Tycobrahe Octavia Debugging

[Bielorusse]

Hi guys!

I have started to build a Tycobrahe Octavia pedal, but I can't get it to work although I thoroughly checked my wiring and PCB. But I must admit that I am new to building pedals: I've only built a couple yet, and I already failed a few.
I have been spending quite a lot of time on this lately, so I'll take a pause for today maybe, and get back to it later with a fresh look and an open mind. But I figured I would post something on this forum after all, maybe someone already had that same problem, or maybe someone will see what's wrong in a second (I guess I want to take every chance to make the pedal work )

Here is a more detailed description of the problems that I'm having:

1.What does it do, not do, and sound like?
The bypassed signal works perfectly
When engaging the effect, i just get a slightly boosted sound, very nice to hear, but with no gain at all.
Turning the PreGain pot would lead to a loud scratching noise, and eventually reduce the output of the sound (when reducing the PreGain).
When the octavia effect is engaged, I just get a slightly distorted, but very awful sound.

2.Name of the circuit =  Tycobrahe Octavia from GeneralGuitarGadgets.

3.Source of the circuit (URL of schematic or project) =  http://www.generalguitargadgets.com/effects-projects/octave/tycobrahe-octavia/
I also used this layout for the PCB: http://tagboardeffects.blogspot.com/2013/04/tycobrahe-octavia.html

4.Any modifications to the circuit?
5.Any parts substitutions? If yes, list them.
I choosed to install a footswitch to cut the octave sound, as described in the GeneralGuitarGadgets project.
I didn't have a 1.5M resistor for the entry of the circuit (R1 in the GeneralGuitarGadgets project, which is optional)
The transistors that I used were 2N3906 for Q1 and 2N4401 for Q3 and Q3.
One of the diodes that I had was slightly damaged, here's a picture were you can see that the glass enveloping the component is partly broken at the negative side of the diode.
Also, I don't have any voltage at each end of the diodes, and neither at each lead of the tranfsormer

6.Positive ground to negative ground conversion?
It's a negative ground circuit

7.What is the out of circuit battery voltage? =>   9,3
Now insert the battery into the clip. If your effect is wired so that a plug must be in the input or output jack to turn the battery power on, insert one end of a cord into that jack. Connect the negative/black meter lead to signal ground by clipping the negative/black lead to the outer sleeve of the input or output jack, whichever does not have a plug in it. With the negative lead on signal ground, measure the following:
Voltage at the circuit board end of the red battery lead =9,3
Voltage at the circuit board end of the black battery lead =0


Q1
C =2,4
B =2,6
E =2,6

Q2
C=9,2
B=2,4
E=1,9

Q3
C=5,5
B=2,0
E=1,3

D1
A =0
K =0

D2
A =0
K =0

Transformer
Primary
1 =0
2 =0
3 =0
Secondary
1 =0
2 =0


Thanks in advance
Cheers!

[duck_arse]

hello and welcome bielorusse.

there looks something wrong about Q1. the R2//R3//R4 string should have about 3V6 on the base of Q1, which would make its C about 4V2. check your resistors around that transistor with your meter, and post us the votages on that string, top to bottom. as for the transformer, no dc at the output is the normal. and you'd probably need to do a diode test on that broken diode, and replace it when you can.

[Bielorusse]

Hello,

Thanks a lot duck_arse for your answer, it's true that the voltages at the pins of Q1 were different from those taken by GeneralGuitarGadgets, now I understand why it makes you think that there might be something wrong with the resistors.

I took a look again this evening, and I noticed that I misplaced the wiring for the input of the circuit: I connected the input coming from the PreGain one strip too low, so that the input came directly into the collector of Q1 (by-passing a couple of caps, the R2,3,4 resistor string, and Q1, I think?).

With the input corrected, I get no sound at all with the effect engaged. There were a few changes in the voltages taken at the transistors pins:

Q1
C =3,2
B =2,7
E =3,2

Q2
C=9,1
B=3,2
E=2,6

Q3
C=3,9
B=2,6
E=2,0

But since the voltages of Q1 still seem wrong, I double checked my soldering for the R2, R3, and R4 resistors, I also checked the label and it looks like they have the correct values. Here are the voltages taken on that string (but unfortunately I didn't manage to measure the resistor values with my meter)

VTOP=9,2
VR4/R3=7,0
VR3/R2=2,7
VBOTTOM=0 (ground)

Does it look like I have to change the resistors?
I could also upload more pictures if it is of any help.

Thanks

[PRR]

Q1 Q2 Q3 are biased correctly.

I believe the values in ggg_toct_instruct.pdf are _wrong_ (probably C and E swapped).

Collector of Q3 is the key spot. Your 4V against suggested 5V is a small difference. You (or the build doc person!) may have 10%-20% tolerance-slack in the Q1 Base bias resistor string. This will not hurt operation.

[duck_arse]

just so we know your transistor directions, is this the circuit you are building to, the "modernised" version, w/ neg ground?

http://www.generalguitargadgets.com/pdf/ggg_toct_sc_improved.pdf

[Bielorusse]

Yes the version that I am building is the modernized version with negative ground circuit

[duck_arse]

well, much as I hate to say against PRR, I think your volts are off. I built that version with only-ish an R3 value change, and my volts around Q2 are about 600mV lower than yours. my Q3 C, however, is at 5V18, so it looks like maybe R11 or R12, or your C6 (maybe C5) is somehow wrong.

I have seen it argued that Q1 can be emitter up or emitter down and not affect the circuit operation, but I quickly looked away.

[PRR]

The Emitter function is clearly "up".

Now it happens that in low-low-voltage chores, a transistor's E and C are not too very different. The E-B junction is optimized for gain, the C-B junction for high breakdown voltage. Here we have very low voltage and ample gain, so it *may* work either way.

[Bielorusse]

Hi guys,


At the first try, when the input came directly into Q2's base, the effect didn't really work but I was getting sound out of the circuit.

Now that I corrected this input mistake, I'm not getting any sound at all. This must mean that there's something wrong with the circuit (it cannot be the wiring, or else I wouldn't have gotten any sound at the first try, right?)


I replaced C5 and C6 with fresh caps (I don't have any spare resistor right now) and I triple checked the labels of R11 and R12, and the soldering in general.

Unfortunately I'm still getting no sound out of the pedal which might mean that it either comes from one of the resistors (for which I'll have to make a new order online) or from something completely different.
The only new thing after changing the caps is a loud "pop" sound that I hear when engaging the octavia switch (it's not on the original layout, I added it following the GeneralGuitarGadgets project) but it may very well not mean anything.

I guess I'm going to have to let this here for a while, I'll get back to it when I order some new parts for another project. But if you have any correction to make about my investigation, or any other idea to suggest, don't hesitate. Any help is welcome


And in any case, a big thanks to you duck_arse and PRR for addressing my issue !

[duck_arse]

bielo - if you've made amendments, can you remeasure yr volts and post the new numbers please? search this forum or the web for the building and using of an "audio probe". you will have enough parts to make one, don't worry. poke around with that, let us know what you find, any troubles using.

and if you can take some photos, clear so we can see the solder quality and read the resistor colours, and so we can see your off-board wiring,  someone might spot something amiss. it has happened before.

[Bielorusse]

The voltages that I'm getting are still the same as before I installed new caps. Which were:

Q1
C =3,2
B =2,7
E =3,2

Q2
C=9,1
B=3,2
E=2,6

Q3
C=3,9
B=2,6
E=2,0


Here are three photos (I can take more if they aren't precise or clear enough):
one of the bottom of my board, for the solder


one of the top of my board, where one can read the resistor colors (hopefully!)


one of the off board wiring


I know that the wiring looks like a mess and I'm really ashamed of it, but I'm still new to this and I haven't been able yet to arrange the wires in a tidy and organized way x)


I completely forget this awesome debugging audio probe trick, now that you reminded me, I just built one and tested my circuit. But, surprise: I get my clean sound with the probe on the input of the board, but I'm getting nothing when probing points after Q1 (clean sound at Q1's base, but nothing at Q1's Emitter and Collector, and nothing at any other point of the circuit that's behind Q1).
And when you think about it, I was getting sound at first when I misplaced the input right behind Q1. Could it mean that the transistor is defective and causing my signal to vanish? In which case I could replace it since I've a spare one



EDIT: Well a defective Q1 wasn't the cause of my problem. I just installed a new transistor (voltages practically unchanged) and there's still no sound after Q1

[duck_arse]

well, after looking at your solder side (you need practise), there may be some shorts between the 5th and the 4th and 6th rows from the top. so, you need to get in and dress all your cuts in the vero, make sure there is no trailing edges of copper bridging anywhere. then run a snap-blade knife, or similar, between all the copper tracks, to cut or identify any solder bridges.

clip-off close any component leads, they'll only cause shorts later. clean-up some of those flying wire solders, there are a few that look grainy/dry/not soldered. also tidy that black wire, seven rows down on the left. it should come down through the board, that will keep it in line some.

I can't see any component funnies, so let's hope it's construction, instead. I'm afraid the off-board wires, being only red or black, makes following them just too hard. this is why we use as many colours wire as we can get our grubby little hands on, it makes it easier to follow, harder to stuff-up, less dependant on lighting in photos. good luck.

[Bielorusse]

Alleluia!

I've made some cleaning on the board as you recommended, and now the pedal is working fine
I guess there was some solder bridge as you suggested, between 4/5/6th rows from the top.

I kinda feel sorry to have brought you down with me through those complicated reflections about the components, when I might have been able to easily solve the problem right away by cleaning the board. 
I guess I've learned that this is the first thing to do when finishing to build a pedal!

One last time, thanks a lot for your messages !

[duck_arse]

think nothing of it, I've got nothing else to do. when we get to this stage I always ask "can you post your working good voltages?".

it's always a good idea to poke around the circuit board with your meter on ohms before the first smoke test, check the resistance from supply or ground to the places they are supposed to go. well done, and how do you like the sound?

[Bielorusse]

The sound is pretty amazing: it's a very powerful fuzz, that can get crazy coupled with the octavia.
And the pre-gain control is also useful to be able to get a nice octavia sound without to much of the fuzz on it.

Here are the working good voltages:
Q1
C 2,7
B 2,7
E 4,1

Q2
C 8,8
B 2,7
E 2,2

Q3
C 4,8
B 2,2
E 1,6


I don't have much time right now, but maybe I'll upload some sound samples for you later