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Jill Valentine
Bronze Member
USA
116 Posts |
 Posted - 01/08/2006 : 02:05:30
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| Just wondering if you can tell if the trim pots have been tampered with by the sound it creates. |
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phostenix
Gold Member
USA
754 Posts |
Posted - 01/08/2006 : 03:33:08
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The pot marked VR1 sets the virtual ground for the audio signal into the BBD delay chip. You need a 'scope to set it exactly, but when it is off, it will cause the BBD to clip the audio on one side of the waveform or the other. This makes it sound like a distortion pedal as well as a delay pedal.  This same adjustment exists in most Chorus & Flanger pedals and is the one that I've seen alot of people claim that you play around with to get your MIT CE-2 sound like a MIJ CE-2. While it IS true that moving this trim pot off where it should be will make the chorus sound weaker, and eventually kill the chorus sound altogether, it does not, in and of itself, make the chorus deeper or fuller, etc. It just makes it so that you can put the hottest signal possible into the BBD without it getting clipped and, therfore, sounding distorted.
VR2 is a little trickier. The clock signal that makes the BBD work is a square wave of a very high frequency (in audio terms, anyway). It is high enough in frequency that you can't hear it. This clock signal rides along on top of the audio signal through the BBD and gets filtered out after the BBD. VR2 helps to "null" it out as much as possible. You really need scope to do this right, but if it is off, you'll start to hear a high pitched whine or clicking sound from the pedal.
VR3 sets the limits of the dealy. It's the easiest to hear. When you increase the maximum delay of the pedal, you reduce the frequency of the clock signal. Get it down below 20KHz and you'll hear that square wave as a high pitched whine in the audio.
Ibanez AD-9 & AD99 delays have another trim pot that lets you adjust the amount of feedback so that you can make it self-oscillate if you want. I don't see that in the Boss DM-2 or DM-3.
Hope that helps. 
Grace and peace,
Steve
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boss freak
Gold Member
USA
663 Posts |
Posted - 01/08/2006 : 04:20:01
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That's WAY over my head!  |
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Roger
Bronze Member
USA
81 Posts |
Posted - 01/08/2006 : 04:46:29
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Great Info Steve.
Could you clarify one thing "This makes it sound like a distortion pedal"...is the distortion you're referring to something that is heard whenever the pedal is on, or is it just the Delay note that is distorted? The reason I ask is that there is a slight buzz that accompanies only the delay note of my DM-2. So slight that you can only hear it when you're playing clean. |
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phostenix
Gold Member
USA
754 Posts |
Posted - 01/08/2006 : 06:53:46
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Roger,
Exactly. Same with chorus or flanger. Your original guitar signal gets mixed together with the output of the BBD when the effect is on. So you hear the original fine, but the delayed signal is distorted.
VR1 is on the corner of the PCB next to the MN3005 BBD chip on the DM-2 according to the service manual I have. If you have a guitar with hot pickups or a clean boost pedal, you can use that to set the level. Strum some big power chords and tweak that pot for minimum distortion. I usually have my wife help me do this when I want to get one close and don't feel like taking it down to the shop. That's love, baby. 
On a delay, I'd set it to a middle of the road delay, 1 repeat, full volume on the repeat. It's a lot easier if you can have somebody else turning the pot while you play, or vice versa.
Grace and peace,
Steve
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Jill Valentine
Bronze Member
USA
116 Posts |
Posted - 01/08/2006 : 07:46:55
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| Thanks for the info guys. Maybe I am a complete idiot, but i'm still confused. So your saying if my Dm-2 is even slightly distorted sounding (with clean channel and no other pedals) that means my trim pots have been jacked with? |
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phostenix
Gold Member
USA
754 Posts |
Posted - 01/08/2006 : 07:53:16
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If your delay sounds are distorted with no pedals in front of the delay and a normal guitar level going in, then it may be that VR1 is not set right. That doesn't necessarily mean that some one tweaked it, it just means it needs to be adjusted.  It could also be some other problem, but that's the first thing I'd check before I put it on the bench to check it out.
Grace and peace,
Steve
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lightburst
Silver Member
Germany
158 Posts |
Posted - 01/08/2006 : 11:37:38
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quote:
Get it down below 20KHz and you'll hear that square wave as a high pitched whine in the audio.
Thanks Phostenix, thatīs what I needed to know for my old LocoBox analog delay. I found it the other day in a shop for 15,- Euros(!) and it sounds beautifull but has this high pitched wine mendtioned by you. I will look for the right pot inside and make an adjustment.  |
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boss freak
Gold Member
USA
663 Posts |
Posted - 01/08/2006 : 17:16:50
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| I have an analog delay that also produces an ultra high harmonic ring. Will adjusting the trimmers fix this? Should there be more or less resistance to remedy this? |
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bossarea
Forum Admin
United Kingdom
3652 Posts |
Posted - 01/08/2006 : 17:36:36
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On some Boss pedals, one trim pot is there only for minimising the clock frequency's effect on the signal. Your delay may have a similar trimpot.
My Dod Gonkulator is almost unusable because of a similar problem. I haven't been able to track down a schematic and until I do it will probably not get much use. |
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boss freak
Gold Member
USA
663 Posts |
Posted - 01/08/2006 : 17:41:01
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| The thing with mine is that it's really only noticeable in a studio setting. Maybe it's not important enough for me to risk damaging the unit. |
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visserman
Platinum Member
1072 Posts |
Posted - 01/08/2006 : 18:45:58
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I have a "method" how you can tweak your trimpots yourself without the help of any other people around you. You do need something which can produce a constant tone, something like a referencetone which can be found on some electronic tuners or metronomes.
Plug the metronome into your DM-2, and aim for a neutral sound [ a little delay which can be turned up or off depeding on your likes] make sure the back of the pedal is open, so you can adjust the trimpots while you listen to the tone, in this way you will hear immediately hear the effect of your adjustment.
Do not know the DM-2, and where the trimpots stand for, but Steve did mention the markings on the trimpots. It does help when you know where each trimpot stands for [repeat rate, echo, intensity]
Just put the metronome on a tone, switch the DM-2 on and tweak first pot slowly, see what the result is for the sound. Tweak carefully, not full turns in one go as these knobs are very sensitive.
Go through all three knobs until you like the sound of the pedal. You do notice that you need to hear all the time what the sound does, also you need to ask yourself what you would like from the pedal.
I did this myself for a DOD delay, the pedal was very moderate at first, could not self-occilate. I have tweaked it so it is a little more versatile, but I can still get the orginal sound as well, that is the sound before I tweaked it.
Really you cannot kill your pedal, as the pots have only been set for the pedal to work in its best way, but you may like the pedal to do something else [like causing feedback on its own] You can put the trimpost in such a way that you can no longer get a good useable sound, but you can easily reverse this by readjusting, so keep listening to the sound, be careful and just try.................Perhaps make a note of where trimpost were originally before you did any adjusting, so you could easily find them back.
Good Luck. |
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Roger
Bronze Member
USA
81 Posts |
Posted - 01/09/2006 : 05:04:15
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Thanks everyone for the input...very helpful. Not sure I'm courageous enough to tweek them yet, but maybe after a few more semesters in the Bossarea forum  |
Edited by - Roger on 01/09/2006 05:05:39 |
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Sunburst
Silver Member
427 Posts |
Posted - 01/09/2006 : 15:00:05
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I would not recommend touching anything inside any pedal, and leave the trimpots alone, keeping things original.
Just looking at the pots is enough in my opinion... |
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RRV-10
Silver Member
Australia
246 Posts |
Posted - 01/12/2006 : 07:30:20
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| I agree. I messed with the trimpot in a PH-2 and ruined the pedal. I was duped by HC reviews that stated if you rotate the trimpot clockwise you introduce more bass into the phase effect, you know, Stock: 6 Adjusted: 10 type reviews. Any increase in bass was minimal IMO and the pedal developed this 'whooshing' effect when engaged, giving the impression that the speaker had just been connected to the amp. What's more, people said 'just mark where it was initially so you can go back to the original settings' - not only is this hard to do but in my case it didn't work. I couldn't dial out the whoosh no matter where I set the trimpot. |
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Dm-2 trim pots
