dbx 2159 Multi Vca for gssl

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Eje2005

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Joined
Apr 4, 2006
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58
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Sthlm SveaRike
Hi.

I have a bunch of Dbx 2159´s and i thought i might try them out in a gssl.

When paralleling these, do i need a input resistor? Is there a need for an buffer op-amp as in the 2002?

Thanks


// Jonas
 
Eje2005 said:
Hi.

I have a bunch of Dbx 2159´s and i thought i might try them out in a gssl.
The 2159 is lower quality than the 2155, which is an out-of-spec (in terms of control law and dynamic range) 2150. The 2155 was used in the multi-chip 202X, on the basis that it would need trimming anyway. Although the 2155 is guaranteed for noise and THD, it seems the 2159 could be somewhat inferior in that respect.
  When paralleling these, do i need a input resistor?
All 21xx chips have a current input, so the all need separate input resistors.
Is there a need for an buffer op-amp as in the 2002?
What buffer are you referring to?
 
Thanks!

In short of coffee i mixed it up. My chips are dbx2155´s, not 2159´s and come from a eela console.

The buffer i was wondering about was the CV buffer.
 
All 21xx VCA's are supposed to operate with 20k input resistors for a max level of +20dBu. That means a peak current of ca 0.55mA (11V into 20k), but in fact the 2155 does not have the same dynamic range as the 2151 and 2150 (ca. 3dB less). You may use a 30k resistor, but the circuit may become unstable; a solution is to add an RC circuit (20k + 1nF) on the input to ground, but it increases the noise. The only solution is to decrease the level.
In the 202X, they chose to have 8 10k resistors, one to each input. And the max level was +14dBu (5.5V into 10k). The input impedance was 10k/8 = 1.25k, so one had to use an additional resistor. The minimum value would be 1.25k, but in fact they recommended a higher value, because the 2155 does not have the same dynamic range as the 2151 and 2150.
 

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