Doepfer

Hello list,

I am thinking about putting together a small A100 system in a portable case to use for 
sequencing/expansion for my ARP 2600. I have a few questions about the A-155:

-How "hot" are the trig/gate outputs on the A-155; does it put out the +10V required to 
trig the 2600's envelopes? Otherwise, does anyone know if there is some simple mod that 
could be done to the A-155 to make the trig/gate outs put out this voltage?

-I would also like to extend the cv range of the two sequencer rows to 0 - 10V to be able 
to, for example, open the 2600's filter or VCA from minimum to maximum. I suppose this 
could be done quite easily by amplifying the cv outs through an A-133 polarizer [?], but 
has anyone tried an internal mod to the A-155 to extend the cv range?

All help most appreciated! 

/Henrik Medquist

Hi Henrik,

On 6/25/07, longforparade <longforparade@yahoo.com> wrote:

>  -How "hot" are the trig/gate outputs on the A-155; does it put out the +10V required to
>  trig the 2600's envelopes?

My A-155 outputs about 9V on the gate/trigger outs. I wouldn't be
surprised if this turns out to be enough to trigger the ARP's
envelope.


>  -I would also like to extend the cv range of the two sequencer rows to 0 - 10V to be able
>  to, for example, open the 2600's filter or VCA from minimum to maximum. I suppose this
>  could be done quite easily by amplifying the cv outs through an A-133 polarizer [?], but
>  has anyone tried an internal mod to the A-155 to extend the cv range?

The lower row on my A-155 outputs 0-7V when the scale knob is turned
all the way up. I don't know if you'd gain much from modding it to
output the extra 3V. I think the idea is that you would normally use
the upper row for precision stuff like VCO's and the lower row for
things that require greater range, like filters. Without bothering to
unscrew my A-155 and try to figure out how I would assume that all you
need to change those ranges is to replace a couple of resistors. But
then, I wouldn't know if those ~7V is the output from the chip(s) that
control which step is active...

Also, if you don't mind me asking, your name could very well be Danish
(or maybe Swedish), so if by any chance you happen to be in or near
Copenhagen and would like to experiment with an A-155 before you buy I
wouldn't mind seeing an ARP 2600 in action so we could probably figure
out something. If I'm totally mistaken you can probably find somebody
within reasonable distance from where you do live that would make the
same kind of offer.

/Silas

Hello Silas!,

and thanks for your reply. Unfortunately I live in Stockholm, but I will see if I can find 
someone here with an A-155 to try it out. I will also make a test to see if 9V is enough to 
trigger the ARP gate. I think 0-7V of cv will be enough for most applications, but would 
prefer to have this range on both rows if it would be possible to change the 4V mode of 
the upper row to 7V, keeping the 1V and 2V modes for fine control of pitch. I suppose, 
like you suggested, this could be done quite easily by changing a resistor or two. Anyone 
who has tried this?

Best regards,
Henrik

--- In Doepfer_a100@yahoogroups.com, "Silas Johansen" <sijodk@...> wrote:
>
> Hi Henrik,
> 
> On 6/25/07, longforparade <longforparade@...> wrote:
> 
> >  -How "hot" are the trig/gate outputs on the A-155; does it put out the +10V 
required to
> >  trig the 2600's envelopes?
> 
> My A-155 outputs about 9V on the gate/trigger outs. I wouldn't be
> surprised if this turns out to be enough to trigger the ARP's
> envelope.
> 
> 
> >  -I would also like to extend the cv range of the two sequencer rows to 0 - 10V to be 
able
> >  to, for example, open the 2600's filter or VCA from minimum to maximum. I suppose 
this
> >  could be done quite easily by amplifying the cv outs through an A-133 polarizer [?], 
but

> >  has anyone tried an internal mod to the A-155 to extend the cv range?
> 
> The lower row on my A-155 outputs 0-7V when the scale knob is turned
> all the way up. I don't know if you'd gain much from modding it to
> output the extra 3V. I think the idea is that you would normally use
> the upper row for precision stuff like VCO's and the lower row for
> things that require greater range, like filters. Without bothering to
> unscrew my A-155 and try to figure out how I would assume that all you
> need to change those ranges is to replace a couple of resistors. But
> then, I wouldn't know if those ~7V is the output from the chip(s) that
> control which step is active...
> 
> Also, if you don't mind me asking, your name could very well be Danish
> (or maybe Swedish), so if by any chance you happen to be in or near
> Copenhagen and would like to experiment with an A-155 before you buy I
> wouldn't mind seeing an ARP 2600 in action so we could probably figure
> out something. If I'm totally mistaken you can probably find somebody
> within reasonable distance from where you do live that would make the
> same kind of offer.
> 
> /Silas
>

Hi Henrik,

I checked the schematics, and it looks like the range of the trigger 
voltage cannot be extended on the A-155, because there a CD4053 is used 
as switch, which can switch only 8 V as far as I know. But you might add 
a simple "pushup"-addon pcb. It requires one opamp (or two transistors) 
and three resistors per channel. Not too difficult of you are able to 
solder.
Similar for the Voltage: also here a CD4053 is used in the S&H stage. So 
the output voltage is limited. And again, a simple DC amplifier could do 
the jobe here (does not need to be precise, because you trim the real 
voltage with the pots anyway).

Florian

Florian,

the CD4051 and CD4053 in the A-155 are supplied with -5V (auxiliary voltage
VEE) and +12V (VDD). Consequently voltages in the range -5V...+12V can be
switched by these circuits.

Increasing the CV voltages can be realized easily by increasing the feedback
resistors in the OpAmp circuits (please refer to my other message).

Dieter

> -----Ursprungliche Nachricht-----
> Von: Doepfer_a100@yahoogroups.com
> [mailto:Doepfer_a100@yahoogroups.com]Im Auftrag von Florian Anwander
> Gesendet: Dienstag, 26. Juni 2007 01:18
> An: Doepfer_a100@yahoogroups.com
> Betreff: Re: [Doepfer_a100] Using A-155 with ARP 2600
>
>
> Hi Henrik,
>
> I checked the schematics, and it looks like the range of the trigger
> voltage cannot be extended on the A-155, because there a CD4053 is used
> as switch, which can switch only 8 V as far as I know. But you might add
> a simple "pushup"-addon pcb. It requires one opamp (or two transistors)
> and three resistors per channel. Not too difficult of you are able to
solder.

> Similar for the Voltage: also here a CD4053 is used in the S&H stage. So
> the output voltage is limited. And again, a simple DC amplifier could do
> the jobe here (does not need to be precise, because you trim the real
> voltage with the pots anyway).
>
> Florian
>
>
>
> Yahoo! Groups Links
>
>
>

> -How "hot" are the trig/gate outputs on the A-155; does it put out the
+10V required to
> trig the 2600's envelopes? Otherwise, does anyone know if there is some
simple mod that
> could be done to the A-155 to make the trig/gate outs put out this
voltage?

The gate and trigger voltages of the A-155 are about +9V and depend a bit
upon the load as there are passive voltage dividers at the outputs which
also work as protection against short circuits. If these voltage dividers
are bypassed a higher voltage can be obtained but in this case the outputs
are no longer protected ! I'd recommend to hold the serial 1k protection
resistors (R10,13,16,19) in any case for circuit protection. But the pull
down resistors (R11,14,17,20) can be removed to obtain a higher voltage. It
should be close to +10V if they are removed.

> -I would also like to extend the cv range of the two sequencer rows to 0 -
10V to be able
> to, for example, open the 2600's filter or VCA from minimum to maximum. I
suppose this
> could be done quite easily by amplifying the cv outs through an A-133
polarizer [?], but
> has anyone tried an internal mod to the A-155 to extend the cv range?

If you are experienced with electronics the A-133 is not necessary. Simply
increase the feedback resistors (sum of R4+P9) to obtain a higher output
voltage. But for the upper row in this case the exact 1/2/4V maximum output
voltage is no longer valid !

I can send you the silk screens of the A-155 pcbs for identification of the
parts in question (use hardware@doepfer.de).

Best wishes
Dieter Doepfer

on my grey 2600, 
the gate out of the a-155 to the gate in on the 2600 works.
the trig out of the a-155 to gate does does not.
put any of the 3 trig outs of the a155 into the A-162 dual trig delay and it
works. 
And this is via the gate in on the 2600, does not work on the trig in, at
least on my unit.
hope that helps.
best,
phil

Silas, Florian, Dieter, Phil - thanks for the replies to my questions about the A-155. I tried the 
inputs on my ARP2600 and found out that 8V is enough to trigger the ext gate input as well 
as the S/H clock input, so I will try an A-155, A-162 combination (I suppose the A-162 could 
also be changed for an A-142 to get cv controlled gate length?). I will also probably do the 
simple modification Dieter suggested to increase the range of the cv rows.

Best regards,
Henrik Medquist

> (I suppose the A-162 could 
> also be changed for an A-142 to get cv controlled gate length?). 

The A-162 is not voltage controlled !

Best wishes
Dieter Doepfer

--- In Doepfer_a100@yahoogroups.com, <hardware@...> wrote:
>
> > (I suppose the A-162 could 
> > also be changed for an A-142 to get cv controlled gate length?). 
> 
> The A-162 is not voltage controlled !
> 
> Best wishes
> Dieter Doepfer
>

Exactly, that is why I was thinking of an A-142 in its place :)

/Henrik

Hello Henrik,
I just tested the gate out of the A-142, it works also, so yes.
best,
phil

On 7/4/07 12:24 AM, "longforparade" <longforparade@yahoo.com> wrote:

> Silas, Florian, Dieter, Phil - thanks for the replies to my questions about
> the A-155. I tried the
> inputs on my ARP2600 and found out that 8V is enough to trigger the ext gate
> input as well 
> as the S/H clock input, so I will try an A-155, A-162 combination (I suppose
> the A-162 could 
> also be changed for an A-142 to get cv controlled gate length?). I will also
> probably do the 
> simple modification Dieter suggested to increase the range of the cv rows.
> 
> Best regards,
> Henrik Medquist