Earthquaker Devices - White Light OD

rigercat · Post by **rigercat** » 11 May 2012, 01:01

This pedal sounded rather awful to my ears, but I traced the circuit anyway.

Would anyone like me to post a hand-drawn schematic? Although I don't have pictures, I'm 99% sure it's correct as I went over it three times.

jrod · Post by **jrod** » 11 May 2012, 02:52

rigercat wrote:
Would anyone like me to post a hand-drawn schematic?

Absolutely!

Post by **modman** » 11 May 2012, 10:27

jrod wrote:
rigercat wrote: Would anyone like me to post a hand-drawn schematic?
Absolutely!

Don't bother asking - just do it!

IvIark · Post by **IvIark** » 11 May 2012, 13:12

Yes please

rigercat · Post by **rigercat** » 12 May 2012, 01:16

Well then, here you go. As you can probably tell, I'm no expert schematic artist. If something is unclear or looks questionable, please let me know.

rigercat · Post by **rigercat** » 10 Aug 2012, 00:23

Lousy hosting site.

I should probably attach it here instead.

jamiefbolton · Post by **jamiefbolton** » 26 Dec 2012, 16:17

so am i correct in seeing that pin 5 is to ground, and 6-7 connected?

Frabbio · Post by **Frabbio** » 26 Dec 2012, 16:59

Yes, you do that when using only one opamp of the dual opamp , to prevent the second half from oscillating.

johnk · Post by **johnk** » 19 Jan 2014, 21:41

I drew up a vero of it according to the schematic posted and built it. it almost works but there's something wrong with the drive part of the circuit.
with the drive all the way down, the weight knob acts like a gain control. as you increase the drive it goes into fizzy oscillation and actually gets quieter.
the comp switch does nothing.
here's a pic of my vero and I've checked it against the schematic quite a few times. I've also checked my build multiple times.
if anyone sees any errors with my vero, please let me know.

Motter · Post by **Motter** » 22 Jan 2014, 21:39

I would guess it is the asymmetrical set of diodes that are controlled by the switch. They have a lower forward voltage than the symmetrical set, so they will always clip first whether the switch is on or off. The way your schematic is drawn explains why the switch doesn't change anything.

Manfred · Post by **Manfred** » 23 Jan 2014, 23:54

rigercat wrote:Lousy hosting site.
I should probably attach it here instead.

Are you sure about the 1N5239 diodes, this diode type got a 9.1 Volts Zener voltage?
There are two of this one connected in series as shown in the schematic,
thus the total clipping voltage value is 18,2 Volts.
This voltage value could never achieved when a 9 Volts power supply is applied.
Maybe it is a tricky thing to bemuse us, the real world clipping is the OP-Amp clipping then,
using the minus compression switch position.

Motter · Post by **Motter** » 24 Jan 2014, 03:49

Manfred wrote:
rigercat wrote:Lousy hosting site.
I should probably attach it here instead.
Are you sure about the 1N5239 diodes, this diode type got a 9.1 Volts Zener voltage?
There are two of this one connected in series as shown in the schematic,
thus the total clipping voltage value is 18,2 Volts.
This voltage value could never achieved when a 9 Volts power supply is applied.
Maybe it is a tricky thing to bemuse us, the real world clipping is the OP-Amp clipping then,
using the minus compression switch position.

With clipping diodes, the voltage we are concerned with is the forward voltage, Vf. My rudimentary understanding is that this is the voltage that must be exceeded across the diode before it will conduct, thus clipping the signal. For this 1n5129 I believe the Vf is 1.1, so two of these in series will clip any signal greater than +/- 2.2VDC.

Manfred · Post by **Manfred** » 24 Jan 2014, 12:01

Motter wrote:
Manfred wrote:
rigercat wrote:Lousy hosting site.
I should probably attach it here instead.
Are you sure about the 1N5239 diodes, this diode type got a 9.1 Volts Zener voltage?
There are two of this one connected in series as shown in the schematic,
thus the total clipping voltage value is 18,2 Volts.
This voltage value could never achieved when a 9 Volts power supply is applied.
Maybe it is a tricky thing to bemuse us, the real world clipping is the OP-Amp clipping then,
using the minus compression switch position.
With clipping diodes, the voltage we are concerned with is the forward voltage, Vf. My rudimentary understanding is that this is the voltage that must be exceeded across the diode before it will conduct, thus clipping the signal. For this 1n5129 I believe the Vf is 1.1, so two of these in series will clip any signal greater than +/- 2.2VDC.

Thanks Motter for the hint.
I see, I did outwit by my self.
I'm sorry, I should have a closer look at the details before writing a post next time.

"For this 1n5129 I believe the Vf is 1.1, so two of these in series will clip any signal greater than +/- 2.2VDC."

Maybe the the "knee" shape of the forward votage-current curve is of interest.

johnk · Post by **johnk** » 03 Feb 2014, 01:03

Motter wrote:I would guess it is the asymmetrical set of diodes that are controlled by the switch. They have a lower forward voltage than the symmetrical set, so they will always clip first whether the switch is on or off. The way your schematic is drawn explains why the switch doesn't change anything.

the assymetrical ones aren't connected to the switch. I removed them completely and have the same results: low output, and nasty distortion. but I also think that the 9.1V zeners are wrong too.
IMO, there's something else wrong with the schematic that was posted.

Manfred · Post by **Manfred** » 03 Feb 2014, 07:03

johnk wrote:
Motter wrote:I would guess it is the asymmetrical set of diodes that are controlled by the switch. They have a lower forward voltage than the symmetrical set, so they will always clip first whether the switch is on or off. The way your schematic is drawn explains why the switch doesn't change anything.
the assymetrical ones aren't connected to the switch. I removed them completely and have the same results: low output, and nasty distortion. but I also think that the 9.1V zeners are wrong too.
IMO, there's something else wrong with the schematic that was posted.

Your are right, the zener circuit in parallel the diode circuit never clips,
since diode circuit's threshold voltage is less than zener circuit,s is.
I guess there is a toogle switch to switch over the both clipping circuits.

johnk · Post by **johnk** » 25 Feb 2014, 10:36

well, I finally got around to solving this one. on the EQD site they even mention that it's based on an MXR distortion +/ DOD 250 but with some modern improvements.
I corrected my vero and drew up a schematic for it and it sounds exactly like the vids posted online. here's 'my version' of what I believe that the schematic should be:

and here's the corrected and verified vero:

brevor · Post by **brevor** » 05 Mar 2014, 17:56

In your schematic the 475 K resistor is connected to the wrong input of the op amp. Also it doesn't show pins 1 and 2 of the weight pot connected, And your layout doesn't have pin 3 of the weight pot connected to the output of the op amp.

Manfred · Post by **Manfred** » 06 Mar 2014, 03:48

I brought the feedback part of the schematic into agreement with the hand drawing.
The circuit in my opinion will work then.
The "Weight Control" behave in a similar manner as the "Bass Control" such as the Walrus Audio Mayflower circuit.

johnk · Post by **johnk** » 08 Mar 2014, 20:24

you're absolutely right about my schematic error

, but I just checked my second vero layout and it matches your schematic so I fixed the above schematic to match it.

thanks!

Manfred · Post by **Manfred** » 25 Feb 2015, 19:08

I redraw the schematic

Earthquaker Devices - White Light OD [traced]