Looking for Feedback on this No Feedback Amp.

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#61
phew, that's good.

Now for a crazy idea.

You would get more swing, a lot more, if you went with a Balanced Bridge output. A kind of cheat for having single supply rails. It probably has good PSRR.
 

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#63
Bigun said:
phew, that's good.

Now for a crazy idea.
Click to expand...


Not so crazy - I considered a kind of bridged super symmetrical idea for higher power, mirroring the circuit to operate on a V- side of a split supply. Still pondering...

For now, for the application I have in mind, I'll leave it as is. I just need to get the time (and motivation) to puzzle out a board.
 
#66
I had some sort of mental block about this amp - I couldn't put together a layout. Maybe lack of motivation, maybe lack of free time or maybe just plain lazy.

Alex has done me a great service, I owe him.


Now, to find the time to etch this board...
 
#71
Well, you know what he looks like, right? 😀

Alrighty then, I did it. A little rough but it will do for the first complete prototype:

DSC_0029.jpg


Silkscreen is printed on the other side. I'm taking tomorrow off so I may do a bit more with it - drill holes, add parts, etc.
 
#73
I don't want to rain on your parade but JFET/BJT CFP is a rather disappointingly sounding gain block (dull, lifeless). IMO it can only be used as a unity gain buffer in guitar preamp - something like this:
 

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#74
You can improve it a bit by putting some resistance in series with
the emitter of the BJT, say 47 ohms.

If you want lower distortion, use another 2SK170 as a current
source to the -9V rail instead of the 820 ohm, and then maybe
load the output with 10K or 20K to ground.

😎
 
#76
Nelson Pass said:
You can improve it a bit by putting some resistance in series with
the emitter of the BJT, say 47 ohms.

If you want lower distortion, use another 2SK170 as a current
source to the -9V rail instead of the 820 ohm, and then maybe
load the output with 10K or 20K to ground.

😎
Click to expand...


Tried all that and it's wasted effort - B1 still sounds better.

The shematic presented above is just for illustration - JFET/BJT CFP looks attractive but results are sonicaly disappointing.
 
#79
juma said:
I don't want to rain on your parade but JFET/BJT CFP is a rather disappointingly sounding gain block (dull, lifeless). IMO it can only be used as a unity gain buffer in guitar preamp - something like this:
Click to expand...
I disagree, I find JFET/BJT CFP input stage the most alive and least dull of the input stages I've tried.
 
#80
Bigun said:
How's it going with the construction MJL21193 ?

I am thinking that if I build this amp I should change the input device to a CFP - it's become my favourite compound device these days - would it work, would it help, did you try this in your sims ?

Perhaps a JFET/BJT CFP - what are your thoughts on this ?
Click to expand...


I'm still stalled. I haven't done anything since.

The CFP (bjt type) works fine in simulation, though there doesn't seem to be any measured improvement - THD the same.
What does make an improvement to this circuit (at least in simulation) is another "gain" block at the input - a high beta, NPN emitter follower at the input. I was playing with this before and may (will) include it in future testing.

As for FETs, I'm still watching and learning. I have some included on my next Digikey order - Zetex ZVN/ZVP to tinker with.
 
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