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BOSS Delay Machine DM-1 schematic


 
5/31/1999 5:39 AM
Anders Westerberg
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BOSS Delay Machine DM-1 schematic
Has anyone got the schematic for this one? Or maybe just some kind of adjustment instruction?  
 
Anders
 
5/31/1999 2:46 PM
Mark Hammer
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Analog delays are a bit like 6L6 tube amps and op-amp-plus-diode-pair clippers - they are pretty generic with respect to mods, adjustments to taste, etc.  
 
What would you like to know or improve?
 
6/1/1999 12:07 AM
Anders Westerberg
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A friend asked me to have a look at it since he thought it sounded funny. I didn't notice anything except for the following:  
As all other (AFAIK) analog delays, it has this threshold at the feedback knob where the sound starts to build up to a garbled noise. The strange thing is that this threshold seems to change with the delay time setting, when I have the rate set to full delay time, I can turn up the feedback knob to almost full but as soon as I turn the rate to faster delay times, the feedback noise builds up rapidly.  
 
I don't know if this normal. Since there's 5 or 6 trimmers in it, I hoped it could be a adjustment problem.  
 
 
 
 
Anders
 
6/1/1999 3:04 PM
Mark Hammer
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That's a lot of trimmers. There is often a trimmer associated with either providing an appropriate bias voltage for the signal entering the BBD chip, and/or another trimmer for balancing the outputs of the clock and anti-clock BBD outputs, depending on the specific BBD chip. I've also seen some analog BBD units that have internal trimpots for setting sweep width or maximum regeneration, so perhaps the various trimpots are related to these functions.  
 
In some instances, the feedback trimpot is to address the kind of problem you describe (or at least cousins of that problem). Bearing in mind that the recirculated signal is added to the original signal entering the BBD, it would make SOME sense that when the iterations are spaced (long delay) the summing is not that big a deal, but become a bigger deal when iterations and about-to-be-delayed signal summate.  
 
I may be talking through my hat here, but some of these problems can be a function of:  
1) the bandwidth of the recirculated signal (lopping off some bass tames it)  
2) where the recirculated signal is being tapped FROM (pre-expander or post-expander)  
3) where it is being summer TO (pre-compressor or post-compressor)  
 
For instance, a full bandwidth regenerated signal tapped post-expander and mixed back in post-compressor would easily crowd whatever little headroom there is in the BBD chip and get you ugly noises in no time at all. Conversely, tapping a pre-expander signal, taking out some low end, and feeding it back before the compressor portion of the compander circuit would ensure that it rarely gets out of hand, no matter how much one cranks the recirculation up.  
 
Since you lack a schematic at the moment, the easiest and quickest strategy is to trace the path of recirculation pot, and stick in a DC-blocking cap about half the value of the one there. So, e.g., it the recirculation pot is a 100k pot with a 4.7uf cap on the output, sub a 2.2uf for the 4.7uf (observing proper polarity). Since the low end generally has the biggest amplitude, slicing off some bass can partly address and headroom problems.  
 
If you can identify a maximum-recirculation trimpot, you may want to adjust that. Bear in mind that the unit may SEEM to be malfunctioning because the front panel controls are treated AS IF they represent the optimal operating conditions. If they only reflect optimal conditions when the trimpots are set right, then clearly and drifted trim pot setting need to be set right.  
 
Just a thought.
 
6/4/1999 12:27 AM
Anders Westerberg
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Thanks for the info, Mark.  
 
I followed the wires from the intensity (appearantly feedback control) pot to the PCB and found a trimmer hooked up in conjunction with the intensity control. I set it down to a point where the feedback almost started to build up (when the rate control was set to short times). When I then turned the rate to max time (which seems to be around one second, BTW), the echoes fades out faster, but long enough anyway (about 5-6 repetitions until it dies out completly). The controls of the effect seems more reasonable now and I guess the pedal is supposed to work this way. My guess is that someone had tinkered with the trimmer settings.  
 
Thanks,  
 
Anders
 
6/4/1999 4:04 PM
Mark Hammer
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Thanks for the happy ending. It's been a hellacious week. I could use a happy ending or two.
 
6/5/1999 12:39 PM
Anders Westerberg
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You're welcome. Thanks for the help!  
 
Anders
 
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