Trouble with tonebender

[frogman]

Just finished soldering together this tonebender mkii clone on vero board.



I didn't breadboard it before soldering it onto the veroboard, I did (sort of) check the transistors before soldering them. I referenced the schematic that came with the pnp transistor set I ordered from smallbear and everything is on point.



I did change the resistor value of the R3 to a 24k resistor by the advice of the schematic.
Everything else matches with the schematic except the R5, which I kept at 470R.

I couldn't easily find the pinout of the transistors anywhere and no pinout was included, so after checking the transistor for shorts I found a method online that involved measuring base-collector and base – emitter with a multimeter in diode reading mode and the highest number was the emitter. I went by this because I checked multiple transistors I had laying around and they all passed the test.  Base - emitter read higher.

Like I said, it is a positive ground pedal, so I placed everything accordingly on a breadboard. Everything "negative" still goes to – and everything positive still goes to +.
At this point I get sound, similar to how it should sound, but there is something off with the tone. The potentiometers for the pedal seem fine, but when I adjust the volume of my multiple guitars I have tried with this, I get a lot of crackling when turning the volume up or down anywhere and tone loss when my guitar gets to 10 (loses bass and get trebly/middy). It sound fine at 8/9. The tone might also be a bit too trebly, however I haven't heard how the pedal is actually supposed to sound with my guitar and amp.

Q1
C = 8.42V
B = 8.34V
E =8.46V

Q2
C= 7.91
B= 8.34V
E= 8.45V

Q3
C=3.4V
B= 7.93V
E= 8.05V

[newfish]

I may be wrong, but are the electro caps the right way round on this layout?

If you were using a -9v supply, they'd be good, but I suspect you're using a conventional 9v supply.

I always thought that positive ground circuits still needed the caps to be correct with regard to 'which one of these points is more positive than the other'.

The positive ground is simply for the transistors.

Is the layout verified?

[LucifersTrip]

the voltages are way out there...too many possibilities of things that could be wrong. 

I'd start by figuring out why Q1/2 E's are not 0 (both are grounded)


here's one set of voltages from a vintage one:

Q1 C: -9.02V
Q2 C: -0.22V
Q3 C: -7.57V

[frogman]

I ended up mixing some things up on the positive and negative terminals of the breadboard, which made me realize that I do not know everything that I need to about a positive ground pedal. Am I correct I when I say that that the positive battery terminal runs to the positive ground and the negative battery terminal runs to -9v ?

I do have it up working with that configuration, I just want to make sure its right.

Do these transistor readings look better?

Q1

C: -6.00
B: -0.08
E: 0

Q2

C: -0.55
B: -0.11
E: 0

Q3

C: -4.80
B: -0.59
E: -0.46

[LucifersTrip]

Am I correct I when I say that that the positive battery terminal runs to the positive ground and the negative battery terminal runs to -9v ?

yes...

Do these transistor readings look better?

Q1

C: -6.00
B: -0.08
E: 0

Q2

C: -0.55
B: -0.11
E: 0

Q3

C: -4.80
B: -0.59
E: -0.46

Q1 and Q3 C's way too low...you can check out a bunch of threads. Q3C is 7.5-8.5+, otherwise, thinner & compressed. try increasing r3

[Tsaddeous]

Yes i think your problem is from R3,24k is really too low.

The layout is ok,mine works fine with R3 : 56K

A good way is to put a 100k trim instead of R3.

[LucifersTrip]

you also may not need the full 100K R1. that may make it too compressed. try to set R1 so you have a good sweep on the attack after you sort out Q3C voltage.

[frogman]

I ended up swapping out a 68k and 100k in the R3.

With a 100k in it, the Q3C was at -8.16V and Q1C was at -5.40

With the 68K, the Q3C was at -7.64V and the Q1C at -5.38V

I dont want to go desoldering from the board too much since the transistors are already there, but my first thought is to try substituting another value for the Q1 collector resistor(R2)?

I havent yet tried a different value in the R1 like you suggested luciferstrip, but I assume that was more a suggestion to change tone rather than voltage.

[LucifersTrip]

I ended up swapping out a 68k and 100k in the R3.

With a 100k in it, the Q3C was at -8.16V and Q1C was at -5.40

With the 68K, the Q3C was at -7.64V and the Q1C at -5.38V

both Q3C's are in a reasonable range...now, it's just what you like better...

I dont want to go desoldering from the board too much since the transistors are already there, but my first thought is to try substituting another value for the Q1 collector resistor(R2)?

I havent yet tried a different value in the R1 like you suggested luciferstrip, but I assume that was more a suggestion to change tone rather than voltage.

you want to screw with R1...the lower you make that, the higher Q1C will be and the closer you'll get to common working voltages there. Also, as you lower that, it'll get less gainy & less compressed.  A I wrote before, try to set R1 where you have a good range from low to high on the attack pot.
If R1 is too high, the attack can get too compressed too soon and you won't get the full range of tones that are possible.

[Electric Warrior]

You want to set R3 so that it sounds neither gated nor hissy at room temperature. 

[frogman]

I set up an A100k pot in place of the R1 and the I got the Q1C to -8V but only when the pots impedance was set down to around 1k. There was a better sweep on the "attack" as it got to around 1k. The (A100k) pot that i put in as the R1 also only goes to 11k at the highest.... I even tried putting actual resistors in (this is all on a breadboard by the way) and i can go down to around 10k without getting much change in voltage of the Q1C.

Thank you so much by the way for the helpful feedback, everyone.

[electrip]

I set up an A100k pot in place of the R1 and the I got the Q1C to -8V but only when the pots impedance was set down to around 1k. There was a better sweep on the "attack" as it got to around 1k. The (A100k) pot that i put in as the R1 also only goes to 11k at the highest.... I even tried putting actual resistors in (this is all on a breadboard by the way) and i can go down to around 10k without getting much change in voltage of the Q1C.

Thank you so much by the way for the helpful feedback, everyone.

Seems Q1 is too leaky.

R1 does not only shunts input signal to ground
also it shunts collector leakage current out of the base to ground
before it can be amplified.
So R1 can control leakage current on Q1 somewhat
at the expense of a reduced input voltage and input impedance.

electrip

[frogman]

So I've been working on this on a breadboard lately and I have the voltages in reasonable ranges as well as a decent sound coming out. However when i crank the volume completely, I only get around unity volume.

Here are voltages:

Q1
C: 8V
B: .08V
E: 0V

Q2
C: .4V
B: .12V
E: 0V

Q3
C: 7.67V
B: .41V
E: .3V

The best way I found to get the Q1 voltage up without tonal compromise was to stick a 2.4k resistor in the R2. I also moved the R6 down to about 3.4k. Would either of these pose problems to the circuit?

[frogman]

The only thing ive found that increases volume is the r6. I stuck a trimpot in and I still cant get it loud while still sounding fuzzy. When it does reach the correct volume, it sounds really muddy with no fuzz; this is when the trimpot is positioned around 2k.

Could the third transistor be too leaky?

Biasing the q2/q1 collector resistors at length is what i am going to do next.

[Electric Warrior]

I have no idea how much your transistors leak, but I doubt that it's too leaky.

Bring R6 back up again and try to increase R3's value. That might bring up the voltage on Q3's collector without sounding too boomy.

[frogman]

I brought R3 up and seems to sound good around toward 100k, as well as taking R2 back up to 10k. I found that both of these things help keep fuzz and keep it from sounding boomy. However, I cant get a good fuzz tone with the R6 below 4.5k. If I go any higher than 5k the volume is too low. This is the most practical place in between that I have found.

The only thing off now is the q1 collector which is at 7.5V. Decreasing either collector resistors compromises the fuzz tone.

I am pretty much asking if its okay to deviate from resistor values and the Q1 collector voltage like I did? I mean it sounds so much better this way, even the resistor values sent on the schematic with the transistor set made for a super quiet sounding pedal. Can any negative effects (not a pun) occur by transistor voltages (such as the Q1 in my case) being off if it sounds good?

[Electric Warrior]

No idea how your build sounds. Even with voltages in the right ballpark it can sound off.
You could try biasing Q1 by adjusting R1 instead of R2.