Film-Tech Forum ARCHIVE: Kelmar Amp question

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Posted by Bernie Anderson Jr (Member # 410) on 05-10-2001, 11:25 PM:

I have a kelmar Amp I believe the model is AS-8800 (Not sure have to look again). It's the one with two little amps and Exciter supply all in one. Not the blue ones but the grey and white one. Anyway, I'm running a kelmar solar cell in my 9050 RCA reproducer. It is hooke up directly to the amp. Shield to shield, red to red and black to black. What's happening is that there isn't a really good high freq play back. It's very bassy and has decent midtones. I was reading in the manual on this site of an older amp that is similar. It says that you have to put capacitors across two of the input wires to get a "Brighter sound". Am I missing something in the soundhead? I ran the 9k test and buzz track. I have to try it again. Any thoughts?

Thanks

Bernie A

Posted by Paul G. Thompson (Member # 655) on 05-11-2001, 12:25 AM:

Hi, Bernie.

Something here does not sound right. If capacitors are placed across the output of the solar cells, the capacitive reactance will cause the sound to become more bassy. The larger the capacitor, the worse it will become. I think if you re-read the manual, it discusses the use of .02 uf to .1 uf capacitors to give a roll-off of the high end.

Capacitive reactance (measured in ohms) is an inverse function of frequency.

In other words, as frequency increases, capacitive reactance decreases.

I would recommend you take a close look at your sound lense to make sure it is up to snuff, and that you check your sound focus adjustment.

I cannot recall at this time if the solar cells have to be loaded with a 600 ohm resistor and coupled to the amplifier with a 10 micro-farad NPO capacitor (in series with the solar cell output). I have no reference on that unit you have. The 7200 unit does not address that issue, either.

The loading resistor will flatten out the cell's response, and the capacitor will keep the small amount of DC the solar cell developes out of the amplifier pre-amp. I don't think it is needed in your case, but again, I am not sure of that.

Posted by Steve Guttag (Member # 268) on 05-11-2001, 08:20 AM:

Bernie,

Generally, the Kelmar AS-XXXX sound systems hook up right out of the box without external components. Most customers have found them to sound quite nice too.

When you say you hooked up straight to the amplifier, I hope you mean to the input connector block on the case of the whole system (has a spot for both projectors and trims plus some other inputs, as I recall). I presume the amplifier is working correctly too. You can always swap monitor and theatre amps to verify the theatre amp is working right. These amplifiers do have a couple of components that fail systematically...there are a couple of 2.2uF electrolytics that tend to die (they are used as decoupling caps between the stages to block the DC)...occasionally, I have found an amp or two where one cap is actually inserted with the polarity backwards.

Steve

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"Old projectionists never die, they just changeover!"

Posted by Rick Long (Member # 213) on 05-13-2001, 02:15 PM:

Are you sure that the problem is with the amp and not sound lens focus? Try peaking the output, using the 9K loop.

Posted by Barry Hans (Member # 477) on 05-13-2001, 07:50 PM:

This may be a dumb idea, but be sure the slit lens is clean and free of oil. Look through and see if there is oil inside also, if so this will surely help kill the high end. Just a thought.