Please help with OCD debug (VOLTAGES INCLUDED)

[skibum1999]

Alright so I built a Fulltone OCD copy from this layout http://s197.photobucket.com/albums/aa131/veroboard/Commercial/Fulltone/OCD/?action=view&current=ocd_vero.png

Followed the layout exactly EXCEPT these substitutions

D2- 1n4148 instead of 1n34a

IC1- TL072 instead of TL082

The effect bypasses properly, the LED works perfectly, there is no buzz or hum, but no sound comes through the effect, just silence. When bypassed, sound comes through. I checked the polarity and arrangment of ICS, Qs, Diodes, all proper.

Heres the voltages I came up with, using a multimeter set on Black Voltage, Not Red Voltage (red appears to be double what black is)

Q1   (2n7000)
S =  5.08
G =  6.23
D =  7.16

Q2 (2n7000)
S=  3.5
G=  5.08
D=  5.08

IC1 (or U1) (tl072)
P1   7.53
P2   4.89
P3   0
P4   0
P5   8.09
P6   8.09
P7   8.09
P8   8.09

Both diodes 1n4148 (checked polarity--AOK)
D1
A = 0
K = 7.57

D2
A = 6.96
K = 6.7

phew..thanks to all who help!

[Auke Haarsma]

I'd say look for shorts around pins 8,7,6,5 of IC1. It seems to short to Vcc (+9V normally).

Also, Pin 3 of IC1 (or something around it) shorts to ground. It should be more around 4-4.5V.

[MikeH]

Yeah, definitely weird voltages for U1... it might be cooked.  Or you migh have a solder bridge connecting 3 to 4 and another connecting 5, 6, and 7 to 8.  One, whopping solder bridge!

[solderman]

Hi
I etched and drilled  the PCB for exactly the same effect today. I'm planing to build it tomorrow. Ill post my reading from that one if you haven't found whats wrong with yours by then. If I get mine working that is
But as sad earlier, the readings round U1 looks spooky to me. I would put my money on a solderbridge or a copper bridge on the PCB. Have you etched it youreself? 

//Solderman 

[skibum1999]

built it on veroboard, could be that the trace cuts arent complete

[skibum1999]

definitely no solder bridges on IC, still no sound passing thru 

[petemoore]

  Is this from a verified scheamtic ?
  The second opamp 'is' tied to the first OA's pin 1 [through the 2 x 10k's], but otherwise is DC blocked.
  IOW I'm not sure I understand the bias scheme on this one.
  OCD obsessive complusive disorder...what's it supposed to do ?

[skibum1999]

im afraid i dont know what you mean....there is only one opamp

[solderman]

Hi

"

IOW I'm not sure I understand the bias scheme on this one.
  OCD obsessive compulsive disorder...what's it supposed to do ?

Its the OCD, Obsessive Compulsive Drive from Fulltune
The OCD is the mojo pedal to have from Fulltune. It has Gained a huge reputation to sound "best" an wond many prices.
The thing that makes the magic in this one is sopose to to be the MOSFET clipping that is pull to Vb instead of GDN. it should give a very dynamic effect that responds to how hard you strum your strings like a real tube amp.
Thats Way I'm interested. I'm getting back with soundsamples as Soon as mine is working.   

here is a link to a comprehensive ODC  page

http://www.pedalarea.com/index.htm

//Solderman

[spudulike]

On the layout, the link wire that runs past pins 5,6,7 & 8 carries Vcc ... it isnt tight against the IC pins is it ?
And check again for a short on pins 3 & 4.

[petemoore]

  I'm known for bad schematic readings at times.
  Other times I read well, but bad schematic.
  "verified" means that schematic has been successfully built, enough times that there is no doubt it is a scheme that will work..
  Looks to me that OA2 has no DC bias, all the 'avenues' are DC blocked by caps...except through the 2x10k's that lead to OA1, atypical at least.
  I 'expect' to see a 'bias' resistor such as OA1 has [470k from the voltage divider], whether it needs it to bias is another matter.
  [and a capacitor separating DC bias between OA1 and OA2...again, if it biases [or the schematic is verified to make biased OA's] with the shown values/connections, then disregard.

[solderman]

Hi Skibum

I have just finnshed the OCD and it works and sounds much better than expected. It really sounds as good as its reputation. So I can confirm the schematics and the PCB layout. I etched mine from the transfer in the link below. The Verobord I don't know if its OK.

I didn't have any TL082 in stock so I used a TL072 but the differens in the readings is probably ner to nothing. Since I only had a 2.2 mF tantal Cap in stock I used that for C10. In the schematicks the R2 is 2K2 but in the PCB layout its 4K7. I used 4K7 in hope of a better highend.   

It is really amazing how well it responds to how hard the strings is starmed. It is possible to get a clean tone out of it Even with the gain at max if you handle the strings gently but if you hit them hard then you have a massive distortion. Almost like with a tube Amp on high volume. I haven't had time to test it at high volume yet, (Its 23.30 here now and I want to stay friends with my neighbors) but I will post soundclips on my site from this one as son as I have time.

The PCB layout and the transfer



Pictures of my build under the test phase






Some voltage reading from mine

U1
1=4,47 V
2=4,56V
3=4,25V
4=0V
5=4,45V
6=4,46V
7=4,46V
8=8,94V

katod on 1N34 (S on 2N7000)=4,36 
Other (Bias networkside) of 2N7000=4,46

Tant Cap C10 Anod=4,45

[skibum1999]

thanks alot solderman...those readings are bad news for me. i checked under the ic socket, nothing unusual, no touching of jumper to pins, no solder bridges, how do i check for an ic short?

[slacker]

Try removing the IC and then measure the voltages on the pins of the socket.

You should get something like

1   4.5         
2   4.5         
3   4.5       
4   0.0
5   4.5     
6   0
7   0
8   9.0

If don't then you've got a short or a misplaced component or a missing trace cut somewhere. If you do then it probably means you've damaged the IC somehow.

The other thing is are you measuring the voltages correctly? I only ask because some of your voltages don't make sense.
For example you've got 7.57volts on the kathode of D1, which must be your battery voltage, and then you've got 8.09volts on pin 8 of the opamp, but you can't have more there than is coming from the battery.

You should be setting your meter to read DC and then putting the black wire on ground, say pin 4 of the opamp and then measuring the voltages with the red lead.

[skibum1999]

yes im getting the readings correctly, i think it could be the battery giving me wierd readings. ill try a fresh one. il check the socket

[skibum1999]

the ic is fine, ill try to get my friends camera to take some hi-res pics for reference

[mojotron]

thanks alot solderman...those readings are bad news for me. i checked under the ic socket, nothing unusual, no touching of jumper to pins, no solder bridges, how do i check for an ic short?

I just built one of these using the OVD layout and moding things towards what I liked best between the OVD and skibum1999's schematic. I really liked these changes from skibum1999's schematic:

1) I used a 1MA pot for gain - just in case anyone used a 1MB pot - the coolest part of the gain is between 50k and 300k on the gain pot.
2) I used 100kB pot for volume with a 50k resistor between the output of the board and the volume pot - so that the volume control works on the attenuated 2/3rds of the signal - it's just too loud. Also, the 100k (well actually 150k) volume control really opens up the sound IMO compared to a 500k pot. I'm going to try a reverse wired 100kA pot next.
3) I used several opamps - I settled for a BB. I did not have a TL082 - I'm going to keep trying more - a TL072 worked well too.
4) Next I'll be trying a Ge diode in series with one of the clipping mos devices

Oh skibum1999 - I ran into the exact same problem, what I found was that I had 3 leads on my drive pot - 2 were correct the third one was connected to ground - which is a very common thing to do when prototyping stuff. Once I disconnected the one terminal of the drive pot from ground it worked perfectly. Seems like your schematic is right on for the V4 - the OVD (Thanks Mark!) is likely good for V1 - with some tweaks either sounds great. One of the better projects I have built. If I was to do this again I would use solderman's layout.

Thanks skibum1999 and solderman - this is a pedal well worth the extra tweaking time. It would have been only 1/2 as good without your info . I guess the bottom line is that this is an excellent pedal, but definitely one you want to tweak to sound best. When I finish my tweaking I'll post my final findings.

[tehfunk]

I've been meaning to ask this for a while, but you know, people here dont seem to like fulltone so it's a touchy topic. Here it is: all of the clones of the OCD that I have found on the internet and on here, dont seem to match up with the internal pictures i have of any of the versions of the ocd. No theory involved here but all the OCDs have 3 transistors, 1 germanium diode, and 2 silicon diodes. all the clones seem to have only 2 transistors. There are more differences, but I think that's enough to determine that no one actually has an accurate clone of it, am I right? Also, is it a voodoo labs overdrive, sparkle drive, or rat, with the mosfet's as clipping stage? I have seen so many different hypotheses, and hopefully someone knows. (Note: I dont presume to be more intelligent than any of the people who have worked hard and then shown us their work, I am simply a confused nub, and am a very curious and meticulous person, I dont see purpose in doing something if you don't do it right) Thank you!

[mojotron]

I pretty much morphed my OVD build into the schematic shown here http://s197.photobucket.com/albums/aa131/veroboard/Commercial/Fulltone/OCD/?action=view&current=ocd_vero.png.

It sounded better and better as I made the changes - so I just implemented all of them - getting there form the OVD layout is not trivial.

All in all - it sounds awesome. I don't know if it's identical to the OCD - does not really matter to me - the circuit in the above link is a real keeper. 

[solderman]

I pretty much morphed my OVD build into the schematic shown here http://s197.photobucket.com/albums/aa131/veroboard/Commercial/Fulltone/OCD/?action=view&current=ocd_vero.png.

It sounded better and better as I made the changes - so I just implemented all of them - getting there form the OVD layout is not trivial.

All in all - it sounds awesome. I don't know if it's identical to the OCD - does not really matter to me - the circuit in the above link is a real keeper. 

Hi
I don´t own a Fulltone OCD myself but I own a Fulldrive 2 (MOSFET version). I have poked around a bit inside that one to find out if the "Fullclone 2" schematics that fly around the net, is correct. 
Fulltone says  that there pedals works well from 9-18V and that they are immune to goofs like connecting a wrong polarized adaptor or an AC adapter to the pedal. I will not work but it will not fry either.  In the Fulldrive there are two Si diodes (half a rectifier) that fix's this. There is also an unusual FET connected to the ON/bypass LED indicator. It seems to be connected like a millennium bypass. Even if the 3DT stomp switch is connected as you would expect. I think this is a double security to use the FET as a switch to eliminate pop clicks from the LED going on off when draining the Cap even with a 1M input resistor. This will count for the third transistor you have seen.
Se this pic on an ODC V3
The transistor/Cap/small Diode/resistor close to the "99" on the tone pot could be this configuration.  The other two could be 2N7000 as used in my Fulldrive. One of the beige standing resistors can be the type of diode (beige looks like a resistor with one black ring I don't know what it is besides that it is a diode) that is in series with one of the 2N7000 in my Fulldrive.
Near the lover edge of the PCB you can see two standing larger diodes (probably 1N4001 or so) this could be half a rectifier.




//Solderman