Variac before toroid...

[MotoMan_Yz400]

I've been looking for toroids for my Gainclone, and I've been finding them with either too much or not enough voltage. These one I found but the rating is 1500VA and thats just massive overkill. So I was thinking, I have a variac around my house (1000VA rated) and I was wondering if I could plug my powersupply into that, and basically have an adjustable rail voltage. I'll have the 15V (or so) for the preamp stuff on a different un-modified powersupply. But has anyone tried this, or is there anything that could go wrong (beside accidentally ramping up the voltage to much).

[Bone]

Variacs have no isolation from the mains and therefore can kill. They only have a single winding. If the output is rectified and then earthed, then a short to earth through the variac would result probably blowing the mains fuse.

Tony.

[Bobken]

Hi,

With so many toroidal transformers to choose from, I am surprised that you are having a problem finding something suitable for your needs. How is it that other Gainclone users can overcome this apparent problem?

It would certainly be possible to use a variac to reduce voltages in the manner you suggest, but I wouldn't do this myself, except for shorter-term testing purposes. Whenever I have used a variac there has been some slight but noticeable degradation in sonic performance, although I accept that my standards are higher than many others might be, but generally-speaking variacs are not designed for continuous usage in this way.

The rotary contacts which are (usually) used to adjust the output voltages in variacs are probably the main reason for the loss of sonic performance which I hear, and unless there is regular adjustment which will tend to 'clean' this junction, I guess that the sonic detereoration might worsen over a longer period of time.

Regards,

[cabbagerat]

Bone is right, so be careful.

If you can't find a toroid which fits your needs, feel free to use a standard frame type. Frame (EI, laminate, whatever) transformers are physically bigger, and emit a big stray field, but as long as you keep them away from the rest of your circuits it'll be fine.

There are plenty of places that will wind custom toroids and frame transformers for you, probably at least one in every decent size town.

[MotoMan_Yz400]

Yeah I know of places that wind a custom coil for me, I was just hoping to use one I had laying around here. And Bone, I'm not talking about using the Vai-ac as a replacement for the coil, just to step the coil down. After thinking about it, I'm not going to do this, just not right (as Bobken said). However I would like to plug my amp into a variac BEFORE I just plug it into the mains, so on the first test, I dont blow my hole board if I did something wrong. I just want to be able to slowly ramp up the rail voltage for my first tests, just was unsure if it would work.