Id like to omit 2 pots and can't get it right...

RobertJay

Member
Believe it or not, I am using the Arachnid just for the Flanger in my build. I'd like to set the MIX and VOL settings at MAX and leave the pots out... Any suggestions? I have a 100k resistor at the VOL pads between 1&3 and removed R20. I have a 10k resistor between MIX pads 1&2, then a jumper between 2&3 as instructed. This did not work. Schematic attached, and thanks in advance.
 

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The changes you describe should have worked. I’m not sure that you’ll actually want the volume at max though, I’d experiment with the resistor value.

R20 didn’t have to be omitted, but it’s probably fine that you did.

I think audio probe to find other issues in the build might be needed
 
Other questions:
-are you using the internal fv-1 flanger, or pedalpcb version?
-if pedalpcb, do you have the eeprom installed?
-do you have pins 16,17,18 set to the proper patch?

Sorry if silly questions, just taking shots in the dark without knowing what problems you’re having.
 
Hi All! And thank you. This circuit worked as designed before I thought to remove the pots. I have the Builder EPROM installed and as far as FV! vs PedalPCB version? I have no idea. It is a FV! Multi FX pcb. I removed R20 because I already populated the PCB and wanted to cut the dry signal going to the mix.
 
I think you also have to modify the instruction code.
What does this mean?... Instruction Code? Do you mean the the programming in the chips? They may not be performing because they aren't getting the expected signals from other places that have been cut out?
 
I’d say, double check that you have the jumper and resistor on the correct pads of the mix knob, pin 1 is the square one, and should have the resistor to pin 2.

Next, check with the multimeter that you’re reading 100kohm from tl074 pins 1-2 (where the volume pot connects).

If those things check out, I’d start using an audio probe.
 
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Kinda resolved. I was given some varying advice. Jumping the MIX confused me and wasn't helpful. Removing the MIX pot and R20 takes the dry signal out of the equation. Jumped out C11 and put 47k resistor across VOL 1-2. Now I'm just trying to see about tweaking a little more out of the remaining pots. I have no change in sound from 7oclock -2oclock. Then all of the change squeezed in from 2-5oclock. ok, maybe 1 o'clock, not 2...
 
Glad you got it working. The control pot behavior sounds lik what would happen if you put log pots (A) instead of linear (B). Or it could be that’s just how the controls work in the code.

If you did install B (linear) taper pots but don’t like the sweep, you could replace with C taper to get more action in the lower range of the knob
 
Glad you got it working. The control pot behavior sounds lik what would happen if you put log pots (A) instead of linear (B). Or it could be that’s just how the controls work in the code.

If you did install B (linear) taper pots but don’t like the sweep, you could replace with C taper to get more action in the lower range of the knob
I took advice that wasn't making sense. The resistor over the vol 1-3 was actually silencing the signal. I needed the R across 1-2
 
According to the schem, pins 2-3 are connected so it should have worked across 1-3. Unless the pcb doesn’t match the schem, though that would be uncharacteristic of pedalpcb I think.
 
Hello all, anyone still here? I'm back at one of these builds and want to figure out why the advice that was given... was given. Jumping out C11, Why? just to reduce the FX signal a bit to compensate for the eliminated dry signal?
The MIX pot eliminated, but what if I did want to fix it 50/50? As easy as an R5k between 1-2 & 2-3? As I am going to use this pcb for a pitch shifter as an octave up and want an even blend of Wet and Dry fixed.
The #2 Lug on the MIX pot goes to VREF Triangle, which represents what? Is that where the unwanted wet or dry signal goes that isn't passed along? It's not the signal source as it's coming from the left... Thanks for bearing with my questions, trying to better understand.
Similar question regarding Control 2 & 3... As a bass octave up pedal, I don't need anything from Control 1 as it's the lower octave.
Control 3 has to be fixed at full CW for the octave. Jump 2/3?
Control 2 also blends the octave 1 and octave 2, but what octave 1? I'm cutting out Control 1 signal all together. So, jump 2/3 there as well? Thanks!.
 
All advice should be taken with a grain of salt and further your own learning. What is the purpose of C11? Capacitors in the signal path like this let the AC voltage audio signal through but block DC voltage. This is important because the FV-1 section is biased at a different DC voltage than the op amp section. So, you need it in there!

The Vref is the 4.5v bias DC voltage. Audio signal will see it like a ground, so yes it dumps the unwanted signal. The 5ks like you said will mix is 50%. The path to Vref through the mix pot also biases the signals, so you can’t just omit the mix pot, need the 5ks like you planned.

I think jumpering Controls 2 and 3, both pins 2-3 will work. Control 1doesn’t really matter, either jump 1-2 or 2-3 (just to keep it from picking up noise).

My suggestion: build a straight ahead arachnid for yourself! It’s awesome and there’s lots of fun patches. Then, you can test with other eeproms for special mod projects like the one you’re describing.
 
The changes you describe should have worked. I’m not sure that you’ll actually want the volume at max though, I’d experiment with the resistor value.

R20 didn’t have to be omitted, but it’s probably fine that you did.

I think audio probe to find other issues in the build might be needed
 
Hey, I'm always reading back to see what's what when building this circuit... R20 was removed because it's in the circuit for the dry signal, no? Not that a 1 cent part is breaking the bank, but I am trying to understand the circuit as well as modify it for my needs... I am confused even though it does work fine. I want to understand more. Where is 2 on the MIX even going? I think someone said to see it as ground? That's where the unwanted mix signal goes while passing the wanted MIX through R20 and R21, I think? So that's why I omitted C6 R4 and R20. And... I don't have the 10k resistor between 2-3. Just a jumper between 1-2 and seems ok. Is the resistor needed between 2-3 for any reason I may not know? Does the circuit need it for its own peaceful environment? So to say... Now the VOL is confusing me because I have one with 100k resistor between 1-2 and it works fine. Not sure why I have it there, maybe a mistake. But 100k across 1-2? Shouldn't that be no sound as it's a 100k pot? I'm still playing with this as in my head, I might have to use resistors to add up to the pot R values? Do I need 100k across 1-3 as that is always constant when turning the pot?... And maybe put a 70k between 1-2 and 30k between 2-3? so as to act like a pot turned up to about 70%?... Which is again really messing with me because CCW Vol is 0 ohms between 1-2. and MAx CW vol is 100 ohms. So something seems backwards as far as this works in my head, no? Maybe it's the direction to and from the chip that I am not familiar with, but I'm working on it.
 
I just realized that I don't need the Mix pot to be replaced by any jumpers or resistors. It seems that with only the effect circuit coming that way and past R21. Unless the circuit is happier knowing it's all connected as designed? Maybe the chip wants to get that bleed off from the MIX pot. IDK... But So far, it sounds fine compared to otehrs with the pot and the jumper/resistor.
 
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