Fuzzhugger - Groundswell Overdrive [guts, schematic]

culturejam · Post by **culturejam** » 21 Aug 2009, 01:17

Pedal info:
http://www.fuzzhugger.com/pedal-groundswell.html

Got this in a trade. It arrived today, so I popped it open to have a look-see.

Very weird PCB design. I've never seen zig-zags like this before.

The bias control is also a bit odd. +9v is connected to lug 2 of a B100k pot; lug three is connected to the collector resistor of both transistors. So the bias of both stages is being affected by this one control. Interesting. I think.

The two gain stages are identical, part for part. Including the pulldown resistor. There is a pot set up like a voltage divider to ground (like a volume control) off the collector of the first stage, with the output feeding the second stage.

In my opinion, the gain stages are derived from the Electra Distortion. This is, of course, up for debate. Have a look for yourself at the schematic below and decide for yourself. A derivative Electra was my guess before I opened it up, based on the sound samples posted on the Fuzzhugger site. I've built enough to know the sound.

Enjoy.

culturejam · Post by **culturejam** » 21 Aug 2009, 01:19

Here's the schematic.

Please don't make fun of my schematic drawing skills.

Greg · Post by **Greg** » 21 Aug 2009, 01:19

How does it sound... to you I mean (I heard the clip) ?

culturejam · Post by **culturejam** » 21 Aug 2009, 01:28

Greg_G wrote:How does it sound... to you I mean (I heard the clip) ?

I'm not a fan, honestly. And using B100K for the volume pot makes the taper all weird. I hate that.

I just now noticed what was written in sharpie on the inside of the lid, so here's a pic. It explains a lot.

Greg · Post by **Greg** » 21 Aug 2009, 01:43

Aha...
It's definitely 2 x Electras together IMO.
I've played around with the Electra (and COT) before and it's a circuit that doesn't seem to work great when you put 2 in series like that.
It just gets kinda spitty.. not natural sounding.

I see he's another who loves the Glue gun..

culturejam · Post by **culturejam** » 21 Aug 2009, 03:20

Greg_G wrote:Aha...
It's definitely 2 x Electras together IMO.
I've played around with the Electra (and COT) before and it's a circuit that doesn't seem to work great when you put 2 in series like that.
It just gets kinda spitty.. not natural sounding.

I also did 2x Electras in series, and I had to tweak the bejesus out of it. But now it sounds good, I think. And loud as hell. Schematic for that is attached at the bottom.

Greg_G wrote:I see he's another who loves the Glue gun..

And electrical tape.

And hey, is it just me, or does the Groundswell circuit really not need the third 100n cap and the second 1M resistor?

Greg · Post by **Greg** » 21 Aug 2009, 03:32

culturejam wrote:
And hey, is it just me, or does the Groundswell circuit really not need the third 100n cap and the second 1M resistor?

Exactly what I thought.. it has the look of someone just trying stuff but not really knowing what it does.

The babylon looks interesting.
i wonder how it'd sound with some diodes at the end too ?

culturejam · Post by **culturejam** » 21 Aug 2009, 12:11

Greg_G wrote:The babylon looks interesting.
i wonder how it'd sound with some diodes at the end too ?

For some reason, I never tried that. As is, it gets a decent amount of clipping, but remains VERY loud in terms of output. It can be used as a dirty boost as well as a standalone drive. A couple guys at BYOC built it as well, and so far everyone has liked it (unless they are lying to protect me ego

)

I should probably post it in the Ready to Build forum.

tommyld · Post by **tommyld** » 23 Jul 2010, 04:33

Greg_G wrote:
culturejam wrote:
And hey, is it just me, or does the Groundswell circuit really not need the third 100n cap and the second 1M resistor?

Exactly what I thought.. it has the look of someone just trying stuff but not really knowing what it does.

Sorry to resurrect, but there IS good reason for the 3rd cap and second 1M...it allows you to easily mod to make either side independently switchable. FH does a lot of custom orders/switching, and it's just easier to build mirrored sides. So modders enjoy!

Jack Deville · Post by **Jack Deville** » 23 Jul 2010, 05:20

culturejam wrote: And hey, is it just me, or does the Groundswell circuit really not need the third 100n cap and the second 1M resistor?

"Collector feedback bias", right? This particular bias scheme has some inherent instabilities. Not my preference, but it can work (I have not run any analysis of this specific circuit).
The third coupling cap will help to "stabilize" the unstable bias scheme of the second stage, the 1M in parallel with the "Gain" control can be omitted. Its basically invisible (inconsequential) to the circuit and provides no benefit (also worth noting is that it doesn't really harm the performance of the circuit either).

Certainly not a "linear" design, but then again, most fuzz isn't! Just my $0.02.

culturejam · Post by **culturejam** » 23 Jul 2010, 16:20

tommyld wrote:Sorry to resurrect, but there IS good reason for the 3rd cap and second 1M...it allows you to easily mod to make either side independently switchable. FH does a lot of custom orders/switching, and it's just easier to build mirrored sides. So modders enjoy!

If that's the case, it sure would make sense also to add some extra pads to facilitate the switch wiring. There are two unused pads, but they are connected to the ground trace, so that wouldn't be helpful in switching.

Just sayin'

Jack Deville wrote:The third coupling cap will help to "stabilize" the unstable bias scheme of the second stage, the 1M in parallel with the "Gain" control can be omitted. Its basically invisible (inconsequential) to the circuit and provides no benefit (also worth noting is that it doesn't really harm the performance of the circuit either).

Maybe that's the reason the cap is there. But having the extra 1M and the cap makes me think otherwise.

tommyld · Post by **tommyld** » 23 Jul 2010, 19:10

The second 1M resistor has zero effect in the standard Groundswell wiring--no tonal reasons for it, only mental ones. Haha. I'd keep the 3rd cap though.

Might be worth noting that Groundswell was never an official part of the FuzzHugger line. It was a "spare parts build" that a few people asked for after seeing the original (so oddities abound, pot tapers vary here and there, and a few with ugly insides!). It was actually built on a PCB that wasn't designed specifically for it!

There are only about 12 out there...kinda odd to see it pop up here. Neat little drive, but probably not the best circuit to seriously analyze.

culturejam wrote: it sure would make sense also to add some extra pads to facilitate the switch wiring. There are two unused pads, but they are connected to the ground trace, so that wouldn't be helpful in switching.

True, true! Though you can always just heat the eyelets from the top, pull, and rewire.

culturejam · Post by **culturejam** » 23 Jul 2010, 19:38

tommyld wrote:It was a "spare parts build" that a few people asked for after seeing the original (so oddities abound, pot tapers vary here and there, and a few with ugly insides!). It was actually built on a PCB that wasn't designed specifically for it!

There are only about 12 out there..

Ahhh. Well, that makes a lot more sense, then.

gus · Post by **gus** » 24 Jul 2010, 13:55

MPSA13
http://www.fairchildsemi.com/ds/MP%2FMPSA13.pdf

The 1meg from the wiper to ground might be a resistor to change the pot taper.

The other part of the circuit one should note is the bias control is it just a adjustable voltage dropping resistor missing a cap from the 47Ks and the bias pot node OR is the lack of a cap from the node to ground a part of the design allowing interacting between the gain stage via the two collector resistors and the bias pot as the bias pot is turned increased the resistance?

By design or ?