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JLH 10 Watt class A amplifier
JLH 10 Watt class A amplifier
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Old 12th June 2019, 07:35 AM   #5541
Ian Finch is offline Ian Finch  Australia
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Join Date: Apr 2010
Location: Coffs Harbour, NSW
Quote:
Originally Posted by reggieSf25 View Post
......I have a problem because id like to use a 100VA transformer with 36volt output. What are the mod I must change in order to use this transformer or should i just buy new transformer?
Is the secondary winding of the transformer centre-tapped by any chance? A transformer with 2 x 18V windings would be just right for a "dual mono" version, where separate power supplies for each channel are required.
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Old 12th June 2019, 08:08 AM   #5542
nigel pearson is offline nigel pearson  United Kingdom
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Join Date: Mar 2007
Location: Oxfordshire
I had a multiplier in a valve circuit using bipolar transistors. It showed signs of instability. I replaced it with a FET version that was better. It however needed work to make it reliable. It also gave a little second harmonic distortion. Having said that it made the amplifier viable.

The CRC idea seems likely. It was argued we should use cheap low grade capacitors as first C then high grade oversized to decouple the power amplifier. The wiring the R. That was class ab. We debated it to death. I could see no harm in it and often some good. What it could do is help the multiplier. If so a 0.1R after it? As it's class a no transient power reduction by doing it.
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Old 12th June 2019, 09:25 AM   #5543
huggygood is offline huggygood  France
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Join Date: Mar 2011
Location: france (bretagne)
all off my jlh69 amp have an 0.1 to 0.33ohm 10w resistor between first and second stage off psu capacitor .
the first stage have a basic quality capacitors 4.7k uF to 8.8k uF and the second stage have a good quality capacitors never less than 15k uF.
the first stage is decoupled by 1/100 MKP capacitor but not the second .
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Old 12th June 2019, 10:25 AM   #5544
fredbloggstwo is offline fredbloggstwo  United Kingdom
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Join Date: Aug 2007
Location: Buckinghamshire, UK
Quote:
Originally Posted by john_ellis View Post
what is the distortion component with/out test?
Hi John
I am sure I replied to this last night, but the post hasn't appeared. Anyway, at 1 watt output, the distortion is about 0.0065 with the test set in circuit and about 0.009 without. The ratio is about the same throughout the power scale.

It is fundamentally not a problem since I am sure I cannot hear any difference, but the change intrigues me.

Regards

Mike
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Old 12th June 2019, 08:38 PM   #5545
nigel pearson is offline nigel pearson  United Kingdom
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Join Date: Mar 2007
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Exceptional measurements. Anything that makes a difference that isn't the result of negative feedback should be treasured.I suspect given time you would hear it. Not the numbers, it's why it happens. My best guess is it gives decoupling.
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