I have an amplifier that is very similar to a Fender Champ, only it is a bit heavier (it's a Kalamazoo Model 2). Around 7 you get a nice overdrive, but above that the low-end starts getting a lot louder than the rest of the frequencies and it starts sounding 'farty'. Do you know why this is, and how I can stop it? Thanks.
This is a characteristic of some amps -- esp tube amps, and you've described perfectly. "Farting" is accepted jargon in amp-speak. I can't positive about the particular cause(s) in your case, as there are several possibilies, three of which are speaker distortion from over excursion and/or doubling (over-large back and/or forth motion and/or plain old low freq distortion), power stage tube perfomance/quality and power supply sag/recovery issues. All occur at low freq, high volume levels, where the largest voltage swings occur at the amp output. The "easiest" fixes to try, would be speaker or tube replacement, but there is no guarantee of success. As a test of the former, you could try hooking your amp up to an external cab with higher power handling capability to see if the problem goes away. (Make sure the impedance is the same as the current speaker!) If it does, the speaker is likely the culprit, if not -- well it's likely to be one of the other two.
For completeness: There is a slight possibility that you are simply getting a mechanical rattle or some tube rattle, but given your rather concise description -- probably not.
Joe forrok_star or Wes might have some valuable insight on this. I'd also try a web search on your amp model and the problem, as often times info on rec'ed mods will pop out.
Good luck -- Greg
-=tension & release=-
Without hearing it or doing some troubleshooting this would be W.A.G. It could be anything from tubes to the Output tubes biased way too cold, power supply problem, decoupling capacitors in the B+ lines. Would you say that maybe its making a putt-putting sound or motorboating?
I did a little searching and found that the speaker and output transformer used in those amps are not the greatest. You haven't been or tried running extension speakers? The Output transformer can't handle the load. You may want to consider replacing the speaker, (and most likely the output transformer).
Have you tried adjusting the tone stack. Its a little different from a standard tone stack setup.
Joe
Here is a nice site about the Kalamazoo Model 2. See Modifications.
There's also the schematic. Maybe Joe can give you more advice after seeing that.
If you know something better than Rock and Roll, I'd like to hear it - Jerry Lee Lewis
Hey, thanks a lot you guys. You three are like the Three Musketeers of the Amp forum! Everytime I ask a question you three all give informative advice! I'm going to look into a new speaker and an output transformer. That seems to be the most likely culprit of this situation. Can you give me a little advice on buying output transformers? Do you have to buy specialized guitar ones, or can you just pick one up at Radio Shack or an electronics store? Also, does it have to be the same (4K input, 8 ohm output)? Thanks a lot.
Unfortunately it doesn't have a lineout jack, but I might try cascading it into another amp I have to see if that has any effect. I'm excited to have a good sounding guitar amp! I'm afraid to get an OD pedal just yet though, because I don't want to buy it and figure out my tone is a farty mess because of the speaker, or whatever the problem is.
