Maxon AD999 Distorted Repeats

[drummer4gc]

I've seen these threads before, so I want to lay out what I know before I catch hell about not searching (I have!):

-BBD delays typically have inherent distortion in the repeats
-This particular pedal is known for it's "dark"/"warm" sound, which some may classify as distorted
-this: http://www.diystompboxes.com/smfforum/index.php?topic=64197.0


So here's my question: this thing distorts way more than it should. I've played AD999s before, they don't sound like this. The repeats on this thing sound clipped, not "warm",moreso with higher output pickups or more string attack.

Based on Mark Hammer's reply in the thread linked above, certain trims provide bias voltages to the BBDs in the AD999. Is checking the bias voltages a reasonable place to start figuring this out? Anyone that can point me in the right direction here would be super helpful. Unfortunately, I don't yet own a 'scope or know how to use one properly, so if that's the answer, I'm worthless, but I'm hoping I can check/adjust voltages and get this thing working right.

Thanks!

Matt

[Mark Hammer]

That is a LOT of bias voltages to check out.  I would not suggest doing it by ear.  Use a scope and a signal generator, and a probe that lets you examine the output point of each BBD.

[drummer4gc]

All right. My leg has been pulled. I'm looking at some cheap scopes, anyone have a favorite? I know there are benefits to the old analog ones, and that cheap tools are never long-term cheap, but it would be worth it to me to save a few bucks now and grab a cheap one off eBay to set this thing up properly and buy a nicer one when my pockets are looking a little fatter. What will work?

[YouAre]

Distorted repeats is very likely a biasing issue.

I used to work for Godlyke, and had the chance to poke around a few of the AD999's. Unfortunately, I wasn't at the skill level of biasing those monstrosities of audio engineering during my stint there. It's difficult enough to bias a single BBD, but the AD999 is comprised of EIGHT BBD's in series. They don't use any tricks to fix the biasing in any way. Everything is individually biased with trimpots, which is what enabled them to have such clean repeats. It's an incredibly labor intensive unit.

It was way over my head at the time, and I'd never touched them. Years later, and I'd still be a little bit wary. My suggestion is that you call or email Kevin Bolembach at Godlyke. He's the most helpful guy, and will definitely help you sort your issues. Fortunately, the dedicated repair guy is an absolute gem (may even be on this forum?), and is capable of handling such a beast.

I only suggest that you contact Godlyke rather than perform the DIY repair is that this job would probably be best suited for someone who already has the dedicated setup to perform this specific task. It's a beautiful pedal, and you deserve to play it at it's optimal conditions.

Check the Godlyke site for which email they use for repairs.

[Mark Hammer]

Besides, a person could get carpal tunnel syndrome from twiddling all those trimpots! 

[YouAre]

Besides, a person could get carpal tunnel syndrome from twiddling all those trimpots! 

To OP: rehouse unit, replace all trimpots with external miniature pots. It gives really extremely fine control over the delay sound. Any audiophile worth his salt can tell the difference between an AD999 with the 5th BBD distorting vs. the 6th BBD. That's precisely the type of control that a gigging guitarist needs live. You can REALLY tailor the sound to the room that way.

Edit: Don't.

[Mark Hammer]

Heh, heh, heh.  Sage advice! 

[armdnrdy]

I contacted Godlyke a few years back to get calibration info on the original AD900. (2 MN3005)

They were very helpful! They supplied the PDF for the 4 MN3008 model and passed on the 2 MN3005 calibration PDF that they requested from Japan. (images of what you should see on your scope included in PDF)

If you have a scope, a function generator, a meter, and a lot of patience, you can probably request the calibration procedure from Godlyke and go to town.......or......as You are suggested......send it in to be calibrated.

[drummer4gc]

Godlyke made me a very reasonable offer to have the unit calibrated to factory specs, so it sounds like that is the way to go. I am ready to step my building game up though and learn how to use an oscilloscope, but if I'm hearing you all right, this is not the project to learn on?

If anyone has any "beginner oscilloscope" ideas or thoughts, from what model to purchase to how to learn to use one, I'd love to hear them! I've got an old Ross flanger that could use some trimpot tweaking....


Matt

[Mark Hammer]

Single BBDs are relatively easy to calibrate by ear.  The problem is when you have multiple BBDs in series and need to treat each BBD in isolation to set it up right.

If you'd like to get into what scoping things permits you to learn, and have the money to do so, by all means go ahead.  But don't feel that something as simple as biasing a flanger requires that layout of money.....which could go to parts or pedals.

[YouAre]

Godlyke made me a very reasonable offer to have the unit calibrated to factory specs, so it sounds like that is the way to go.

Good to hear!

I am ready to step my building game up though and learn how to use an oscilloscope, but if I'm hearing you all right, this is not the project to learn on?

Also good to hear! But I'll be honest and say that this is definitely not a beginner oscilloscope project. If you get a chance, look at the Madbean Aquaboy, which is a great analog delay to practice calibrations on. Then imagine that...times 8. Note: No relation is implied between the AD-999 and any Madbean or Way Huge pedals.

If you want to tinker with an oscilloscope, look up the function generator IC's on smallbear and see if you can successfully build one of those. Use those to scope out your existing pedals, and even precisely bias your FET based pedals.

Also if you ever wanted to tweak LFO's or create your own, you'd have the tools to do so.

If anyone has any "beginner oscilloscope" ideas or thoughts, from what model to purchase to how to learn to use one, I'd love to hear them! I've got an old Ross flanger that could use some trimpot tweaking....

The Ross can be tuned by ear. Flangers/Choruses (Chorii?) are not nearly as finicky as delays.