Using a Variac ?

JB007 · Post by **JB007** » Wed Dec 15, 2004 11:17 pm

If you use a variac and set it to 100v, will this also lower the overall volume of the amp ? I know you have to rebias the amp when you do this. Just not sure if the amps volume will drop real low or just give you a different sound.

5150loveeddie · Post by **5150loveeddie** » Thu Dec 16, 2004 1:15 am

It will reduce your overall volume a little, actualy the variac voltage control knob will act just like a volume knob. But I wouldn't do it really, not on a super lead!!!!!!!! I did try it on JCM900's and it did warm up the sound and smoothed out the tone but you don't need to do this on a 1959 (well not me anymore) unless YOU think it's doing something YOU like..............

And they are other technical considerations involved to watch out for......

Billy Batz · Post by **Billy Batz** » Thu Dec 16, 2004 8:34 am

I have a seperate filiment tranny on the way to run the heaters. I want to try using a variac as a power scaling. So far, other then cathode stripping which is bypassed by the filiment tranny, the only other negative side effect Ive been able to find is the caps forming a 'memory' of the voltage and possibly not handling a high voltage well when run at lower voltages for extended periods. Ive only read that one place though. Im wondering if theres any other concerns or if thats it?

5150loveeddie · Post by **5150loveeddie** » Thu Dec 16, 2004 10:17 am

yep that's the deal....keep your heaters at 6.3 volts and this should do the trick, rebias the tubes. BUT if you go back to normal 115-120volts REBIAS the tubes again.........

For other technical stuff I beleive it's all covered up but I'm not 100% sure thaught!!!!

Billy Batz · Post by **Billy Batz** » Thu Dec 16, 2004 1:13 pm

Oh yeah. And of coarse, rebias

Im not an engineer by any means but I dont know what the difference is doing it this way or using the london PSK kit? Other then the fact that as far as I know that kit enables you to bias each tube and 'intonate' it so you can lower the B+ with no need to rebias. Someone said using a variac and the seperate filiment tranny wouldnt sound as good because the B+ on the preamp and PI is dropped as well? Is it not dropped on the preamp in the PSK also? Well it was only a cheap 6v tranny to try it out

Guest · Post by **Guest** » Mon Jan 24, 2005 12:09 pm

I too use a seperate heater tranny but there is another factor besides capacitor memory and that is if you lower the B+ too low and sure you can rebias but the current drawn by the power tubes(not bias current) may become too high and burn up your power tranny.
Of course replacing your power tranny with one of higher current capabilities solves that problem and "it is written" that evh had beefier power tranny's put in his marshalls by his amp modder jose, this could be the reason why.
Check out tube data sheets to see what kind of current changes occur at lower voltages to be safe.

Billy Batz · Post by **Billy Batz** » Mon Jan 24, 2005 1:09 pm

Believe me. Im not goin for house volumes. I decided not to use this anyway. When the feeling hits me to play my 100 watters at home (I dont know why!!!) I use a load box and slave to poweramp setup which works as well as anything else can. I just dont buy the people who say the PSK sounds 100% clear all the way down to appartment volumes. Im sure it sounds great and has its own problems that you notice after the honeymoon but 100%?

Trem Abuser · Post by **Trem Abuser** » Mon Feb 21, 2005 1:09 pm

Do you guys use a variac to slowly bring the filter caps up for a first time power-up? Is this a good thing to do with the multi-cap style caps?

If so, how do you recommend doing this?

1Way · Post by **1Way** » Wed Mar 30, 2005 6:46 pm

Billy Batz,
You said

Believe me. Im not goin for house volumes. I decided not to use this anyway. When the feeling hits me to play my 100 watters at home (I dont know why!!!) (1) I use a load box and slave to poweramp setup which works as well as anything else can. (2) I just dont buy the people who say the PSK sounds 100% clear all the way down to appartment volumes. Im sure it sounds great and has its own problems that you notice after the honeymoon but 100%?

(1) Could you please unwrap that for me? I'm new to tube amps and such. Started playing electric guitar when I was a teenager, and now that I'm 41, I feel like getting back into it and this time, actually learning how to play.

(2) I've never heard anyone say that Power Scaling is perfect, especially at the lowest volume levels. I've heard it's better at preserving the amp's natural sound, even at lower volumes, especially when compared to power attenuators. Why are you down or skeptical on Power Scaling?

I'm seriously looking into fitting my JCM 800 50 watt amp with power scaling. I like the three different functional benefits, not the least of which is supposedly the best lower volume attenuator.

Power scaling
Drive Compensation, combines with the power scaling knob or the amps normal master volume to variably control the proportion between your preamp and the power amp.
Individual tube biasing (tube mania), which allows for using unmatched tubes, different tube sets, and different tubes within a set! Magnify and scrutinize each portion of the amp's tube sections for critical testing and comparison.

And all for a lot of savings compared to most popular power attenuators, "if" you install it yourself that is. I'm considering doing the mod myself, but I'd prefer just having enough money to pay someone else to do it. I am not amp tech, but I like learning this stuff.

Billy Batz · Post by **Billy Batz** » Wed Mar 30, 2005 8:18 pm

First off Im not downing power scaling. I have no doubt it is the single best way to get low volume power tube saturation. But many people have and do act like it sounds the same as a fully cranked amp which I just cant believe. Ill have to hear it to believe that. Ill bet its the best way but I cant believe its 100%. Not that I expact anything to be.

The load box and slave set up is the basic EVH setup. What I do is run the speaker out of my amps to a Weber MASS (THD Hotplatewould work well too). I set the MASS for load (so its totally 100% attenuated and dead). Then I take the line level signal from the Line Out of the MASS and I send that to a Solid State Poweramp to amplify that cranked tone at any volume. You can go from the Line Out to the poweramp by way of effects if you got em. I think its very important the poweramp is solid state because SS poweramps dont color and mess with the tone like tubes. Thats not good if you want to use it as a guitar poweramp but you already have your cranked tube sound and you just want to amplify it faithfully which SS amps are all about. Theyre smaller, cheaper and lighter. A 150W studio monitor poweramp is very small and very cheap. That is basically what the Ultimate Attenuator, which people rave about as the clearest attenuator, is.

Another method I enjoy that works great unless you need absolute bedroom level, is to use an attenuator in conjunction with a set of THD Yellow Jackets. If you dont know the THD YJs are socket converters that allow you to use EL84's with almost any popular amp and drop its output considerably. Despite what anyone says attenuators arent that bad at all to a point. I believe that point is around -12dbs which some people can stand and others cant. With the YJs I can get away with my 100W Marshalls at -8dbs at home but its still pretty loud by bedroom standards. i didnt like how trashy the EL84s sounded in my Marshalls until Myker sent me some NOS EL84s which are much tighter and cleaner and sound much better. Even new stock EL84's of other brands are better then the stock YJ JJ brand EL84s.

The main problem that arises with all these methods is you get to a breaking point with the speaker when as you turn the volume lower you drastically change the way the speaker smooths out the signal. So the bass gets farty and rumbly and the treble gets fizzy, glassy and shrill. Its the nature of the beast. Thats my main bone of contention with anyone who says something is clear all the way down to bedroom levels. Then your ears must be dogshit. Sorry. You can always use speakers that break up at lower and lower volumes but none break up that low.

If your up to the PSK mod then by all means do it.

Thats about all the stuff I can think of on this subject.

1Way · Post by **1Way** » Wed Mar 30, 2005 9:14 pm

Dan, I appreciate the discussion. I pretty much agree, except for perhaps one area. But first, you mentioned that there's a lot more to cranked amp tone that voltage (~=power). But your EVH pumps your high powered amp, into an almost no power line out, and then into a clean SS amp for reproduction at mostly lower volume, which roughly equals lower power! So in your (very admirable) setup, you crank up the amp, and then scale down the power, which sounds an awful lot like what power scaling does, only within one single amp, and includes longer lasting tubes, and a (post PI MV) drive compensation control. So if power scaling is crap, then what is your setup? Or maybe you intended some of the (errent) claims that some power scalers have made.

I agree with you that cranked amp tone is more than just voltage. Just pulling your leg somewhat because you sort of left it sticking out there. All in good fun.

To the point, you said.

The main problem that arises with all these methods is you get to a breaking point with the speaker when as you turn the volume lower you drastically change the way the speaker smooths out the signal. So the bass gets farty and rumbly and the treble gets fizzy, glassy and shrill. Its the nature of the beast. Thats my main bone of contention with anyone who says something is clear all the way down to bedroom levels. Then your ears must be dogshit. Sorry. You can always use speakers that break up at lower and lower volumes but none break up that low.

I believe you are mixing up the natural effect that power attenuators have on the sound/tone, and the effect of speaker breakup. Here is how I would distinguish these to issues.

Setup your favorite hot revving rock and roll amp. Set it up for high volume jam fest. You should get speaker break up in there, perhaps speaker breakup will start a few notches back on the MV.

All you have to do to invoke the speaker breakup point, is, keep playing, but then have someone slowly turn down your master volume until you stop getting that same juicy vibe from your speakers. You will be doing two things though. One is you are reducing the amount of power amp distortion by cleaning up that end of the amp, and secondly you are lowering the volume to the point that speaker breakup is no longer happening (at some point). However, when your speaker stops breaking up, you do NOT get flabbier bass and fuzzy highs, instead you tend to get clear articulation, almost a transparent representation of the amp and guitar since the speaker is not providing distortion as part of the mix.

I have read many different reviews about power attenuators, and they inevitably go into descriptions like the ones you gave about "flabby lows" and the treble getting fizzy, etc. It's an issue of power attenuation "compression" and what happens when you power attenuate, not an issue of speaker break up or not. That is why power attenuators often promote treble boost or low range boost, etc. To help with the tonal losses that power attenuation causes. But even that does not fix the problem entirely, especially at the lowest power attenuation levels where compression and tonal losses are greatest.

At least that is my take on that issue.

As for the amp slaving bit, wow, that sounds really excellent!!! I already have a solid state amp that just might work with what you are talking about! All I would need is a faithful line out from a power attenuator, I hear that the Weber Mass does a great job with their line out stuff. Wow, I will have to give this option a whirl.

1Way · Post by **1Way** » Wed Mar 30, 2005 9:21 pm

Dan, say, how about using the DI from the Marshall amp itself? I wonder if that would work if I used a dummy load instead of speakers...

Billy Batz · Post by **Billy Batz** » Wed Mar 30, 2005 10:23 pm

Billy · Post by **Billy** » Thu Mar 31, 2005 8:23 am

1Way wrote:Dan, say, how about using the DI from the Marshall amp itself? I wonder if that would work if I used a dummy load instead of speakers...

Yes. Of coarse. Just be sure the DI is not from the preamp but tap'd from the output signal.

1Way · Post by **1Way** » Thu Mar 31, 2005 4:12 pm

Billy, cool! Any idea how I could find out about the DI tap and whether or not it's from the preamp or after the power amp? I sense a new topic coming on. This would be outstanding if my own amp's DI line out would serve as an amp slave driver for a clean SS amp for this cranked amp tone at low volumes!!!

Billy Batz,
Are you a different Billy?

I accept your input about the technical stuff about speaker break up and how that plays more of a part than I might have already assumed. But I disagree that flabby and shrill is what my amp sounds like at lower, less than speaker break up volumes. Although, I admit that I stand to learn more about all this. I am certainly impressed about the tube amp line out to a SS amp. So, BTW, what do you do to get rid of the flabby lows and shrill highs? Seems like you need a

tube amp
a line out device of some kind,
a proper dummy load to protect the amp's power section
a speaker simulator to smooth out the flabs and shrills
a SS (or clean amp) for reproduction of the cranked amp tone at lower volumes
and a glass of chilled ale ready for partaking in such an awesome musical achievement!

Is that about right? What do you suggest for parts 2 and 3? I think I have a cab simulator in my Digitech RP100, at least it has some cab's and mic locations to choose from.

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