[sdiy] New to sdiy but w/ some knowledge

[Ben Bradley]

Hi Bartek!

> Are there any no-brainer/commonly used parts and ICs used particularly in
> audio modules and which I should buy in larger quantities? For example, in
> university I got along with HC14/AC14, BC547/557, 555, µA741, LM358, LM385
> and TL431.

   Out of those, discrete bipolar NPN and PNP bipolar transistors and
op-amps seem to be the most common thing I've been using, along with
signal diodes such as 1N4148. The most common op-amps discussed seems
to be TL071/TL072/TL0714 as they have FET inputs and thus very high
input impedance. Comparators are good to have, as well as
transmission-gate switches, CMPS parts 4016 and 4066, but they have
limitation such as max 15V supply (often powered as +7.5 and -7.5V
relative to ground). More recent, more expensive but better performing
DGxxx series (such as DG401) will run on the full +/- 15V supply that
most op-amps run on.

   There are some more specialized chips such as the LM13700 you'd
likely use for VCFs and VCAs. It's basically the modern replacement
for the now-obsolete but often-used CA3080 and CA3280 that you're sure
to see in older schematics.

   But for many devices, it's better to know what you want to make and
have a schematic in front of you, and then order the parts you need to
make it.

> I was taught that structures like Eccles-Jordan circuits are archaic and we
> shouldn't use them, but is this also relevant in analog synthesis? Any other
> examples?

   The name rung a bell (I probably saw those names in college circa
late 1970s), but I had to look it up to see that it's basically a
flip-flop. Wikipedia discusses a patent from those two, dating to
early use of vacuum tubes.

   In my observation, if it does what you want, you should use it.
Perhaps the most venerated and honored voltage-controlled filter
design is one of the first, if not THE first design from the 1960s.
Look for the ladder filter schematic on a patent and on at least one
arm (human appendage, not 32-bit processor).

> I can't find any good materials explaining typical audio voltage levels? I'm
> talking about line level. instrument level, signal from microphone/electric
> guitar, and most importantly CV and voltages used in modular synthesizers.

   In general, "audio voltage level" can be all over the place. I
won't say there's no standard, because that's not true - there are
many standards! Take for instance line level. Do you mean African or
European swallow? Er, I mean, do you mean pro equipment line level, or
consumer equipment line level? Even with consumer equipment, the
output level of CD players was significantly higher than that of
previous consumer stereo audio equipment.

   Line level usually means level of the"average" signal in normal
operation, but there's also a maximum level where something starts to
clip, and the difference between the two is headroom, etc.

   Then there's the actual numbers, in volts average, volts RMS, volts
peak, volts peak-to-peak ... then the dB measurements with a suffix
saying relative to what, such as dBm, dBv, dBV and a few others such
as dBSPL for actual sound level. We haven't even mentioned impedance,
which varies greatly between different devices. Most modern
microphones are balanced and low impedance, whereas virtually all
electric guitars are unbalanced and high impedance.

   This site describes those and more - especially look up all the dB
definitions and line level:

http://lossenderosstudio.com/glossary.php

> I'm assigned to make a linear power supply, and I don't have any specific
> parameters specified. Could you suggest what voltage level and power it
> should probably give so I could use this in future synth/audio projects?

   Eurorack uses +/-12V (I've always wondered why, it unnecessarily
limits the peak voltage compared to +/-15V), but most everything else
uses the "standard" voltage most op-amp manufacturers use on their
datasheets for normal operation, +/-15V. The most recent power supply
I made uses the dual-secondary transformers that are common now (for
many decades transformers for +/- supplies used a center-tapped
secondary, but the two identical secondary windings are more
versatile). I used it to make two separate, identical 15V supplies
using LM317 regulators. They come out to banana jacks and I can use
them independently, but they're usually used with the + of one tied to
the - of the other to generate +/- 15V. I scaled the transformer and
such for a 1 amp output, which seems reasonable for me.

   If you use any sort of microprocessor or microcontroller, it will
run at +5V or +3.3V. If the current pull is low, you could run a 5V
linear regulator off the +15V line, but for higher current it would
get hot and waste a lot of power, so you'd need a separate +5V supply.

> Are there any good wikis/sites/forums for people like me? It was really
> tough for me to find anything except this mailing list
> Is there anything else I should probably know?

   I think others listed all the usual suspects. The late Ray Wilson
who operated the "Music From Outer Space" site also wrote a book,
"Make: Analog Synthesizers." I haven't looked through it myself, but
from seeing his website and a few of his videos, I'm sure it's good.