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Old 20th November 2012, 07:58 AM   #751
atupi is offline atupi  Romania
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Old 20th November 2012, 08:19 AM   #752
bcmbob is offline bcmbob  United States
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OK, Dario provided a little space to prevent the chip from touching, so if you mounted them correctly (small gap under chip) there shouldn't be interference. Double check the tightness of the LM3886 mounting bolt/nut also.

I have 27 VAC from the 300 VA toroids so yours would appear to be in spec.
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Old 20th November 2012, 09:56 AM   #753
atupi is offline atupi  Romania
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I've checked this aspect and is ok. As i never heard how SPIKE behaves i don't know if my problem is related to Spike protection.
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Old 20th November 2012, 11:34 AM   #754
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Quote:
Originally Posted by atupi View Post
I've checked this aspect and is ok. As i never heard how SPIKE behaves i don't know if my problem is related to Spike protection.
atupi,

I don't have any personal experience with Spike, but maybe this from the datasheet would help.

"SPiKe protection means that these
parts are completely safeguarded at the output against ov-
ervoltage, undervoltage, overloads, including shorts to the
supplies, thermal runaway, and instantaneous temperature
peaks. "

Just checking, are you using 4 ohm speakers? Others have found that 24 V transformers have too much voltage for 4 ohm speakers and recommend 22 V. I have 4 ohm speakers with a 3 ohm minimum impedance and 22 V transformers. I haven't gotten to full volume, but I play pretty loud and don't have any issues.

I also remember reading a FAQ answer on Twisted Pear where they suggest that the LM3886 has a current limit of about 11 amps. In that case, they were using 2 LM3886 bridged to provide twice the voltage, but were still finding a limit in current.

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Old 20th November 2012, 11:42 AM   #755
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Default Early Morning, Bob?

What were you doing up at 3 am?

Anyway, I made another measurement, just out of curiosity. I disconnected the input and shorted it with a clip lead. With the amp turned on, the voltage between safety ground and PGND was:

0.04 mV DC (floating around and at the limit of my VOM)
1.1 V AC

I thought the voltage would be higher since the ground reference through input was disconnected, but the voltage only went up a little in AC.

I wish I knew how this explained your 88 V, but I don't.

Jac
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Old 20th November 2012, 02:38 PM   #756
bcmbob is offline bcmbob  United States
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Saw a PBS special where they said Einstein and Edison worked four hours and slept four hours. Thought I'd try it to increase my brain power. So far the only result is dark circles, puffy eyes and a headache.

Guess I'm stuck with RTFM.
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Old 20th November 2012, 04:17 PM   #757
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Hi,
Today I tried to measure values to fix one of the broken channel.

C102 = 1.86 [Floating]

C202 = 14.46

Audio is coming from both the channels. But DC offset to the faulty board is >3v. Any suggestions?

Thanks
Badri
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Old 20th November 2012, 09:16 PM   #758
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Quote:
Originally Posted by badrisuper View Post
Today I tried to measure values to fix one of the broken channel.

C102 = 1.86 [Floating]

C202 = 14.46

Audio is coming from both the channels. But DC offset to the faulty board is >3v. Any suggestions?
that's the problem... C102 should measure +14.6VDC and C202 -14.6VDC

Take other measures and post them:

Click the image to open in full size.
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Old 21st November 2012, 05:01 PM   #759
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Originally Posted by ClaveFremen View Post
that's the problem... C102 should measure +14.6VDC and C202 -14.6VDC

Take other measures and post them:

Click the image to open in full size.

I think i have shorted transistors and the regulator. What if the defined values are not getting? Do I need to change this components?
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Old 21st November 2012, 06:55 PM   #760
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Originally Posted by badrisuper View Post
I think i have shorted transistors and the regulator. What if the defined values are not getting? Do I need to change this components?
Yes, probably only the transistor but to be absolutely sure I'd change also the LM317
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