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Opamps stage design questions - Page 2

post #16 of 23
Thread Starter 
One nice user pointed out, that the brum is not like 5 - 6kHz, but rather 100Hz!

lemonadesoda: 5-6Khz brum? My *****... 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!
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 ( Digi-Key - 6A05-TPMSCT-ND (Micro Commercial Co - 6A05-TP) ) 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.

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...

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

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: ImageShack - Hosting :: geniussw51htcapaddedbk9.jpg
(on the very same pic you can clearly see, that the resistors R109, R111, R156 and R157 are not present)

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

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

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

I don't know.
post #17 of 23
Thread Starter 
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
Next move - add a toroid L filter coil in the IC9 input voltage. I will kill the ripple on IC9, somehow!

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Damn, I'm lost.
post #18 of 23
Thread Starter 
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...!


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...
post #19 of 23
Sounds like a ground loop.
1st Plug the sub into the same power strip
2nd Did you try lifting the ground on the sub?
post #20 of 23
Thread Starter 
I think I found the bug - now just get a spare transformator for the Genius SW-5.1 HT to test this!

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

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

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

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

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

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

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

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

INPUT-AC 230v/50Hz
OUTPUT-AC 28VCT/2.4A & 12v/1A & 40VCT/1.2A
TYPE FUSE 3.15A/250V


PS. pictures of my mods for your viewing pleasure:

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

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

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

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

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

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

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

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

Bottom look at added L7805 regulator instead R89 and Zener diode D8
post #21 of 23
Thread Starter 
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

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?
post #22 of 23

Dear Trodas,


I appreciate your effort to make sound better the SW-5.1 HT


I own one of this model and I am interested to adapt a digital (coaxial or optical) input module in order to make a digital link between the computer' soundcard and the Genius Speakers.


What do you think about that?


I think this upgrade will revive these speakers


Kind regards,



Edited by Doru2010 - 12/5/10 at 2:45am
post #23 of 23
Thread Starter 
Since all that I had managed is to kill the speakers, then I don't know why you believe that I could give any meaningfull advice to you...

But thanks for trying!

As far as adding a digital input goes, then I would suggest that someone skilled propose a circuit, that would convert the digital signal to the six channels and feed it to the opamps inputs. That could be probably done... wink.gif
Edited by trodas - 7/21/13 at 1:51pm
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