Son of Ben advice

[Mike McLane]

I recently built a Son of Ben. On clean to mid-gain end it puts a beautiful "jacket" on the tone, but I don't really need the high level of gain it puts out. Other FET boosters (Six String Singer, EP Booster, Katana) seem to impart this pleasing effect, but have limited EQ & gain flexibility. I was looking at building up a Wampler Black 65 from a vero layout cause it has the EQ and gain features like the SOB (but supposedly less gainy and more "Fendery", and I'm a Fender kinda guy). But in the end would it really be much of a departure from the SOB? I'm guessing not. Seems like playing with the FET biasing or sub'ing a part or two could make this guy a bit more of the sedate always-on type of pedal I would enjoy. Any suggestions?

 

[tcpoint]

An easy change would be to change the FETs. Some or all of them. Suggestions would be 2N5457 or or MPF102. MPF102 would be lower gain than the 2N5457 which is lower than the J201. If you wanted to go all out you could measure the FETs and change the source resistors. For more info, you could read Fetzer Valve.

 

[Mike McLane]

I'm thinking something with a top end gain approaching a Timmy, Lightspeed, etc. I play a Deluxe Reverb and keep it right on the edge of breakup so I can throttle back for balads, etc. This would be like having a second crunch channel. Based on your suggestion I guess I could socket the the mounting holes and experiment. In slumming thru my bag of left overs from previous builds I have 2 - 2N5457, 2 - 2N5458 & 2 - 2N5484. If I can make heads or tails outta the schematic it looks as though there is an intitial gain stage prior to the BASS EQ, then a DRIVE fader regulating the signal level into two additional gain stages, then a TREBLE cut followed by a VOLUME fader. I assume the filtering is designed such that there is a "fixed" mid range notch that the BASS & TREBLE controls operate around. I assume that the initial gain stage (as with a traditional amplifier) is there just to create enough signal "umph" to begin to apply BASS EQ filtering and then remaining stages of makeup gain/dirt (why two gain stages, do you need two cascading gain stages to deliver the level of dirt this thing puts out?) So I'm thinking leave the J201 in Q1 and try the 2N5457's (or one of the others?) in Q2 & Q3? As far as measuring FET's, changing source resistors and otherwise reading the travails of Mr Fetzer that's completely above my pay grade. I'd just have to take your word for it. That being said based on your suggestions I've got to say, "I gotta reel gud feelin' about this thang."

 

[Mike McLane]

Arrgh! Nobody else has any input? I was hoping for more. Maybe this entry will bump the thread up in people's feed and elicit some additional response. Hope so.

 

[DAJE]

On mine, I tried a mod I found on this forum, and left out C5 and C10. That makes it a low gain pedal, and it sounds good enough to me that I haven't felt the need to try it with them in. I put sockets in so I could, but they'll probably remain empty forever.

Edit: You can do this by snipping the leads of the E caps in question, if you've soldered them in. No need for a full de-solder, unless you want to install sockets or re-install the caps later.

 

[Mike McLane]

Hmmm. Sounds interesting. I'll hunt for the thread. Thx.

 

[Mike McLane]

C10 is more of a gain boost than a bass boost. You can leave it out for less gain/distortion or make it smaller for more of a mid-boost effect. Some pedals have a switch to select a big or small cap.
Changing C3 from 250pF to 300pF will be barely noticeable. When I'm fooling around with filter caps, I usually go in 2x steps until I get close to the sound I want.

DAJE: Thx! I found the above comment from Chuck Bones in the thread you probably referenced. It would appear that playing with the bypass caps C5 & C10 may be more direct and effective than the JFET sub tcpoint suggests above. I'd be curious if Chuck (et al) are out there watching to opine in greater depth. Since Q2 drives Q3 can I consider the modding/elimination of the bypass caps be analogous to putting a booster before or after an OD in that . . . sans C5 you have a lower gain stage driving a higher gain stage (result is more dirt, less volume) . . . or sans C10 for the flip side (less dirt, higher volume)? Perhaps too hair-splitty in real world practice, but does it wash in theory? My guess, you could play with mod'ing/eliminating both if you've got time on your hands and Eric Johnson ears, but if you're wanting to get on with the show the most practical solution is removing C10 (as Benson did) and maybe dinking with C5 if you're really hard up for something to do? Would appreciate some feedback.

As to the C3, does increasing the value allow lower frequencies to cross, thus bypassing the BASS pot and lowering the cutoff point of the BASS control?

 

[DAJE]

DAJE: Thx! I found the above comment from Chuck Bones in the thread you probably referenced. It would appear that playing with the bypass caps C5 & C10 may be more direct and effective than the JFET sub tcpoint suggests above. I'd be curious if Chuck (et al) are out there watching to opine in greater depth. Since Q2 drives Q3 can I consider the modding/elimination of the bypass caps be analogous to putting a booster before or after an OD in that . . . sans C5 you have a lower gain stage driving a higher gain stage (result is more dirt, less volume) . . . or sans C10 for the flip side (less dirt, higher volume)? Perhaps too hair-splitty in real world practice, but does it wash in theory? My guess, you could play with mod'ing/eliminating both if you've got time on your hands and Eric Johnson ears, but if you're wanting to get on with the show the most practical solution is removing C10 (as Benson did) and maybe dinking with C5 if you're really hard up for something to do? Would appreciate some feedback.

As to the C3, does increasing the value allow lower frequencies to cross, thus bypassing the BASS pot and lowering the cutoff point of the BASS control?

That'd be the thread, there may be others. When I'm about to put a pedal together I search the forums pretty thoroughly to check other people's results and hopefully avoid errors.

I built mine without adding C5 or C10. I installed sockets for them, but haven't used them because I like the way it sounds without them, kind of a raspy clean, like an amp that's starting to break up. I'm really not that far into understanding how this stuff works, just following directions and advice for the most part.

 

[Chuck D. Bones]

The other thing you can try is putting 1K trimpots in series with C5 & C10 and tweaking them to get the desired gain / distortion. As long as you can drive Q3 to saturation, you get pretty much the same volume with or without C5 and/or C10. If you're serious about modding the SOB, I suggest breadboarding it.

 

[Mike McLane]

OK, I've got the breadboard, but I don't know where to stick the wires !?!?!?

But seriously, folks. . . . I assume that 10K resistance is sufficient to squelch the current flow through the cap (10K vs 1K, some "leakage" will still occur), thus taking the cap substantially out of the circuit. The trimmer allows variance from 0-100% so I can get what I want (cue the Stones ). Now for a teachable moment . . . this portion of the circuit running from the JFET Source to ground reminds of a cathode ground on a traditional tube amp. The resistance value and optional bypass cap influences the tone and aggressiveness of the amp circuit. JFETs are analogized to tubes (biasing, etc) is this the same deal?

 

[Chuck D. Bones]

Yes, you have it right. The top half of the travel on a 10K trimmer in parallel with a 1K resistor won't make much difference, which is why I suggested a 1K trimmer. But use wehatcha got. Smaller resistance from source to ground (directly or thru a cap) = more gain. Bigger cap = more bass.

 

[Mike McLane]

Sorry, I was thinking 10K trimmer, but it was 1K. I misread. Chuck, you need to start a pedal electronics school.

We could all be Boneheads. . . . .