Doepfer

Hi all,

I've just aquired an A-126 Frequency Shifter and on power-up I notice 
that it self oscillates. Is this normal ? 

I noticed in the archives that another person has experienced this 
behaviour but I was wondering if this is a feature of all A-126 units 
or if mine is defective in some way ?

Any comments appreciated.

Cheers

Simon

> I've just aquired an A-126 Frequency Shifter and on power-up I notice
> that it self oscillates. Is this normal ?
>
> I noticed in the archives that another person has experienced this
> behaviour but I was wondering if this is a feature of all A-126 units
> or if mine is defective in some way ?

All A-126 have a small feedthrough coming from the internal sine/cosine VCO.
If it is in the -50dB range (or better) compared to the full level signal
there is no defective. The A-126 has no built in squelch circuit that turns
off the output if no signal appears at it's input. A suitable squelch
circuit is described in the A-114 manual on page 4 (envelope follower +
VCA).

If the feedthough is more than ~ -50dB probably a re-adjustment of the A-126
will help. We have a pdf file available that describes the adjustment of the
A-126. It is essential that the A-126 is operated with a +12.0/-12.0V power
supply (like the A-100 PSU1 or PSU2) as the supply voltage affects the
adjustment and the sine feedthrough. The A-126 are adjusted in the factory
with a +12.00/-12.00V A-100 power supply. If another power supply is used
that outputs not exactly +12.0/-12.0V (e.g. +12.1V/-11.9V) the A-126 has to
be re-adjusted in any case.

Best wishes
Dieter Doepfer