Nicholas,

I will have to look at the A-155 documents and compare it with a "real"
A-155 to find this out. So far we discovered no errors in the A-155 service
manual but maybe that's because they had no influence on the "normal" A-155
production and operation but possibly for circuit modifications. This might
be possible as the A-155 was designed many years ago with an old CAD
software that had no backward annotation between schematics and pc board
(i.e. one could modify the pc board without automatic readback to the
schematics).

As I'm very bus at the moment I ask for a bit patience. Maybe Matthias could
do this for me. Please contact me directly ( hardware@... ) if I will
forget to answer.

Best wishes
Dieter Doepfer

> -----Ursprüngliche Nachricht-----
> Von: Doepfer_a100@yahoogroups.com
> [mailto: Doepfer_a100@yahoogroups.com ]Im Auftrag von n keller
> Gesendet: Montag, 7. November 2005 06:21
> An: Doepfer_a100@yahoogroups.com
> Betreff: 1 RE: A-155 mod question
>
>
> Dieter,
>
> A while ago I asked you about the mod mentioned at the bottom of this

page,

> creating an insert to the A-155 GLIDE section for returning a

156-quantized,

> PRE-OUT signal. You said that such an insert should be placed between

Pin

> 8/TL064 --- and ---- Pin 4/CD4053. I asked Shawn ( US Rep ) to
> cross-check your instructions with the service manual since they did not
> seem to match my A-155 PCB. I think the service manual and therefore your
> advice might have been "backwards".
>
> According to Shawn, the service manual shows, as you said, Pin 8/TL064
> connecting to Pin4/CD4053, and Pins 3 and 5 of CD4053 connecting to the

S/H

> polarity jumper. My PCB has this "switch" and jumper the other way
> around....so Pin 8/TL064 connects to center pin of jumper, outer pins of
> jumper still connect to Pins 3 and 5 of CD4053, and Pin 4/CD4053 connects

to

> a cap and Pin 12/TL064. Phew.
>
> OK, so the mod should actually go between pin 8 of TL064 and the center

pin

> of S/H jumper, correct
>
> While you have the schematics at hand........ I also asked about adding a
> set of AC coupling caps and a switch for when I want to use A-155 as

graphic

> VCO. I've been trying to decide where to place them so that I can effect
> both PRE and POST outs with one cap per CV row. I could wire things

around

> Pin 8/TL064 to make it work, but can I put the caps between Pin7/TL064 and
> R3 so that both outputs are AC coupled
>
> I sincerely appreciate you time and your help. Thank you.
>
> Nicholas Keller
>
> =============================
>
> >From: "Dieter Doepfer" < hardware@... >
> >Reply-To: Doepfer_a100@yahoogroups.com
> >To: < Doepfer_a100@yahoogroups.com >
> >Subject: AW: 1 A-155 mod question
> >Date: Mon, 19 Sep 2005 12:53:37 +0200
> >
> >
> >
> > > -----Ursprüngliche Nachricht-----
> > > Von: Doepfer_a100@yahoogroups.com
> > > [mailto: Doepfer_a100@yahoogroups.com ]Im Auftrag von Nicholas Keller
> > > Gesendet: Sonntag, 18. September 2005 21:00
> > > An: Doepfer_a100@yahoogroups.com
> > > Betreff: 1 A-155 mod question
> > >
> > >
> > > I would like to add a send/return loop to the voltage rows of my A-155
> > > so I can run the signals to A-156 Quantizer before routing them back
> > > through the slew limiters inside A-155.
> > >
> > > Any ideas Dieter
> > >
> > > I know I could use the PRE-OUT as my send, so a single normalled
> > > socket interrupting the signal going to the slew limiter would be all
> > > I'd need to add...... but where exactly can I make this
> > > interruption Shouldn't it be between the center pin of J2
> > > (potentiometer board)....and where that trace branches off to C2 and
> > > IC3,pin12
> >
> >No. That's not the right point.
> >
> > > That seems correct to me, but all help is appreciated.
> >
> >No. You have to make the insert between pin 8 of the TL084 (output OpAmp
> >O3)
> >and pin 4 of the electronic switch (CD4053) that is used for the S&H
> >circuit. An of course an additional socket is required for the insert
> >function.
> >
> >Best wishes
> >Dieter Doepfer
> >
>
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