Brownout Overdrive

falco_femoralis

falco_femoralis

Well-known member
I've been on an "amp in a box" kick lately and just finished up this Brownout Overdrive. The pedal art on the original is AC/DC themed with their font and the lightning bolt, but AC/DC was never known for using a variac, so I'm not sure why Subdecay chose that name. The "Brownout" name also suggests Van Halen, but despite this, I went the AC/DC way because I love them and I used Marshall knobs and painted the pedal in colors reminiscent of the Bonfire box set.

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I moved the controls around vs the PCB because I like to make it hard for myself, and I made the LED change color along with the toggle switch setting.

Actually I installed two LEDs
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And a double pole switch to control them
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I also off boarded one of the pots, and I was super glad when this thing worked when I first fired it up
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This is a really interesting pedal. The Pentodes control and the Phaser Inverter switch are supposed to be simulating different kinds of tube amp overdrives (I think?) I wish I understood what was going on. I was not ready to try to understand any of it after blasting my mind building this pedal the past two hours.

When I play thru it, the Pentodes control adds more treble response and a super nice saturation when turned up - you have to turn down the Treble control to adjust for it. The Phase Inverter toggle switch is fairly subtle, but now that I've taken a look at the schematic I can see it seems to be reactive to the Pentodes control, so I'll have to flesh it out a bit more and see if there's a setting where the toggle makes a more substantial difference.

With the Preamp and Pentodes controls dimed, I was getting some superbly awesome feedback, reminiscent of the Let There Be Rock Movie live recording from 1979.

This one is going to be on my board for a while.
 
Nice! I have one of these in the mail. Kinda worried now though as I didn’t realize it used so many 2N5457s. How does fair to the Plexi Breed, Pussy Melter or Ultisol?

I have “The Second One” built but waiting on one part. I’m very excited to try it it’s a clone of the Colombo Audio The One based on the old JMP-1 preamp. Demos sound great.
 
I think it's similar in ways to the Plexi Breed - similar thick, ampy sound. Both excellent ODs.

I wish the Variac had the tone knobs reversed and below the other three knobs. I always try to have the Gain top right, Volume top left, Bass lower left and Treble lower right. That helps me with my typical graphics scheme.

Nice build, BTW!
 
HamishR said:
I think it's similar in ways to the Plexi Breed - similar thick, ampy sound. Both excellent ODs.

I wish the Variac had the tone knobs reversed and below the other three knobs. I always try to have the Gain top right, Volume top left, Bass lower left and Treble lower right. That helps me with my typical graphics scheme.

Nice build, BTW!
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That’s seems to be the most popular layout. Check out the Ultisol distortion if you haven’t already its layout will really throw you off. It’s a great distortion based off the Dawner Prince Red Box.
 
I quite like the Dawner Prince Red. I'll have a look at the Ultisol.

(edit) Oh I see what you mean! When I built that I moved the knobs around!
 
Looks like the phase inverter switch allows you simulate two different phase inverter designs. Long Tail Phase Inverter or Cathodyne mode. I’m no amp tech but a quick search reveals that LTP mode “should” provide more gain and symmetrical clipping while Cathodyne mode provides unity gain and more balanced sound. However, and this is a guess, increasing the Pentode knob while in either mode should simulate more power amp distortion.

Also, the pedal can be run from 7.5 to 15 volts which is interesting. Running it at lower voltage should be similar to using a variac while 15 volts of course would allow more headroom. This would be an interesting pedal to use a battery with.

I can’t wait to build this one as I’m kind of on a MIAB mode after building the Plexi Breed, Jump Drive, Rock Star distortion, 8 ball, 59 sound, Ultisol and the The Second One. The Second One is by far the best for all out heavy riffing with the Plexi Breed being the closest to feeling like a Plexi. The 59 Sound is better for edge of break up low gain tones. All have their differences but those three are my favorites in their respectful levels of distortion if that makes sense.
 
The toggle switch is very subtle - it just makes the signal a bit brighter and doesn't interact with the Pentodes control. It has a touch more clarity in the up position and I've found that I'd prefer to leave it there. If I built another one of these I would omit it entirely.

I like the pedal with the Pentodes control fairly high and the Preamp control around 11 o'clock. To me that's the perfect 70's AC/DC sound.
 
bluedmc777 said:
You just shit on all my research. 😂😂😂 Maybe I overthought it lol.
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I thought they were related at first too, the way the schematic is drawn. Both Q5 and the toggle switch section draw from R17. But after playing around with the toggle on and off at various settings of the Pentodes control, it really has no bearing on the way the power amp section of the pedal behaves. It just makes the signal a little brighter and more focused. Maybe if you like a slightly more woofy sound then try it in the off position, but even then it's so subtle you have to wonder why it's not doing more than what they designed it to do.
 
Well a 12AT7 normally used in phase inverters do produce a higher frequency response than say a 12AX7…so I’ve read. That’s probably why I’ve never liked a 12AT7 in any main preamp role other than having less gain. They sound thin and bright to me. Can’t wait to build this one. Did you blindly choose the 2N5457s?
 
bluedmc777 said:
Well a 12AT7 normally used in phase inverters do produce a higher frequency response than say a 12AX7…so I’ve read. That’s probably why I’ve never liked a 12AT7 in any main preamp role other than having less gain. They sound thin and bright to me. Can’t wait to build this one. Did you blindly choose the 2N5457s?
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I just installed what I had

This is easily one of my top 3 favorite pedals. Just playing open chords is so satisfying with the Pentodes knob cranked and the preamp knob at about 10 o'clock. It is absolutely the sound of AC/DC. I wish the Pentodes control had more to give. I might make a second pedal and alter R22/R23 to get more current into Q5.

There is also a lot of treble with the Pentodes control turned up, so maybe I'll try increasing C18 to 220pF or so
 
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