Low-Draw Devi Fuzz Needs More Than 9v... Why?

[Ginsly]

I built a stripboard Devi Ever US Fuzz, and it sounds great! Super gated at most settings, really nice texture. I noticed something strange, though - it needs a little more than 9v in order to function, even though the mA draw is really, really low - reads 2mA on my Truetone meter.

I have one of those Danelectrode variable voltage power supplies, and at full juice it works fine - I roll the voltage back just a bit and it gets thinner and thinner right away, pretty much disappearing at around the 9v mark. Same thing with batteries - a fresh 9.5v carbon zinc works great, but nothin' doin at 9v and below.

Any idea why this might be? I'd think with such a low mA draw I could roll the voltage back to well below 9v and still have some signal coming through. Maybe it needs over 9v in order to kinda "push through" the extreme gate it has? I think I'm just missing something, would love to hear some thoughts about it.

 

[GAStan]

Verify what kind of diode is D1? Check voltage drop on it.
Verify the type of diode installed at D1. Check the voltage across it.

 

[Ginsly]

Verify what kind of diode is D1? Check voltage drop on it.
Verify the type of diode installed at D1. Check the voltage across it.

Thanks for chimin in - it's a 1N5817 as indicated in the layout, and I just measured .2V across it.

 

[spi]

picture?

 

[Ginsly]

Guess I should have posted this in Troubleshooting! Seems to be working normally, I figured this was just a quirk of the circuit; if something is a little off then I'd love to figure that out, though.

I'll try to get some pics, but it ain't pretty... this is from months ago when I was messing around with different sockets, screw terminals, etc...

 

[Ginsly]

To add to the confusion, looks like there's more than one schematic/layout of the US Fuzz floating around. Here's DE's "multi-use" board and "build doc" to make it a US Fuzz. Compare to the vero layout and there are some differences.

 

[GAStan]

Thanks for chimin in - it's a 1N5817 as indicated in the layout, and I just measured .2V across it.

That wouldda been too easy but was worth a shot.

 

[Ginsly]

The plot thickens, as that "verified" layout (which actually does work) differs from the US Fuzz configuration in DE's "multi-schematic". BOTH of Q4's 100K B-C resistors are removed, not just one. Q1 (the first 2N2222A) is flipped between the layout and this schematic. I'm sure there are other differences, too. Hmm.

 

[BuddytheReow]

I've breadboarded from this exact schematic. You mention Q1 (the first 2N2222A). It does absolutely nothing sonically. The biasing comes from the 2M2 resistor.

All the biasing comes from the 2N2222A due to the voltage drop. That 2M2 resistor does nothing. Similar to how you'd throw a BJT in a feedback loop as soft clippers.

 

[Ginsly]

I've breadboarded from this exact schematic. You mention Q1 (the first 2N2222A). It does absolutely nothing sonically. The biasing comes from the 2M2 resistor.

Funny, I'm breadboarding it right now! Wondering how it differs from the one I built.

Huh, that's very strange about the first 2N2222A... why the heck is it there?? I take it the US sounded good when you breadboarded it based on the above schematic. The (slightly different) stripboard layout I used worked as well, but I'm still pretty perplexed as to why it would just kinda die out at 9v and below... Any thoughts on that Buddy? My guess is it has to do with the extreme gate on the US...

 

[BuddytheReow]

I've updated my previous comment above.

Start measuring voltages and you'll find the culprit pretty quick.

I did a deeper dive of Devi Ever circuit blocks a few years ago. Most Devi Ever circuits are a handful of circuit blocks done in different orders. Chuck and I had a discussion too.

Post in thread 'Buddy's Breadboard and Circuit Design Notes'

Jul 1, 2022

So, yesterday I put together in the resources section a handful of Devi Ever snippets that she uses in a lot of her fuzz pedals. For Devi, it's usually a mix-and-match type of situation and slap a new name on the circuit. As a due diligence process for myself before posting anything I have to try them out for myself. Here's my Devi Breadboard project for mix and match. The top left is a pre-gain or fuzz section, top right is a volume pot/output section, bottom left is high and low pass control that I cooked up. There are 4 Devi snippets in the middle that I wanted to mix and match to...

• BuddytheReow

• 

 

[Ginsly]

Start measuring voltages and you'll find the culprit pretty quick.

I did a deeper dive of Devi Ever circuit blocks a few years ago. Most Devi Ever circuits are a handful of circuit blocks done in different orders. Chuck and I had a discussion too.

Post in thread 'Buddy's Breadboard and Circuit Design Notes'

Jul 1, 2022

So, yesterday I put together in the resources section a handful of Devi Ever snippets that she uses in a lot of her fuzz pedals. For Devi, it's usually a mix-and-match type of situation and slap a new name on the circuit. As a due diligence process for myself before posting anything I have to try them out for myself. Here's my Devi Breadboard project for mix and match. The top left is a pre-gain or fuzz section, top right is a volume pot/output section, bottom left is high and low pass control that I cooked up. There are 4 Devi snippets in the middle that I wanted to mix and match to...

• BuddytheReow

• 

Thanks I'll give that a look!

Could you elucidate on the voltage measuring situation? It's honestly something I haven't done a lot of. Not sure what the protocol is and what red flags to look for. I really appreciate it!

 

[BuddytheReow]

So, like measuring voltages for troubleshooting, black to ground and the red probe to the part in question. In the schematic above you have 3 transistors that get powered. Measure the voltages at the collectors and base of all three. You don't need emitter voltages since they're tied to ground. Write them down and make sure you're giving it more than 9V of power. Then do the same thing again but this time with only 9V or less power.

If memory serves me right, it only takes about 0.7V at the base to "turn on" the BJTs. Red flags would be seeing 7V and up at the base to state the obvious.

 

[Ginsly]

So, like measuring voltages for troubleshooting, black to ground and the red probe to the part in question. In the schematic above you have 3 transistors that get powered. Measure the voltages at the collectors and base of all three. You don't need emitter voltages since they're tied to ground. Write them down and make sure you're giving it more than 9V of power. Then do the same thing again but this time with only 9V or less power.

If memory serves me right, it only takes about 0.7V at the base to "turn on" the BJTs. Red flags would be seeing 7V and up at the base to state the obvious.

Thanks so much, that helps a lot Buddy.

I just breadboarded a US based on the above schematic, and for one thing it does indeed look like there are no 100K resistors between the 2nd 2N2222A's B and C - tried it with a single 100K as it seems to indicate and it sounded... bad. Obviously the 100K going from that transistor to power still needs to be there, though.

Funny thing - this version has the same voltage quirk as the stripboard one I built months ago. With a normal power supply or fresh 9v battery it sounds great - starve the voltage even a tiny bit and it gets very quiet then disappears.

I've only measured transistor voltages on this breadboard version at "full power" so far, but here are the results (E-B-C):

MPSA18 #1 - 0 / .53V / .72V
2N2222A #1 - .53V / .72V / .72V (collector connected to nothing)
MPSA18 #2 - 0 / .57V / 6.3V
2N2222A #2 - 0 / -2.3V / 9v

That seem about right? Again, I have very limited experience with this side of troubleshooting, so this is very helpful. Kinda skipped this part along the way...

Edit: Here are the bb voltages when lowered to exactly 9v:

MPSA18 #1 - 0 / .53V / .72V
2N2222A #1 - .53V / .72V / .72V (collector connected to nothing)
MPSA18 #2 - 0 / .6V / 7V
2N2222A #2 - 0 / -1.3V / 8.95v

 

[BuddytheReow]

Q1 collector seems off. Try lowering the value of the 220k resistor to 200 or lower until it starts to sound better with a lower input voltage.

 

[GAStan]

Are you  sure the base of 2N2222A #2 is a negative voltage? This seriously has me puzzled.

 

[Ginsly]

Q1 collector seems off. Try lowering the value of the 220k resistor to 200 or lower until it starts to sound better with a lower input voltage.

Tried a bunch - 180k, 100k, 47k... not a huge difference when it comes to the "low" 9v behavior. Hmm.

Are you  sure the base of 2N2222A #2 is a negative voltage? This seriously has me puzzled.

Yep! No clue. The breadboarded circuit works great, it's just odd that it quiets/fades so severely with a voltage that's still around 9v... Since the stripboard pedal and this breadboard (one based on a layout, one on the schematic) exhibit the same behavior, I have to assume it's normal for the circuit... ??? 2mA power consumption, but starts to lose tons of volume/texture at like 9.2v...