Calibration Boss DM-2 Clone (Aion FX Amethyst)

[jonlucasman]

Hi,

I've recently assembled the Aion FX Amethyst which is a Boss DM-2 clone. Light turns on, passes signal. I've checked all voltages and IC2 Pins 1 and 16 which are 1.02 and .99. Both are low.

I checked voltages because calibration as been difficult. I've followed the instructions for calibrating without an oscilloscope. I've tried a lot so a little lost where to start. But when I follow the instructions it doesn't sound good. I can get the delay to either shorten or lengthen with the delay knob without much distortion. So that seems ok. But the feedback knob seems to not function well. If I understand the feedback function it should be repeats. The knob goes into unending feedback just after noon position. And doesn't seem to provide repeats but more of an ambiance. I've adjusted the clock function by ear and been able to get better repeats.

I'll attach pictures and you can see my voltages as well.(Note I circled 9 on IC2 it should have been 16).

Any insight into calibration and potential issues would be much appreciated.

Thank you,

 

[MattG]

I can't provide specific help, but I too initially had trouble getting my Amethyst calibrated correctly. See my build report and my troubleshooting thread. Basically, I found the bias calibration to be extremely sensitive. So sensitive that I ended up using a multi-turn trim pot. I bought a cheap oscilloscope, but in the end, relied mostly on my ear. There's a video on YouTube that walks through calibration of the DM-2 (or maybe it's the same-topology Way Huge delay). I don't have the link handy now, but I think it's mentioned in Aion's build docs. Definitely watch that.

 

[jonlucasman]

I can't provide specific help, but I too initially had trouble getting my Amethyst calibrated correctly. See my build report and my troubleshooting thread. Basically, I found the bias calibration to be extremely sensitive. So sensitive that I ended up using a multi-turn trim pot. I bought a cheap oscilloscope, but in the end, relied mostly on my ear. There's a video on YouTube that walks through calibration of the DM-2 (or maybe it's the same-topology Way Huge delay). I don't have the link handy now, but I think it's mentioned in Aion's build docs. Definitely watch that.

Did you ever check voltages on your IC's? Did they match the ones provided?

 

[MattG]

Did you ever check voltages on your IC's? Did they match the ones provided?

I did, but I no longer have my notes. I know most voltages were pretty close to the documented values, but there were a few that I thought were "suspicious" - different enough from reference values to suggest the possibility of a soldering or component value mistake. But in hindsight I'm pretty those values were fine.

I've recently assembled the Aion FX Amethyst which is a Boss DM-2 clone. Light turns on, passes signal. I've checked all voltages and IC2 Pins 1 and 16 which are 1.02 and .99. Both are low.

Help people help you by including more context - what is IC2, what are the expected values? A direct link to the docs would be handy too.

I checked voltages because calibration as been difficult. I've followed the instructions for calibrating without an oscilloscope. I've tried a lot so a little lost where to start...

Did you find and watch the YouTube video on DM-2 calibration? And did you read @blackhatboojum's excellent remarks on the DM-2 in my troubleshooting thread?

Without pulling up the docs, if I remember correctly: one trimpot can be easily set with a DMM, one you can just set to the mid point, leaving the bias as the tricky one. An oscilloscope helps, but, at least in my experience, only gets the bias trimpot in the right neighborhood.

I'll attach pictures and you can see my voltages as well.(Note I circled 9 on IC2 it should have been 16).

There are no pictures.

If indeed you think the voltages are off enough to be problematic, then the next step is to look at the schematic, and highlight everything leading up to, or coming out of, the pins with erroneous voltages. Double- and triple-check all those components. Be extra careful with "classic"/easy-to-make errors such as using 4M7 instead of 4k7, or 200nF when you should have used 200pF, or 100k vs 100R, etc. How's your soldering skill in general? Even experienced builders sometimes need to reflow solder joints.

From where did you source your integrated circuits?

 

[jonlucasman]

Here are some pictures. Let me get back to you on the rest.

 

[MattG]

Pins 1 and 16 of IC2 (NE571) connect to C9 and C25, respectively. Those caps in turn connect to ground. They are both 220n.

From your pics, it looks like you're doing the kit build, so I'm assuming all the parts came directly from Aion? If so, then I don't think you have to worry about any fakes.

Since Aion has those resistors made with their value printed on (rather than the standard color bands), it should be easy to at least check all those. I would print off a copy of the board and BOM from the docs, then go through and check to make sure all the installed values are right.

A picture of the back of the board would allow us to comment on your solder work.

I too had weird/inconsistent readings on some of my NE571 pins (but I don't remember which ones). But I just ignored those and focused on calibration. There's a decent amount of info here, but also other forums (e.g. diystompboxes) that have info on calibrating a DM-2. Read those for inspiration. What I found best was to use a looper pedal, so I could keep making minute adjustments to the bias, and instantly be able to hear if it was better or worse.

I'm planning on someday building a second one of these, and for that, I'll definitely be using a multi-turn trimmer for the bias adjustment.

 

[jonlucasman]

Thanks Matt. Aion FX actually responded and said the voltages on pin 1 and 16 are likely ok and want matter much because they are the rectifier for the compander.

I've double checked all components and reflowed any suspect joints. I've made a few amps and a handful of pedals so my soldering (I thinks) is descent.

Seems like you may be right that it is just a calibration issue. Aion is actually sending over an 50ka instead of 50kb which they are testing to see if that works better for the feedback function. I'll definitely consider multi turn trimmer pots if that doesn't help.

I've been able to calibrate it where the delay's time and distortion are not an issue but it has been the repeats that have given me trouble. I go from negligible effect (no repeats) to almost endless feedback.

I've looked at your posts (actually did before I posted this) but will check more at boss dm-2 calibration in particular and see if I can make any progress.

Thanks!

 

[MattG]

Seems like you may be right that it is just a calibration issue. Aion is actually sending over an 50ka instead of 50kb which they are testing to see if that works better for the feedback function. I'll definitely consider multi turn trimmer pots if that doesn't help.

I've been able to calibrate it where the delay's time and distortion are not an issue but it has been the repeats that have given me trouble. I go from negligible effect (no repeats) to almost endless feedback.

There is a non-zero chance the repeat pot is bad. I don't think bad pots are too common, but it does happen. I can conceive of a bad pot causing the behavior you describe. Replacing a pot isn't terribly hard or invasive, so it might be worth a try if you're out of easier/simpler things to try.