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Old 29th July 2005, 08:27 AM   #1
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Default x-pro come in

quato:JLH 10 Watt class A amplifier


i have built your circuit and left a cap C5 unsolder , i dont know how much value is it , pls tell me which value is best.
now , my amplifier without this cap is not stable , when i touch the input , bias current will jump to about 2a high , i dont know why , only know this cap is useful.
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Old 29th July 2005, 09:47 AM   #2
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Default Much better than any schematic posted, is that China is with us

This is wonderfull, great and civilized.

Good to be alive those days.

regards,

Carlos
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Old 29th July 2005, 09:53 AM   #3
jaycee is offline jaycee  United Kingdom
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Try 100pF here. This capacitor is called a "Miller capacitor" and serves to make the amplifier stable. If the amplifier is still unstable try increasing the value, but over 220pF and something is wrong with your PCB layout. You may also be able to make it smaller and have the amplifier stable but 100pF is a safe value.
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Old 1st August 2005, 03:36 AM   #4
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Default circuit singing

i try 100pf ,then this circuit can sing with no noise.
but ,when th input is open ,i touch the input with my finger , the bias still jump to high current , why this happened ? maybe my body became antenna , so seduce some RF to this circuit , make the circuit unstable . i dont know why , how to solve it. is it must that heatsink connected earth? thx
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Old 1st August 2005, 04:06 AM   #5
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hi,john-china:
you can do same thing to your another amp,this will happen too,try it!
I think human body has a very low votage(static ),so when your finger touch the input end,it seems to input end accept the signal,
and you will heard the"hooter " from you lound speaker...

regards
WINCO
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Old 1st August 2005, 04:12 AM   #6
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by the way:
tell me the sound of this amp,can it process good bass?
I have build one not long before,it's treble is excellent,
but I don't satisfy with it's bass,very weak!

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Old 1st August 2005, 03:03 PM   #7
x-pro is offline x-pro  United Kingdom
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C5 could be in the range of 47-100 pF . Bass performance may be improved by adjusting the C4 value. Try 470 uF 25-35 V there.

Quote:
Originally posted by john-china
i try 100pf ,then this circuit can sing with no noise.
but ,when th input is open ,i touch the input with my finger , the bias still jump to high current , why this happened ? maybe my body became antenna , so seduce some RF to this circuit , make the circuit unstable . i dont know why , how to solve it. is it must that heatsink connected earth? thx
It would be useful to put a passive RC filter on the input to cut the HF at around 50-70 kHz. Try 4K7 and 470 pF.

Cheers

Alex

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Old 1st August 2005, 03:53 PM   #8
edl is offline edl  Hungary
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Very nice design!

I think I will use this topology.

Congrats!

Regards
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Old 1st August 2005, 04:41 PM   #9
x-pro is offline x-pro  United Kingdom
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Quote:
Originally posted by edl
Very nice design!

I think I will use this topology.

Congrats!

Regards
Thank you!

Alex

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