This is topic Photodiode / cell suggestions in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by David Rigby (Member # 1301) on 08-04-2002, 11:18 AM:
I'm going to have a bash at fitting a stereo cell to my Microcine portable. Currently it has a mono cell and mono integrated amp, but I'm hooking that up to a switch so I can switch the cell output to an external amp. While I'm at it I may as well fit an extra cell (especially since I can fit the new cells on ther reverse of the shaft and leave the current cell in place in case it all goes horribly wrong...) Anyone got any good tips for specific photo diodes to use? Just how bad would the noise be if I was to take the output from the projector via 1.5m of reasonable cable to an external amp - is it crucial that I shove a stereo preamp in projector? Would a standard phono preamp suffice in that case?Thanks for any advice folks!
David
Posted by Gordon McLeod (Member # 33) on 08-04-2002, 11:22 AM:
A phono preamp will have a RIAA curve for eq so it will roll off a lot of highs worse than the academy curve also its input impedance is very high the cell would like to see a virtual ground or at least a very low impedance
Also the cell must be close to the film plane to get any degree of seperation
Microcine has stereo cells available
Posted by David Rigby (Member # 1301) on 08-04-2002, 11:55 AM:
Thanks Gordon. I'm planning on rotating the shaft 180 degress, getting it ground flat to the same depth as the mono side and fitting the new cell(s) on there. The cells from Microcine seem somewhat expensive (aren't they like $300?) - although this includes the preamp. Have you seen the cells as supplied by Microcine first hand? It may be that the $300 includes the shaft and plate and a VERY good preamp...Thanks
David
Posted by Richard Fowler (Member # 893) on 08-04-2002, 02:46 PM:
Dolby has a raw stereo cell chip 33008 which as a list price of $75.00 / 47.77 GBP / 75.75 Euro if you are into building something.
Richard Fowler
TVP-Theatre & Video Products Inc. www.tvpmiami.com
Posted by Patrick de Groot (Member # 858) on 08-04-2002, 05:56 PM:
You can use some mic preamplifier to amplify the signal. I have succesfully used the following preamp: Vivanco MA 222. It has a variable impedance and two inputs/outputs L&R. Just go to www.vivanco.com and search for MA 222.You can also use a mixer, but then you need to pay attention to the input impedance (or hope for the best...). You should buy that vivanco and put the output signal to the mixer's cd input or directly to you're amplifier.
The cable length isn't a real issue. Make you're own mic cable's.
Posted by Josh Jones (Member # 447) on 08-04-2002, 07:12 PM:
I would do it right and spring for the $300 upgrade. It will usually work better and in the end be well worth it. But after all, I just had payday. 
Josh
Posted by David Rigby (Member # 1301) on 08-08-2002, 10:41 AM:
OK, so I've decided to cough up the dough and buy the Microcine parts (assuming that $300 gets what I need for the job...). With that in mind I need to run the output from the preamp to an external amp since the internal one is mono. There are situations though where I'll probably still want to use the internal amp, so I hooked the preamp output up to a switch so I could switch between internal and external amplification. Trouble is, though the internal amp sounds great (seems to have improved since I rewired the cell), if I route the output through a hi fi amp it sounds absolutely dreadful...what have I overlooked?! I recently bought a CP50 but I wouldn't expect that'd make any difference to a mono source - or am I wrong? Should it go via the CP50 to the amp? I'm still learning when it comes to setting up my sound - as you can probably tell!!!David
Posted by Josh Jones (Member # 447) on 08-08-2002, 10:53 AM:
Assuming that the kit comes with a new preamp, why are you trying to rewire the old one if it will be taken out anyway? That cp50 of yours should have a pair of cell preamps in it so you could run the cell leads to the CP50 and have better sound than anything homebrew ever would.just a though,
Josh
Posted by David Rigby (Member # 1301) on 08-08-2002, 11:37 AM:
I rewired the old cell when I figured that with the new one coming in at $300 it might be a little while before I get one! (...and it takes time to get stuff from Microcine 
)Great tip about the CP50 - I hadn't realised it'd have a direct cell input.
David
Posted by John Anastasio (Member # 607) on 08-08-2002, 11:51 AM:
It sounds like you've wired the preamp output to another preamp input. Yup, that'll sound like hell, all right. The levels will just overload the preamp and it will clip like crazy. Only wire the preamp out to the input of a power amp.
Posted by Josh Jones (Member # 447) on 08-08-2002, 03:10 PM:
ah, IC well, in the mean time, you'll have a good sounding mono setup. We all started somewhere.Josh
Posted by David Rigby (Member # 1301) on 08-08-2002, 06:01 PM:
John - odd thing is, it sounded distorted both through the the phono preamp direct from the cell and via the aux input from the projector preamp (but sounds great through the projector amp...). Oh well - now that I'm aware of the cell inputs on the CP50 I'll be using that instead (thanks Josh )David
Posted by Rick Sanjurjo (Member # 1365) on 08-09-2002, 08:02 AM:
David,It will sound funny through a phone preamp because it adds an equalization curve intended for use on records. An aux input is normally intended for line level signals that the solar cell is not, so that will also sound funny if it works at all. The cell inputs on the CP50 are the way to go.
Rick
Posted by Josh Jones (Member # 447) on 08-09-2002, 10:43 AM:
You could use the phono input, but you would have to turn the bass down, as the RIAA curve emphasises the bottom end and cuts the treble.Josh
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"Film is made of silver, video is made of rust"
'nuf said