Hi, Paul,
I've had this one on my "to do" list and finally got to it a couple of days ago. I built it with the diodes socketed and initially put red LEDs in to get a sort of "baseline" before trying some germanium diodes. You're dead on. With the LEDs it was a decent overdrive but did not blow me away. I auditioned the germanium diodes I had on hand and after settling on a pair of Russian D310s this is one of my favorites ODs. TONS of character!
Just some insights from my build:
- VR2 sounds best with an anti-log pot. With a linear pot the dirt increase all happens around 8-10 (on a 1-10 scale, basically the last 20% of the rotation). Of course you did not specify what kind of 50k pot worked best, so this is just me letting you know what worked best for me.
- I discovered that I did not have any TL081 chips. Not sure how I managed not to have those stocked. I went with a TL051 which, according to my pitifully limited understanding, is supposed to be like a posh version of the TL0X1 op-amps. Anyway, I'm not sure what mine would sound like with a TL081, but it sounds damn good with a TL051.
- Here are my Germanium findings:
- D310, my favorite in this. Volume is a fair bit lower than LEDs and the lowest of the germ diodes I tried, but this circuit has TONS of volume so it really isn't an issue. They give the overdrive a nice smooth creamy crunch. The little nuances of strings are also nice and clear even on full dirt.
- 1N270, Not great. Not much different from the LEDs. LOUD, but not much character.
- 1N34a, these were either from Tayda or from a Chinese dude on Ebay. The small DO-7 kind. Decent. Same volume as the D310s, but the clipping is a little sharper and a little more generic. Still, if I did not have the Russian germanium diodes, I'd be fairly happy with how these sound in this circuit, but it would not have made me smile like it did with the D310s.
- 1N60, Another one I could have lived with. These are the clear glass with red-band diodes, not the little blue ones from Tayda and other places. I'd say slightly better than the 1N34As. Still has that nice creamy-crunch character to the clipping.
- OA91A, great sounding in this circuit. Made it into the final round of deciding what I wanted in this circuit permanently. Creamy, crunchy, and very nice. Very similar sounding to the D310 but with slightly less... it's hard to describe.. basically it's how the distortion can potentially mush the individual strings "ringy-ness" together... this one does a decent job, but not to the degree the D310s seems to preserve it. On the whole, though, I'd be quite satisfied with these diodes in this circuit.
- D9E, supposedly almost identical to the Unicorn Pube diodes in the Klon Centaur. I wouldn't know. They do sound great in this circuit though. Very similar to the D310s but still lacking just like the OA91As, except I like the OA91As a little bit better than these. Otherwise very similar clipping and quite decent.
- 1D507A (some random military grade soviet surplus germanium diodes I bought on a lark), I almost went with these over the D310s. The decision was difficult as these sound amazing int his circuit. These seemed to have a teeny tiny bit more kick to them than the D310s but, once again, lacked some of the "sweetness" of the D310s in the way I could hear more of the individual string ringing.. not much though! If I did not have the D310s, I'd have used these and it would still be one of my favorite ODs.
My selection of germanium diodes is pretty small compared to most, but there you have it.
If I could change one thing about this circuit it would be a bit more volume at the lower gain settings.
Oh, I almost forgot to mention!!! The Tone control on this thing is wonderful. I was testing this out through an LP Jr. doubecut with a very high-end
HB-sized P-90 pickup (Mullinax, the best pickup I own. I'm not a "thegearpage" cork sniffer, I just try to make sure I use the best equipment I have when reviewing someone's personal work). It actually gets a little painfully Treble at full clockwise (as it should in order to accommodate a wide array of pickup types) and I was very pleasantly surprised to find that when turned the other way it doesn't devolve into a muted mush like most "bass ends" of a tone control. Even FULLY counter-clockwise it has a usable sound. For once I can set a Tone control straight up the middle and have it sound right! I'm almost always having to turn the Tone all the way up on pedals to get a decent sound.
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