20/20 mono : problem?

Hello!
I have a problem with my Mesa 20/20 power amp.
An output transformer is burnt, and I must have it replaced, and it
seems very expensive.

The technician told me that it was a recurrent problem with this amp,
when used mono.
In the manual, they say that there is no problem using it mono, if you
don't load the unused input, and put the unused channel volume to 0
end presence to 10.
But the technician says it's not true, and this amp should never be
used mono. He gets 20 20/20 per year with channel 2 output transformer
burnt, just as mine, because of a mono use, he says.

So, did anyone experience such problems?

I usually use it in a mono configuration, with a Palmer PGA04, and it
wouls be a real problem if I can't use it this way.

Hope you can help.

The problem might rather be matching the impedance with the outputs of your amp. Suppose you use the 8 ohm outputs the combined load must be 16 ohms. Also the outputs must be in phase.

From a designer's point-of-view the diff between a 2x20W amp and a 40W amp is the number of output transformers. Since the signal is split equally the transformers shouldn't overload in any way.

Thank you for your help.
The problem is not to use both outputs in a mono configuration, but to use only one output, according to what the technician told me.
He says that you have to load the unused output, even if there's nothing in, otherwise you can burn the output transforer, just as it happened to me.

Fot him, putiing the master level off and the presence at full level is not enough...

I had one for about 4 years and used it mono and never had a problem but who knows if it would of blown in year 5 of use. I am now using a 50/50 mono and don't have a problem either...as of yet. I would give Mesa a call and not just take the technicians word for it. I am sure Mesa feels comfortable with it being used in mono for them to say you can do itin the manual.

I really hope you are right.

I said the same thing in a french forum, and another technician told me the same : he has 15 20/20 per year with the same problem. He says Mesa certainly has an interest in this problem : this piece is very expensive!

I hope he is wrong, and all those problems come from a bad use, but now I have doubt. As far as I'm concerned, and don't think I made any mistake with my 20/20... But who knows?

Please let me know when you have an answer from Mesa (even if I can't imagine them saying "yes, indeed, there can be problems with a mono use, but we never told it!") :?

Thank you!

Edit : oh, sorry I thought you told me you would call Mesa...
I can't do it , I live in France and there is no Mesa contact here, as far as I know.

I can't see why there has to be a load on the output if the volume isn't turned up to begin with. Should however the input be fed a signal and the volume be cranked up we're in for some trouble.

An amp tech in France sees TWENTY blown 20/20's each year? That doesn't sound right. And my first guess would be that people are forgetting what jack needs to be empty and what control always needs to be set to zero when running the amp in mono. And I'd call Mesa from France--you're looking at hundreds in repairs anyway, the cost of the phone call is small change on top of that.

Personally, I'd buy a 2x10 cab wired for stereo to forever prevent that mishap. Not that much heavier, not that much louder, but 100% safer than the mono setup.

Thanks.
I think you are right...

I'm planning to buy a 1x12 cabinet, and load the other output with my PAlmer.
But I did not think about a stereo 2x10...

This might be another topic, but do you think it would sound as good? Do you have models of such cabs to tell me?

I used to use a Rivera half-open 2x10, and it was great. Could be used in mono or stereo. Depending on your processing, you could make one speaker dry and one wet, or whatever. Some soundguys don't like stereo effects or dedicating two mics to "just" the guitarist. Avatar will also make a 2x10 for you.

I'd say it depends on the tone you want to go with. More bite by the number of speakers and firmer tone the smaller you go. I used to think the more drivers and the larger box the better, but I've come to like few high power drivers in open/ partially open cabs lately.

Many thanks for your help!

For information, I usually play pop, rockfunk, and a little jazz, no metal...
Do you think a 2x10 could do with these styles?
I know the best thing I could do would be try some of them, but I think it will be difficult...

Sorry to bother you again, but I have the opportunity of buying a 1x12 Mesa Thiele with EVM-12L speaker.
Do you think it could fit? Don't you think the 200w capacity of this speaker isn't too much fot my 20w amp? Wont it be too "rigid"?

I have found no 2x10yet... Any advice?

Many thanks!

My 20/20 set is with two 1x12" cabs, one open back, one thiele, both loaded with 200W EVs. IMHO a match made in heaven!
And when I can't be bothered to take the second cab I run the set-up in mono through one channel. I concur with tiktok, 20 per year, just in France?
Ian

Thank you!
What is the sound difference between your two cabs? Even if it's subjective, which one do you think would be the best for my musical tastes?
Yes, 20 per year in France, that's what I've been told... But thanks to your contributions, I'm now almost sure the problem is mainly due to a bad use...

daillou said:

Sorry to bother you again, but I have the opportunity of buying a 1x12 Mesa Thiele with EVM-12L speaker.
Do you think it could fit? Don't you think the 200w capacity of this speaker isn't too much fot my 20w amp? Wont it be too "rigid"?

I have found no 2x10yet... Any advice?

Click to expand...

I think a 2x10 would sound fine for what you've described, but they are not very common. You'll probably have to order one custom.

I usually use a pair of EV Thiels with my 20/20, and it's a great sound. One man's "rigid" is another's "tight definition".