Preamp idea / help please

[cliffmustard]

Hi guys,

I've got a spare power amp that's been lying around for ages (marshall valvestate 50/50) so thought I might try and make a pre-amp to go with it as an experiment.  So far my idea is boxing up a few circuits as follows: ROG Mr EQ to ROG Tonemender to Joel Purkis Buff and Blend (as an fx loop) and then split the output for two jacks to supply either side of the power amp.

I guess the answer is build it and find out but if my thinking here is fundamentally flawed any tips would be great. I'm also using a Shakka Brada 5 at 18v, could there be any problems with signal level being too high for the 9v circuits above?

I've been building pedals for about 2 years now but admittedly my actual knowledge of electronic theory is fairly low, slowly improving though. I haven't been able to contribute much here as yet but I read this place most days and it's been a great source of knowledge and inspiration.  Much thanks.

[StereoKills]

Take advantage of the stereo power amp to pop at least one stereo fx in after the preamp. The built in stereo chorus in my old VS265 was the best sounding chorus I've used - and I'm convinced it was the stereo aspect.

[cliffmustard]

Thanks StereoKills, good plan, saves on the buff and blend. No problem with plugging the effects straight into the power amp then?

[zambo]

Im not a real rocket scientist so check it with out but I think the input of the amp wants a certain impedence. Matching that is probably easy but I think you need to do it or will have better results if you do anyway. So a chain that was in whatever order but ending with an impedance matching stereo buffer/booster. JOK3RX has been working on a hi gain solid state preamp that seems pretty wicked. I would check that out.

[StereoKills]

The signal present between pre and poweramps is larger than between guitar and preamp. Sometimes this will not play well with just sticking an effect in between. Check out some fx loop circuits in amps, there's usually an stage to set the signal to fx level, and then post loop there's a gain stage bringing the signal back up to line level.

[Seljer]

The signal present between pre and poweramps is larger than between guitar and preamp. Sometimes this will not play well with just sticking an effect in between. Check out some fx loop circuits in amps, there's usually an stage to set the signal to fx level, and then post loop there's a gain stage bringing the signal back up to line level.

I haven't gotten a scope out and measured it, but I'm pretty sure I can drive the SS power amp section of my amp into clipping just from a 9V pedal.

The power stage has 34dB of gain and runs on +-22.5 volts
34dB is a voltage gain ratio of 50:1
2 * 22.5volts / 50 = 0.9volts

So a 1 volt peak to peak AC signal is already hitting the rails of the power supply on the output side.

It however does have a relatively low input impedance so a buffer is a must

[cliffmustard]

Thanks guys, would something like this do the trick http://www.diystompboxes.com/smfforum/index.php?topic=95948.msg832427#msg832427

(although I might look for a stereo alternative).