Valve Jr Master Volume Mod

Gavin · Post by **Gavin** » Fri Jun 08, 2007 6:35 am

Ok. So RobRoe's thread about that Valve Jr mod book reminded me that I never had the balls to try fitting a gain switch or a master volume into mine.

Now I'm feeling a bit fruity and I've decided to give it a try.

Sooo...

I found THIS page, where the dude says that you just short out R6 to get more gain, and R7 if you want even more. So I'm thinking if I take out R6 & R7 and replace them with a volume pot, I'll have myself a master volume, yes?

Here is a circuit diagram of the Valve Jr stock and a picture of what it looks like for reference (although the pic is a modded VJR, the R6/R7 are stock).

Gavin · Post by **Gavin** » Fri Jun 08, 2007 6:47 am

THIS Seems like an alright deal. That would eliminate a lot of the hassle. Why would you need a gain switch though if you had a master volume?

DaveB · Post by **DaveB** » Fri Jun 08, 2007 6:56 am

Get the kit if it has instructions. I think I would put a 100k pot in place of R1 and R2 for a master volume. Get the kit. It takes the guess work out.

Gavin · Post by **Gavin** » Fri Jun 08, 2007 7:11 am

Yeah, fuck it. It's only Â£15 quid delivered, half the work is done for me and it'd probably cost me around that anyway to buy the separate bits n' pieces.

Well that was fast.

What do youse think of putting in a standby switch? Pointless? I'm sure someone gave me a plausible reason why a standby switch wasn't necessary in a Valve Jr.

filtercap · Post by **filtercap** » Fri Jun 08, 2007 7:12 am

A "master volume" control goes after the pre-amp section and right before the power amp section, where it doesn't affect the amount of crunch you get by driving the pre-amp (that's the job of the volume/gain control). In that schematic, a master volume would replace R5. I'd try a 250K audio taper pot there. That'll give you a little more gain than stock when turned all the way up also.

If you have a simple single-pole single-throw switch lying around, you could try wiring it in parallel with R6 to bypass R6 for boost. Or you could wire it in series with R7 for boost, though if you do this it may affect how your gain control behaves. If it were me, I'd try a switch that bypasses R6, and if that gives me too much added gain, I'd put another 1M resistor in series with my bypass switch to reduce the effect.

You could mess with different R1/R2 values for more gain, but that is not where a master volume goes.

DaveB · Post by **DaveB** » Fri Jun 08, 2007 7:19 am

Yeah, what filtercap said (that's why it's safer to get the kit

) I don't think a standby switch is pointless on any tube amp. It allows the heaters to warm up before you lay the B+ to the plates. There is no center tap coming off of the power transfomer to lift. That would probably mean a switch laying right in the B+. I don't think switches last all that long in that environment.

filtercap · Post by **filtercap** » Fri Jun 08, 2007 7:29 am

Gavin wrote:What do youse think of putting in a standby switch? Pointless? I'm sure someone gave me a plausible reason why a standby switch wasn't necessary in a Valve Jr.

I read about small single-ended amps like this not needing the protection offered by a standby switch. I forget the reason why, tho some Web searching will remind me. Fender Vibro Champs and the like don't have standby switches either.

Post by **Mike** » Fri Jun 08, 2007 9:26 am

Filtercap has this one covered

Sloan · Post by **Sloan** » Fri Jun 08, 2007 7:05 pm

wtf do you want a master volume on a valve jr? hly sht

Gavin · Post by **Gavin** » Fri Jun 08, 2007 7:44 pm

I want to get some od without making my neighbours shit themselves.

Sloan · Post by **Sloan** » Fri Jun 08, 2007 7:53 pm

valve JR.

Gavin · Post by **Gavin** » Fri Jun 08, 2007 7:56 pm

I don't live in the woods in Tennessee. My neighbour complained the other day because I had my music slightly loud, and it really wasn't that loud, at 10 o'clock at night.

Sloan · Post by **Sloan** » Sun Jun 10, 2007 4:36 am

just buy your neighbor some pizza d00dz!

Bacchus · Post by **Bacchus** » Sun Jun 10, 2007 1:13 pm

I think I'll probably get the 'bitmo' mods at some point this summer, and perhaps even buy another Valve Junior for different mods.

It would look cool, too. A marshall 412, a marshall head, then two wee valve junior heads, all modified up. Fuck knows if it would sound good, but at least it'll look rockin'.

Gavin · Post by **Gavin** » Thu Jul 05, 2007 10:20 am

Well, it finally arrived so I replaced R5 with a 500K pot and I now have a master volume on my Valve Jr. I can't post a sound clip 'cause I sold my soundcard a wee while back. I could record a clip on my mobile if anyone really wants, but the sound quality would probably not make it worthwhile. I almost completely fucked my amp up by accidentally pulling a spade connector right off the board, but I just jammed it back in and it works(for th now anyway).

It sounds pretty much like I expected, which is alright but not exactly very gainy at all. I reckon I'll probably install a gain switch.

filtercap · Post by **filtercap** » Thu Jul 05, 2007 6:37 pm

Congrats!

Yeh, using a 500K pot instead of the 220K fixed resistor will cause the amp to "throw away" less of the signal right before the output tube (with the master volume most or all the way up), and thus push the output tube a bit harder. With the master volume wide open, this'll either result in the sound being:

-- somewhat louder with no change in overdrive characteristics, OR

-- somewhat louder with a little compression but still no additional overdrive, OR

-- louder with some warm compression/clipping.

I'd expect one of the first two unless the stock amp was designed to run the power tube pretty warm (not likely). In none of these three cases will you get more stompbox-type overdrive than you did with the stock amp, because the pre-amp stages aren't being pushed any harder than they were originally.

No problem, because now you have a master volume that, from your description, appears to be working the way a master volume should -- letting you turn the volume down even when the preamp section is going full-tilt. And now you go on to do your gain tweak(s) in the preamp section to get that higher-gain sound.

I'm curious -- do you notice a change in the amp's overall tone? More or less high-end when the master volume's all the way up?

Post by **Mike** » Thu Jul 05, 2007 6:41 pm

filtercap got teh skillz

filtercap · Post by **filtercap** » Thu Jul 05, 2007 7:49 pm

Shux.

By the way, Gavin -- I read back over the thread, and maybe I'd better clarify what I mean by "gain". I think of "gain" as "getting a bigger signal out than you put in." This may cause clipping, which gives us that overdriven sound, but gain and clipping are two different things. For example, a powerful home-stereo amp might have vast amounts of gain (tiny signal in, huge signal out) with no clipping at all. So when I mentioned that the master volume pot would result in higher gain when turned up, I simply meant a stronger signal reaching the output tube -- not necessarily any more clipping.

Of course, guitar amps are designed so that one stage or group of stages within the amp can provide so much gain (relative to the input from guitar) that the next stage in the amp is forced to clip the signal and distort. With guitar amps, "gain" is so closely associated with distortion that the words often get used interchangeably. Like everybody else, I always consider a "high-gain" guitar sound to mean distorted and compressed. That kind of breaks the original definition of "gain," but it's a guitar thing....

Gavin · Post by **Gavin** » Sat Jul 07, 2007 9:53 am

filtercap wrote:Congrats!

Yeh, using a 500K pot instead of the 220K fixed resistor will cause the amp to "throw away" less of the signal right before the output tube (with the master volume most or all the way up), and thus push the output tube a bit harder. With the master volume wide open, this'll either result in the sound being:

-- somewhat louder with no change in overdrive characteristics, OR

-- somewhat louder with a little compression but still no additional overdrive, OR

-- louder with some warm compression/clipping.

I'd expect one of the first two unless the stock amp was designed to run the power tube pretty warm (not likely). In none of these three cases will you get more stompbox-type overdrive than you did with the stock amp, because the pre-amp stages aren't being pushed any harder than they were originally.

No problem, because now you have a master volume that, from your description, appears to be working the way a master volume should -- letting you turn the volume down even when the preamp section is going full-tilt. And now you go on to do your gain tweak(s) in the preamp section to get that higher-gain sound.

I'm curious -- do you notice a change in the amp's overall tone? More or less high-end when the master volume's all the way up?

I'd say the middle one. It gets distorted depending on how hard you hit the strings, but not all that distorted. I can't say I've noticed any change in the general tone of the amp. My old usual setting would be 3 on the normal volume, which these days is three on the normal volume and the master all the way up, sounds the same to me. Maybe a little quieter actually.

What I mean and want by gain is distortion, like, zeppelin drive distortion. Not just a louder output signal.