Prescription Electronics Depth Charge

[Silver Blues]

I saw this one on JohnK's page and decided I wanted one, so I went forum-diving for a schematic and put this layout together. Haven't built it yet but I checked it over twice and it looks good, so should be fine. Sounds like a really awesome bass fuzz, I'm sure it's usable on guitar too. It has an interesting topology that is admittedly refreshing after seeing so many rehashes. It's probably an adaptation of something I'm not aware of  I've incorporated a few simple mods to improve the functionality of the Blend control as described in the FSB thread (namely the 390K resistor and the 47uF booster cap on Q3. Original mod was 100uF but chirping at high gain was reported, so try values as big as you can go without noise).



If anyone goes to look at the schematic, please note that the transistors are not labelled consistently with the schematic. Q1 and Q2 are the same, but then Q3=Q6, Q4=Q3, Q5=Q4 and Q6=Q5 (layout=schematic). I've also omitted the filter cap from the board but it was only 22u and I suppose you could just add it to the jack. I think it was actually done this way in the original.

EDIT Just cross-referenced the 2N3707 and apparently NTE199 is the equivalent, for those whom obtaining NTE parts is easier. The 3707 are actually quite expensive on eBay.

[Shaggy45]

Anyone ever build this one? i did and it works. kind of. the volume blend and tone are all wonky. i don't have any germanium diodes so i put some 1n914 in it. i'll go back over it when i have more time.

[Silver Blues]

Yeah shit I did this layout a long time ago, never got around to building it myself even though I was interested in having one. Let me know what you find out and if the layout needs any corrections.

[reddesert]

According to a thread on FSB and my quick comparison of the schematics, it is related to a Univox Superfuzz. I see a few capacitor changes, addition of a Blend control, and replacing a Tone switch with a pot. There may be some other differences, but the general topology is Superfuzz.

[Shaggy45]

Looking at the schematic it looks like you left out a couple of 0.2u caps.

[Shaggy45]

I'm trying my best to figure this out lol I've only built 17 pedals and have managed to figure out any of the ones that did t work. I need to learn this stuff. I can only imagine the level of fun it would be to fully understand and make layouts. I get the concept of schematics and that everything is connected, but this is a pretty big one for a newbie like me.

[GrooveChampion]

I've seen some forums where they said that 2n5088s were substitutes to the 2n3707 in some 1176 units, think the same can be done here?

[reddesert]

The two 0.2 uf caps aren't missing - the layout has them as 220 nf film caps.

These are the caps that are 0.1 uf in the Univox Superfuzz, I think.

[Silver Blues]

Yeah I gleaned that this was Superfuzz based some time after I made this post ahah. I'd say that 5088 as a replacement is fine, I don't see why you couldn't just use whatever NPN BJT that sounded good in here.

[Shaggy45]

Built this again today.  it works, but still only sort of. Volume and gain work, but blend does not blend and tone acts as another volume knob. anyone got suggestions on what could be wrong? I've been looking at the layout and schematic over and over and can't seem to figure it out.

[reddesert]

On the layout above, there's a problem in the right side of the top row.  Tone 1 should be connected to a 1n cap and a 10K resistor, and this junction should not be connected to ground.

Some of the parts could be shuffled around to revise the layout. For an already built board, you could desolder the Tone 1, 1n, and 10K from the top row and join them off-board.

Also, the notes say Tone 2 to Blend 3, but it should be Tone 2 to Blend 1.

[Alamondm]

The schematic above shows them going to ground. Am I missing something. I’m thinking about giving this one a shot. Has anyone successfully built it?