Easyvibe: replacing LED's with light bulb?

[nico13]

In the Easyvibe schematic is it possible to replace the LED's with a light bulb like these

http://www.banzaieffects.com/bulb-6-12V-20-40mA-pr-17371.html

http://www.banzaieffects.com/bulb-3V-40mA-pr-17370.html

and use the same bulb / LDR arrangement in order to get a sound closer to the Neovibe?


Does it need to mod the LED driver?

[Mark Hammer]

I suppose you could replace an LED with a filament bulb but keep in mind it takes much more juice to make that filament heat up enough to glow.

[nico13]

Yes that's what I thought.

I use only wallwart (regulated with a 7809) with my easyvibe. Do you think there's enough current available to power a small bulb?

Has anybody already tried to do such a mod?

[solderman]

In the Easyvibe schematic is it possible to replace the LED's with a light bulb like these

http://www.banzaieffects.com/bulb-6-12V-20-40mA-pr-17371.html

http://www.banzaieffects.com/bulb-3V-40mA-pr-17370.html

and use the same bulb / LDR arrangement in order to get a sound closer to the Neovibe?


Does it need to mod the LED driver?

Hi
The circut will probably not support the needed current to get the bulb to light up. but that's besides the point. The light it self has no (almost since the LDR are more sensitive to a specific wavelengths but that has no direct sound effect) effect on the sound. The LED/LDR is there to work the LFO rhythm. Its other parts of the circut that decides the sound eg caps/IC etc.

If you read what M Fulltones has written about the Mini-DejáVibe and the filament in the bulb and the LDR:s on the Fulltone site you will get the impression that the this will get you higher up in the sky then prohibited pharmaceutic drugs.

Copied From the Fulltone site
The Photocells: we're the only small company who can quite frankly afford to have the correct Glass covered, hermetically sealed photocells Custom-made. (click here for photo and more info)

The bulb: getting the correct Voltage rating on this is no big deal, but  does size really matter? Yes, but don't look at the size of the Glass, look at the size of the Filament (wire inside the glass)! We got it right.. And this is crucial to achieve the correct amount of brightness... it also has to flash consistently at all speeds. Our does.


To my ears this is only marketing BS.

Most LDR:s are extremely fast and sensitive to light. I discowered that when i was tweaking a DOD Compressor that I used a LED/LDR in a shrinktube. I thought that the black shrinktube was enough to block the light in the room. The circut behaved odd and it was not until i covered the whole thing that it worked OK. Even the dime light from my amp,s controll light effected the thing ( 1/2 m from the circut ) when i had put out the light in the room.


So my suggestion is to stick with the LED for the Easy Vibe and do the R.G speed ramp UP/Down really cool fetcher that the Mini-DejáVibe  does not have or build the R.G neovibe.

//Solderman


     

[nico13]

In the Easyvibe schematic is it possible to replace the LED's with a light bulb like these

http://www.banzaieffects.com/bulb-6-12V-20-40mA-pr-17371.html

http://www.banzaieffects.com/bulb-3V-40mA-pr-17370.html

and use the same bulb / LDR arrangement in order to get a sound closer to the Neovibe?


Does it need to mod the LED driver?

Hi
The circut will probably not support the needed current to get the bulb to light up. but that's besides the point. The light it self has no (almost since the LDR are more sensitive to a specific wavelengths but that has no direct sound effect) effect on the sound. The LED/LDR is there to work the LFO rhythm. Its other parts of the circut that decides the sound eg caps/IC etc.

You're right Solderman. I measured the current feeding the LED's: it's only 0.5 mA. Not enough for a bulb.

[Mick Bailey]

You could use the op-amp output that feeds the LEDs (off the 220R resistor) to drive a power MOSFET (such as an IRF740) and take the +ve feed to the bulb directly off the supply. You may need to play around with biasing to get the right sound, otherwise the bulb may tend to over or under modulate the LDRs. Rather than the 1k pot and 220R resistor, you may be better taking the op-amp output to (say) a 1Meg pot. connect the other end of the pot to 0V and use the wiper connection as a variable level output to the MOSFET Gate. Source would connect to 0V and Drain to one side of the bulb. The other side of the bulb would be to +V. Some experimentation is needed here to get the right values and results. You probably wouldn't need to heatsink the MOSFET.

One of the claimed benefits of an incandescent bulb is the hysteresis which contributes to the lopsided nature of the modulation. I've found that this is naturally present in the easyvibe anyhow and is adjustable via the trim pot. I still think it would be worthwhile to play around with a bulb in this design as the wide range available may give some interesting variations just by plugging in different rated bulbs.

[nico13]

Thanks for this precious advice.

The other side of the bulb would be to +V.

You mean the other side of the bulb connected to 9V, right?

Here is the schematic I used to build my Easyvibe:

http://www.aronnelson.com/gallery/main.php/v/Roobins-Album/DIY-Layouts/render.gif.html?g2_imageViewsIndex=1

So the idea is to take take the output from IC3 / pin 2 (through pot / IRF740) and then feed the bulb instead of LED4?
As I will put the LDR's around the bulb, can I leave all 6 LED's connected?

Did you already try this mod? If so what bulb ratings would you recommend?

[Mick Bailey]

You could omit LEDs 1 to 4 - the bulb replaces these and they will then effectively be redundant. The other LEDs (5 & 6) are there to give a constant voltage reference and are not directly part of the modulation circuit - these two need to be left in.

If you give me a couple of days I can breadboard the circuit and give you a better idea - I haven't tried this yet but I'm pretty sure that its workable.

The other side of the bulb will go to +9v. A consideration with bulb rating is the 'on' resistance of the MOSFET. This can be seen from data sheets. A wide variety of devices would be suitable for driving a bulb - I mention the IRF740 because I've used them in other circuits. Its very much over-specified for this application (10A, 400v). The on resistance is 0.48 Ohm, so the voltage drop is not too much.

Will give it a go and let you know..............

[orangetones]

Out of interest, why not just build the Neovibe?

As well, remember that the audio path here is different than that of the neovibe.

It has been said that the characteristics of a lightbulb lighting up and then dimming at different rates due to the cooling off of the filament, is what gives part of the signature sound to the univibe.  You might toy around with a variable lfo like the one from the tremulus lune with the symmetry modification.  I found that it was a good way to get an aysymmetrical waveform to drive the leds, thus trying to mimick the response of a light bulb to a symmetrical lfo waveform.

Just a thought!

[Mick Bailey]

Just tried this and it works OK. Needs some fine tuning with biasing. I strapped a 1Meg resistor from Drain to Gate and this improved the action of the circuit. I used a 12v bulb rated at 0.183A. What I can clearly see is the very significant hysteresis when the bulb goes from on to off, compared to off/on. this is much greater than the LED arrangement, so I think it is worthwhile to go down the bulb route to get a more authentic Univibe sound. The hysteresis also changes with speed.

A 6.3v bulb is too bright when fully on, though a series resistor could be used to improve this.

What I've done is really simple, but as it stands the bulb somewhat under modulates on the slowest speeds - the bulb is off completely for part of the cycle. It probably needs developing to give an upper/lower level adjustment to the brightness to get the best out of using a bulb.

[solderman]

 You might toy around with a variable lfo like the one from the tremulus lune with the symmetry modification. 

I have tested to used the tremulus lune LFO to do many different things like Compression and distortion in stead of tremolo and in phase experiment. The tremulus lune LFO is grate to use tush its versatility.
I still do not believe that one light source can do Any differens since the LDR does not care what kind of light that hits it as long as it is light within its wave length.
//Solderman

[nico13]

Just tried this and it works OK. Needs some fine tuning with biasing. I strapped a 1Meg resistor from Drain to Gate and this improved the action of the circuit. I used a 12v bulb rated at 0.183A. What I can clearly see is the very significant hysteresis when the bulb goes from on to off, compared to off/on. this is much greater than the LED arrangement, so I think it is worthwhile to go down the bulb route to get a more authentic Univibe sound. The hysteresis also changes with speed.

A 6.3v bulb is too bright when fully on, though a series resistor could be used to improve this.

What I've done is really simple, but as it stands the bulb somewhat under modulates on the slowest speeds - the bulb is off completely for part of the cycle. It probably needs developing to give an upper/lower level adjustment to the brightness to get the best out of using a bulb.

Thanks for your experimentation.

I'll give it a try after I make my next order.

[orangetones]

 You might toy around with a variable lfo like the one from the tremulus lune with the symmetry modification. 

I have tested to used the tremulus lune LFO to do many different things like Compression and distortion in stead of tremolo and in phase experiment. The tremulus lune LFO is grate to use tush its versatility.
I still do not believe that one light source can do Any differens since the LDR does not care what kind of light that hits it as long as it is light within its wave length.
//Solderman

What I meant was to use the LEDS with the Tremulus Lune LFO, not use a lightbulb with the Lune LFO. 

Steve

[solderman]

 You might toy around with a variable lfo like the one from the tremulus lune with the symmetry modification. 

I have tested to used the tremulus lune LFO to do many different things like Compression and distortion in stead of tremolo and in phase experiment. The tremulus lune LFO is grate to use tush its versatility.
I still do not believe that one light source can do Any differens since the LDR does not care what kind of light that hits it as long as it is light within its wave length.
//Solderman

What I meant was to use the LEDS with the Tremulus Lune LFO, not use a lightbulb with the Lune LFO. 

Steve

Me too , Sorry for being unclear
And to clarify an other thing, I think Mick Bailey has done a tremendous design effort to get the Easy vibe to work with a light build. I just don't think it will improve the sound just because its a light bulb.  But I have been wrong many times before
//Solderman

[Mick Bailey]

The difference in sound comes from the bulb behaving in a non-linear fashion compared to an LED. An LED responds quickly and (fairly) uniformly, and its brightness accurately follows the shape of the waveform fed to it. Because of the reasonably fast response time of an LED, this accuracy is maintained over a fairly wide frequency range and can be regarded as linear within the frequency range of modulation in audio effects.

Now a light bulb behaves very differently - the filament cannot react as quickly going from light to dark as it does from dark to light. This is because the filament stores heat which cannot be instantly dissipated and therefore gives a level of persistence to the light output. As the frequency of modulation increases, the bulb cannot dim enough before it is hit with the next rising voltage swing and this has a bearing on the modulation depth at higher speeds.

In most modulation circuits the characteristics of a light bulb would not be suitable due to the asymmetric response, which cannot accurately follow the modulation signal. However, in the Univibe clones and variations, this is considered to be a feature due to the desire to recreate the sounds of Hendrix, Trower, etc.

I'm pretty sure that if LEDs were commercially available at the time they would have been used in preference to light bulbs, as in outright design terms the bulb creates a flawed, lopsided sound.

[orangetones]

Again, it is important to note that the audio path is IC based and not discrete transistor based in this desing and that the audio path is not that of the Univibe. 

And, again, if you wanted to keep this audio path, you might just have an easier time getting that lopsided sound with an LFO that has a symmetry function.

Finally, I understand that the modulation depth changes with speed, but I feel that most people adjust the depth knob on their univibes as they increas the speed to negate this problem.  I know I do.

Best of luck in this adventure though.  I would be interested in an A/B/C comparison of the easyvibe with bulb versus the easyvibe with LEDS, and the Univibe circuit.  Same amp/guitar/recoring set up.

Cheers,

Steve

[Mick Bailey]

I happen to like the Easyvibe pretty much 'as-is' (apart from the bass reduction when turning the depth down) and the bias control gives a good lopsided effect when set correctly. Ultimately, I agree that the best way to get a Univibe sound is to build a clone of the original design to preserve the audio path. It's an interesting departure to experiment with bulbs in the Easyvibe, though.

[solderman]

Now a light bulb behaves very differently - the filament cannot react as quickly going from light to dark as it does from dark to light. This is because the filament stores heat which cannot be instantly dissipated and therefore gives a level of persistence to the light output. As the frequency of modulation increases, the bulb cannot dim enough before it is hit with the next rising voltage swing and this has a bearing on the modulation depth at higher speeds.

Yes. One can see that by hitting the light switch at home but........my point was not really the bulb. It was the LDR. Since the whole point with a light emitting source is to effect the LDR. I got some crazy behaviour from a DOD compressor I made my own LDR/LED for. When I measured the LDR I discovered that it had a reverse logarithmic and fast (talking a five milliseconds) to rise and fall in resistance in no time. (from 2K at light to -2M dark in no time at all then from 2M to 10M ~2 sec) I was also amazed over that the LDR needed nearly no light at all to react. I just checked again from 2K to >1M is so fast that it's done at ones on my DMM. And I redid the dark room and light my amp control lamp from ½ m and the LDR reacts with 500K at ones. So if the LDR acts like a switch between 2K-500K for almost no light at all and in no time at all the origin or behaviour of the light source will be of little or no importance.

However This discussion has made me queries and I'm gonne build the Easy Vibe with the Termolus Lune LFO and have the 4 LDR:s together round 1 red dim LED and 1 white high luminance LED to switch between. I will also have one 4DTP switch (on-off-on) to switch between half--stock--double the value of each of the 4 caps in the signal path.


//Solderman

[orangetones]

However This discussion has made me queries and I'm gonne build the Easy Vibe with the Termolus Lune LFO and have the 4 LDR:s together round 1 red dim LED and 1 white high luminance LED to switch between. I will also have one 4DTP switch (on-off-on) to switch between half--stock--double the value of each of the 4 caps in the signal path.

Sounds like a good plan!  The one thing I noticed with the Lune LFO was it needed modification to drive 4 LEDs (mind you, you are suggesting using only one)  Interesting experiment!  Let us know how that one turns out!

[nico13]

I got some crazy behaviour from a DOD compressor I made my own LDR/LED for. When I measured the LDR I discovered that it had a reverse logarithmic and fast (talking a five milliseconds) to rise and fall in resistance in no time. (from 2K at light to -2M dark in no time at all then from 2M to 10M ~2 sec) I was also amazed over that the LDR needed nearly no light at all to react. I just checked again from 2K to >1M is so fast that it's done at ones on my DMM. And I redid the dark room and light my amp control lamp from ½ m and the LDR reacts with 500K at ones. So if the LDR acts like a switch between 2K-500K for almost no light at all and in no time at all the origin or behaviour of the light source will be of little or no importance.

When I built my Easyvibe I first heatshrank the LDR facing and touching the LED's top. The sound was more like a phaser with a fast changing in the sweep. Like the on/off way you describe.

I then changed the way the LDR's are attached to the LED's. I still put the LDR facing but not touching (space of about 3mm) the LED's top in a simply tube (in fact a non heatshrunk tube) and the sound is smoother and closer to a Univibe than before.

I think the specific sound of the Univibe also comes from the way the LDR's react to the light reflections inside the shield (even the cheap Danelectro Cool Cat Vibe is built like this). Would another bulb/LDR's arrangement make the same sound ?