Here's a circuit for pulsating Phase 90 rate LED

[Tim L]

Hi Folks,

I've been playing around with a simple voltage follower circuit tacked on to the Phase 90 LFO to  get a pulsating LED that rises and falls with the LFO output for a better "feel" as opposed to the square wave output on/off blinking.
I used two 47k resistors (one across pins 2&1 and one from 2 to ground) to give a voltage gain of 2. I added a 0.1 cap to block the DC component (without it I found that the LED brightened and dimmed but was never fully off).

Hope this is usefull to folks.

Is there a better way? Since there is a DC offset on the LFO output, would clamping the input provide any benefit to providing a smoother "off" to "full on" transistion for the LED?

This circuit addition is based a comment from R.G. in a previous thread:
"On pedals where the voltage is not suitable for LEDs directly, you will need increase the voltage level (such as in MXR P90-esque things) by using an opamp follower with gain to boost the signal up. For pedals where the signal is 'way big, you use a resistor divider to divide it down, or a bigger resistor in series with the LED to cut the current down"

[drummer4gc]

Sorry for the resurrection, but I really want to understand this!

I'm trying to get a smoothly pulsating LED in my Phase 90, and for all of the threads on this topic, I can't find any true solutions. I've tried RG's suggestion quoted in this post, using a 2n5088 to buffer the voltage from the LFO, but that only gets me an LED that blinks on or off, not a smooth brightening/dimming action. I attempted the circuit above, but am not sure I built it correctly. I got the LED to blink more smoothly, but it was super dim and didn't seem to change much at all on fast settings.

Has anyone actually had luck getting smooth rate indication in a Phase 90, and are you willing to share how?

Here's my inspiration: http://youtube.com/watch?v=H6nkfHxVRRk

[armdnrdy]

I implemented two rate LEDs in a stereo panner.

With a little experimentation, I was able to achieve a "ramping" effect as you described.

This is the circuit I came up with for the panner:



Try bread boarding half of it for one LED to see if it works for you.

[Electron Tornado]

Here's a couple of ways you can do it.

Refer to this schematic for part numbers: http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/MXR_Phase_90_Script.gif.html


Method 1: 5mm red LED with 3k resistor on the anode. Connect resistor to pin 7 of IC1 (or "U1b" as it's labeled in the schematic) and connect the cathode to ground.

Method 2: 5mm red LED with 22k resistor which can be connected to either leg. Connect one leg to pin 7 of IC1 (U1b), and connect the other leg to the leg of R6 that shares a connection with R23 and Q5. Notice that there are a number of components that share that same connection. I think I used R6 because it was convenient. If the LED doesn't light up on the part of the sweep you like, just swap the connections around.

I don't recall if method 1 was silent or not, but method 2 will work without adding noise to the audio signal. The red LED I used in both cases was the original status LED from the pedal. I used a different color LED for the status LED, and drilled a separate hole for the pulse LED.

[Mark Hammer]

Hi Tim, I kind of thought it was you.

Welcome! 

[drummer4gc]

Thanks for the responses!

Electron Tornado - I gave your methods a shot, and although I get the light to blink in time with the effect/LFO, it doesn't give me that cool "ramping", or smooth on/off with the effect, that I'm looking for.

armdnrdy - your setup is next on the list, but I'm not sure I completely understand how to implement it. I see V+, I'm assuming this is 9v+? And then, if I'm going to use the top half of the circuit, the "A" node gets connected where? To the LFO voltage? Also, will a common npn work in place of the 2SC945? (2n5088, mpsa18, ??)
Thanks everyone.

Matt

[armdnrdy]

I see V+, I'm assuming this is 9v+?
Yes
And then, if I'm going to use the top half of the circuit, the "A" node gets connected where? To the LFO voltage?
Yes
Also, will a common npn work in place of the 2SC945? (2n5088, mpsa18, ??)
Yes

Matt

[drummer4gc]

Woo! Very rarely do I get some shit right three times in a row!

All right. Here's what I've got so far. I played with armdnrdy's circuit and came up with this:



The 0.1uf cap gave it more of a fade than a blink. Here's a video:

It's not bad, but I feel like it could be better. At higher speeds, you can see that the LED never shuts off completely, and at the highest speed, it just stays on. At low speeds, it comes on almost instantly, then there is a small fade as it goes off.

I know that the blink is really supposed to be an indicator for when you're playing, and this would work just fine I'm sure. But the tinkerer in me wants to see it look better! And unfortunately, I'm really at the trial and error stage of all of this and not totally sure of what I'm doing - any suggestions for things to try would be appreciated! Thanks for all the help you've given me already!

Matt

[armdnrdy]

Hey Matt,

I'm glad it work out for you.
At faster speeds it may be your perception that isn't "turning off."
There may be such a fast turn around time that your eyes/brain (I'm not implying that you have a defective brain  ) are not perceiving the LEDs full turn off.

Let me explain in another way....Motion picture film........Each frame is a still photo. When you look at the still photo...you perceive no movement. When you roll the film at a slow speed you see each movement. When you speed up the film, certain movements start to get lost because they happen too quickly for the human eye to perceive.

Now when you slow the rate of the LED down, it appears to fade in and fade out correct? All you are doing is speeding up that event.

[drummer4gc]

Yeah, I get that. Check the video though - when going fast, it appears that the LED doesn't get to turn off before getting hit with current again. It could be perception for sure...but since perception is all that really matters, I'm wondering if there is a way to get a little more action out of it at high speeds.

At low speeds, it sort of fades...but it's not smooth. It's almost like it turns on and off too fast at low speeds and not fast enough at high speeds. I'm totally nitpicking I know, but really I'm just taking this as a learning exercise to figure out what is going on in the circuit and how changing components around will affect the final product.

[armdnrdy]

I was pretty happy with the way mine turned out for the panner.

You might try fiddling with the resistors upstream from the tranny some more. I tried adding a cap for a RC time constant delay......it didn't work out so well.