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Old 9th June 2012, 02:47 PM   #21
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by p robertson View Post
i was wondering since you like to modify have you tried different method of compensation,i.e cap from vas collector to ltp base? thanks and good luck
I have tried that on simulator with no success. Don't know if actual implementation will be different, but if there is no candidate values from simulation, then what value to implement?
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Old 9th June 2012, 02:53 PM   #22
Jay is offline Jay  Indonesia
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Originally Posted by sakis View Post
in my case instruments is before ears ...
Does it always conform? Do you also measure the ESR/ESL of the generic cap you use? Easier (and accurate of course) for me to plug and play because I have many parts.

And different brand has different performance.
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Old 9th June 2012, 03:35 PM   #23
raul_77 is offline raul_77  Spain
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Add a local filtering before the differential input usually works well in many amps, clean the suplly, 'messed' for the power output.

Add a 100uF capacitor afther Q4 are a easy and cheap trial that can sometimes give good results.
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Old 9th June 2012, 07:36 PM   #24
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Default p3A mods

HI all i can say with a fully regulated supply the bass frequencies are more 'solid' and any hum and ripple is virtually eliminated. If anyone is interested i will dig out the schematic and a pcb design(from J-L HOOD) and post.
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Old 10th June 2012, 07:53 AM   #25
Jay is offline Jay  Indonesia
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Default Best preamp for P3A

This is slightly off-topic but I guess still in the spirit of getting the best out of P3A.

Rarely we seen here people simulating pre+amp (while actually there is usually matching issues between pre and amp). So here is my little experimentation with B1+P3A in simulator. B1 is chosen because it is popular, easy to build and seems very suitable with P3A (a buffer shouldn't change much the character of an amp).

I started with very simple questions: what potentiometer value to be chosen, where to put the potentiometer, before or after the B1.

What I'm looking for is the minimum distortion at around 5W output (I think it is the most power used in domestic listening). This is associated with 0.3V input into the P3A (slightly less than 5W actually).

The B1 is "specified" with 25K pot at the input. I tried 50K, 25K, 20K, 10K (I believe a CDP has no impedance matching issue). The result is: the lower the potentiometer the better.

Now I put the potentiometer after B1 (I believe CDP performance has small effect). The result is better than putting the potentiometer in front of B1. And the best result is for 20K potentiometer.
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Old 10th June 2012, 08:54 AM   #26
sbrads is offline sbrads  United Kingdom
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Have you tried bipolar electrolytics for C1 & C3? Less distortion with zero bias than a normal electrolytic. 40v/63v rated caps seem to be best....
Ref: http://www.waynekirkwood.com/Images/...ap_Sound_5.pdf

Last edited by sbrads; 10th June 2012 at 08:58 AM.
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Old 10th June 2012, 02:29 PM   #27
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well ... The B1 has less dynamics in this level than any preamplifier with a bit of gain Also to my ears the B1 tends to round a bit the ends of the graph

A discrete preamp with proper semis and proper psu if made properly can beat the B1 in how real and how clear the sound can be and add the missing dynamics in low levels .

One thing here that is important and remains a complain among the people that listen to P3A is that the amplifier is way too real ..IE ..signal is getting amplified without anything changing on it so in a good production it will rock while in a bad production it will reveal all the negatives from it and throw them in to your ears ...With a B1 as a pre things are better at this point since the B1 tends to round the ends as i said and in a way ""cover mistakes in this area""

Generally for this amount of power i would go with a preamp with some little gain use a 50K pot at the input of the pre ...and skip a DC block capacitor either in the amp or the preamp

This type of setup i listen for 4 years now and in a range of 400-500 amplifiers per year that i repair and listen next too , i have found very very few that can beat the combo ...
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Old 10th June 2012, 03:01 PM   #28
raul_77 is offline raul_77  Spain
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Quote:
Ref:
Capacitor Sounds, Speaker Cables and Crossover Inductors.
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Old 23rd July 2012, 12:56 PM   #29
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Hi, thanks for sharing your knowledge on the p3a
Build one with stock bench components, been extremely impressed by its sound, and im rebuilding it with quality parts.
Do you think its sonically worth to replace the BD140 VAS with a low cob one ( 2SA1360)?
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Old 23rd July 2012, 02:00 PM   #30
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Perhaps, distortion will decrease but this is measurement, sonically you may prefer the bd as many prefer the sound of distortion. Look at tubes, some produce 2 3 percent distortion and some people love it that way. As these parts cost max around a dollar I dont think its expensive at all to just try and listen.
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