Fulltone - OCD  [traced]

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Re: Fulltone - OCD

Postby telecaster » 01 Jul 2011, 23:24

I find that the more i turn up the gain, the more compressed it gets. I keep the gain around 1 to 2 o clock, sounds more open that way.
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Re: Fulltone - OCD

Postby Barcode » 01 Jul 2011, 23:24

Seiche wrote:maybe i should add that i play an epiphone casino with p-90s and they have a lot of output.

Guessing that is most of your problem...

try tweaking R2 to a higher value, that will reduce the signal going into the opamp and maybe smooth out your issues. Then if you find a value you like you can put it on a switch and have a single-coil/humbucker switch.
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Re: Fulltone - OCD

Postby Seiche » 01 Jul 2011, 23:42

telecaster wrote:I find that the more i turn up the gain, the more compressed it gets. I keep the gain around 1 to 2 o clock, sounds more open that way.

yeah thats what i use max, but the sizzle already annoys me when i turn the gain down to 0 :|

Barcode wrote:try tweaking R2 to a higher value, that will reduce the signal going into the opamp and maybe smooth out your issues. Then if you find a value you like you can put it on a switch and have a single-coil/humbucker switch.

thanks! :thumbsup i will give it a shot, maybe i should also try experimenting with diodes with higher forward voltages also, leds for example, instead of the mosfets to get more headroom? the maximum gain is much too much for me also, i prefer stacking lower gain ODs for more distortion.

Barcode wrote:Guessing that is most of your problem...

but they sound so great usually! :oops:
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Re: Fulltone - OCD

Postby Barcode » 02 Jul 2011, 00:13

Seiche wrote:
telecaster wrote:I find that the more i turn up the gain, the more compressed it gets. I keep the gain around 1 to 2 o clock, sounds more open that way.

yeah thats what i use max, but the sizzle already annoys me when i turn the gain down to 0 :|

Barcode wrote:try tweaking R2 to a higher value, that will reduce the signal going into the opamp and maybe smooth out your issues. Then if you find a value you like you can put it on a switch and have a single-coil/humbucker switch.

thanks! :thumbsup i will give it a shot, maybe i should also try experimenting with diodes with higher forward voltages also, leds for example, instead of the mosfets to get more headroom? the maximum gain is much too much for me also, i prefer stacking lower gain ODs for more distortion.

Barcode wrote:Guessing that is most of your problem...

but they sound so great usually! :oops:

Let us know how it turns out!
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Re: Fulltone - OCD

Postby Seiche » 03 Jul 2011, 22:49

hmm, i substituted a 10k resistor for R2 (i socketed it), not much of a change except maybe in perceived volume, but i'm starting to think there is really something wrong with my build. the fizzy decay is always present, it's exactly the same in duration (3-4sec) no matter where i set the gain (the gain goes up, but the fizzyness remains the same, it's hard to explain). It's there if i change the clipping diodes for leds, etc, or take them out completely. And no matter what i substitute for R2 (2k2, 5k, 10k).

the ic voltages on my unit are as follows (why haven't i checked them earlier :slap: ):
1. 7.31
2. 7.31
3. 6.99
4. 0
5. 7.31
6. 7.31
7. 7.31
8. 8.91

they seem weird don't they? :(
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Re: Fulltone - OCD

Postby Seiche » 06 Jul 2011, 22:51

it actually sounds very much like this (notice the fizzy decay when he lets the first chord ring out with the ocd engaged)

maybe that's normal, but i don't like it. anyone else have that problem?
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Re: Fulltone - OCD

Postby geiristudio » 15 Nov 2011, 11:18

Image

Will this layout be able to run on 18v properly ?

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Re: Fulltone - OCD

Postby hbo » 15 Nov 2011, 11:45

geiristudio wrote:Will this layout be able to run on 18v properly ?


If you use caps rated for 25v or more you should be fine.
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Re: Fulltone - OCD

Postby geiristudio » 15 Nov 2011, 12:10

Okay, thanks!
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Re: Fulltone - OCD

Postby geiristudio » 16 Nov 2011, 02:01

Hey one idea. I really like the low gain setting or the LP setting so I was wondering what to do to hardwire it at that setting and loose the switch ? I use the vero layout posted above.

Thanks in advance!
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Re: Fulltone - OCD

Postby bubstance » 16 Nov 2011, 03:46

You can just remove R12, swap R10 for anything around 13.2K and not bother with the switch.
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Re: Fulltone - OCD

Postby geiristudio » 16 Nov 2011, 11:29

bubstance wrote:You can just remove R12, swap R10 for anything around 13.2K and not bother with the switch.


Thanks man! I really appreciate it!
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Re: Fulltone - OCD

Postby ebuprofen » 09 Dec 2011, 12:49

build another OCD (like 5th or 6th :D) and this one is oscillating :( have absolutely no idea what is wrong.
used the same pcb with every OCD I build, only in this one used 220p cap made by Wima, not SilverMica, the whole difference.
when GAIN is min, no oscillation, when raised a bit and to the end it start to squeal with high pitch.
replaced the GAIN pot, no difference, what could be worng?
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Re: Fulltone - OCD

Postby Seiche » 09 Dec 2011, 13:37

ebuprofen wrote:build another OCD (like 5th or 6th :D) and this one is oscillating :( have absolutely no idea what is wrong.
used the same pcb with every OCD I build, only in this one used 220p cap made by Wima, not SilverMica, the whole difference.
when GAIN is min, no oscillation, when raised a bit and to the end it start to squeal with high pitch.
replaced the GAIN pot, no difference, what could be worng?

real pcb or vero? maybe the cap is not a 220p, but 220n? wima sometimes only writes numbers on them.
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Re: Fulltone - OCD

Postby ebuprofen » 09 Dec 2011, 16:51

real pcb, my own layout, 220/630 5mm pitch, so I guess it is 220p
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Re: Fulltone - OCD

Postby Seiche » 09 Dec 2011, 17:13

ebuprofen wrote:real pcb, my own layout, 220/630 5mm pitch, so I guess it is 220p

i have never seen a wima with anything below 1000pf=1nF. I'd try a different cap for that one. even if its a ceramic.

edit: obviously I'm wrong :scratch:
are you sure all the other caps are the right value? all the legs are soldered to the pads?
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Re: Fulltone - OCD

Postby ebuprofen » 10 Dec 2011, 08:18

the soldering looks ok to me, haven't noticed any shorts too, will try different caps for 220p today at evening, but in as I remember i already done one clone with Wima caps and it was ok.
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Re: Fulltone - OCD

Postby Seiche » 10 Dec 2011, 12:44

i had that squealing oscillation once with my Klone, turned out to be a micro trace between strips on the veroboard. stranded wires are also notorious to split and then one of the tiny wires just shorts something.
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Re: Fulltone - OCD

Postby ebuprofen » 11 Dec 2011, 07:44

cleaned the pcb, checked very carefully, no difference.
but, when unsolder the 68n cap, the squeal dissapears, also, the squeal only presence when guitar is not attached to the pedal, so it is working ok, when connected as it should, but if guitar is unplugged from the pedal and the pedal is connected to the amp and engaged, then it starts to squeal.
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Re: Fulltone - OCD

Postby geiristudio » 06 Jan 2012, 01:00

I'm making a modified version of this, without the switch (as in, hardwired in low-gain mode) and some tonal difference.

Anyways, I also want to make it even more "low-gain" so I was wondering because it's a dual opamp, do I need to lower the value of the 1M pot (Drive) which is in the first feedback loop, or the 150k in the second feedback loop, or both ?

If I'd go from, let's say, 150k (in the second feedback loop) to 68k (the closest I have in stock to being half the value), would it make a huge difference or should I go even lower ? I'm going for looooow gain.
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