Fulltone - OCD  [traced]

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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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Re: Fulltone - OCD

Postby jymaze » 06 Jan 2012, 14:10

On first intention, just put a jumper instead of the 18k resistor in the first opamp feedback loop (the one in series with the 1Meg pot). The minimum gain will then be merely a slight boost.
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Re: Fulltone - OCD

Postby geiristudio » 06 Jan 2012, 19:16

jymaze wrote:On first intention, just put a jumper instead of the 18k resistor in the first opamp feedback loop (the one in series with the 1Meg pot). The minimum gain will then be merely a slight boost.


Alright, I'm gonna try that, thanks!
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Re: Fulltone - OCD

Postby ebuprofen » 26 Jan 2012, 23:24

hey guys, what would be a good value for pot instead of 22k resistor in HP mode? so I could adjust the amount of boost? 500kB?
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Re: Fulltone - OCD

Postby yongki » 22 May 2012, 07:20

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Re: Fulltone - OCD

Postby Branimir » 27 Sep 2012, 06:27

Trying to find info...

What type of capacitors are use in OCD V4?
Electrolytics are tantalum? All of them? What about the others?
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Re: Fulltone - OCD

Postby batteryacidtea » 27 Sep 2012, 15:49

Theres just one capacitor (one of the 10uF's) is Tantalum, the others are eletrolytics. The tantalum cap is usualy highlighted in the schematics, I don't remember wich one it is, but is easy to find out
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Re: Fulltone - OCD

Postby jymaze » 28 Sep 2012, 02:31

Just a correction to the statement above:

Quote: "There's just one capacitor (one of the 10uF's) is Tantalum, the others are film capacitors."

The big polar capacitors of 10uF or more are electrolytics, except C7 that is tantalum (electrolytic here would be just as good).

Actually tantalum capacitors are the worst thing for signal (huge hysteresis) so even an electrolytic for C7 is better in that respect.
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Re: Fulltone - OCD

Postby Branimir » 28 Sep 2012, 11:15

Hm, I've never actually payed attention to capacitors, I used polypropylene capacitors, does film capacitor means polyester capacitor in this case, and does it really matter? 8)
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Re: Fulltone - OCD

Postby jymaze » 28 Sep 2012, 13:57

Polyester are the cheapest of films caps so that is what is used usually (versus polypropylene, polycarbonate or polystyrene). It does not matter that much anyway for guitar application, just take the cheapest. At least, I would avoid tantalum for sure.
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Re: Fulltone - OCD

Postby batteryacidtea » 28 Sep 2012, 17:20

jymaze wrote:Just a correction to the statement above:

Quote: "There's just one capacitor (one of the 10uF's) is Tantalum, the others are film capacitors."

The big polar capacitors of 10uF or more are electrolytics, except C7 that is tantalum (electrolytic here would be just as good).

Actually tantalum capacitors are the worst thing for signal (huge hysteresis) so even an electrolytic for C7 is better in that respect.


I was refering to the polarized ones, now I see I didn't answered the question properly. The pF values are ceramic, the nF values are greenies and the polarized caps are eletrolytic, just C7 (as jymaze stated above) is tantalum
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Re: Fulltone - OCD

Postby Branimir » 28 Sep 2012, 17:55

I never really payed attention to the caps, I just bought the ones that are available, okay so it's not critical to use that tantalum after all... Though I'm stupid, I have tried the V4 original and built mine and frankly, they sound the same, I just don't have them next to each other to A/B them properly.
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Re: Fulltone - OCD

Postby Intripped » 22 Aug 2015, 03:28

Just wanted to put some light on how exactly the clipping transistors and the germ. diode are connected.
I have a V4 here on my bench and I see that Source and Gate are connected together (trannies are 2n7000).
So we have S+G and D, where D corresponds to the striped end of a normal diode.

---->|---[S+G] [D]----
This represents how the germ diode and the 2n7000 are connected in series

For this message the author Intripped has received thanks:
howmuch (22 Aug 2015, 16:42)
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Re: Fulltone - OCD

Postby howmuch » 22 Aug 2015, 17:07

Intripped wrote:Just wanted to put some light on how exactly the clipping transistors and the germ. diode are connected.
I have a V4 here on my bench and I see that Source and Gate are connected together (trannies are 2n7000).
So we have S+G and D, where D corresponds to the striped end of a normal diode.

---->|---[S+G] [D]----
This represents how the germ diode and the 2n7000 are connected in series

Thanks for posting some first hand evidence on the connections.
It still seems to be widely (and wrongly IMHO) accepted that the gate is connected to the drain (as in the schematic yongki posted above), even though people have hinted otherwise earlier in this thread.
So does your OCD have the same clipping configuration as the Joyo clone's corrected circuit I posted here - the "Circuit when D2 is in the "correct" orientation"?
Image

You've got ---->|---[S+G] [D]---- and the corrected Joyo is electrically the same with ----[S+G] [D]---->|---
Or put another way, on the schematic yongki posted above, move the gate connections from the drains to the sources?
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