Air guitar Pre
- Thread starter sandford
- Start date
PigletsDad
My intelligence test came back negative.
No, its all discrete!
Some of the techniques are used in op-amp design, but don't hold that against them.
The circuit has quite a lot of transistors, at least compared to a Naim stage, but half those are just come from the use of complementary symmetry, which allows one side to act as load for the other.
I have got it to simulate; found one mistake - self bias resistor for JFET CCS was wrong. So far I have just checked behaviour for 1kHz sine wave; very low simulated distortion, at accuracy level of software (0.00033% for 10Vrms out into open circuit).
Will do PSRR and frequency responses next, then correct schematic.
Circuit uses 2SK117 fets (mostly because I have some at home). Other N channel JFETS can be used, but will need a tweak to self bias resistor.
Some of the techniques are used in op-amp design, but don't hold that against them.
The circuit has quite a lot of transistors, at least compared to a Naim stage, but half those are just come from the use of complementary symmetry, which allows one side to act as load for the other.
I have got it to simulate; found one mistake - self bias resistor for JFET CCS was wrong. So far I have just checked behaviour for 1kHz sine wave; very low simulated distortion, at accuracy level of software (0.00033% for 10Vrms out into open circuit).
Will do PSRR and frequency responses next, then correct schematic.
Circuit uses 2SK117 fets (mostly because I have some at home). Other N channel JFETS can be used, but will need a tweak to self bias resistor.
martin clark
pinko bodger
Aw, you say that like it's a bad thing.
tee hee...
martin clark
pinko bodger
Carl , thats some of the innard s of my preamp; the spare boards you kindly sent me are salted away as spares.
Andrew L Weekes
Reverse Engineer
One day yo're gonna draw a circuit of that thing - you know you want to Martin
I'd love to see it, it's so goddam complex in terms of semi count, it's amazing.
As for the Naim circuit, there's three things I dislike about it, the input cap, the output cap and the feedback cap.
Unfortunately it's not easy to eliminate any of them with that circuit.
As for alternatives, there's almost no better way to amplify something than with a properly designed long tail pair.
I guess that leaves the 'proper design' but as the challenge then
Tee hee.
Anyway, it's not on my urgent list at present, I've got Class D amps to finish (to start, even) and then long term projects to finish.
Andy.
P.S. Piglets Dad, I've never got any distortion results out of a simulator that are remotely accurate
Useful tool though.
martin clark
pinko bodger
I'm working on it (have been for a while) but it's so bloody small and multilayered! Drop by sometime and I'll soon rope you in...
PigletsDad
My intelligence test came back negative.
Andrew L Weekes said:P.S. Piglets Dad, I've never got any distortion results out of a simulator that are remotely accurate
I really, really know that- I have worked on simulation software, and written specialised ones from scratch - but if the simulator says distortion is very bad, it is very bad!
If a circuit doesn't simulate cleanly, you should usually move right along; the real world stuff that is not included almost never improves things.