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Topics - Ken W

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Preamps and Effects / Want to build insane preamp
« on: December 21, 2007, 03:27:55 AM »
Hi.  I'm new here, but not to musical electronics (age 9-49), and I want to build an insane solid-state preamp.

The situation is, I was given a busted Marshall IBS MOSfet bass amp.  The pots are nearly all broken or previously broken and badly repaired, but the unit works. I don't need a 200 watt bass amp, let alone one with this fancy EQ.

On the other hand, a 200-watt portable PA/guitar amp would be super.  I have a nice little Mackie mixer, so I don't need more mixer controls, just an external input.  I don't need much volume, I don't play out much, and a 200-watt PA would nicely suit instruments, laptop, and vocals at the scale I do play at.  I am not particularly a purist for tube guitar sound, although playing my new Strat through a solid-state Fender and then my old Zoom 9030 recently made me want to put the Zoom back to work processing drum sounds in bizarre electronica.

Anyways, my (tentative) plan is to do the project in a modular manner as follows.
1. remove existing preamp, leaving power amp input jack on rear
2. build small mixer/fx loop circuit to allow preamp signal, external inputs, and effects loops into power amp.
<at this point, I have a functional 200w power amp>
3. build variation of LXH2 Fender preamp.
4. build LXH2 Fender speaker simulator.
5. using what I've learned so far, build variation(!) of LXH2 Marshall preamp.
6. build LXH2 Marshall speaker simulator
<at this point, I have to decide whether I am REALLY insane>
assuming the answer is "YES", then..
8. drill the 10 more knob holes the chassis has room for
9. design an over-the-top lead channel - I have some ideas here
10. build the third channel

1 & 2 will happen real quickly, as soon as this project has enough priority to take over my mini-shop (i.e. I have a design for the first preamp).  One major change I'm considering is to replace some of the early opamp stages with triode-biased FETs.  I'm thinking if I choose the FET carefully, I can run them from the +/-15v supplies, use higher-pinchoff FETs, and keep them a bit more linear (i.e. cleaner) at lower levels.

Any thoughts?

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