SOLVED Soul Vendor - gated sounds

[ReinoutVrijhoef]

Hi everybody,

I'm quite new to pedal building, the Soul Vendor is my 8th endeavour. The behaviour of the pedal is not as I expected, so I would like to ask you for help. You can watch and hear the pedal on Youtube:

I recorded the video with a Strat in the bridge position running into a Kemper with a fairly clean profile of a Marshall Bluesbreaker, like, why not? The input on the Kemper isn't clipping, and the pedal behaves just the same on my tube amps.
I bought this pedal in a kit from Musikding, including a special set of AC125's, matched for a ToneBender mk3. The battery is running on 9.32V, the temperature is on room temperature (19°C, 66°F) and the humidity is about 57%. I haven't checked the hfe myself, because my cheap multimeter is being an *ss about it.





My circuit looks like this, you can find the schematic here.


If you can help me fixing this pedal, I would be very grateful. I can't seem to find the "right" voltages for the germanium transistors. I already built the Analog Sun (PCB Mania) which sounds great! Also the Rift (Aion) is a great sounding fuzz. Any help is greatly appreciated!

 

[Cybercow]

You will need to futz with values of the bias resistors to eliminate the gating.

Proper FF, TB sets typically have a set of matching biasing resistors accompanying them. But not all vendors go thru that process.

When building a FF, TB or other germanium based dirt circuit, I like to use a "Trimmer" accessory daughterboard from PedalPCB for the biasing resistors and find the correct (nearest neighbor) resistance value.

 

[mdc]

A photo of the underside of the board, please and thanks?

The voltage on Q3-C is a little high, but I'm not sure if that would be causing that sputtery gating. TBMKIIIs are extremely forgiving and usually sound excellent with any ol' transistors in them. They sound pretty good with silicon transistors, so I'm not sure appropriate leakage would be much of an issue either. Probably best to start by checking out the undercarriage.

 

[ReinoutVrijhoef]

Thank you for these responses. I made some photos of the underside of the board, after cleaning out the flux:

I think I did a pretty good job soldering here, but if you think otherwise: please let me know!

I could try swapping R6 (10k, feeding the collectors of Q1 and Q2 and R7 (18k, feeding the collector of Q3) with 50k trimpots. Musikding is a very respectable vendor here in Europe, and I trust Klaus completely.

 

[Nic]

You should add a dust cover on that bottom pot, right now it could short on the board and is located just under the IC...

 

[ReinoutVrijhoef]

You should add a dust cover on that bottom pot, right now it could short on the board and is located just under the IC...

There is a pad on the pot, so no shortage there.

 

[Nic]

There is a pad on the pot, so no shortage there.

Ok, just making sure. Soldering looks good indeed

 

[mdc]

Again, just checking some basic stuff... make sure the transistors are firmly seated in the sockets and try it again with the back off the pedal and the pedal upside down. It doesn't look like the transistor legs are tacked into the socket so it could be a loose connection there which could be exacerbated when the pedal is rightside up (and the transistors are upside down).

 

[mdc]

Oh - D1 is backwards.

 

[mdc]

That's a russian diode, the stripe is on the anode.

 

[Cybercow]

When socketing transistors or other parts, before solder-tac-ing them into the sockets, I prefer to lightly "wrinkle" the ends of the legs a bit so they seat firmly, yet still allow for easy removal and swapping.

 

[ReinoutVrijhoef]

Thanks for your replies. The D9E has the stripe on the cathode, so it should have the right direction. The D9E’s I put in other builds (King Centaur) also work like this.

 

[ReinoutVrijhoef]

Again, just checking some basic stuff... make sure the transistors are firmly seated in the sockets and try it again with the back off the pedal and the pedal upside down. It doesn't look like the transistor legs are tacked into the socket so it could be a loose connection there which could be exacerbated when the pedal is rightside up (and the transistors are upside down).

Thanks! The back was off the pedal, and I’ll try again. I inserted the legs of the transistors with pliers, one leg at a time.

 

[ReinoutVrijhoef]

When socketing transistors or other parts, before solder-tac-ing them into the sockets, I prefer to lightly "wrinkle" the ends of the legs a bit so they seat firmly, yet still allow for easy removal and swapping.

View attachment 44719

This is a great tip, thank you very much! I think the transistors are firmly in their sockets though, I checked the voltages on the legs too.

 

[ReinoutVrijhoef]

So thanks everyone! Tonight I replaced R6 and R7 with B50K trimpots, I don't have the fancy daughterboard:



I set up R6 at 3.5K, with the collectors of Q1 and Q2 at -6.41V. R7 is set at 30K with the collector of Q3 at -2.08V. The gated sound is almost gone, it's only there when "Dirt" is maxed out. I will record a clip soon, so you can hear for yourself. I'm starting to like this pedal a lot more now!

 

[mdc]

Oh - D1 is backwards.

I'm not sure if you missed this - you have a diode in backwards.

 

[ReinoutVrijhoef]

I'm not sure if you missed this - you have a diode in backwards.

I saw your post and replied to it above, the diode is in the right way, so that should not be a problem.

Edit: I measured the diode, and presumably it's indeed backwards. I will try to flip it today and report back.

 

[Cybercow]

So thanks everyone! Tonight I replaced R6 and R7 with B50K trimpots, I don't have the fancy daughterboard:

View attachment 44737

I set up R6 at 3.5K, with the collectors of Q1 and Q2 at -6.41V. R7 is set at 30K with the collector of Q3 at -2.08V. The gated sound is almost gone, it's only there when "Dirt" is maxed out. I will record a clip soon, so you can hear for yourself. I'm starting to like this pedal a lot more now!

Nice. Yeah, the Trimmits aren't necessary, just handy sometimes. On a whim, I'd try putting trimmers in the R4 & R5 positions as well - just to see if the gating can be further reduced when the "Dirt" is maxed. Maybe even R7. Not saying it will help. And it's possible the trimmers at R6 & R7 may need to be further tweaked back & forth using your ear instead of just bias voltage setting.

Now you can see that not all dirt circuits sits are created equal. Preset bias resistor values in schematics are seldom spot on for Germanium BJTs and can often require a bit of experimenting. And you probably already know already that Germanium BJTs, (even tho they are of the same type number), are not created equal and all are quite subject to temperature changes. And during operation, they tend to warm up a bit and that temperature change can alter their performance. So there's that.

The specified NKT275 (now unobtanium) was a Germanium rarity in that they were rather consistent across their gain & temperature performances, but still suffered a wide range of leakage values. Almost every black glass Mullard Germanium I've ever encountered exhibit a gain range within their respective datasheet specs with extremely low leakage. But still, like ALL germanium BJTs, exhibit the same subjugation to temperature changes.

 

[ReinoutVrijhoef]

Nice. Yeah, the Trimmits aren't necessary, just handy sometimes. On a whim, I'd try putting trimmers in the R4 & R5 positions as well - just to see if the gating can be further reduced when the "Dirt" is maxed. Maybe even R7. Not saying it will help. And it's possible the trimmers at R6 & R7 may need to be further tweaked back & forth using your ear instead of just bias voltage setting.

Now you can see that not all dirt circuits sits are created equal. Preset bias resistor values in schematics are seldom spot on for Germanium BJTs and can often require a bit of experimenting. And you probably already know already that Germanium BJTs, (even tho they are of the same type number), are not created equal and all are quite subject to temperature changes. And during operation, they tend to warm up a bit and that temperature change can alter their performance. So there's that.

The specified NKT275 (now unobtanium) was a Germanium rarity in that they were rather consistent across their gain & temperature performances, but still suffered a wide range of leakage values. Almost every black glass Mullard Germanium I've ever encountered exhibit a gain range within their respective datasheet specs with extremely low leakage. But still, like ALL germanium BJTs, exhibit the same subjugation to temperature changes.

Thanks for your reply. R4 (10k) and R5 (3.3k) are on the emitters of Q1 and Q2, what will their effect be on the sound or the behavior of the transistors? I already have a trimmer on R7, do you mean R8 perhaps?

I know germanium transistors are finicky, which makes them very interesting to work with. I’m not all that experienced with fuzzes, but learning a lot on the way. Soon I’ll start working on the Monolith and the Muffin Factory, slowly working my way up the amount of transistors in the pedals :-D.

 

[mdc]

I saw your post and replied to it above, the diode is in the right way, so that should not be a problem.

You might want to check it - for russian diodes, the stripe almost always marks the anode. AFAIK the ones with a single blue stripe follow this standard (stripe = anode). I'm sure there's some variation, so maybe yours is an exception?

(This is also assuming the board you have in front of you matches up with the image on the webstore).