71 twin reverb adding master vol

[mikepukmel]

Is this the right place to add a master vol to this circuit? If so, what value should the pot be?



Ive seen some odd looking mod's that go across the outputs of the phase inverter, wondering why that would be better or worse.

[The Dude]

Here's a twin schematic with a MV. You could just copy it.

http://www.thevintagesound.com/ffg/s..._100_schem.jpg

FWIW: Tone is in the ear of the beholder, but If you think you're going to get any kind of decent overdrive sound by having a MV with the twin, forget it. IMO, you're much better off with a stomp box.

[bob p]

Fender amps don't generate enough gain for a MV to be useful for distortion control. That's not to say that they're worthless, however.

Most people find the big Fender amps without MV to be difficult to control at ultra-quiet levels. Sometimes the taper of the channel volume pot is just jumpy at around 1-2, which makes it difficult to play quiet jazz in a bar with a Twin Reverb. Unlike the rockers who think that BF amps rule, jazzers prefer the Fenders with MV controls because they allow you to obtain very fine control over a big amp at low volumes. That's an absolute necessity if you're playing jazz standards while people are having drinks or dinner.

The MV allows jazz guys to have one amp that does everything. They can take their Twin Reverb to any gig. If they didn't have MV controls they'd have to pack smaller amps for smaller gigs. Some guys do that, some prefer a big amp with the MV control for everything.

MV are useful for other things besides overdrive. I like having two volume knobs so that I can fine tune clean volume levels more easily.

[mikepukmel]

Fender amps don't generate enough gain for a MV to be useful for distortion control. That's not to say that they're worthless, however.

Most people find the big Fender amps without MV to be difficult to control at ultra-quiet levels. Sometimes the taper of the channel volume pot is just jumpy at around 1-2, which makes it difficult to play quiet jazz in a bar with a Twin Reverb. Unlike the rockers who think that BF amps rule, jazzers prefer the Fenders with MV controls because they allow you to obtain very fine control over a big amp at low volumes. That's an absolute necessity if you're playing jazz standards while people are having drinks or dinner.

The MV allows jazz guys to have one amp that does everything. They can take their Twin Reverb to any gig. If they didn't have MV controls they'd have to pack smaller amps for smaller gigs. Some guys do that, some prefer a big amp with the MV control for everything.

MV are useful for other things besides overdrive. I like having two volume knobs so that I can fine tune clean volume levels more easily.

Thanks Bob! Yeah, re "Most people find the big Fender amps without MV to be difficult to control at ultra-quiet levels. " its the vol adjustment I remember from way back when we were kids with these amps. Adjust the vol control up a TEENY bit and the sound jumps and you're shaking the window sills. This is a great "clean" amp, so just looking to get the output reasonable at a lower volume. My brother suggested an 'amp cabinet' room, small room double or triple 5/8" sheet rock walls, that I could mic. Not quite there yet with that kind of mod to our house.

Got some more photos of one of the twins I want to make an offer on. Way too clean inside the chassis, I don't have the heart to 'hack' it. I hope I can get this one, will just clean it up and replace whatever it needs (looks like only needs a tube set). "I will NOT be a destroyer of 1970's fender Twin's. I will be a LIBERATOR of them!!"

[Chuck H]

re: The stock volume control...

Bourns makes a 10% log pot that would be an enormous improvement in control at lower settings. I think the stock pot is a 25% taper. You'll need to read some of the Bourns literature because there are part number specs for the specific taper, shaft type and rotational torque. Don't get the rotational torque wrong or it'll bug the crap out of you. Basically you just DON'T want the guitar pot because it has a super low torque. I know Mouser has what you would want but I don't have the part number off the top of my head.

As to master volume location...

I would probably use a post PI master since it AT LEAST does something different from the stock volume control. Since there isn't a lot of useful distortion in the preamp a post PI master will allow for the addition of PI distortion (for better or worse). And if you're only using it to mitigate clean volume it still does the same thing a pre PI master would do up to that level. Basically, there's nothing to be gained with a pre PI master and a post PI master will do the same job and add a new trick if you ever want to use it. I've tried all the post PI masters at one time or another and I can't really say that the Marshall type, Trainwreck type (lar mar?) or simple shunt type are all that different in effect at moderate settings. I'd probably start by putting a simple 1M pot across the downstream side of the PI coupling caps to get a feel for whether I wanted to bother. If I liked it at all I'd wire it up with the Lar Mar only because I think it's the least intrusive on stock circuit function. It's a good and eloquent design.

JM2C

[Leo_Gnardo]

Way too clean inside the chassis, I don't have the heart to 'hack' it. I hope I can get this one, will just clean it up and replace whatever it needs (looks like only needs a tube set). "I will NOT be a destroyer of 1970's fender Twin's. I will be a LIBERATOR of them!!"

What goes down must rise back up, right? Maybe in the future some big rock star will be seen on stage / in studio twanging thru his stock MV Twin, then the prices will go thru the roof. Let's hope so! It's worked for a lot of other gear so why not...