20/20 low volume troubles

[chimpinatux]

Hey guys, just joined this forum

Anyway i just got hold of a used 20/20, everything points to these amps being very loud for 20w, so i was quite shocked that i cant seem to get it above a 'loud bedroom' volume :?

First thought was 'old tubes' so i had a set of JJs i was going to stick in anyway, but that doesnt seem to have changed much.

Volume knob seems to have a short zone of 'no sound' before steadily increasing volume up to that level, to about 11 oclock, then above that there is no extra volume at all, even up to full, even though there is noticable increased tube saturation (actually kinda interesting to be able to accurately hear those effects without volume change but thats not the point...)

Tried it on both channels, same problem

 

[ando]

Sounds like you need a service. It's definitely not normal for a 20/20 to be bedroom quiet. Might be just the volume pot needs replacing. Is it the behaviour the same on both channels?

 

[chimpinatux]

Yes its both channels, so i wouldnt have thought it would be one cranky pot.

I am running it through 16ohm cabinet i got told that was the problem before, which is fine, and i know would mean a volume drop, but this is just ridiculous

 

[talltxguy]

My 20/20 also has a point where the volume kind of just stops and the saturation increases. I actually like the effect. Anyway, could the volume issue be one of those driver 12AX7's? My 20/20 is only running through a 1X12 Roadster cab, and it is ferociously loud. My ear can't tell the difference - volumewise, that is - between my 20/20 and the 50/50 I used to have. And the 50/50 was a beast!

Please keep us updated on the problem and solution.

 

[chimpinatux]

I took it to a local Mesa dealer and i think the guy there was trying to BS me, basically kept saying that 20/20s running through a 16ohm 1x12 wont be any louder than say, a valve jr :? and it would be louder through an 8ohm cab say (i think i really should go and see an amp tech but thatl have to wait at least a week)

As you say if theres a large region where its just saturation and little extra volume being normal thats not really a problem, its kinda cool too i guess, but problem is that its not even at a properly usable volume at that point.

Anyway, the tubes was the first thing on my mind, i replaced EVERY tube in the thing, all 4 EL84s and the 12AX7s too, so i cant imagine it would actually be down to dead tubes

This is just really weird

 

[Old BF Shred]

Sounds like it might be a power supply issue. A cap that won't take a full charge could do it. Hopefully the transformer is OK.
You may want to call Mesa directly and get their opinion. And if a tech becomes available in your area, time to pay a visit.
While we may all have different ideas of what defines "really loud", my Studio 22, at 22 watts with only one channel, will absolutely scream long before you hit full volume.

Good luck!

 

[chimpinatux]

Sounds like it might be a power supply issue. A cap that won't take a full charge could do it. Hopefully the transformer is OK.

I just did a little research and that seems fairly likely, operating at normal just not LOUD enough. Really hope it isnt the transformer, but if that were the case shouldnt it either be not working or the be smoke/flames etc.

 

[elvis]

Transformers are funny things. You could get an open winding and no sound, or shorted windings and almost any sort of wierdness along with it. Low volume and heavy saturation that seems like clipping doesn't sound normal. I used to have a 20/20 that would SCREAM. It did get pretty overdriven after about 12:00 on the volumes, but it was deafening in a closed space.

You could also have bad bias on the driver tubes. If the plate voltage on the preamp tubes is low due to a bad cap or resistor, you'd get exactly what you've described. I think there's a probably a series choke that could also be bad.