[Born2bwire]

I just got a MG Head OTL amp, I believe the second version, and I noticed that on the transformer mode when I switch to no negative feedback loop, the balance shifts to the right. When I use the amp in transformer w/ feedback or OTL the balance is correct. Any suggestions?

 

[Kevin P]

Check out this thread: Is there something wrong with this MG Head OTL? - Vitalstatistix had a similar problem but he was getting no sound at all in the no feedback position. Methinks your problem is similar, albeit on one channel only.

It appears that the negative feedback switch/circuit is wired incorrectly on some MG Heads. Perhaps your dealer can straighten it out for you.

KJP

 

[Born2bwire]

Yeah, I've kept up with that post. I was afraid y'all would tell me to return it to my dealer because he's a two and a half hour drive away.

The problem is not that I don't get the left channel, but that the increase in the volume when removing the NFB is greater in the right channel than in the left channel. I opened the amp up and what puzzles me is that when I switch the NFB off, it just connects the switch to a open circuit in that nothing is wired to the third pole. The signal going to the switch and out of the switch to the transformer jack is all connected to the middle pole (I hope this is the right term) of the switch. Thus, if there was a problem with the solder point on the input and output of the jack, shouldn't it show up when the NFB loop is put in the equation? Unfortunately, the solder points are hidden by the NFB loop wires, so I would have to remove them first to get at the others, which I am hesistant to do so considering the many misadventures I have had with a soldering iron.

 

[Vitalstatistix]

The best way is to return the amp to the dealer. Don't try to fix it if it's too dangerous. Better be safe than sorry.

 

[Joe Lau]

Quote:

Originally posted by Vitalstatistix The best way is to return the amp to the dealer. Don't try to fix it if it's too dangerous. Better be safe than sorry.

It may be cause by problem of balance of 12AX7 of EI. It ma be nothing wrong inside th eamplifiers.

 

[Kevin P]

That's a good idea. See if you can get your hands on another 12AX7 or 5751 and see if the problem goes away. Another thing to try (though it's probably not this) is try switching the two 6BQ5s (or EL84s or whatever power tubes you have) and see if the problem shifts to the other channel. If it does it's with one of the 6BQ5s.

KJP

 

[Born2bwire]

I have three other tubes, a Sylvania Blackplate 5751, Raytheon/Westinghouse 5751, and a Mullard 12AX7. I have switched in the Sylvania and switched the EL84's with my EI tubes (the EI are matched, I got them from Upscale Audio). I tried the EI and the Sylvania and got the imbalance. But just to be sure, I just checked the Westinghouse and Mullard. The vocals are more central and there doesn't seem to be a shift in the vocals when I change the NFB status, however, I lose softer sounds on the left channel so the volume is still off. I'm now thinking that this is a problem with the volume control. When I have it soft, I only hear the right channel and the more I turn it up, the more the left comes in. With OTL and no NFB and Trans, the gain is so high that the volume is much lower, thus if the volume control was the culprit, this would explain why Trans w/ NFB would sound correct since I have to turn it up and at the higher settings the volume control would be outputting both channels at the same volume.

Oh, almost forgot. Arrrggg, matey!!! See the Member's Lounge if you're clueless.