Doepfer

Hi there, I've just been playing with my new a126 VC Frequency
Shifter, and I notice now that the initial rush of joy subsides that
the oscillator bleeds through to the output, quite loudly. Is this
normal, or can it be fixed with some recallibration, twiddling a few
potentiometers? A question for the great Dieter I guess...

--- In Doepfer_a100@yahoogroups.com, "partlydrone" <partlydrone@...>
wrote:
>
> Hi there, I've just been playing with my new a126 VC Frequency
> Shifter, and I notice now that the initial rush of joy subsides that
> the oscillator bleeds through to the output, quite loudly. Is this
> normal, or can it be fixed with some recallibration, twiddling a few
> potentiometers? A question for the great Dieter I guess...
>

yes, it is normal behaviour that the oscillator bleeds through,
you find that on all frequency shifters.

Not sure that's true.

Anyway, found the callibration instructions, will have a fun time with
these in the next week or so. Looks like it can be done without an
oscilloscope, which is good because mine is for some reason missing
its leads at the mo...

http://www.doepfer.de/service/A126_adjustment.pdf

--- In Doepfer_a100@yahoogroups.com, "selfoscillate"
<synaptic_music@...> wrote:

>
> --- In Doepfer_a100@yahoogroups.com, "partlydrone" <partlydrone@>
> wrote:
> >
> > Hi there, I've just been playing with my new a126 VC Frequency
> > Shifter, and I notice now that the initial rush of joy subsides that
> > the oscillator bleeds through to the output, quite loudly. Is this
> > normal, or can it be fixed with some recallibration, twiddling a few
> > potentiometers? A question for the great Dieter I guess...
> >
> 
> yes, it is normal behaviour that the oscillator bleeds through,
> you find that on all frequency shifters.
>

afaik all analogue frequency shifters, no matter which brand,
share the same problem. please somebody correct me if i'm wrong.
the modulator signal cannot be suppressed for 100%, there is
always a portion of the modulator signal intruding the shifted
output. with careful calibration this bleedthru can be minimized,
but not totally eliminated. some designs have a sort of automatic
noise gate (bode used the term "squelch"), which mutes the output
when the input signal level drops below a certain threshold,
consequently cutting out the bleedthru and other unwanted
artifacts during signal intermissions.
this trick can be done easily by using an a119, a vca and maybe
a slew limiter or envelope to get smoother transitions between
"on" and "off".

best wishes

ingo



--- In Doepfer_a100@yahoogroups.com, "partlydrone" <partlydrone@...>
wrote:

>
> Not sure that's true.
> 
> Anyway, found the callibration instructions, will have a fun time with
> these in the next week or so. Looks like it can be done without an
> oscilloscope, which is good because mine is for some reason missing
> its leads at the mo...
> 
> http://www.doepfer.de/service/A126_adjustment.pdf
> 
> --- In Doepfer_a100@yahoogroups.com, "selfoscillate"
> <synaptic_music@> wrote:
> >
> > --- In Doepfer_a100@yahoogroups.com, "partlydrone" <partlydrone@>
> > wrote:
> > >
> > > Hi there, I've just been playing with my new a126 VC Frequency
> > > Shifter, and I notice now that the initial rush of joy subsides that
> > > the oscillator bleeds through to the output, quite loudly. Is this
> > > normal, or can it be fixed with some recallibration, twiddling a few
> > > potentiometers? A question for the great Dieter I guess...
> > >
> > 
> > yes, it is normal behaviour that the oscillator bleeds through,
> > you find that on all frequency shifters.
> >
>

> Hi there, I've just been playing with my new a126 VC Frequency
> Shifter, and I notice now that the initial rush of joy subsides that
> the oscillator bleeds through to the output, quite loudly. Is this
> normal, or can it be fixed with some recallibration, twiddling a few
> potentiometers? A question for the great Dieter I guess...

The frequency shifter uses two internal ring modulators that usually have a
feedthrough in the -50dB range (in relation to the max. audio signal). If
it's more it can be adjusted as described in the internal service document.
I'll send the document as an pdf attachment to your email address.

To obtain a complete suppression of the carrier signal a squelch circuit
should be patched like shown in the A-114 manual (page 4).

Best wishes
Dieter Doepfer


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

> afaik all analogue frequency shifters, no matter which brand,
> share the same problem. please somebody correct me if i'm wrong.
> the modulator signal cannot be suppressed for 100%, there is
> always a portion of the modulator signal intruding the shifted
> output. with careful calibration this bleedthru can be minimized,
> but not totally eliminated. some designs have a sort of automatic
> noise gate (bode used the term "squelch"), which mutes the output
> when the input signal level drops below a certain threshold,
> consequently cutting out the bleedthru and other unwanted
> artifacts during signal intermissions.
> this trick can be done easily by using an a119, a vca and maybe
> a slew limiter or envelope to get smoother transitions between
> "on" and "off".
>
> best wishes
>
> ingo

You are right. No matter which multipliers are used in the ring modulators
(e.g. MC1496, AD633, AD534 ...) there is always some feedthrough of the
carrier signal. Only the squelch circuit you mentioned will cancel the
feedthrough. After all it's the question if such a sqelch circuit has to be
an integral part of a ring modulator or frequency shifter or not.

Best wishes
Dieter Doepfer