aphelion / DOD 250

Started by eh la bas ma, November 26, 2020, 01:08:57 PM

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eh la bas ma

#20

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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 ?
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"We must not confuse what we are and what society has made of us." Theodor W. Adorno.

willienillie

Quote from: ElectricDruid on November 30, 2020, 09:13:30 AM
Quote from: willienillie on November 29, 2020, 07:51:51 PM
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

Quote from: eh là bas ma on November 30, 2020, 12:49:23 PM
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

#23
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 ?
"One Cannot derogate, by particular conventions, from the Laws which relate to public Order and good Morals." Article 6 of the Civil Code.
"We must not confuse what we are and what society has made of us." Theodor W. Adorno.

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
friendly reminder: all holes are positive and have negative weight, despite not being there.

cheers

Govmnt_Lacky

Quote from: eh là bas ma on November 26, 2020, 05:23:24 PM
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?

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eh la bas ma

#26
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.
"One Cannot derogate, by particular conventions, from the Laws which relate to public Order and good Morals." Article 6 of the Civil Code.
"We must not confuse what we are and what society has made of us." Theodor W. Adorno.

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".
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