Ungula - Germanium Transistor voltages

[PangeaDestructor]

Hey All, I got my Ungula built and it sounds pretty terrible, like sound is struggling to get through and there's a dying battery involved.

I audio-probed it, there are some spots I noted to check again later. The tone and shift pots both sound odd, like they're adding and taking away volume at certain points though that may just be due to the bass/mids coming through and fading out. There's very little volume available, with fuzz and volume dimed my clean signal is still a bit louder.

I checked the collector voltages on the 2N1308s that I got off ebay. 1.27 on Q2 and 7.71 on Q3, yikes. Unfortunately I don't have the leakage or HFE, but that seems like there must be an error elsewhere based on those, unless I just need to buy some subs from a more reputable source. Here's what I got: https://www.ebay.com/itm/192918001829

 

[PangeaDestructor]

I just noticed those pics get a little grainy when zooming, i can try and add bigger ones if needed.

 

[giovanni]

Do you have a transistor tester? eBay can be a decent source of transistors but I wouldn’t trust them without personally testing them myself the biasing issue you have may be caused by issues other than bad transistors. Can you double check component values?

 

[PangeaDestructor]

Do you have a transistor tester? eBay can be a decent source of transistors but I wouldn’t trust them without personally testing them myself the biasing issue you have may be caused by issues other than bad transistors. Can you double check component values?

I don't, but I grabbed another handful of MP35s from pedalhacker last night that are super low leakage. Will go through and triple check all the values later today when i start avoiding work.

The only other thing I can think of is that I did rip off a solder pad on leg 2 of the shift pot, but it was only on one side and I've never had a problem as long as one side is still attached.

 

[Chuck D. Bones]

The correct collector voltage for Q2 & Q3 will be around 3.5V.

Those pics lack detail. Try posting something higher resolution if you want us to be able to see what's going on. You'll know the resolution is good enough when you can read the numbers on the transistors. Are the transistors socketed? If so, plug in some good silicon transistors to see if the problem is with the Q2 & Q3 or something else on the board.

Inspect everything under magnification and correct any bad solder joints, incorrect components, etc.

 

[PangeaDestructor]

The correct collector voltage for Q2 & Q3 will be around 3.5V.

Those pics lack detail. Try posting something higher resolution if you want us to be able to see what's going on. You'll know the resolution is good enough when you can read the numbers on the transistors. Are the transistors socketed? If so, plug in some good silicon transistors to see if the problem is with the Q2 & Q3 or something else on the board.

Inspect everything under magnification and correct any bad solder joints, incorrect components, etc.

Thanks, I'll post larger pics later if I haven't figured it out, but putting a pin in this for now. I measured the bottom row of resistors just now and something went really wrong when I was populating it apparently.

 

[PangeaDestructor]

The correct collector voltage for Q2 & Q3 will be around 3.5V.

Those pics lack detail. Try posting something higher resolution if you want us to be able to see what's going on. You'll know the resolution is good enough when you can read the numbers on the transistors. Are the transistors socketed? If so, plug in some good silicon transistors to see if the problem is with the Q2 & Q3 or something else on the board.

Inspect everything under magnification and correct any bad solder joints, incorrect components, etc.

Ok, better pics attached. I went through and checked all the values, replaced the resistors that were off, and it sounds maybe a little better but still very low output and the transistor voltages haven't changed. There is a small nick on the bottom of the pcb but i've had those before without issue. I'm out of 15k at the moment, so R4, R10 and R15 have 16k resistors. Previously it looks like I tried using 12k.

 

[Chuck D. Bones]

Only slightly better. You can see they're poorly focused, right?
Still can't read the transistors. Tell us everything that is printed on them. My best guess at this point is the "2N1308" transistors are crap.

Recommendations:
1. Install sockets for Q2 & Q3.
2. Try 2N3904s for Q2 & Q3. If the pedal starts working, then you know it was the "2N1308s."
3. Find a reliable source for Ge trannies. If you can get MP38A, those work well.

In reality, using Ge trannies for Q2 and Q3 is more of a gimmick than a real feature. What makes a Hoof sound like a Hoof are the LED clippers and the Tone network. Personally, I think EQD did a poor job on the SHIFT control. Try making C10 10nF or 15nF, it works much better. Increase R18 to 4.7K, then you can use the entire range of the SHIFT knob.

 

[PangeaDestructor]

Thanks Chuck, I'll make these changes. I managed to find some MP35s on pedalhacker with "VERY low leakage" that hopefully do the trick.

 

[Chuck D. Bones]

You don't need low-leakage trannies in there. Won't hurt, but not req'd. The MP38As I have in mine at the moment are fairly leaky but work fine.

FYI, we can tweak R8 & R13 to accommodate leaky transistors. I did not have to do that, but I knew the option was there.

I'll wager that if you put your eBay transistors on a tester, it would indicate they were either non-functional or so far out of spec as to be useless. I've had pretty good luck on eBay so far. I test everything right away so I can get a refund if stuff is not as advertised. The one time I received crap transistors was from a Chinese vendor, not on eBay, selling 2N1308s & 2N1309s. I paid with PayPal. When 95% of them turned out to be shit, I requested a refund with the full knowledge that if they didn't refund my $$$, PayPal would. After a little hemming & hawing, they issued a refund.

Good luck and let us know how it goes.

 

[PangeaDestructor]

Good to know, all the reading I did on here last night seemed to point toward low leakage being key. Any recommendations for a budget tranny tester?

 

[Chuck D. Bones]

https://forum.pedalpcb.com/threads/transistor-ideas.6224/#post-51935

 

[Chuck D. Bones]

Good to know, all the reading I did on here last night seemed to point toward low leakage being key.

Who said that?

 

[PangeaDestructor]

Who said that?

[IMG alt="Chuck D. Bones"]https://forum.pedalpcb.com/data/avatars/m/0/163.jpg?1647065236[/IMG]

Chuck D. Bones​

Circuit Wizard​

• Dec 20, 2019
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• #2

Nice work! We learn by doing. There is nothing magic about 2N1308s, you can try other Ge transistors. I saw a gut-shot of a EQD Hoof and it had 2N647 transistors. For the Hoof / Ungula, the transistors need to be low leakage. Socketing Ge transistors is a good idea because chances are, you will want to try different ones.

 

[Chuck D. Bones]

That guy's full of