Do you need a separate phono pre amp with a decoder?

[elguapo511]

I have a modern 5.1 amp with analog inputs... so no phono inputs.

So when I play a quad LP into a decoder, then into the four analog inputs it sounds alright...

Will an phono pre amp help. I dont have one, so cant A/B

Does the JVC 4dd5 demodulator have a pre?
Does a Lafayette SQ-w need a pre amp? It has a volume attenuator
Does the Sansui QSD-1 need a pre amp?

Do the Soundmasters require a pre amp?

Or will more amplitute just blow the signal?

 

[DuncanS]

I'm not sure about the other decoders as I have no old Quad equipment.

The Involve Surround Master SM2 requires a phono pre-amp I use a Project-Audio Phono Box S2 Ultra with mine https://www.project-audio.com/en/category/hifi-electronics/s2-line/phono-s2-line/

 

[par4ken]

I have a modern 5.1 amp with analog inputs... so no phono inputs.

So when I play a quad LP into a decoder, then into the four analog inputs it sounds alright...

Will an phono pre amp help. I dont have one, so cant A/B

Does the JVC 4dd5 demodulator have a pre?
Does a Lafayette SQ-w need a pre amp? It has a volume attenuator
Does the Sansui QSD-1 need a pre amp?

Do the Soundmasters require a pre amp?

Or will more amplitute just blow the signal?

Yes you require a preamp for all of the above, except for the JVC 4dd5. CD-4 Demodulators can be used as a phono preamps to feed other equipment however the high end will be filtered at 15Khz, necessary for CD-4 but less than optimum for Stereo or Matrix Quad.

 

[Electric Moo]

Is there a difference between feeding a CD4 demodulator an RIAA affected signal from a phono preamp, vs going directly into the CD4 demodulator ( which has it's own phono preamp ) ?

I guess I am wondering if a CD4 demodulator works better without RIAA

 

[par4ken]

Is there a difference between feeding a CD4 demodulator an RIAA affected signal from a phono preamp, vs going directly into the CD4 demodulator ( which has it's own phono preamp ) ?

I guess I am wondering if a CD4 demodulator works better without RIAA

All demodulators have the phono (RIAA) preamp built in. They were not intended to receive an input that has already been RIAA equalised. All demodulators require that a phono cartridge to be directly connected to its input. Connecting an already amplified source to the demodulator will severely overload it; also the RIAA network would filter out almost all of the subcarrier.

 

[Electric Moo]

Aha! That is good to know, thanks

I had no idea of the 15kHz cutoff on CD4

 

[elguapo511]

Anythoughts on technics cd-4? I have a sa-8000x.

 

[MidiMagic]

It depends on what pickup cartridge you have and if your turntable already has a pre-amp:

Most devices require line-level signals at their inputs. Phono inputs on amplifiers may or may not have preamps. Read the manual.

A phono pre-amp amplifies low level phono signals to line level signals. It also provides the RIAA equalization.

If your turntable has a ceramic cartridge, it already outputs line-level signals. And ceramic cartridges have RIAA compensation in the way the ceramic is cast.

Because of this, the ceramic cartridge needs more force from the record groove to make the higher signal level. But it needs no preamp.

A magnetic cartridge puts out a much lower signal. It must be amplified and equalized for RIAA for other devices to use it.

The preamp can be in one of three places:

- Built into the receiver or master preamp.
- Built into the turntable base.
- A separate device connected between the pickup output and the line input.

Some moving coil pickups need an even stronger preamp.

A CD-4 demodulator has a special two-stage preamp. The first stage amplifies the signal to line level. The second stage applies RIAA to the baseband signal.

The carrier demodulator uses the output of the first stage.

 

[MidiMagic]

Aha! That is good to know, thanks

I had no idea of the 15kHz cutoff on CD4

The CD-4 system has 15 KHz as the separation point between baseband and carrier.

The baseband covers a band of 15 Hz to about 14.7 KHz.

The 30 KHz carrier has a bandwidth of about 15.3 Khz to 44.7KHz. The carrier audio has a response of 15 Hz to 14.7 KHz, matching the baseband.

So no CD-4 record has a frequency response greater than 15 Hz to 14.7.

I have some stereo and matrix records that go up to 22KHz.

 

[elguapo511]

Why is it referred to as “carrier”?

 

[DuncanS]

Why is it referred to as “carrier”?

Carrier is a term used in RF engineering, its the frequency that is used to produce the frequency shifted signal. In CD4 the Lf-Lr & Rf-Rr signals which sit on the L & R grooves above the lower band (15-14.7kHz), are mixed in frequency with the 30kHz (the carrier) so that they form a band above 30kHz with the BW range (15.3kHz-44.7kHz) described by MidiMagic. Essentially/conceptually CD4 is two stereo FM radio stations (one on each side of the groove) which are demodulated and combined to give Quad.

 

[par4ken]

Why is it referred to as “carrier”?

It's the same thing as with a radio station, its frequency or channel is referred to as the carrier, the audio modulates (changes) that carrier in some way (altering its amplitude or frequency) in order to carry the audio signal.

 

[Doug G.]

Yes, so the higher frequency "carries" the lower frequencies. Hence, the term, "carrier".

Doug

 

[Electric Moo]

This may be veering off topic a bit, but to continue the CD4 question: discrete tape ( reel to reel ) would be preferable to CD4 records then: presumably the reel source wouldn't have a 15kHz cutoff applied?

 

[Sonik Wiz]

This may be veering off topic a bit, but to continue the CD4 question: discrete tape ( reel to reel ) would be preferable to CD4 records then: presumably the reel source wouldn't have a 15kHz cutoff applied?

Yes. There is a high frequency roll off for tape depending on tape speed (the faster the better) but no pre-disposed sharp cut off like CD-4.

 

[Doug G.]

I wonder what would happen in a double blind test if one source was limited to a 15K cutoff and another, identical, source was not. Methinks I would be willing to bet money one way.

Doug

 

[Electric Moo]

Ha, depends on the age of the listener though

Anyone under 25 might be able to tell easily

 

[DuncanS]

Ha, depends on the age of the listener though

Anyone under 25 might be able to tell easily

Not if they'd ever been to a Motorhead gig!

 

[J. PUPSTER]

Ha, depends on the age of the listener though

Anyone under 25 might be able to tell easily

My little on-line freq. hearing test with headphones revealed that I top out at around 14K; I've mentioned before, and actually feel pretty good about that, as I'm in Medicare territory.
Would be interesting to know a study on average hearing test statistics for various age groups.

 

[Doug G.]

I could hear out to at least 20K when I was in my twenties and even into my late thirties. It's now down to about 16K and music sounds exactly the same to me now as it did then.

I know all about the idea that it happens slowly and you don't notice, etc, but I have always had certain "benchmarks" to keep track. The high frequencies in the tinkling of a ride cymbal, the "sweetness:" of violins, the ability to hear clocks/watches ticking. It all still sounds exactly the same. I am 68.

Doug