phatt: Thanks for the input

Here's a quick follow up question. The schematic shows a 22k followed by a .047 cap at J2. In your opinion, will putting the .01uf in front of the 22k serve to filter frequencies lower than about 100 Hz? Something that keeps coming up in my mind is that these "thumps" are transients and not really continuous low frequencies. It reminds me of the thump you sometimes hear when powering on/off an amp. So I guess what I'm asking is, will a capacitor filter out (or block) transients?

Thank you again for your input and suggestion.

Ben Price
San Antonio, Texas

J M Fahey: Thank you for your reply. I have posted the schematic to my original post.

Just to clarify. I can force the amp to make the thumping sound by patting the strings of my guitar with the palm of my hand. The amp is a solid state 80 watt combo with a 12 inch speaker. It has the standard low, mid, high controls, with a presence switch. I'm only using the clean channel. I would expect the amp to make a bit of a thumping sound when I pat the strings, but the speaker excursion seems totally out of line with the input. I would expect the amp to have some sort of transient filtering to take care of power pulses and stuff like I'm doing.

I may, or may not, end up giving the amp back to the fiddle player, but I'd like to get a handle on why this thumping is happening. My other amps don't seem to have the issue to this extent.

So, my questions are:
1) Does anyone have a Crate GX-80 with this issue?
2) Your thoughts on handling the low frequency transients.

As you suggested, I'll look into buying a used pedal on e-Bay (like a Boss GE-7), but if there is fix for the amp, I'd like to address this issue at the source.

Thank you again for your input and help.

I have a Crate GX-80 in good condition (along with a number of other makes/models of amps). I don't use this amp often and recently loaned it to a fiddle player. He told me that the amp makes a thumping noise when he is playing on the low strings.

So I've done some tests and I've noticed that when I lightly pat the strings of my guitar with the palm of my hand, the amp makes the thumping sound. When I touch my finger to the cone of the speaker (open back cabinet) and lightly pat the strings, it seems the excursion of the speaker is quite excessive. I believe the fiddle player is dropping his bow on the strings while playing and the amp doesn't seem to be filtering out low frequency transients.

I have the schematic and would have no issue changing discreet parts.

I am looking for your input on two questions:
1) Does anyone else have a Crate GX-80 that has the same issue (or is it just mine)?
2) Your thoughts on how to suppress the low frequency transients?