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Author Topic: need exellent clean preamp  (Read 9685 times)

baene123

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need exellent clean preamp
« on: December 21, 2009, 06:53:13 PM »
hi, i need to built a preamplifier for LM3886 and i want to do a low noise preamp, a very low noise preamp... i dont know if is better to use jfet or opamps (TL072) (single supply)... i've tried to use BF245 for clean preamp ,but i didn't like them bacuse they were noisy  .... I want to do a preamplifier with 4 knobs like 3 band equalizer (bass, mid, treble) and a switch for bright mode, and level...
I 'd like to have a great clean amp because i really like blues, and jazz....
I hope in your opinion... :D
THANKS!

J M Fahey

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Re: need exellent clean preamp
« Reply #1 on: December 21, 2009, 07:02:02 PM »
Hi.
Search for Rod Elliott project 27
That's a good clean classic (somewhat Fendery) preamp, similar to what Yamaha and Roland used in their very clean JC and G212 series.

rowdy_riemer

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Re: need exellent clean preamp
« Reply #2 on: December 22, 2009, 11:16:35 PM »
One thing I did for a nice clean preamp was to setup a few fetzer valve stages(see fetzer valve article at runoffgroove.com). I used an 18v supply. The first two stages use mpf102's and I added a third stage using a j201 for some overdrive. 2n5457's might be better than the mpf102's, but I didn't have any at the time. Two or three 2n5457 stages should give you plenty of gain without preamp overdrive. However, using the mpf102's and the j201 gave me plenty of clean noiseless gain. Then, you can just put whatever tone control you like afterwards. mpf102 or 2n5457 source follower stages might be good for buffering a tone control circuit. Then again, I'm sure you can get suitable results with op-amps. If you want to go with jfets, you should definately check out the fetzer valve article and use jfets with a relatively high cutoff voltage.

Or just do what J M Fahey suggested. He seems to be pretty squared away and knows his stuff.

Another thing, regardless of weather you use jfets, bjts, or op-amps, have a good clean regulated power supply. I went the easy route, and used two 9v batteries, but I'll probably eventually build a decent supply.


baene123

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Re: need exellent clean preamp
« Reply #3 on: December 23, 2009, 11:22:56 AM »
One thing I did for a nice clean preamp was to setup a few fetzer valve stages(see fetzer valve article at runoffgroove.com). I used an 18v supply. The first two stages use mpf102's and I added a third stage using a j201 for some overdrive. 2n5457's might be better than the mpf102's, but I didn't have any at the time. Two or three 2n5457 stages should give you plenty of gain without preamp overdrive. However, using the mpf102's and the j201 gave me plenty of clean noiseless gain. Then, you can just put whatever tone control you like afterwards. mpf102 or 2n5457 source follower stages might be good for buffering a tone control circuit. Then again, I'm sure you can get suitable results with op-amps. If you want to go with jfets, you should definately check out the fetzer valve article and use jfets with a relatively high cutoff voltage.

Or just do what J M Fahey suggested. He seems to be pretty squared away and knows his stuff.

Another thing, regardless of weather you use jfets, bjts, or op-amps, have a good clean regulated power supply. I went the easy route, and used two 9v batteries, but I'll probably eventually build a decent supply.


ok, thaks, i'll try to use a few fetzer valve stages from ROG.... maybe i'll make a mix between opamp and jfet, i'd like to an inverting adder oamps with 3 bands control (bass,mids,highs) for tone control...
I have no dproblem for regulated supply because i use this preamp for LM3886, tht's need +/-35V dc... i'll put a 7812 or 7824....
« Last Edit: December 23, 2009, 11:25:50 AM by baene123 »

Minion

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Re: need exellent clean preamp
« Reply #4 on: December 26, 2009, 01:47:24 PM »
I recently built a clean preamp for Bass or acoustic guitar , It used a simple dual opamp with a dual 100k pot to controll the gain (shared gain preamp) then it went into a BA3812 5 band EQ chip , so it had a 5 band eq and a clean preamp section with a single gain pot , I also added switchable clipping diode for a fuzz tone and a switchable Trebble boost ...... I run the whole thing on a single regulated 15v DC supply .....

very good sounding and dead quiet when you want it to be ....


Cheers

J M Fahey

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Re: need exellent clean preamp
« Reply #5 on: December 27, 2009, 01:46:26 PM »
Hi Minion.
Sound very interesting.
Why don't you publish it here?
A couple pictures and MP3s would help also.