That corp.'s "One Knob Squeezer"

[wayne kirkwood]

Here's a schematic of a 3PDT bypass suitable for the One Knob Squeezer:


Modified 3PDT Bypass.

The 3PDT Bypass configuration shown above doesn't bring the input signal directly over to a switch contact that is adjacent to the output to reduce input/output coupling capacitance.

I also leaned that the 4316 does not have the requirement for a low inductance op amp output for the Ec pins that the 2180, 2181 and 2162 VCAs do. Though it doesn't say it in the 4316 datasheet that a low output impedance vs. frequency is required, it does say that the Ec pins have an internal resistive 2:1 voltage divider.

On THAT's traditional VCAs, the Ec pins connect directly to the gain cell transistor bases and have a sensitivity to the source impedance driving them. The 4316 apparently does not use a true "Blackmer" gain cell. The Blackmer gain cell control constant is 6.1 mV/dB; the 4316's internal gain cell is scaled at ~3mV/dB and includes an internal voltage divider so the scale factor matches the 6.1 mV/dB of the RMS detector. The internal resistive dividers isolate the gain cell from the Ec pin.

Bottom line is that you can use TL072s for the Ec driver if you want to but only with the 4316, not the 2180, 2181 or 2162 dual VCA.

FWIW the MC33178 is a very low cost part in quantity and popular with wireless mic and belt pack manufacturers due to its low power and low voltage audio performance. Like many DIP-packaged products however it is going EOL in DIP but not SMT. I haven't gotten that EOL notice but I see from ON's website Rochester will be sourcing it in DIP. The 4316 however is available in SMT only and in commercial OEM products it's anticipated that the entire board would be surface mount. For DIY and prototyping THAT offers DIP adapters for the 4316.

[dfiction]

Wayne,

it's so cool that you shared your ideas here. i know this is an old thread, but i really benefitted from you sharing your thoughts and your process.

have you worked much with the THAT chip series besides this circuit?

best,
daniel