A couple new builds

chongmagic

chongmagic

Well-known member
Nice set! What do you think of the Dirt Wolf? Found some favorite settings? This one would definitely light up those internal LEDs with the COMP cranked.
 
The Dirt Wolf has lots of gain, I put in some matched DV9 diodes and it gives it an almost Tubescreamer feel in that position. D1 definitely lights up.. Definitely a great sounding pedal, still dialing in the FAT trimmer for the best sound to my ear. The comp can almost give it a fuzz sound depending on how you dial it in.
 
D3 is backwards on the schematic and on the board. It matches VFE's schematic, but that has to be wrong too. I can't find an assy diagram for VFE's board. The way it is, no current can ever flow thru D2. When the SLA switch is in the leftmost position, only D3 conducts. In the middle position, only D1 conducts. This is particularly problematic because it also exposes D1 to excessive reverse voltage which can damage LEDs. In the rightmost position, only D4 & D5 conduct.

If D3 is turned around, then the SLA switch is (left-to-right):
D1 in parallel with D2+D3 (LEDs with a little asymmetry)
D1 in parallel with D3 (LED/Si with a lot asymmetry)
D4 & D5 in parallel (symmetric germanium)
I gotta believe that is what Peter Rutter intended.

One more thing, with COMP maxed out, the 2nd opamp's output can go into current limit, which is a very different kind of clipping from the voltage limiting that happens when the output hits the rails. No doubt Mr. Rutter did this on purpose. Different opamps will definitely sound different under these conditions.
 
Last edited:
Chuck D. Bones said:
D3 is backwards on the schematic and on the board. It matches VFE's schematic, but that has to be wrong too. I can't find an assy diagram for VFE's board. The way it is, no current can ever flow thru D2. When the SLA switch is in the leftmost position, only D3 conducts. In the middle position, only D1 conducts. This is particularly problematic because it also exposes D1 to excessive reverse voltage which can damage LEDs. In the rightmost position, only D4 & D5 conduct.

If D3 is turned around, then the SLA switch is (left-to-right):
D1 in parallel with D2+D3 (LEDs with a little asymmetry)
D1 in parallel with D3 (LED/Si with a lot asymmetry)
D4 & D5 in parallel (symmetric germanium)
I gotta believe that is what Peter Rutter intended.

One more thing, with COMP maxed out, the 2nd opamp's output can go into current limit, which is a very different kind of clipping from the voltage limiting that happens when the output hits the rails. No doubt Mr. Rutter did this on purpose. Different opamps will definitely sound different under these conditions.
Click to expand...
So I guess it would be best to change the orientation of D2?
 
Either reverse D3, or reverse D1 & D2. Looking at the schematic, D2 & D3 should point the same way, D1 should point the other way.
 
D3 should be simple to reverse. I notice there isn't much difference in tone unless the switch is in the down position.
 
Down must select the 1N34As. I don't think there was much compression with the switch in the other two positions because you were getting LED limiting on only one half cycle. The other half cycle was running wide open. I experimented with one-sided clipping on my Rat / Expandora and decided I didn't much like it.
 
Chuck D. Bones said:
Down must select the 1N34As.
Click to expand...

That's correct.

If anyone has a stock Dark Horse pedal, a close up of the clipping LEDs would be quite helpful. The orientation of D3 has been confirmed as correct but D1 and D2 could have been installed backwards (compared to the schematic / PCB layout) in the original.

It definitely does make more sense that way.
 
Yep, I saw that one, there's a bigger one floating around as well, but it's too far away to see which way the LEDs are actually oriented.
Comparing to the original schematic / PCB layout, you can see that D3 is oriented correctly.

I suspect we're going to find out that the LEDs (D1 and D2) are installed backwards (in the original) compared to the original VFE schematic / layout....

For anyone just tuning in, until a "Rev 2" PCB is released installing D3 backwards would achieve the same end result.
This is purely speculation though, since the Trojan Horse PCB does match the original schematic as drawn.
 
Robert said:
Yep, I saw that one, there's a bigger one floating around as well, but it's too far away to see which way the LEDs are actually oriented.

Comparing to the original schematic / PCB layout, you can see that D3 is oriented correctly.
Click to expand...
Do you think I should try flipping around D3?
 
Robert said:
If you think you can do it without damaging the board... I think you'll have more variation from the toggle switch.
Click to expand...

Also, the signal level should be closer to equal for each toggle switch position because now the two sides of the toggle switch will be working together.

You'll know it's working right if D1 & D2 both light up when the SLA switch is in the middle "L" position. In the "A" position, only D1 will light up. When the Ge diodes are selected ("S" position), neither LED lights up. GAIN, COMP & FAT will all affect the LED brightness.

It's not uncommon for a schematic to have an error that gets corrected on the assy drawing, and the schematic never gets updated.
 
Chuck D. Bones said:
It's not uncommon for a schematic to have an error that gets corrected on the assy drawing, and the schematic never gets updated.
Click to expand...

I have the PCB layout as well, it appears to match the schematic..... but that doesn't mean they weren't installed backwards.
 
chongmagic said:
I flipped D3 and now both LEDs light up in the middle and one in the top position. It should be correct now .
Click to expand...

We're going to call this correct.... I'll make a note in the build docs for the current PCBs and will get a new revision worked up.
 
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