Vintage Simmons Drums (UK) Users Group

The SDS III has no tone generator. If you want to produce tone, you drive the (original moog...) filter into self oscillation by raising the resonance to a certain level. To understand the circuitry, call the "pitch" pot "cutoff frequency", the "noise tone balance" is "resonance", "impact click" is a short additional pulse on the "cutoff frequency".
In the schematics the 1485 you describe is the filter output amp. CV in is at T2, all CV's are added there. The filters input is IC4, Pin12, the only source of the beast is noise. Feedback is supplied by connecting the output via the noise/tone control and R56 back to the CV input.
Michael 
From: jesper@electronic-obsession.se 
  To: Simmons_Drums@yahoogroups.com 
  Sent: Monday, April 02, 2007 4:20 PM
  Subject: Re: [Simmons Drums] SDS-III vs SDS-IV internally


  So there _are_ 3086's... I didn't see those on the schematics. I'll gladly 
  take a few pictures when I dig into it again. I bet it's the same then...

  But do you say that the 3086's are the tone generators so to speak? From my 
  limited experience and todays values I have my suspicion set at a 1458 which 
  in connected to both waveform and noise/tone potentiometer.

  electronically yours, jesper
  - -- --- ---- ----- ---- --- -- -
  www.electronic-obsession.se

  Order your own copy of the Machinepop/Imiafan
  split-EP at www.electronic-obsession.se/label.asp

  "Varför har du så många pianon?" (Nora Persson, 9 år)

  ----- Original Message ----- 
  From: <michael.buchner@...>
  To: <Simmons_Drums@yahoogroups.com>
  Sent: Monday, April 02, 2007 3:49 PM
  Subject: Re: [Simmons Drums] SDS-III vs SDS-IV internally

  Hi Jesper,
  this is exactly the thing I want to know. The III is the four channel 
  device, as far as I know and the IV the two channel device, but the IV is 
  not only half III. The IV has no master section with run generator and lfo, 
  but may be the single channel is also different to the III.
  I repaired Wolfgangs III two month ago. It has no oscillators at all, the 
  tone is nothing but a resonating ladder filter, copied 1:1 from good old bob 
  moog. If you turn the Noise/Tone pot to noise, the resonance is completely 
  off, so also the impact click will not be audible. But on my schematics of 
  the III there are 3 3086 per channel, these are containing transistor arrays 
  to build this filter.
  What I am wondering about is this pot on the IV called "Waveshape". Is this 
  an osc or only an lfo? Maybe a good photo of both solder side and parts side 
  would help.
  Michael
  ----- Original Message ----- 
  From: jesper@electronic-obsession.se
  To: Simmons_Drums@yahoogroups.com
  Sent: Monday, April 02, 2007 3:01 PM
  Subject: [Simmons Drums] SDS-III vs SDS-IV internally

  Hi List!

  I'm looking inside my newly arrived SDS-IV due to a dead oscillator and 
  I'm
  comparing it to the schematics of SDS-III. Is it just me or aren't they
  alike? There are no 3086's on the SDS-III schematics but quite a few in 
  the
  SDS-IV...

  Anyone with a SDS-IV schematic around?

  electronically yours, jesper
  - -- --- ---- ----- ---- --- -- -
  www.electronic-obsession.se

  Order your own copy of the Machinepop/Imiafan
  split-EP at www.electronic-obsession.se/label.asp

  "Varför har du så många pianon?" (Nora Persson, 9 år)

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