

    As for trying the other opamps, well, does Fairchild NE5533 count as generic opamp?
    Fairchild Semiconductor - Site Search - Operational Amplifiers

    I just recieved 4pcs of the DIP8 ones today and - no change at all.
    In a desperate attempt to cure the problem, I even desolder the shorts I made on the input switcher, because the RR channel was sometimes nonpresent - eg. the contact is not good anymore there...
    No change again.

    To make things real simple, I included the switch part in the schematic and keep just the L channel in it:

    [​IMG]

    Comments? Suggestions? :confused:
  9. lemonadesoda

    lemonadesoda

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    I've now got to the limits of my knowlegde/guesswork. Sorry I cant help further.

    Q1./ What software are you using for drawing these circuit diagrams?

    Q2./ Please update this thread with your discoveries... I have found the discussion quite interesting and would like to learn more
  10. spud107

    spud107

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    do you think this needs shielding from rest of pc components? a cover from an old hd is a cheap/free solution i used:D
  11. trodas

    trodas

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    lemonadesoda - not to worry, I learning new things each day, working in audio field now :) I wish more people come and share the knowledge, but, you know...

    I did not draw anything. I used the pdf that come from Genius AND i just modify the scheme a bit in Photoshop :)

    Working on that and will keep this updated. You can learn a lot there: http://tangentsoft.net/audio/hs-opamp.html


    spud107 - I think that a little shielding could come handy. At least for the input opamps part of the box... I think I put a cooper sheet on the interior walls of the place where the input parts are. A proper shielding material like the TI SHIELD:
    http://percyaudio.com/
    ...will be much better solution...
    ATM I batting the noise, trough.

    ...and...

    Big success! :D

    I managed to quiet the R, L, RR and RL channels! :D At least for like 30% of the volume, witch is what I use daily. So, this is very good for me - if it was not that the center speaker brum is not gone ... (and subwoofer also product some noise, but at very low level, since the noise is like 5 - 6kHz and the subwoofer is optimized for much lower frequency anyway)

    What I did over the original schematic?

    Removed C117, C118, C119, C120, C121 and C122.
    Replaced the C7, C8, C33, C34, C59, C60 and C63 with 12pF caps (original 100pF).

    That almost instantly kill most of the noise from the R, L, RR and RL channels. Adding R100 resistors instead of C9, C10, C35, C36, C61, C62 and C64 seems to helped a bit too.

    No hearable pot noise as others suggested that this is why these caps are there in the first place.


    Current situation.
    -----------------
    The noisy center is VERY ANNOYING. However hear this - the the volume pot is at like 30% of volume, the R, L, RR and RL channels seems dead silent. But as soon, as I increase the volume, then the center channel noise quiet and all other channels become noisy...!!! :twitch:
    This is nuts.

    It, however, I think clearly demonstrate one thing. That the oscilation is happening because of the output resistance.

    I'm I right?

    Also caps size on the opamp output seems to play a role, too. Notice that I complain about the noise in the center channel most. (because at 30% volume are the other channels dead silent, so... even later I wand them to be silent at ANY volume, right now I want get rid of the noise at all costs - except for unpludging the center speaker, that it is :) ) Then notice the C5 cap capacity. 0.22uF for center output from opamp?! Are you kidding me! I want there 22uF 25V Elna RFS cap and I think it will stop the noise - at least in the 30% volume settings.
    Also notice the C116 cap - a 470pF one. It is NOT present in the recommended TDA 7360 schematic. I vote for removal... ;)

    Input resistances
    TDA 7269A - 20k (R, L, RR and RL)
    TDA 7360 - 50k (CENTER)
    TDA 7296 100k - (SUB)

    So, do I get it right that these input resistances are maybe too high, and that cause the oscilations, because high input resistance mean high voltage and that cause high feedback and that, possibly, cause these oscilations?

    I replaced almost all the audio decoupling caps with the Elna RFS 22uF 25V ones. All the input ones, and all four for the R, L and RR, RL channels. Can that be significant too?
  12. trodas

    trodas

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    Yesterday FedEx delivered the 4pc of RC4580 opamps and 4pc TLE206 opamps, listed my TI as compatible with NJM4558. Both produced very similar oscilation noise, so, no help. Probably not THAT compatible...

    So, I got the idea that I can make the opamps to run with like 10k load. That mean put a resistor 12k parallel to the 50k pot = 10 or 9.6k load resistance for opamp.

    I tried it for center channel first and the noise it did really limit a lot the oscilations for center channel, but only at given volume, so I tried it for all channells and it make matters a LOT worse after power-on, but in just a short while 10 - 15 sec the noise deacrease to level witch is very nice.
    Still noisy, but much more enjoayble. now.

    I also tried bump the capacity of C7 & siblings from the 12pF to 330pF, but no change. Maybe it is even slighly worser now... :banghead:

    Maybe the grounding is not perfect and the voltage supply suxx too? Dunno.
  13. lemonadesoda

    lemonadesoda

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    What kind of noise is this exactly trodas? Can you catch it on the scope? Can you describe the frequency.

    1./ Maybe it is a dirty power supply, and unstable or noise on VCC or VSS is giving you this problem. We've been looking at the inputs... but mabe the noise is on the powerline. Noise on VCC or VSS will come through directly onto output. Get a scope on the diode bridge. Cheap diodes?

    2./ Are you 100% sure the source (line in) is clean?

    3./ If you can scope the noise... see where it first appears. Again, you might be trying to fix something that isnt broken and the problem is later down the circuit. (Or higher up).

    4./ In your OP, I never liked that centre channel and how it was mixed. Perhaps take the centre OUT for a moment. Let's take out ANY cross channel mixing and work with individual channels to find root of noise.
    Last edited: Jun 27, 2008
  14. trodas

    trodas

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    Brum about like 5 - 6kHz. Constant one. Irritating.

    Sure. Scope says differently from what I think I hear. On the right speaker I says:
    AC - 115,9kHz, 97.5mV, DC - 163.7mV

    115kHz?!
    I hear something completely different.

    Possible. All caps used are known bad caps and not all are yet replaced, sadly...

    I dubt that now. There are 7812 and 7912 voltage regulators, a known good cap before them (Samxon KM 10 000uF 25V and two known bad caps after them (Su'scons 1000uF 16V) and then two good caps (Panny FM 1000uF 16V) and then two 10uF 16V X7R ceramic Murata caps on each opamp voltage input legs.
    No way in hell that there could be still noise. I could measure that with scope, tough.
    I can't wait to replace the Su'scon caps with Samxons, tough.

    Quite possible. However a good point to start with - I did not mess with them before and there was NO NOISE AT ALL.

    Nah. But it sound good in headset, tough.
    My X-Fi output is nowhere near great, true.

    X-Fi output DC offset measuring with LM4562 opamps
    ---------------------------------------------------
    L: -190mV DC, 10mV AC
    R: -174mV DC, 10.2mV AC
    RL: -210.2mV DC, 10.1mV AC
    RR: -204.7mV DC, 10mV AC
    CENTER: -209.5mV DC, 10mV AC
    SW: -231.9mV DC, 10.2mV AC


    Hmmm, but the problem started when I replaced the opamps... It is true, that at first, I got mistaken and put the 10uF 16V Murate X7R voltage filtering caps on pins 1 and 5 to ground, instead of 8 and 4... (I got it inverted, eh...)
    1 is first amp output and 5 is second amp inside of the dual opamp noninverting (+) input to ground...
    Do you think that the resulting noise CAN damaged something and my amp is still playing well, except for the noise? I dubt that, but this is easy to check - just unplug the opamps PCB from the amplifiers and try it power on :D

    I did not like or even understand this cross mixing at all. But you are wrong. The CENTER channel is not interconnected with anything. It is just the R, L and RR, RL with SUB channels. Someone should tell me ONE good reason why to keep the R157, R156, R111 and R109 there.
    Perhaps this is done to add the SUB channel some "feel" from these channels, but... I have a grave doubts about that and how this affecting the SUB ...



    WoW!

    NJM4558 operating current - 3.5mA typical ; 5.7mA maximum.

    What worry me is, that I can't find in the LM4562 spec what current it draw
    trodas: LM4562 - Dual High Performance, High Fidelity Audio Operational Amplifier

    But there I find: http://www.head-fi.org/forums/f6/stax-srm-001-mod-thread-277049/#post3536731
    That the LM4562 draw 5-6mA/amp - but it is double amp (10 - 12mA) and that is true, when "amplifier current draw when using 3.7V lithium batteries"...!!!

    While using +/- 12V voltages, then we talking probably a hell of more current!

    I see the guy claiming that LM4562 draw notably more that others - (whole amp= 500m ) while with TL082 it is just whole amp current draw is 320mA.

    So instead of the stuuupid R11 and R12 resistors and nonexisting D4 and D5 Zener diodes (they are NOT present in reality!) I slap a 7812 and 7912 regulators there and we see what happnen then.

    With the TO-220 package, they should do about 1000mA, so heatsinks is probably not yet required :)



    Work in progress update
    I used L7812CV and L7912CV from STMicroelectronics in TO-220 to make better and nicer the +/-12V voltage supply for opamps. Luckily, I check the datasheets.... the 7912 is NOT like the 7812 - eg. pins view from top is INPUT, GROUND, OUTPUT - the damn 7912 is GROUND, INPUT, OUTPUT...!!!

    And I'm NOT use ANY resistor now :) Recommended caps near these regulators are 0.33uF on input and 0.1uF on the output minimal. I used 1uF SMD ceramic on the input, and 0.1uF on the outputs of both ones. Soldered almost directly on the L7812 and L7912 legs.
    Replaced C49 from the cursed 10 000uF CapXon to Samxon KM - also 10 000uF, but 25V only, as it is only 16V on the cap top.
    Replaced C112 from bad cap Su'scon 1000uF 10V to Panny FM of same capacitance and voltage.

    But damn! Brum is not gone... even the voltages going to the opamps are now very nice, a -11.96V and 11.95V - VERY close, very nice... but the amp play now MUCH louder, so the resistors are obviously overhelmed with the replacement opamps current, so, this was a good change...

    Sadly no other changes. The amp still produce a lot of brum at start, and it slowly get away... as things heat up or what the hell...

    Time to revert most modifications in the opamps stage back to what things way. I keep the voltage filtering and new regulation as well, as the quality caps, but put back the C7 & spol. caps of 12pF values as that sound best and most quiet, IIRC.
    I consider the C117 & spol., but I would like it to keep off.
    I remove all the 12k resistors added on all the opamps outputs to ground.
    I put back C9 & spol.

    But if that does not fix things up, well... I'm out of ideas :eek:
  15. lemonadesoda

    lemonadesoda

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    When I refered to "centre", I wasnt clear. My mistake. Sorry.

    Look at circuit. There is a "mixing of L&R" to create a mono signal channel. It does this BOTH to Front and Rear inputs. Then it is mixed with "sub".

    [​IMG]

    OK, so something bad on SUB or SUB circuit will affect L&R front and rear, likewise, channel talk between Front and Rear.

    IMO you need to PULL that whole centre ("sub") channel mix thing. AND pull all unused inputs to GND. What a mess.

    Get the scope in and see what is happening on the OTHER channels, not just your main L&R.

    PS.
    "Brum about like 5 - 6kHz". Are you sure. Thats a high pitch. Not a brum. Check that, or record it and post it.
  16. trodas

    trodas

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    Good thinking! ;)


    Work in progress update
    I removed all the 12k resistors added on all the opamps outputs to ground.
    I put back C9 & spol. deblocking caps.
    Caps C41 & C42 are now nice Nichicons VR 4700uF 35V suxxkas.
    Caps C47 & C48 are now Rubycon XYF 1000uF 16V, taken from one old PSU for DVD player, looks genuine and sure better that Su'scons :)
    Replaced R89 and D8 (near C26, top right part of schematics, close to the front L/R repros) with a L7805 regulator, 1uF ceramic on input (16V cap and the voltage there as well) and 100nF on the output. PCB under R89 was very much darker, so I consider that as safe replacement. Also the output was like 5.3V and not 5V as it should be.

    Resulting changes.
    Removing the 12k resistors increased the noise level to the before-known situation. Not good, not cool. Caps have no change on the subject, only the C64 seems to put the bass line under control (it was weird, overblown and just blurred before...).
    I regret removing the resistors and I planing on puting them back to battle the noise.

    Still weird.
    It still act kinda weird. When I power the amp up, it lack the before-mod strong SUB kick, but very shortly a strong (oscilating?) noise come from all speakers, and it slowly fade (as things heat-up?) to more acceptable levels. Weird at least. Still lack caps to do complete recap and starting to fear the caps was not the issue, as from the main power caps only C37 & C39 remain as original bad caps...

    Futher testing.
    I'm somewhat confused that when I power the amp on my balcony, where I solder and work on it, there is no noise from the subwoofer. It might not be even when I power it on with all the speakers, because they simply produce too much noise, that I can't be sure about that. I'm sure about all the 5 other channels, tough.
    So first I power the suxxka w/o my PC/watercooling pump nearby and so on. No change.
    Then I got idea. I unplug the PCB with the opamps from the rest of the amp. That way, only the output stages are "in game" and they should be very quiet, no noise, as it was before? Right?
    Well, wrong.
    SUB and CENTER seems dead-quiet, but these L, R and RL, RR channels are full of - wait a minute - MUCH stronger noise that WITH the opamps (and resistors on their inputs to ground!) ...!

    What I think of that?
    I strongly beginning to suspect that when I at first connected the ceramic 10uF caps to the wrong opamps pins (1 and 7 to ground for all the there opamps), it has consequences. The oscilating noise was unbearable, true... So that lead me to question the TDA7269A amps.
    CENTER and SUB use different amps, but the L, R and RL, RR channels use the two TDA7269A ones. What if they are somewhat damaged, so they produce the noise all-by-itself? It is normal that amp produce so strong noise when not connected to any source? I doubt that, and at least CENTER and SUB are fine then.
    Their voltage filtering caps (C41 & C42) are quality new Nichicons from Digikey now, so... can't be a issue there.

    This would ALSO explain the noise in SUB and CENTER channel too. These channels are interconnected by R109, R111, R156 and R157, so the noise CAN get there by this way.

    It would ALSO explain why the resistors helped to battle the noise. Of course opamps does NOT need so low load, but if the noise come the other way, then these quiet it down for obvious reasons. 12k is reasonably low, so it helped...

    I think I should remove the R109, R111, R156 and R157.
    If that kill the noise from CENTER and the very little noise from the SUB, then these TDA7269A are damaged and replacing them fix the problem. Higher quality parts drop-in replacement (okay, I willing to add few components as well, but the basic pinout has to be the same) suggestion welcome.



    lemonadesoda -
    Well, but you was right ;)
    And this:
    Still stand valid.


    Definitively will do. But... what unused inputs you mean? These opamps are all used, every bit of them... so, what inputs?
    Regardless, these mixed channels are not connected with CENTER, witch is problem. If they are, then that would explain my problems, but they are seems not to be...


    The same sound if comming from all these speakers :( So, what is happening is probably the same crap... What I did not understand is the 115.9kHz. I think I hrear about 5 or 6kHz, but maybe it is much less... Time to record a sample of what is going on.
    I know, it is hard to describe. I think I record what is happening when powering the suxxka up.
  17. trodas

    trodas

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    This is a little attempt to show how the amp behave on power on and power off/on by remove control. Turn the volume up to get an idea what I hear now all the time...
    http://www.youtube.com/watch?v=iiPEJ2KgnQk
    lemonadesoda says thanks.
  18. lemonadesoda

    lemonadesoda

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    Thanks for the video.

    5-6Khz brum? My ass...

    That's a 100Hz sawtooth. Download a tone generator, great a 100Hz tone, play it, and then go "geee, OMG, thats main interference". (Possibly rectifier). Like I said, get a scope in, not just a voltmeter. Hunt it D.O.W.N. :)

    http://www.esseraudio.com/ttg.htm (random google)
  19. trodas

    trodas

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    lemonadesoda - well, you are welcome. Any input or suggestion what to try are most welcome, of course. I sort running out of ideas anyway.

    Now when I yesterday at night read this, I was like... wow! Why I never thing about blown-out rectifier from the initial failure when I place the ceramics wrong on the wrong opamps legs and the whole thing oscilate unbearably loudly!
    WoW!
    Even the slovak moder of these amps suggested replacing these rectifiering diodes with higher rated ones - so I was like - yea, that has to be it, you got it!

    So, luckily, I have 10 pcs of these 6A diodes 50V ( http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=6A05-TPMSCT-ND ) so I get right to it today. Took 8 pcs of them, yes, they are HUGE, and started with the B3 rectifier block, powering the TDA 7269A for the L, R and RL, RR channels. And... no change. Then I exchanged the rectifier block B1, powering the noisy center speaker and... no change at all.

    Damn. And it looked so so promising...

    Few scope ripple measuring on the amp.
    C37, C39 - 69.9 - 70mV AC ripple (+19, -19V on them)
    C41 - 41.5mV AC ripple (+29V)
    C42 - 38.9mV AC ripple (-29V)
    C49 - 31.2mV AC ripple (+16.2V)
    C45 - 0.6 - 0.7mV AC ripple (+12V)
    C46 - 0.6mV AC ripple (-12V)
    C26 - 0.8mV AC ripple (+5.04V)
    opamps IC6, 7 and 8 (+/-12V powered) on each 4 nd 8 pins has 0.9mV AC ripple
    opamp IC9 (+15.8V powered) has ripple 30.2mV on pin 8...! 100Hz ripple too, BTW.
    (still the sub seems to be quiet - at least very much, compared to the cursed center...)

    The center is weird anyway. At some point only the center speaker was noisy (not the L/R, RL/RR ones) and then I measured what is ON the speaker anyway and found this:

    CENTER speaker - 8.23V DC (!) and 6.4mV AC ripple, noisy. Weird.
    RIGHT speaker - 0.2mV DC, 0.9mV AC ripple, quiet.

    Errata :)
    I don't know how I made it happen, but my previous statement that the L/R and RL/RR speakers only made strong noise (much stronger that with opamps board presend) when the opamps board is disconnected was FALSE.
    When I unplugged today just the signal wires, all of them, the amp was quiet. In all channels. At least on balcony and when I have only one testing speaker that I just connect to different outputs...

    R109, R111, R156 and R157 are NOT even present in reality, much less connected. Same as, for example, the Zener diodes D7 and D8 drawn in dashed line box, are not present in reality in the amp, the resistors R109, R111, R156 and R157 are not present at all.
    What I like is that this somewhat confirm my determination to remove them - eg. I was right about them being unnecessary and possibly even bad for the sound...
    What I did not like is, that this mercilessly kill my idea about how the terrible noise is spreading to other channels... damn :mad:

    Reducing the noise.
    Since the 12k resistors in parallel to the main 50k pot surpressed the noise nicely to notably lower levels, I tought that I "quiet" at least the center. So from the output of C61 to the ground, I added the 12k resistor as before. And quess what. No notable change. Since before I had these resistors where w/o the cap, then I put it, next time, on the C61 input, not on the oputput - so it will be directly on the opamp, not only after the cap.

    This, together with the very high DC offset (8V?!) is sure a good hint to where to get the source of the problem, however... no luck. On the opamps outputs are very low AC ripple levels. VERY low...

    Making better ground for the opamps PCB.
    As part of attemt to cure the noise, it was suggested to make the grounding of the opamps PCB better. So, I took a nice, strong wire (originally a PC PSU black wire) and SOLDERED it to the ground on the opamps PCB as well, as on the back PSU/amps section.
    So upon diassembling, I need to unsolder it from the PCB first.
    No change at all. Sadly.

    Attempt to cure the 30mV AC ripple in IC9 opamp voltage supply.
    First I thought that the ceramic 10uF 16V Murata cap must be dead, so I desolder it from under the opamp and check and... it is fine. About 11.5uF capacity. So I solder it back and added another 10uF 16V Murata SMD ceramic cap on the legs of the added Samxon GC 470uF 16V cap shown there: http://img357.imageshack.us/my.php?image=geniussw51htcapaddedbk9.jpg
    (on the very same pic you can clearly see, that the resistors R109, R111, R156 and R157 are not present)

    Still, adding another ceramic does not fix the voltage at all, still about 30.2mV ripple there, in clear contrast to the 0.9mV ripple on other there opamps. Why is that, well, I don't know.

    From the ripple measuring on the power caps it is clearly visible that the C37/C39 give almost twice the ripple the new caps show. Su'scon caps are crappy bad caps, that is why. However the 30.2mV ripple on the 10 000uF Samxon KM 25V cap is present all the way to the CENTER amp - TDA 7360.

    I wonder why the Samxon GC did and the ceramic caps not help to make the voltage cleaner. This is beyond my understanding. Perhaps the better choice there will be some "softer" caps, that are also optimized for lower frequency, like Samxon KM or RS, or GF, or GK, or GT... Just not the superfast super-low-ESR ones.
    Perhaps time to try the Panny FM there, if they works so well on the other there opamps?

    I don't know.
  20. trodas

    trodas

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    Work-in-progress report.
    Todays I tried again to kill the cursed noise, and, well... What I did was that I put back the C117 & siblings and changed the C7 & siblings to the original 100pF value.
    Then I moved the 12k resistor that was quieting a bit the noise from center speaker from the output of the C6 to the input of the C6.
    Then I tried to fix the high ripple on IC9 opamp. While others (IC6 - 8) enjoy only 0.9mV ripple, thanks to the regulators and caps, this one is suffering at 32mV of ripple. I know, I know, power supply ripple rejection >80dB fix that, but I still did not quite like it. So... so the filtering cap Samxon GC 470uF 16V I changed the 1000uF 16V Panny FM and also added an another 100nF ceramic cap before the Panny FM one. On the bottom of the Panny FM cap is another 10uF Murata 16V X7R SMD cap and the last 10uF SMD Murata is on the opamp leg 8 against ground.
    Ripple get lowered to 27mV :D
    Next move - add a toroid L filter coil in the IC9 input voltage. I will kill the ripple on IC9, somehow!

    Then I tried the another opamps I get on my hands in meantime. A big thanks to French user pilli from diyaudio forums for sending my 4pcs of the NJM4558 opamps.
    So I put these original opamps into the almost identical circuit, and quess what. NOISE! Still the same, or... maybe even louder one. Damn!

    This confirming my belief that something must be damaged, somehow, when I placed the ceramic caps wrongly... because there was now not a significant difference between the circuit before I touch it, and now.
    Yes, the diodes on most of the power supply lines are now 6A, yes many caps are replaced for better ones, yes the 10uF CapXon bad caps are replaced with 22uF Elna RFS audio caps... but that it is. No other change. Well, okay, except these regulators providing clean voltage!

    I also tried the OPA 2132 opamps todays. Same terrible noise. Definitively no opamps change could cure that, I'm affraid.

    Opamps outputs voltage/ripple/frequency on no audio output from X-Fi
    -------------------------------------------------------------------------
    CENTER: -5,8mV DC, 18,6mV AC 33kHz
    RL: -3.0mV DC, 34mV AC 83kHz
    L: -1.8mV DC, 7.9mV AC 1.6kHz
    R: -1.8mV DC, 8.1mV AC 1.8kHz
    RR: -3.0mV DC, 33.8mV AC 81kHz
    SUB, first stage (IC8 pin 7): -7.2mV DC, 73.7mV AC 111kHz
    SUB, second stage (IC9 pin 7): 7.45V DC, 9.6mV AC 0Hz

    Interesting, huh?
    My X-Fi is a bit into the negative voltages, so that could be the source of them:

    X-Fi output DC offset measuring with LM4562 opamps
    ---------------------------------------------------------------
    L: -190mV DC, 10mV AC
    R: -174mV DC, 10.2mV AC
    RL: -210.2mV DC, 10.1mV AC
    RR: -204.7mV DC, 10mV AC
    CENTER: -209.5mV DC, 10mV AC
    SW: -231.9mV DC, 10.2mV AC


    X-Fi output DC offset measuring with AD8599 opamps
    ---------------------------------------------------------------
    L: -219mV DC, 9.5mV AC
    R: -205mV DC, 9.8mV AC
    RL: -209mV DC, 9.7mV AC
    RR: -205mV DC, 9.3mV AC
    CENTER: -210mV DC, 9.6mV AC
    SW: -232mV DC, 9.7mV AC


    Conclusion - X-Fi opamps stage design does produce the -200mV DC offset. That probably can be cured by just increasing the positive opamps supply voltage from 5V to 5.2 or 5.4V ...

    But the second stage of the SUB with the 7.45V is kinda interesting one. I did not pretend that I understand the circuit. If someone can, please... explain.

    I also again measured the voltages/ripple on the speakers.
    CENTER: 8V DC, 36mV AC 70kHz (next measuring show 13mV AC, 12kHz)
    RL: -122mV DC, 100mV AC 110kHz
    RR: -125mV DC, 105mV AC 112kHz
    L: -183mV DC, 86mV AC 119kHz
    R: -158mV DC, 42mV AC 70kHz

    I was a hell lot worried about the 8V DC on center speakers, but davmax is saying that this is normal, since the TDA 7360 is in bridge configuration and hence on pins 8 and 4 should be about half of the powering voltage, witch is almost 16V (very close to it) and half from that is 8V, so, it is okay then.

    Nothing still does not explain the noise.
    Moving the 12k quieting resistor on the C61 input seems to INCREASE the cursed noise. AND change it - before the move, most of the noise come from center. Now the noise from L/R speakers overshadow the CENTER noise, witch is sort of bad... definitively worser that before. The resistor had to go back on the C61 output.

    What if the output amplifiers are somewhat damaged and sending the oscilations back to their inputs...? Could that be a result from the misplaced ceramics 10uF caps?

    How to explain that the amp is quiet when only single speaker and output by output is connected to it to check the silence, when the opamps are disconnected?
    How to explain the terrible noise w/o opamps from L, R, RL and RR speakers when connected? And quiet center and sub at the same time?

    Damn, I'm lost.
  21. trodas

    trodas

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    Attempt to clean the IC9 opamp voltage. Since the change of filtering capacitor from Samxon GC 470uF 16V to Panny FM 1000uF 16V and added the 100nF ceramic bring down the ripple on the +16V IC9 voltage from 32mV to 27mV, I tried go futher todays.

    So I thought - what about LC filter? If I add a L coil, the voltage might be clean! So, I did. I made my first toroid filter, sadly the wire is 0.8mm thick (a bit too thick, IMHO):

    [​IMG]

    [​IMG]

    ...and result? No change in behaviour. And, what is worser, the voltage ripple on IC9 increased from 27mV to 28.3mV...!

    Damn!

    I thought things has to be better, but... Probably the coil impedance is too low for the 100Hz - or it might even help the ripple... :mad:
  22. trodas

    trodas

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    I think I found the bug - now just get a spare transformator for the Genius SW-5.1 HT to test this!

    Many people from the very beginning suggested ground loop problems. I was investigating the PCB, the wires... well, everything. Despite many any many hours and days spent on the relatively simple circuit I was not able to find any wrong conenction, wire or so. Much less on the seriously made grounds there. Regardless, yesterday I got a idea. I heard the transformator has fuses included INTO his body (!).

    So, what about if, when I at the start wrongly connected 10uF SMD caps on the IC6 - 8 opamps oputputs/-inputs caused, as I put it, "unbearable noise" ... I don't know what you guys are make off when someone say "unbearable noise", but believe me, it was so noisy, that is was unbearable as I put it. Now that could cause the meltdown in the transformator, because believe me or not, that was not something (considering the decibel levels) you experience on the concert of rock band - that was MUCH louder, it was as I put it - unbearable... seems the repro and the TDA circuits make it, but the transformator give up.

    When I saw how thick the cooper wires are, well, I said to myself - this is impossible. The TDA must be melted well before these wires give up. But still, since the transofmer is connected to the rest of the circuit (except for the AC mains) by connectors - I unpluged it and measured the voltages.

    I had a hard time explaining this to my friend (or ex-friend?) Davmax who told me that I'm crazy, however... I better draw what I measured to explain it better:

    [​IMG]

    I marked the wirings by the Gretz bridges labels where they will go then in the complete schematics:

    [​IMG]

    Now as you guys probably agree, the B1 wirings should NOT have shown any voltage against the middle of B2 wiring, UNLESS connected to the Gretz bridges and PCB itself. It should "hang in air" and did not show significant voltage. But because it does, I bet that somewhere inside of the transformator a solder was melted, when the ouput was so crazy high thx for my mistake and hence I bet that this cause shortcut somewhere...

    By looking what all the B1 wirings powering and seeing that all these circuits behave weirdly since then - I think I found the bug. It is NOT the fuses, I checked:

    [​IMG]

    So, who know, where to get a transformator from bad Genius SW-5.1 HT subwoofer? The type precisely go as follows:

    CTP-10311U-2
    INPUT-AC 230v/50Hz
    OUTPUT-AC 28VCT/2.4A & 12v/1A & 40VCT/1.2A
    TEMP FUSE M330F
    TYPE FUSE 3.15A/250V

    Anyone?



    PS. pictures of my mods for your viewing pleasure:

    My modification for the better opamps power +/-12V - instead R11/D4 and R12/D5 are L7812 and L7912 used:
    [​IMG]

    Exchanging the diodes for 6A ones - you can also see added filtering by 1000uF 16V Panny FM cap for the CENTER TDA 7360 amp withch reduced the noise significantly!
    [​IMG]

    Situation around TDA 7296 - SUB channel, caps almost all changed to Panny FC, for audio are used Elna RFS and added 2x 330uF 35V Panny FM for better voltage cleaning and support :)
    [​IMG]

    Powering of the L, R and RL, RR channels are getting better diodes too, in the back you see added two Panny FM 470uF 25V caps, in fround Panny KG 0,1uF and L7805 instead of resistor and Zener diode for 5V...
    [​IMG]

    Second from these L, R and RL, RR channels - again two Panny FM 470uF 25V caps, in front you can see added C83 cap that marketing removed and that is used to filter the mute voltage.
    [​IMG]

    L, R and RL, RR channels still using the main caps as Su'scons (Samxon 6800uF 25V caps did not made it yet)
    [​IMG]

    Bottom of the PCB - how I added these two L7812 and L7912 regulators for the +/-12V opamp power - holes after them are ready for 1N4001 diodes
    [​IMG]

    The bottom way of adding the filtering caps for the TDA 7269A amps L, R and RL, RR channels
    [​IMG]

    Bottom look at added L7805 regulator instead R89 and Zener diode D8
    [​IMG]
  23. trodas

    trodas

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    Work in progress update - sumarizing what I did
    - replaced all electrolyte caps, all audio one are 22uF Elna RFS 25V ones now
    - replaced all rectifiers diodes to 6A 50V ones
    - replaced all the regulators with zener diodes, using 7805, 7812 and 7912 chips
    - added the last missing 1N4001 diodes tor the "latch-up" troubles, as datasheet suggest
    - completely reworked the opamps section, new OPA 2132 opamps utilized, added many voltage filtering caps
    - added 10uF 16V SMD ceramic on the voltage legs / ground of the TDA 7360 (CENTER channel, datasheet suggest 100nF)
    - added two 10uF 50V SMD ceramic on the voltage legs / ground of the TDA 7296 (SUB channel, datasheet suggest 100nF)
    - replaced the center amp, TDA 7360 to a new one

    Results.
    The damn noise is just a bit stronger, not fixed at all. I fear that the "sharper" more intimidating noise is result from the added ceramics to the TDA CENTER/SUB channels amps, resulting in way better / sharper amps characteristics - witch is why I felt the noise as increasing.
    Can be also that the center TDA 7360 need burn-in time.

    So far, this is very depressive result.

    Next move?
    Well, it is then either the two TDA 7269A for L/R and RL/RR channels, or the TDA 7296 in SUB channel. Hence I think that I will start with the TDA 7269A, because they was emiting the very strong noise, when the whole opamp section is diconnected, so...
    They can be the culprit.
    Also I pick them, because they has few legs and hence are easier to desolder and replace... ;)

    Any suggestions?
  24. paulktreg New Member

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    Hello Trodas

    On here as well!

    Regards

    Paul

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