No CD-4 on my Sansui QRX-7001

[Macdude]

So I've got this receiver, the indicator lamp is definitely not burnt out. I just can't seem to get the CD-4 to decode properly. I've tried multiple turntables and cartridges, nothing. I understand I need a cartridge capable of reaching into the 30-50KHz range, which I think I have, an Audio Technica AT8008 with a line contact stylus. From what I understand they compare to Shibata. I don't have a CD-4 calibration record, unfortunately. All of the turntables have been aligned with a Geo-Disc and play without any distortion whatsoever. The only thing I can think of would be the wrong type of RCA interconnects. Any ideas quad fans?

Ah, and when I play a CD-4/QuadraDisc, I hear the same thing out of the front and rear speakers, just like the unit is in 2CH Plus Back mode.

[tcdriver]

The five important elements required to get good CD-4 performance are:

1) A CD-4 compatible cartridge. i.e. A cartridge capable of reasonably flat frequency response to 45 kHz.

2) A tonearm with low capacitance wiring.

3) Low capacitance interconnects between the turntable and the CD-4 demodulator.

4) A properly set up and working CD-4 demodulator.

5) A CD-4 record, aka Quadradisc.

The arm, interconnect capacitance and preamplifier capacitance should be less than or equal to 100pF per channel. During the quadraphonic era, certain tonearms and interconnects were made specifically with low capacitance in mind for use with CD-4 systems. Excessive capacitance can attenuate the higher frequencies to the point a CD-4 system will not work. If you have not done so already, make sure you have low capacitance wiring in your tonearm and low capacitance interconnect cables.

Good luck.

[Macdude]

Hmm, well the light had never come on with any combination of equipment I've used.. It seems that most newer cables are low capacitance, so out of the four tables, all with cartridges capable of re-producing the high frequencies needed I would have gotten something. Currently I've got a Technics SL-110 connected with a Shure V15 Type III (Jico SAS Stylus) and a Shure SME-3009 arm/original cables. Anyone know if that'd be sufficient? I think my demodulator is shot.

[tcdriver]

Hmm, well the light had never come on with any combination of equipment I've used.. It seems that most newer cables are low capacitance, so out of the four tables, all with cartridges capable of re-producing the high frequencies needed I would have gotten something. Currently I've got a Technics SL-110 connected with a Shure V15 Type III (Jico SAS Stylus) and a Shure SME-3009 arm/original cables. Anyone know if that'd be sufficient? I think my demodulator is shot. I would not expect that the Shure V15 type III would be a good cartridge for CD-4. I have tried elliptical stylus cartridges to play CD-4 records and the results were always poor. I would not assume that newer interconnect cables are low capacitance or that the arm wiring used in the Technics SL-110 is low capacitance. Remember that the total capacitance in the arm + interconnect + preamp input should be less than 100pF for best results. Many turntable arm’s wiring capacitance exceed 100pF.

A signal generator could be used to test the demodulator’s ability to detect a 30kHz. tone and the light.

[Macdude]

Ah, that would give me piece of mind.. I'll try the signal generator method. Yeah I think I've been a bit frustrated by the whole thing. I don't have a way to check capacitance at the moment. I have an audio technica shibata that is definitely made for CD-4 use. I'll check the capacitance and mount that cartridge and go from there. First off I'm going to check the demod. using that 30KHz signal to make sure the trouble will be worth it :thmbsp:. Thanks for your help, don't mean to come off as an over-eager "why doesn't this work now?!" person, it's been a long week.

[tcdriver]

Thanks for your help… Glad to help. I hope that you do get your setup working. The very best results playing CD-4 discs was with the demodulator in my Sansui QRX-9001 receiver when used with an AR turntable fitted with Grace 707 tonearm and a Shure V-15MR cartridge. Although the Shure was not sold as a CD-4 compatible cartridge, its Mircoridge stylus shape and lower coil resistance allowed it to perform well when playing Quadradiscs. Good luck.

[Doug G.]

I'll join in here because I hope you can get your CD-4 working too!

It really is something when working correctly.

The signal generator idea sounds good to me. That way, you eliminate all the stuff before the demodulator and, in fact, this is the way demodulators are calibrated. Feed in the carrier frequency and make the adjustments.

In your case, if you put in 30 kHz and the radar lights, the demodulator is at least reacting to the carrier and then you know you have to get the front end right.

Good luck!

Doug

[Jim M]

Hi
Yes, CD-4 was one of the most challenging of the quad formats to decode properly. But it is worth the challenge.
Next to the QRX-9001 the QRX-7001 is one of the best decoders out there (I believe they actually have the same decoder). Your TT setup is not ideal for quad at this time but you should have seen some sign. Something is definitely wrong.
Do you have a manual for your receiver?. If you have the wrong button pushed, or a selector in the wrong position, it will not work. PM me if you don't.

Yes you need a turntable and cartridge combination setup specific for quad. Yes they must have a low capacitance path all the way to the receiver.
I have a Dual 1229Q (Q is for quad in this case). I have 2 cartridges I can use for CD-4. A NOS AT331LP and AT15Sa cartridge with Shibata stylus. Both are out of production but I managed to find them new. They were and are some of the best at decoding Quad / CD-4, and they sound good too. There are other cartridges out there that will also work, but not many that are currently in production. Part of the CD-4 challange
Presently I am using a Marantz 4270 with SQA-2 decoder module and a separate CD-400B CD-4 Decoder Box.
I also have a QRX-9001 but it is not in the system right now. The 9001 is actually a better setup for decoding, but I am a Marantz fan and have it out of the system for now.

Go over to the QuadraphonicQuad forums (http://www.quadraphonicquad.com/forums/). Research there and ask questions.
They are like this site, only for quad. They do not get near the traffic this site gets but they are a good and very knowledgeable group.
Jim