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Boss DM-3 making odd overtones

8/30/1999 6:33 PM
F Yang
Boss DM-3 making odd overtones
Hi - I've got a Boss DM-3 analog delay which seems to begun generating a strange overtone overtop of the delayed signal. My original note comes through fine, but the repeats have a strange electronic note behind them. Faint, but definitely audible. I'm fairly sure it wasn't doing this before. Any ideas on what's happened and what to do about it? Thanks.
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8/31/1999 1:04 PM
CJ Landry

This is a long shot but, I have seen the 2SK30A JFET's do wierd things like this. They will short across the D and S and then you get these wierd sounds into your FX signal. I would try replacing the 2 2SK30A's in the circuit and see what happens. BTW, you can use a J111 or J113 in place of the 2SK30A, just make sure you pay attention to the pin outs among the two.  
8/31/1999 2:09 PM
paul perry

If it is a very high-pitched note, it is probably associated with the sampling frequency of the BBD clock. Some BBD delays have a kind of doubled parallel system to make filtering out the clock easier. Sometimes there is a trimmer to adjust clock breakthrough. For a real longshot, imagine that the signal going in has some ultrasonic freq mixed in (oscillation or clock). Then, it might hetrodyne with the BBD clock & give an alias type whine. But, if it is only there when there are notes present, I back clock bleedthrough.
8/31/1999 2:47 PM
Hi Paul,  
I have the same problem when I play high notes with an  
Ibanez AD-9 (no reissue). Do you know which pot (how could it be labeled) I might check?  
Or can it be just a design flaw, i.e. the anti aliasing filter is not tuned right?
9/1/1999 1:27 PM
paul perry

Sorry, I have no idea which (if any) pot might help. But, these things dont usually have any trimpots except for the balance of the null. That business of only the high notes giving problems sure sounds like aliasing/hetrodyning. All you can do here is speed up the BBD clock & live with the reduced delay. Or, put an EQ in front and drop the highest notes, just echoing the lowest part of the spectrum, and adding back some straight top end signal to make up.
9/1/1999 2:53 PM
F Yang

Thanks to everyone for their help - it confirmed that I'm in over my head on this one. My experience with pedal DIY-ing is limited to distortion and fuzz pedal mods... analog delays are out of my league.  
The problem isn't really noticable - I just happened to pick it up and started listening for it. I'll probably hang onto it until the new Ibanez 707-series delay comes out, and sell the Boss. Thanks again.  
9/2/1999 5:47 AM
What are the 707's gonna be like??  

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