Big success! 
I managed to quiet the R, L, RR and RL channels! 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...!!! :wired:
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?
I managed to quiet the R, L, RR and RL channels!
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...!!! :wired:
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?
trodas said:
Capacitors act like inductors. Inductors act like capacitors.
At some frequency a component acts more like an inductor, at another frequency it acts more like a capacitor. This is why you can make a radio with just a coil and a diode. The coil is capacitor and inductor at the same time.
Why not read The Art of Electronics by Paul Horowitz and Winfield Hill? There's some digital stuff in there too...
w
wakibaki -
True. These frequency characteristics are properly described in the pdf datasheet linked above and as you can see, these Murata X7R SMD ceramics act like caps even way up in Ghz clocks.
Hence even theoretically your point is right, in reality it fall short, as we talking about low-frequency audio application. We aren't building there a satelite reciever pre-amp
That is where it is valid that short to ground is not short, if it's lenght is above the wavelenght
All I was asked was, why one should lower so much the capacity of ceramic voltage filtering caps near to the opamps legs, according to some people AND quite in contrary of what was verified countless times in the overclocking game.
Eg. the more capacity in ceramics near the legs of CPU/chipset/GPU, the better. I even measured the differences in few cases
So by my experience, these people are dead wrong.
Witch is maybe why they did not want to answer...
Iain McNeill - well, if you are driven by the noise comming at you from your center speaker, located less that 2 feets from you, you will sure run fast!
And you did not seems to understand what I write. I made the change that I put back the 7, C8, C33, C34, C59, C60 and C63 with 12pF caps (original 100pF), keep out these C117, C118, C119, C120, C121 and C122...
...and at about 30% volume setting the oscilations for the R, L, RR and RL channels seems nonexistant.
At the same moment, the CENTER channel oscilate like mad!
When I change the volume to 100%, the CENTER channel STOP oscilating and being noisy, but at the same time the R, L, RR and RL channels start oscilating.
I think the modern opamps does not like higher resistance load that like 10k (10k as maximum value for output voltage swing was mentioned in all the NJM4558 or LM4562 datasheets, tought the NJM4558 mention 10k and higher, while LM4562 datasheet says only RL = 10k ... ) ...
That would explain why the oscilation differ on different volume settings as well, why some channels differ from others.
Input resistances
TDA 7269A - 20k (R, L, RR and RL)
TDA 7360 - 50k (CENTER)
TDA 7296 100k - (SUB)
At the output of the opamps are always the 50k resister pot to the ground. 50k is way too much and to me it looks like I should add a 12k resistor in parallel to it for each channel, and that should give the opamps the required 10k load (9.6k in fact) and hence they should be happy now.
First I test that on center channel, that should be kinda easy job too
True. These frequency characteristics are properly described in the pdf datasheet linked above and as you can see, these Murata X7R SMD ceramics act like caps even way up in Ghz clocks.
Hence even theoretically your point is right, in reality it fall short, as we talking about low-frequency audio application. We aren't building there a satelite reciever pre-amp
That is where it is valid that short to ground is not short, if it's lenght is above the wavelenght
All I was asked was, why one should lower so much the capacity of ceramic voltage filtering caps near to the opamps legs, according to some people AND quite in contrary of what was verified countless times in the overclocking game.
Eg. the more capacity in ceramics near the legs of CPU/chipset/GPU, the better. I even measured the differences in few cases
So by my experience, these people are dead wrong.
Witch is maybe why they did not want to answer...
Iain McNeill - well, if you are driven by the noise comming at you from your center speaker, located less that 2 feets from you, you will sure run fast!
And you did not seems to understand what I write. I made the change that I put back the 7, C8, C33, C34, C59, C60 and C63 with 12pF caps (original 100pF), keep out these C117, C118, C119, C120, C121 and C122...
...and at about 30% volume setting the oscilations for the R, L, RR and RL channels seems nonexistant.
At the same moment, the CENTER channel oscilate like mad!
When I change the volume to 100%, the CENTER channel STOP oscilating and being noisy, but at the same time the R, L, RR and RL channels start oscilating.
I think the modern opamps does not like higher resistance load that like 10k (10k as maximum value for output voltage swing was mentioned in all the NJM4558 or LM4562 datasheets, tought the NJM4558 mention 10k and higher, while LM4562 datasheet says only RL = 10k ... ) ...
That would explain why the oscilation differ on different volume settings as well, why some channels differ from others.
Input resistances
TDA 7269A - 20k (R, L, RR and RL)
TDA 7360 - 50k (CENTER)
TDA 7296 100k - (SUB)
At the output of the opamps are always the 50k resister pot to the ground. 50k is way too much and to me it looks like I should add a 12k resistor in parallel to it for each channel, and that should give the opamps the required 10k load (9.6k in fact) and hence they should be happy now.
First I test that on center channel, that should be kinda easy job too
The op-amp 10K load in the data sheet is the value at which it is tested. It is NOT a min or max value.
All op-amps will work fine without a load, so I don't know where you get the max 50K problem from. Illogical.
As I said earlier, lots of people here would like to help you but it is difficult to know where you are at. So far, you have taken a functioning unit and ruined it by
1) changing things without understanding
2) changing more than one thing at a time!
Why don't you put it all back as it was and discuss each change, one at a time, BEFORE you reach for a soldering iron.
Some of your understandings about caps, CRs and op-amps are just plain wrong, based on what you say.
All op-amps will work fine without a load, so I don't know where you get the max 50K problem from. Illogical.
As I said earlier, lots of people here would like to help you but it is difficult to know where you are at. So far, you have taken a functioning unit and ruined it by
1) changing things without understanding
2) changing more than one thing at a time!
Why don't you put it all back as it was and discuss each change, one at a time, BEFORE you reach for a soldering iron.
Some of your understandings about caps, CRs and op-amps are just plain wrong, based on what you say.
trodas said:
- well you certainly won't be anytime soon anyway.
Try to imagine for a moment that you might be wrong.
If your experience wasn't so limited, you'd know that while what you say may be true of the particular Murata caps you cite, that as a general rule for all capacitors it is not, and you'll find anyway that it is true even of the Murata caps within their range. Look how the frequencies change with capacitance.
You think because you overclocked a motherboard you gonna come over here and tell us all how it's done. We all sitting here looking at your posts thinking, "What a dumb feck!"
Everything a digital engineer does in hardware, an analog engineer had to do first.
w
You need to put a scope on the op-amp outputs and see whats going on. I suspect HF oscillation due to parasitics.
Replace C117-122. These prevent oscillation.
You really need to see what's going on. You're just guessing at what you think is going on without the knowledge of why the designer put the parts in for a reason. There will be a reason for every component - designers don't put parts in a design for no reason.
Do you have a scope?
Replace C117-122. These prevent oscillation.
You really need to see what's going on. You're just guessing at what you think is going on without the knowledge of why the designer put the parts in for a reason. There will be a reason for every component - designers don't put parts in a design for no reason.
Do you have a scope?
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...
Maybe the grounding is not perfect and the voltage supply suxx too? Dunno.
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...
Maybe the grounding is not perfect and the voltage supply suxx too? Dunno.
I get the 10k load from tadasheets, just check them.
But looks like you are right, they can go up a lot... But...
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: http://www.national.com/pf/LM/LM4562.html
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
But looks like you are right, they can go up a lot... But...
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: http://www.national.com/pf/LM/LM4562.html
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
janneman - to me it looks like it IS changing with the voltage supply:
Sadly no table that show current draw with +/- voltage supply. I think the +/- 12V equals roughtly 24V supply, and this is then like 12mA or so.
Considerably higher current draw that the NJM4558 has.
It is noticably more that NJM4558, so... I probably add a better grounding wire AND the regulators instead of resistors. Wish me luck.
An externally hosted image should be here but it was not working when we last tested it.
Sadly no table that show current draw with +/- voltage supply. I think the +/- 12V equals roughtly 24V supply, and this is then like 12mA or so.
Considerably higher current draw that the NJM4558 has.
It is noticably more that NJM4558, so... I probably add a better grounding wire AND the regulators instead of resistors. Wish me luck.
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.
oshifis -
Heh. I probably already did. It is "loudest noise comming from amplifier" or "worsest dB ratio"... Actually this is no anymore about the difference between signal levels of noise and signal - but more likely now about between the signal and noise...
AndrewT -
You could be right. But check on the maximal ouput current as well, 26mA. That is on the top of the 10mA, probably.
Each way around, there was SIGNIFICANT, at least 2x higher (if not more) volume after I added these 7812 and 7912 regulators AND kicked the R11/R12 off the amp.
So that was a good idea and good change in the end. However the resistors should be keept there... the noise is not significantly higher
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.
oshifis -
Is it something similar you want to achieve with your current project?
Heh. I probably already did. It is "loudest noise comming from amplifier" or "worsest dB ratio"... Actually this is no anymore about the difference between signal levels of noise and signal - but more likely now about between the signal and noise...
AndrewT -
You could be right. But check on the maximal ouput current as well, 26mA. That is on the top of the 10mA, probably.
Each way around, there was SIGNIFICANT, at least 2x higher (if not more) volume after I added these 7812 and 7912 regulators AND kicked the R11/R12 off the amp.
So that was a good idea and good change in the end. However the resistors should be keept there... the noise is not significantly higher
Hey trodas
You could build a whole amplifier and put in really good stuff.
Seen this?.
Very simple, but should sound good. Or maybe a different one. There are lots of kits and designs on the web. Buy another amplifier for 5.1.
Speakers are fun to build. You can build really good speakers for a lot less than you can buy them. Fullrange (1 driver) speakers can be surprisingly good.
Or you can make a turntable and tonearm.
w
You could build a whole amplifier and put in really good stuff.
Seen this?.
Very simple, but should sound good. Or maybe a different one. There are lots of kits and designs on the web. Buy another amplifier for 5.1.
Speakers are fun to build. You can build really good speakers for a lot less than you can buy them. Fullrange (1 driver) speakers can be surprisingly good.
Or you can make a turntable and tonearm.
w
cliffforrest - hi, mate. What is your problem? I trying my best. I don't know yet what the problem is, but I working on in. How yours submission to the thread help?
wakibaki - thanks. No, I did not seen this. The guy is rather interesting moder. I heard about that the LMxxxx amps would be a much better choice that the TDA ones, but I don't know if some LMxxxx ones are pin compatible replacement...
But effectively - that is what I doing. Rebuilding the amp
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
wakibaki - thanks. No, I did not seen this. The guy is rather interesting moder. I heard about that the LMxxxx amps would be a much better choice that the TDA ones, but I don't know if some LMxxxx ones are pin compatible replacement...
But effectively - that is what I doing. Rebuilding the amp
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
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