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<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial>Hi Busby,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial>Here's my advice:</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial>1) Learn how to read the datasheet. It's chock
full of useful info.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial>2) The 2164 is a current amplifier. It takes a current
input (the input pin is a virtual ground -- if you don't know what that is, then
you have no business doing electronics, so quit now) and amplifies it to a
current output. The gain factor is a function of the voltage at the VC
pin. 0V is unity gain (current out equals current in). The current
approximately doubles for each 200mV decrease at the VC pin (negative
control voltages give high gains, positive voltages give low
gains).</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial>3) The rating of the 2164 is about -100dB full scale.
This is five decades (20dB/decade -- again, if you are confused about dB and
decades, it might be best if you took up another hobby). The datasheet
says that the gain factor is -33mV/dB, which is -200mV/6dB which is
-200mV/octave (an octave means a doubling of the current). That means that
the minimum gain of the device is reached when the VC voltage is about 3300mV,
or 3.3V. Hence, a control voltage of 3.3V more or less completely turns
off the VCA. The maximum useful gain of the 2164 (where it just starts to
distort) is about +20dB (about one decade of gain), which is reached at a VC
voltage of about -660mV. In general, I try to avoid using the 2164 at
gains higher than unity. Hence, the useful VC control voltage range of
2164 is roughly -3.3V to +0.7V.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial>4) The 2164 VCA must terminate at virtual ground. That
is why all the circuits you see have the 2164 feeding into the negative input of
an opamp (and that opamp better have some negative feedback). If a 2164 is
not fed to virtual ground, it goes absolutely apeshit (I know this from bitter
experience). This is the single most inconvenient aspect of using
2164s. The only other thing they can be fed into is another 2164 VCA
(because the input is virtual ground). This quality of being able to stack
2164 VCAs in series can come in quite handy. However, be careful about
using 2164s in parallel, as they will not retain independent control (I
learned this the hard way as well).</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial>5) The maximum current you ever want to feed into a 2164
VCA is about 330uA. This is why the input resistor is always 30k,
because this will give 330uA at an input voltage of 10V. It can go higher,
but it will distort. Bottom line, just always use 30k resistors (or
higher) into the 2164 VCA.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial>6) Also note that the VC pin has an input impedance of
5k. This can complicate designs if you are not aware of it. If you
look at the schematic in the datasheet, it shows an internal 5k resistor to
ground at the VC pin. Take this into account if you are dividing voltages
into this pin.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial>7) Make absolutely sure that you have all the power and ground
pins connected to their respective power rails and ground before powering up the
2164, as failure to do so will fry the chip, guaranteed, particularly failure to
connect the negative rail.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial>I can't really think of anything else about 2164 at the
moment. It's a bloody useful chip, and has quite literally put my kids
through college.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial>Cheers,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=796453306-09032017><FONT color=#0000ff
size=2 face=Arial>Dr. Sketch-n-Etch</FONT></SPAN></DIV><BR>
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<FONT size=2 face=Tahoma><B>From:</B> Synth-diy
[mailto:synth-diy-bounces@synth-diy.org] <B>On Behalf Of </B>Busby
Bergson<BR><B>Sent:</B> Wednesday, March 08, 2017 10:20 PM<BR><B>To:</B>
synth-diy@synth-diy.org<BR><B>Subject:</B> [sdiy] the obscure output of a
2164<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV dir=ltr><SPAN style="FONT-SIZE: 12px">hi list-</SPAN>
<DIV style="FONT-SIZE: 12px"><BR>
<DIV>my eyes glaze over a bit with datasheets - and experts have better
advice, anyway :</DIV>
<DIV>i'm seeing a lot of designs with the output of a 2164 directly patched to
an op-amp....an inverting amplifier arrangement, with a feedback loop, usually
somewhere between 30k and 300k..... i have no idea how to calculate the gain
of this, though, because i'm unclear on exactly what's coming out of the
2164.. any pointers?</DIV>
<DIV><BR></DIV>
<DIV>-bb</DIV></DIV></DIV></BLOCKQUOTE></BODY></HTML>