Brownout (Subdecay Variac) dirt pedal - wow. Anyone else as impressed as me?

H

HamishR

Well-known member
I've had this PCB for ages and while bored today thought it was time to build it. All I can think right now is wow! This is a great pedal!

I assumed that it was more of a pedal aimed at shredder crowd, one of whom I am not. So when I tested it I was surprised that it has beautiful low gain sounds of quite a few styles because of the way the Preamp and Pentodes knobs work. Great midrange, great control over treble and bass and just a wonderful sounding and responding circuit. I tried it with a Strat, a 335 and a Gretsch 6120 and had equally killer results with all three guitars into both a Brown Deluxe and a Marshall style 1x12 combo. I can get some smoky blues/jazz sounds from the semis and some fat Strat sounds. My Gretsch sounds huge and still twangs through it. I could use it for some hard rock sounds, early ZZ Top sounds or some old school blues and rockabilly sounds. It's very versatile.

This pedal is quite a revelation to me! Is anyone else as impressed? What are you guys using it for? I think I'm gonna have to order a couple more PCBs...

FWIW it worked brilliantly first go with Central branded 2N5457s from Tayda. Which is a relief because it uses a lot of them.

(EDIT) I used a 100µF cab for the filter cap because I don't have a 220µF cap which would fit. It works but I wonder if it's a bit noisier than it should be because of this? It's not that noisy, but noisier than my simpler ODs..
 
what kinda noise we talking? I see quite a few gain stages...a 220uf cap is probably necessary? Maybe piggyback 2 of em just to see what happens
 
That's a good idea. I'll see if I can add one under the board or something. The noise isn't really that bad but if I can lower it I will.
 
I built this one a couple of years ago and never boxed it. Funny enough, I tested it again a couple of days ago and was really impressed! Will for sure box it up the next time I order enclosures.
 
What type of circuit is that? Sounds a bit like a BSIAB with 2N5457. I recently swapped pedals and got a CMatMods Brownie with extra jfets in the box.
 
The only way the PCB could be better is if it actually had room for the 220µF cap (!) and was a tiny bit narrower so I could fit it into a 1590B.

:)
 
The 220uF cap is not critical. 100uF works just fine.

Can you describe the "noise?" Hiss? Hum? Radio pickup? This pedal has a fair amount of gain when you dial up the PREAMP and PENTODES knobs, so it is going to amplify everything that comes in thru the input jack. I know you're using quality parts and cleaning your board. Make sure there's no paint on the inside preventing the jacks, switches and pots from making good electrical contact with the enclosure.

How did you go about setting/verifying the bias on the JFETs?

Finally, yes, IMHO the Variac is one of the best dist/OD pedals I've played. I liked it so much I built 3 of 'em!
 
The noise is just regular hiss. It's not that bad, just a bit more than I get with my normal ODs. I would guess it's simply a result of the gain.

I haven't felt the need to check the JFET bias because it sounds so good anyway. I have aways had good luck with the 2N5457s I have - They always seem to work without issue. It's J201s I have problems with. Even my J113s are easy to work with.
 
HamishR said:
The noise is just regular hiss. It's not that bad, just a bit more than I get with my normal ODs. I would guess it's simply a result of the gain.
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with all due respect, it doesn't sound like you're really comparing apples with apples.
this subdecay variac appears to be more of a distortion. and distortions are generally noisier than ODs. is it noisier than most of your other distortion pedals? i.e. another MIAB?
 
I'm comparing it to my regular ODs set to a similar sound, so I would say it's operating as an OD. I'm not sure where an overdrive becomes a distortion anyway! My overdrives have a similar gain range to the Variac. So I thought I was comparing apples to apples, or at least circuits which create similar amounts of distortion. :)

My guess is that the noise is a result of the clipping being achieved by overdriving transistors rather than by clipping diodes, so it makes sense that the amplification is what's increasing the noise.

FWIW I don't really use distortion pedals like the Rat. Anyway it's not a big deal - just something I noticed.
 
HamishR said:
I'm comparing it to my regular ODs set to a similar sound, so I would say it's operating as an OD.
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ahhh yep. i had a feeling you might be comparing in this manner. in which case - fair call.

HamishR said:
My guess is that the noise is a result of the clipping being achieved by overdriving transistors rather than by clipping diodes, so it makes sense that the amplification is what's increasing the noise.
Click to expand...
yeah makes sense to me.

are your other JFET ODs as noisy? i'm guess the bias settings would probably affect the amount of gain available (and resulting noise).
 
Like you say, it's been luck. No reason to believe that the batch of JFETs you buy will be anything like the batch the pedal builder bought, tested and selected.

J201s are finicky because of the way they are used. Some pedals run them at or close to Idss. No amount of fiddling resistors will make a J201 with the wrong specs (for that particular circuit) sound right.
 
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