HeadWize: DIY Workshop > M³ headphone amplifier (part 2)

Message [#181] posted on: 12-11-2008 07:35 AM CST (US).

Joined: Apr. 1, 2004
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[Quoting odilon_df]
Do you see any problem on changing the R5 and R8 values from 100 ohms to 91 ohms ? I have good set of 91 ohms resistors , but I just found trash 100 ohms in Brazil...

Should be fine.

lcp

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Message [#182] posted on: 12-13-2008 08:09 PM CST (US).

Amb,

It is my fault in measuring the wrong pin. What a shame!

I think you are right. the loading is too high from amp.

Message [#183] posted on: 12-15-2008 11:34 AM CST (US).

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AMB

Thanks for you help.

odilon_df

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Message [#184] posted on: 12-16-2008 11:45 AM CST (US).

Hi guys, is there any problem using bipolar electrolitics os C4 and C5 instead of polarized ones?

amb

Message [#185] posted on: 12-16-2008 03:21 PM CST (US).

Joined: Apr. 1, 2004
Locale: Sunnyvale, CA. USA
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[Quoting odilon_df]
Hi guys, is there any problem using bipolar electrolitics os C4 and C5 instead of polarized ones?

If you could find suitable bipolar caps that have comparable ESR specifications as the recommended caps, then yes. However, I have a feeling that you won't...

Message [#186] posted on: 12-17-2008 01:32 AM CST (US).

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I was built σ11 for 24V output,I read output is 33V.

Power transformer is 24V out to σ11

need help

aos

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Message [#187] posted on: 12-17-2008 03:14 AM CST (US).

Are you sure your R8 and R10 are correct values - 10k each? There's no way you'd get 2.85V at the differential amplifier input (resistor divider) if they were equal (unless something is wrong with Q4).

Message [#188] posted on: 12-20-2008 01:24 PM CST (US).

Joined: Dec. 8, 2008
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[Quoting aos]
Are you sure your R8 and R10 are correct values - 10k each? There's no way you'd get 2.85V at the differential amplifier input (resistor divider) if they were equal (unless something is wrong with Q4).

The R8 and R10 is correct values both is 10K
I was change all NPN BJT BC546B and PNP BJT BC556B include MOSFET IRLZ24N still do not work.

amb

Message [#189] posted on: 12-20-2008 04:08 PM CST (US).

Joined: Apr. 1, 2004
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dualxeon, the voltage at your Q11 C is higher than E, which is impossible unless one or more of the MOSFETs have a short from D to G. Also, you show voltgae drop across R4 and R5, which indicate some current flowing through them. A functioning MOSFET should have virtually no measurable gate current.

After you've replaced all your BJTs and MOSFETs are you still getting the same measurements? Are you sure you have all the right parts installed in the correct board locations and are in the proper orientations?

Btw, this is more appropriate in the σ22 and σ11 thread.

Message [#190] posted on: 12-21-2008 02:03 AM CST (US).

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Btw, this is more appropriate in the σ22 and σ11 thread.

will post to σ22 and σ11 thread

Message [#191] posted on: 12-23-2008 03:17 PM CST (US).

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I just finally managed to get the OPA on my M³ in the right direction.

Now going through the initial check everything is ok
except a offset of about 5V on OR.

AC offset is also a bit high on the other channels, ~ 3mV.

I'm about to go crazy ... <frown>
I don't have much time for DIY these days and nothing works.

Where could the problem be?

[Edited by Sathimas on 12-23-2008 at 03:18 PM.]

amb

Message [#192] posted on: 12-23-2008 04:41 PM CST (US).

Joined: Apr. 1, 2004
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[Quoting Sathimas]
I just finally managed to get the OPA on my M³ in the right direction.
Now going through the initial check everything is ok
except a offset of about 5V on OR.

Did you happen to power up with that particular opamp in the wrong way? Maybe it's damaged.

[Quote]
AC offset is also a bit high on the other channels, ~ 3mV.

Don't worry about this until you have the amp board all wired up and installed in a case. Some DMMs can't measure low mVs accurately anyway.

Message [#193] posted on: 12-23-2008 05:20 PM CST (US).

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I just made a test and put the ground OPA in the place of
the right OPA and vice versa - right offset stays at 5,3V
while ground and left offset are perfect.

I think the OPA should be OK then.

amb

Message [#194] posted on: 12-23-2008 06:33 PM CST (US).

Joined: Apr. 1, 2004
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Sathimas, if I understand you correctly, you exchanged the ground and right opamps and the problem stayed on the right channel. If so, then the opamps should be ok.

The next thing is to examine all your right channel solder joints carefully. Make resistance measurements to verify continuity where there should be. Since you have a good left channel, it's convenient to compare the two.

Does your build have the bass boost pot installed? If not, then you need to put a jumper across SbbL and SbbR.

Message [#195] posted on: 12-24-2008 02:48 AM CST (US).

Joined: Aug. 19, 2007
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You understood correctly, I just exchanged the OPamps (they're identical).

The jumpers you mentioned are installed.

I'll test the circuit later this day.

Could you perhaps give me some hint what I'm searching for?
A short - disontinuity - anything else?

As far as I'm through, I found no cold solderjoint.

[Edited by Sathimas on 12-24-2008 at 04:15 AM.]

amb

Message [#196] posted on: 12-24-2008 04:16 AM CST (US).

Joined: Apr. 1, 2004
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[Quoting Sathimas]
Could you perhaps give me some hint what I'm searching for?
A short - disontinuity - anything else?

Yes, for cold solder joints and for solder bridges.

wldthistle

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Message [#197] posted on: 12-24-2008 04:22 AM CST (US).

Accidentally posted this as a new thread. Mods, please feel free to delete that.

Hello experts...

So, I had a working M3 for a matter of days before I managed to kill it. The M3 was going to be part of an integrated amplifier (paired with a chip amp). Tonight, I finished wiring everything up, and poof! Smoking circuit boards are no fun. Luckily the chip amp's power supply took most of the damage. Still, the M3 is in pretty bad shape. From the looks of things, it seems there was a short to ground (including the signal ground [M3 OG]), originating in the right channel chip amp.

Symptoms:
With no input, the M3 is basically silent.
With input, the left channel is louder than the right, and both channels are very noisy. It's not a hum... sounds more like static.

Voltages:
Input: 27.1
Ground pin 4 to 7: 23.3
Right pin 4 to 7: 21.7
Left pin 4 to 7: 21.7
Ground pin 7 to IG: 20.7
Right pin 7 to IG: 20.7
Left pin 7 to IG: 20.7
Ground pin 4 to IG: 1.3
Right pin 4 to IG: 1.3
Left pin 4 to IG: 1.3
R5G: 0.016
R5R: 0.025
R5L: 0.001

Any ideas? I'd sure like to get my M3 working again.

Thanks,
Greg

amb

Message [#198] posted on: 12-24-2008 04:37 AM CST (US).

Joined: Apr. 1, 2004
Locale: Sunnyvale, CA. USA
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Just answered in the other thread your created:
http://headwize....=7651&pid=73620