Adding more LEDs on a Neutron envelope detector.

[SaBer]

I built a Neutron with the filter and the envelope detector in seperate enclosures, so that I could use the envelope detector with two (or more) effects the same time. (I also added a couple of extra controls.)

So, the thing I would like to do, is to add more LEDs to it. Actually I would like to have an other "output" for it and an indicator led to be able to set the controls without having the effect on.
I tried a couple of things but all I got was burnt leds...  :roll:

Anybody got ideas how to do it (simply)?

[smoguzbenjamin]

You put the LEDs in parallel. Make sure that the LEDs are almost identical though, because otherwise one will light up and the other will be kind of dim.

[mikeb]

I'm not sure I understand completely what you are trying to do, but you can connect as many of these...

... as you like to the output of the envelope detection circuit to drive LEDs (and the single LED could be replaced by multiple LEDs, just adjust Rcurrent as appropriate).

Mike

[SaBer]

You put the LEDs in parallel. Make sure that the LEDs are almost identical though, because otherwise one will light up and the other will be kind of dim.

I know you can put them in parallel, but the problem is I don't want to use identical LEDs. The ugly yellow ones worked best with the LDRs, but I would rather have a red one as an indicator, and, in the future it will be hard to find identical leds.

[SaBer]

I'm not sure I understand completely what you are trying to do, but you can connect as many of these...

... as you like to the output of the envelope detection circuit to drive LEDs (and the single LED could be replaced by multiple LEDs, just adjust Rcurrent as appropriate).

Mike

Yeah, I figured you could use something like that, but the problem with the Neutron follower is that the LED isn't connected to ground, and I can't figure out how to wire something like that...

[SaBer]

Here's the schem from geofex


Maybe Mike's suggestion would work after all... I never really understood the last stage completely...

[puretube]

...series...

[Mike Burgundy]

series would allow one LED with a high threshold to hold all the rest back. This could work, but requires the opamp to come up with ample voltage to get past ALL voltage drops.
Hooking everything up in parallel will also work (the opamp will force the "correct" voltage), using different LEDs will result in different envelopes.
This will require the opamp to supply ample current to feed all LEDs.
The suggested buffer schem should work just fine, just hook it up to the output of the driver opamp - exactly *at the output of A6*. So between it's output and the LED's anode. This would also allow you to hook up a jack to the driver opamp output, and have the other pedals carry their own buffer. If you have these pedals have both an "envelope IN" jack and a "thru" jack (just parallel all connections for both jacks) you can daisy chain as many as you want.

[R.G.]

The simplest thing to do is to use another opamp with its inputs parallel to A6's. That means it will take its cues from the same input voltages, but will make a totally separate LED behave.

To do this, duplicate A6, the two 120K resistors, LED and current setting resistor. Then connect the new (+) input in parallel with A6's (+) input, the 120K to the new (-) input where A6's 120K attaches. Do NOT parallel the new opamps's (-) input to A6's. This means the two opamps are computing the same thing in parallel. The existing A6 runs the filter, and the new one does a parallel job with whatever is on its output.

LEDs in series work if
(a) their light/ma outputs are usable at the same currents
(b) you don't run out of power supply room to run the LEDs, which get up to about 4V for the LEDs alone.

[SaBer]

Hooking everything up in parallel will also work (the opamp will force the "correct" voltage), using different LEDs will result in different envelopes.

Well, the "different envelope" of one of the LEDs, is not much an envelope at all. That's actually what I did very first, and had problems finding what was wrong with it. One of the LEDs was "enveloping" so dimly I could barely notice it.

I'll have to try that buffer thing when I have the time...

[SaBer]

The simplest thing to do is to use another opamp with its inputs parallel to A6's. That means it will take its cues from the same input voltages, but will make a totally separate LED behave.

To do this, duplicate A6, the two 120K resistors, LED and current setting resistor. Then connect the new (+) input in parallel with A6's (+) input, the 120K to the new (-) input where A6's 120K attaches. Do NOT parallel the new opamps's (-) input to A6's. This means the two opamps are computing the same thing in parallel. The existing A6 runs the filter, and the new one does a parallel job with whatever is on its output.

Well, at the moment I have a pot wired as the current scaling resistor. So doing that would add another pot. Or then I could have that control on only one of the "outputs"....   :?

The current scaling resistor seems to be the problematic part in all designs...

At the moment I have the following controls on the envelope detector: gain, attack, decay, sensitivity (current scaling resistor) and direction.

Playing with the gain and sensitivity gives you some more freedom, but i think I'll have to compromise if I'll want to have multiple LEDs.

[mikeb]

Well, if you are going to use any more opamps then you might as well add a bit more functionality .... get the main LED setup and working as you like, then try this circuit:

... which will give you adjustment both of the voltage amplitude (within the limits set by the opamps and operating voltages), where it is 'centered' AND the brightness of the LED (by adjusting Rcurrent). Note - just threw this together quickly, but think it is correct. You can reverse the order of the 'centering' and 'amplitude adjustment stages', depending on the needs of the circuit. I use something like this very often when the need arises to change the amplitude and center of CVs.

Mike