Gaussmarkov Pearl OC-7 Octaver - help needed

[Brainbender]

Hi!
I have some problems with my clone. I found project file at Gaussmarkov page (November 15 '07 version), built it but it doesn't work as it should. It acts like some cross between bassy envelope filter and equalizer with bass frequencies maxed. I can't hear the upper or lower octave. Pots are doing their job, there's no any hum. I've checked the wiring three times, pcb, there's no bad solder joints. I noticed there's a ground connection on baby board which doesn't make any changes to sound whether connected or not. I don't have an audio probe or oscilloscope unfortunately. I used J201 and 2SK30's. For power supply I'm using Boss 9V adapter. Any help would beappreciated!! 

IC voltages (from pin 1):

IC1 TL072C
5.04
5.04
2.54
0.00
8.98
8.37
8.37
8.98
IC5 TL074C
5.04
5.04
5.00
8.96
2.92
5.04
5.04
5.04
5.04
2.93
0.00
5.00
5.03
5.03

IC6 TL074C
5.04
5.04
5.01
8.97
5.01
5.03
4.85
5.03
5.01
0.00
5.01
5.03
5.04

IC2 TL074C
7.69
7.31
7.95
8.98
7.95
7.26
7.70
0.00
8.20
7.23
0.00
8.20
7.32
7.70

IC3 4013BM
8.98
0.00
0.00
0.00
0.00
7.45
0.01
8.98
8.98
0.00
0.00
0.00
0.00
0.00

IC4 4013BM
0.00
8.97
0.00
0.00
8.98
0.00
0.00
8.97
0.00
8.97
0.00
0.00
0.00
0.00

[Mustachio]

I was just soldering on the same project last night. Mine is working but the upper octave is in-audible maybe a hint of it in the background.

But let me see if I can help ya a bit. In the pdf with the component layout it has the J201 in backwards. Try flipping that around . Also make sure both boards are grounded . There's a ground on the right side of the main board then there's two more on the bottom as well as one on the second board once I had the grounds in and the j201 flipped the oct2 oct1 and clean worked as expected and sounded rather nice. Now to tackle the upper octave.

I was tired last night so I couldn't do any more debugging. But I'm going to trace back around the board that controls the upper octave. Trimmer does nothing at this point and I'm wondering if it has something to do with the way the upper octave pot is wired gonna check that first.

Try that out and if you figure out the upper octave let me know

Good luck

[Mustachio]

Pin 12 on IC6 for me was not fully soldered. Now I have upper octave, its just very quiet. I'm gonna see if doing the mod in the madbean pdf will help. ( it has to do with removing one of the caps C10 or 12 and jumpering possibly changing one cap to 1nf I believe)

I thought I read in another thread that scruffie came up with a mod to help out the upper octave. I'm not sure if that's whats noted in madbeans layout or not. I couldn't find the thread that was mentioned though. If any one has some info on modding the upper octave let me know please

The trimmer did seem to have some but very little effect of the upper octave. I think if I can raise the level of the upper octave it will sound fine.

Really check all your grounds. And maybe spin the j201 around on board 1. I went over my circuit with a jewelers loop to get a good look at everything it really helps seeing those smd chips.

Hope this helps. I haven't done a voltage test on the IC's yet. Ill try to test em and write em down later if it helps you.

[Brainbender]

Thanks for so much info!
I messed with it all day and i found something what maybe is causing the problem, but i need to confirm it. Your IC measurements would be helpful. Soon I'll let you know what I've came up. 

cheers!!

[Mustachio]

I removed C12 and changed C10 to 1nf (0.001uf) and it made the upper octave jump right up ! it is a lil fuzzy so I might try playing with values here but at least the upper octave is working.

Did you try turning the J201 around ? Its the only transistor on board 1 I used sockets so it was easy to pop it in and out. Id suggest a socket here , I tried 2 different j201's so far and one of them made my circuit much less noisy. It was not terribly noisy to begin with but my set up is not inside a box at the moment and I have all the power/ground connections running thru my bread board in a room with overhead florescent lights. I'm guessing once its boxed up it will be fine.

When I was first wiring this up I only had board 2 going to ground and I was not getting much sound. It had some level but was sorta gated and volume would jump up funky. Added the grounds at the bottom of board one and figured it wouldn't hurt to run power and ground to all the board connections that call for it even if it looked like they where connected and just extra spots for hook up. All of that helped make it work better but it didn't function correctly until I spun that transistor around.

Just got done eating dinner ill try to volt test all the IC's tonight and post em for ya.

Good luck

[Mustachio]

I wouldn't do the up octave mod yet. Might have messed up my amp last night 

I changed it back to stock and ended up getting it sounded really nice.

Worried I might have messed up the front end of my 1973 tweed tube amp......

[Brainbender]

I accidently touched R54's (1M next to IC3 on babyboard) solder pad (the one which connects to middle leg of Q2) with unisolated tweezers and i could hear some octave. Not sure what to do... Yes, sockets are cool. I use them on mostly all my builds. I swapped few J201, however, they work only as drawn on layout. I also contacted  Krister (zeta55) by email. This is what he wrote:

"Looking at your voltage readings I see that it's missbiased. Something is pulling your bias voltage down or pushing it up. For example IC1 pin3 is way down and pin7, 8, 9 is way up."

Yes, boxing up will help you to reduce ground noise. I'm sorry for your amp. I hope it's nothing serious. 

[Brainbender]

I removed ICs from baby board, and changed other ones but it still doesn't work... I'm thinking to start all over again, starting from new baby board.

[Mustachio]

I would go back over the board with a fine tooth comb. Check for solder bridges and make sure all the resistors are correct values. make sure the ic's are facing the right direction. You said the j201 only worked in the direction it was drawn in the pdf? That's weird to me because mine only works reversed. But mine does work so maybe if you follow the traces from the j201 you might fin an issue with either resistor or solder bridge.

Maybe post pics of the board so we can look and maybe spot something . It helps to get a fresh set of eyes some times. Also to make an audio probe you just take something like a 0.1 uf cap and solder it on to the + of a 1/4" jack and a wire with a clip to ground and ground it to the circuit and then probe around with the lead off the cap, the other end is plugged into an amp. I think there's a link to a simple one in the debug thread.

I got mine sounding pretty good now. the upper octave is weak but the overall sound is great with all controls at noon or higher. But yeah post pics and maybe we can spot something for ya.

[Brainbender]

Ok, I'll post photos soon, and will make a probe. I'm glad you're pedal is working.
What's with amp?

[Brainbender]

Ok, I've made a new board and populated it with metal film resistors (previous were carbon film) for more precise values, but now it doesn't work at all. I will post IC voltages later. My values are correct, board is tidy. Checked few times for bad solder joints and everything that could come to mind in debugging situation... I made many pedals and this is the first that got me in into debugging more then two weeks. 

[Brainbender]

[Brainbender]

i've replaced some jumpers and now i can hear some lo-fi fuzz effect.

[Brainbender]

i used an audio probe and found that i overlooked at the jumper under TL072 (i've soldered it wrong). now it sounds like MXR Blue Box with blend pot at 1-3 o'clock.  
Any ideas?

[Brainbender]

I've fixed it and it's working. Very good tracking.

[Burdin]

Hi,

I finished my OC-7 recently, but it doesn't work how it's supposed to. Basically upper octave seems that it works, but there's no change for 1st and 2nd octave when i turn the pots. Norm pot works strangely. I'm not sure how it should work, but if I'm right it should make distribution of clean and modified signal, so in one extreme position it should be a full clean signal and in another it should be a fully modified. So, this works only when upper octave is audible, when it's off norm pot works like a volume.

Scheme for this effect is also gausmarkov http://gaussmarkov.net/wordpress/circuits/octaver-clone/
I used all parts as are in part list, no substitution, when I made voltage readings at IC's some of them are similar to first post and some of them are totaly different and I'm not sure if the readings in first post are ok.
So here are mine:


 
   
 
   
   
   
   
   
   
   
   
   
   
   
   
   
   

pin	IC1 TL072	IC2 LM324	IC3 4013	IC4 4013	IC5 TL074	IC6 TL074
1	4,67	7,79	0,3 mV	8,96	4,7	4,69
2	4,67	7,42	6,35	8,96	4,7	4,69
3	2,3	8,9	0,3 mV	6,32	4,67	4,69
4	0,3 mV	8,9	7,28	0,3 mV	8,94	8,94
5	2,78	8,9	0,3 mV	8,9	2,74	4,67
6	4,67	7,34	0,8 mV	0,3 mV	4,69	4,6
7	4,67	7,79	0,3 mV	0,3 mV	4,69	4,69
8	8,9	´-5,2 mV	0,3 mV	0,3 mV	4,69	4,69
9		7,4	6,31	0,3 mV	4,69	4,69
10		6,72	0,3 mV	0,3 mV	4,48	4,67
11		0,3 mV	6,32	0,3 mV	0,5 mV	0,7 mV
12		7,34	6,32	0,4 mV	1,39	4,67
13		6,72	0,3 mV	8,96	1,39	4,67
14		7,8	8,96	8,96	1,39	4,67

voltage readings at transistors are:

Q1 J201
G  2,31
S 5,18
D 8,93

Q2 2SK30A
S  4,5
G 2,24
D 4,66

Q3 2sk30A
S 4,66
G 2,98
D 4,66

I looking for any advices, meanwhile I try to use an audio probe, but I'm worry that this problem couldn't be solved by an audio probe, thanks for any help. If you need more informations, feel free to ask.

[Burdin]

it seems that it's ok now, it was few small shorts, few cold joints and one bad wire