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Old 16th July 2004, 09:50 PM   #1
OliverD is offline OliverD  Germany
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Default Simple discrete preamp

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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Old 16th July 2004, 10:00 PM   #2
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isn't that a diamond buffer? would it have been easier to just use one of those diamond buffer ICs (like the LH from National)?
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Old 16th July 2004, 10:11 PM   #3
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Simple !!

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Old 16th July 2004, 10:17 PM   #4
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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 ?
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Old 16th July 2004, 10:26 PM   #5
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Quote:
Originally posted by Upupa Epops
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 ?
Hi,
Discrete can sound better, but necessarily so.............
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Old 16th July 2004, 10:42 PM   #6
OliverD is offline OliverD  Germany
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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"?
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Old 16th July 2004, 11:00 PM   #7
sam9 is offline sam9  United States
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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!
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Old 17th July 2004, 12:46 AM   #8
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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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Old 17th July 2004, 01:24 AM   #9
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Quote:
Originally posted by AMT-freak
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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Old 17th July 2004, 02:27 AM   #10
Bonsai is offline Bonsai  Taiwan
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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.
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