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Topic: Freq responce

Sam Hunter
Jedi Master Film Handler

Posts: 779
From: West Monroe, LA, USA
Registered: Jan 2002

posted 11-07-2002 11:07 PM

Well, just when you thought it was safe on the forums I come back for more.
It sure seems like my audio off my rig is partial to lows. I have a Kelmar Transducer on my Soundhead and have aligned it with 7Khz tone alignment film. According to Kelmar you have to connect a 560 Ohm resister in parallel with the cell and run it into your amp. Now mind you I am using an old RCA tube amp out of a Panoram and a speaker from my RCA 400.
I think if nothing else that I should use a speaker setup with a crossover that will get the most out of the high freq responce. Also, I dont think the slit on my soundhead is the .7mm so that may be hindering me a little, but I still think it should sound better.
Anyway, I tried running it into my home sound system but there wasn't enough drive there to run my system.
I didn't win the CP100 I spoke about in a previous thread so I am having to use what I have.
So anyway, maybe some new suggestions or ideas may be of use to me.
Thanks guys.

------------------
Samual Hunter Sr.

KC5ZSL

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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 11-08-2002 12:13 AM

Try running the cell into your phono inputs on your stereo. That will work, just turn down the bass on account of the RIAA curve built into all phono preamps.

Josh

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 11-08-2002 12:27 AM

....and be sure to put that 560-Ohm resistor in parallel with the cells. The value is really not that critical as far as I know. I used anthing from a 330 Ohm to a 1K-Ohm, and I could not really tell that much of a difference.

Also, use some 10uf NPO electrolytics in series with the red AND green (one on each lead) to keep the small DC component out of the pre-amp's input circuit. With some pre-amps, an additional loading resistor might be needed to keep the capacitor from floating and to give a better impedance match.

Oh, by the way - I hope you had the emulsion side to the rear of the soundhead. If not, an error as much as -3DB or more will be introduced into the system, and the HF will really suffer from it.

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Jeff Stricker
Master Film Handler

Posts: 481
From: Calumet, Mi USA
Registered: Nov 1999

posted 11-08-2002 06:13 AM

Sam, Yes just as Paul says a modern solar cell needs to drive a load resistance 300 - 1K ohm. Then capacitor couple to audio preamp.

I use a graphic audio equalizer between the output of the preamp and the audio power amp. (Don't have Dolby, I'm too cheap!) Just play with the controls on the eq. until you are happy. Cheers Jeff

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Sam Hunter
Jedi Master Film Handler

Posts: 779
From: West Monroe, LA, USA
Registered: Jan 2002

posted 11-08-2002 08:11 AM

You know Paul, you may have a point about the emulsion side. Hmmmmm.
Shit, I hope I didn't screw up on that.
Somebody fire me

I will look into that possibilty.
Thanks.

------------------
Samual Hunter Sr.

KC5ZSL

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 11-08-2002 08:40 AM

A better solution is to use an impedancematching transformer such as a mic to line input (typically 600-10K) Radio Shack used to sell one in a XLR to 1/4 adapter

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Adam Fraser
Master Film Handler

Posts: 499
From: Houghton Lake, MI, USA
Registered: Dec 2001

posted 11-08-2002 08:46 AM

Gordon,
Do you still need a resistor if you are going the mic preamp route, I am currently doing the same thing as sam is right now. Would I directly wire the 3 wires (red green and black) into an xlr to line convertor straight into the mic preamp?
I think it is a Kelmar solar cell.

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Adam Fraser here

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John Anastasio
Master Film Handler

Posts: 325
From: Trenton, NJ, USA
Registered: Sep 2000

posted 11-08-2002 09:47 AM

Don't just wire the stereo cell to the two sides of the XLR with the ground on pin #1, or you'll have the two cells wired out of phase with each other and any in-phase information (like a mono track) will just cancel out.

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Jeff Taylor
Jedi Master Film Handler

Posts: 601
From: Chatham, NJ/East Hampton, NY
Registered: Apr 2000

posted 11-08-2002 10:33 AM

Adam: In a previous setup I used to run a mono solar cell into the low z mic input of a 100w Bogen PA amp. Frankly, it didn't make a huge difference with or without the resistor, but I did pad it down with a +/-600 ohm resistor (the closest I could find in my junk box). The only major difference without the load was a bit of escessive sibilence which the eq could deal pretty well. Conventional logic would say that the output should be very low without some load, but in my case that didn't happen. The sound was great.

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Sam Hunter
Jedi Master Film Handler

Posts: 779
From: West Monroe, LA, USA
Registered: Jan 2002

posted 11-08-2002 04:30 PM

Ok, apparently I did align the sound head with the emulsion on the wrong side.
After realigning the thing properly and adding a 10mfd cap in line with the cell my audio sounds a lot more balanced.
I like the transformer idea and I have a 1:1 600 ohm around here somewhere that I will install later.
Thanks guys.

P.S. What else ywould you expect from a guy who can't spell (response).

------------------
Samual Hunter Sr.

KC5ZSL

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 11-08-2002 05:22 PM

Sam, I think Radio Smack stocks them if you can't find yours.

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