Film-Tech Forum ARCHIVE: SMART SR300 Questions

This is topic SMART SR300 Questions in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Jon Bartow (Member # 241) on 08-04-2000, 04:24 PM:

I was sent, by my DOO, to perform an a-chain and b-chain calibration at one of our theaters this week. Six out of the seven screens have a SMART SR300 Deluxe Decoder for the processor..
My Question is: Where do you connect the scope for the A-chain? Also, how do you get pink noise into the system?.
Each system also includes a SMART EQ600, SMART TU242 amps and a SMART MN520 monitor.
BTW... I'm using an R2 unit.

Posted by Gordon McLeod (Member # 33) on 08-04-2000, 05:08 PM:

It has been a long tie since I worked on those but if my memory serves me right
the scope connects to the Left and right main outputs. There is no slit loss pot
The B chain is set by feeding pink noise in to either the generator or the mag input and selecting that.
If my memory is right it was .707v =79dbc slow in the theatre
Hope that helps

Posted by Russ Kress (Member # 461) on 08-04-2000, 11:28 PM:

I used to run some of those units. I always connected the pink noise generator to the inputs on the equalizer.

In a pinch, you "could" use a pink noise test loop. Play the film and eq the center channel. You will have to turn the left and right amps off while doing the center channel. Short the right cell input to common to force the left channel to play and short the left cell to common to hear the right channel.

This technique was "developed" while working for a now defunct chain that often did not have the ability to get the test gear to arrive in a given location at the same time I was there! Ah! Memories!

The scope does connect to the left and right main outputs on the processor.

Oscar should catch this thread soon and will know exactly what to do.

Russ

Posted by Gordon McLeod (Member # 33) on 08-05-2000, 10:36 AM:

Actually if you connect it to the gen input I believe you pass through the fader and can also input to the sub

Posted by Mark Gulbrandsen (Member # 72) on 08-06-2000, 05:44 PM:

That was always my main beef on Smart processors. They did not include test points for any test gear hookups. The later processors I believe now do have test points though. On the SR-300 you have to adjust slit lens azimuth/focus, and processor null very carefully for decent decoder results. Not one of the better processors around in my opinion. Smart has done many modifications to them over the years, and if yours do not have the mods they should be done. If you call them with your serial numbers they may be able to tell you if they have been or need to be done. The new Smart processors run rings around the older ones. The decoders are among the best today.
Mark

Posted by Stan Gunn (Member # 554) on 08-06-2000, 07:59 PM:

The best way to do B chain is to connect noise gen to inputs of the E/Q module.
I service two of these units and have found them to be the most reliable of any of the analoge only units, including dolby,they perform well even when all the odds are against them, dirty optics,black exciter lamps,ect

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Posted by Oscar Neundorfer (Member # 458) on 08-07-2000, 06:20 AM:

Jon,

Sorry it took me so long to pick up on this topic. I did not look at this forum or anything else on the web all weekend.

The SR300 was designed sometime in the early 80's, and it was not the most convenient product in terms of setup. However, it was a popular product that allowed many theaters to have stereo who could not otherwise afford the higher priced brand. There are still very many in use today, even though the product was discontinued around 1985.

Regarding the a-chain scope hookup, there were no test points available, a serious oversight. However, if you have some small grabber clips on your scope test leads, you can try clipping on the right hand terminal of each of the preamp gain trimpots which are accessible behind the left hand security cover on the front panel. These are hard to get hold of, but these points will give you access to the preamp signals before they go through the trimpots. These are good places to look at soundhead alignment for checking focus and azimuth.

You can inject pink noise directly into the EQ600 inputs after first removing the input leads from the EQ600. Instead of removing the EQ600 input leads, you can just ground the MUTE terminal on the SR300 which will effectively disconnect the inputs to the EQ600. One of these techniques is necessary to avoid loading down the pink noise generator with the low output impedance of the SR300. Then just eq as you normally would.

Another method is to put the SR300 in MAG format and inject the pink noise into the SYSTEM IN terminals on the SR300. If you use this method then the SR300 MASTER FADER and output trimpots will affect the house pink noise levels. Again, do the eq as you normally would.

You may also want to download the SR300 manual from the SMART website if you do not have one. It is available at
http://www.smartdev.com/pdf/sr300.pdf

Thanks to all for the other suggestions made here. And MANY thanks to Mark and Stan for the kind comments.

------------------
Oscar Neundorfer
Chief Engineer
SMART Devices, Inc.

oscar@smartdev.com

Posted by Aaron Sisemore (Member # 145) on 08-07-2000, 06:22 PM:

No offense to Oscar, but in my experience the SR300 is a huge gigantic pile of CRAP. I have had the unfortunate priviledge to have had to service several of these monsters, and can safely say that I have NEVER had one that was quiet. Every last one of them hums (sometimes so loudly that it can modulate the rest of the soundtrack to 60 Hz), crackles, hisses, pops, etc. Installation wasn't the problem; I have completely rewired two racks that had these processors in them (that were wired by a rank amateur several years previous) and NO CHANGE. Grounding has no effect. Of the 5 SR300 systems I have serviced, 2 were replaced with CP55s, two were changed back to MONO(!) (which sounds 1000% better than stereo did with the SR300), and the other one is still in service, albeit with a nasty HUM, until another CP55 can be acquired...

Personally I would stay far, far, away from the real old Smart processors. Anything MODII and later are excellent processors for those on a budget!

Aaron
http://www.cinema-west.com

Posted by Oscar Neundorfer (Member # 458) on 08-08-2000, 08:29 AM:

Aaron,

No offense taken. However, even though the SR300 left a lot to be desired, noise was not typically a problem, your experience to the contrary. Considering the hum and noise problems you had, I am not surprised at your opinion of this product. I can honestly say that I have heard a number of systems that used SR300's, and they were as quiet as anything else out there at the time.

There is a jumper inside near the right rear corner that connected the circuit ground to the chassis ground. Sometimes this jumper could be cut to eliminate ground loops which caused hum. This was not directly the fault of the SR300, but rather it was a system problem.

The SR300 also had some problems with rigid header connections between the main board and the back panel board which could get intermittent and cause crackling and pop noises. We updated the product with flexible headers which pretty much solved that problem.

We offered several updates over the years to improve the reliability and quality of the product.

I am not trying to change your mind or rationalize the problems you have seen, but I do want you to know that many customers did not experience the problems you have witnessed. And for many customers, the product did a more than acceptable job of providing a decent stereo capability where price was a consideration.

What amazes me is that more than 18 years after its introduction, there are still quite a few out there working every day. Heck, we still have SR130's out there working every day, and that product is even older. And in case anyone is wondering, we still support and repair these old products although I for one am in favor of discontinuing support for these antiques.

Come on, guys, buy something new!

Best regards,

------------------
Oscar Neundorfer
Chief Engineer
SMART Devices, Inc.

oscar@smartdev.com

Posted by Jon Bartow (Member # 241) on 08-08-2000, 09:06 PM:

Thanks Guys (esp. Oscar

)