Doepfer

i checked the MPU 101 and it's putting out solid 1 v/oct, i'll start at 1 volt and attempt adjustment of the octaves from there...where should i set the VCO high end trim when adjusting the octaves, and to what degree will it affect the octave adjustment? in other words, if the high end adjustment is out (and it is at this point), will it be impossible to adjust the octaves?

----- Original Message ----
From: "hardware@doepfer.de" <hardware@doepfer.de>
To: Doepfer_a100@yahoogroups.com
Sent: Thursday, January 10, 2008 3:24:31 AM
Subject: AW: [Doepfer_a100] A110 calibration help needed

> i have two A100 oscs that are at least ten years old i beilieve,
> and they aren't tracking correctly... i read over the info from
> here: http://www.doepfer. de/a110_tec. htm and i've attempted
> adjust the tracking, but i'm not doing to well...i understand
> what the basic idea is, but i'm not too sure on the best
> procedure... i've adjusted the tracking on two SCI Pro One synths
> before and got pretty close, but the SCI repair docs were more
> specific on the exact procedure...
>
> i'm using a Roland MPU 101 to provide cv, and i'm tuning by ear
> to a digital synth, single raw waveform, no modulation.. .i'm
> tuning to a lower octave, raising an octave and adjusting the vo
> scale and high trim and checking differnent octaves, etc, but i'm
> not getting the tracking any better..if anyone thinks they could
> give me some tips, i'd very much appreiciate the
> help...unfortunatel y there arn't any techs in my area (Chicaago,
> USA), so i'm kind of on my own here...
>
> thanks,
> rg

First of all you have to adjust the scale trimming potentiometer until the
scale is OK (independend of the absolute pitch). I'd recommend to apply
control voltages 0, +1.00, +2.00, +3.00 V ... to CV1 of the VCO and adjust
the scale trimming potentiometer until exact octave jumps appear. The
measuring instrument for that is the human ear. If the scale is adjusted the
offset trimming potentiometer is adjusted to the desired absolute pitch
(i.e. the pitch in the center position of the tune knob).
The CV could come e.g. from a correctly (!) adjusted CV source. Pay
attention that the CV source is not misadjusted (the MPU-101 in your case).
We had already users who tried to adjust the scale of the VCOs until they
discovered that the CV source (e.g. A-190, midi-to-cv interface, sequencer
...) was the reason for the wrong tracking. So first of all make sure that
the CV source is OK.

Best wishes
Dieter Doepfer




[Non-text portions of this message have been removed]

> i checked the MPU 101 and it's putting out solid 1 v/oct, i'll
> start at 1 volt and attempt adjustment of the octaves from
> there...where should i set the VCO high end trim when adjusting
> the octaves, and to what degree will it affect the octave
> adjustment? in other words, if the high end adjustment is out
> (and it is at this point), will it be impossible to adjust the octaves?

Please contact Matthias Marass (keyboards@doepfer.de). He is responsible for
the final adjustments of the A-110 and can give you some hints.

Best wishes
Dieter Doepfer

Hi Ross

> i checked the MPU 101 and it's putting out solid 1 v/oct, i'll start at 1 volt and attempt adjustment of the octaves from there...where should i set the VCO high end trim when adjusting the octaves, and to what degree will it affect the octave adjustment? in other words, if the high end adjustment is out (and it is at this point), will it be impossible to adjust the octaves?
This is my procedure as I tune VCOs (it is a bit different from the most 
descriptions because it attaches some value to the fact that the lowest 
note MUST read real 0 volts at the summing point of the VCOs CV-mixer). 
Here we go:


- Set from MPU101 that way, that it reads 0Volts; the MIDI note played 
for this I will call "lowest note".
- Connect the MPU101-CV with CV1 of A110.
- Set tune (front) to an extreme position (so it cannot move occasionally).
- Set VCO-Offset (trim pot P6) that way that Pin 2 of summing Opamp 1 
reads really exactly 0 Volts (setting the rotary octave switch may be 
required). After that try not to touch or move the front tune pot.
- Set P8 (high end trim) to center position

Now play 1/2/3 octaves up from this lowest note on your MIDI-keyboard 
and adjust P7 until the A110 playes these three octaves in tune. It does 
not matter which absolute note this is (must not be a C), but it must be 
clean octaves. Do not try to adjust more than 3 octaves!

Now remove the external CV from CV1, and use instead the rotary octave 
switch from the front for 1/2/3 octaves up. If the octave switch does 
not produce clean octaves, then adjust P5. Do NOT touch P7! Do not try 
to adjust more than 3 octaves!

After the octave switch is adjusted. Play 4 and 5 Octaves (or switch 
them with the octave switch) from the lowest note and if required adjust 
P8. Do neither touch P7 nor P5 for this.

For all these settings you may control at Pin 2 of summing Opamp 1 
whether your 1V/Octave is still true at this point. It is very 
recommended to monitor this - especially to check, whether your lowest 
note still are exact 0 Volts.

Finally:
If all this is done. Adjust P6 that way that the vco is tuned for the 
notes you are playing on your keyboard.

Florian