BBD Delay input impedance issues....

MichaelW

Well-known member
This is not really a troubleshooting thread but I've noticed some curious behavior with my recent MBP ManOWar (Maxon AD-900) delay build.

Actually, I'm not even sure it's an impedance issue but I suspect it is.

So here's the behavior:

If I run it in my normal pedal chain at the end of the chain with nothing else turned on, it works as expected. Plenty of gain, I can set the "Mix" knob pretty high and get at least unity on the repeats as my dry signal. BUT, turn on an overdrive of any kind and it sends it into wild self oscillation and I have to turn the mix down to almost complete CCW.

My use case is running dual analog delays in series, one into the other with different delay times. I have a buffered loop where my delays and reverb live.
If I put the MOW in the loop BEFORE my TourBus, it behaves pretty well but for some reason I lose a LOT of mix. In other words, I have to max the mix knob to even hear the repeats. If I put it AFTER the Tourbus any delay signal from the Tourbus sends it into the same crazy self oscillation as with an overdrive.

I've tried running it outside of the buffered loop but at the end of my chain (before the loop) but I can't run any overdrives without it going into that gonzo self oscillation.

So right now I have it IN the loop and BEFORE the Tourbus. It's working and sounds great for my needs, but I have the MIX knob maxed to make it work as a dual delay.

I've tried re-calibrating following the instructions for the trimmers a couple of times and it does not seem to affect this behavior. I'm not sure if I should just chalk this up to idiosyncrasies of this pedal and roll with it. But I am curious as to what's going on and why in standalone mode it behaves like it should but clearly doesn't like to play well with most other pedals.

My other BBD Delay (The AquaBaby - Boss DM2) doesn't do this but I like the sound of the ManOWar better.

TIA!!

Here's the schematic:

Screen Shot 2022-11-29 at 11.11.44 AM.png
 
Having built the non deluxe version of this delay, I can tell you that the self oscillation thing you’re having is not normal behavior. What is normal with this circuit is the lower output. If you find yourself thinking “Wow, I have my mix knob up way higher than my other delays”, well… that’s the nature of the beast with this delay and how Maxon originally designed it. Running it after distortion or in the effects loop of an amp, you’ll find yourself racking the mix knob almost, if not all the way up. The AD-900 also doesn't do the space ship noise / self oscillation thing well nor was it designed to. That being said, if you don’t have your level and t1 trimmers properly balanced with each other, this circuit will do some wacky stuff. These two trim pots are very interactive and if the volume trimmer is set too high, it will take off into oscillation even if you have t1 dumped to minimum. Here is my method for setting those trimpots. Set your delay knob to max, feedback knob to minimum and your mix knob to max. Input a 400hz sine wave into the pedal. If you don’t have a signal generator, use this website.


You can use the headphone out on your phone, tablet or whatever to connect to the pedal using 1/8” to 1/4” adapters. Once you have a signal going into it, use your multimeter meter to measure the ac volts on the input jack. Personally, I like to adjust the volume of my signal going in to .78v but it’s not really necessary. Now that you have a voltage reading going in, probe pin 14 or 15 of your compander with your multimeter on ac volts, and adjust your level trimmer to match the ac volts of your input signal. Now that’s done. Unhook all of that signal generator garbage, plug in your guitar, and hook up the pedal to an amp. Leave your delay maxed, set the feedback to 3 o’clock, and mix knob to max. Play a note or whatever on your guitar and adjust the t1 trimmer until you have 10 repeats and the signal fades completely out on the 11th. That should put you in the sweet spot.

If adjusting these trimmers doesn’t solve your issue then we’ll need to go back and reexamine some stuff but, try this first.
 
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Thanks man! I'll give it another shot with the trimmer. Wierd thing is, stand alone it sounds very different that in the chain.
Anyway, I ordered a dedicated 12v wall wart for it to rule out any power related issues. I spent some time today adjusting the trims in the AquaBaby today and actually after a lot of A/B'ing think it sounds better running into the Tourbus than the MOW. It's got a bit of a "sharper" attack which works well running into the more "mushy" sound of the DMM. I'll take another crack at the MOW when the power supply gets here.
 
You’re welcome. Keep me posted on how the calibration revisit goes with this one. There’s definitely something weird going on with your MOW and my absolute love for this delay wants to help you figure it out.
 
You’re welcome. Keep me posted on how the calibration revisit goes with this one. There’s definitely something weird going on with your MOW and my absolute love for this delay wants to help you figure it out.
Have you built the DOD FX90? (MBP SetBack) That's the only one I'm missing now from MBP, unless I decide I need a second DMM and build the Total Recall:)
 
Have you built the DOD FX90? (MBP SetBack) That's the only one I'm missing now from MBP, unless I decide I need a second DMM and build the Total Recall:)
I have not built that one. Not enough delay time for my tastes. I’m an ambient 400 plus milliseconds kinda guy. You definitely can’t go wrong with the total recall. It’s the king of the memory man circuit.
 
I have not built that one. Not enough delay time for my tastes. I’m an ambient 400 plus milliseconds kinda guy. You definitely can’t go wrong with the total recall. It’s the king of the memory man circuit.
Is there enough difference between the Total Recall and Tourbus? I am the opposite, I use like 300ms max.....
Honestly the only reason I didn't choose the Total Recall and went with the Tourbus is because of the power requirements, but I'm winding up with needing a dedicated wall wart for the MOW anyway, why not make it a 24v and just run 2x DMM's and be done with it, right? heh.....(I'm exposing my justification process in public here.....feeling kinda vulnerable......) :ROFLMAO:
 
Is there enough difference between the Total Recall and Tourbus? I am the opposite, I use like 300ms max.....
Honestly the only reason I didn't choose the Total Recall and went with the Tourbus is because of the power requirements, but I'm winding up with needing a dedicated wall wart for the MOW anyway, why not make it a 24v and just run 2x DMM's and be done with it, right? heh.....(I'm exposing my justification process in public here.....feeling kinda vulnerable......) :ROFLMAO:
On paper they are the exact same circuit. The only real difference is the power requirements. I’ll help your justification process by saying that if you build the total recall, omit resistor R31. Not having that resistor in, eliminates the gating of your degrading repeats. The repeats then open up and degrade more naturally. Also making it more akin to the original big box dmm.
 
Is there enough difference between the Total Recall and Tourbus? I am the opposite, I use like 300ms max.....
Honestly the only reason I didn't choose the Total Recall and went with the Tourbus is because of the power requirements, but I'm winding up with needing a dedicated wall wart for the MOW anyway, why not make it a 24v and just run 2x DMM's and be done with it, right? heh.....(I'm exposing my justification process in public here.....feeling kinda vulnerable......) :ROFLMAO:
If you look at the schematic, you could make the same few changes in the power section of the tour bus to the total recall and run that at 18 volts. The difference being using 1/4 resistors and no low profile caps in a simplified layout. Just something to think about.
 
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