Need Discrete 4 channel lesson

[soesbeout]

Hello, Would someone be kind enough to give me a little instruction on the relationship between meter movement in the rear channels on the QRX7500 receiver,and the lite that comes on when playing disrete 4 channel records.I am trying to find out if the bulb for the demodulater is out.Will I get meter movement regardless of what frequncey the cartridge is capable of, or the lite will not go on because I don't have the right cartridge or am I trying to troubleshoot this in the wrong direction. Thanks for helping a newbie.

Ken

 

[Quadzilla]

Hello, Would someone be kind enough to give me a little instruction on the relationship between meter movement in the rear channels on the QRX7500 receiver,and the lite that comes on when playing disrete 4 channel records.I am trying to find out if the bulb for the demodulater is out.Will I get meter movement regardless of what frequncey the cartridge is capable of, or the lite will not go on because I don't have the right cartridge or am I trying to troubleshoot this in the wrong direction. Thanks for helping a newbie.

Ken

Hi Ken, the meters will have nothing to do with whether or not the demodulator sees a quadradisc subcarrier or not. They will only show if a signal is present. I could be wrong, but it is likely that you will see rear channel information that is the same as the front if the demod is not functioning. What cartridge are you using? How have you adjusted the levels? Try playing with the adjustments if you do not have a set-up disk ... starting with the subcarrier adjustment. The separation controls will not effect the light coming on or not. Good luck! Mike.

 

[The Quadfather]

Dear Ken:
The meters will show audio signal whether the demodulator is working or not. It will be the same signal as the fronts and will be a combination of the front and the rear for that channel if the demod isn't working. If the demodulator is working, you will hear a thump as the demodulator locks up just before the music starts. This coincides with the "radar" light coming on. (they actually called it that) That shows that the demodulator has detected the subcarriers on the record. However, I don't know if your receiver mutes the thump, but I don't think so. The Audio Technica AT331LP will work with CD-4 and is still made. There are others as well, but I don't know the model numbers. Shure makes one. They must have a Shibata or a Line Contact stylus, and an extended high frequency response to work. If you turn the separation pots all the way down, you will get only the audio from the subcarriers. It will sound hollow. If there is no sound at all, your demod has not achieved lockup. If you do hear the subcarrier audio, adjust the carrier level slowly for best fidelity of the signal. This signal usually has some noise, and the idea is to reduce that noise as much as possible. This will be impossible if the stylus and cartridge are not up to snuff. The scratchy noise is caused by the demod losing lock momentarily, as the stylus skates over the fine modulations on the record instead of following their contour. A good CD-4 stylus will not do this, but it usually requires tracking a little heavier than the manufacturer recommends, about 2 grams for the AT331LP. I have found that 1 3/4 grams works pretty good. Once you have the fidelity as good as it can be with the subcarriers, turn up the separation pots to bring in the main audio. When the main audio matches the level of the subcarrier audio, maximum separation will be achieved. You can improve fidelity by raising the main audio beyond this point, but you sacrifice more separation the more you do it. This is usually worth it if you don't do it too much. I run mine a tad over, and still get good separation. Happy Listening!

The Quadfather

 

[soesbeout]

Thank you very much for the help with my CD-4 education. I hope my learning curve gets better the more I tune in here.I did a little research on my Stanton cartridge and discovered it only goes up to 20K? What is the minimum,this could be my solution to the problem.

Thanks Again Ken

 

[Obbop]

A CD-4 cartridge (the good ones) are typically rated up to 50,000 Hz.

A believe the subcarriers are in the 30,000 plus range.

 

[The Quadfather]

The subcarriers are 30KHZ, however, the modulation deviation swings it to between 15KHZ to 45KHZ. Most workable CD-4 carts are rated at least 30KHZ at the high end. I realize that this appears to be inadequate, but cartridges are rated for flat response and at 30KHZ, they usually have enough response tapering off into the 45KHZ range to perform well. At any rate, this is far less important that stylus shape and agility, whether it can actually track a complex FM modulated subcarrier at these frequencies or whether the stylus tip will actually fit between the modulations, and thus not skate over them. The Trackmaster 8 I use which is the forerunner of the AT331LP is rated at 30KHZ on the high end, but it performs well. I certainly have not tried all of the modern carts that are supposed to work well with CD-4, but I found a good one and I'm sticking with it, though I might try that Shure cart, or a Pickering stylus for my Stanton cart. (the Stanton quadrahederal stylus was a disappointment when I tried it new back in the eighties.) I understand the pickering stylus is a different story. I was once told that the cartridges were the same. Anyway, You can get good CD-4, but you have to work at it. Once there, it is well worth the trouble. Also, always clean your quadradiscs before each play. This is obvious, since one should clean any LP record before play as a routine record quality maintenance procedure, but is doubly important with quadradiscs, because it takes a lot less dust on a quadradisc to make it sound crappy than on a standard LP. Anything that interferes with tracking those fine modulations is going to make it sound bad.

The Quadfather

 

[soesbeout]

Hi Gang, Happy Holidays, After digesting all the info I recieved (thank you very much) on the CD4 troubleshooting, I think a new cartidge is in order.Even with an E-mail to Audio-Technica about the AT331LP saying its no longer made,I have found several sources for it.But I would beg one more favor and that is to sound off your pros and cons of the Walco ES30 cartridge 10-35Hz, Shibata Hyper-Ellip parabolic styus that i found on the web or the AT331LP that has the linear contact stylus.

Ken

 

[The Quadfather]

I tried the Walco. It is inferior to the Audio Technica. It is also substandard for CD-4 use. It will not play without noise and breakup. It's ok for stereo, but not for CD-4 quad.

The Quadfather

 

[radioheadrox]

Quadfather,

Do you have any opinions about the Grado Prestige series of cartridges for CD-4 use? I've heard positive comments about using the Grado Prestige Blue cart and i'm thinking of buying a Grado Green or Blue.

James

 

[soesbeout]

Thanks Quadfather, I will go with the Audio-Technica the price is not too bad either 51.00. :woopie

Thanks Again
Ken

 

[The Quadfather]

Yeah, the AT is a pretty good cart to get started, even if you upgrade to something else later. I don't know if anything else performs better, but I've known several that perform worse. I had an AT14S, and I put a new stylus on it, and it did OK, but the Trackmaster 8 (AT331LP) performed better. The stylii are about $22.00 . As far as the Grado goes, I have never tried one, so I couldn't vouch for it. I did try one of Ed Saunder's carts, and it was OK, but the Trackmaster still out performed it. So, I'll stick with what I know works.

The Quadfather

 

[sspsandy]

I have both a Grado blue, and an Ed Saunders cartridge. For CD-4 I use the Ed Saunders since it is a Shibata needle, and it has worked just fine. I run it through a nicely adjusted JVC 4DD5, and I get very little scratchy noise, and better highs and lows than any other surround format. I have used the Grado blue for CD-4, and it lights up the radar light just fine. But since CD-4 records are so fragile with regard to the high frequency tracks, I hesitate to use anything other than a line contact or shibata needle on them. Could just be superstitious, but with lps this rare, why chance it?

 

[soesbeout]

Oh Yea I almost forgot, during the time of me whining about my cd4 problem, in the last week or so here, I run into a member of this forum while shopping for used LPs. He works at a record store that sells record collectors albums on consignment here in Portland.They have a pretty fair section of SQ and Discret 4 stuff in good condition. What a small world.

Ken

 

[The Quadfather]

I'm not so sure that CD-4 subcarriers are as fragile as legend would have it. Sure, you can wipe them out with a crystal cart on an Electrophonic with a BSR changer that is not much more than an electronic grammophone. But I had given up on CD-4 for years when I couldn't find stylii. So I played my records through my Tate with an obviously worn Shibata, and for awhile with a conical. (for awhile I couldn't even get a decent stereo cart for what money I had back then.) Anyway, when I found a JVC 4DD5 in an Alabama flea market, I decided to try again. When I wient through several carts, and then tried the Trackmaster 8, even well played records came to life in beautiful non scratchy quad. So, I seriously doubt fragility. I believe that was a problem that existed before the super vinyl was developed. I'm sure I'll get disputed on that one, but that's my story an' I'm stickin' to it! As for the Saunders cart, I believe the cart is the same or similar to the Trackmaster 8, so the stylii are interchangeable. Ya might want to try a line contact stylus on it. For $22.00, it might be a worthwhile experiment. The stylus number is ATN3472LC. If you're interested, try it and tell me which you like better! Happy Listening!

The Quadfather

 

[quadjoe]

Hi all!

I use a Grado Prestige Blue for CD-4 with no problems. I also have an AT331LP, but haven't tried it yet as I had to replace the stylus, now that I have, I will give it a try. I would like to try the Shure V15xMR also, but $$ for sound equipment are kinda tight right now.