SOLVED Tone Vendor MKII Enigma...

[Coda]

Just completed the Tone Vendor MKII build. I plugged it all in, and got nothing. Bypass tone was fine, LED was on, but no fuzz...just a very high-pitched whistle...like something a dog could hear. After about 2 hours of checking and re-checking everything, I finally got sound. However, it sounds like the fuzz is on 5...even though the fuzz control is maxed.

It seems that after poking around (I literally was just pressing my finger against the board...especially around where the fuzz control/output ground/9v hooks up), it just came on. Is this a bad connection? What would make the fuzz control useless, while delivering a half-assed fuzz? Should I just chuck this build in the ocean and start over?

 

[benny_profane]

Not a whole lot to go off here. Pictures, substitutions, source(s) of transistors, etc. would all be very helpful at figuring out what’s going on.

 

[Coda]

Not a whole lot to go off here. Pictures, substitutions, source(s) of transistors, etc. would all be very helpful at figuring out what’s going on.

I’ll get those posted in the morning.

 

[Coda]

Below are pictures of both sides of the board. When the pedal is on, I get a mild overdrive, that's a tad too bassy (for my tastes, at least)...definitely not a MKII fuzz. The transistors are Dutch made 2N281 Germanium transistors (Q1: 74, Q2: 86, Q3:128). They recommended replacing R3 and R4 (normaly a 4k7 and a 100k) with a 2k2 and a 91k, which I did. I swapped the 5u caps for 4.7u.

The only other issue I am having is the LED. It is in a super inconvenient spot. That's not a technical issue, but a design issue. I may move it on the enclosure.

 

[benny_profane]

Are you sure about the pin outs on the transistors? How did you orient them? And where did you source them from?

 

[Coda]

Are you sure about the pin outs on the transistors? How did you orient them? And where did you source them from?

Small Bear. They have a dot on the side. Does that align with the tab on the pcb?

 

[benny_profane]

Small Bear. They have a dot on the side. Does that align with the tab on the pcb?

The dot indicates a collector for many European transistors. The tab on the PCB indicates the emitter.

 

[Coda]

The dot indicates a collector for many European transistors. The tab on the PCB indicates the emitter.

Hmm. Looks like I made a mistake. Would the transistors being reversed result in the issue I'm having?

I have also noticed that sometimes the pedal wont turn on. I think this is an issue with the dc jack. Its metal barreled shaft that I wired to work center negative. This whole build has been a mess, honestly.

 

[benny_profane]

The transistors not being oriented correctly would definitely cause the circuit to not operate properly. Reinstall them with the correct pinout. In the future, consider using sockets.

I'd also replace the DC jack with a plastic barrel option to ensure that nothing is shorting and the polarity is correct.

 

[Coda]

The transistors not being oriented correctly would definitely cause the circuit to not operate properly. Reinstall them with the correct pinout. In the future, consider using sockets.

I'd also replace the DC jack with a plastic barrel option to ensure that nothing is shorting and the polarity is correct.

Thanks for the help. I'll swap them around and see about getting the proper jack installed.

 

[Chuck D. Bones]

Be very careful desoldering the transistors. Germanium trannies are very sensitive to heat and can be permanently degraded by overheating. Also, make sure the transistor case is not touching anything conductive. On many transistors, the case is tied to the collector. Not sure about these.

 

[Coda]

I don’t think can get the transistors out..:not without 2 more soldering irons and about 15 hands.

 

[Coda]

Update: I cut the transistors out correctly oriented them. Now I get what I was expecting, fuzz-wise. However, I now have an incredible hum. The hum lessens slightly when I roll off the fuzz control. Strangely, the fuzz level stays the same.

Could the hum be a ground issue? I’m still waiting for my negative center jack to arrive. What could explain the non-function of the fuzz control?

 

[benny_profane]

You mentioned that the DC jack has a metal barrel but that you wired it for center negative—what does that mean? With this circuit, you have +9V on the sleeve of the DC jack and 0V on the center pin. The audio jacks are wired for negative ground (i.e., 0V with a 9V potential); however, The circuit has a charge pump that is giving you the -9V rail so you can use PNP transistors while being able to daisy chain the effect or just use a normal DC supply.

The metal barrel of the DC jack is going to connect to the enclosure, sleeve of the jacks, and the ground connection(s) on the PCB. So you’re effectively creating a +9V ground.

I would either 1) take the circuit out of the enclosure and see if you get different results or 2) wait until you have the proper DC jack before messing with it any further.

Down the road, you may find that the FUZZ control is a bit bunched up. You have a linear (B) pot for that control. A common modification for the TB/FF circuits is to replace that pot with a C-taper (i.e., inverse or anti-log) to get a more useful range out of the control. Reference the graph below to get an idea of why that’d be the case:

 

[Coda]

You mentioned that the DC jack has a metal barrel but that you wired it for center negative—what does that mean? With this circuit, you have +9V on the sleeve of the DC jack and 0V on the center pin. The audio jacks are wired for negative ground (i.e., 0V with a 9V potential); however, The circuit has a charge pump that is giving you the -9V rail so you can use PNP transistors while being able to daisy chain the effect or just use a normal DC supply.

The metal barrel of the DC jack is going to connect to the enclosure, sleeve of the jacks, and the ground connection(s) on the PCB. So you’re effectively creating a +9V ground.

I would either 1) take the circuit out of the enclosure and see if you get different results or 2) wait until you have the proper DC jack before messing with it any further.

Down the road, you may find that the FUZZ control is a bit bunched up. You have a linear (B) pot for that control. A common modification for the TB/FF circuits is to replace that pot with a C-taper (i.e., inverse or anti-log) to get a more useful range out of the control. Reference the graph below to get an idea of why that’d be the case:

View attachment 5388

I wired the DC jack based on help from Switchcraft technical support, as well as the attached image from Small Bear. Outside of the case I get a tremendous buzz. The fuzz is there, and at full bore, but so too is the hum. When I turn the fuzz knob down, the hum is less, but the fuzz is still at full bore. I will keep the C-taper pot mid in mind the next time I place a parts order.

 

[benny_profane]

Okay, yeah it looks like the sleeve is connected to the barrel of the plug. This type of jack would need insulation from the enclosure to properly work with a center-negative input and a conductive enclosure. It's meant for a center-positive plug (i.e., what every other device beside pedals uses).

You're not getting any shielding outside of the enclosure, and the transistors are basically radio antennae at that point. Wait until you receive your replacement DC jack and go from there. You can check voltages in its current state outside of the enclosure to make sure that everything is how it should be. If it checks out, you'll be set to go when the new jack arrives.

 

[Coda]

Update: I have installed the proper jack and the hum is gone. However, a new issue exists: the pedal sounds great...with the volume on two and the fuzz on 0. With the fuzz on 10 the tone opens up, but there is no difference in the level of fuzz. Setting the volume passed 5 results in your ears imploding and almost instant feedback...even with the guitar volume on 0.

What could be going on here? Is it possible that the transistors are to blame? Do I need to swap out some transistor values?

 

[Coda]

Another update: I was going over my supply of parts and I noticed that I used a pair of resistors that were 1/2 watt and not 1/4 watt. Would this make a difference?

 

[Chuck D. Bones]

Nope. They probably don't fit very well is all.

 

[Coda]

Nope. They probably don't fit very well is all.

They kind of look like if you normally wear an XL t-short, and you accidentilly grabbed a medium...

So they aren’t the issue. The transistors are oriented correctly. Can it be anything else?