Dual Caliber & Caliber series Output/Master MOD

[EightySix]

Anybody here know about this little mod? Supposedly the DC-2/3/5 have a weird resistor placed across 2 lugs of the Output pot, or some soldered straight to the PCB on later models.

Heres the original thread, I posted on the last page--
http://www.thegearpage.net/board/showthread.php?t=229027

Basically, I dont know if its the same way on the .22/.50 cal/cal + series yet so Im trying to find out for sure. On my .50 cal + the resistor is a Blue/Grey/Brown/Red - w/ brown tolerance band (680 ohm?) on the Master pot. Anybody with a Caliber/Dual Caliber series amp might want to look into this simple mod.

Heres the schematics, theyre pretty useless to me. But might be useful to any techies out there.

.50 cal + Schem's --
http://www.freeinfosociety.com/electronics/schemview.php?id=504
http://www.freeinfosociety.com/electronics/schemview.php?id=503

 

[EightySix]

Anybody with tech. skills see anything else weird going on with this 50 circuit?

 

[Monsta-Tone]

That's a 68k I believe.

I don't see it on the drawings for the .50, .50+, 22 or 22+.

On the DC's, it is a 220 or 250 k resistor in parallel with the Output volume.

 

[EightySix]

That's a 68k I believe.

I don't see it on the drawings for the .50, .50+, 22 or 22+.

On the DC's, it is a 220 or 250 k resistor in parallel with the Output volume.

I wish I had a camera, but let me to try explain how it looks on my 50+.. marked 6/92, so I guess its a newer model

Looking at the amp from the front-

The 'extra' resistor is going from the left leg to the center leg of the Master pot. The left leg of the Master is then connected with a grey lead to the front of the PCB, pcb marked 'GRY' The center leg of the Master pot is then connected w/ a grey lead to the left leg of the presence pot. The right leg of the master pot is connected with an un-insulated lead to the right leg of the Volume, Lead Mstr., Mid, & Presence pot. The right leg of the Volume pot looks like its going to input and ground.

 

[Monsta-Tone]

HMMM!
That is weird. It is possible that this was a transitional model, especially if it was made right before the Dual Calibers.

If you lift one leg of the resistor and the amp still works fine, but the Master is working better than before and has a much smoother taper, then I would say leave it off.

 

[EightySix]

(Snip) I decided to wait 30 min for the caps to drain, so I cant say it was a night & day difference, but noticeable... more 'open' sounding (highs I think) and the Master is actually functional now at '1' and not so **** sensitive. Its probably more noticeable on the DC series since the resistor is 3x what this one was... I wonder how many other .22/50/+'s have this, and why the hell Mesa started doing it in the first place if it wasn't in their own schematics?

 

[Monsta-Tone]

They have done a lot of experimental stuff over the years. When they get enough upgrades to an amp, they come out with a new version or maybe a new amp.

It's entirely possible that this resistor was added by someone else too.


As for 'Why?'
The general consensus is that it simply makes the amp much louder on 1 than any other amp. Sort of like a 'Wow Factor!'
The bad side is that it makes the amp completely un-usable at lower volumes.

 

[briguy1960]

OK on my DC-3 there is no resistor accross the pot but it looks like its sitting on the circuit board FYI my serial number is
DC3 00882. What vintage might that be? And where is the correct resistor to disable?

Thanks so much

Brian