Tiny terror clon Problem

[leanr]

Hi everyone, I've done a tiny terror clone.

The problem is that, when i rise the gain control (over 10% ) the noise increases too much.
I looked at the signal with the oscilloscope (signal on pentode grid) and i saw clearly a square wave at full gain.
It seems like a sinusoidal noise is there and when i get full gain logically it gets distorted (squared). Even if do not touch the guitar.
It is like i loose snr when i turn up the gain control. Make that any sense?

Any idea?
This is my first project, i'm a hobbiest.
Sorry about my bad english.
Thank you all.

 

[Richard Ellis]

A square wave is a symptom of far far too much gain in the preceding stage.
Think about how square waves are typically generated. Take a plain sinusoidal signal, amplify it with an outrageous gain, as the signal tries to hit the impossibly high positive peak, it squares off from the limitations of the power supply.
Do you have a schematic we can see? Perhaps a tube in the front-end is incorrect & has way too high a gain value. Or...???



_________________________________________________Rick.........

 

[TonyTecson]

moved thread to right forum....

 

[leanr]

I agree with you Richard. This sinusoidal wave must be noise , because i appears even when guitar is not played.
The schematic below..

Thank you all,
Sorry about my mistake AJT

 

[leanr]

I forgot to mention that i test the amp with an audio oscillator & everything looks fine on the oscilloscope. I can rise the gain control an it does what it has to.
But if i connect an small and cheap speaker it seems like i can't still rise all gain.

 

[Richard Ellis]

I'll assume you just built this & it's not performing correctly?
Did you use a "LOG" potentiometer? That one pot runs a lot of functions....check & double check all your connections to make fully sure it's wired correctly, OK?



_______________________________________________Rick..........

 

[famousmockingbird]

Is this test with an input signal or not? If no then is the input shorted to ground? Are you using shielded cable for your signal runs?

Some good quality pictures for us to look at will help us help you.

 

[leanr]

I use log pots...and check several times with a friend. The wired is correctly.
It's strange that when i connect an audio osc it seems to work ok, but not with a guitar.
With guitar works ok for low gain and any position of volume pot

 

[leanr]

famousmockingbird .. the test was with an audio oscillator for the input. I use shield cable for the signal, even a tried changing all wires of the tube for shielded ones, just in case. It does not any difference.
I used an universal board (that one with multiple holes) so, i think that you will find extremly hard to find the problem with pictures.