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gray_wolf October 27th 19 03:33 PM

Mike and Scott
 
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.

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.

It really doesn't matter much. I'll be 80 in February and will most likely never
build anything again. Still I like to think about what I could have done better.
:-) My gut tells me a +- 24 volt front end would be a start.

Mike Rivers[_2_] October 27th 19 05:03 PM

Mike and Scott
 
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?!! 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.


--
For a good time, call http://mikeriversaudio.wordpress.com

gray_wolf October 27th 19 07:44 PM

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?!!* 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.




Scott Dorsey October 29th 19 04:26 PM

Mike and Scott
 
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.


That's probably enough. My tendency would be to crank the source voltage up
a little more so you can deal with a little more voltage swing. Somebody
will plug some crazy thing in there... two or three volts would be a good
thing to aim for and your front end won't be any more noisy if you move the
bias point up a little.

>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.


That's a crazy amount of power. Yeah, back in the seventies people had crazy
backlines like that but these days I think it's more fashionable (and better
sounding) to have small amps and mike them into the PA.

>It really doesn't matter much. I'll be 80 in February and will most likely never
>build anything again. Still I like to think about what I could have done better.
>:-) My gut tells me a +- 24 volt front end would be a start.


My feeling is that you can never have too much headroom, and if you don't have
high voltage rails you can always stick a couple 10M resistors into a pad on
the front end. Do it right and you get a higher impedance seen by the pickup
for free in the bargain. You get a little more noise but you have to balance
that.

Don't give up! Build something! Even if it's just a pad!
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."


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