| trodas |
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:
Complete scheme:
Input swichboard:
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:
http://www.diyaudio.com/forums/show...&postid=1535720
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? |
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| Iain McNeill |
My thought is you do actually need all those components.
C1 is ESD and RFI filtering - more essential every day!
C3 is input decoupling - at your discretion.
C9 and C13 are needed to stop loud pops from occuring if the pot wiper momentarily disconnects from the track such as when if rides over a bit of dust or fluff. |
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| wakibaki |
| quote: | Originally posted by trodas
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? |
Modding analog circuits is a bit different from computer stuff, where voltages are frequently compatible across equipments and many 'mods' are software based anyway.
Analog circuits often behave in ways which are non-intuitive. Most people find that some years of study are required to acquire a basic understanding. In fact most electronics graduates leave university after 3 years with no clear understanding of how to build a transistor amplifier.
After you get some real understanding of what is going on is plenty soon enough to start modifying stuff, unless you are simply implementing modifications designed by someone else or substituting higher quality components. Even this can contain traps for the unwary. Changing components on the basis of half-understood ideas will almost certainly result in poorer performance if not complete economic destruction of the unit.
Doing things the recommended way is the recommended way of doing things.
Right?
w |
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| trodas |
Iain McNeill -| quote: | | My thought is you do actually need all those components. |
I hope not, as they obviously killing the audio quality... :)
| quote: | | C1 is ESD and RFI filtering - more essential every day! |
But it also kill the quality of audio signal. I prefer my shielded wires :D (sme goes for the C99 that is not in the zoomed schematic, but if you look at the switchboard scheme... there you go)
| quote: | | C3 is input decoupling - at your discretion. |
I think unnecessary. I would decouple the signal and kill DC offset just before the amplifier - at C13 position. A Elna RFS 22uF 25V seems to be good for the job.
I think that even like 2V DC offset after the opamp is not going to clip my signal at all, when powering the opamp from +/- 12V lines, so...
| quote: | | C9 and C13 are needed to stop loud pops from occuring if the pot wiper momentarily disconnects from the track such as when if rides over a bit of dust or fluff. |
You sure? I think it is just a decoupling and the designer just took the recommended circuits for opamp and the amp and put them together, not realizing that he create triple decoupling...
wakibaki -| quote: | | Modding analog circuits is a bit different from computer stuff, where voltages are frequently compatible across equipments and many 'mods' are software based anyway. |
Well, almost all my mods are HW based anyway. Just check there:
http://capsmod.net/forum/viewthread...&extra=page%3D1
http://capsmod.net/forum/viewthread...&extra=page%3D2
http://capsmod.net/forum/viewthread...&extra=page%3D2
http://capsmod.net/forum/viewthread...&extra=page%3D1
http://capsmod.net/forum/viewthread...&extra=page%3D1
http://capsmod.net/forum/viewthread...&extra=page%3D1
http://capsmod.net/forum/viewthread...&extra=page%3D1
http://capsmod.net/forum/viewthread...&extra=page%3D1
http://capsmod.net/forum/viewthread...&extra=page%3D1
http://capsmod.net/forum/viewthread...&extra=page%3D1
http://capsmod.net/forum/viewthread...&extra=page%3D1
http://capsmod.net/forum/viewthread...&extra=page%3D1
http://capsmod.net/forum/viewthread...&extra=page%3D1
http://trodas.wz.cz/index.php?act=ST&f=16&t=337&s=
However the problem is, that capacitors in computer circuits are straight-forward used for voltage filtering. And there you almost can't screw things up, when replacing caps with better ones... with capacitance as well as specs bump.
Audio seems to be totally different horse.
At least I think I understand the voltage filtering part of the amplifier. Except for that there: http://tangentsoft.net/audio/hs-opamp.html
I read that the recommended voltage decoupling ceramic caps near the opamps pins is 0.1uF and one "need to go down to 0.01 µF for faster op-amps" :confused:
I don't understand. I would like 10uF X7R Murata ceramics there! The specifications of ceramic SMD capacitors todays did not change much (if at all) with the increasing capacity. Hell, it is possible to buy a 100uF 6.3V 1210 size SMD ceramics now! (almost $4, but you can)
So, since I don't know about anything that could prevent this 10uF capacitor to filter well even in the Mhz range (specs looking damn good http://search.murata.co.jp/Ceramy/i...A18X/C2ED01.pdf ) ...
So, why not use 10uF caps on the opamps legs?
| quote: | | Analog circuits often behave in ways which are non-intuitive. Most people find that some years of study are required to acquire a basic understanding. In fact most electronics graduates leave university after 3 years with no clear understanding of how to build a transistor amplifier. |
Good point. I have an idea, but dunno if that will work ;)
| quote: | | After you get some real understanding of what is going on is plenty soon enough to start modifying stuff, unless you are simply implementing modifications designed by someone else or substituting higher quality components. |
Well, I just wanted basically to do that... but looks like the opamps started to oscilate :(
| quote: | | Even this can contain traps for the unwary. Changing components on the basis of half-understood ideas will almost certainly result in poorer performance if not complete economic destruction of the unit. Doing things the recommended way is the recommended way of doing things. Right? |
Well, that is why I asking there about opinions to get the recommended ideas - and modify them, of course. But I must say I thought it would be far more simple...
I get the precise DIP8 sockets, so I thought - what the hell - let's start doing first steps on the speakers. The first step was cut legs of all the 4 opamps, desolder the rest, clean holes, solder sockets. Push the LM4562 opamps inside. Looking great! :D
I wanted to do things by small steps, so when something went wrong, I know what I had done, but... when I start soldering, I sometimes don't know when to end. So I removed and shorted C9, C10, C35, C36, C61, C62 and C64. All opamps output DC offset filtering caps... and all the unnecesary ones, because later are the C13, C14, C20, C21, etc.
I remember czech guy recommending some mods on these speakers speaking about how the C64 0.1uF (!!!) capacity kill the bass of the thing, so a 22uF audio cap should be there.
Nevermind.
When I was in action (again, small steps... damn), then I took 7 pcs of 10uF 16V SMD Murata caps and solder them between pin 8 and 4 and ground for IC6, 7 and 9. For IC9, as it is powered from only positive voltage, only between pin 8 and ground (pin 4 in this case).
I measured and double-checked no shortcut was made by this.
And if meddling with computers teach me something, it is, that clean voltage is required and what better way to get the best voltage that add filtering caps - elyte ones on the voltage line, and ceramic as close to the pins of the IO in question, as possible.
Maybe 10uF is overkill?
Regardless, I was thinking about the C99, C100, C101, C102, C103 and C104, but I did not touched them ATM. Instead I soldered a six wires between the pins of the switcher, so the audio will be taken only from the 6 channels input now. I have no desire to use any other inputs, so...
So I double check again for shortcuts and power on the speakers - first w/o anything. Sounded good, the start "boom" was very small, a improvement? Then connected thru the cable hell and... DAMN!
A very strong noise from all the channels! WTF! :rolleyes:
Switching to the other inputs (just for show now) seems to lower the noise a little, maybe because only 2 inputs are taken into consideration? Dunno.
Regardless, when I unplug the X-Fi, everything is fine. The X-Fi itself play well, tested on headphones I wearing now, but... as soon as I connect any signal to the speakers, the noise happens.
So I hought that by hard-wiring the switcher I was connected something (how that can be, lol) to the signal path that is picking the noise, so I removed the shorts.
And no change :(
Then I get another idea. The C7 can go too, because it only limit the opamp gain on high frequency (that should prevent the oscilation in the first place!) and as I look at it, it can very well ALSO cause some oscilations like these (looks to me the noise existing in input is amplified a lot?), so... I removed all these, that mean C7, C8, C33, C34, C59, C60 and even C63.
Also I finally move on the inputs and removed the C99, C100, C101, C102, C103 and C104.
Any no change again :(
Next thing to try - remove the C117 and all corresponding caps... or you guys got better suggestions?
Sadly I can't try back the original JRC4558 ones to see if they will oscilate or not... I cut their legs in order to prevent desoldering damage to the PCB... :rolleyes: |
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| unclejed613 |
the reason for decoupling the volume control pot is quite simple... it's a very bad idea to have any DC across the volume pot, because it causes the carbon particles in the element to generate noise. the DC isolation is for the potentiometer, not the op amps. also your comment about resistors creating distortion, only applies to carbon composition resistors. metal film and carbon film resistors don't create distortion, though carbon film resistors are a little bit noisier than metal film. it would have been better if they had the pot in the opamp feedback loop. that would make the gain of the opamp variable, and they could have eliminated those "extra" capacitors.
the 100pf and 330pf caps across the inputs are to keep RF out of the input stages, because RF can cause some nasty sounding side-effects.
most engineers designing consumer electronics will not add unneccesary components to a circuit, because they must design first and foremost with cost in mind. that is why so much stuff on the market has a lot of "shortcuts" in the design, using the cheapest electrolytic caps, running 1 amp devices at 950mA, using 5 watt resistors to dissipate 4.9999 watts of heat.
the fact that there are so many caps in this design (more than i'm used to seeing) means that this was a squirrely design to begin with, and had to be "tamed" with bypass caps on the op amp inputs, integrating caps in the feedback loops of the op amps. and there are some caps missing from where they should be. zener diodes are somewhat noisy creatures, and 99% of the time should have bypass caps across them. |
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| wakibaki |
| quote: | Originally posted by unclejed613
most engineers designing consumer electronics will not add unneccesary components to a circuit
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Actually, once you've got it working, it's not that uncommon when cost reductions are required, or even before, to mess around seeing what you can take off before it stops working.
trodas, the Universe has seen fit to instruct you in some of the most fundamental engineering principles: -
1) If it ain't broke, don't fix it.
2) Only change one thing at a time.
I would have thought that even a digital modder would have known these...
w |
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| trodas |
unclejed613 -| quote: | | it's a very bad idea to have any DC across the volume pot, because it causes the carbon particles in the element to generate noise |
Good point. But a AC signal is basically half-full of DC, so, no help there. The signal still has to pass thru the potentiometer...
| quote: | | metal film and carbon film resistors don't create distortion |
Vishay claim othervise:
http://www.diyaudio.com/forums/show...&postid=1535720
...and I would believe them.
But the main problem I have with this explaination lies in C13. When we have the DC offset gone thanks to the C9 - why add another decoupling cap just after the pot?!
wakibaki -| quote: | | 1) If it ain't broke, don't fix it. |
Well, it IS broken. Now... :))) And I wanted to improve the speakers, so... I had to mess with them. At least I learn something... :)
| quote: | | 2) Only change one thing at a time. |
Good point. Who would thought that this will be so hard. I just replaced opamps and... things go wrong :o
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 ... :o
No wonder the amplifier did not play well at all...
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 I removed before, 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 **** 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 the noise is in other channels anyway...)
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:
See? No C117 from my amplifier... |
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| Nordic |
lol, I tried modifying a sound card once... it had 10uf lytics on that were the size of rice.... so I replaced it with nice elna audio caps...
Well it played beautifuly for 2 minutes then died.. PC locks up if I try to put that card in now....
I have one soundcard that is pre windows 95, A terrasound something... now that sounds sweet... very strong output, feels like twice the output of regular cards... I miss the good old days. |
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| trodas |
Well, the circuit in question looks like this now:
Opamps nicely in sockets, all modifications reversed back to original. Still noisy. Not like 1:1 to the signal, as it was thanks to my silly mistake, but like 0.1:1 to the signal. Useless.
So todays work - add a voltage filtering caps missing in the design near the opamps:
This 470uF 16V Samxon GC suxxka is supporting now the +15.8V for the IC9 - a subwoofer-dedicated opamp.
No change. Noise from subwoofer still comming.
Later I added two pieces of Panny FM 1000uF 16V caps to filter these +12V and -12V for the IC6, 7 and 8 - eg. for the rest of the opamps.
Even I think I did good job, no change on the noisy behaviour.
So I started again (sigh) removing weird looking caps, started with C117, continuing on the C118, C119, C120, C121 and C122.
And quess what. No change at all. Still noisy, oscilating.
I beginning to think that these LM4562 was either damaged (but all of them? and also - audio is playing right now as I type and well, except the noise, of course) or too cranky to be used in this design.
What to try now?
Put back the 10uF 16V Murata X7R 1206 caps near each the opamps legs? Or use the much smaller values (0.1uF or even 0.01uF) as suggested there?
http://tangentsoft.net/audio/hs-opamp.html| quote: | | you may need to go down to 0.01 µF for faster op-amps |
I still not understand why use so small values, because as I look into the Murata specs, these ceramics go way up to GHz, regardless of capacity and when come to voltage filtering, then the more capacity the better...?!
If not help, then remove the C7 and siblings? (that mean C8, C33, C34, C59, C60 and C63)
And what if that does not change a thing? :( |
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| Iain McNeill |
| quote: | Originally posted by unclejed613
the reason for decoupling the volume control pot is quite simple... it's a very bad idea to have any DC across the volume pot, |
Exactly, and you have to deal with the output offset voltage of the input op-amp 4558, =C9 (which will get worse if you eliminate all coupling caps) but also the input bias current of IC3, =C13. These combined effectively prevent crackly pots for the life of the product. I'd be interested in hearing your ideas on how to retain this feature while eliminating the series caps.
Have you got a spectrum on the noise? You said:
| quote: | | And quess what. No change at all. Still noisy, oscilating. |
Is the noise tonal? That might indicate a different problem. I was thinking random broadband noise due to thermal activity. Some scope shots or preferably an FFT with a full scale tone for reference would tell you a lot.
Are you sure you haven't changed the gain anywhere? |
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| Iain McNeill |
| quote: | Originally posted by trodas
Iain McNeill -
I hope not, as they obviously killing the audio quality... :)
But it also kill the quality of audio signal. I prefer my shielded wires :D (sme goes for the C99 that is not in the zoomed schematic, but if you look at the switchboard scheme... there you go)
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Your shielded wires could add 0.1nF of capacitance if they're long enough. 100pF will roll off a 600ohm source at 2.6MHz so I'm not convinced this has any audible effect. It does however, provide great value against ESD and RFI, which I think should be mandatory in todays wireless, plastic world? |
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| Iain McNeill |
| quote: | Originally posted by trodas
No change. Noise from subwoofer still comming.
|
Sorry Trodas, I'm confused now. The noise is an oscillation in the subwoofer channel only? Could you give me a description of what you are hearing, I've been thinking of something completely different. |
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| trodas |
Iain McNeill - thanks for detailed response, man! ;)
| quote: | | you have to deal with the output offset voltage of the input op-amp 4558, =C9 (which will get worse if you eliminate all coupling caps) but also the input bias current of IC3, =C13. |
C13? The bias current is already decoupled by C9. C13 seems unnecessary at all to me.
| quote: | | These combined effectively prevent crackly pots for the life of the product. I'd be interested in hearing your ideas on how to retain this feature while eliminating the series caps. |
You sure? Because my volume pot is cracking anyway... :o So I can remove it w/o remorse :)
| quote: | | Have you got a spectrum on the noise? |
To me it looks (okay, sounds) like a steady "Hnnnnnnn" sound, I would quess it at around 1,5kHz or so. Scope says differently. On the right speaker I says:
AC - 115,9kHz, 97.5mV, DC - 163.7mV
115kHz?!
I hear something completely different.
| quote: | | Is the noise tonal? |
A little bit.
| quote: | | Are you sure you haven't changed the gain anywhere? |
I did not touch the resistors at all, but come to think... is not the gain ZERO? And can modern opamps handle that?!
| quote: | | Your shielded wires could add 0.1nF of capacitance if they're long enough. |
Luckily, they are not :D About 2m total, from X-Fi thru the amplifier...
| quote: | | 100pF will roll off a 600ohm source at 2.6MHz so I'm not convinced this has any audible effect. It does however, provide great value against ESD and RFI, which I think should be mandatory in todays wireless, plastic world? |
I still fear of the audio distortion by these caps. This is not just the C99, a 100pF one. There is also the C1 - a 330pF one...
| quote: | No change. Noise from subwoofer still comming.
Sorry Trodas, I'm confused now. The noise is an oscillation in the subwoofer channel only? Could you give me a description of what you are hearing, I've been thinking of something completely different. |
No, from all channels. That point was that I tried JUST the subwoofer ATM. In fact, the SUB channel is the quietiest one about the noise, because it does not like the frequency of it :D
So it is almost hard to heard it even from - while the other speakers almost scream... :o
Votage filtering for IC6, IC7 and IC8 - all channels input opamps in short, powered from +/-12V, now this is filtered:
by 2x Panny FM 1000uF 16V ( P12366-ND ) caps.
Voltage filtering on the opamps pins
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:
Comments? Suggestions? :confused: |
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| Iain McNeill |
| quote: | Originally posted by trodas
Iain McNeill
C13? The bias current is already decoupled by C9. C13 seems unnecessary at all to me.
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no, I mean the input bias current of IC3, the next stage. Get rid of the cap and there's an extra DC path for this current.
C13 blocks the input bias current of the TDA7269. Where else does it come from (the output of course) |
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| Iain McNeill |
I fear you are so focused on the tree in front of you that you have forgotten you are in a forest.
From what I can gather you have replaced the op-amps in an integrated sound system i.e. the pre=amp, power amp and speakers are all part of a single manufacturers product line family.
I don't see a relative measurement of the noise level from now to before any changes were made. My reading of your notes doesn't speak to the noise level before you started mods, only after. Was the noise always there?
If there are no answers then your only recourse is to replace the LM4562 with JRC4558D (easy now you got sockets) and get back to the zero noise condition. I think you took something important out. |
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| trodas |
| quote: | | C13 is for input bias current of IC3, the next stage - the input bias current of the TDA7269 |
Holly... you think the TDA7269 send considerably bias current even to it's inputs?! I never thought of that.
http://www.alldatasheet.com/datashe...S/TDA7269A.html
Non Inverting Input Bias Current - 500nA
I think the pot can handle that :D
| quote: | | I fear you are so focused on the tree in front of you that you have forgotten you are in a forest. |
Could be, with all the noise that is comming at me it is hard to think straight. Mainly I'm very ****ed that the opamps exchange that was supposed to help things out screw things up. And bad. VERY bad.
| quote: | | From what I can gather you have replaced the op-amps in an integrated sound system i.e. the pre=amp, power amp and speakers are all part of a single manufacturers product line family. |
True. A Genius SW-5.1 HT. Check there:
http://www.diyaudio.com/forums/show...threadid=124502
| quote: | | I don't see a relative measurement of the noise level from now to before any changes were made. My reading of your notes doesn't speak to the noise level before you started mods, only after. Was the noise always there? |
Jeeez... NEVER! It was never a noisy amp. Even with volume all the way up it was hard to pick any noise when ear to the speaker!
Now it roar to me like ...
Of course there was never the cursed noise. Do you think I bought a speakers that play so bad from the start or what? :)
| quote: | | If there are no answers then your only recourse is to replace the LM4562 with JRC4558D (easy now you got sockets) and get back to the zero noise condition. I think you took something important out. |
But I swear I did no futher changes. I reversed all of them. Of course, I can't reverse using Elna RFS caps 22uF 25V instead of bad caps CapXons 10uF 25V, because I throw them away.
I'm also VERY SORRY I cut the legs of these JRC4558D opamps, because for that reason, I can't put them back on... :mad:
And see if the noise is causing just the sockets for opamps... because that would be the only one significant change there.
Puting a filtering caps into the power lines can't hurt a thing. Regardless it was noisy as hell even before I put them there and things did not change. Not at all. So basicaly I put back every cap I desolder and no change. Still the cursed oscilation noise, or what the hell...
I think these opamps have kinda different input impedance over the original and hence the feedback resistors need to be adjusted.
At some point I think the cursed LM4562 and NE5532 cannot handle the zero gain, but then I look again and even the L/R and RL/RR channels are with gain 0, then the CENTER (witch screams most at me now, grrr) and SUBwoofer channels are all with reasonable gains.
And both oscilate as well... :(
Getting clueless. |
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| wakibaki |
| quote: | Originally posted by trodas
I think these opamps have kinda different input impedance over the original and hence the feedback resistors need to be adjusted.
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NO! Do not feck with the feedback resistors!
w |
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| trodas |
You sure?
I mean - I run out of ideas anyway. But take a look - what if the LM4562 / NE5532 opamps simply did not like so low values on the gain controlling resistors?
I mean - in the Chu Moy's example they are 470k / 120k ... in my case they are 10k / 10k ...
That is like 12x less at least.
Could that be a reason to the oscilations, producing this nasty noise?! |
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| cliffforrest |
| quote: | Originally posted by trodas
You sure?
I mean - I run out of ideas anyway. But take a look - what if the LM4562 / NE5532 opamps simply did not like so low values on the gain controlling resistors?
I mean - in the Chu Moy's example they are 470k / 120k ... in my case they are 10k / 10k ...
That is like 12x less at least.
Could that be a reason to the oscilations, producing this nasty noise?! |
Please do read a simple primer on op-amps and audio. :D
Please also try and think about what posters are saying to you.
At the moment you are thrashing around like a blind bull in a china shop. You will NEVER get it fixed like this until you slow down!
And since you are totally convinced that a 100pF RF filter capacitor MUST "obviously kill the audio quality", without understanding of the source impedance or CR filters, there seems to be little point in trying to advise you.
Go ahead and swap all the bits at random - it will work. Eventually. |
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| trodas |
Well, and how that was supposed to help? :o
I tried educate myself there:
http://tangentsoft.net/audio/hs-opamp.html
But my questions to the autor remaining unanwsered.
| quote: | Hi Warren.
I read your article "Working with Cranky Op-Amps" with great interest. I never played much with the audio stuff, I specialize on the mainboard and GFX/sound/PSU recap stuff.
However I have a question about the voltage filtering, where you proposed to add 0.1 µF ceramics for each voltage supply lines (pin 8 and 4 typically) with a suggestion "need to go down to 0.01 µF for faster op-amps" ...
That was "Because the effectiveness of capacitors for bypassing relative to frequency goes up as the value goes down...".
Hmmm.
I don't understand. I would like 10uF X7R Murata ceramics there! The specifications of ceramic SMD capacitors todays did not change much (if at all) with the increasing capacity. Hell, it is possible to buy a 100uF 6.3V 1210 size SMD ceramics now! (almost $4, but you can)
So, since I don't know about anything that could prevent this 10uF capacitor to filter well even in the Mhz range (specs looking damn good http://search.murata.co.jp/Ceramy/i...A18X/C2ED01.pdf ) ...
So, why not use 10uF caps on the opamps legs?
When overclocking components it is always valid the more capacity and less ESR the better overclock. That is because the more ripple current go thru the caps that the CPU, the better (cleaner) voltage the CPU have and hence it run better and overclock higher.
Do you really want me to add a 0,01uF cap on the legs instead (or in parallel) to 10uF 16V X7R Murata ones? :)
Thanks for letting me know.
Pavel |
Also I order 4pcs of samples of the RC4580IP and the supposed (by TI) equivalent of the 4558 opamps, the TLE2062CP. They are supposed the arive at Thursday.
What till then? Try 10 - 22pF in the C7 positions while the C117 remain unused? |
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| trodas |
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...!!! :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? |
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| wakibaki |
| quote: | Originally posted by trodas
I still not understand why use so small values, because as I look into the Murata specs, these ceramics go way up to GHz, regardless of capacity and when come to voltage filtering, then the more capacity the better...?!
( |
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 |
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| Iain McNeill |
| quote: | | Adding R100 resistors instead of C9, C10, C35, C36, C61, C62 and C64 seems to helped a bit too. |
:spin: :spin: :spin:
You crazy guy Trodas!
You run so fast I can't even see your dust.
So what did you CHANGE that made the oscillation noise go away? |
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| trodas |
wakibaki -| quote: | | 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. |
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 :D ;)
That is where it is valid that short to ground is not short, if it's lenght is above the wavelenght :D
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... :cheerful:
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 :D |
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| cliffforrest |
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. |
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| wakibaki |
| quote: | Originally posted by trodas
wakibaki -
We aren't building there a satelite reciever pre-amp
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- 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 |
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| Iain McNeill |
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? |
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| wakibaki |
| quote: | Originally posted by wakibaki
you'll find anyway that it is true even of the Murata caps within their range. Look how the frequencies change with capacitance.
|
Should read: - 'anyway that what I said is true'
w |
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| trodas |
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... :mad:
Maybe the grounding is not perfect and the voltage supply suxx too? Dunno. |
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| wakibaki |
| quote: | Originally posted by Nigel
...these go up to 11... |
trodas, you sure as hell full of energy, optimism, enthusiasm, ideas and persistence.
w |
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| trodas |
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/st...49/#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 :) |
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| janneman |
| quote: | Originally posted by trodas
[snip]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/st...49/#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![snip] |
The 4562 draws 10mA from the supply. This does NOT vary with supply voltage. It is in the data sheet. It is in English.
Jan Didden |
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| cliffforrest |
"I get the 10k load from tadasheets, just check them.
But looks like you are right, they can go up a lot... But... "
I give up!
FX: Ignore topic! |
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| trodas |
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. |
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| oshifis |
trodas, I read on your website:
Achievements
1st in World in CPU-Z underclocking - 10,74Mhz
Is it something similar you want to achieve with your current project? :) |
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| AndrewT |
| quote: | Originally posted by trodas
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. |
I think those current consumption graphs are for dual polarity supplies even though the Voltage scale shows V (indicating V+).
Note that the typical 10mA matches the 15V current value.
To these should be added the tolerance that National quote: 10mA typ, 12mA max. |
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| trodas |
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 -| quote: | | 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 -| quote: | I think those current consumption graphs are for dual polarity supplies even though the Voltage scale shows V (indicating V+).
Note that the typical 10mA matches the 15V current value. |
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 :( |
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| cliffforrest |
This is like watching a train-wreck unfolding ....
Trodus, please, get yourself a basic primer on volts, amps and ohms law.
You are demonstrating that you have no idea what you are doing or why you are doing it!
You ignore the advice you have asked for.
It is very sad. |
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| wakibaki |
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 |
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| trodas |
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 |
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| trodas |
One nice user pointed out, that the brum is not like 5 - 6kHz, but rather 100Hz!
| quote: | | lemonadesoda: 5-6Khz brum? My a$$... 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. |
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/D...=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...
| quote: | | Resistors R109, R111, R156 and R157 and interchannels connections |
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?...capaddedbk9.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. |
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| unclejed613 |
| sounds like you may have an open ground somewhere. you shouldn't have ripple on the center connection between P/S caps. |
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| trodas |
Well, I think this ripple is pretty normal stabilization ripple and up to 30mV is pretty good result, after just four diodes and one cap... yep, bridged with 100nF ceramic cap too...
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
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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
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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
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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. |
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| trodas |
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):
...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: |
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| wakibaki |
Muting is not working. Pin 10 of TDA7295. Big buzz that fades a bit. First guess - you have a problem in your power supply.
How are you making your measurements? Have you got a scope? If not, buy one of these: - PC oscilloscope or something like it so you can see where the noise is, and where it is not.
Look at the PCB with a magnifying glass. Look for shorts or broken tracks or bad solder joints. Start at pin 10 of the TDA7295 and work towards the PSU. Check every connection pin-to-pin with a continuity meter.
Look for wrong components or wrong way round components. You can look at these a dozen times and still miss a mistake.
Years ago I built an amplifier with a Sinclair IC-12 chip when they first appeared . ~ 1971. It suffered from a momentary loss of output that occurred when there were crescendos in the bass. I cannot remember how many times I tried without success to find the fault, since it was a non-trivial expense for me in those days.
About 10 years later I came across the PCB and circuit and idly started to examine it. Almost immediately I spotted an incorrect electrolytic cap value. I was stunned that I could have gone through the motions of checking the circuit so many times, and still have missed it. I replaced the cap and the fault was gone.
When I worked on production test as a student, we did repeated tests on complex military radios. Each type required the assembly of a different test rig. Sometimes you would get stuck and couldn't get the results you wanted. If someone did get stuck and ask for help, often one of the other testers could come over, look at the setup, change one thing (doh!), and everything would work. It happened to everyone.
Get someone else to check the circuit, even someone with no electrical knowledge. I don't imagine you've got a girlfriend?
w |
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| trodas |
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? |
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| wakibaki |
Always do the hardest things first, because if you get them wrong, then you don't have to do the easy things.
w |
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| lineup |
Can I have the circuit you use, currently.
If it is not power supply hum (like ground-loop)
it may be that you have some problems with CHIP input pins.
Any Op-Amp, JFET input or BIPOLAR input
has got either Gate or Base connected to input PIN.
If not is any gate/base stopper resistor,
you may have to put like 1 kohm resistor into Input PINs.
This is very common practice in op-amp schematics.
If not put such base-stopper for all input pins
at least you may benefit from having such
at where the INPUT Signal comes into amplifier first input transistor. |
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