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Old 17th March 2006, 12:41 AM   #1
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Default leach preamp

I would like to get schematic of Leach peamplifier, an old transistor circuit with tone control in feedback loop.

Is there somebody that know where I can find it ?
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Old 17th March 2006, 12:47 AM   #2
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Old 17th March 2006, 01:46 AM   #3
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merci beaucoup exactly what I was looking for
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Old 17th March 2006, 06:17 AM   #4
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Anybody know how good is the preamp of Leach??
I was thinking to build it, but i don't know...
Because of the "old" design...


P.S. But i think the simle is the best...!!
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Old 17th March 2006, 06:48 AM   #5
AndrewT is offline AndrewT  Scotland
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it was discussed in a thread a year or so back.
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 17th March 2006, 11:56 AM   #6
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I did want the desing for consultation not construction.

The output stage with 2 NPN transistor is not ideal, voltage gain in négative swing and no gain in positive swing not very linear, a lot to compensate with feedback .... this is my opinion but I may be wrong....
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Old 17th March 2006, 12:40 PM   #7
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I built this circuit years ago and compared it to others of the day and it was not better. HOWEVER, parts, layout, etc., are everything and mine did not have it. Also, the circuit is I believe a bit outdated and one could do better with a more modern approach. Back in those days, preamps did not seem to get the full attention that amps did IMO. One thing I see that has not changed is that if you still want the best, DIY is the way. Good luck!
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Old 17th March 2006, 07:44 PM   #8
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Location: virginia
The Leach circuit is very dated. The basic circuit is in my college textbook on transistor amplifiers dated 1966. However the circuit was a big improvement over the typical 2 or 3 transistor preamps that were common then.

I have the jfet version and the performance is quite good. Dr. Leach stated the jfet version had about 20 pF input capacitance and a 200v/us slew rate. Thats where the low transconductance of the jfets is an advantage. It was an excelent match for my high inductance Shure V-15 cartridge.

It would be an interesting project to simulate the circuit in spice with modern transistors and see if it could be improved.

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Old 20th March 2006, 05:58 AM   #9
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I just finished my 1st DIY Project!!!
It's a preamplifier with the AN5534 - AN5532..
It has line, phono and balanced (XLR) stages.. I'm very happy that i designed the PCB from the start and - almost - everything is correct, on and working!!

So now, with the expirience of the 1st project i want to build some more !!

I've got the full description of the preamp from Leach site, i'll read the forum threads and if everything goes ok i'll go for it!

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