CD-4

CD-4

This is the “odd man out” in the quad world. Extremely ‘fine’ grooves were etched onto the vinyl record to provide frequencies between 35,000 and 50,000 hertz. The CD-4 demodulator sensed these high frequencies then converted them to a range of around 100 to 15,000 hertz. These frequencies were then sent to the amplifier and on to the rear channels.

A matrix decoder can not sense the high frequencies on a CD-4 record, it can only synthesize the stereo output of a CD-4 QuadraDisc LP.

Conversely, a demodulator can only convert those high frequencies to the audible range, it can not synthesize quad from any source.

CD-4 is not my favorite quad medium for various reasons. Other quaddies prefer it. I guess you’ll just have to listen to both formats, the matrix-type and the CD-4 type to see which is best you.

Jerry Minter of Components Corp. suggested using a 38Khz carrier frequency to handle 2 extra channels of audio information waaaay back in the early 1960s. In May 1972, RCA introduced the CD-4 Quadradisc, using the high frequency method, to the buying public.

A review of CD-4 cartridges in the Feb. 1974 Radio-Electronics magazine found that the best tracking occurred at 2 or slightly more grams.

CD-4 required a special needle shape which contacted a larger surface area of the record, thus lessening the pressure on the vinyl. This helped preserve the high-frequency etchings which carried the rear channel info. The special needle style had various names. The first was “Shibata.” Some stylus/cartridge makers concocted their own name. MicroAcoustics called theirs a “Quadrapoint” stylus. Pickering ultimately called theirs a “Stereohedron,” after first using the “Quadrahedral” moniker. Stanton also used “Quadrahedral.” Bang & Olufsen, those fun-loving Swedes, called their CD-4 stylus a “Multi-Radial” type. On their M24H, Shure used the “Hyperbolic” name.

A Quadradisc plays in regular stereo when a demodulator is not present. Thus, a matrix decoder can operate on the regular stereo signal to synthesize a quad sound from the record. Realize that this synthesized quad sound will not be what would be created if a demodulator was present to extract the quad sound the recording engineers intended to be heard.

Opinion??? Sure, gotta bunch of em’

I don’t use the CD-4 demodulator in my receivers, nor my free-standing unit. I don’t care for CD-4. I let my matrix decoders synthesize the music from stereo that came out on Quadradiscs. Why?????………………..

Vinyl has a limited ability to ‘hold’ the high-frequency carrier signals.

The high-freq signals in vinyl are subject to wear.

Only new, untouched by a standard stylus LPs, are assured of having the high frequency grooves in the vinyl.

Not compatible with any other quad system.

Noise and distortion are common problems.

Poor carrier signal lock-on can cause audible distortion.

A cartridge/stylus combo capable of reproducing 25-45Khz is required.

Cartridge tracking adjustments must be near perfect.

Some turntable tonearms are incompatible with CD-4.

Anti-skating adjustments can be crucial to proper playback.

Some of the earlier records were inferior, wearing quickly.

Can only be recorded onto a 4-channel tape recorder.

Turntable leads, in some cases, need to be low impedance for CD-4 to function properly.

Channel separation of 30-35db max can be matched by a good matrix decoder.

I think CD-4 has an “artificial” sound.

The demodulator needs to be manually ‘aligned’ via 2 or 3 adjusters.

Because JVC, CD-4’s creator, never paid me to say something nice.

Buying Tip

In June 1974 a new IC chip for demodulating CD-4 appeared. Tests showed it did a better job than earlier chips. Try to buy a later-model demodulator that has the new chip. I can’t find a list of these improved demodulators, but, name brand units made after June 1974 are more likely to have it.

The earliest CD-4 records were limited to around 20 minutes playing time per side. Also, due to lax cleanliness standards at the pressing plant, many of the early LP’s (1972 to 1973 or so) had impurities that found their way onto the vinyl, which degraded the playback quality.

In 1976, a high-end demodulator was capable of 35db channel separation at 1Khz, and 25db at 10Khz

WARNING

Don’t feed a demodulator’s output into the turntable input on your receiver, the power level is too high. To avoid damaging your quad receiver, plug the demodulator into aux or auxiliary inputs or into the special 4-channel aux inputs. If your quad receiver doesn’t have 4-channel aux jacks, it’s an el cheapo and it’s time to find a better unit.

A demodulator can be used as a pre-amp. On new receivers without turntable jacks, you should be able to use a demodulator to amplify the turntables’ output and feed it into a receivers “aux” auxiliary input. This works on stereo systems. I’ve never tried it, so it may be a good idea to check with a technician first.

The Shibata-style stylus used on CD-4 cartridges was named after its inventor, a Japanese hombre named… Shibata!!!

A CD-4 cartridge measures at 100,000 ohms versus the 47,000 ohms of a stereo cartridge.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s