PAIA Gator-"Paging Dr. Markov"

the recluse · July 10, 2008, 03:16:09 PM

I am planning on building a Gator clone from the project files on Gaussmarkov's site

Here:
http://gaussmarkov.net/wordpress/circuits/gator-clone

But I have a couple of questions, I have tried to get ahold of the man himself to answer them, but so far, to no avail.

Anyway, the project calls for three 250K pots, but doesn't specify taper. I assuming this means they should be Linear, but confirmation would be great before I order parts.

Also, the project asks for a momentary switch, but I can't figure out what for. My best guess is that this is part of the trigger function, which I don't plan to include initially. So if I can leave it out, do I jumper it, or leave it open?

Mark Hammer · July 10, 2008, 03:36:56 PM

Dr GM is in the process of moving across the continent. Joe Kramer and I visited him shortly before he and his wife packed up the house (good thing too, or we would have had to sleep on the floor!). So you may need to wait a bit to receive a replay...or maybe not.

I have the PAiA instructions at home so I can't confirm here from work, but my sense based on the schematic is that its log for the threshold pot, lin for the gain, and maybe log for the attack.

dschwartz · July 10, 2008, 04:05:36 PM

OT, but i would like to publicly thank GM for his fabulous PCB's and Eagle information..and he give it for free..

the recluse · July 10, 2008, 04:39:04 PM

Quote from: Mark Hammer on July 10, 2008, 03:36:56 PM
Dr GM is in the process of moving across the continent. Joe Kramer and I visited him shortly before he and his wife packed up the house (good thing too, or we would have had to sleep on the floor!). So you may need to wait a bit to receive a replay...or maybe not.

I have the PAiA instructions at home so I can't confirm here from work, but my sense based on the schematic is that its log for the threshold pot, lin for the gain, and maybe log for the attack.

Thanks for the info, if you are able to confirm the pot tapers, that would be awesome!

StephenGiles · July 10, 2008, 05:22:14 PM

There is one small mistake in the well drawn circuit, the cv should go to pin 5 of the 3080!

dschwartz · July 10, 2008, 05:28:27 PM

the level pot is audio taper, the other two are linear..

don´t let the taper of the pots bother you, the circuit will work anyway. different taper mean different "feel" when turning the pot, but it is definetly non-critical.

if you use all linear it would be ok too.

stobiepole · July 10, 2008, 11:37:11 PM

I've got the prototype build here...threshold is linear, the other two are audio taper. Yes, Paul's moving house right now, but I'm to blame for any mistakes in the schematic. My original files are lying around somewhere...

The level control is connected to pin 5 of the 3080, through a 10k resistor. I think it's right...there isn't really a cv input, but I suppose that's the place you'd put one.

Chris

Paul Perry (Frostwave) · July 11, 2008, 12:45:45 AM

Just adding, if you are putting CV to it, then the CV absolutely MUST go through a 10K resistor, NOT directly to the pin 5 of the 3080.
Applying an actual voltage (with nothing to limit the current) to the control pin of an OTA type chip is sudden death.
I have a bunch of 'single' LM13700s to prove it

the recluse · July 11, 2008, 06:10:06 AM

Quote from: stobiepole on July 10, 2008, 11:37:11 PM
I've got the prototype build here...threshold is linear, the other two are audio taper. Yes, Paul's moving house right now, but I'm to blame for any mistakes in the schematic. My original files are lying around somewhere...

Can you shed any light on the momentary switch? It is just part of the trigger function, or something else?

Mark Hammer · July 11, 2008, 09:03:46 AM

It's not momentary, just SPST. That's the way Craig Anderton designed most of the pedals he made for PAiA. Either the SPST switch defeated the effect directly, or else it switched a quad CMOS switch to do the bypassing. For instance, in the Rocktave, an STS switch simply reduces the gain of a particular op-amp to near zero, effectively disabling the octave path. In this instance here with the Gator, the switch overrides the fluctuating input-based control signal fed to the 3080 with a constant fixed one. Those of you who worship at the altar of true-bypass may find it less than desirable for the signal to always pass through 2 op-amps and an OTA, but hey, we were considerably less concerned with true bypass in the mid-80's when this product/design emerged.

If the lack of true bypass is perturbing, then I suggest you do the following:

build it into a 1590BB with a DPDT or 3PDT bypass swicth to override the entire circuit
replace the latching SPST with a momentary SPST (or equivalent)

This will let you remove the 3 chips completely from the signal path, OR let you apply the Gator on a riff-wise basis with the 2nd footswitch. When you step on the 2nd (momentary) footswitch, you will defeat the slow attack aspect for as long as the switch is held down, re-engaging it when your foot is removed. Just keep in mind that you may need to tweak the circuit a bit to achieve volume-balance between overall bypass and engage.

the recluse · July 11, 2008, 10:12:22 AM

Thanks for the explanation MarK,

The parts list in the GM file calls for a momentary, which is what led to the confusion for me. I knew that the Rocktave uses an SPST to select a buffered bypass and wasn't sure if this was something similar.

Mark Hammer · July 11, 2008, 11:21:56 AM

GM probably needs to correct that bit of info on the site when he gets unpacked and installed.

The Rocktave doesn't select a buffered bypass so much as provide a unity-gain clean signal at all times, which is mixed in with all the other signals. The SPST simply makes the rest of the circuit work or not work. It's actually a clever idea to have an inverting op-amp stage with an SPST straddled across it's feedback path. Remember that for inverting op-amps, gain = feedback/input resistance. So, if the feedback resistance = zero ohms, then gain is so much less than 1 as to be akin to open circuit.

Joe Kramer · July 11, 2008, 03:39:36 PM

Haven't visited here in a while, but my ears were ringing.

(Hi Mark!)

Sorry I can't offer any help with the Gator, but IIUC, the good Dr. G-M officially relocated as of July 1st, so he'll probably be in touch any day now.

Regards,
Joe

stobiepole · July 11, 2008, 09:22:18 PM

Yes, what Mark said. The SPST switch was listed as a momentary switch to be used as a temporary effect bypass. So you have a normal bypass footswitch, and a second footswitch that can be used as a momentary bypass. It's a very versatile effect that way.

gaussmarkov · July 23, 2008, 06:57:55 AM

hey! "reports of my death are greatly exaggerated."

but that move took a bit more out of me than i expected.

i still have not set up my bench, but i will get restarted online today. more soon!

gtown_caps_fan · February 04, 2012, 10:56:39 PM

I started building this pedal yesterday. I am only missing 1 part, the LM308N, which is on order from Mammoth. I used a CA3080E instead of LM3080N, and TL072CN for IC4 and IC5. I finally found a pedal which can use these 250K pots I have had forever.

I would love to see a demo of this pedal in action, either Gaussmarkov's clone, or the original PAiA kit, but finding a demo on YouTube has proved fruitless. Anyone have an audio clip or video? If there is an opinion of how this compares to the Boss Slow Gear (and its clones), that would also be helpful.

Thanks,
Bruce

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PAIA Gator-"Paging Dr. Markov"