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Old 28th October 2011, 06:58 AM   #1
tmblack is offline tmblack  United Kingdom
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Default Single BJT VS JFET Preamp

I am comparing a simple JFET common source design to a similar gain BJT CE design.
Both running on 16V and gain around 20-25dB.

Which do you think has less distortion and which sounds better or even tube-like?
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Old 28th October 2011, 04:34 PM   #2
tmblack is offline tmblack  United Kingdom
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I'm starting with a JFET BOZ design by Nelson Pass. Will see how that one works out.
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Old 1st November 2011, 08:02 PM   #3
tmblack is offline tmblack  United Kingdom
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I built a CE amplifer, then added a current source to replace the collector resistor.
Now can someone tell me how to reduce the gain with feedback?
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Old 1st November 2011, 09:58 PM   #4
AKSA is offline AKSA  Australia
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Yes, single resistor, carefully chosen, from output of CE amp (collector) to base.

This is the simplest way.......

Hugh
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Old 1st November 2011, 10:58 PM   #5
Bigun is online now Bigun  Canada
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Quote:
Originally Posted by tmblack View Post
I am comparing a simple JFET common source design to a similar gain BJT CE design.
Both running on 16V and gain around 20-25dB.

Which do you think has less distortion and which sounds better or even tube-like?
It's sometimes the simplest circuits that are the hardest because they depend a lot on component choices, operating point, etc.

So it's impossible to consider a single device like this in isolation - the sound will depend on the load you hang off it and how clean the power rails are.

It will also depend on how large a signal you put into the base - more swing means higher distortion.

You might find this link interesting: The Trioderizer - a solid state triode
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Old 2nd November 2011, 02:06 AM   #6
Jay is offline Jay  Indonesia
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Originally Posted by Bigun View Post
It will also depend on how large a signal you put into the base - more swing means higher distortion.
Mark Houston (the author of the 5 Watt ZCA) talked about the use of a big 2N3055 for line level amplification. Any insight on his ideas?
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Old 2nd November 2011, 02:39 AM   #7
Bigun is online now Bigun  Canada
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The ZCA places significant demands on the power supply - I believe people are using large chokes to keep ripple out of the signal chain. If you like this approach check out the SEWA, an earlier design that had some good reviews. Otherwise I have no insight into the idea of using an old 2N3055 for line level - there's no obvious benefit that I can think of.
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Old 2nd November 2011, 06:05 AM   #8
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by Bigun View Post
The ZCA places significant demands on the power supply - I believe people are using large chokes to keep ripple out of the signal chain. If you like this approach check out the SEWA, an earlier design that had some good reviews. Otherwise I have no insight into the idea of using an old 2N3055 for line level - there's no obvious benefit that I can think of.
Yes, I used chokes for simple circuits like the ZCA or BOZ or tube amps. I have also built the SEWA. The attractive thing about the ZCA is that I can make use of transistors that I have only in one pair

About 2N3055, if I'm not mistaken, Mark said that it has good low level amplification properties. Quite controversial but I have many old transistors that I have only in one pair (or NPN only), such as the old RCA 2N3055. That's why I'm keeping an eye on thread like this
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