problems sourcing parts

[sammy]

Hi everyone,

I'm part way through building the Geo Univibe clone and I'm having problems sourcing some of the components.
In Particular I can't find the right LDRs.

The Geo spec mentions a mouser part number (338-54c679) which is a 50-200k LDR

I've checked with the Mouser partners and non of them have it (at least those that are here in Australia)

The best I can get is the following from Radio Parts in Melbourne

RD3480 LDR .
-   Similar to Philips ORP12.
-   Dark Resistance: min10M
-   Light Resistance: 48k - 140k
-   Max Dissipation: 30mW
-   Rise Time: (0~63%) 40mS
-   Decay Time: (100~37%) 10mS-

I'm worried about using these LDRs as the resistance is not what the spec asks for.  (I haven't checked the other characteristics yet)
Anyone know where I can the right ones, or if there is a way of using the above LDR in its place?
Thanks in advance
Sam

[R.G.]

Didn't David Crosby do a song titled "Love the One You're With" ? 

My suggestion is always: if you can't get the perfect part, use what you can get and see if it works OK. It may. Or it may work partially. Then use what you have working until you can get the perfect part some day in the future.

Just as a note, the original photocells from the univibe are not available anywhere. The ones I "specified" were picked because they were available and seemed to work OK in my board. Use what you can get, and if it's not perfect, spend some time getting the perfect ones later.

[PRR]

> RD3480 LDR .
> -   Similar to Philips ORP12.
> -   Light Resistance: 48k - 140k

That's clearly some sort of typo. I have never seen an LDR which won't go a lot lower than 48K.

The spec for Philips ORP12 is 2.4K at 50 lux, which is roughly "Family living room" (about 5 FC in the US).



> Univibe clone

That's a small incandescent lamp only an inch away from the LDR(s), right?

That lamp can get to FAR brighter than 5 Lux. You can slam the LDR to 1K or less. I don't think it needs to be slammed that hard. That's why the Univibe clone has a lamp trimmer.

LDRs are "all the same" for this purpose, if you trim the lamp brightness to get a useful range. The minimum and maximum resistances don't matter because this circuit doesn't go there. The dissipation and max voltage do not matter because the power is trivial.

[SoundPerf]

Am I misunderstanding what the OP is asking for, or is there a reason why this has not been suggested?

Anyway, this is what I used for my Neovibe. (NSL-7530)
http://www.smallbearelec.com/Categories.bok?category=Photocells+and+Photocouplers

[sammy]

thanks everyone,
wasn't aware of small bear, apparently they have all the right stuff so I'm looking at getting what i need from there.

PRR
Not sure if its a typo. check out the following site
http://www.radioparts.com.au/ProdView.aspx?popup=1&Category=SXLL7475&Product=38250050&ProdDesc=RD3480+LIGHT+DEPENDENT+RESISTOR

SoundPerf
how does the unit sound with those LDRs?

RG
yes your right , and I do 'love the one I'm with - (unless she's nagging me !)' ..... but I'm still new(ish) to electronics, and although I've built a few bits and pieces, I still haven't the confidence to experiment & deviate too much from what the specs say works ....

for example .. the Geo spec calls for 1/4w carbon resistors but I just realised I am using .5w metal ones ... I assume it will make no difference so I didn't bother replacing them.
I've since read that carbon resisters sound better?? is that true ??
anyway , I have metal ones so that's what I'll use.
Hearing all your thoughts is invaluable and aids in my learning process - I'm very grateful folks.

Sam

[SoundPerf]

It sounds great. Those LDR's will be what you want. I do suggest incorporating what are known as the "bulb driver mods" to get it tweaked. I used the GGG board, but extensively read through the "ForumVibe" informatin multiple times, along with RG's Technology of the Univibe and his build instructions. I also did the "darlington pair mod" for the buld driver.

I would have more info for you if I didn't make a collosal mistake over the holidays when upgrading my computer to Windows 7. I deleted all my gathered DIY pedal stuff by accident without having a proper backup. I thought I did, but it was 3:00 AM and wasn't thinking clearly.

Here are some links. Read as much as possible and get a good understanding of the circuit. I've been wanting to get a good sound sample together, but haven't had the time yet. I have some recordings of me playing, but i'm also using other effects with it and I think it wouldn't be a fair sample.

http://classicamplification.net/Forumvibe/ForumVibe2.pdf
http://www.geofex.com/Article_Folders/univibe/vibeupdate.pdf
http://www.geofex.com/article_folders/univibe/univtech.htm

[SoundPerf]

Oh, and the carbon comp resistor question. For the vibe use the most accurate metal film. The "carbon comp being better" information is more about amp building and perhaps overdrive and distortion effects. IMHO, accuracy is more important for most applications. Also, all you need is 1/4 watt, but the 1/2 watt will be fine. I don't think there's an appreaciable size difference.

[sammy]

hi SoundPerf ,

great stuff !!

thanks for the help and advice (and links) in particular , the first link to the classic forum pdf is fantastic !
I'll do the Bulb Driver mods once I get the unit up and running
I'm really looking forward to finally getting  all the parts and finishing it.

thanks
Sam