Cannot get Tonepad Tonebender 3 knob to work

[glweid]

Hi

Pulling my hair out trying to figure out why my build of the Tonepad Tonebender 3 Knob is failing miserable


I have built numerous Fuzz faces and other pedals with no problem but this one has me stumped ...

I have the following PNP Ge Transistors with voltages:

Q1 OC44  - 62 HFE - B 1.9, E 1.9, C 1.9
Q2 OC44 - 70 HFE - B 1.8, E 1.6, C 1.9
Q3 ASX12D - 122 HFE - B .2, E 0, C .2

Clearly there is an issue with Q3 not biasing ... Also when I have the fuzz pot anything less than wide open (fully clockwise) I get buzzing -

I replaced the 18k in the voltage divider with a 10k trimmer and I can get fuzz out of it but super low volume ... When I removed the 18k the pad came off ! not sure about the quality of this board as it should not come off that easy ...

Any advice is welcome and thanks in advance

[bukas]

picture pls. and chech are lugs 1 and 2 connected

[LucifersTrip]

>Q1 OC44  - 62 HFE - B 1.9, E 1.9, C 1.9


you realize this means all 3 lugs are shorted...

[glweid]

Well I do not see that the lugs on any of the 3 transistors are shorted

Thought I had all linear pots (for the 100Ks) but they are audio's .. waiting for replacements from mouser but not sure that would be causing this issue.

Also TP switched manufacturers and it took 1 1/2 months before I got this board ... the pad and quality are not very good IMHO as I have now lost 3 pads on the board just resoldering .. not that this is causing my issue but other boards I bought in the past from them were much better in quality and presented no problems

Will update as I keep troubleshooting

I anyone can give me reference voltage points in the circuit that may help

Thanks again !

[PRR]

> give me reference voltage

As Luci says... the *same* voltage on *all* pins of a transistor is not a happy operating point, and also not likely to happen by accident.

The fact that no voltage is even 2V suggests some bigger problem. Very-weak battery? Battery backward? Missing connection? 10uFd cap backward?

Collector of Q3 should be near negative 4.5V; its B and E would (unusually) both be Zero with no signal.

[glweid]

Uhhhhhh ... had voltage reversed ..... 

thanks for throwing that out as a possibility !

no on to playing with different gains on Q3 as it gets pretty nasty at full fuzz

[Electric Warrior]

Don't forget to try transistors with different leakages as well!

[glweid]

OK I am getting gobs of distortion ..

Here are the new Transistors voltages

Q1 - OC44 - E 1.7, B 1.6, C 2.9 - HFE 60
Q2 - OC44 - E1.65, B 1.7, C 2.9 - HFE 70
Q3 - Russian - E 1.7, B 0.1, C 6.1 - HFE 60 - still too much distortion - I have a 50K trimmer now in place of the 18K on the collector and even when I drop Q3 to 3 volts there is still too much distortion

I have bypassed the 220K between the tone and volume pots

Seems like the gain coming into Q3 is too high from Q2

[glweid]

Found another bad pad that came loose on the 220K ( near Q1)

Fixed that ... now have these voltages

Q1: E 1.15  B 1.0  C 3.2    Leakage .08   HFE 62
Q2: E 1.1    B 1.1  C 3.2   Leakage 1.0    HFE 71
Q3: E 0       B .05  C 5.2   Leakage 1.0    HFE 111

Still waaay too much distortion (fizz) even when fuzz is turned all the way down and super crazy fuzzzzz when maxed out ..

Still swapping out trannies

[LucifersTrip]

look at your Q2 voltages. E& B are shorted...and remember, Q1E should = Q2B

[glweid]

Replaced the diode and it sounds better not as much fizz and better fuzz, although it still puts out a lot when the fuzz pot is maxed ... dialing back on the guitar volume cleans up pretty decent ..

Will also try different diodes to the 1n270 .. any recommendations there are welcome

So going to try a 250K for the fuzz pot next and see how that goes but overall it seems I am much closer ...

Thanks !

[LucifersTrip]

Will also try different diodes to the 1n270 .. any recommendations there are welcome

Any germanium diode or the BC or BE of a ge transistor will be cool. But, the point's moot until your voltages are sorted out.

Once you have good working voltages, try different gains & leakages in Q3. The leakage will drastically change Q3C voltage and the tone (bass/treble).
Since Q1/Q2 is darlington, they make little difference...just use your 2 lowest gain ones with lowest leakage.

In my last few MKIII's & MKIV's, Q3C voltage was less than 4.5V, usually in the 3-3.5V range. Set that voltage (with transistor gain, leakage and Q3C resistor) so that your tone sweep sounds good from bass to treble.  For instance, if you set Q3C voltage too high, there'll be too much bass when your tone knob is turned full to the bass side.

[glweid]

OK latest Transistor voltages, can someone post what they should be ?

Q1 E 1.4  B 1.08  C 3.4  HFE 52  leakage .1
Q2 E 1.2  B 1.4    C 3.4  HFE 52  leakage .1
Q3 E E 0  B 0       C 3.2  HFE 61  leakage .1

Still tons of distortion pumping out ..

[LucifersTrip]

It would be cool to have voltages from an original, but I don't think I have any. I can only give you voltages from one of mine, when it sounded good to me.

I'll dig one out shortly, but for now, I can tell you that Q3B should not be 0

[LucifersTrip]

Ok, I dug out one of the ones that people who've played thru seemed to like the most.

This one's NPN.

Q1: 2N533 (44 hfe/ < 50uA leak)
Q2: TR09 (61 hfe/ < 50uA leak)
Q3: 2N1000 (89 / 270uA leak)

9.6V supply

EBC
Q1: .70, .78, 2.95
Q2: .58, .70,  2.95
Q3: 0, .06, 3.42

I have a 22K resistor on both Q1/QC and Q3C.

One note on the Tonepad layout you're using. You may want to consider decreasing the 220K between the
tone & vol to bring the overall vol up. It's a common mod. But, I don't recommend just connecting them
directly or the tone changes (gets boomier). It's good to have some resistance in there. On the build above
I have a 22K.

[mac]

Q1 E 1.4  B 1.08  C 3.4  HFE 52  leakage .1
Q2 E 1.2  B 1.4    C 3.4  HFE 52  leakage .1
Q3 E E 0  B 0       C 3.2  HFE 61  leakage .1

Q1 base should not be lower than the emiter.
Q3 base should not be zero.

Note that this circuit is never clean even when the fuzz is at max.

mac

[Arcane Analog]

100% agree with Lucifer - the leakage of Q3 is key.