This Week on the Breadboard: Animals Diamond Peak Overdrive (with some mods, of course)

[szukalski]

I just verified my layout today (pics to come). MMBF4393 and 2N2218A (~100hFE). Very nice with a Strat so far!

 

[lrgaraujo]

Robert's layouts are as good as they get, but it's a lot of fun seeing how different people (all very capable) approach board designing

 

[szukalski]

Here’s my build. I’m still waiting on a faceplate so there’s no front shot. I really enjoy this, especially with a GeFET boost up front!

 

[Chuck D. Bones]

Sehr schön!

What's with the siamesed resistors?

 

[szukalski]

I try to keep to E6 series components, so there are a few values which need a series or parallel approach.

 

[Chuck D. Bones]

The values are not that critical. You could sub 100K for 91K in that circuit.

 

[szukalski]

And with the faceplate:

 

[HamishR]

Bloody hell! I just ask Chuck some advice about a pedal and look what happens! I am so impressed with what everyone has come up with. I basically just wanted a bass pot because i really like this circuit and wanted some more grunt. Mr Skreddy is a very talented designer and has an excellent ear for great guitar sounds.

Anyway this is what I have built and I love it. I'm no PCB expert and am perfectly happy to mess around with Vero.

 

[Chuck D. Bones]

Yeah, it kinda took on a life of its own. Respect to Marc Ahlfs!

 

[MattG]

The circuit topology appears to be virtually the same as the Hybrid Overdrive. (Not surprising, same designer, same circuit lineage as e.g. Lunar Module, Screwdriver, etc.)

In fact, after reading this TGP thread, Animals Pedals/Skreddy Info?, I suspect the Diamond Peak is a tweaked Hybrid Overdrive specifically for Animals Pedals. Lots of direct commentary from Skreddy/Marc Ahlfs in that thread.

We've clearly got a lot of mileage out of this topology. I don't think it would be too hard to make a "universal" PCB that supports all these variants (Lunar Module, Screwdriver, Hybrid Fuzz Drive, Major Overdrive, Hybrid Overdrive, Diamond Peak). Kind of like the Big Muff, there are BOM spreadsheets that describe all the different flavors that can be built. (Hint hint @Robert)

 

[Chuck D. Bones]

Absolutely. The difference between the variants comes down to how the gain is apportioned between stages and the tone shaping in various places. As much as I like the Screw Driver, the MOSFET front-end is too noisy. I prefer a JFET there, although a BJT works well too. Getting the bias right with the Screw Driver and Hybrid Fuzz Driver is tricky due to the germanium transistor, but it's doable and sounds great when dialed-in.

 

[MattG]

I'm joining the PCB party. I fired up my prototype last night, it works great (except that I wired three of the pots backwards). It sounds awesome though!

For low gain silicon Q2/Q3, I used these 2n4123 parts from Tayda. Cheap and plenty of stock. The one I happened to measure on my CCT said HFE of 94.

What is the reason for using low-gain transistors in the Q2/Q3 positions? What would happen if high(er)-gain transistors (e.g. 2N5088, BC549, 2N3904) were used?

Also, encouraged by how this sounds, I'm flirting with the idea of picking up the Major Overdrive for an "inspection". I would expect the circuit topology to be the same as the Diamond Peak/Hybrid Overdrive, but with different component values.

Has anyone experimented with other JFETs for the Q1 position? Earlier in this thread, it was suggested that J113 with Vp < 2V should work. Just curious if anyone's actually tried any alternatives. (I used MMBF4393, works great; but I have a fair amount of random TO-92 JFETs.)

 

[Chuck D. Bones]

Has anyone experimented with other JFETs for the Q1 position? Earlier in this thread, it was suggested that J113 with Vp < 2V should work. Just curious if anyone's actually tried any alternatives. (I used MMBF4393, works great; but I have a fair amount of random TO-92 JFETs.)

Try it and see for yourself. Adjust R4 to set the bias, R2 to set the gain and C3 to set the bass response, in that order. Iterate as req'd. If you use a low Vp JFET like J201, R4 will end up being so small that you won't be able to control the gain with R2. A good starting point is Vp between 1 and 2V. Not a hard & fast rule, just a guideline.

What is the reason for using low-gain transistors in the Q2/Q3 positions? What would happen if high(er)-gain transistors (e.g. 2N5088, BC549, 2N3904) were used?

Low-gain transistors have a smoother tone with fewer high-order harmonics. The Ge transistors in the original FFs had low HFE because that's what was available at the time. Ge sounds great, but bias stability is an issue.

Try some high-gain trannys see for yourself. Q2's HFE affects the bias, so plan on adjusting R10, R11 or R14 if you significantly increase Q2's HFE.

For low gain silicon Q2/Q3, I used these 2n4123 parts from Tayda. Cheap and plenty of stock. The one I happened to measure on my CCT said HFE of 94.

I recommend something with HFE down in the 50 to 60 range.

Also, encouraged by how this sounds, I'm flirting with the idea of picking up the Major Overdrive for an "inspection". I would expect the circuit topology to be the same as the Diamond Peak/Hybrid Overdrive, but with different component values.

If you get one, we'd love to see the schematic.

 

[lrgaraujo]

Has anyone experimented with other JFETs for the Q1 position? Earlier in this thread, it was suggested that J113 with Vp < 2V should work. Just curious if anyone's actually tried any alternatives. (I used MMBF4393, works great; but I have a fair amount of random TO-92 JFETs.)

I've used a 2sk246-Y for Q1. If I recall correctly, it had Vp of around 1.5V and Idss ~ 3mA.
As Chuck has pointed, I've played with R4, R2 and C3 in LTSpice to get similar biasing and gain. There's a small gain difference, but it was close enough for me to avoid ordering new parts. Pedal sounds really good.

 

[MattG]

I have acquired an Animals Pedals Major Overdrive, I'll post pics later today or tomorrow of the guts.

I just posted my build report for this circuit built around a PCB I made: Hard Rock Pinnacle Purebred Drive.

I have a handful of low-gain silicon transistors on hand. Very few are down to the 50-60 HFE Chuck recommends, but here are my notes in case it helps anyone:

• MPSA06 - HFE around 213-214
• 2N4123 - HFE 84-106, most at 94
• PN2222A - HFE around 213
• MPSA42 - HFE 85-108, most 85 or 95
• 2N2369A (plastic case) - HFE 55-106, most around 94
• 2N2369 (metal can) - HFE 59
• 2N3903 - HFE 119-169, most 119 or 140

All measurements taken on my cheap Chinese tester (CCT). I used 2n4123 in my prototype build, and metal can 2n2369 and MPSA42 in my two recent builds.

I have a few extra PCBs I'm happy to give away, PM me if interested.

 

[MattG]

Here are some pics of the Major's internals.

The two TO-92 transistors are 2n5172. The third transistor is SMD and appears to have "1QI" (one queue eye) on it, but I'm not 100% sure about that.

 

[Chuck D. Bones]

Cool. Let's see the front panel. What are the transistor part numbers?
We're going to have to guess at the SMD cap values, unless you want to remove them to measure.
I see two types of markings on the resistors. Some have three numbers, which we can read directly. Others have a combination of letters & numbers, which we have to look up in a table.

 

[MattG]

I edited the previous post to include a picture of the front panel and also that the through hole transistors are 2n5172.

 

[Chuck D. Bones]

"1Q" refers to a number possible of SMD part numbers, MMBT5088 being the most likely because Q101 is definitely not a regulator, zener diode or PNP transistor.

I'll work up a candidate schematic and then you can confirm it.

 

[pingpongcomputer]

Great looking circuit, would you be willing to explain the function of C6?