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p3a amp
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Old 11th March 2007, 06:28 PM   #1
p robertson is offline p robertson
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Join Date: Jul 2002
Location: london uk
Default p3a amp

has anyone modified the p3a amp?I have build a couple of versions one with 2n3055 and mj2955 and the other with 2sa2193 and 2sc5200 and i would say they sound good but not great(a little harsh,sharp and not smooth) its not oscillaton i checked!I was thinking of removing the miller cap and having it btween vas collector and ltp base(as jlh) and also deceasing the ccs in ltp and increasing the 560 ohm resistor in ltp to 2k-4k7? i would be grateful for any feedback!
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Old 11th March 2007, 10:50 PM   #2
vynuhl.addict is offline vynuhl.addict  Canada
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Join Date: Mar 2006
Location: Vancouver, BC,Canada
For the bootstrap cap c5 use the best you can find, a Panasonic FC or similar will be sufficient. Experiment with different values for lag compensation, try 47pf and see how this works and should be sufficient, you may even be able to go lower. sometimes removving c6 in the negative rail output half may be sufficient altogether to eliminate this harshness, at30 mhz these devices arent lightning quick. you could also try 10-100 ohm base stoppers before the drivers.. dont change the 560 to a higher value, you will throw off the dc offset by bring it more positive and higher in value. The real critical stage here is the vas, if you want to use phase lead back to the ltp use a combination of small lag 5-10pf, and phase lead of 22-47 pf and see how this sounds, i have had great success with this combo.

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Old 12th March 2007, 01:30 AM   #3
jaycee is offline jaycee  United Kingdom
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Join Date: Apr 2004
Location: Norwich, UK
P3A is a good beginner amp but you can do better. A major sore point I feel is the use of CFP outputs, in order to keep them stable the miller compensation is probably quite heavy.

Personally i'd say, for only a bit more complexity and similar output power, build MikeB's symasym.
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