| Author |
 Topic  |
|
Laurie
Double Platinum Member
Canada
4854 Posts |
 Posted - 05/25/2008 : 01:05:35
|
Instructions are at the web site below, but this thread is to further explain:
http://www.godiksennet.com/images/sch/DM2PG2.jpg
You will need a scope and a 200Hz test tone (I generated mine out of my computer sound card).
STEP 1
Take the base off the pedal and swing the board out. Identify TP-1 (written on the board), VR1, VR2 and VR3.
STEP 2
Hook the scope up to TP-1 (with the ground clip of the scope clipped to the metal pedal body. Plug a lead into the input - but don't plug the other end of the lead in (this is only so the pedal will turn on). Plug the ASA adapter into the pedal if you are using one. Turn the pedal on. The clock signal is "free running" - it doesn't need an input signal to be there. On the scope, set the sweep to 50 micro-seconds/division, and volts per division to 2. Check that you can see a clean square wave. Don't worry about the service note that says "power supply 8V". Make sure the pedal knobs are set to fully counterclockwise (e.g. set to "minimum"). Adjust VR-3 until the square wave you see ("T" in the service notes) is just less than 3 divisions on the scope. That's it.
STEP 3
Put a 200Hz sine-wave tone into the input of the pedal (I just used a test tone WAV file I made using cool edit, sent out of my laptop's sound card). Check the "size" of the tone with the scope - the input is at terminal 3 of the circuit board. Make sure the signal is about 300 milli-volts peak-to-peak. Hook the scope up to terminal 7 on the circuit board (purple wire on my DM-2). Set the scope to 3 milliseconds/division and volts per division to 0.5 Set the pedal knobs to "off" (maximum counterclockwise). You may not see anything but a flat line on the scope at this point. Turn VR-1 until you see a sine-wave appear. Adjust the volts/division on the scope until it fills the screen on the scope. Now carefully adjust VR-1 until the waveform on the scope is as pure a sine wave as it can be, with the maximum amplitude you can get - a smooth wave is what you are looking for (it won't be exactly perfect, but it will be close). That's it.
STEP 4
Leave everything as it was for Step 3, but set the scope input to "AC" and change the volts/division to 0.1. Touch the scope probe to the wiper of VR-2 (of the 3 solder pads for VR-2, it's the one closest to the NE570 chip). You should see what appears to be two strange waveforms. When you adjust VR-2, the waveforms will move "closer together" or "further apart". Adjust VR-2 until the two waveforms sit exactly on top of each other. That's it. Close up the pedal, you are done.
EDIT:
I've just looked at the schematic for the DM-3 and from a trim-pot setting persprctive, it appears to be identical to the DM-2. I don't have a DM-3 to try it on, but I'd say you are safe doing the steps above where:
- in step (2) you would adjust RT-3 in the DM-3. I'm not sure if "TP-1" exists in a DM-3, if not the signal you want is on pin 4 of the 3102 IC.
- in step (3) you would adjust RT-1 in the DM-3
- in step (4) you would adjust RT-2 in the DM-3 |
Edited by - Laurie on 05/27/2008 00:12:18 |
|
|
BASN
Copper Member
USA
17 Posts |
Posted - 05/25/2008 : 03:55:36
|
Thank You Laurie--great post!--very informative and very helpful! I have no doubt that your step by step guide to adjusting the DM-2's trim pots is going to make many DM-2 owners very happy!
Thanks very much for your efforts and for your willingness to share the information with all of us! |
 |
|
|
BASN
Copper Member
USA
17 Posts |
Posted - 05/25/2008 : 07:13:48
|
Hey guys--I just finished adjusting the trim pots in one of my two DM-2's according to Laurie's step by step guide and what a difference it made!--now I understand why the DM-2 is so popular and why it's sought after.
Thank You Laurie for posting the step by step trim pot adjustment guide--you made my day. |
|
|
|
Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 05/25/2008 : 07:34:18
|
Hi BASN
I would be interested to know:
Where the trim pots mis-adjusted by some tweaker?
Was it just age & component drift?
In either case, by how much were they off trim?
Regards Dr. Bob
2800 |
Edited by - Dr. Bob on 05/25/2008 07:35:07 |
|
|
|
BASN
Copper Member
USA
17 Posts |
Posted - 05/25/2008 : 08:22:12
|
Hello Dr. Bob,
I have to confess that I did experiment once or twice with VR1--the bias pot. Before I did anything I carefully made markings on the circuit board and on the pot itself so I'd be able to return to my original starting point. I knew I was taking a chance when I decided to experiment with the bias pot setting but I wasn't 100% satisfied with the DM-2's overall sound quality. Although my DM-2 didn't sound bad, it seemed to me as though the pedal had the potential to sound better--which is why I decided to experiment with the bias pot. I returned the bias pot to the original starting point after each of the tests. I'm not sure if my DM-2s were ever tweaked by their previous owners. I suspect that the reduction in overall sound quality was probably a result of age and component drift--that's my best guess anyway. One thing for sure--I'm really gratefull to Laurie for posting his step by step trim pot adjusting guide--it brought my DM-2 back to life! |
|
|
|
BASN
Copper Member
USA
17 Posts |
Posted - 05/26/2008 : 07:04:29
|
Hello again,
I just finished tuning up my second DM-2 using Laurie's step by step "trim pot adjustment guide". My second DM-2 was my backup DM-2 and to be honest for a DM-2 it didn't sound all that great--(that is until tonight). Now both of my DM-2 are properly adjusted and what a difference! Thanks again Laurie for posting your trim pot adjustment guide--using it brought my DM-2's back to life. |
|
|
|
Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 05/26/2008 : 13:49:10
|
| You are quite welcome! |
|
|
|
Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 05/26/2008 : 16:50:15
|
Hi Laurie
I don't suppose you managed to get any pics of the traces on the CRO
while you were doing the re-alignment of your DM-2?
You can taunt me with them, I still don't have a DM-2 or DM-3
Regards Dr. Bob |
|
|
|
Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 05/26/2008 : 17:24:44
|
quote:
Originally posted by Dr. Bob
Hi Laurie
I don't suppose you managed to get any pics of the traces on the CRO
while you were doing the re-alignment of your DM-2?
You can taunt me with them, I still don't have a DM-2 or DM-3
Regards Dr. Bob
Noooo... I didn't. Sorry ;-)
|
|
|
|
BASN
Copper Member
USA
17 Posts |
Posted - 05/27/2008 : 10:24:36
|
After adjusting the trim pots on two DM-2's I decided it was time to put the DM-3 on the bench. I studied the schematics of the DM-2 and the DM-3 and it appeared to me that with the exception of some noise reduction circuitry in the DM-3, the two pedals were pretty much identical. I opened up the DM-3 and looked it over carefully--it appeared as though the trim pots in that pedal were never tampered with--(so far so good). I wanted to play it safe so I made markings on the trim pots and on the circuit board, that way I'd have a point of reference to return to if need be. Some things to know--the DM-3's circuit board does have a "TP-1" located in the same general location as TP-1 on the DM-2--however--it's not marked "TP-1", instead it's marked "W3" with the word CLOCK directly beneath it. Another thing to be aware of is that the "input signal" can be found at terminal "1" of the DM-3's circuit board--at least it is on my DM-3. When performing the second part of "Step 3", instead of connecting the scope's probe to terminal 7, you need to connect it to terminal 13 on the DM-3.
The bottom line on the DM-3 trim pot tests I did is that everything was right on the money. The trim pots in my DM-3 didn't require any adjustments. So there you have it--the DM-2 and the DM-3 trim pot adjustment procedures are basically the same--(with the exception of the two different terminal test points). I hope this information will be useful for some of you.
|
|
|
|
ButterFlo˙
Copper Member
France
23 Posts |
Posted - 03/18/2009 : 15:02:59
|
Hi there,
I just wanted to ask what the point is in adjusting the trim-pot. What does it change in the sound ? (sorry for this dumb newbie question in french english)
I'm new on this forum, but I have been using Boss pedals for quite a long time, and have finally got my hands on a DM-2. I had a DM-3 before, and I compared them, they sound a bit different, the DM-3 is a bit more percussive (the attack doesn't fade when the sound is repeated), the DM-2 is more on the muddy side, which was what I was looking for. Could it be because of a different adjustment of the trim-pot ?
Thanks.
Flo˙ |
|
|
|
Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 03/18/2009 : 15:50:19
|
Hi ButterFlo˙
Welcome to the forum from Australia.
Regards Dr. Bob |
|
|
|
ButterFlo˙
Copper Member
France
23 Posts |
Posted - 03/18/2009 : 19:15:04
|
Hi, Dr. Bob's bot.
Thanks for answering.
Flo˙ (the real one) |
Edited by - ButterFlo˙ on 03/18/2009 19:16:04 |
|
|
|
bossarea
Forum Admin
United Kingdom
3652 Posts |
Posted - 03/18/2009 : 19:25:49
|
Hi Butterflo˙ and welcome to the forum.
A badly adjusted delay often produces some awful distortion.
The adjustment will ensure that the BBD circuit is working correctly and doesn't distort. |
|
|
|
ButterFlo˙
Copper Member
France
23 Posts |
Posted - 03/18/2009 : 21:27:36
|
You mean, even on the first repeats ?
One last question. Is there an adjustable resistor to control the muddiness, you know, that kind of strange filter that makes the analog recognizable ? 'Cause I'd like to make the sound on my DM-2 decay quite fast, if it is possible..
Thanks for answering !
Flo˙ |
Edited by - ButterFlo˙ on 03/18/2009 21:55:10 |
|
|
|
Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 03/18/2009 : 22:30:47
|
Hi ButterFlo˙ and welcome!
I need to jump in here with my standard rant about the trim-pots... 
<engage rant mode>
The trim-pots are designed to set the operating points of the components in the pedal. These are the electrical engineering operating points, and any effect on the sound is purely coincidental - they are not intended to be used as an additional control knob. For the DM-2 and DM-3 to operate correctly, the trim-pots need to be set to factory specification, and then left there.
<end rant mode>
|
|
|
|
Topic |
|
DM-2 and DM-3 trim-pot adjustments... EASY
