amplifier clipping early

gruni · 14th March 2010, 04:21 PM

hello everybody!
i just got another defective amplifier to repair. it starts clipping very early at about 0,6V AC. i desoldered all transistors in the output stage and all were ok in diode and hfe check with a DMM. do these checks verify that the transistors are okay? where else could the problem of the amplifier be?

nigelwright7557 · 14th March 2010, 04:27 PM

It could be anywhere prior to the output transistors.
I would whip out the other transistors and check them and while they are out check the other discrete components.

I assume you have checked the dc supply voltages ?

sakis · 14th March 2010, 06:01 PM

state model topology and or schematic ...it could simply be a couple of fuses for example

Th3 uN1Qu3 · 15th March 2010, 12:57 AM

First check the input stage, ie signal transistors and/or opamps. I once fixed an amp that insisted on distorting the right channel a lot earlier than the left. Pulled out all the signal transistors and one checked out as having a beta of like 10 vs 150+ for all the others. Sure enough, replacing that transistor made the right channel operate to spec.

14th March 2010, 04:21 PM	#1
gruni diyAudio Member Join Date: Feb 2008	amplifier clipping early hello everybody! i just got another defective amplifier to repair. it starts clipping very early at about 0,6V AC. i desoldered all transistors in the output stage and all were ok in diode and hfe check with a DMM. do these checks verify that the transistors are okay? where else could the problem of the amplifier be?

14th March 2010, 04:27 PM	#2
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	It could be anywhere prior to the output transistors. I would whip out the other transistors and check them and while they are out check the other discrete components. I assume you have checked the dc supply voltages ? __________________ http://www.murtonpikesystems.co.uk PCBCAD40 pcb design software.

14th March 2010, 06:01 PM	#3
sakis diyAudio Member Join Date: Jan 2006 Location: nea makri athens greece	state model topology and or schematic ...it could simply be a couple of fuses for example __________________ SERVICE ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr

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15th March 2010, 12:57 AM	#4
Th3 uN1Qu3 diyAudio Member Join Date: Feb 2010 Location: Bucharest	First check the input stage, ie signal transistors and/or opamps. I once fixed an amp that insisted on distorting the right channel a lot earlier than the left. Pulled out all the signal transistors and one checked out as having a beta of like 10 vs 150+ for all the others. Sure enough, replacing that transistor made the right channel operate to spec.

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