aphelion / DOD 250

[eh la bas ma]

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peer into the glass body, look for the ittle disck - it will be the kathode-end in both types. both diodes same way will mean no clipping one half cycle.
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You are right. I just turned OA1182 around and the clipping is more pronounced. Thank you !

There is a significant volume drop between diode-lift mode and the two other clipped modes. Almost one quarter turn on the Volume pot is required. Is that to be expected ?

[willienillie]

The Dist+/DOD250 isn't a very high gain pedal, more like an overdrive.

The OP has 1M and 4K7 as the values in the feedback loop, so that's x213 gain, or +46dB. That's quite a lot of gain, I'd say. Or it should be.

It's enough gain to slam a 45mVpp signal into the 9V rail. Given that even quiet guitars put out a 100mVpp and that we're clipping the signal using diodes (so a lot earlier than 9V) I'd expect there to be quite a lot of crunch possible. I'm still not convinced the pedal is working correctly.

The same values as the MXR, right?  I have a clone that I built, it has quite a bit of distortion when the gain knob is maxed, but still nothing like a cascaded "heavy metal" distortion type of thing.  I rarely use it, but when I do it's with the gain knob about half way up, as an OD, and that cleans up totally if I roll my guitar volume down some.

[aion]

There is a significant volume drop between diode-lift mode and the two other clipped modes. Almost one quarter turn on the Volume pot is required. Is that to be expected ?

Yep - in hard-clipping (diode to ground) configurations, the diodes cut off the waveform at a certain point (the diodes' forward voltage) which directly impacts the volume. The 250 doesn't have a gain recovery stage after the clipping, so the diodes are a hard limit on the max volume.

Germanium or Schottky will be lowest volume (~0.3V), silicon (1N914) will be louder (~0.7V), and LEDs will be loudest (~1.8V, depending on color).

[eh la bas ma]

thank you very much !

I really like the sound.

Quote from Iainpunk :

"the comp switch's effect is super subtile, its affected by C2, CX1 and CX2. [CX3 is for tone control at the end].
the values in the file seem really large to me, i recommend the following values to make it way more pronounced, but sockets are quite usefull here:
C2    - 560pF
CX1  - 1nF
CX2  - 10nF
also, making C3 larger, like way larger, makes the comp switch more effective. i recommend 470n or bigger instead of 47n "

Do you think it could be a good idea to do this ? Can this mode get the comp switch more effective without changing the distortion's character ?

I am currently using one 1N4148 facing two other 1N4148, and one OA1182 paired with one D9E, this is the best combination I could find . You allowed on this circuit to use up to twice 4 diodes : Did you have something in mind ? Is there an Aion's secret clipping mode ?

Final question: I've heard DOD 250's name comes from the center frequency of the pedal, set around 250Hz. Is it true ?

[iainpunk]

what i wrote there is in combination with a bigger C3, which is 47n according to the schematic, but i think if you want the comp switch to do something noticable, it should be atleast 470nF, 1uF or bigger.
this cap blocks a bunch of low end gain and only lets the mids and treble be amplified a bunch. this basically 'minimizes' the stock comp switch function which is designed to let a lot, even more and all of the bass through. making that C3 bigger lets the gain stage amplify the bass more, making it muddy/over-compressed/loose.
this is where the comp switch mod comes in, the comp switch chooses between several capacitors to take out the bass BEFORE the gain stage, getting the same thinning/tightening of the sound, but actually switchable bu the comp switch.
those original values are taken from the different original pedal variants, but the values i gave are calculated to replace C3's function, making a much bigger change to the sound and character.

it won't ruin the pedal, but it will make the comp switch do something, giving you 3 distinct sounds from fat to tight.

cheers, Iain

[Govmnt_Lacky]

I give you my readings on the IC (RC4558 this time) just in case .

1= 4.50 v
2= 4.66 v
3= 4.41 v
4= 0.01mV
5= 8.65 v
6= 0.01mV
7= 8.65 v
8= 9.19 v

I may have missed it however, has the issue with pins 5, 6, and 7 of your RC4558 been addressed? Why is Pin 6 shorted to GND?

[eh la bas ma]

The circuit only uses half of this chip : IC2 4558 is dual op-amp and IC1 LM741 is single op-amp.  That's why there is some unusual readings on IC2 : instructions mentions that "you can use half of a more modern dual op amp such as a JRC4558 or OPA2604"

On schematics (page 4) RC4558's 6th pin
is grounded.

[bluebunny]

That scheme for wiring the unused half of the dual opamp looks wrong to me.  The more usual arrangement is to wire it as a buffer, so pins 6 and 7 linked (inverting input and output).  The remaining non-inverting input (pin 5) should be connected to "VA".