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I just bought a valve standard off ebay - it appears to be in perfect physical condition, with the exception of the DSP chicken knob, which is missing - but as soon as I turned it on and turned up the master volume it began to buzz.
After some basic troubleshooting, I have determined the following:
1) I miked the amp and pulled the frequency of the buzz, which is 120hz. It definantly sounds like buzzing, and not a hum... It sounds to me like a sawtooth waveform.
2) The buzz is dependent only on the master volume knob: I can turn the gain knob all the way down and the buzz remains. Whether I have a guitar plugged into the amp or not, the volume knobs on the guitar all the way up or down, the gain knob all the way up or down, or any combination of the above, the buzz remains constant, varying only with the master volume.
3) The volume and contour of the buzz changes as the I rotate the master volume knob: From about 0 to 2, there is no buzz, then it gets gradually louder until about 5 or 6. (12 o'clock on the knob) After about 7 or so, the buzz goes away, and remains gone all the way up to 10. There is, however, some other noise with the master volume cranked, but it is a much more reasonable noise that I would expect from turning any amp up to 11.
4) The tone of the amp itself appears to be unaffected. The buzz isn't louder then my actual playing, but anytime that I stop playing its definantly noticable unless the MV is way down, which is fine for the bedroom but won't be fine when I take this to band practice.
This is my first tube amp so I would love to have some suggestions on how to go about fixing this problem. I pulled the schematic to the amp from a post on this site, which I'll attach to this post in case it helps anyone.
I'm eager to go digging around, but first I need to know where to look. Am I correct in assuming that the issue is probably close to wherever the bigger power tubes are? Basically, I just need to know what I ought to change or what I need to look at and test to narrow the problem down further. I really like the looks and tone of this amp, and don't want to blow $80 in lost S+H charges to return the amp to the seller I got it from.
*** Edit ***
The thread I pulled the schematic from: http://music-electronics-forum.com/s...ead.php?t=3020
The guy seems to have had the same problem as I do, but the solution post talked about noise from the DSP: whether I have the DSP switched on or off doesn't affect the buzz... Plus, I'm really out of my league here (co-axial cable in an amp? I had no idea...) so could use a more thorough explanation of the why's and how's of fixing this, or a link to someone else giving a more thorough explanation, if one is available
*** /Edit ***
After some basic troubleshooting, I have determined the following:
1) I miked the amp and pulled the frequency of the buzz, which is 120hz. It definantly sounds like buzzing, and not a hum... It sounds to me like a sawtooth waveform.
2) The buzz is dependent only on the master volume knob: I can turn the gain knob all the way down and the buzz remains. Whether I have a guitar plugged into the amp or not, the volume knobs on the guitar all the way up or down, the gain knob all the way up or down, or any combination of the above, the buzz remains constant, varying only with the master volume.
3) The volume and contour of the buzz changes as the I rotate the master volume knob: From about 0 to 2, there is no buzz, then it gets gradually louder until about 5 or 6. (12 o'clock on the knob) After about 7 or so, the buzz goes away, and remains gone all the way up to 10. There is, however, some other noise with the master volume cranked, but it is a much more reasonable noise that I would expect from turning any amp up to 11.
4) The tone of the amp itself appears to be unaffected. The buzz isn't louder then my actual playing, but anytime that I stop playing its definantly noticable unless the MV is way down, which is fine for the bedroom but won't be fine when I take this to band practice.
This is my first tube amp so I would love to have some suggestions on how to go about fixing this problem. I pulled the schematic to the amp from a post on this site, which I'll attach to this post in case it helps anyone.
I'm eager to go digging around, but first I need to know where to look. Am I correct in assuming that the issue is probably close to wherever the bigger power tubes are? Basically, I just need to know what I ought to change or what I need to look at and test to narrow the problem down further. I really like the looks and tone of this amp, and don't want to blow $80 in lost S+H charges to return the amp to the seller I got it from.
*** Edit ***
The thread I pulled the schematic from: http://music-electronics-forum.com/s...ead.php?t=3020
The guy seems to have had the same problem as I do, but the solution post talked about noise from the DSP: whether I have the DSP switched on or off doesn't affect the buzz... Plus, I'm really out of my league here (co-axial cable in an amp? I had no idea...) so could use a more thorough explanation of the why's and how's of fixing this, or a link to someone else giving a more thorough explanation, if one is available
*** /Edit ***
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