Cross line master volume

[txstrat]

I'm about to add a cross line master volume (see blue oval in schematic) to my dual channel sort of vibrolux/deluxe amp.
Since the power section of the brown vibrolux (that's what I copied) has no grid resistors (see red ovals in schematic), do I need to add those?

[tubby]

If your design works fine without those Rs, you won't need them just because of the MV.
After all the MV will only attenuate the signal due to phase cancellation and one of the reasons
to have the grid Rs is reducing blocking distortion because of excessive signal input to the power tubes.

Personally, I'd go for the voltage-divider type PPIMV with a dual-ganged pot to ground.
It will be a bit more expensive on parts, but is IMHO worth the money and the effort soundwise...

[txstrat]

I tried the PPIMV in a build and it sounded good.
Regarding the CLMV I thought I'd give it a try just out of curiosity what it sounds like.

[tubby]

the one (and only) build i tried a CLMV sounded kind of trebly and thin at very low volumes compared to the PPIMV. that's kind of a limited experience, cause they'll sound different in different PI and output environments. it's probably best to A/B it anyways, since it's a matter of personal taste. if you do so, I'd be glad to hear what you think...

[txstrat]

Gimme some days

[Steve A.]

the one (and only) build i tried a CLMV sounded kind of trebly and thin at very low volumes compared to the PPIMV. that's kind of a limited experience, cause they'll sound different in different PI and output environments. it's probably best to A/B it anyways, since it's a matter of personal taste. if you do so, I'd be glad to hear what you think...

With the CLMV at low settings the two signals essentially cancel each other out, leaving mainly the differences (which is basically assymetrical distortion). Some people like it because they can get a really distorted sound at the lowest volumes. I do prefer the PPIMV design, in particular the Ken Fischer Type 2:

http://www.blueguitar.org/new/schem/..._mv_type_2.gif

You may need to compare this drawing to the layout of a Fender PP amp from the 60's to see that the dual ganged pot replaces the two 220k bias splitters (not shown in the drawing).

Steve Ahola

P.S. We are speaking about the Fender designs from the 60's- I do think that the CLMV works okay in an AC30 style amp with EL84's, mainly to give you control over the voltage hitting the output tube grids. Like fine-tuning your sound rather than trying to reduce your volume to Bedroom Warrior levels...

[mac1amps]

Let's face it guys, ANY master volume turned down to low levels is absolutely NO COMPARISON to the REAL tone you get when you're turned up to levels that will bring some power tube clipping into the mix (if that's too loud, your amp's got too much power). I guess if you're going for METAL calibre distortion, you need SOME kind of processing for that ultra-break-up, but for a "classic" sound, NOTHING beats power tube clipping! (I hate master volumes)

[hasserl]

Let's face it guys, ANY master volume turned down to low levels is absolutely NO COMPARISON to the REAL tone you get when you're turned up to levels that will bring some power tube clipping into the mix (if that's too loud, your amp's got too much power). I guess if you're going for METAL calibre distortion, you need SOME kind of processing for that ultra-break-up, but for a "classic" sound, NOTHING beats power tube clipping! (I hate master volumes)

On the other hand, a master volume allows you to use some amps in applications where you wouldn't be able to without one. Of course they effect the tone, but that doesn't mean they don't have a useful purpose. Besides, in many amps there is not a lot of power tube distortion going on anyway, so a good MV allows you to achieve most of the tone of a cranked non-MV amp at volume levels that are much kinder to your ears, and much more appreciated by the listening public. Does it effect the tone, yes. Is it better than to not even use the amp rather than subject yourself to the tonal effect of a MV? Not in my opinion, maybe in yours, to each their own.

Anything you do to redude the volume of an amp is going to effret the tone, ANYTHING. You say it's too much power? OK, so use a lower powered amp, simple right? Except that is not going to sound the same either. You simply cannot take a high powered amp and build a low powered version and have it sound the same at reduced volumes as the higher powered/higher volume amp. Power scaling, attenuators, master volumes, lower powered amps, they all effect the tone, but the upside is they all allow the use of an amp that otherwise would not be usable, and that's a good thing IMO.

BTW, It's not good to hate, try channeling your emotions in other directions that are more productive and beneficial.

[txstrat]

Anything you do to redude the volume of an amp is going to effret the tone, ANYTHING.

I agree.

Actually I'll use the master pots (there'll be two of them) to switch in between two levels of volume (simply to "switch in" a lead volume). I don't think I'm gonna play the amp with the master turned far down.

Even one pot would be enough to turn down the volume a little for the rhythm sounds.

The amp is for rehearsals and stage only. For the living room I have other amps

I believe the master volume pots will be set at 90 - 100 percent most of the time. I don't expect a much attenuated tone at this level.

[Steve A.]

hasserl said "Anything you do to redude the volume of an amp is going to effret the tone, ANYTHING."

I agree.

Actually I'll use the master pots (there'll be two of them) to switch in between two levels of volume (simply to "switch in" a lead volume). I don't think I'm gonna play the amp with the master turned far down.

Even one pot would be enough to turn down the volume a little for the rhythm sounds.

The amp is for rehearsals and stage only. For the living room I have other amps

I believe the master volume pots will be set at 90 - 100 percent most of the time. I don't expect a much attenuated tone at this level.

I dunno- I've been reduding the volume of my amps for years and have never noticed it effretting the tone at all...

As you say, I think that master volumes are best used in moderation- just turning down the overall level a little bit. (Remember, going from 50 watts to 25 watts is barely noticeable.) The idea of getting bedroom levels from *any* amp is kinda stretching it (even for a 5 watt Epiphone Valve Junior). Although a power soak like the THD Hot Plate or the Marshall Power Brake will give you "real tube distortion", the load is still not the same as a speaker. For authentic tube sounds at low volumes you want to get a tube amp that has an output of maybe 500 milliwatts... like the Nano Head that ZVex sells. Since that came out a lot of people have been building low wattage versions of classic amps like Marshalls and Trainwrecks, and some of them have posted schematics and layout drawings so that you can build your own.

Steve Ahola