[sdiy] MN3207 and MN3102 Reissues

[mirwin at qouest.net]

Gavin,
The guitar lists are really the most suitable place to discuss the 
cloning of vintage guitar fx units - half the discussion revolves around 
 cloning, subs, copyright issues etc.

Regarding substitutions, most of the original Japanese parts are still 
available, including the different transistors, the MN3207 (and the  
companion MN3102 driver) are about as mainstream as it gets with BBD's, 
relatively easy to find compared with ther BBDs, the NE570/571 compander 
is also a mainstream part. Parts warehouses that cater to the consumer 
electronics repair industry usually have these (check Main Electronic 
Supply in  Vancouver or www.bdent.com). The single supply op amp used in 
the clock circuit (IIRC a BA718) may be hard to find, I tried several 
single-supply op amps with better specs (including TLC272) but achieved 
the best results with a lowly LM358.

The neat thing about the Dimension choruses is that they try to achieve 
a "vibrato-free" chorusing through "static" pitch detuning by means of 
two parallel delay lines modulated by complementary LFO triangles. 
Listened to individually, each delay line output has it's pitch shifted 
alternately up and down (sounds like a VCO being slightly freq-modulated 
by a slow square wave). When the two delay outputs are combined, the 
result sounds like two static pitches, slightly detuned, with a slow 
beating taking place. A wonderful effect. Roland patented this technique 
in the early 80's. The "D" has a better clock circuit than the "C", as 
well as more elaborate cross-mixing and filtering, plus the line drivers 
and bar graph, etc.
Regards, Mike