Doepfer

Hello,

I'm facing some issue with module A138e, in the three way crossfader mode.

The patching :

I have in the A138e an S&H output (input A), an LFO square wave output (input B) and a QRV A149-1 output (input C).

This is modulating a VCO.

If the potentiometer is fully ccw, I should get only the effect of the S&H, BUT somehow the S&H is affected by the LFO.

The LFO itself doesn't seem to be affected by the S&H or the QRV.

The QRV is also not affected by the other modulations.

I tried on different inputs of the 138e and same thing occurs.

If I plug only two modulation sources, like the S&H and LFO, it works fine.

With audio sources, at high volumes, I have some leakage also, like for example with high resonance values from 106-1 or 101-6 I can hear it on B when its in the A input. But this I can understand better and get the volume down.

Where it gets weird (back to the CV sources problem) is that if I unplug everything and re-patch, slowly, putting first input A, then input C, then having the module to work as a two-way crossfader and ONLY THEN add the input B, it works fine !

Just curious if there is any explanation to that or if the module is just not working properly (still under guarantee).

A

Hello,

I'm sorry about the problems with the module. I assume that the bleed is in
the range -40dB (i.e. about 1/100 of the signal). The phenomenon is related
to the output impedances of the CV sources (S&H, LFO, Random). The A-138e
circuit is working 100% perfect only with sources that have zero output
impedance. But virtually all A-100 modules have a protection resistor (typ.
1k) in the output which protects the output against short circuits (e.g. if
two outputs are patched together by mistake). In case of the A-138e this
leads to a small bleed. I see two workarounds to solve the problem: shorten
the protection resistors of the modules (but then the outputs are no longer
protected against mis-patching) or use buffers with zero output impedance
(e.g. A-180-3 or the planned quad buffer A-180-4).

Best regards
Dieter Doepfer

> -----Ursprüngliche Nachricht-----
> Von: Doepfer_a100@yahoogroups.com [mailto:Doepfer_a100@yahoogroups.com]
> Gesendet: Mittwoch, 29. August 2018 08:43
> An: Doepfer_a100@yahoogroups.com
> Betreff: [Doepfer_a100] A138e - patching and leaking
>
> Hello,
>
> I'm facing some issue with module A138e, in the three way crossfader mode.
>
> The patching :
>
> I have in the A138e an S&H output (input A), an LFO square wave
> output (input B) and a QRV A149-1 output (input C).
> This is modulating a VCO.
> If the potentiometer is fully ccw, I should get only the effect
> of the S&H, BUT somehow the S&H is affected by the LFO.
> The LFO itself doesn't seem to be affected by the S&H or the QRV.
> The QRV is also not affected by the other modulations.
> I tried on different inputs of the 138e and same thing occurs.
> If I plug only two modulation sources, like the S&H and LFO, it
> works fine.
> With audio sources, at high volumes, I have some leakage also,
> like for example with high resonance values from 106-1 or 101-6 I
> can hear it on B when its in the A input. But this I can
> understand better and get the volume down.
> Where it gets weird (back to the CV sources problem) is that if I
> unplug everything and re-patch, slowly, putting first input A,
> then input C, then having the module to work as a two-way
> crossfader and ONLY THEN add the input B, it works fine !
>
> Just curious if there is any explanation to that or if the module
> is just not working properly (still under guarantee).
>
> A
> 
>
> Posted by: 2494axe@gmail.com

If you own another buffer module you may try it out if it helps. It will
still take some time until the A-180-4 is available.

Best wishes
Dieter Doepfer

> -----Ursprüngliche Nachricht-----
> Von: Doepfer_a100@yahoogroups.com [mailto:Doepfer_a100@yahoogroups.com]
> Gesendet: Donnerstag, 30. August 2018 17:05
> An: Doepfer_a100@yahoogroups.com
> Betreff: Re: AW: [Doepfer_a100] A138e - patching and leaking
>
>
> Hello Dieter,
>
> Thank you very much for yr fast and precise answer. Its always
> appreciable.
> I understand yr explanation and am looking forward the upcoming A180-4.
>
> Best regards.
>
> Alexandre
>