OC71/OC47 Tonebender

[Rockhorst]

Meet Bender



After putting it off for way too long, I finally decided to build a Tone Bender on a MBP Pastyface board. The build took me three hours, including drilling and transistor testing. Fired up the first time. There's a Road Rage in there for the -9V. I mixed some component values of the Sola Sound and the Soulbender based on educated guessing. It absolutely rips, so I'm definitely going to document the component values for future reference. It is nice, full, creamy and aggressive if it needs to be, but not as wooly as a Fuzz Face. I took it to my two fuzz-aholic friends at the local guitar shop and they both ordered a copy within 10 seconds of playing. Mind you, these guys audition every fuzz pedal that goes through their shop, so I guess there's something good in there

Q1 is an OC71 from my late grand dad's stash, Q2 and Q3 are OC47.

I fiddled with the bias knob, but I'm not really sure what I should be looking for. It sounded great about everywhere (but I keep the fuzz knob mostly maxed).

[Blues Healer]

nice job

Benders are my favorite fuzz!
When built right and biased properly, they are so vocal and expressive, with just a little bit of unruliness.

[Rockhorst]

I didn't really go through the trouble of auditioning the transistors and checking their bias. Even though the TB circuit is a bit notorious, it came out just fine. Also note that I didn't use sockets for the transistors. I always just solder them onto the board directly. I've never destroyed one of 'em by soldering, contrary to popular folklore.

[Blues Healer]

you may have gotten lucky with your transistor gains!
I've found some OCxx batches are very consistent ... I have a batch of OC75s that are all right around 80.

it's not so much a problem if you're doing a one-off pedal, but if you want to reproduce a few, it's probably a good idea to go with the conventional wisdom and check the gains.

[Rockhorst]

Oh I did check the gains, with a Philips PP 3000 from the 60s (google it ), but only roughly. But I didn't check them in circuit on a breadboard. I did put them in ascending order (Q1 low, Q3 highest), which is the most important part from what I've read. OC47s are generally well behaved transistors, very close in sound to OC44s but better gain consistency.

More details on the 'mods': I build it to Soulbender specs, but took R14, C6, C7 and C8 from the Sola Sound specs. It happened by accident: I had my iPad zoomed in on the Soulbender, then after scrolling put landed it on the Sola Sound and only noticed afterwards. No clue how much of a difference this makes, biggest change seems to be C6. It sounded great though Any thoughts?

[Bret608]

Looks great, Rutger! Glad you like it. I'm about to build mine up too if my parts ever get here.

I think it's fine if you didn't worry about the gains and leakage too much. This is a MkIII Tonebender, so it's not at all fussy about bias like a MkII would be. Actually you can even use fairly low-gain transistors (40-50 hfe) in Q1 and Q2 and it will be pretty much fine since they're working as a darlington pair. Also, the bias trimmer isn't essential here; it just lets you starve the circuit for some fun. Chromesphere's Hydra Fuzz demo video helped me understand this.

I think it's good you took C6, C7 and C8 from the Sola Sound specs. That's basically the tone section and what the Souldbender does there is kind of smooth things out and reduce the bite. Sounds good, but to my ear it takes it closer to Fuzz Face territory. On my build, I'm basically going to do Sola Sound for the resistors but still jumper R10 like the Soulbender--it boosts the output volume apparently.