[sdiy] SSM2164 Phaser - another way?

[Mattias Rickardsson]

On 20 February 2014 16:13, Tom Wiltshire <tom at electricdruid.net> wrote:
> On 20 Feb 2014, at 13:29, Neil Johnson <neil.johnson71 at gmail.com> wrote:
>
>> Just a wild thought: professional audio typically runs at +4dBu
>> nominal.  So to keep the 2164 in its optimal input range at 0dB gain
>> (normal operating point) we would need to scale that 30k by 4dB.
>> Which works out rather conveniently to 47k.
>
> I don't understand the implications of what you're saying here, Neil. Can you explain a bit further?
> Are you suggesting that there's situations in which we should be using 47K on the input? on the I-to-V?

Definitely - higher resistors for higher input voltages and vice
versa, in order to keep the input current at a well chosen magnitude.
The input current is the signal that the VCA gets. Just like an
ordinary OP-amp, the VCA doesn't know what voltage is connected to the
other end of some external resistor, it only knows what current comes
through it.

30k input resistor is good for the nominal input level of 0.775 V rms
(which I guess equals 1.1 V peak), with good performance and 22 dB
headroom to the clip point. In other words, the VCA clips if you
connect around 13-14 V to that 30k resistor. I guess. :-) Last week I
happened to get clipping somewhere around 6 V with 15k resistors, and
it wasn't beautiful! The peaks kind of folded down in another fashion
than OP-amps react...

/mr