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Old 10th September 2015, 08:47 PM   #1
abpea is offline abpea  United States
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Default Help Troubleshooting JLH1996

Just built a JLH96 using this schematic:

Click the image to open in full size.

I built it on a breadboard, point-to-point. Everything started out fine... I set my power supply for 0.2 amps and 0 volts. Attached the power supply, turned it on and rolled the voltage up to 2 volts. So far so good. I increased the voltage to 5 volts. All good. Then I went to 10, 15 and finally 22 volts. No smoke!

I have an 8 ohm 35 watt resistor attached to the output terminals. The dc offset was ~76 millivolts so I used VR1 to reduce it to 0 volts. Everything still seems good.

Next I increase the current to 1 amp. After which something must have blown. I didn't hear or smell anything but I could't read any voltage on the output terminals any longer. I turned the power supply off and waited a few minutes. Turned it back on and tried to change the dc offset with VR1 but it had no effect. The output transistors never got warm.

I have no idea where to start or how to begin troubleshooting this thing. Could anyone give me an idea of what to check or where to start??

Thanks much for your help -
Bruce

Last edited by abpea; 10th September 2015 at 09:45 PM.
 
Old 10th September 2015, 09:45 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

Breadboard ? If it didn't include a large heatsink you've fried the outputs.

rgds, sreten.
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Old 10th September 2015, 10:01 PM   #3
abpea is offline abpea  United States
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Quote:
Originally Posted by sreten View Post
Hi,

Breadboard ? If it didn't include a large heatsink you've fried the outputs.

rgds, sreten.
Thank you for your reply sreten, I'm using this one:

Click the image to open in full size.
 
Old 10th September 2015, 10:36 PM   #4
sreten is offline sreten  United Kingdom
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Hi,

Model it in the free TinaTi simulator. Check DC voltages against the model.
Nearly always a fault upsets the DC conditions, if DC is right it usually works.

rgds, sreten.
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Last edited by sreten; 10th September 2015 at 10:40 PM.
 
Old 11th September 2015, 12:24 AM   #5
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Join Date: Feb 2004
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Hi abpea,
Frustrating! Look there is a very large thread here (over 3,000 posts) on this amp/circuit at "JLH 10 Watt class A amplifier" (use search function). That is where all the JLH aficionados/gurus hang out. I think you'll get a quicker response from them if you post your question there. And that thread is also frequented by very civilized and helpful people.
Cheers,
Jonathan
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Old 11th September 2015, 03:01 PM   #6
abpea is offline abpea  United States
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Thanks Jonathan!

I'll post a help request over there and see what happens.

Much appreciated -
Bruce
 
Old 12th September 2015, 12:43 PM   #7
AndrewT is offline AndrewT  Scotland
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Abpea now now moved to the JLH Thread
JLH 10 Watt class A amplifier

Could we now close this Thread?
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Old 13th September 2015, 06:16 AM   #8
Mooly is offline Mooly  United Kingdom
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Continued here,
JLH 10 Watt class A amplifier

Thread closed.
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