Vibe's Photocell... Mojo?

[no one ever]

Fulltone says its product is superior due to the fact that its photocells are exact replicas of the original's... any fact behind this?

[markphaser]

i would like to know about that also

I mean he would have to get the same bulb resistance,watts,illumination, the spacing from bulb to LDR's, carbon comp LDR, the timing of the LDR, the curve,sweep,slope,timing,resistance taper curves VS light or illumination down, the same material and process of the manufactors back then.

I think its a marketing thing he is pulling off if he had graphs about all this

[MR COFFEE]

Hi all,

As the former owner (hey, $400 is too much to pass up) of a Univibe, and some one who has checked out quite a few while working on them, I can tell you the bulb and photocells in a Univibe ain't all that special. A LED works just as well (and won't burn out after a few years, either) if you set the current level\brightness carefully by ear. A *bright* LED and a slowish photocell selection is helpful if you want the vintage *sway*. I have seen several real-deal Univibes, and on all of them the bulb more or less just flashes on and off at slower VCO settings. Think about the "snap-on" effect of dimmers and incandescent lights. The bulb doesn't smoothly ramp up it's light output, either, whether or not the VCO has sharp edges. Most of the smoothness of the sweep is due to slow photocell response.

Yeah, at faster speeds it's not on off, but the photocells have got to be pretty slow if they sweep smoothly on the really slow speed, which is *real* slow - slower than a real Leslie I think. Keep in mind that a univibe is mostly a phaser with different value caps in each of the four stages. And yeah, I think it sounds good that way. 

But alot of the buzz is a "vintage" -mania thing. Kinda like audiophools and $300 speaker wires. 

Don't bite. 

[markphaser]

Thanks for the information Mr. Coffee

What u mean by "Sway" ?

a slowish photocell what timings? what kind are slowish photocells that are replacements?


The bulb shouldn't be just turning off and on it should ramp up and down like dimming up and down also

[no one ever]

i would like to know about that also

I mean he would have to get the same bulb resistance,watts,illumination, the spacing from bulb to LDR's, carbon comp LDR, the timing of the LDR, the curve,sweep,slope,timing,resistance taper curves VS light or illumination down, the same material and process of the manufactors back then.

I think its a marketing thing he is pulling off if he had graphs about all this

M.F. is the same person who says his choralflange has only "expensive and extremely high quality JFETS" in its signal path and thus is superior in tone to anything else.

I am curious as to his "sounds like 'House Burning Down'" claim.. I LOVE that song.


I didn't know LDR's had response times.

[markphaser]

LDR's had response times

What response times does the univibe use?
What are some common response times for LDR's to have?

[MR COFFEE]

Hi markphaser,

LDR's had response times

What response times does the univibe use?
What are some common response times for LDR's to have?

Perhaps you could consolodate your posts a bit, since you are asking very similar questions in multiple threads? Answered these in your other thread.

[markphaser]

Sorry just trying to help out others thats would like to know about the vibes photocells slow response times
and which ones are used for replacements they are similar

[no one ever]

that dang mike fuller and his combination of mojo and actually creative modifications that make his pedals great... why must he be so secretive and never post on this forum. i've much respect for zvex and mr. huge and their pro-diy efforts, but mike! you can make powerful enemies here.. 


anyway, i'm sure these photocells aren't the only thing that make the deja vibe the best vibe out there, but i'd still like to know how vintage specs should affect my parts choices for my vibe build.

[Gus]

go to geofex  look for

The Technology of the Univibe

R.G. and Jamie(sp) did a lot of work early in the life of the web with schematics and infromation you could not easly find.

This thread brings up something else

Mark H.  I keep thinking someone should doc the history  the effect/amp/guitar sites on the web over the years

When I read some of the posts here I keep noting  alot of what is asked has been asked years ago and sometimes answered.

  Now it is a good thing people ask questions.

  I also know that the older posted stuff might have gone away and can be very hard to find.

  One of the interesting stories of an effect is the rangemaster.  Someone was making a clone and the question of what a rangemaster was came up at ampage.  There were a few good threads going on R.G. got a unit to look at other had schematics sent to them and then R.G. put together the article and also noted the biasing etc. then there were more rangemaster clones being sold when there was only one clone company before.

Maybe a page a wikipedia on the history of effect sites or a wiki with a few trusted editors?

What the web has "done" with effects, amps, guitars, HiFi etc. is amazing. I think effect sites  realy "got going" about 1995 IIRC.

[Paul Perry (Frostwave)]

mike! you can make powerful enemies here.. 

Powerful? no way! But, I do think that people on this board are (rightly) pretty cynical about manufacturers claims. As always, I recommend people to let their ears be the judge. And as has been pointed out, the photocell response is only part of it.

[MR COFFEE]

Hi again markphaser,

What u mean by "Sway" ?

The time constants of LDRs are not symmetrical; they go down in resistance faster than they go back up. The phasing doesn't follow the exact LFO waveform, which is also altered in shape and amplitude by the time constants of the bulb filament, which has a delayed onset of light emission followed by an abupt onset of emission followed by a slower decay of light emission. The actual phasing rate of change is therefore far from sinusoidal in the Univibe, despite the phase shift oscillator sinewave VCO. The sound of the fast down, slower up phasing has been described as "sway" by others striving to duplicate the exact sound of the Univibe.

The bulb shouldn't be just turning off and on it should ramp up and down like dimming up and down also

"Shouldn't" as in what?

Filament-based light bulbs have 1/10 the resistance at full on voltage that they have when the filament is cold. So the only up-in-brightness ramping you get is when the VCO is running fast and the filament doesn't have time to cool back down much between cycles (and go back up in resistance). It's called "snap on" - Try increasing your dimmer setting slowly on your home lighting dimmer; It doesn't ramp up does it, it just ramps when you turn it back down, right?

[no one ever]

mike! you can make powerful enemies here.. 

Powerful? no way! But, I do think that people on this board are (rightly) pretty cynical about manufacturers claims. As always, I recommend people to let their ears be the judge. And as has been pointed out, the photocell response is only part of it.

i meant that if one of us just happened to figure out what makes his effects sound so good, then

a) there would be an article about why the improvements work as they do and how they work (and thus opening the floodgate for implementing them in other builds)

b) there would most likely be fullclone projects made somewhere.

ie loveclones, most notably ring stinger. and even the xxl! once we find out whats going on in something, we usually publicize it. Unless the one person who finds an interesting tidbit happens to decide that the cost to the manufacturer in creative property loss far outweighs the benefit to diy-ers (R.G's said to me he abstains from dissecting Deja Vibes.)

anyway, so we can conclude that photocells make little, if any, difference in the tone of a circuit, given correct biasing and such tinkering.

[markphaser]

Thanks Mr. Coffee for the information about this

Time constants of the bulb filament?

Time constant of a LDR?

"LDRs are not symmetrical they go down in resistance faster than they go back up. The phasing doesn't follow the exact LFO waveform, which is also altered in shape"

Are u saying the LDR is a waveshaper? because its not symmetrical and its time constant
The LDR waveshapes the LFO waveform?

[R.G.]

Are u saying the LDR is a waveshaper? because its not symmetrical and its time constant
The LDR waveshapes the LFO waveform?

The LDR/bulb combination is an accidental waveshaper on the LFO waveform. The bulb has a time constant for heat up/cool down, and the LDR has both a positive and a negative going time constant, that are indeed different. So the change in resistance on the LDR is not a linear function of the change in voltage across the bulb.

[markphaser]

Thanks R.G for the information

I heard that Roger Mayer use to what he called was "tuning up a univibe" was i think getting the Lamp's time constants and LDR's time constant in sync with each other so the Lamp and LDR didn't have any displacement or was out of sync with each other. From what i read was he talked about tuning up the LFO and the LDR's to work better he didn't go into detail but this is my guess

[no one ever]

ah, hello R.G.

mark, i've never seen any article about/quoting RM... could you tell me where you read that, if you could? i love to read articles with interviews with the big names in effects.