Two variacs for dummies...

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mightymike
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Re: Two variacs for dummies...

Post by mightymike » Thu Oct 08, 2015 10:53 pm

Oh ya.

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Re: Two variacs for dummies...

Post by jnew » Tue Dec 15, 2015 5:11 am

Just an update for this thread. I run the amp backwards through the 2nd variac because the knob changes the impedance on the output, or secondary side of the variac. So you can actually get a 15 or 16 ohm reading on the secondary side which is what the head wants to see. The primary side measures 3.2 Ohms no matter where the dial is. Now does it matter once signal is going all the way through to the cab? I don't know but there is a very noticeable difference in tone. 8)
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Re: Two variacs for dummies...

Post by Robocop101985 » Thu Dec 17, 2015 11:11 pm

Jnew,

As you know I purchased that red variac with the binding posts. For the life of me I can't get an ohm reading from it at all. I hope I'm doing something wrong that is an easy fix to help me get a reading but maybe you can help me (and anyone else for that matter) with what I'm doing.

As I figure it, if the cabs cable is connected to the variac I should have some sort of ohms passing through the variac. Tell me if I'm completely wrong there.

I connected the cabs wires to the "In" on the variac and tried getting a ohm reading on the "Out" posts. No luck. I also tried it in reverse as well. Cab on the "out" posts tried to read the "In" posts. (Which was the original set up for this variac. Amp to the "in" posts and the cab to the "out" posts, right?) No luck there.

Anyway, no matter what I do I can't get a reading. No matter where the knobs at. multimeter is set to ohms and all.

What am I doing wrong? Any help would be appreciated. Thanks guys.

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Re: Two variacs for dummies...

Post by jnew » Fri Dec 18, 2015 8:40 am

As I have since figured out, you won't really get a reading on through the variac because the signal passes through inductance, rather than like a direct connection. But you can measure the impedance on the "IN" post's and the "OUT" post's. In other words, each side of the variac will have its own impedance. On my variac, the IN measures 3.2 Ohms with no deviation when turning the knob. The OUT will swing all over the place as you roll the knob. So I run backwards now and am able to show the head around 15 ohms. So try measuring each pair of lugs, to see what you get. 8)
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Re: Two variacs for dummies...

Post by fhn_lopes » Fri Jan 08, 2016 2:42 pm

jnew wrote:As I have since figured out, you won't really get a reading on through the variac because the signal passes through inductance, rather than like a direct connection. But you can measure the impedance on the "IN" post's and the "OUT" post's. In other words, each side of the variac will have its own impedance. On my variac, the IN measures 3.2 Ohms with no deviation when turning the knob. The OUT will swing all over the place as you roll the knob. So I run backwards now and am able to show the head around 15 ohms. So try measuring each pair of lugs, to see what you get. 8)
how? with the variac unplugged from the amp? plugged into the wall??
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Re: Two variacs for dummies...

Post by jnew » Fri Jan 08, 2016 2:58 pm

NO! :shock: NO VARIAC USED BETWEEN HEAD AND CAB IS EVER PLUGGED INTO THE WALL.
A variac has an AC in and an AC out. Those AC connections become + and - speaker connections when used between a head and cab. Hence, the above BOLD statement. You can measure each side (in and out) for impedances separately.
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Re: Two variacs for dummies...

Post by fhn_lopes » Fri Jan 08, 2016 3:06 pm

got it, just thinking of measuring it pluged into the wall but not into the amp, if you know what I mean. Just to chek witch is primary and which is secondary.

thanks man, deciding here if going to trade my attenuator for 2 variacs
76' JMP 50w w/ 71' metro board
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93' Fender Japan HSS Strat
4x12 w/ 2x 25w rola creambacks /2x 25w m75 Scumbacks

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Re: Two variacs for dummies...

Post by jnew » Fri Jan 08, 2016 4:51 pm

If you have a two stage, NMV plexi circuit, then FU@& YEAH. :lol:
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Re: Two variacs for dummies...

Post by fhn_lopes » Fri Jan 08, 2016 5:11 pm

yes it is sir :lol:

Actually I'm just a bit afriad BC I need it to be VERY quiet to play at home, not that quiet for rehersals or gigs of course. But at home it's bedroom volume.... I'm afraid I can't get that with the variacs ....
76' JMP 50w w/ 71' metro board
93' Fernandes SSS strat
93' Fender Japan HSS Strat
4x12 w/ 2x 25w rola creambacks /2x 25w m75 Scumbacks

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Re: Two variacs for dummies...

Post by jnew » Fri Jan 08, 2016 9:18 pm

You can. Trust me. With the first variac at 60VAC and the second variac dialed down to about 70 on the dial, you will be bedroom quiet. I've been able to get close to whisper volume. Never need for an attenuator. 8)
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Re: Two variacs for dummies...

Post by fhn_lopes » Tue Jan 12, 2016 10:31 am

Interesting.... 60v sounds like the tone will be too loose without rebiasing.... even though, is still safe?
76' JMP 50w w/ 71' metro board
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93' Fender Japan HSS Strat
4x12 w/ 2x 25w rola creambacks /2x 25w m75 Scumbacks

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Re: Two variacs for dummies...

Post by jnew » Tue Jan 12, 2016 11:58 am

It changes a little but really not as much as you might think. More so because the cab isn't being hit as hard but most definitely, perfectly useable for practice at a low volume. Then you just roll it up as desired for rehersing/gigging.
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Re: Two variacs for dummies...

Post by fhn_lopes » Tue Jan 12, 2016 12:40 pm

nice... I can find PLENTY of ohmite-ish variacs here in Brasil (with the bind posts) that are the deal for the 2nd one but I'm having a hard time finding one with the 3 prong female plug... Using a regular 2 pole is a pain in the ass to ground :palm:

BTW, is a 0,5kva 2A max ok for the 2nd variac?

thanks man!!
76' JMP 50w w/ 71' metro board
93' Fernandes SSS strat
93' Fender Japan HSS Strat
4x12 w/ 2x 25w rola creambacks /2x 25w m75 Scumbacks

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Re: Two variacs for dummies...

Post by jnew » Tue Jan 12, 2016 1:35 pm

Most definitely. There are very low amperage requirements for the variac between head and cab. 8)
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Re: Two variacs for dummies...

Post by rgalpin » Wed Jan 13, 2016 9:13 am

regarding the idea of IN vs OUT when you say you are running it backwards... my thinking is that:

NORMAL USAGE:
in normal usage: wall voltage goes IN thru the plug that you plug into the wall (MALE)
>> VARIAC reduces voltage >>
reduced voltage comes OUT of the FEMALE receptacle on the variac

with that thinking i go:
AMP TO CAB USAGE:
AMP SPKR OUT >> MALE variac plug >>[variac @ 60V] >> FEMALE receptacle on variac >> speaker cab

when i do this, i see the variac needle jumping when i play.

is this the same as what you do jnew?

I love the name of this thread!! awesome.

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