[sdiy] bass pedals? How low is too low?

[Gene Stopp]

Yup good VCO for this purpose.

Don't forget everybody that the real name of the ASM-1 VCO is the "Terry
Michael's VCO" from Electronotes circa 1976. Just a periodic reminder so I
don't go down in history as the originator. :)

For bass pedals I would probably advise the digital scanner route, so the CV
comes out of a DAC. For long sustaining bass tones it would be important to
be drift-free after all pedals are let up, since low frequency notes
(especially throbbing air-moving notes) kind of establish a "beat". Bass
notes should be exactly in tune at all times or else you kind of look around
and think "something is wrong but I can't put my finger on it".

A resistor divider plus S/H will drift over time, but a DAC will be
drift-free. One of the Electronotes scanner designs is really simple - when
a note is depressed, the scanning stops and the DAC gets latched. When the
note is let up, the scanning starts again. This design is less favorable for
"normal" hand-played keyboards since it is a time rule (first down) rather
than a position rule (low priority or high priority) i.e. you can't do
trills. Bad for fingers, maybe OK for feet?


- Gene


-----Original Message-----
From: Oren Leavitt [mailto:oleavitt at ix.netcom.com]
Sent: Tuesday, June 24, 2003 1:09 PM
To: MED; synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] bass pedals? How low is too low?


Hi MED,

Regarding the VCO:
The ASM-1 VCO can go well below 1Hz on the bottom end and should have very
good 1V/Oct tracking over the entire audible frequency range, if you build
and calibrate it carefully.
The ASM-1 VCO can go from LFO to ultrasonic with a single control voltage
sweep using the existing timing capacitor as is.
It can be optimized for low frequency use by using a slightly bigger
capacitor (but not to much bigger as it may not discharge fully due to the
'on' resistance of the JFET and the short duration of the reset pulse from
the LM311).

Controller:
Your two-octave pedal should output 0 -> 2 volts in linear 1/12 volt steps.
This output can then be transposed to whatever desired range.

Electronotes and Barry Klein's 'Electronic Music Circuits' book had some
designs for resistor divider based controller interfaces that provide a CV,
gate & trigger output from a single bus keyboard.
Other options would be MIDI or a PIC microcontroller based keyboard scanner.
There have been many threads on this stuff in the past - Search the SynthDIY
archives for many more ideas...

HTH,
Oren


-------Original Message-------
From: MED <teenagewasteland at prodigy.net>
Sent: 06/23/03 08:26 PM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] bass pedals? How low is too low?

> 
> Hey group, I've got tons of newbie questions about a possible future
project:
I'm thinking of hacking the two-octave bass pedals off of my organ and
building a stand-alone Taurus-style device. What kind of input
voltage/resistor ladder should I use to get a 1v/oct response?
Also, I am wondering where the bass range of a VCO stops and a LFO begins.
Obviously a reference I could use is the E1 of a bass guitar, and simply
go
to the C that is lower than that. But I *really* like low-frequency bass.
(but not in the range of "can't even hear it but it still sends you
reeling")
So what note should I decide upon as the threshold of hearing? A0? C0?
That's around the 20hz limit... Would, for instance, the ASM-1 oscillator
remain 1v/oct in that area, while still leaving me the option to switch
the
oscillator as high as, say, C5 or C6? I assume that I would need a fairly
large charging capacitor. What other things would I have to change/should
I
look out for?
(i can imagine this being a pain to tune at such low frequencies.)

In addition to that, what's the lowest note that I could consistently send
through an amplifier and speaker cabinet (possibly also home-built if need
be) at a volume that is audible (and at the best concert-acceptable) and
not
completely destroy them due to it looking like DC?
Obviously this is different for tube amps and the various solid-state
amps.
Maybe i'll have to do separate amplifiers for the different frequency
ranges. But that comes after I've already got this stuff all figured out.

-MED, who keeps thinking up questions, but it'll wait until after this
gets
sorted out...


>