DEMO Seabed Delay #2 (w/Modulation) - Mad Professor Deep Blue Delay

This post contains an audio or video demo

MichaelW

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So last week I built the Seabed Delay (Mad Professor Deep Blue Delay).

Absolutely love it, it's the best sounding PT2399 delay I've built yet. Very analog sounding and voiced extremely well. I see why it's so popular with a lot of people.

I made a comment in my build report that the only thing that could make it better would be if it had some modulation.

@swyse DM'd me and told me about a hack he had done to get modulation from a PT2399 without having to add an LFO circuit.

It was discovered by Rob from DeadAstronautFX kinda by accident. Here's the thread on DIYStomboxes for those interested.

He discovered that if you jumper pins 6 & 8 on the PT2399 with a 1m resistor you could access the chorus affect of the chip on the repeats of a delay.
So of course I had to mess with my build and test it. I found that with a 1m resistor I could definitely get modulation on the repeats but the repeats died off after about 3 or 4 repeats. Following the advice on the thread I tried tacking on 470n cap to the resistor in series and was able to get the repeats working properly with the feedback control on the board.

So then I got to thinking....hmmm...what if instead of a 1m resistor I used a 1m pot instead, so that's what I tried next and found that I could get some different types of modulation on the repeats from a vibrato to chorusey effect. I tried a bunch of different ways to hone in on where the modulation was happening on the sweep by using 100k, 250k, 500k pots with 910kr, 760kr and 510kr resistors respectively but oddly enough trying to narrow the sweep of the variable resistor gave me less effect than just using a 1meg pot. Then I tried an A1M, C1M, and B1M to see which taper worked the best and wound up using the linear pot.

So instead of trying to hack up my original build I ordered a second board and used a 125B this time to give me a little more room to add a toggle switch to turn the modulation on and off and I turned it into a 4 knob delay pedal with a dedicated pot for tuning in what type of modulation I wanted.

I have to say it works GREAT! It's not as "in your face" as an LFO but it's a really cool hack that extends the capability of an already great delay pedal.

Thank you @swyse ! Great hack!

Here's prepping the drilling, I moved the Feedback pot to off board wiring and located the new modulation pot as a 4 knob pattern.
I put the toggle switch at the top.

IMG_4233.JPG

I would have liked to have hid the wires going to the toggle under the board but wasn't too confident that I'd have a robust connection soldering onto the nib of the DIP socket for the PT2399 on the back of the board. So instead I rigged up a couple of soldering points with buss wire on the DIP socket itself making sure that it wouldn't ground out against the adjacent pin.

IMG_4234.JPG

All wired up gut shot. I probably could have done this in a 1590B but the toggle would have been pretty tight. Glad I didn't try:)

IMG_4235.JPG

Finished pedal. The cream knob is the modulation knob. Helps me keep things straight heh.
IMG_4236.JPG

I recorded a demo showing how it sounds. Interestingly it seems the modulation is triggered by signal strength, making it a dynamic thing. The harder you pick the more modulation affect you get. At the end of the video I show some extreme examples of this. Super stoked about how this sounds and it's already part of my rig running as part of my dual delay setup.

 
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Nice I played around with that mod on a breadboard with a vero build I had done of the deep blue delay several months back. I never got any great results perhaps I’ll have to try the pot.
 
Very very nice! I do love the Deep Blue, but am usually not crazy about the way modulation sounds on most delays—this sounds worthwhile though. Also, the fuchsia and deep lilac really look great together.
 
This came out awesome! I've never tried it with a pot, but I loved how it sounded in your demo. The more subtle settings were super usable and the more crazy settings seem like a lot of fun. I'll have to try this on mine when I get the chance.
 
This came out awesome! I've never tried it with a pot, but I loved how it sounded in your demo. The more subtle settings were super usable and the more crazy settings seem like a lot of fun. I'll have to try this on mine when I get the chance.
If you notice at the very end of the pot rotation it kinda craps out. This happened no matter which taper pot I used. But it didn't happen when I used a 1meg resistor. There's a lot I don't understand what's going on here and I suspect there's probably more tweaks to be made by breadboarding this circuit and messing around. Of course I have no patience for that......hahaha.
 
If you notice at the very end of the pot rotation it kinda craps out. This happened no matter which taper pot I used. But it didn't happen when I used a 1meg resistor. There's a lot I don't understand what's going on here and I suspect there's probably more tweaks to be made by breadboarding this circuit and messing around. Of course I have no patience for that......hahaha.
The way it's wired, as you turn it to the right there is decreasing resistance right? Maybe there is a minimum to keep it happy. If you don't like having that as an option and feel like taking it apart you could measure right where the circuit starts to drop out on the pot and then place an additional series resistor there? It might unlock even more subtle tones as a result which could be cool.
 
The way it's wired, as you turn it to the right there is decreasing resistance right? Maybe there is a minimum to keep it happy. If you don't like having that as an option and feel like taking it apart you could measure right where the circuit starts to drop out on the pot and then place an additional series resistor there? It might unlock even more subtle tones as a result which could be cool.
Yah, I'd definitely breadboard the hack circuit for something like that to make it easier to figure out. But as it is, the way I use delay it's all very much in the background and a subtle effect. But it's a very cool bed of "slight modulation on the fairly short repeats I use to give my tone a 3 dimensional sound to it.
 
This is dope as ****! I have to try this. I’m not going to mod my current seabed (going to order a 2nd board like @MichaelW.

I’ll probably be adding more to this thread eventually because I’ll no doubt need your counsel along the way…have never done anything like this before but have try it. I know I’ll regret it if I don’t
 
This is dope as ****! I have to try this. I’m not going to mod my current seabed (going to order a 2nd board like @MichaelW.

I’ll probably be adding more to this thread eventually because I’ll no doubt need your counsel along the way…have never done anything like this before but have try it. I know I’ll regret it if I don’t
@geoffrey When you're ready give me a holler, I can walk you through what I did. (It's mostly in the pics above). Actually a very simple mod.
 
The way it's wired, as you turn it to the right there is decreasing resistance right? Maybe there is a minimum to keep it happy. If you don't like having that as an option and feel like taking it apart you could measure right where the circuit starts to drop out on the pot and then place an additional series resistor there? It might unlock even more subtle tones as a result which could be cool.
Maybe a trim pot in series to dial in the max before it craps out?
 
Thanks for pointing this out.

I just tried this with good results, I find a simple switch with the resistance value chosen by ear to be my fave use. With the pot variability I found myself often dialing back to the same sweet spots. With higher settings its a bit too pitch bendy, and with highest it craps out.

I’ll probably settle on a spdt on/off/on with cap off center and two resistor values chosen for a light/off/heavy mod.
 
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