Using a Variac as an attenuator.

[erigm]

Here's a trick ****** posted back on the Plexi Palace:

Amp's speaker out -> variac AC line in ... in parallel with a load resistor (or hotplate set to load or whatever). -> variac out to speaker cabinet.

Now you have to make your own cables for this. Go to the hardware store, get an extension cable (16ga), cut it in half, and solder a 1/4" plug on either end.

Now the plug of the variac that you normally plug into the wall gets plugged into the amp's speaker out. The socket on the variac (the one that usually has the variable voltage) plugs into your speaker cabinet.

Note: Set your variac for 120V (or one-to-one)

Now as you turn down your variac your sound will get quieter, but your amp is seeing an ever increasing load (resistance going up). This is harder on the amp and also can start to cause high frequency oscillations. That is why you run a resistive (or any kind of load) in parallel with the variac/speaker combo. Then as you turn down the variac your load is always in parallel with the speaker load seen through the variac's transformer, so as the amp see's the speaker load through the variac rise it never can get any higher than the load you have in parallel with the variac (ohm's law).

This is too neat a trick not to share. Will it affect tone? YES, but doesn't anything? If you have a variac and a load, give it a try and see if you like it.

If you don't understand what this is doing than you probably shouldn't try it.

Hopefully somebody finds this useful.

[45auto]

interesting idea for sure. i used to just drop the input voltage way the hell down & attenuate like that. it damages the tubes i believe, but i never had a problem back then. as always the disclaimer: do this at your OWN risk!

[MarkCameron]

Here's a trick ****** posted back on the Plexi Palace:

Amp's speaker out -> variac AC line in ... in parallel with a load resistor (or hotplate set to load or whatever). -> variac out to speaker cabinet.

Now you have to make your own cables for this. Go to the hardware store, get an extension cable (16ga), cut it in half, and solder a 1/4" plug on either end.

Now the plug of the variac that you normally plug into the wall gets plugged into the amp's speaker out. The socket on the variac (the one that usually has the variable voltage) plugs into your speaker cabinet.

Note: Set your variac for 120V (or one-to-one)Now as you turn down your variac your sound will get quieter, but your amp is seeing an ever increasing load (resistance going up). This is harder on the amp and also can start to cause high frequency oscillations. That is why you run a resistive (or any kind of load) in parallel with the variac/speaker combo. Then as you turn down the variac your load is always in parallel with the speaker load seen through the variac's transformer, so as the amp see's the speaker load through the variac rise it never can get any higher than the load you have in parallel with the variac (ohm's law).

This is too neat a trick not to share. Will it affect tone? YES, but doesn't anything? If you have a variac and a load, give it a try and see if you like it.

If you don't understand what this is doing than you probably shouldn't try it.

Hopefully somebody finds this useful.

Yep....it works great..you can also just run it like a....big volume knob for the speaker. Check the ohms of your variac....I think you will see around 20 ohms...Look at badcat ...its another old trick.

[MikeO]

is this basically what the Blankenship Variplex is doing?

[dirtycooter]

So what does it do for the tone?

and how much does it cut volume?

Is this a different effect than being on the AC power plug gives?

Anything else tonally valuable to it?

[erigm]

is this basically what the Blankenship Variplex is doing?

No. Blakenship is using their variac in the conventional manner. It is used to lower the AC voltage that the amp sees. The unique and cool thing about the Variplex is there is wiring that constantly feeds a filment transformer, so the tubes don't suffer cathodic stripping from heater under-voltage. You can lower the variac much lower safely with the variplex without any harm to your amp than you can with just using a variac on a normal plexi type amp.

London Power's Power Scaling takes this a step further, allowing you to do the same thing, but all internal in the amp. It's pretty cool! And now Kevin is offering Power Scaling PCB's and different variations, so its getting easier to install and use. Man, I sound like a commercial.

[erigm]

So what does it do for the tone?

and how much does it cut volume?

Is this a different effect than being on the AC power plug gives?

Anything else tonally valuable to it?

It lowers volume! I think tonally it doesn't affect the tone any more than using a resistive attenuator ... might even sound better. But that's for your ears to decide. It cuts the volume to zero, but gets a little jumpy towards the bottom (at least with my variac) but you can get the volume very low.

Yes, its different from using the variac as an AC voltage regulator. It works as an attenuator, and has the same tonal effects. You might find it similar to an Airbrake, but with much more adjustability. Mark C implied above that this might be similar to the BadCat Leash, which has received very good reviews. Like he said, its an old trick, that I just learned about a few years ago.

[erigm]

[quote="Yep....it works great..you can also just run it like a....big volume knob for the speaker. Check the ohms of your variac....I think you will see around 20 ohms...Look at badcat ...its another old trick.[/quote]

Mark, I need to get my learn on concerning these loads. Let's take the resistive load out of the equation. If the amp is just hooked up to the variac and speaker, and the variac is 20ohms (on the "primary" side) and the amp cabinet is 8ohms, and the amp is set to 8 ohms, what impedance load will the amp see?

Then, what impedance load will the amp see as the variac is turned down?

I guess when I get home I could just do some imperical testing, but I'd like to get the theory behind it.

[erigm]

[quote="Check the ohms of your variac....I think you will see around 20 ohms.

Mark, I need to get my learn on concerning these loads. Let's take the resistive load out of the equation. If the amp is just hooked up to the variac and speaker, and the variac is 20ohms (on the "primary" side) and the amp cabinet is 8ohms, and the amp is set to 8 ohms, what impedance load will the amp see?

Then, what impedance load will the amp see as the variac is turned down?

I guess when I get home I could just do some imperical testing, but I'd like to get the theory behind it.[/quote]

Mark (and all),

I checked my variac, and I get ~2ohms on the primary side. About the same on the secondary. Ohmage stays the same no matter where the dial is set. Ohmage on the primary side does not change no matter what load is connected to the secondary side or where the dial is set.

It makes sense that the ohmage doesn't change because I believe the multimeter is looking at DC resistance. The load your amp is looking at is AC resistance or impedance. Is this correct Mark?

[IloveMyMarshall]

Can someone here explain in detail how this power scaling works please? I see the parts are like 50.00 not bad, MarkC can you chime in here since you are the master builder, please?
Parts http://www.londonpower.com/catalog/prod ... ucts_id=28" onclick="window.open(this.href);return false;
Thanks
ILMM

[erigm]

Can someone here explain in detail how this power scaling works please? I see the parts are like 50.00 not bad, MarkC can you chime in here since you are the master builder, please?
Parts http://www.londonpower.com/catalog/prod ... ucts_id=28" onclick="window.open(this.href);return false;
Thanks
ILMM

ILMM,

I think their website explains it better than any of us can. Check out the powerscaling FAQ at http://www.londonpower.com" onclick="window.open(this.href);return false;.

[erigm]

Can someone here explain in detail how this power scaling works please? I see the parts are like 50.00 not bad, MarkC can you chime in here since you are the master builder, please?
Parts http://www.londonpower.com/catalog/prod ... ucts_id=28" onclick="window.open(this.href);return false;
Thanks
ILMM

Also, someone from the plexi palace had made a great page comparing powerscaling to some other volume reduction methods. I think it might have been "marshallmaniac". I think his actual name was Bruce Clement ... or something like that. He had comparison clips and pics and stuff.

Also, check out amps like Reeves, Suhr Badger, Stephenson Stage Hog, Soultone. They all use powerscaling as well.

[erigm]

Can someone here explain in detail how this power scaling works please? I see the parts are like 50.00 not bad, MarkC can you chime in here since you are the master builder, please?
Parts http://www.londonpower.com/catalog/prod ... ucts_id=28" onclick="window.open(this.href);return false;
Thanks
ILMM

You would need this kit http://www.londonpower.com/catalog/prod ... ucts_id=27" onclick="window.open(this.href);return false; for Marshall style amps. The one you posted is for cathode biased amps.

[Type O Neg]

I have been using the above trick as suggested. Does not sound bad running my Slient speaker as the load and a variac as the volume control. This causes oscillation with certain postions of the control on the Variac. I am running the amp at 8 ohms. I also lower the input voltage of the amp to 90 volts. Result is a very good sound when compared to other attenuators, very warm with brown sound there with the right eq settings. Just wondering if others have tried this trick?

[IloveMyMarshall]

Erigm thank ya man for all the help and info...So many ways to skin this cat which one is next?