Variac tone change

[RhoadsRocks82]

hey all i am trying to achieve the EVH "Brown Sound" from Van Halen I album. i am close with my Marshall 100watt Super Lead i am not looking for any info on how to get the tone just a question on the variac set to around 90 volts thing he did. what does this do to the tone / is this necessary to achieve the brown sound / why does it change the tone thanks a lot / are the safe to use on a super lead when you set it that low??? thanks a lot!

[jh45gun]

I have heard using a variac is a good way to blow up a amp, Makes sense to me as you are changeing the voltages other than what the amp was designed to run. Others may disagree I know I would never try it.

[scopeboy]

I heard it can wear out the power tubes prematurely, because the heaters don't get hot enough for proper operation. It is possible to modify an amp so that the tube heaters still get the full voltage while everything else is turned down, but it's quite complicated to do. Also, if you take a variac to gigs, it's one more thing to lug, and what if your bass player turns it up to 140V while you're not looking...:eek:

Power tubes are not too expensive, so if you get the sound you want with a variac set to 90v, maybe you should just do it. Personally I think the main ingredient in EVH's "Brown tone" is EVH himself. I would leave the variac in the cupboard, and spend more time practising. And get a guitar with a funky paint job and some ripped jeans.

[John Phillips]

I have heard using a variac is a good way to blow up a amp, Makes sense to me as you are changeing the voltages other than what the amp was designed to run. Others may disagree I know I would never try it.
It's safe if you know what you're doing. It's just giving you control over another variable that often varies all by itself :) (though not usually to quite the same extent).

The supply voltage can vary substantially - often 5% away from the specified value (in the UK - I believe it's even more in the US). Using a Variac allows you to do two things:

To correct the power supply variances to give you a more consistent sound, if you find that it's sensitive to changes. (This includes running old amps that were designed for lower supply voltages than are common today, in the US, which may be necessary for reliability.)

To deliberately vary the supply voltage to change the tone.

There are certainly risks with going too far in either direction - going too far up will raise all the internal voltages in the amp, and could exceed the ratings of some components fairly quickly. If you're going to do this it's essential to monitor the internal voltages and currents while experimenting, so you can find the safe upper limit for the supply voltage. It's then important to check the supply voltage while you're running the amp, so real supply variances don't then take it over the top.

(Remember that a Variac doesn't put out a fixed voltage, it puts out a ratio of the input voltage, so if the supply voltage rises, so will the output of the Variac.)

Going too far down sounds like it should be safe, because all the amp's voltages are reduced so you might think it's under less stress, but actually not all the voltages have the same degree of effect, and reducing some too far (especially bias voltages, which are very sensitive) can then put other things outside the safe range. Also, running tube filaments too cold causes damage and will shorten their life, although it isn't actually 'dangerous'. There's probably less risk in going a little too low than a little too high though.

As a general rule of thumb, running between 20% under and 10% over the correct voltage is probably safe for most amps, but there are definitely exceptions and I wouldn't do even that (especially not the 10% over) without checking thoroughly.

The interesting thing is that I've never found that small changes make much of a difference to the tone. Maybe it's just me, or the type of amps and sounds I use, but I really don't hear anything much happen for small voltage changes of the kind that normal supply variances cause. With large changes (downwards) I do, but I don't like the sound at all, it sounds like the amp is struggling to work properly... which it is.

While EVH did apparently use his amp with a Variac (though which way he turned it is arguable, and he said different things at different times), he also did a fair few other things to get 'that sound', and I don't think the Variac was the most important factor. (I actually think he and his tech may have used it mainly to prevent the amp blowing tubes as often.) Certainly, just Variac'ing a Marshall Plexi won't give you the sound.

[Johnny Z]

As stated in many Amp Tech books "don't use a variac". If you still want to do it anyway just to get a sound like EVH, remember he could afford the repair bills. I don't think it's worth the trouble.

[drfrankencopter]

I heard it can wear out the power tubes prematurely, because the heaters don't get hot enough for proper operation. It is possible to modify an amp so that the tube heaters still get the full voltage while everything else is turned down, but it's quite complicated to do. Also, if you take a variac to gigs, it's one more thing to lug, and what if your bass player turns it up to 140V while you're not looking...:eek:


It's not a complicated mod to make the heater voltage independant of the B+. You just need a second transformer. Of course the amp will be heavy as hell with effectively two power transformers and a variac....but it will let you drop the voltage down without worrying about cathode stripping.

Of course you could avoid all this and just go with a power scaling kit (which would probably cost less than a good variac alone).

cheers,

Kris

[johndara]

Just to throw in my 2 cents...I've been using a Variac on my Marshall 1969 Super Lead for the past year now and had no issues at all (so far). I'm running the voltage at 75. I wasn't after the Van Halen brown sound, I was just doing it to cut back on the volume and it's been working fine. I don't find any change of tone at all. Of course I'm not using my everyday, I just fire it up once a week for either a gig or a rehearsal.

[vibroverbus]

Good info from the usual suspects above, I'll add that there is also evidence that EVH did NOT use a Variac but in the style of many urban myths, made an off-hand joking comment once that led to the legend. At times since he & techs have said that he just used nice, dimed, Marshalls. Another technical detail was his famously (miserably) hacked guitar with no tone control, and just a (again dimed) volume pot for max output and minimal tone bleed at the source.

All that considered, I +1 to the idea that much of the sound is in the player in this case.

On to the technical details on Variacs...

In my testing, I've generally found running a Variac at the common numbers quoted (sometimes it's 90% other times 90VAC) results in the tubes being biased EXTREMELY cold, to the tune of about 1/2 the dissipation. In effect, the bias voltage 'scales' less than the plate if you will (although that's not technically true - really the voltages are probably 'scaling' fairly linearly but the tube operating characteristics aren't linear, i.e. for 10% reduction in plate voltage you may need a 15% reduction of bias voltage to achieve the same idle power dissipation that you had before). Anyway, I always find this interesting as the same guys who say "you have to bias hot!" say "Cranking down a Variac is great!" Hmmm... which izzit?

The tech spec on heater voltage for tubes is officially +/-10-20% so unless you're lower than the usual 90V (i.e. 75V) you probably aren't going to have too much trouble. Running hotter than line voltage as John says, is a whole difrint ballgame and I would very much not advise it.

Re: an outboard filament Txfr, that would work fine, and shouldn't actually even be that heavy. On the other hand my General Radio Variac weighs about as much as a small anvil... Having one with both Volts & Amps displayed is great because you can not only monitor the voltage 'scaling' but quickly see if you are going into some runaway condition (and it also doubles up on your fuse protection as well - I've popped the 2A in the Variac before a 2A in the amp before).

http://j2c3.com/misc/genradio.jpg

[Johnny Z]

Just to throw in my 2 cents...I've been using a Variac on my Marshall 1969 Super Lead for the past year now and had no issues at all (so far). I'm running the voltage at 75. I wasn't after the Van Halen brown sound, I was just doing it to cut back on the volume and it's been working fine. I don't find any change of tone at all. Of course I'm not using my everyday, I just fire it up once a week for either a gig or a rehearsal.

I'll call you lucky.

Don't you have a volume control on the amp or the guitar?

[John Phillips]

Don't you have a volume control on the amp or the guitar?
I'm assuming you know that turning either of those down reduces the amount of distortion as well as the volume ;).

I think what johndara wants is the same amount of distortion, but quieter :).


I'm actually very surprised that running as low as 75 volts does not change the tone, but some of us listen for different things in sounds, and if it does what you want it obviously works for you. It's probably not great for the tubes either, but then neither is attenuating, often.

[johndara]

Don't you have a volume control on the amp or the guitar?


I'm using the Variac on a non Master Volume amp to get my distortion at a decent volume. If I wasnt using the Variac I would just be getting a loud clean tone (unless I turned it up to 10) but I wouldnt want to be standing in the same room. Now with the Variac, I can use the volume on my guitar to bring it down further then crank my guitar volume for my solos.

[Johnny Z]

I'm assuming you know that turning either of those down reduces the amount of distortion as well as the volume ;).

I think what johndara wants is the same amount of distortion, but quieter :).


I'm actually very surprised that running as low as 75 volts does not change the tone, but some of us listen for different things in sounds, and if it does what you want it obviously works for you. It's probably not great for the tubes either, but then neither is attenuating, often.

There are better ways and safer ways to do this. Get a good pedal or power break. Maybe he just needs to learn how to play clean.

[vibroverbus]

Just thinking more about this, if I was to go down this road, I'd probably grab a cheap voltage regulator chip and transformer rated for 4-5A, then get the double bonus of quiet regulated DC heater supply AND de-coupling from the main PT...

[johndara]

There are better ways and safer ways to do this. Get a good pedal or power break. Maybe he just needs to learn how to play clean.


I've tried pedals and they don't like it in front of the Marshall, partially because channel 1 is too bright...Channel two is too dark. IMO the power break would be doing the same thing as the Variac. By the way, I do play clean by turning down the volume on my guitar. It's not sparkling clean, after all it is a Marshall, but it does clean up fairly well.

[Hacksaw]

read this thread.. about evh's marshall "kitchen", look for Roccaforte amp post. ;-)

http://www.thegearpage.net/board/archive/index.php/t-44940.html

[rockon1]

There are better ways and safer ways to do this. Get a good pedal or power break. Maybe he just needs to learn how to play clean.


Each to their own.:)