Regarding the other RCA
Discrete Quadraphonic Disc system:
Quoting from the Book "RCA and the VideoDisc"
The gap between the status of the system in
November 1972 and the goals they defined was
summarized in a few key measurements:
Goal of four stereo channels: one achieved
Were any RCA CED Selectavision VideoDiscs
ever made (perhaps test discs) with 4
(FM based) discrete channels of sound?
Regarding CD-4 Encoding in 2008:
Using an RCA Quadulator to make CD-4 master discs
would avoid CD-4 Intellectual Property issues.
I think an "offline" CD-4 encoder could be built
and would work with a 1/2 speed record cutting
system (as I described in some previous posts)
but I also think there'd be some CD-4 Intellectual
Property issues to resolve before it could be
used to make CD-4 master discs.
In a previous post I mentioned a method of using
noise to test the ability of a 1/2 speed record
cutting system to make CD-4 master discs.
I don't have the resources to make this test
material and have a test disc made.
Maybe a vacuum tube RIAA section and amplifier
for the line outputs could be substituted in
the 2008 CD-4 Demodulator.
Just a note to let you
know that the CD4 Unit has gone up 15pc
in the last month
Of course, the vacuum tube demod would be simply a challenge to see if it could be done. It is doubtful that it would out perform any other demod. But peope who love tubes do think they sound better. I have always thought that a good DC coupled solid state amplifier will out shine a tube amp any day. Of course, I may have never heard a really good tube amp. On the other hand, if all my gear was tube gear, I'd have to up the tonnage on my air conditioner.
P.S. Incidently, does anyone at RCA even care if someone built a quadulator and began making CD-4 records?
The patent was filed June of 1972 and issued April of 1974, so I expect there would be no Intellectual Property issues.
We are well beyond 20 years.
Regarding Phono Cartridges Suitable for CD-4:
(I just found this link)
CD-4 Phono Cartridge Requirements
Peakiness in this supersonic range (or in any other range for that matter)
indicates a poorly damped mechanical resonance which results in
mistracking and/or wildly fluctuating phase response around the
amplitude response peak. This is probably the major problem with
pickups purporting to be suitable for CD-4 use.
Quoting from the 1976-11 issue of High Fidelity:
CD-4 Channel Separation (20kHz to 50kHz)
Shure M24H Left>8dB,Right>15.5dB
Satin M-117X Left>10dB,Right>6.5dB
The review states "separation decreases toward
as little as 6.5dB, but this is no impediment to
Where did High Fidelity get their information about
the minimum required separation?
Hello All Receptors of Quadraphony,
I am back from the recording studio and the West Coast Songwriters yearly conference which my equipment company sponsors each year (this was the 12th). So let us get down to business!
The turntables and internal wiring do not cause problems with CD-4 reproduction. The biggest problem is the RCA interconnecting cable. Some older cables had high capacitance. At a termination resistance of 50,000 Ohms this can cause some roll off of the sub-channel frequencies (20 KHz to 45 KHz). Low capacity cable is available from companies like Digikey. I will post some part numbers in my next post for any one who wants to replace their interconnecting cables. This by the way is real cable and not the overpriced, under performing junk like "Monster Cable" and all of its clones.
kfbkfb, Lucanu, Doug G., ress4278, Quadro-Action, bmoura, proufo, Quadfather,
For the time being I will let the speculation about a CD-4 cutting system remain with you all. By the way all of the CD-4 patents including mine have run out. All of the current info is now public domain.
Now it is time for Technical Soap Box.
Todays subject is Tubes vs Transistors, the myths are exposed!
This controversy has been going on since semiconductors overtook and replaced thermionics. The statements of warm tube sound vs harsh transistor sound only have validity based on the operation of the devices. In this post I will provide the conditions, the facts, and the realities of this controversy, and set the technical record straight.
What is the real controversy? It is how the devices sound when they are not operating in the linear portion of their transfer characteristics (transfer characteristic are defined as the change to the output of a device for a given change to input to that device).
What is an amplifier? Many think that an amplifier is a box full of tubes or semiconductors ( I use semiconductors instead of transistors because today’s technologies use integrated circuits which have large amounts of transistors, resistors, diodes, etc on a single silicon chip) that takes a small signal at the input and makes this small signal a large one at the output. That is in fact the result of what the amplifier does but not quite how it does it.
A basic amplifier consists of two sections. They are the power source and the control circuit. The power source has the ability to deliver the maximum output energy (voltage, or power- tubes are voltage amplifiers) that the amplifier system is rated for. The control circuit varies the output energy based on the input signal variations. The British appropriately named the vacuum tube a “valve” which is a good description of what it does. As the small input signal varies the “valve” controls the flow of energy from the power source to the load (load being a resistor, headphone, speaker). The gain or amplification is the ratio of the small input variance to the large output variance. As a metaphor, a small varying stream of water on the control valve will create a large varying stream of water from the reservoir. Transistors work in the same way but are current, instead of voltage amplifiers.
If you have a tube amplifier and a semiconductor amplifier side by side, and both amplifiers are being driven in their linear regions, the resulting output from either amplifier will be indistinguishable. If, however, you force the amplifiers into the non-linear portion of their transfer characteristics, then there is a perceptible difference in the sound. Why is this you ask? It is the way each device handles non-linear distortion.
As a vacuum tube approaches the non-linear portion of it’s transfer characteristic, the output no longer changes in a linear fashion with the input. Here is an example. Let us say that you have a tube amplifier that has a gain of 10. That means that for every small change on the input voltage, the output voltage change will be 10 times larger. A 100 millivolt (.100 Volt) input will produce a 1 Volt output, 200 millivolts (.2 Volts) in = 2Volts out, 300 millivolts (.3 Volts) in = 3 Volts out etc. Now let us assume that the linear portion of this tube amplifier stops at 5 Volts output. The numbers would look like: 500 millivolts (.5 Volts) in = 5 volts out, 600 millivolts (.6 Volts) in = 5.4 Volts out, 700 millivolts (.7 Volts) in = 5.8 volts out and so on. You can see that the output change becomes gradually less as the input continues to increase. The power source still has more energy to deliver but the control valve does not have the control range to deliver it. This is a non-linear characteristic called saturation. Saturation is the point on the transfer characteristic of the tube where the output can no longer follow the input in a linear fashion. This condition creates a gradually larger amount of even harmonic distortion. The sound of this type of distortion is quite pleasing and the term “warm” has been given to it.
Lets now look at a semiconductor amplifier that has a gain of 10. For every small change in the input current, the output current change will be 10 times larger. A 100 milliamp (.100 Amp) input will produce a 1 Amp output, 200 milliamps (.2 Amps) in = 2Amps out, 300 milliamps (.3 Amps) in = 3 Amps out etc. Now let us assume that the linear portion of this semiconductor amplifier stops at 5 Amps output. The numbers would look like: 500 milliamps (.5 Amps) in = 5 Amps out, 600 milliamps(.6 Amps) in = 5 Amps out, 700 milliamps (.7 Amps) in = 5 Amps out and so on.
As you can see this non-linear distortion is different. Any current from 500 milliamps and above yield the same output current. This non-linear characteristic is called clipping. The power source energy limit has been reached but the control valve could control more energy if it was available. This condition creates an immediate large amount of odd harmonic distortion. The sound of this type of distortion is very irritating and the term “steely” has been given to it. It is almost like fingers on a chalkboard.
Now all of this information should tell you one thing. Don’t run your amplifiers, tube or semiconductor in their non-linear transfer characteristics. After all of this which type of amplifier is actually better. When it comes to linear operation semiconductors have much better performance then do tubes. High fidelity means sound reproduction that is transparent and with out coloration from the electronics used to record and playback the sound. Today’s semiconductors are capable of at least 4 orders of magnitude (10,000 times) lower distortions (Total Harmonic Distortion, THD, Inter-modulation Distortion, IM, and Transient Inter-modulation distortion, TIM). Noise levels of these same semiconductors can be 6 orders of magnitude (1,000,000 times) lower then the best tubes. The key to obtaining this real time performance is how to operate your amplifier.
One characteristic of music that should be understood by anyone interested in the best high fidelity playback is dynamics. The most important is crest factor which is a fancy name for Root Mean Square (RMS) to Peak ratio. While a conventional Sine wave has a crest factor of 1.414 to 1 or 3 dB, music has a maximum crest factor of 10 to 1 or 20 dB.
So what does this mean to you? If you want to reproduce your music at a power level of 20 Watts and do it in linear portion of the amplifiers transfer characteristic, you need to have a 200 Watt amplifier. This is because the music peaks at 20 Watts average will be 200 Watts. Any peaks that exceed 200 Watts will be in the non-linear portion of the amplifiers transfer characteristic and will distort those peaks. I like to have a little headroom to make sure I stay in the linear portion. For this example I would use a 250 Watt amplifier for 20 Watts linear.
So what is happening in the amplifier real world? First let me divide the amplifier real world into two segments. Segment one is high fidelity playback monitoring and recording, while segment two is music instrumental amplification. As shown in the previous paragraph, the highest fidelity performance is obtained by operating your playback monitoring amplifier in the linear range. If you maintain this type of operation, semiconductor amplifiers are the best performing especially phono cartridge playback, microphone pre-amplifiers, mixers, and power amplifiers.
There are some audio “experts” who cheat. They do not maintain the music crest factor of 20 dB and hide it by using tube amplifiers. As pointed out earlier, tube amplifiers saturate gradually, which means the non-linear distortion rises slower then semiconductor amplifiers which don’t saturate but clip. Even with this cheating the linear performance is no where as good as the semiconductor amplifier.
What about musical amplifiers? Let me put on my recording engineer hat for a moment. Tubes prove to be better in this application because the distortion they create is part of the sound effect for the instrument. When I record an amplified music instrument, I put a pickup microphone in front of the amplifier cabinet so that I capture the total effect of the instrument, the effects pod, and the amplifier and speakers. The tube saturation is a large part of the instrument sound.
The conclusion is that for high fidelity monitor playback or recording, use a semiconductor preamp and amplifier operating in the linear portion of the transfer characteristic and observe the crest factor to maintain ultra high fidelity. For amplified music instruments, tube amplifiers provide a great effect.
Kirk, CD-4 cartridges that worked well had no resonance in the sub-channel frequencies but above (50 to 60 KHz) with amplitude variance of 3dB in the sub-channel band and a Bessel phase response. To achieve this the cantilevers were made smaller in diameter and shorter to reduce the mass. Shure and Satin were far from the state of the art cartridges at the time. High Fidelity Magazine got that information from me during and AES session I gave on CD-4 demodulator playback.
Well folks that is all for now,
Last edited by loudorren; 09-26-2008 at 09:21 PM.
I might add that when you operate a semiconductor amplifier in the clipping mode, or as Lou says, the non linear portion of the curve, the harmonics generated have a lot of energy in the high frequency range, usually supersonic. This can and will destroy tweeters. Tweeters cannot be made heavy duty, because their cones have to be light enough to move fast. Since most of the power is in the bass end, the tweeters are built to handle a small fraction of the total power that the speaker set is designed to handle. This works, until there is a disprorportionate amount of high frequency power caused by clipping. As a stereo repairman, I have replaced many tweeters for people who liked loud music. They often had an amp that was rated well below the power rating of the speakers. My usual recommendation was to get a bigger amp, but not necessarily bigger speakers.
Just to add life to this old post, how is the prototype unit coming? Has it gone through it's field test stage yet?
The voices in my head come from Right Rear only!
In Germany we are also very curious about the first test.
Hello Lou, now it is 2 monthes ago, since we have had a message about the sitation by developing the new Demodulator. I have hope, that the long time since the last message will not have reasons by healthy problems. If there are only further on technical problems (you have said at 25 August, that there are unforseen changes by circuits) we have always therfore an understanding. But without any informations about the reasons for the long time stillness since now, some of us have an uneasy feeling. May be, that it is difficult to find the suitable programmable circuit (a real extra Motorola is much too expensive), but why you don't talk about this problem? I think, information are very important by such a project of developing a new demodulator and interesting buyers.
Meanwhile some of our 14 fans here (Germany) with an order ask me often about the actual situation. They are afraid, that they can't get really a new Demodulator. And I am afraid, that a few from them will make later not really orders with paying money by such an unpaque situation. If the problems are outside of the general working of an demodulator (for excample by the modes of an separat output for the sum and different signal) I can abstain of such modes. I would be very happy to have "only" a modern Demodulator with fewer noise distortions, more dynamic sound and real better channel separation.
Now - Lou - please give us a message about the actual situation, which will have a big interess aof many of the fans with an order for your Demodulator - and that I can inform also those fans without an internet-connection.
So far there are no problems with the new demodulator design. There is however a time problem, Mine. My business ventures are taking a large portion of my time because of end of the year deadlines. I will have some interesting posts about the new demodulator and the Urban evaluation will be coming soon.
Sorry I have not been posting lately, but my record and electronics sound equipment companies have been taking all my time lately.
As Paul Harvey says "Stand by for News"!
Hello Lou, thank you for the quick answer. So we have now a good information, that it is looking well for the Demodulator. But please don't be overworked - we need you.
Regarding CD-4 Demodulator
Automatic Carrier Level System(s):
(Marantz and Lafayette demodulators)
Are the Marantz and Lafayette automatic carrier
level system(s) similar to the system used in the
2008 CD-4 demodulator?
EDIT: Not adjustable might be a better description
Last edited by kfbkfb; 10-29-2008 at 08:03 AM. Reason: Better wording
I, for one, have positive experiences with automatic carrier level adjustment:
The automatic carrier level system in my Pioneer QX-749A works very well, whereas the manual adjustment of the carrier level in my three B&O Beogram 6000 causes hassles.
I have had excellent results with my 4DD5's manual carrier level adjustment. It's a hassle to get it right, but once you do, it stays set.
Lou's system is not an automatic carrier level. It is a limiter system. The carrier is over amplified, and the waveform is truncated on the top and bottom to make essentially a square wave. The square wave is then sent to the PLL at an optimum set level. Small level variations have no effect at all. Is that about right Lou? It's the same thing that is done in an FM radio and that makes a radio more resistant to static and signal level fluctuations.
In an automatic carrier level system, the unmodified waveform, a sine wave, is sent to the PLL circuit after it's level is controlled by a variable gain amplifier stage. A level detector is used to detect the level to control the amplifier. A workable system , but not as good.
Happy CD-4 Holloween,
Kirk, I have a better one, Not Needed. The key to an FM system is the complete removal of any incidental AM. The problem with all of the carrier level systems is that they do not remove the incidental AM. In fact the automatic systems create additional incidental AM by the hysteresis in the detector gain control.
I had a big argument with the Technics engineers about this for the SH-400. It added a lot of extra circuitry which did not improve the performance.
Quadfather's explanation is perfect. Armstrong found that the limiter made the FM receiver (in our case the CD-4 demodulator) completely impervious to the effects of incidental AM for FM radio and CD-4 demodulators.
No trick, a great treat is coming,
Regarding the (JVC) CD-4 FM-based Difference
Signals and 1970s JVC FM Tuner Technology:
JVC FM tuners sold in the early 1970s didn't have
FM sensitivity adjustments, why didn't JVC use their
FM tuner technology in the first generation CD-4
demodulators and avoid carrier level adjustments
there is a privat message for you in the members area.
Please take a look.
Hello All New CD-4 QQ 2008 Signature Series CD-4 Demodulator People,
Time is getting close. This and next four posts will contain the 9 page final schematic of the new demodulator. This is the working circuit and the Urban evaluation is coming soon. Jon will be getting a preproduction unit that physically will not look exactly like the final production, but the inside will be the final production electronics. I have incorporated the features that you have requested and if any of you have questions please feel free to ask.
Each post will define the section of the schematic that comes with it.
Every body enjoy, and I will answer hanging questions in 10 posts from now.
This post contains the Left channel and Right channel Phono preamps.
Hello All New CD-4 QQ 2008 Signature Series CD-4 Demodulator People,
This is the Left and Right Subcarrier Processors and Front Plus Back LPF,