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Messages - wayne kirkwood

#1
Thanks for the link to the post.

Let me clear up this bit of confusion...
QuoteA bit concerned that it's a 5V chip.
QuoteProbably because 5v is more than sufficient for its stated purposes, none of which are guitar pickups.


The 5V maximum supply voltage of the 4316 doesn't limit it's overload or operating capability to <5V because the VCA inputs/outputs and RMS detector input are currents, not voltages. (V-I by virtue of R10 and R20, and I-V by R12 and Op Amp D.)

The resistors which convert the input and output currents to voltages can be scaled upward in value for use at elevated levels which exceed the 5V supply of the 4316. (THAT have an application note here which applies to the 218X-series but the current-in/current out aspects are the same. http://www.thatcorp.com/datashts/dn123.pdf)

The RMS detector output is not constrained by supply voltage since it scales at ~6mV/dB or ~120mV/20dB around a mid-supply value of +2.5V.

With input/output resistors scaled properly and a supply voltage to support the final output stage I-V converter's signal swing, the part can be used at pro levels of +21 dBu or more.

I do realize that most people might prefer a higher input impedance (or full bypass). Those that do need a higher input Z can scale R1 and R2. R1 could easily be 10M; R2's maximum value is limited by the MC33178's bias current.

For someone not wanting to use a variable gain output stage (Op Amp B) there is a trick that can be used to center bias Op Amp D, the VCA I-V converter, from 2.5V to 4.5V. A resistor from the inverting input of Op Amp D (also the 4316 pin 13) can be taken to ground to give the stage additional DC gain. This shifts the bias center point from 2.5V typically to 4.5V. It increases the noise gain of Op Amp D slightly and burns some current but its a useful trick.

Wayne