Cyrus 7 amp gets hot with no load!!!

Fidelity Audio · 18th March 2009, 12:53 PM

Hi

I have been given this amp for repair. The pre outs had a horrible dc popping when switching between inputs. I have cured that fault (The volume ic and input selector ic were faulty) but have noticed the amp gets very very hot when no speakers are connected but fine when they are.

I have also chenged the pre out op amp to a lm4562ma and swapped the crap signal caps for BG N.

The amp is used as a pre to mono blocks.

I never tested the amp for very long when I got it due to concentrating on the popping fault.

Is this normal or does anyone know what causes it.

cheers
Brent

Ragnwald · 18th March 2009, 01:17 PM

Sure you got some oscillation problems, after the OPA switch.
Time for oscilloscope work.

Fidelity Audio · 18th March 2009, 01:45 PM

Thats what I was thinking, could do with a service manual.

Brent

jaycee · 18th March 2009, 03:21 PM

See if you can find a zobel network on the output, perhaps the resistor has gone open circuit. If it has though that could be a sign that theres a stability problem with the power amp.

Fidelity Audio · 19th March 2009, 12:01 PM

Everything seems ok.

Does anyone know what the bias should be set at. I have 52mV one channel and 70mV the other. You can probably guess the hotest side of the amp is the side thats 70mV.

Brent

18th March 2009, 12:53 PM	#1
Fidelity Audio diyAudio Member Join Date: Dec 2005 Location: Doncaster England	Cyrus 7 amp gets hot with no load!!! Hi I have been given this amp for repair. The pre outs had a horrible dc popping when switching between inputs. I have cured that fault (The volume ic and input selector ic were faulty) but have noticed the amp gets very very hot when no speakers are connected but fine when they are. I have also chenged the pre out op amp to a lm4562ma and swapped the crap signal caps for BG N. The amp is used as a pre to mono blocks. I never tested the amp for very long when I got it due to concentrating on the popping fault. Is this normal or does anyone know what causes it. cheers Brent __________________ Fidelity Audio - Home of quality products & upgrades - What HiFi 5 Star Headphone amp » Hifi World 5 Star Pre amp » HiFi Choice 5 Star Group test winner HPA-100

18th March 2009, 01:45 PM	#3
Fidelity Audio diyAudio Member Join Date: Dec 2005 Location: Doncaster England	Thats what I was thinking, could do with a service manual. Brent __________________ Fidelity Audio - Home of quality products & upgrades - What HiFi 5 Star Headphone amp » Hifi World 5 Star Pre amp » HiFi Choice 5 Star Group test winner HPA-100

19th March 2009, 12:01 PM	#5
Fidelity Audio diyAudio Member Join Date: Dec 2005 Location: Doncaster England	Everything seems ok. Does anyone know what the bias should be set at. I have 52mV one channel and 70mV the other. You can probably guess the hotest side of the amp is the side thats 70mV. Brent __________________ Fidelity Audio - Home of quality products & upgrades - What HiFi 5 Star Headphone amp » Hifi World 5 Star Pre amp » HiFi Choice 5 Star Group test winner HPA-100

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18th March 2009, 01:17 PM	#2
Ragnwald diyAudio Member Join Date: Feb 2008 Location: Gotland	Sure you got some oscillation problems, after the OPA switch. Time for oscilloscope work.

18th March 2009, 03:21 PM	#4
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	See if you can find a zobel network on the output, perhaps the resistor has gone open circuit. If it has though that could be a sign that theres a stability problem with the power amp.

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