waveforms

[lenny]

my amp is transitorised.it distorts,if i inject a signal in input,should it be distorted at the o/p of the preamp.i can isolatethe o/p stages.
i use a/f sig-gen.and a scope.
wonder if someone out there can help!!
lenny

[oc disorder]

Firstly what sort of level are you feeding in to the input and what is the input expecting?
I use about half a volt peak to peak (measured on the scope) for guitar
and try to set the tone controls for a flat response.which often is an illuminating exercise.
To do that I reduce the output drastically and feed in a square wave (yes I know there is no such thing but for the purpose of explaination) and then adjust the tone controls for the best result ie output shape close to input
shape.
Then switch back to sine wave with aprox.5v p to p.
The pre amp output should be like the input but sometimes with eq built into the circuit it can look a bit strange...
Try it at different frequencies 1kHZ 1000cps is or was the norm some people use 2k but you should be able to see where it rolls off by going down to
50 hz and below and 16k and above.

BTW I heard the old Gibson EBO bass pu's the big fat ones like Jack Bruce used to use in Cream were capable of 1volt output but I have never had one to test.

The preamp should just faithfully boost the input signal un distorted likewise the power amp should also Usually the power amp cracks up before the preamp but there are so many variables it depends on the design.

Again see what your sig gen is putting out into the input...
A classic bad example is when CD players first came out some "users"
plugged the output of the cd into the phono or magnetic cartridge input
totally overloading the input. They reasoned (incorrectly) that as it was the new replacement for their old turntable thats where it went...

Hope thats some help...some more detail would be helpful like... what sort of input.,... are there any resistors on the jack (assuming its a guitar input) like
1 meg to ground etc

Hope thats some help at least it might get the ball rolling..

[lenny]

waveform

hi
2khz o/p at socket turned vol control up & down, less distortion when down.
used a sig gen & scope,looks like it is my preamp.the level @ the i/p is about
100mv
cheers len

[lenny]

waveform

hi!!
forgot to tell you the amp is a maine 100c guitar amp,scope is 12mhz b/w
the preamp uses bc/143/x85/212/182/548/238/558.
loudness is ok,distortion is on top strings mainly.
i do not have a cct.
cheers!. (tried square & triangle same results)
i also variad the i/p freq avove and below 1khz
help please!!!!!!!
lenny