[sdiy] DBX202 VCA questions

[Tristan]

Hi Cheater,

I have the 1975 schematics and specifications here for the original
202 module and it consists of 8 bipolar transistors, a FET and some
other passive components. The 202XL may well have these stacked in
parallel as this and the 202X integrated the discrete circuit design
into a single piece of silicon. If you would like a copy of the
documentation please let me know :)

-- 
Best regards,
Tristan                            mailto:tu at alphalink.com.au



Monday, September 14, 2009, 1:08:45 AM, you wrote:

cc> Hi guys,
cc> I have been reading up on VCAs a little bit and found some more info
cc> about the Harrison 4032 burried in Google results. It turns out that
cc> they use the DBX202 VCA for the channel level. Researching a bit about
cc> this, the gyraf.dk page says this about the 202:

cc> http://www.gyraf.dk/gy_pd/ssl/ssl.htm

cc> "The DBX 202XT VCA can be very hard to get these days, so I designed a
cc> substitution circuit based on the THAT2180/2181 type VCA - a recent
cc> version of the DBX2150 that SSL also uses for their channel
cc> compressors. This substitute circuit is based on reverse-engeineering
cc> a 202XT VCA - it turned out to consist of ten paralleled 2150's with a
cc> common low-impedance buffer for the control inputs."

cc> Now... why would they ever do that? DBX weren't just throwing in more
cc> because they *could* were they?

cc> One of my theories is that ten VCAs can deliver a higher output
cc> current than one - and therefore, if the input impedance of what comes
cc> after the VCA bank is not high enough to be 'ideal' (and that's always
cc> the case), then the better current performance would give the VCA bank
cc> more 'strength' to move what they're being fed into. This is a purely
cc> uneducated guess.

cc> What do you guys think?

cc> Cheers
cc> D.
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