Photocells for easyvibe

[jeff g]

I'm putting in an order at Futurlec, and wondered if any of their photocells would be suitable for the easyvibe.  They seem to be different specs than smallbear

they're found here: 
http://www.futurlec.com/Photocells.shtml

thanks

[oldrocker]

I made mine with what Radio Shack sells as a multi pack of LDR's.  I bought the multi pack of LED's from them too and used the larger standard size red ones.  My Easyvibe rocks.

[RedHouse]

Speaking from a univibe perspective, you could do a lot better, those have a range of 10k-100k and 3k-300k which isn't great.

A univibe will ideally want an LDR that ranges between 1-10/20k in the light and 1-10/20M in the dark, and as fast as you can get which is difficult to assess as the speed of the cells isn't widely advertised.

Of course if you only use slower speeds on a 'vibe (Trower, Hendrix, Gilmore) the speed of the cells is hardly an issue, but you'll most certainly want greater range from light/dark in a univibe, but the easyvibe might be different.

That is not to say they won't work, they probably will, but your results may be less effect than is possible from your build.

These are all known to work well, while the resistances vary quite a bit, notice that their range is always high:
338-54C679  (Small Bear)
54C679 (Ceramic)    50k~200k/Lt  20M/Dk (200v, Small Bear)
5H69   (Hermetic)   50k~100k/Lt  20M/Dk (MKY-5H69)
54C79              100k~200k/Lt  20M/Dk (200v, Small Bear)
CL9P4   (Clairex)         20k/Lt  20M/Dk (200v, Small Bear)
NSL-5540 (Silonex)       30k/Lt  20M/Dk (60v, Allied)
NSL-5152 (Silonex)       15k/Lt   5M/Dk  (60v, Allied)
NSL-4140 (Silonex)       14k/Lt   8M/Dk  (60v, Allied)
Vactrol VTL5C3 ...equvivalent with... Clairex CLM6000

   

[SteveB]

...A univibe will ideally want an LDR that ranges between 1-10/20k in the light and 1-10/20M in the dark, and as fast as you can get which is difficult to assess as the speed of the cells isn't widely advertised.... 

Wow, I guess I hadn't read that before. I built a Neovibe 10 years ago, & part of R.G.'s  commentary mentioned a "Photocell with 10K to 250K light to dark range" I just got the one's from Radio Shack. Now, you've sparked my interest in trying different ones.

Steve

[RedHouse]

I can't comment on RG's comments, but as for me (I've built 14 univibes so far, sold 9) I feel I have some insight.

Note that I use JC Maillet's bulb-bias mod in all my builds (with his express blessing) and having the wide range on the LDR's allows me to "tune" my univibes.

YMMV, but I find the LDR's that go from like 10-20k (light) to like around 8-10M (dark) to be most useful in my builds.

[oldrocker]

Well if you're looking for a Trower sound the RS LDR's will work fine IMHO.  Check out tungngroove's videos.
http://home.grics.net/tungngruv/EZVibe/EZVibeDiary.AVI
http://home.grics.net/tungngruv/EZVibe/EZVibeBridge.AVI

[RedHouse]

Just went into my shop and measured the remaining eight 338-54C679 LDR's I got from mouser a couple years ago before they stopped selling them and it seems they get quite a bit lower light resistance than I posted above.

All eight got down to about 1k in bright light, they rose up to 8M in dark but the time was long, they got up to 2M rapidly and then the speed of which the resistance was increasing tapered off and it took them like 10 seconds to reach the last few megohms. They changed fastest in the 10k-1M range.

I noticed the Mouser verbiage from the sticker on the baggie says the range of the 338-54C679 is 50k-200k.

Measuring the LDR's I currently use (they're not 338-54C679) I see I'm also dwelling in the 8-10k light and 1-3M dark, please excuse my figures in my previous post they were incorrect. I was going by memory when I posted this morning, and, err, umm ...never mind.

I removed the light shield on my testbed univibe board and noted the behavior of the bulb when the bulb bias and bulb drive trimmers were set to the best sounding 'vibe'ing. The bulb appears to be running in the range of OFF to about 25-30% ON.

So the LDR's appear to be actually running in their upper range of resistance, in the few-to-several hundred-K Ohm range when 'vibing at what I think is the best Trower-like B.O.S. throb.

This surprised me as I was thinking the exact opposite was going on (my boards are tuned with trimmers so each can be dialed in so I never really had any need to remove the light cover off after setting the initial bulb drive trimmer). Since this is the case I wonder if there would be any merit to running a larger resistor in series with the LDR (replacing the 4.7k with say 20k or so).

I can see I'm going to have to do some more bench experimentation to see if I can closer define the resistance range my LDR's are running  when my 'vibe's are tuned.

[SteveB]

....I removed the light shield on my testbed univibe board and noted the behavior of the bulb when the bulb bias and bulb drive trimmers were set to the best sounding 'vibe'ing. The bulb appears to be running in the range of OFF to about 25-30% ON.

So the LDR's appear to be actually running in their upper range of resistance, in the few-to-several hundred-K Ohm range when 'vibing at what I think is the best Trower-like B.O.S. throb.

This surprised me as I was thinking the exact opposite was going on (my boards are tuned with trimmers so each can be dialed in so I never really had any need to remove the light cover off after setting the initial bulb drive trimmer). Since this is the case I wonder if there would be any merit to running a larger resistor in series with the LDR (replacing the 4.7k with say 20k or so).

I can see I'm going to have to do some more bench experimentation to see if I can closer define the resistance range my LDR's are running  when my 'vibe's are tuned.

Very interesting stuff indeed. Are your photocells facing up, parallel to the board, or grouped around the bulb? If I set my bias that low with the LDRs facing up, the effect is not very deep. When grouped tighter around the bulb, it works.

I'm having a time getting the right ratio of swish & thump. The original schematic has a 47k between the 10uf cap & base of the lamp driver. I changed it to 4.7k quite a while back, but the "lump, lump" got too intense on anything higher than 2:00 on the intensity knob. I recently put it back to 47k, but that doesn't give enough depth. I tried a friend's older Deja, & it is the same way. I experimented with 33k & 10k, & it was better. I also covered each LDR, one at a time to see how it affected the sound, & I found that most of the "lump" is coming from the one connected to the .22uf cap. JC suggests using a .1uf to lessen the bass. It might be worth a try. But I really need to put that 4.7k back in & then try some other things.

Any sound clips of yours?

Steve

[oldrocker]

I'm confused. The headline for this thread is Easyvibe which uses 4 LED's separate to each of the 4 LDR's.  Everyone is saying Univibe or Neovibe which is using a different bulb setup for the LDR's.  Would these comments about LDR's apply to the Easyvibe too?  Just wondering.

[SteveB]

I'm confused. The headline for this thread is Easyvibe which uses 4 LED's separate to each of the 4 LDR's.  Everyone is saying Univibe or Neovibe which is using a different bulb setup for the LDR's.  Would these comments about LDR's apply to the Easyvibe too?  Just wondering.

Sorry, I sorta' strayed from the original subject, & got caught up on Neovibe photocells.

Steve

[RedHouse]

Yeah same here, I strayed from the topic, verry sorry.

My view and experience is more toward Univibe and not easyvibe, please disregard.

Steve, my LDR's are not facing up, they are facing the bulb. I tried the angling away from the bulb thing and it did'nt seem to offer anything. Mine are facing the bulb, in circle around the bulb (as Univbe's do)

I tend to agree with the .22uF cap issue, I have been using .15uF or .18uF cap when I can (in my own, and when customer doesn't care about originality) and it seems to be a less thumpy "vibe". There must have been some wide variation in sound in the original univbes as Trower didn't sound like Gilmore, which didn't sound like Hendrix etc.

Have you checked out the ReslyTone? is used way different caps (.0047, .0033, .0022, 001) and I have experimented with alternate values like using .047 in all stages (very Pink Floyd)

I have sound clips (on an ADAT) I just need to get them into MPG to post so you can hear.
(soon I hope)

[Ardric]

Does it matter which way the bulb faces?  I mean, the bulb filiment doesn't look the same from all angles.  Isn't it brighter on two sides where the filiment is broadside, and dimmer where the filiment is end on?  Maybe even a bit of shadow from the filiment posts?

I'm thinking that if the bulb was spun until the least light landed on the .22 LDR, it might make a slight difference.

[jeff g]

thanks for the replies

it sounds like the lower range values aren't ideal, so i'll probably order from smallbear

also, the neovibe discussion may be useful to me if i ever get mine working (my frustration with that build is why i've decided to build the easyvibe)

[captntasty]

This post got me to thinking - rather than "rolling your own" photocouplers ie. combining a LED and photocell, why not just go the manufactured photocoupler route?  I poked around enough to find out that in the easyvibe a 20k - 20M resistance spread is desired/recommended.  I didn't find any VTL's or CLM's etc. that fit the bill.  Are there any other options out there?  Are there any out there that might not hit 20k-20M but still be suitable for the easyvibe with perhaps reduced depth (I have a univibe clone and prefer depth at really no more than 50% anyhow so wouldn't mind the reduced performance)?  Been contemplating building an easyvibe to replace my clone - it's great but for what it cost it's not that great!  I'd rather DIY.

[slacker]

Whats the reason for needing LDRs with such a wide range of resistance?
I've done a few calcs and to keep the frequency at which the phase shifts happen within the audio range you only need the resistance to swing between about 1k and 200k. Within that range a change in resistance of about 10 - 1 seems to produce a good sweep. Even then the stage with the 470pF in it seems to only just be within audio frequencies.
The only reason I can think of is that using ones that go to a very high resistance means that because you're only sweeping a small part of their range you get a fast and more linear sweep.

[captntasty]

Hmmm... I wouldn't (because this type of circuit is completely new to me) have thought about in terms of linearity but there might be something to that.  If that's the case, a component such as the CLM6200 (edit: I guess this would be a hard one to find) with a range of 10K - 10M might work with a different effect character - but what would that difference be?  Less depth or slower speeds?  I could live with either of those.  An un-smooth cycle/vibe?  What other specs off the datasheet determine if a component would be suitable for this effect?  Maybe there is only one way to find out?  Time to start preparations for another build! 

[finkfloyd]

This will be my first build using photocells, Im looking for that slow Floyd vibe, and the bridge of sighs sound.

I ordered these last week:

Code Select Expand

A compact cadmium sulphide light dependent resistor (LDR) housed in a small package.


5mm diameter
Clear epoxy finish
Resistance reduces as the light falling on the device increases


Dark resistance 1MΩ 
Resistance @ 10 Lux 10-20kΩ 
Resistance @ 100 Lux 2-4kΩ 
Peak spectral response 540nm 
Max. voltage 150V peak AC or DC 
Power dissipation 100mW 
Operating temperature –30°C to +70°C

As you can see they only are 1M in the dark, but these should sound OK for a slower sounding vibe?

[slacker]

I think they should be fine, according to the FAQ on John Hollis's site almost any LDR should work as you can adjust the drive pot to compensate for any differences.

[fusionid]

it seems to me that using Vactec's would be the way to go. seems easy as everything is in the component. Any objections???

[slacker]

If you can get some that have the right range of resistances then they'll work fine. I think they are more expensive than LEDs and LDRs though.