Thread: Mike and Scott
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gray_wolf gray_wolf is offline
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Default Mike and Scott

On 10/27/2019 11:03 AM, Mike Rivers wrote:
On 10/27/2019 10:33 AM, gray_wolf wrote:
If you were designing a solid state guitar preamp for guitar, pedal steel and
fiddle for the cleanest possible sound what would be the maximum signal input
you would design for. I built some amps Using j-fets.My first stage would
handle 1.0 Vrms, with a gain of 10.


A hot pickup can put out about twice that voltage when played hard, but remember
that these things vary a lot, and players play with a lot of dynamic range. I
think what you have on the front end is pretty reasonable for most instruments,
though.

This worked well but I, later on, upped the power amp to 240 watts and felt I
could use a bit more front end gain and eliminate the master gain control for
low noise studio work.


Geez, how loud do you want it?!!Â* If you aren't driving the amplifier as hard as
you want to, you should put another stage of gain between your preamp and the
power amplifier. Try to push the preamp gain by another 6 dB and you'll probably
be running into clipping at the output.






The idea of a master gain is that you can overdrive the preamp stages to get as
much distortion as you want, and then bring the volume down to a tolerable
level. I don't think that you have either of those problems. But if you want to
be able to get the distorted front end sound, then you might indeed want to pad
down the input of the power amplifier rather than boost it up to full level with
another gain stage.


Mike,
Thanks for the reply. I increased the second stage gain to realize full output.
The master was to lower the noise from this gain for studio use. I realize now
I should have just added a toggle switch to control the second stage gain.
I suspect the road traveling concert guitarist these days doesn't need that kind
of power. Back in the '70s it was common to do both. I should have built one
for each job but the market would handle it. They wanted one to do it all.

I had no idea a 6 string could put out 2 volts. I got my 1 volt idea from fanning
the strings of a ten string double neck. I was just thinking about a front
end that was immune to overload, low noise and able to drive the power stage
to full output with out breaking your fingers to get more volume.