"Ron(UK)" wrote in message
...
N Cook wrote:
Ron(UK) wrote in message
...
N Cook wrote:
Ron(UK) wrote in message
...
N Cook wrote:
The gain on both channels is too high in my reckoning.
Feeding only a 1mV RMS, 400 Hz, (600 ohm source) into a guitar amp
input
I
would not expect the output to be on the uncomfortable side of
listening
to
continuous sine at vol setting 3.
0.12V ac rms over 8 ohm speaker at "3" and 0.39V ac at "6".
At "3" setting 0.19V ac (measured as if it was sine RMS) on both
splitter
driver outputs
No distortion at that sort of low level input.
What and where in the preamp to look for somethiong amiss?
Have you tried it with a guitar?

Ron
Nope, I've always intended picking up a magnetic pick up from somewhere
but
never have, let alone a guitar.
But all other amps i've fed this sig gen into then around 100mV is the
norm
for just speaker output signal monitoring purposes, rather than dummy
load
checking
How do you repair guitar amps if you dont have a guitar? It`s not all to
do with specs and test gear you know, some guitar amplifiers have huge
amount of gain and are intended to produce a quite specific colour of
distortion.

Do you have a typical stage microphone to test PA amps?

Ron

Balanced or unbalanced Sure mics for those tests and sig gen for guitar
amps.
I repair amps, not disrepair them. So a good sine in and a good sine out,
with any luck a clean channel, or at least minimisable distortion.
If its a "repair" job concerning the wrong sort of distortion then I turn
them away.
I find muso terminology for such stuff impenetrable as do they, not
understanding temminoloy as cross-modulation, clipping etc.

I have quite enough clutter here without a guitar as a test instrument
and I
still would not understand what they're interpretation was for the wrong
distortion/s anyway.

Don't you understand that striving for a clean distortion free sound isnt
right with a lot of guitar amps? A perfect waveform doesn't give the sound
a player might want. It`s the distortion that gives them their
characteristic sound. Setting up the bias for example - the technically
correct bias isnt necessarily the right bias (if you get my drift) They
aren't hifi amps, they are designed to colour the sound the way a
guitarist likes.

Ron

As you say Ron, part of a valve amp's sound is the fact that it can be made
to go smoothly dirty, and often even has a channel designed to do just that
by deliberately overloading the second or third stage with pre and post gain
controls. I always think of the old Canned Heat number 'Let's Work Together'
as a premium example of how a guitar sound can be horrendously distorted,
whilst still being sufficiently musical to find its place in the song. I've
no idea as to whether that guitar was pre-processed with a fuzz pedal, but I
have heard stage musicians get a similar sound from just making use of the
overdrive facilities on their amp. 100mV does sound like a lot of input
compared to a guitar pickup, though. About the maximum that I normally drive
these things with, is 20mV.

Arfa