MOTM

Hello to the group!

I was looking at the 800 modification on Dave Bradley's web site
(www.hotrodmotm.com/800_mods.htm) and was thinking about the discussion
that took place about Paul's reluctance to include LED's because of the
noise introduced into the system.

My thought here was to place a transistor in series (emitter/collector)
with the LED (a 2N2222 would probably do). The base of the transistor
could be set high with a toggle switch to allow the LED to function
during trouble shooting, and the take the base low for playing,
eliminating the noise issue. The 470 ohm resistor is probably sufficient
for current limitation through the transistor.


               +15 -----\/\/\/------*    *-------|
                         10K      on \   off     |
                                      \          |
                                      *          |
                                      | B        |
    |--------|                      -----        |
    |        |            |---|>|---/   \--|     |
    |--|\    |            |   LED   C   E  |     |
      -| \   |     470    |          NPN   |     |
       |  >--|----\/\/\/--|--|\            |     |
      +| /                  -| \           |     |
-------|/                    |  >----------|     |
                            +| /                 |
                          |--|/                  |
                          |                      |
                          |----------------------|
                          |
                   grnd  ---
                          -


This would suit my style of studio work, as once the patch was
functioning correctly, the LED becomes unnecessary (except for those who
like watching the blinky lights). A circuit could even be devised to
allow one switch to perform this globally for all 800's in the system.

Note: this is an idea, NOT a tested circuit.

Any thoughts? Is this interesting or a total waste of time?

Scott

At 9:30 AM -0800 2002/02/28, Scott Evans, Gen Mgr wrote:
>Any thoughts? Is this interesting or a total waste of time?

Hi Scott, pleased to meet me.

Would it not be easier to just put a switch in series between the 470 
ohm resistor and the op amp that drives the circuit (the left most op 
amp in your drawing)?

>>>>
I was looking at the 800 modification on Dave Bradley's web site
(www.hotrodmotm.com/800_mods.htm) and was thinking about the 
discussion that took place about Paul's reluctance to include LED's 
because of the noise introduced into the system.
<<<<

Scott, fear not. The decision to exclude LEDs on envelope generators 
in the MOTM system was shortsighted and unnecessary, IMHO. It's 
absolutely necessary to have indicators in a system of any size to 
see what's going on. This goes doubly for the monster you are 
creating. I couldn't conceive of using envelopes in any modular 
system without an LED indicator to give a visual indication of the 
signal. I have added six to the Synth of Doom without problems. 
Others have done this mod as well, and there have been no issues 
reported so far.

LEDs are standard on MOTM LFO modules without any havoc being 
created. I say go for it. As always, you need to be sure that you 
don't overtax your power supply - allow 8 to 10 mA extra current draw 
for every added LED. If you are still squeemish, just modify one EG 
and try it for awhile. Betcha can't resist then!

Moe (gimme an LED) Bradley

Thanks for the replies. Comments in line.

--Scott Juskiw--
Would it not be easier to just put a switch in series between the 470
ohm resistor and the op amp that drives the circuit (the left most op
amp in your drawing)?

--Scott Evans--
Yes, but the transistor control would allow for one master switch to
turn off many 800's at a time. The transistor could be located on the
leg you mention, as well.

--Moe Bradley--
LEDs are standard on MOTM LFO modules without any havoc being 
created. I say go for it. As always, you need to be sure that you 
don't overtax your power supply - allow 8 to 10 mA extra current draw 
for every added LED.

--Scott Evans--
OK, I'm convinced.

--Moe Bradley--
Whoops, I've confused Scott Evans with Scott Juskiw, hence 
my "building a monster" remark was perhaps misaimed. Although I'm 
sure that you (Scott Evans) will build a monster too if given the 
chance.

--Scott Evans--
Heh, Heh, Heh.