Testing a Marantz CD-400B ( or any CD-4 decoder ) without a CD-4 turntable.

[tonyE]

I just picked up a Marantz CD-400B on eBay.

The seller could not test the phono preamp at all but he did test, at my request, the four channel high level bypass, which doesn't test much but at least the switch and power supply work.

I wonder how to test this device. My turntable and cartridge won't work. I got a Linn LP12 and Grado Master 2 with a 1.0mV output. So, that won't work and I really won't change it.

I'm not too keen on getting a second turntable, because knowing myself, I will spend a fortune to "do it right"... I think I'd rather spend half a fortune and upgrade my Linn set up.

So, I have several 24/96 and 24/192 capable DACs and PCs and Android tablets to drive them.

So my goal would be to have a front end program that can encode a two channel signal, do some monkeying around with L+R and L-R and FM the L-R with 30Khz. I don't think I need the LF+LR, LF-LR, RF+RR and RF-RR, I guess that just having the FM modulation will enable to "radar" detector to turn on... I suppose the mixer won't do any rear decoding this way....

I guess, if the front end gizmo could derive a surround signal from the L and R, calculate the LF+LR, RF+RR and then FM the LF-LR, RF-RR and then I could output that in two channels to a line level (with RIAA modulator) to phono converter, I could use that to drive the CD-400B ( and my Akai AS980 ) as well.

Ideas?

Note: I did a search for this, but couldn't find any threads that were specific about this.

Update... I found a guy in ebay, motronix2012 who sells an RIAA inverse filter converter... I asked him about the bandwidth of his device.

But I still need to software to generate the test signals.

 

[quadsearcher]

Disclaimer: I haven't done this and I've only been able to play the first couple songs on any CD4 through my CD-400B before distortion sets in (probably setup issues):

If there's a record output on your preamp/receiver/?, run that record-out to the line to phone converter with inverse RIAA. The cartridge specs look good and if you don't have a CD-4 record, play a 12" 45. I think most of my 12" 45s activate the radar.

It won't tell you if the demodulator is working, just that it recognizes the carrier.
I don't know that even developing a CD-4 modulator or software emulator (which would be a huge undertaking with no return on investment) would help test it, one would still need a known good reference, the simplest (maybe only) way would be a CD-4 record. The cartridge specs look promising, is this it? Grado Labs - Reference2 / Master2 Says it has frequency response to 60K and 4.85mv output, maybe all you need is a step-up transformer with wide frequency response

Does the Akai AS980 have moving coil inputs or is there a preamp or step-up transformer in-between? If your existing front end that the turntable plugs into simply boosts gain to moving magnet level (and has great freq. response), you might have all you need! I've read here that moving coil carts can be the best carts for CD-4! (and I hope to try one someday).

 

[tonyE]

Disclaimer: I haven't done this and I've only been able to play the first couple songs on any CD4 through my CD-400B before distortion sets in (probably setup issues):

If there's a record output on your preamp/receiver/?, run that record-out to the line to phone converter with inverse RIAA. The cartridge specs look good and if you don't have a CD-4 record, play a 12" 45. I think most of my 12" 45s activate the radar.

It won't tell you if the demodulator is working, just that it recognizes the carrier.
I don't know that even developing a CD-4 modulator or software emulator (which would be a huge undertaking with no return on investment) would help test it, one would need a known good reference, the simplest (maybe only) way would be a CD-4 record. The cartridge specs look promising, is this it? Grado Labs - Reference2 / Master2 Says it has frequency response to 60K and 4.85mv output, maybe all you need is a step-up transformer with wide frequency response

Does the Akai AS980 have moving coil inputs or is there a preamp or step-up transformer in-between? If your front end that the turntable plugs into simply boosts gain to moving magnet level (and has great freq. response), you might have all you need!

Thanks for the ideas...

(1) There are two versions of the Grado Master 2. I have the low output version, 1.0mV, which sounds better. I suppose I could take the output of the phono preamp (2V) and drive it into the input of the RIAA encoder/converter... hmm... I got two phono preamps of sufficient gain, but the one in tubed CJ might not have the bandwidth, for sure the the Grado preamp (solid state) does. I think.

(2) The guy on eBay believes his passive converter has the bandwidth. He also has an active one... I'm awaiting for his response.

If (1) and (2) above work, that ought to be kludgy but it will work.

(3) Those old vintage receivers only support MM cartridges with 47Kohm loading and gain for a 5mV cartridge.

(4) The step up transformers, as a rule of thumb, don't have the bandwidth, or so I'm finding out. That was my first attempt, to get a step up transformer for my Grado to drive the CD4 decoders. Mind you, that route ain't cheap!

(5) Hmm... maybe just driving a 30Khz carrier signal might trigger the "radar" detector... that ought to be easy to do. Just need some software to drive a 30Khz detector and drive that one of my DACs at 24/96 encoding (the DACs have sufficient bandwidth for this).

(6) I ought to note that I don't have a CD4 calibration LP... only a handful of CD4 LPs I got over the years... and a few QS/SQ as well. This is not meant to be a long term set up, just a test rig to ensure the hardware works. If i set up four Maggies for quad in my living room ( hey, I have the stuff to do it, I got a spare set of 12s and the amps to drive them: Aleph 2s in front, Aleph 5s in the rear and the Kimber 4TC cables to reach...) my wife will surely kill me.

Hasn't anybody else done this before?

 

[quadsearcher]

Anybody else?.... Sorry, me again,

(5) is what I was talking about with a 12" 45, maybe its just my setup but that triggers the radar light last I checked using a AT MLa440.
Still, that doesn't tell us much if anything about how well the unit will demodulate a record. I mean there might be disappointment in a real world application, so why not start there if you want to know if it works?

I'm interested because I'm in a similar place. I would really like to get into a MC cart, but would like to know if I can play the few CD4s I have. There was a step up made for this use I read about here, and there must be solid state preamps as well.

 

[furui_suterioo]

Just try playing the cd-4s with the marantz and your current TT setup, it might work if the Grado has decent seperation in the ultrasonic range.You can't really determine much from just playing a non-cd4 record through the demodulator.
The radar may also activate too easily which basically eliminates the demodulator's ability to function as a 2ch phono preamp(you can still play cd-4, but need a separate preamp for 2ch use).

 

[tonyE]

Just try playing the cd-4s with the marantz and your current TT setup, it might work if the Grado has decent seperation in the ultrasonic range.You can't really determine much from just playing a non-cd4 record through the demodulator.
The radar may also activate too easily which basically eliminates the demodulator's ability to function as a 2ch phono preamp(you can still play cd-4, but need a separate preamp for 2ch use).

The issue is not with the performance of the Grado Master 2 I got, or the Linn LP12. ( I have the Lingo, so I can play both 33 and 45 ).

The issue is that I have the LOW OUTPUT, 1.0mV, version and that will not drive a MM input. Not enough gain.

 

[tonyE]

Anybody else?.... Sorry, me again,

(5) is what I was talking about with a 12" 45, maybe its just my setup but that triggers the radar light last I checked using a AT MLa440.
Still, that doesn't tell us much if anything about how well the unit will demodulate a record. I mean there might be disappointment in a real world application, so why not start there if you want to know if it works?

I'm interested because I'm in a similar place. I would really like to get into a MC cart, but would like to know if I can play the few CD4s I have. There was a step up made for this use I read about here, and there must be solid state preamps as well.

Solid state High End phono preamps should have no issues. The issue, IMHO, is the the CD4 decoders are all hooked up to back side of the MM phono preamps. So, you can not separate them. If I could, this would be easy.

 

[par4ken]

The issue is not with the performance of the Grado Master 2 I got, or the Linn LP12. ( I have the Lingo, so I can play both 33 and 45 ).

The issue is that I have the LOW OUTPUT, 1.0mV, version and that will not drive a MM input. Not enough gain.

A step up transformer should work fine, provided it has wide enough bandwidth. The MCA-76 Ortofon pre-preamp was made for CD-4 but any good pre-preamp should also work.

 

[Doug G.]

You must get a front end going meant for CD-4. Otherwise, you're just mucking around because the CD-4 system relies on the ultrasonic carriers to correctly reproduce all four channels, not just the back channels. Also, getting the radar to light is merely the beginning. It will light with almost any stereo cartridge on a CD-4 record unless it is woefully inadequate.

Once you get that, as others have stated, get it all hooked up and see if the works. If not, the correct thing to do is get the alignment procedure and the equipment, admittedly a bit of an expense but troubleshooting a CD-4 demodulator is unlike any other piece of HiFi equipment and you need the right stuff. A DMM won't do it.

Doug

 

[tonyE]

A step up transformer should work fine, provided it has wide enough bandwidth. The MCA-76 Ortofon pre-preamp was made for CD-4 but any good pre-preamp should also work.

Hmm... there's one on sale right now.... but I think I've blown my monthly budget for such things.

 

[tonyE]

You must get a front end going meant for CD-4. Otherwise, your just mucking around because the CD-4 system relies on the ultrasonic carriers to correctly reproduce all four channels, not just the back channels. Also, getting the radar to light is merely the beginning. It will light with almost any stereo cartridge on a CD-4 record unless it is woefully inadequate.

Once you get that, as others have stated, get it all hooked up and see if the works. If not, the correct thing to do is get the alignment procedure and the equipment, admittedly a bit of an expense but troubleshooting a CD-4 demodulator is unlike any other piece of HiFi equipment and you need the right stuff. A DMM won't do it.

Doug

I beg to differ, I looked at the schematics and block diagram of the CD-400B. The "radar" light only lights up when it detects the 30Khz carrier. I could plug in a signal that carries that and I would see the detector light up, it would also verify that the preamp works. Sure the mixer at the back end will not work right since there will be no difference signal. The carrier detector is there to enable the mixer to work and for the FM demodulator to retrieve the difference signals. If you don't have the correct difference signals, you will have a complete mess in your hands. Please read my original post about the RF-RR and LF-LR signals!

Remember than in a CD4 record, there are NO pure L and R. you have four signals: RF+RR, LF+LR in the lower frequency band and the RF-RR, LF-LR FM modulated. That's the job of the detector circuit: to enable the demodulation of the difference signals and enabling the mixer. There are NO pure front or rear signals at all!

And not "any" stereo cartridge will work, you need something with at least 40 Khz... and note that the 50 Khz bandwidth may be an issue. That's why the Ortofon MCA-76 step up transformer has a low pass filter for CD-4 signals. Most likely though, most non Hi-End stereo cartridges won't reach that high anyhow and the capacitance of the cables will present a low pass filter.

I proposed one way to recreate the output of a CD-4 signal going into the MM phone input of a quad receiver, but I think using the likes of the Ortofon transformer might be the best solution so I can use my current turntable set up.

Now, I need to get a CD-4 calibration LP.

Oh, btw, the Marantz CD-400B IS a "a front end going meant for CD-4". It is THE CD-4 front end for ALL Quad Marantz's. I'm getting specifically to complete my 4415 set up. I have the SQA1 (yeah, I know, not an SQA2B) and the wired remote and I had the receiver rebuilt. I want to complete the collection.

 

[jupp369]

Hi, the Warner Demo PR-186 is a good and cheap LP record:
A1A Left Channel Seperation Adjustment Tone
A1B Right Channel Seperation Adjsutment Tone
A1C Channel Balancing Tones
A1D Channel Location Tones
A1E Carrier Level Adjustment Tones

If your PC/DVD-Player is able to send the 24bit/192kbps from a wav, you can put that signal direct behind the RIAA circuit. Needs a wire and a plan of your Marantz.
Works great, I recorded all my CD-4 and play it back without loss.
There is another solution from StereoLab also here in this forum and at Stereo Lab - JVC CD-4 Decoding in software , but depends on a computer (Apple?).

 

[jaybird100]

A step up transformer should work fine, provided it has wide enough bandwidth. The MCA-76 Ortofon pre-preamp was made for CD-4 but any good pre-preamp should also work.

That should work, as long as you don't have an impedence mismatch. Check the output impedence of the Grado, compared to that of an Ortofon MC cartridge. If they're the same or close, you should be OK. If not, it may adversely affect the performance.

 

[quadsearcher]

There are some voices of experience here.
1. Merely lighting Radar doesn't mean much at all. (semantics could be argued here, but it is meant in context of proposed "tests")
2. Many stereo cartridges will, yes, in fact, light the radar on a CD-4 but will be a mess of distortion in actual use.
3. See (1).

I hope you have success.
Every time this topic comes up I want to revisit CD-4. It is amazing when it works well.

Cheers!

 

[MidiMagic]

Anybody else?.... Sorry, me again,

(5) is what I was talking about with a 12" 45, maybe its just my setup but that triggers the radar light last I checked using a AT MLa440.
Still, that doesn't tell us much if anything about how well the unit will demodulate a record. I mean there might be disappointment in a real world application, so why not start there if you want to know if it works?

I'm interested because I'm in a similar place. I would really like to get into a MC cart, but would like to know if I can play the few CD4s I have. There was a step up made for this use I read about here, and there must be solid state preamps as well.

The 12-inch 45s probably have plenty of audio past 15 KHz. Since a CD-4 record has no response above 15 KHz, the audio on the record is aliasing into the carrier band. This could Trigger the radar light.

Try eBay for a used CD-4 turntable.

 

[jupp369]

see also: CD4: Marantz CD-400B

 

[tonyE]

That should work, as long as you don't have an impedence mismatch. Check the output impedence of the Grado, compared to that of an Ortofon MC cartridge. If they're the same or close, you should be OK. If not, it may adversely affect the performance.

The Grados, being moving iron, like to see 47Kohms but I've been doing fine driving them into the 100 ohms of a tubed CJ. But then, this is a tubed preamp so who knows what it does to the ultrasonics.... it just sounds... GREAT.

I also have the Grado phono preamp, that one provides the correct impedance and gain ( a little bit too high for 1mV, it was originally designed for the 0.6mV).

In this case, I'd be using the phone preamp in the quad receivers... time to do some checking on the physics I guess.

 

[tonyE]

The 12-inch 45s probably have plenty of audio past 15 KHz. Since a CD-4 record has no response above 15 KHz, the audio on the record is aliasing into the carrier band. This could Trigger the radar light.

Try eBay for a used CD-4 turntable.

I thought the carrier detector is looking for a 30 Khz signal... not 'anything' above 15 Khz?

I'm on the record saying that I'd rather upgrade my Linn LP12 ( Karousel? ) than spend the money on a turntable setup specifically for quad. I would likely end up buying another used LP12 or evil SL1200 Technics ( yikes, direct drive, bent arms...) with some kind of a moving magnet cartridge. And I would NOT do eBay for this... likely go through hifishark.com and going to audiogon or one of the audiophile forums. I do NOT buy audiophile stuff from eBay if I can help it.

I also don't want to change the cartridge, I love how the Grado sounds.

I'm just trying to test the CD4 decoders!

 

[Doug G.]

I beg to differ, I looked at the schematics and block diagram of the CD-400B. The "radar" light only lights up when it detects the 30Khz carrier. I could plug in a signal that carries that and I would see the detector light up, it would also verify that the preamp works. Sure the mixer at the back end will not work right since there will be no difference signal. The carrier detector is there to enable the mixer to work and for the FM demodulator to retrieve the difference signals. If you don't have the correct difference signals, you will have a complete mess in your hands. Please read my original post about the RF-RR and LF-LR signals!

Remember than in a CD4 record, there are NO pure L and R. you have four signals: RF+RR, LF+LR in the lower frequency band and the RF-RR, LF-LR FM modulated. That's the job of the detector circuit: to enable the demodulation of the difference signals and enabling the mixer. There are NO pure front or rear signals at all!

And not "any" stereo cartridge will work, you need something with at least 40 Khz... and note that the 50 Khz bandwidth may be an issue. That's why the Ortofon MCA-76 step up transformer has a low pass filter for CD-4 signals. Most likely though, most non Hi-End stereo cartridges won't reach that high anyhow and the capacitance of the cables will present a low pass filter.

I proposed one way to recreate the output of a CD-4 signal going into the MM phone input of a quad receiver, but I think using the likes of the Ortofon transformer might be the best solution so I can use my current turntable set up.

Now, I need to get a CD-4 calibration LP.

Oh, btw, the Marantz CD-400B IS a "a front end going meant for CD-4". It is THE CD-4 front end for ALL Quad Marantz's. I'm getting specifically to complete my 4415 set up. I have the SQA1 (yeah, I know, not an SQA2B) and the wired remote and I had the receiver rebuilt. I want to complete the collection.

Great. Have fun.

Doug

 

[Doug G.]

A step up transformer should work fine, provided it has wide enough bandwidth. The MCA-76 Ortofon pre-preamp was made for CD-4 but any good pre-preamp should also work.

I know Linda used, and I presume still uses, a moving coil cartridge with either pre-preamplification or step up successfully.

Doug