Doepfer

Hi folks,

Some time ago I bought an MS404 on Ebay Germany and was surprised when 
it turned up as it looks a little different to the ones I'd seen in 
pictures.  I think it's an early version, it has the pots mounted on the 
front panel then wired up to the main board which sits at the back of 
the case.

The circuit board is dark brown and has no printed markings, making it 
difficult to identify the trimmers.

I have the following instructions to set the VCO scale (translated by 
Google!):

	
The device should be before this adjustment is already about 30 minutes 
into operation in order to exclude subsequent variances.

      * 1 MIDI Referenzton of MS-404 to make C1 (MIDI code 36)
      * 2 P2 (Tune on the front panel) and P18 (VCO high end trim) in 
middle position.
      * 3 The VCO with a P17-Scale initially grossly einjustieren so 
that the game on the MIDI keyboard connected Oktavsprünge on MS-404 
really played (at the keyboard Oktavsprünge have a frequency doubling 
effect of VCOs).
      * 4 Press F3 (F 2 1 / 2 octaves above the reference C). VCO 
frequency with P16 (VCO offset) to 174.6Hz einjustieren.
      * 5 F1 key press (F above the reference C). VCO frequency with P17 
(VCO Scale) to 43.6 Hz einjustieren.
      * 6 Steps 4 And 6 Repeat until the frequency values stable.
      * 7 Press F5 (F 4 1 / 2 octaves above the reference C). VCO 
frequency with P18 (VCO High End trim) to 698.4 Hz einjustieren.
      * 8 Steps 4 To 7 Repeat again and possibly nachjustieren.

The VCO offset trimpot P16 is the absolute pitch einjustiert situation 
so that middle position of P2 (Tune) and the receipt of the reference 
tone (tiefstmöglicher sound) a VCO frequency of about 32 Hz resulted. 
32703 Hz in accordance with the pitch of a "C" with MIDI code 24 
(decimal). At the customer's request, the VCO also tuned an octave 
higher, (65406 Hz = "C", with MIDI code 36). Since the MS-404 probably 
bass in the area frequently used, but should be enough reserve to 
bottom, and therefore the standard adjustment to MIDI code 24th
---

With these instructions I should be able to tune the MS404 if someone 
can tell me which trimmer is which on the circuit board.  I have 
uploaded a photo of it here:

http://www.rolamtech.com/synths/ms404_board.jpg

Regards,

Giles

On Feb 14, 2008 12:29 AM, Giles Ward <giles@rolamtech.com> wrote:
>
> I think it's an early version, it has the pots mounted on the
> front panel then wired up to the main board which sits at the back of
> the case.

I guess you're right on that - the IC in the upper left corner is
marked "MS-404 Beta Version" by hand.

> Hi folks,
>
> Some time ago I bought an MS404 on Ebay Germany and was surprised when
> it turned up as it looks a little different to the ones I'd seen in
> pictures. I think it's an early version, it has the pots mounted on the
> front panel then wired up to the main board which sits at the back of
> the case.
>
> The circuit board is dark brown and has no printed markings, making it
> difficult to identify the trimmers.

That's definitely a prototype (probably the very first one from 1993)
because in the production series all potentiometers were pcb mounted. Even
the later prototypes had pcb mounted potentiometers. It will be a problem to
identify the trimming potentiometers as the positions and values may have
been changed compared to the final version that is described in the service
manual. I'm sorry but we have no records of this prototype as it's about 15
years ago (the MS-404 has been developed in 1993).

Best wishes
Dieter Doepfer

Hi

as far as I know this is only the first half of the setting: there is a 
width setting for the CV coming from the DA-Converter too.

Florian

> That's definitely a prototype (probably the very first one from 1993)
> because in the production series all potentiometers were pcb mounted. Even
> the later prototypes had pcb mounted potentiometers. It will be a problem to
> identify the trimming potentiometers as the positions and values may have
> been changed compared to the final version that is described in the service
> manual. I'm sorry but we have no records of this prototype as it's about 15
> years ago (the MS-404 has been developed in 1993).

Well, I suppose that makes it a collectable!  I've just had another 
fiddle with it and noticed the screw trimmer accessed through the hole 
in the back of the case, the MIDI to CV scaling I believe, and this has 
let me fix it.  I don't think I've got it set exactly right but at least 
it is not playing 13 semitones to the octave now!

Giles

> as far as I know this is only the first half of the setting: there is a
> width setting for the CV coming from the DA-Converter too.

Thanks Florian, I should have stated in my other post this made me take 
a closer look at it.