Hi Martin,

The SSM2164 is made by Analogue Devices:

http://www.analog.com/UploadedFiles/Data_Sheets/15183786ssm2164.pdf

which with the right know-how can be turned into a 4-pole 24dB
filter, or from what Allen Heath have at their website for thr VF-1,
2 x 2-pole state-variable filters (so basically 12dB each), which
thus give low-, high- and band-pass, and which if run one after the
other gives 24dB (hence the 'mono' switch on the back).

I suspect a lot of the quality of the sound comes from the
overdrive/clipping introduced by the valve input section, but that's
only a guess - the total sound will depend on both chip and valves,
but how much it would change, say, if the valves were replaced by
transistors would probably be difficult to guess without trying it!

Tim

> I´ve asked Allen & Heath tech support what chips they used for the

VF-!

> analogue valve stereo-filter. I didn´t get much wiser from the

answer

> though.
> Maybe some one here knows about the chip SSM2164
>
> (As you will see this is cuts from 2 different e-mails)
>
> >>>The active circuitry in the VF-1 is based on the SSM2163 Quad

VCA IC in

> an analogue filter configuration, supported by standard TL072 op-

amps

> and of course a pair of ECC82 valves.
> >Thanks for your reply. Please note the typo in my last reply and

the fact

> >that it is the SSM2164, not 2163 IC that is the active VCA.>>>
>
> I´m curious, cuz I really love the sound of this machine, and I

wonder how

> much of this amusement is due the valve/overdrive section...
>
>
> >
>