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Old 28th June 2011, 11:45 AM   #141
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I suggest you try the Fairchild 5200 and 1943...
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Old 28th June 2011, 02:18 PM   #142
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i actually did .... in many stress tests it looks like a very good quality device ...seems though that it has specs on its own and diferent from toshibas ( against the law i try to mix toshibas and faichild which ofcourse didnt work ) still the sound next to the original 2SA 1302 3281 combo is not5 that good

kind regards sakis
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Old 30th December 2011, 06:59 PM   #143
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preparing a new year's gift for me .... a P3A on the ....wild side hopefully its going to be ready same time tomorrow... i ll keep you posted ...

regards
sakis
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Old 30th December 2011, 10:09 PM   #144
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Whatever the components choice , the bootstrap is to be eliminated
and replaced by a current source of equivalent iddle current.

This will greatly reduce crossover distorsion at low values of bias.
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Old 31st December 2011, 12:03 AM   #145
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Quote:
Originally Posted by wahab View Post
....the bootstrap is to be eliminated and replaced by a current source of equivalent iddle current....
Then you simply don't have a P3a anymore.
Don't be surprised also that the combination with CFP output stage adds up to something awful.
I've built a couple of such simple amplifiers with MJ15003/4 transistors and that's how most people
judged the sound with standard low bias.

With high bias, like 300mA, most amplifiers sound good but not often as specially good sounding for the money as a well built P3a
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Old 31st December 2011, 06:57 AM   #146
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thanks wahab for the input and the PM .. let's not mix up here is a discussion of a different story ...

Ian is right .... few of the builders keep the P3a in low bias most of them is working above 70ma .. still the bootstrap will be more musical than the CCS ...one may choose from that ..

As about the P3A i have no intention to change the basis ... will play around though ....

happy new year !!
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Old 31st December 2011, 09:40 AM   #147
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all right then ....

its been bugging me for some time to play with a couple of things ... one to try a P3A modified for higher input impedance... aim was something like 100K but finally i started with 47K

Target was to make he amp more friendly to a preamplifier which i am very happy with the DOZ i am listening the past one year but if dynamics are better with the 47K at low levels i might as well go back to a passive thingy .

Then since the specific amp will work for my bench the load is Z=8 R and that will be a fact that will not change and also the actual required power will be less than 20W for every day casual listening i though about boosting the rails to 50+50 volts to gain room for dynamic peaks ...

first listening impressions are more or less spectacular sound is more analytic bass is very tight ( middle got a bit better than previous setups ) high is plenty and crisp while everything is crystal clear ....

with bias of 70 ma for starts all seem to be fine i might as well stay there but next week i am going to see what happens with higher ...

Other than that all the rest is pretty much standard ...here is a description of the setup

----2*35 volt trafo rated at 1kva
---120.000 mfd of total capacitance
---220mfd +2.2 mks decoupling on board
---MJE 150xx Vas with 100pf miller
---my favorite drivers Bd 829-830
--- Drivers on a common heat sink with the VBE attached to it
---closely matched LTP with thermal junction

---and of course legendary original 2SA1302 2SC 3281 pair for the output

enjoy some foto and i am willing to post also measured scope readings after playing with bias and miller caps

kind regards and a very happy new P3A to everyone..... oooops i mend new year !!!

Click the image to open in full size.


Click the image to open in full size.


Click the image to open in full size.


Click the image to open in full size.
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Old 31st December 2011, 10:21 AM   #148
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forgot to mention that offset remains at +-20mv even with 50v rails
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Old 31st December 2011, 11:58 AM   #149
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It seems all good, Sakis but I wonder about the big MJE150xx lump of silicon as VAS, I would have thought even any video driver would be best.

Anyways, it is 2 minutes to New Year! Happy 2012, everyone!
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Old 31st December 2011, 01:17 PM   #150
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happy new year Ian ... yeap you might be right .... no time for more tweaks now .... will see next week and post my findings here ..

Regards sakis
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