Phasey Swells

[Decko]

Hi,

I am playing my new 5 watt Wreck inspired amp based off Chappells 440.

The clean tone is crisp and full however when I increase the volume to overdrive I notice a phasey distorted swell.

For example, I will play one note and let it ring out. Immediately following that note a hear a short, quick, phasey swell.

I am not sure where to start trouble shooting.

Can any of you experienced builders provide some technical advice?

Thanks,
Decko

[KT66]

can you post a schematic ?

[Decko]

Here are the links:

Schematic:
http://ax84.com/static/4-4-0/AX84_4-4-0 ... 080927.pdf

http://www.ax84.com/4-4-0.html

Thanks in advance for the help.

Regards,
Danny

[John_P_WI]

I'll take a stab, albeit without studying the schematic, that you have grid blocking distortion (you are driving a grid positive) most likely either at the PI or power tubes.

Make sure you have grid leaks in place, proper interstage attenuation and appropriate power supply decoupling too.

John

[KT66]

Blocking distortion was my first thought too. I looked at the links you posted and one of the schematics for that amp shows 5.6K grid resistors, while another shows 82K. If you used 5.6k I think you should change them to 82k. You could also temporarily patch in a dual ganged pot ( 500k ?) and dial in a value that keeps the amp stable, and then measure it and use that value for the grid leaks.

[Decko]

Gents,

Thanks for your advice! I will work with the grid resistors and play with those values. I will get back to you with the results.

Thanks,
Danny