Simple discrete preamp

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This is what I intend to build as a matching preamp for my CFB power amplifier.

It's a simple discrete design consisting of a unity-gain input buffer, volume pot and output buffer. A low-impedance recording output is available. Input and output buffer share the same voltage reference for their current sources. The output buffer uses current feedback and drives almost everything.

Not shown in the schematic: PSU decoupling, compensation caps, input source switching.

What do you think?
 

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"Why are you doing this from discrete devices, if you have rails only +/ - 15 V and this connection copy many internal structures of modern op amps ?"

Pehaps he is doing it for the same reason i once made a discrete headphone amp even when a dual opamp and a couple of TO-126 output transistors would have done as well and taken up far less space -- it's more fun!
 
Well, if you will make all good, this will be very fine amp. Input diamond buffer work very good, with supermatched trasistors ( attention on temperature feedback ) you get distortion bellow 0.001 %. Second stage, which is by connected as latest generation of LT opamps, give similar results. Both connections are very fast, so you must do PCB very carefully. But remember, that good preamp is't only active circuits, but mainly overall concepcion ;) .
 
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AMT-freak said:
Compared to an opamp, my circuit is really simple! Also I can use much higher quality parts and match the active devices.

Elso, I suppose you forgot the "not"? ;)


you sure can use high quality parts. But it is hard to assure anyone that your high quality discrete parts are of higher quality than those ICs unless you know what quality those ICs are.
 
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Me to!

That circuit should sound good. I've seen it in some really good preamps in general form. The units I've seen this in normally run 25-30 V supplies.
I'm thinking of doing a simlar thing too, that's what I think of your circuit.
-Chris
 
ACR said:
Looks a lot like the Elektor preamp from a few years ago - why don't you just build that - you can even get a nice PCB for it.

Why DIY? Who not buy a ready-made?

Much, if not most, of the quality come from the implementation. Component selection, power-supply.

And dont forget that building with discrete allows you to fine-tune the earthing-arrangement. At least if you recognize how much this affect the musicality of an amp.
 
So the input buffer is what you call a "diamond buffer"? I thought there's no secret in there, guess I'll have to read the threads about it ;)

The second stage is not like the Elektor preamp, they build a pretty standard discrete opamp while what I have is a buffer with an output stage to be able to use current feedback. I will probably be able to avoid capacitors in the feedback network.

I'll consider higher supply voltages. The power supply has in fact a great influence on overall performance, one more reason to ditch the Elektor design. I think I'll use a simple non-feedback FET regulator and lots of R-C-filtering afterwards, as that gave excellent performance in past projects.
 
I like the ides of buffering the volume control........how abou using a shunt volume control, it has a lot of advantages and almost no disadvantages now that you are using a buffer.

How about posting the schematic of your amp? I am a big fan of current feedback designs and non-global feedback designs using similar topology.

Regards,
Jam
 

This sch is like the Pioneer CZ-5 pre?
Both are the Gm amp?

I don't know a Pioneer CZ-5. What is a Gm amp?


How about posting the schematic of your amp? I am a big fan of current feedback designs and non-global feedback designs using similar topology.

You mean the power amplifier? It's been a long time since the last post, but is is here:

Prototyping a 100W CFB amplifier


I like the ides of buffering the volume control........how abou using a shunt volume control, it has a lot of advantages and almost no disadvantages now that you are using a buffer.

You mean something like this? Why do you think it sounds better?
 

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