Colorsound Overdriver/Black Arts Toneworks Black Forest Voltages

[Zounds!]

I finished up a vero build of a Black Arts Toneworks Black Forest last night using this layout: http://3.bp.blogspot.com/-XND5oym60TY/U1fuy7F970I/AAAAAAAAG3Y/lJmOvgaTaLg/s1600/Black+Arts+Toneworks+Black+Forest.png

For reference, it's a slight variation on the Colorsound Overdriver, so as far as I know the same schematic applies, just different values used. I'm using BC109s. I didn't have a 470pf cap so I used three 1.5nf caps in series (which makes 500pf). I also didn't have a 200nf cap so I used two 100nf caps in parallel (which makes 200nf). I've omitted the rotary switch and soldered the input straight to the base of Q1. I'm getting very, very low output. All knobs are working. I'm using BC109s  My voltages are:

Q1
C - 7.7
B - 1.3
E - 0.7

Q2
C - 6.9
B - 7.7
E - 6.8

Q3
C - 7.3
B - 1.3
E - 0.6

Compared to Q1 and Q3, E and B of Q2 look way off. Do my other voltages look ok? Any tips on what could be going wrong with Q2? I found two wrong value components this morning but have checked it over and things all look good now - correct values and component placement throughout. For such a basic-seeming circuit this one's giving me some trouble! Thanks.

[duck_arse]

a circuit diagram would be nice. but, check with yr meter that the collector of Q2 has 1k8 between it and 9V. also check you have no short, or about 4k resistance, between Q2 C and Q3 C.

[Zounds!]

Thanks for the response! Here is a schematic, albeit with the Colorsound cap values: https://www.dropbox.com/s/zca674d7xa0lpm9/Forestschematic.png?dl=0

I checked the board and I have 1k5 between the collector of Q2 and 9v and 2.9k between Q2 C and Q3 C...

[duck_arse]

whelp, while you're waiting for someone who knows how to fix a fuzz face, check resistance from Q2 E at the pin to ground.

and can you post some photos of your build, clear so we can see resistor values and solder joints?

[Zounds!]

I have 470ohms resistance between Q2's emitter and ground.

Here are some pics (camera phone quality unfortunately): https://www.dropbox.com/sh/0e0b691eo09j7oj/AAASfUbQiVrRqL_WtXSYq470a?dl=0

Fear not, I pulled the transistors out so you can better see the board after the first picture. It's hard to see, but I have them oriented with the tab pointed down towards the bottom row. Thanks again for the help!

[Tony Forestiere]

Low Output + Pots Working = Audio Probe Time.

[Zounds!]

Agghh something I should have clarified in the first post: When I plug my guitar into the input and my amp to the output, the circuit has barely detectable signal if I turn my amp way up. When I strum it just sounds like a farty kind of noise. I did audio probe, though not very precisely because, honestly, I don't totally understand what every component does and where I should have signal. For instance, when probing from the output, I have signal at the end of the 220nf cap connected to Volume 3 (C10 on the schematic), but not at the end connected to Q3s collector. Not sure if I should or not...

That said, I have low but audible output if I plug into the input and use my probe as an output, getting signal at the base of Q1 but not Q2. If I do the opposite (probe using my input signal, starting at the output of the circuit, I get signal at the base of Q3. Again, nothing at Q2. The output at the bases of Q1 and Q3 is clear and slightly distorted, not the ugly farty sound that I get when I plug straight in/out.

[slacker]

I would check that the 1k8 resistors are actually that value, it might just be your photos but the bands don't look like the right colours, they should be Brown, Grey, Black, Brown and some other colour depending on the tolerance. Take one out and measure it to check.

Another thing, if you are not using the rotary switch you need to add an input capacitor before the base of Q1, basically one of the caps the switch selects, the Colorsound uses 220n. This doesn't explain your high Collector voltages though.

[Zounds!]

You're right - they're 1.5k. I didn't have any 1.8ks. Also should have mentioned that in the first post, my bad! 

[duck_arse]

to use the audio probe (gibsonGM, where are you?), you inject some sort of signal on the left-er side of the circuit, and listen to the right-er side of the circuit. so to test Q1, put signal (bash at yr guit, a test tone, the radio/cd) to "in", listen at Q1 base, then at Q1 collector. sound? no sound?  if sound, then listen at the collector of Q2. and we are pretty sure there will be no sound here.

then to test the tone section, (lift Q2 to save trouble) inject yr sig into C4 instead and listen at Q3 base. signal? does it vary with the tone controls? it may well be very down in level, but at least it's there. then listen at the Q3 collector. sound? still sound at the right of the 220nF? still sound at the wiper of the vol pot, and does the pot vary the level?

so, inject at the base, and listen at the collectors (there isn't much to be heard at the emitters in these circuits). when you get nuthin, you've found a trubble site.

[Zounds!]

I have signal at Q1 base but not collector. No signal at all on Q2. I think the the 4u7 electro coming off the collector of Q2 is C4 on the schematic (the cap values don't match up between the vero and the schematic and I'm using the vero values). In that case, I don't have any signal there and can't check the other side of the board by injecting my signa there. If I inject my signal at the base of Q3, then I do have signal all the way to the output jack and it does vary with the tone controls. But no signal at any of the collectors. I have signal to the right of the 220nf but not at the end that connects to Q3's collector. I have signal at the volume pot and the pot works. I've been trying to take a look at the components placement every day with a set of fresh eyes but haven't found an error yet  Obviously there is one....

[duck_arse]

well now you know Q3 is good, and seeing as you're socketed, why not pull Q2 and stick Q3 in its stead, inject at the input and listen at Q2 collector? and if still bad, leave Q2 out, see if you got a working anything from Q1. after that, I'd put back Q1 and Q2 and lift the 12k on Q1 E, to see what happens then. after that, I'm all tapped out.

or, pull Q1 and then remeasure the Q2 volts, pull Q2 and remeasure Q1 volts, that might show something.

[deafbutpicky]

with the given voltages from your first post I'd say something around Q1 is the culprit. Uc on Q1 is way too high and Q2 is driven into full saturation, shunting everything to ground around it, therefore no signal around it's base/collector.

Another thing I noticed is the resistor coming from Q1 emitter to Q2 collector. 12K is brown red black red brown but they seem
to look weird to me in your picture.

[slacker]

If you haven't got 1k8 resistors you're probably better with larger resistors rather than smaller. Try 2k or 2k2 these should get your collector voltages down closer to 4.5-5 volts, which is where they're supposed to be.

[jatalahd]

As said by deafbutpicky, primarily you have a biasing problem, where Q1 is near cut-off and Q2 in saturation. With these biasing voltages one cannot expect to have much gain, which you have noticed as low output.

To help you out, I simulated the biasing part of Q1 and Q2 and built a breadboard proto to measure the voltages. I used a pair of 2N3904 (hfe = 180) and as a second reference a pair of BC549C (hfe = 550) transistors. The simulation and measurements on both transistor types lead to following (approximate) biasing voltages:

Q1:
C - 1.5
B - 0.8
E - 0.2

Q2:
C - 5.5
B - 1.5
E - 0.9

This proves that the direct-coupled configuration is stable despite the transistors used. So, you should re-check all biasing resistors which affect the biasing of Q1 and Q2. These resistors are (according to the schematic) R1, R2, R3, R5 and R6. Additionally, it does not matter if you use 1.5k at Q2 collector, I tried it as well and it did not have any noticeable difference to the biasing voltages. Also check very carefully the pin-out of the transistors and use a multimeter to measure the hfe of both transistors (one of them might be broken...)

If you have the possibility, I would recommend building the circuit first with the above mentioned components only, verify that biasing is in order and then start adding in the rest of the circuit one-by-one.

I hope this helps you forward.

[Zounds!]

Thanks so much for chiming in everyone! I decided it was time to start pulling components and testing them (deafbutpicky - you were right, I subbed an 11k for the 12k and didn't make a note of it). Starting at the left side of the board, I pretty quickly found that my 100k from 9v to C of Q1 only measures 130 ohms. I bought a baggy of a ton of 100ks off ebay a few years ago so I pulled another from the bag...and it read 130 ohms. Then another --same. They all have brown-black-black-orange-brown stripes but all measure 130 ohms -- aka they all have brown-orange-black-black-brown stripes and were read backwards by the seller.

I also found a couple 3k resistors in the bag too. I tested a 150k just to make sure my meter wasn't having problems in that range....hit 150k spot on, so I know my meter is fine.

Having only 130 ohms between 9v and the C of Q1 seems problematic, and maybe that would account for having 7.7v there when it should be 1.5v (thanks jatalahd!). I'm going to continue on and test everything else just to make sure, but hopefully once everything's soldered back in with a tested 100k to Q1 C things will improve. Back to work!

PS - worried now about how many hours I've wasted troubleshooting doomed builds loaded with 130ohm resistors where there should've been 100k.  

[Zounds!]

Update: all of the other resistors tested fine. I swapped the 1.5k resistors that I'd subbed in out and put in 1.8ks. Also took out the 11k I had on the emitter of Q1 and put in a 12k. Now all of my resistors are tested and exactly what the layout calls for. Still no real signal passing through, but my voltages look better, except now Q3 is all wonky!

Q1
C - 1.87
B - 0.90
E - 0.35


Q2
C - 4.73
B - 1.87
E - 1.16


Q3
C - 0.12
B - 0.63
E - 0.01

[jatalahd]

Now Q1 and Q2 are looking fine (for DC values at least), but Q3 is saturated near ground, some component around it is short-circuited perhaps? The Q3 collector should sit at around 5.5 volts with those biasing resistors, and it looks Q3 was working for you earlier. Anyway, Q3 has a gain of 3, so it just gives some make-up gain after the tone control. If you have a relatively clean and audible signal at the base-pin of Q3, then the problem concerns only the components around and after Q3 and should be relatively easy to debug. Otherwise more investigations are needed.

[Zounds!]

I can't for the life of me get all 3 transistors at the right voltages. I've desoldered every component, tested, put them back in, and run a razor between the traces. Q3's voltages are back where they were originally, but now Q1 and Q2 are just shorting to 9.5v.

Q1
C 9.40
B 0.00
E 0.07

Q2
C 9.50
B 9.40
E 0.00

Q3
C 7.00
B 1.30
E 0.60

The 100k from 9v to Q1 C and the 1.8k from 9v to Q2 C are tested and in the right place... I wish there was an emoticon on this forum for "tearing my hair out over here."

[jatalahd]

Oh no! This looks bad. Basically there was no reason to desolder everything, because Q3 is isolated in DC  from Q1 and Q2 using capacitors. The situation was still good when Q1 and Q2 were at the correct voltage levels.

I am running out of advices, but what I would do in this situation is to build from scratch in following steps:

- Put in Q1 and Q2 with R1, R2, R3, R5 and R6 including battery connection. Measure that bias is ok.
- Put in Q3 with R11, R12, R13, R14 and C10, C11. Measure that bias is ok for all three transistors.
- Start placing the components for the tone section one-by-one. After each added component, measure bias for all three transistors. This way you'll notice if any added component breaks the biasing. This approach should isolate the problematic part, if any.

In my previous posting I claimed that Q3 had a gain of 3. Actually the gain from Q3 is 50, I did not notice that C11 was bypassing R11. The gain from Q1 and Q2 together is that 3,  (6.8 + 12)/6.8, because of the feedback loop of R4 and R2. So the signal at the base of Q3 should be at the same level as it comes from the guitar. Sorry if my mistake confused you.