Type C. OD (reworked OCD)  [documentation]

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dylan159
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Post by dylan159 »

bmxguitarsbmx wrote: 31 Aug 2021, 04:12
warsavius wrote: 27 Aug 2021, 06:30 great and interesting job. I'm having some issues (not really issues but features i guess) with my last build, a standard v1.4 ocd from effectlayout: the volume is quite low at noon, and above all, when i switch on the clean boost (mxr microamp) after the OCD there's too much volume jump, even with the mxr potz at zero.
I'll build one with your schematic to solve those issues.
You should troubleshoot this before moving on. Starting a totally new build is not logical.
I wasn't sure how much on topic it was to answer. I completely agree that waste should be avoided, but components can be reused, and there's a little chance there's an intrinsic flaw. I have a guess that these volume issues, at least the volume jump but maybe also the issues with the volume sweep, are caused by the high output impedance of the ocd. sure, you can tack on a buffer like I did at first, or you can make me happy and try this one :D
On the subject of tacking on, why use a separate boost when the second stage can be exploited for it, switching to a second fixed or variable gain? It would have the same headroom of the micro amo anyway. I like this kind of efficient choices.
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Post by warsavius »

The prototype is done: standard OCD v1.4, followed by an output buffer after Volume pot. the volume pot changed from A500KA to A100K.
The buffer is a copy of the Ocd v2 buffer. Basically it's a Ocd v2 without the buffered bypass.
Sound good, like before, but with unity gain at noon, and no strange volume jumps with the following mxr microamp. Exactly like @dylan159 said.
Next build will be this topic's schematic.

I've tried also the interesting plasticizer switch. Really great sound, in my ears better than Plexi tone (I've built a couple of them). there's a biiiig amount of gain, sounds like van halen... but...
if i raise the gain past 2 o'clock, it become silent with a rythmical noise like a rattle... if the gain is lowered at zero it stops, the starts again with the gain raised, seems to me caused by the load/unload cycle of the large 470nf capacitor in the plasticizer switch.
I'm not an electronic engineer, i'm just a R&D taps designer, and I'd like to know how the plasticizer mod works, and which components values are suitable for this circuit, how they change the tone. I'd like to experiment a bit.

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Post by dylan159 »

warsavius wrote: 31 Aug 2021, 19:38 The prototype is done: standard OCD v1.4, followed by an output buffer after Volume pot. the volume pot changed from A500KA to A100K.
The buffer is a copy of the Ocd v2 buffer. Basically it's a Ocd v2 without the buffered bypass.
Sound good, like before, but with unity gain at noon, and no strange volume jumps with the following mxr microamp. Exactly like @dylan159 said.
Next build will be this topic's schematic.

I've tried also the interesting plasticizer switch. Really great sound, in my ears better than Plexi tone (I've built a couple of them). there's a biiiig amount of gain, sounds like van halen... but...
if i raise the gain past 2 o'clock, it become silent with a rythmical noise like a rattle... if the gain is lowered at zero it stops, the starts again with the gain raised, seems to me caused by the load/unload cycle of the large 470nf capacitor in the plasticizer switch.
I'm not an electronic engineer, i'm just a R&D taps designer, and I'd like to know how the plasticizer mod works, and which components values are suitable for this circuit, how they change the tone. I'd like to experiment a bit.
Hi! As I said in the post what you have is similar to what I had done previously, which I had synthesized in a picture:
ABC.png
I'd say the 100k volume is fine, although it does slightly change the response of the tone control by loading it more.
I've run with this for a while before starting over with the type C, which feels less of a band-aid fix to me.
About the plastic mod, there's nothing special about it: the gain is set by (gain pot/R2)+1. Switching the other two parts in parallel increases the gain by reducing R2 by 10 times, and also switches to an higher cutoff with its own cap. The original leg is still in parallel but it's so big that it doesn't make much difference.
About your issue, it's not one that I encountered ever, but maybe there's DC leaking where it shouldn't there. Check your build and your capacitor. Thanks by the way
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Post by warsavius »

I've done quite the same "abc" schematic, with the same output buffer on a daughter board.

About plasticizer mod, I've breadboarded the cap and resistor in parallel with 68nf-2,2k. The max cap value accepted is 47nf. with greater values, 100, 150, 220 and 470nf, starts the oscillation at high gain, that can also be seen with the multimeter, the Dc goes from 2 to 7 volts instead of stable values around 4.5v. I think it's an issue of the op-amp that not tolerate such values (TL082). I should try the TL072.

Finally I've found a great alternative to standard sound with 47nf-220r in parallel. More gain, more crispy sound, adding to ODC a greater versatility.

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Post by dylan159 »

warsavius wrote: 01 Sep 2021, 19:11 I've done quite the same "abc" schematic, with the same output buffer on a daughter board.

About plasticizer mod, I've breadboarded the cap and resistor in parallel with 68nf-2,2k. The max cap value accepted is 47nf. with greater values, 100, 150, 220 and 470nf, starts the oscillation at high gain, that can also be seen with the multimeter, the Dc goes from 2 to 7 volts instead of stable values around 4.5v. I think it's an issue of the op-amp that not tolerate such values (TL082). I should try the TL072.

Finally I've found a great alternative to standard sound with 47nf-220r in parallel. More gain, more crispy sound, adding to ODC a greater versatility.
that's not good, I think you should check it thoroughly. 072 or 082 it doesn't matter, the network isn't connected directly to the output so it doesn't load the op amp much.
Your choice of values results in an high pass with cutoff at 15khz (although it's limited by the lowpass). Crispy indeed :D
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Post by bmxguitarsbmx »

Warsavius, This is going OT and making a bit of a mess of Dylan's thread.

Additionally, I am having a hard time following what you are doing. It seems you are needing troubleshooting help, but also talking about modifications at the same time.

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Post by dylan159 »

bmxguitarsbmx wrote: 02 Sep 2021, 16:10 Warsavius, This is going OT and making a bit of a mess of Dylan's thread.

Additionally, I am having a hard time following what you are doing. It seems you are needing troubleshooting help, but also talking about modifications at the same time.
you're right, I've tried to answer by keeping it in relation to the circuit in question here and giving more details about it and its history. The issue is very much a matter of troubleshooting though.
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Post by bmxguitarsbmx »

Warsavius, start a new post here:
viewforum.php?f=73&sid=503baedfaedeb2b156976714eb2f0f77

It seems to me that Dylan is on the right track about the problem being an input Impedance issue. Plugging into a line input, for instance. But, we shall see over there. :)

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