How do I boost the brightness of clipping LEDs?

[Ell]

I'm trying to use 5mm blue LEDs in the clipping section of an MXR Distortion Plus. They don't light up. Basically, as stupid as it sounds, I just need a blue light to flash with my playing. It's just for a visual effect. Is there any way I can boost the brightness? The LED has to be blue, and if it's possible to have more than one LED flashing (let's say 6 is the perfect number), that would be lovely. Does anyone have any ideas? I was wondering if I change some values so it distorts more bass, that might work?

[Mark Hammer]

Well, for starters, subbing blue LEDs for germanium diodes is not going to get you much clipping in a Distortion+ circuit. Bear in mind that a pair of blue LEDs likely won't start to clip audibly until the signal probably hits around +/-2000mv.  A pair of Ge diodes, as per the circuit, will clip when the signal hits around +/-340mv, and sometimes less.

The other thing is that  forward voltage varies with LED colour, and blue is rather demanding in that respect.  This is why those clipping circuits that use LEDs, whether in pedals or amps, opt for red, because red LEDs have the lowest forward voltage, thus requiring less signal amplitude and gain to push them into clipping.  In any event,few clippers that use LEDs expect them to glow.  And even when they do it's VERY very brief and not especially bright.

So, I'm afraid you've put in a rather tall and somewhat impossible order.  You could try reducing the 10k resistor on the output of the op-amp to something much lower, like 470R, to provide more current.  But between that, and blue LEDs, you've no longer got a Distortion+.

More bass?  That's an easy one.  Change the 47nf cap connected to the Gain pot on the ground leg to 100-220nf.  Stock, the circuit rolls off bass at around 720hz when gain is up full.  Increasing the cap value will keep more bass at higher gain settings.

[Ell]

Thank you Mark! I appreciate your wisdom. I'm sorry for the ridiculousness of this assignment. Basically, it's a Godzilla themed thing, so it needs to glow blue like Godzilla when he is about to fire off some nuclear breath... It's one of those wacky throw-away ideas that come from a dream.

I'll try your recommendations. Are there any other circuits that might glow more? Maybe a tubescreamer, or autowah?

[Ell]

I tried it out Mark! The 470R trick at the output of the opamp worked perfectly. It's currently lighting up 3 blue LEDs with no problem. Thank you for sharing your wisdom with me! I really appreciate it!

[marcelomd]

Hi,

Suggestion: don't use the clipping elements as indicators. Keep the circuit original (or not), but add a secondary circuit that only drives the blue LEDs. Use the effect's output (or connect it somewhere in the middle) as input to this LED flasher. High impedance so it doesn't change the tone. This is more or less how the "clip" or "overload" LEDs in amps work.

Reason is that LEDs are also photodiodes, which means that shining lights on them will produce a (small) current. This may or may not have an effect on the tone depending on ambient conditions.

That said, it's a Godzilla themed Distortion+, it's all about unintended consequences =)

[Ell]

Hi,

Suggestion: don't use the clipping elements as indicators. Keep the circuit original (or not), but add a secondary circuit that only drives the blue LEDs. Use the effect's output (or connect it somewhere in the middle) as input to this LED flasher. High impedance so it doesn't change the tone. This is more or less how the "clip" or "overload" LEDs in amps work.

Reason is that LEDs are also photodiodes, which means that shining lights on them will produce a (small) current. This may or may not have an effect on the tone depending on ambient conditions.

That said, it's a Godzilla themed Distortion+, it's all about unintended consequences =)

Interesting. Thanks for your input Marcelo! I think you might be right. Maybe something like an octave fuzz will SOUND more Godzilla, and then just have the lights shining with the notes for the visual-element.

[bluebunny]

I'm with Marcelo - have the light display driven by a separate circuit.  Quite often when LEDs are used for clipping, you might struggle to see them light up at all.

[FiveseveN]

That second circuit can be Deadastronaut's Sound 2 Light, which has plenty of current for more LEDs:

[antonis]

Are there any other circuits that might glow more?

A typical blue led exhibits a 3.4V drop across its Anode-Cathode and needs about 30mA for full brightness..
The former results into practically no clipping (unless you use a true rail-to-rail op-amp) and the later calls for op-amp output heavy loading..

[GibsonGM]

I've messed with the Sound 2 Light circuit, it works well.  It would change a Dist+ a little from stock, but what about adding a buffer at the input, and tapping off it into the S2L? 

[stallik]

By using an AMZ splitter and a separate PS for the sound to light circuit, I get no colouration of sound and can happily run as many sets of 3x super bright LED's as I want in addition to 5 meter lengths of led strips.

All overkill perhaps but just look at those flashing lights 

[GibsonGM]

Yup, Jack's splitter will drive basically...anything....   

[FiveseveN]

Use a dual op amp, one for a buffer and the other for the Dist+.

[amptramp]

Going along with what Marcelo said, we once designed a touch panel with green LED's driving green LED's connected as photodiodes and found the reverse leakage varied with ambient light and temperature.  The sensitivity to ambient light means that if you are on a stage with fluorescent lighting, the light will modulate the current flow and you will get 120 Hz or 100 Hz modulating your signal.  Definitely make the visual indicators separate devices from the actual limiting LED's and beware of the leakage currents - our version of the touch panel did not work because excessive leakage overrode the signal above 25°C.

The idea of green LED's was to be able to use a green optical filter to eliminate sunlight, since most of the sunlight is infrared, so we thought we might be able to do better in sunlight than with infrared emitters and photodiodes.  That experiment failed.

[R.G.]

I thought about it. I could only come up with doing it as a side indicator. Imagine building two of the D+ circuits, one for sound and one for the indicators. The indicator side exists only to make the signal that trips the external LEDs, while the sound side just makes the sound. There is an additional set of stuff on the indicator circuit that senses when the signal goes above or below the clipping diode threshold and then lights the indicator. This lets you choose the indicator intensity and color/voltage independent of the actual sound circuit.

There is the obvious problem - the indicator circuit is twice to a few times as large and complicated as the sound side. I couldn't come up with anything that just changed or added a few parts to the original circuit that worked as described.

[Ice-9]

My thoughts are that you could add a simple op amp rectifier side chain to drive an LED.

[Fancy Lime]

My thoughts are that you could add a simple op amp rectifier side chain to drive an LED.

+1 to that. Half wave would be sufficient and really simple. Those GaN LEDs are super bright even with a fraction of a milli Volt, so a second half of, say, a TL072 should be plenty to drive a couple.

[Matthew Sanford]

+1 to R.G.'s on doubling the distortion to run the LEDs to have it follow the effect not just your guitar clean signal, though may reduce the variation...whatever you do, put reflectors all around the LEDs!!!

[Ell]

Thanks for the feedback everyone. Does anyone have a layout for Deadastronaut's Sound 2 Light? It seems to be missing from the page now. It's currently working really well. I removed the output and knobs from the Distortion Plus. However, the LEDs aren't super blindingly bright. This might be a bit ridiculous, but, would an amp like a ruby into diode clipping give me the insane brightness I want?

[FiveseveN]

would an amp like a ruby into diode clipping give me the insane brightness I want?

That's basically what the Sound 2 Light is: