Film-Tech Forum ARCHIVE: New noise when reverse scans were installed

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Posted by Tim Sherman (Member # 569) on 08-19-2002, 03:17 PM:

First off this is a drive-in, we just changed over to the component engineering reverse scans, and since we did i have noticed a couple of things i really don't like in the quality of the sound. Anytime someone talks on the sound track that contains the letter "S" it becomes elongated and sounds kinda distorted. (kind of like what people would say a snake sounded like SSSSSSSSS) But it only happens on the "S". They were set up with a scope and an RTA and all of the levels check out. I even turned down the high frequency trimpod alittle to see if that would help. but still no luck. i never had this problem before when we used the exciters. On the one screen i also seem to have a low freq. hum, sounds to me like it would be right around 60hz. Bad ground or ground loop maybe?

We run Simplex XL & 35 projectors, XL soundheads (SH-1007 i think) component engineering analog ony reverse scans, Smart Mod2 B-Dit, Beheringer Compressor/Limitors and then a FM modulator.

Any Ideas?

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http://www.autoramadrivein.com

come on out to the drive-in and spend a night out with the stars"

Posted by John Pytlak (Member # 331) on 08-19-2002, 03:47 PM:

That's sibilent distortion. Laboratories use a special test known as "cross-mod" to measure and control distortion caused by non-linearities in the printing process:
http://www.kodak.com/US/en/motion/support/h44/h442.shtml#123404

With traditional cyan+magenta+silver analog soundtracks, the optimum printing point is slightly different for red LED and "white light" readers, so one may hear slightly more distortion on the reader that the lab did not optimize for. "High Magenta" (magenta+silver) tracks are more compatible with both readers.
http://www.kodak.com/US/en/motion/support/dyetrack.shtml

Current surveys show that a majority of theatres now use red LED readers, but there is still a high percentage of "white light" readers. "High Magenta" tracks are an interim step until enough theatres use red LED readers to allow the use of cyan dye tracks.

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

Posted by Gordon McLeod (Member # 33) on 08-19-2002, 05:15 PM:

The extended hi frequency may be making the NR in the processor effectivly fight your compressor
The Noise reduction is basically an expander
There is a memo on Smarts Website re correct wireing between a reverse scan and there preamp

Posted by Manny Knowles (Member # 1171) on 08-19-2002, 05:46 PM:

We experieced this too with both the Dolby CP-45 and also the Smart MOD IIB.

I don't recall what, if anything, was done to cope with this for the Smart processors. It's been ages since I serviced the MOD IIB's.

We turned the HF Gain all the way down for the Dolby units. Is there such a thing on the Smarts?

~Manny (ready when you are.)

Posted by Darryl Spicer (Member # 711) on 08-19-2002, 06:21 PM:

Actually you probably would have been better off using the JAX light than the Component Engineering reverse scan.

Posted by Jim Alexander (Member # 226) on 08-19-2002, 08:04 PM:

We ran into the same problem when we installed the ASR-40C reverse LED reader by Component Engineering. What we found was two part. First the shields for the signal line must be complete from one end only (Grounded at one end only) also, even doing this the sound head audio line must be clear of any power lines (12" clearance should be good).
The second part dealt with the LED intensity. With the setting of the LED according to Component Engineering, I noticed a faint 60Hz background hum. What I found, through experiment, was the intensity set the signal to noise ratio of the reader. I found that increasing the intensity slightly would increase the signal to noise sufficient enough to reduce the 60hz backgound hum to the point where it was imperceptable. Although the LED runs slightly warmer, I feel the trade off was worth it.
In the end, I found that the ASR-40 (which is based on the design of your unit), not only increased the frequency response, from that of our exciter lamp reader, but also resulted in a higher dynamic range. On the whole, I am very pleased with the results.

------------------
Jim Alexander
Owner/Manager
Zedex Theatre
Greenwood, Nova Scotia, Canada

Posted by Gordon McLeod (Member # 33) on 08-19-2002, 08:31 PM:

The only hum issue should be the proper grounding that the Mod2B requires and that is different from the norm since they use a quasi balanced input circuit

Posted by Steve Guttag (Member # 268) on 08-19-2002, 08:32 PM:

Nope, a Jaxlight is not the solution. First off, is the film you are listenting to a high-magenta or conventional track? If the color fringe around the track edges (between the soundtrack and picture) is magenta or pink, it is high-magenta. If it is violet, then it is conventional. My guess is you have a conventional track.

Then there is the SMART NR circuit that is most likely mistracking to show off the problem (you will have the same problem with the Dolby CAT 222SR/A which is used in the CP-45 and lesser CP-65s).

As to the hums...that is poor grounding issues, pure and simple. I've installed CE's 20, 30 and 40 series units and you could put your head in a speaker with wide open gain and not get a hum out of it.

Steve

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"Old projectionists never die, they just changeover!"

Posted by Bill Purdy (Member # 202) on 08-20-2002, 10:44 AM:

You are getting good advice in the responses above. On the hum question I would add that sometimes hum can come from room lights, particularly if they are fluorescents. This may have been the case in Jim Alexander's situation. Stick your finger over the lens and see if there is any change. (Be careful not to touch the lens.)

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Bill Purdy
Component Engineering

Posted by Richard Fowler (Member # 893) on 08-20-2002, 11:56 AM:

Jaxlights with the boost amps will pick up florescent lights with ease, which has turned out to be almost all the 60HZ hum problems.
Richard Fowler
TVP-Theatre & Video Products Inc. www.tvpmiami.com

Posted by Randy Stankey (Member # 64) on 08-20-2002, 12:31 PM:

Hold a cigarette lighter about 2 feet away from the sound head, turn on your optical sound and "Flick your Bic" a couple of times. If you hear a "THUMP!" in the speakers you definately have an ambient light problem. Try this in various places to find out the angle where you get the best and worst results. Use this information to try to shield the sound head from stray light.

It may be very tough to keep all the light off the cell/sensor. I had one situation where the light from the lamp itself was reflecting off the sound head door and causing a "Brr-brr-brr" sound from the flickering light. Keeping the sound head door shut during running cured that. Some black gaffer's tape over the window on the door might help as well.

Posted by Martin Dean (Member # 1416) on 08-20-2002, 12:43 PM:

My first encounter with the problem of higher end sibilance was at a preview theatre. They rand me to complain that the clients (from the advertising) industry were very unhappy with the analogue sound they were hearing in the prints. They found the digital track to be fine and so initially I believed it was the new projectors the theatre had just had installed (Sondor's with Basement readers). After fine tuning the optics several times the problem did was not resolved, so as a compromise I even tried rolling off the slit loss as far as I could and still keep it within Dolby spec. But this was still not satisfactory so I reverted back to a flat response.

So I am left scratching my head as to what the problem is. But several things began to point me in the right direction. 1) A feature reel used as a test seemed to play fine in analogue without the noticeably sibilance. 2) The clients where reporting that the same advert played at another preview house sounded fine. So we duly took the advert to this preview house, where we did indeed find the problem was not noticeable, we also took it to a third theatre, equipped with Sondor's also, and lo and behold the problem was there.

The second preview house was a very dry room and for a while I thought this could be a factor, but then this would not explain why Digital was fine in the theatre I was investigating. Eventually the pieces began to fall into place. After a few discussions with the Chief Engineer and a phone call to Dolby we discovered the problem mentioned in previous posts about the cross-mod effects of silver sound tracks on red light readers.

The adverts were being printed at one of the smaller processing houses near London and despite a lot of pressure from Dolby had not yet converted over to High Magenta, something all of the major film printers had done, which is why the feature test reel sounded fine, but the advert was sibilant. And, of course, the second preview theatre was still running with tungsten lamps, so no problem with silver prints.

So at the end of the day both the production company that owned the preview theatre and their clients discovered that they should be insisting on magenta prints in order for the products to sound as good as possible in cinemas.

Since then we have discovered that problem is more noticeable eon the latter processors (i.e. the CP500, CP45 and CP650), but does not seem to be a problem on CP-65’s a lower. This may have something to do with sound processing in the digital rather than analogue domain.

So what is the remedy for running older prints (all new prints should be hi-magenta), well the only one I have heard suggested so far would be to mount an older Dolby analogue pre-amp in an interface box so that it could be switched into the system to run older prints. I don’t believe this has been tested yet so I have no idea if would actually work. Of course it would require using non-sync input or the like to work, and switches in the cell lines (not a good option), but it may be an option where places run older prints.

The fact that the problem had not been widely publicized is interesting. A compromise was obviously decided upon in favor of newer prints and of course it is now too late to go back.

------------------
Martin Dean

martinidean@charter.net

Posted by Martin Dean (Member # 1416) on 08-20-2002, 12:58 PM:

No disrespect to JAX lights, but there pre-amps are known to be sensitive to electrical noise. Not a problem in a good clean system, but in a lot of systems (especially where ancient wiring or micro-invertors are involved) lots of extra noise can appear.

The only other alternatives to the JAX light I know of are using reverse scan units, which give great results, have space for the digital reverse scan, but cost more, or use a laser replacement. Lasers are a pig to line up (for the engineer) but work well with existing cells with no need of any extra pre-amps, can often use the existing exciter supply (if it is regulated), give good results and cost less than reverse scan. The only caveat with lasers is that the optic assembly has to be in good condition. But even the cost of a new optic is factored in it is still cheaper than reverse scan.

Interestingly the response from the lasers can in fact be too good. I have installed several on systems consisting of Westar 2001’s with CP-45’s, along with new optics and discovered even when the slit loss is fully rolled off that there was still a light peak at the HF end (only 1dB or so, so not critical). The theatre did complain of the occasional sibilant film, but I latter put this down to the cross-mod distortion effects of red-light readers with silver soundtracks.

------------------
Martin Dean

martinidean@charter.net

Posted by Steve Guttag (Member # 268) on 08-20-2002, 01:32 PM:

The REAL solution? Easy, junk the red lights...use Infrared LEDs...you will gain signal quantity and quality.

Steve

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"Old projectionists never die, they just changeover!"

Posted by Tim Sherman (Member # 569) on 08-20-2002, 03:18 PM:

Ok thanks for the help so far. I have narrowed down the hum to the lamphouse. If the Lamp is lit there is a hum. I checked the ground at the rectifier and all is good their. No matter what i seem to do at the lamphouse nothing helps get rid of the ground loop. Any other Ideas?

And you were also asking weather it was conventional film or the high-megenta. I havn't checked yet but i would asume high-magenta. The films playing right now are "xXx" "spy kids 2" "Blue Crush" so they are all new releases if that helps. I'll be sure to check tonight though

------------------

http://www.autoramadrivein.com

come on out to the drive-in and spend a night out with the stars"

Posted by Martin Dean (Member # 1416) on 08-20-2002, 03:34 PM:

Sadly infra-red LED's won't work with the cyan track's when they (eventually) start to appear, as there is no component in the dye to prevent the infra-red light going through them. This is the main reasons soundtracks have the silver in them in the first place as Tungsetn Lamps have a high infre-red content and the silver blocks this (simply black dye does not do this).

I believe the infra-red LED's still work with high-magenta prints as there is still some silver content, but when cyan tracks final arrive, infra-red LED's will be as unusable as tungsten lamps.

I strongly suggest anybody with infra-LED's should be looking to upgrade to visible red LED's. Note that for the compenent engineering units with infra-red LED's this may mean a small mod to the power supply to correct the current supplied as they were original sent out a fixed voltage, other than that the upgrade is simple.

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Martin Dean

martinidean@charter.net

Posted by Steve Guttag (Member # 268) on 08-20-2002, 05:17 PM:

"when cyan tracks arrive"....or NOT. The studios will not force the issue if the theatres don't have the red readers and a simple majority is not enough.

I strongly recommend not downgrading to visible red LEDs...it is a downgrade, afterall.

Steve

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"Old projectionists never die, they just changeover!"

Posted by Darryl Spicer (Member # 711) on 08-20-2002, 05:34 PM:

Yes, the Jax lights have many issues when it comes to extranious noises. In the instalations that we have installed in our theaters we changed out the wiring frome the solar cell all the way to the processors. We also grounded the Jax light power supply, wich are DC transformers, to the electrical outlet cases. Also we ran a ground wire from the ground point on the Jax light pre-amp to a screw on the sound head casing. Doing this pretty much eliminated all the noise. We also replaced any belts that may of had cracks in them.

For a drive-in aplication I think the Jax lights would have been a better choice than reverse scan. Do all the propper grounding and there are no problems. Another plus is that if the LED goes out you can put a replacement into the existing socket and the show goes on. You can't do that with a Reverse Scan reader.

Posted by Richard Fowler (Member # 893) on 08-20-2002, 06:03 PM:

The BACP led heads have two thumbscrews and you can pop in a replacement as fast as a JaxLite.
Richard Fowler
TVP-Theatre & Video Products Inc. www.tvpmiami.com

Posted by Jim Alexander (Member # 226) on 08-20-2002, 07:53 PM:

Although the surrounding amient light can also play havoc, especially if it is flourescent light, we eliminated that cause early in the process. The upgrade to the ASR-40 was one step in the process to upgrade our system to analog sterio...on the cheap. Since we do not have the luxury of vast somes of money, and because of my background in audio electronics, we opted to carryout upgrades using off the self sterio and DJ components. Since I was fully aware of the unique requirements of film readers and their impedance issues, a simple resistive/capacitance network solved this problem. As to the levels, by using a simple Radio Shack 4-Mic mixer into a preamplifer and then via a 12 channel equalizer to a 5-channel Sony home sterio unit, I was able to go sterio and increase the power from the old 55watt mono system to 300 watts behind the screen and 560 watts for the surrounds.
There were many noise issues I was forced to deal with throught this whole process. The first was the poor grounds located in this antiquated building...I couldn't get proper shielding. To fix this, I allowed the shields to float at the same level as the Microphone mixer. The second was an inherent 60hz produced by the power supply for the mic mixer (remember these are really low levels 10-33mV). To fix this I built a kick-ass filter for it. And the last was the light hum produced by the flourescent lights. Simple fix, keep them off or place masking on the door and close it. We opted to keep them off.
When it came time to install the ASR-40C, many of the proplems were already solved. I was, however, able to move the shield ground source to the ASR-s power supply thus ensuring proper gounded shielding and I was able to elliminate the impedance compensation for the reader. Once I found the "happy" place for the LED intensity that produced the best signal to noise ratio, we were off to the show.
All in all, we were able to upgrade to reverse scan Analog sterio with simulated surround sound and 860 watts for under $4000.00 Canadian. And yes, our customers love it!

------------------
Jim Alexander
Owner/Manager
Zedex Theatre
Greenwood, Nova Scotia, Canada

Posted by Oscar Neundorfer (Member # 458) on 08-21-2002, 06:49 AM:

There are at least 2 potential problems which I will address.

NUMBER 1

Steve said, "Then there is the SMART NR circuit that is most likely mistracking to show off the problem (you will have the same problem with the Dolby CAT 222SR/A which is used in the CP-45 and lesser CP-65s)."

One of the "problems" I have found is that the reverse scan readers are, in a sense, TOO good. That is, thay have such an extended high frequency response that they pick up a great deal of very high frequency noise from the soundtrack. I doubt that most release prints have a useable frequency response to 13 or 14 kHz (if that high) and above that is just noise. Since the reverse scan readers read well past that frequency, the noise they pick up is likely to mess with the NR characteristics and produce strange results.

Now the SMART NR does a creditable job in playing SR encoded prints, but because of the simplicity of the design and the band splitting arrangement utilized, it is possible for excessive hf noise to cause sibilance problems due to mistracking.

Couple the excess noise with the slit loss compensation circuit characteristics, and you have a very real problem in some cases with some prints. The slit loss compensation is not needed for reverse scan readers. It is there to compensate for hf rolloff when using standard solar cell/exciter lamp soundheads. Reverse scan readers don't roll off the highs very much, so no compensation is needed. HOWEVER, the slit loss circuit is still there even when it is turned all the way down!!! It is a peaking circuit, and adjusting the slit loss control simply moves the frequency of the peak. When all the way down, the peak is at about 35 kHz, which is above the audible range, but is still low enough to possibly cause problems.

Tim, please contact me directly, and I will give you instructions on how to remove the slit loss circuit from your preamp card.

NUMBER 2

I saw this a while back, and I almost went crazy until I figured it out. Actually, I did not personally figure it out, but one of our good friends in Canada, (I think it was Eldon at King Cinemas) handed it to me on a silver platter.

He told me that if the LED source is even SLIGHTLY too far away from the film, you will get this kind of distortion. I had a customer in Michigan who was using MOD IIC processors (same preamp and NR as used in MOD IIBDIT) and had just upgraded to reverse scan readers and was having this problem. The problem was not there with the old soundheads. He was using Kinoton projectors as I recall, and he had to have a special mounting bracket machined so he could properly adjust the LED-to-film distance. It apparently was not adjustable in its original configuration. Once he got the distance set correctly, ALL the problems disappeared.

Hopefully this information will help you.

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

oscar@smartdev.com

Posted by Richard Fowler (Member # 893) on 08-21-2002, 07:22 AM:

The distance of the LED is a noticeable factor in reproduction quality. On a Cinemeccanica there is a small tool available to verify corrrect distance from the film. In older Century soundheads and most Westrex the sound drums may need the inside of the drum edge machined thinner or new sound drum installed.
Richard Fowler
TVP-Theatre & Video Products Inc. www.tvpmiami.com

Posted by Steve Guttag (Member # 268) on 08-21-2002, 07:54 AM:

The distance of the LED to the film will indeed affect response and how noisy the track appears to be...the closer the quieter, keeping it far enough away to illuminate the entire track and not touch the film nor cause a static discharge. I believe Dolby has the specification of the optimal distance somewhere.

As to the lack of need of slit-loss...perhaps but that would merely be a cover up of two problems...the incorrect light source (visible red) with a mistracking NR circuit. The problem isn't the slit loss. Fix the above two problems and the problem also disappears and with extended frequency response to boot. As to how wide a range the optical tracks have, one would have to ask the recording engineers as to what they are putting down.

Steve

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"Old projectionists never die, they just changeover!"

Posted by John Pytlak (Member # 331) on 08-21-2002, 08:13 AM:

Richard Fowler wrote: "The distance of the LED is a noticeable factor in reproduction quality" in a reverse scan LED reader.

That's not surprising. If the LED array is located too far from the film, the illumination of the track becomes more specular. It is therefore more prone to be scattered by the grains or any surface roughness of the film, affecting distortion, frequency response and noise level.

Posted by Gordon McLeod (Member # 33) on 08-21-2002, 09:22 AM:

If the hum is comming from the lamphouse check a couple of items
Is the Powersupply for the Reader by chance mounted on the base and plugged into the same recepticale as the lamphouse

I have usually found it is best to put the PS in the rack and feed it off the same power as the processor

As for the comment of sibblence more noticable on the CP45 and 500 and not on the older 65's it is simple the combo NR card Cat222SR/A is not real SR noise reduction but a emulation The older CP65s had the seperate SR cards installed

Posted by Tim Sherman (Member # 569) on 08-21-2002, 12:44 PM:

Gordon the supply is mounted on the pedistal but i have tried moving the plug to different places. currently(until i get the bugs out) it is run on an extention cord to the amp rack. I think i may have gotten rid of the Hum last night, but i want to double check before i make everything permanant. You mentioned maybe moving the power supply onto the amp rack. If i do this would i have realign the unit or anything, or reset the dolby level to 50% modulation to make up for the longer wire run (voltage drop).

------------------

http://www.autoramadrivein.com

come on out to the drive-in and spend a night out with the stars"

Posted by Gordon McLeod (Member # 33) on 08-21-2002, 01:19 PM:

The reason that I was asking about the mounting of the powersupply is that the powersupply output is ground referenced + and- voltage to the preamp and since the ground is being carried back to the processor via the signal cable and at the same time the powersupply bonded to (hopefully) grounded pedastal with (hopefully grounded) lamphouse attached may be causeing a ground loop
depending on the cable run all you may have to do is run a cat69T and reset the level

I have never had to remove the slitloss circuit on a Mod2serries processor.
Also a compressor is really not needed if one is carefull about setting the levels

Optical soundtracks have a finite limit to the level that can be recorded since there is physically only so much width to the track. Full width is considered 100% modultion
Dolby cat69T is recorded at 50% modulation so one can set the levels to each transmitter so that it is impossible to overmodulate it by determining what input level is required for 100% modulation and then setting the input to it with the dolby tone running at half that amount

Most transmitters will sound a lot cleaner and less distortion done this way

Jim Alexander there are several problems in your method
First the RS mixer is unbalanced inputs so unless you have input transformer on each of the inputs that is probably one of the starting points for hum
second you need proper noise reduction of some form to correctly decode the encoded noise reduction in the LT and Rt optical tracks
third your equalizers should not be on the input of the matrix as you can introduce phase shifts (almost all graphs are phase shifting) which will cause false directional tracking of the matrix.
Also equaliztion is for speaker/room accoustics and that requires the use of an eq on the output to each channel

Almost all of the theatres that I have gone to that have these home brew system don't sound all that good and in fact several of them the old mono system was far less fatigueing (end of sermon put on flack jacket)

Posted by Gordon McLeod (Member # 33) on 08-21-2002, 09:57 PM:

I did some checking and there have been many Dolby CP50's sold on ebay for $300.00 or less and that would have provided far better sound system basis than any of the home brew gear

Posted by Ray Derrick (Member # 1001) on 08-22-2002, 04:46 AM:

The recommended distance of a red LED from the film surface is 1mm.

Any closer will bring the individual elements of the LED array into focus, resulting in uneven illumination across the width of the soundtrack, causing amplitude distortion. Any further away will cause excessive magnification of the LED elements and more significantly, the gaps between them, likewise causing distortion.

Distortion caused in this way is a little different from the more familiar harmonic distortion (THD) or intermodulation distortion (IMD) in that it may cause more complex artefacts like splatter and sibilance.

------------------
Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935

Posted by Mark Gulbrandsen (Member # 72) on 08-22-2002, 07:21 AM:

I seem to remember the thickness of a dime is close to the specified distance for the LED. I've done quite a few reverse scan installs and Mod 2 drive in processors tog ether with excellent results. One place even going so far as to add in an EQ module for the ramp speakers themselves. Set up the mic in my van at the time and actually looked at the ramp speaker respopnse. They sure sound alot better with some minor cut eq in the mid band and they've been no trouble what so ever.
My feeling is that the problem you have is to get rid of the Behrenger limiter. They are really not that good of a piece of equipment to begin with, especially for your particuluar use. The attack time may be way too slow and you might be causing over mod to the transmitter. That can also cause as pitting type sound. I always fed the AM and FM transmitters directly anyway setting the mod level with some SMPTE level film that I have. Never had a complaint.
I love the link to www.georgelucasbites.com on your site. Thats really good for some laughs!

Daryl,
Putting in a JAX light in a drive in has no advantage at all over a reverse scan except for the lesser performance you will end up with. The JAX light preamp is inherently noisy itself and may have only added to the grief. Like most good techs will do, I've only installed one or two of them and then it was back to the real thing.

Mark

Posted by Gordon McLeod (Member # 33) on 08-22-2002, 09:51 AM:

Of interest I haven't had any problems with booth lights and noise with any of the reverse scan readers The Jax lights now that is a different story

Posted by Darryl Spicer (Member # 711) on 08-22-2002, 10:09 AM:

>>Putting in a JAX light in a drive in has no advantage at all over a reverse scan except for the lesser performance you will end up with. The JAX light preamp is inherently noisy itself and may have only added to the grief. Like most good techs will do, I've only installed one or two of them and then it was back to the real thing.<<

Mark

Mark,

I agree with you to some extent about the Jax light. We use them in all of our theaters here except for one auditorium. In that one we put a Prototype of a Component Engineering reverse scan reader. Model I can't remember off the top of my head. We had the LED fail on it once and it was not an imidiate fix. After doing all the grounding of the Jax lights we have very good sound and no noticeable sound artifacts. Using the transformers like you would use for a calculator or something, we found to be a lot better than using the existing exciter supply. I felt that for a drive-in you could have gotten good results with the Jax light and propper grounding since the source is going to be either in car speakers or a cars stereo system wich can all vary in quality.

Posted by Tim Sherman (Member # 569) on 08-22-2002, 04:49 PM:

I got the ground loop taken care of just ended up being wires run to close to one another. I did disconect the compressors and it didn't help any. What i did find out that helped some was turning down the high frequency trimpots on the preamp card of the modIIB did help with the "S" type distortion. There is still pleanty of the high frequeny comming through the system so i will turn down the trimpots just alittle more to see if i can get it to a good level.

With the reverse scans the differece with the channel seperation and the dynamics is amazing compared the exciter. How does the crosstalk look on the scope using the jaxlite and how does it look running reverse scan. I know how it looked between the exciter and the reverse scan.

------------------
http://www.autoramadrivein.com

come on out to the drive-in and spend a night out with the stars"

Posted by Gordon McLeod (Member # 33) on 08-22-2002, 04:54 PM:

There is a slight improvement in seperation and respnse with the jax light