Need Help With QRX-7500 CD-4 Demodulator Settings

mdamico

Member
I just bought a Sansui QRX-7500 on e-Bay recently and need to know how to set the CD-4 controls on the front panel. I'm using the Sansui with a Dual 510 CD-4 turntable and a Pickering XUV-4500 cartridge. I had a QRX-3500 and the separate QC-04 demodulator in the early 70's (used with the same Dual turntable) and I don't think I had as many things to adjust on the separate demodulator. I remember maybe a 30 KHz carrier level set and one other knob that you would adjust while playing the Sansui CD-4 Adjustment record that came with the demodulator. I remember there was a bright read carrier LED on the front of it that would go in and out if you were playing a worn out CD-4 record. My QRX-7500 didn't come with any owner's or user's manual, so I need help with this CD-4 setup subject. Also, if anyone has a copy of the user's manual that I could copy I would really appreciate it. Maybe someone has a scanned in PDF version they can share.
BTW, it's been good to find this forum. I could read the posts for hours!
 
I found the service manual O.K.; it's the operator's manual nobody seems to have. The service manual only has things like schematics, photographs, and parts lists. It really doesn't tell you how to operate the receiver.
 
As you're aware, proper CD4 alignment requires the use of a special test disk ... if you still have the disk from your QC-04, that should work fine.

They all set up about the same. Check page 12 in the 7001 manual ...

http://www.vintageshifi.com/repertoire-pdf/pdf/telecharge.php?pdf=Sansui-QRX-7001-Owners-Manual.pdf

That said, if you don't have the test disk, you can come real close just using a 1k test tone. Set the main CD4 carrier level so it doesn't distort, then set individual channel levels for proper balance. You can tweak those on the fly during a session if you're losing the carrier light or getting noise.

So, how much CD4 material do you have? I've been playing the quad game for many years now and probably have a dozen real disks in the collection. Just way too finicky for my tastes. I do have a lot of SQ and QS stuff here, but that doesn't require any special equipment (other than the decoders) or procedures, dancing naked under a full moon, the sort of things involved with proper CD4 playback ...
 
Here's my "sansui" test record ...

shipping-records-006.jpg
 
As you're aware, proper CD4 alignment requires the use of a special test disk ... if you still have the disk from your QC-04, that should work fine.

They all set up about the same. Check page 12 in the 7001 manual ...

http://www.vintageshifi.com/repertoire-pdf/pdf/telecharge.php?pdf=Sansui-QRX-7001-Owners-Manual.pdf

That said, if you don't have the test disk, you can come real close just using a 1k test tone. Set the main CD4 carrier level so it doesn't distort, then set individual channel levels for proper balance. You can tweak those on the fly during a session if you're losing the carrier light or getting noise.

So, how much CD4 material do you have? I've been playing the quad game for many years now and probably have a dozen real disks in the collection. Just way too finicky for my tastes. I do have a lot of SQ and QS stuff here, but that doesn't require any special equipment (other than the decoders) or procedures, dancing naked under a full moon, the sort of things involved with proper CD4 playback ...

You were asking how many CD-4 records I had. I think I have maybe a dozen CD-4 records too. I thought I was becoming a ham operator with all of the tweaking I had do between adjusting carrier levels, adjusting anti-skating,, and worrying about blowing a speaker when the carrier dropped out and back in again on a worn record. I use to record them right away on an AKAI GX-208DSS reel to reel recorder. Some CD-4 records I know I have are Mike Olfield's Tubular Bells; Doobie Brother's "The Captain and Me"; Iso Tomita "Snowflakes are Dancing". I'll have to dig them out of my record boxes and make an inventory. I have some Quad 8-tracks too, but I'm not sure they'll still play since I saw the felt was gone (freekn' evaporated) of some of them. Imagine having to re-work an 8-track?
 
Something else worth mentioning - ONE pass with a non-Shibata tip on a CD4 vinyl - or a worn Shibata for that matter) is enough to trash it for accurate playback. That alone makes suspect a majority of what may still be available in the used market.

Not so with SQ and QS, which didna need any specialty stylus or table. I've got quite a few of those here, and they're all special. And worth repeating, a LOT of the music of that era was recorded with QS equipment but labeled stereo, so be prepared to be surprised there.

PS ... I'd think in this day and age, a vinyl rip to digital would be the way to go. That should also capture the rear channel carrier cleanly from a good source. I should give that a try with what I got and see what happens.

Mitsubishi DP-EC10 table
AT12s cartridge w/shibata
DJ PRE II stage
... and rip at 96/24 ...
 
I'll have to take a look at my Pickering XUV-4500 stylus and see what it looks like. I always took good care of my records, but I did use the stylus on regular stereo records as well as CD-4 records.
 
I'll have to take a look at my Pickering XUV-4500 stylus and see what it looks like. I always took good care of my records, but I did use the stylus on regular stereo records as well as CD-4 records.

A shibata tip won't hurt standard stereo recordings. If anything, it might etch the bottom of the grooves a bit, but that won't affect playback. Could also effect longevity of the stylus, but not so's you'd notice. I've run a lot of stereo using my AT shibata. It's going the other way that's a problem as a standard stylus can scrub the sides of the groove and distort or destroy the four channel carrier.

* If you do use a shibata for stereo playback, chances are good that any crud the stylus digs out of the deep end of the groove will be stuck to the sides where the music is from static if nothing else. Be sure to give the record a good cleaning between plays.
 
I have some Quad 8-tracks too, but I'm not sure they'll still play since I saw the felt was gone (freekn' evaporated) of some of them. Imagine having to re-work an 8-track?
Quad, Q8, 8-track tapes can be pretty nice. There are repair kits available. I practice on the ordinary two-channel stereo carts and then repair the Q8s.

repair kit source:
http://www.katestrackshack.com/deluxe_repair_kit.html
 
Last edited:
Back
Top Bottom