TKO the Master Volume on a Super Reverb

[cjlectronics]

I am wanting to remove the master volume feature on my 1979 (Chassis s/n A993561) Super Reverb. I have obtained the schematic for the Super Reverb AB763 and compared the differences and they seem to be minor. I have attached a scan that I have traced on my 79 super's schematic of what needs to be done to kill the master volume feature and wire it just like the BF Super. I was hoping someone would bless my scan and say you shouldn't have any problems or please give me some pointers on what I am overlooking.

Thanks in advance!

CJ

[Steve L]

It looks good to me. I am assuming that you are turning the line out jack to another speaker output jack. I would leave that alone in case you need it as a line out someday, but it is not going to change the tone either way.

The amp should sound much better, however it will not be exactly the same as a 60's blackface version. The larger transformers do affect the tone as well. Not that it will be bad, just slightly different.

Steve

[JoeM]

I had the same amp, the UL version of the SR. I took out the push-pull stuff too. Also, on mine I always had to turn the middle control nearly on 10 to get the sound I wanted. Measured the middle pot and it was only 8k, so I added some additional resistance between the bottom of the pot and ground (I cant recall the number, maybe only 4K or so). Very clean amp compared to the earlier SR, more like a Twin, but with 4x10s.

I dont think I changed the .01 at the PI to .001, IIRC the amp wasnt as bassy as earlier SR. You might try it as is first and see how you like it. I left the 330k stock too.

Incidentally, the link for the AB763 posted, is for the UL versions.

[cjlectronics]

Thanks guys for your input. I was changing the two resistors at the Line Out jack only to be consistent with the AB763 version. Leaving it like it is sounds good, I may want to use it as a line out someday... good suggestion!

Thanks for the heads up on the middle control... I'll check mine out and see what is measures. I'm feel the same way with my SR, I can't seem to dial in a sound that I like and I'm hoping the master switch mod will give me the edge I am looking for.

I want to get a clean sound which is no problem with this amp, but I also want to be able to dial in some bite and bluesy grind that I just haven't been able to find without putting a boost pedal in front of it.

[hasserl]

This is a bit late, but your best bet is to not remove the MV completely, but convert it to a post PI master volume. You can do it very easily, even using the original pot wired as a crossline MV. It works very good to allow you to turn the amp up and get some grind going yet keep the overall volume under control. Some folks don't like the crossline MV, and I understand that. It's not stellar but it works fin in this amp. You could always ditch the pot and use a different post PI style mv if you prefered. The beauty of it all is there is already a hole located on the front panel of the amp, you don't have to go hacking up a vintage chassis and mucking up the face plate. You'll have a far more versatile amp than you will have with the MV just removed, and there is no advantage to going without the MV.

[cjlectronics]

Cool, is there any schematics or info on wiring a post mv? I'd like to investigate it a little more.

Thanks,
CJ

[hasserl]

Originally Posted by cjlectronics

Cool, is there any schematics or info on wiring a post mv? I'd like to investigate it a little more.

Thanks,
CJ

Schematics are all over the place, there are several versions of post pi master volumes. The easiest to implement, as I posted above, is the cross line style MV used in many Matchless amps. Do a search for a Matchless Clubman (You'll probably find it at Schematic Heaven) and you'll see the MV in that schematic. Again, it's not the best sounding MV, best used for scrubbing a few db's off the volume, not too good for bedroom playing. As you get it turned down to past say ~9:00 it starts to really degrade the tone, kind of squashes it. But I've been using that style on my SR for years. I just don't use it for bedroom playing. And like I said, for scrubbing a few db's off the volume it works great. You can implement it in about a half hour, tops. Just use the stock MV pot and remove the stock MV wiring and wire it up the Crossline, piece of cake.

Another very nice sounding post PI MV is the Ken Fisher MV, do a google search on that and you'll find a schematic. Some folks don't like that MV though because the DC bias voltage runs thru the pot, and if the pot should loose continuity you'll loose the bias voltage and could suffer a runaway condition. So another version of the KF MV is to add 2M2 resistor between the wipers of the dual pot and the bias terminals, in case the pot looses continuity the resistors will provide a path for the bias voltage, to prevent runaway. I've instaqlled several of this kind of MV without worrying aout the extra resistors, and so far have not had a problem with bias voltage. I think this may be the most transparent MV of all, it really does not color the tone at all; very, very good performance.

Also, our own Bruce Collins of Mission Amps has a schematic floating out there on the net for a post PI MV that uses 4 caps to isolate the pot from all DC voltage. I've used that one on tons of amps, works great.

Check Steve Ahola's The Blue Guitar site, Bruce's schematic is listed there somewhere, probably a few other MV schematics too. The Blue Guitar