Variac vs attenuator to lower an amp's volume?

Figaro

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Anyone use a variac to lower an amp's volume? Do you think it sounds better than using an attenuator?
 

Leonc

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Absolutely, but it's not capable of lowering the volume to nearly the same degree. It's good for knocking (guessing here) maybe 2 or 3 dB off.
 

somedude

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7,603
A couple of my amps have a built in variac (drops the current from ~120v to ~90v). I prefer it to attenuation but it does change the sound/feel quite significantly. Whether you'll like the changes is subjective and you'll never know until you try.

Edit: I agree with Leonc. It's good for knocking the edge off your tone but it won't turn a stage amp into a bedroom amp.
 

GAT

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18,679
I'm just using variacs now, about 2-4 db down, perfect for my needs, and it retains the tone and feel.
 

DGTCrazy

Mod Squad
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Anyone actually crank their Variac up above 110? I noticed a clarity and focus that's not there at 110 or below. And when you do back off the voltage, where are folks usually running the variac? Or is it just to taste? At what point do you start to starve the tubes/x-former or other components too much and possibly cause damage?

Also, how does, (if at all), using a Variac affect the amps speaker? I was using a newish Marshall 1987x with a Bogner 1x12 cab loaded with a 16 ohm Creamback 65, and after about 20 minutes, the speaker started fizzing out.


Just curious as I get into experimenting.


thanks!
 

GAT

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I haven't noticed anything weird with mine.

Correct me, but isn't wall voltage 120? I run mine anywhere between 85-110.

Fredrick told me that the guys in McCartney's band run theirs at 85-90.

100 seems really nice, just take the edge off an amp, depending on the amp's wattage, of course.
 

ronzie

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486
You guys are crazed. If you don't mind shortening tube life for a 3db drop in volume, go for it(?). If your'e looking for a certain tone, go for it (?)... Otherwise, not generally recommended.

Stay above 5.7 v.a.c (at least) on the output tube filaments. Cathode stripping and all that...
 

Figaro

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Gat, What amps?

I have Fender amps so how does a variac sound with Fenders, a 4x10 Bassman in particular?
 

Leonc

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Herb, it's going to depend on the amp and speakers of course. But that said, if you get the volume down far enough, then your amp is less likely to be pushing the speaker into overdrive. But the thing is...I don't know that you can really knock off enough volume for it to make that much difference.

Yeah, the standard wall voltage in the US is typically 120V, AFAIK...but it definitely varies.

I notice a slight bit more "give" in the feel/response when I get down below 95V or so...depends on the amp; I imaging the difference in feel would vary more with certain types of amps....probably fixed bias amps (which I never do this with...I used almost all cathode-biased amps anymore). I think that when you drop the AC voltage to a fixed bias amp the reduction to the bias won't scale proportionally with the voltage drop to the anodes and I think this can result in overheating at a certain point.
 

GAT

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18,679
I've tried mine with:

Divided By 13 BTR23
Longhorn El Vaquero and Texas Tru Tone
'75 Marshall JMP
'64 Vibrolux Reverb.

All sounded fine. I mainly need it for the BTR and El Vaquero, just to take the edge off. It also seems to warm the tone a bit. Sometimes a cranked amp gets the harsh clipping, the Variac seems to soften that a bit.
 

Figaro

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Could you take a 4x10 tweed Bassman with it's volume at 7 down to bedroom volumes using a variac?
 

GAT

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18,679
No, it would just shut the amp off once you went below certain voltage. They are good for taking an amp and quieting it down a bit, for gigging, etc.
 

Billm

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574
Do you guys park your cars by ear, too? There's no doubt that out-of-spec voltage shortens heater life and can lead to cathode stripping. Lowering voltage, depending on the circuit, will often lead to increased current, possibly causing early transformer burnout.

Line voltage is not a tone control.
 

Winnie Thomas

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Do you guys park your cars by ear, too? There's no doubt that out-of-spec voltage shortens heater life and can lead to cathode stripping. Lowering voltage, depending on the circuit, will often lead to increased current, possibly causing early transformer burnout.

Line voltage is not a tone control.
What he said.

A variac will also drop the voltage on the heater filaments. Bad idea
 

wishkahdaddy

Member
Messages
2,171
I just put a bigger transformer in a 68 Bandmaster and the amp sounds awesome-better than with the old original. If I burn it out, I'll get another. No sweat to me. $150 is cheap IMO. Most spend more than that on a worthless pedal to flip...
I'm getting a variac soon to try. It sounds like it may be just what I'm looking for when I gig. I'll know when I hear it. Can't park my car by ear but I sure can use my ear to guide me in tone. Thanks again for the tip GAT!

Do you guys park your cars by ear, too? There's no doubt that out-of-spec voltage shortens heater life and can lead to cathode stripping. Lowering voltage, depending on the circuit, will often lead to increased current, possibly causing early transformer burnout.

Line voltage is not a tone control.
 

tonemeister20

Supporting Member
Messages
862
I've tried mine with:

Divided By 13 BTR23
Longhorn El Vaquero and Texas Tru Tone
'75 Marshall JMP
'64 Vibrolux Reverb.

All sounded fine. I mainly need it for the BTR and El Vaquero, just to take the edge off. It also seems to warm the tone a bit. Sometimes a cranked amp gets the harsh clipping, the Variac seems to soften that a bit.

Background: I enjoy reading your post(s) which are very informative. I am picking up a BTR 23 from Frederick today and asked if he could put in a half power switch, he recommended a variac instead.

We had quite a long discussion about power scaling, attenuators, master volume and his preferred use of a variac. I have quite a number of amps and the gigs I play are usually in small clubs. My 65 amps have power scaling which works quite well and a I have a Sommatone with a master volume that also yields good results. While I am in his shop I am going to use his variac, listen without the benefit of a band but would appreciate more notes from your experience.

I have a Bad Cat unleashed which I use with my Friedman Dirty Shirley for outside gigs just to help the master when necessary. Once again great tone when used together.

I might be trying to solve a problem that does not exist but would still like your feedback.

I never know what a room is going to sound like before we set up in a new venue. Wooden floors, tile floors, glass in the room (doors windows etc) all impact the sound. For first gigs I always take a 65 because they work well in every situation and I know I can control the stage /audience volume. Unfortunately despite my request to Dan Boul they do not make a JTM 45 style amp thus the BTR 23.

Which brand of variac do you use?

How do you measure the voltage? For example some have a digital readout.

Several mentions of damage. Any negatives such as tube replacement so far?

Thanks in advance.
 
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GAT

Gold Supporting Member
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18,679
I use a Variac that Fredrick sold me and the other one I posted a link on.

So far no issues at all with these amps.

BTR23
Germino Lead 55LV
'64 Vibrolux reverb

I just use the knob and don't measure. I'm only running about 100-110 so I'm not really cutting it way down.
 

ant_riv

Supporting Member
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5,231
I used a Variac to reduce voltage to a '77 JMP 2204 and a '78 JMP 2203 for five years, playing six nights a week for two - three hours. I've tried attenuators and never liked them.

I never had any problems with either amp using the Variac.

Sound men loved me. They would see us pull in with my two full Marshall stacks and give me the "oh no" look. I would sound check with the voltage just above where the on/off light would flicker off and let the sound man tell me how much louder to get.

I did notice that I didn't get the same speaker break up, but otherwise it served me well. Stage volume was never a problem.

I have been using it for years with my '67 Bassman, '72 Ampeg V-2, '81 JCM 2204 & '83 JCM800 4104 and not had a single issue with any of these amps.

I appreciate the wisdom of those who caution against it, but I have been using a Variac since 1977 without ever having an amp-related problem with any of the amps I use it with.

As always, this is IMO and YMMV.
 

Silent Sound

Member
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5,031
Do you guys park your cars by ear, too? There's no doubt that out-of-spec voltage shortens heater life and can lead to cathode stripping. Lowering voltage, depending on the circuit, will often lead to increased current, possibly causing early transformer burnout.

Line voltage is not a tone control.
I'm not going to disagree with you here. But I will say that using an attenuator to tame a fully cranked amp isn't doing your tubes or OT any favors either.
 




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