I got this description from the product section:

"In addition to the decoding, the CD4 Modulators boosted all four channel signals to line level, and although CD4 records are now rarely seen, the line level output is now a most useful feature of the quad decks as it allows their use with equipment not fitted with RIAAs."

 I'm not at all clued up about this but does that mean that if I put the switch on to CD4 that I can connect the Beogram to an Aux for example?

Actually, you don't need to switch it. The RIAA works in stereo as well. So yes.

Make sure you have the Modulator fitted. You can get BG4002's with the switch, but no modulator. Had one myself just like this, I was going to look for a Quad Beomaster when I got it until I found out there was no Modulator.

 

Craig

Oh maybe there is no modulator? As it didn't work when I tried. I actually have another non-functional BG4002 that has about half that amount of components compared to the functional one. A lot is different. I know there were different type but I didn't realise that their could be such a vast difference!

My 4002 has the switch, but no modulator. If you take the wood trim off and remove the metal panels on top, you'll see the space under the control keys where the board would sit if you had one. If I recall correctly, there's some kind of blanking plate in there in my Beogram.

Well that must be it, but why out the switch you aren't going to have the modulator? Did the tell the buyers that the switch is there but serves no purpose. Surely the buyers would want one with a modulator if it was going to have the switch?

 Also how come my both Beograms have such a marked difference in the amount components. The one has also like two din plugs inside which the other doesn't abd what look like huge capacitors?

The one with the capacitors has an AC motor. The other one has a DC motor.

Yes, the AC and DC versions are VERY different regarding electronics. I think that B&O made room for the switch and mounted it to ease installation of the optional CD4 module, hoping that it would be much more popular than it did. I've seen a few 4002's where the cutout in the bottom frame was made and then covered with a black sticker, no switch mounted. Maybe these were made later than the others.

Martin

Dillen:

 I've seen a few 4002's where the cutout in the bottom frame was made and then covered with a black sticker, no switch mounted. Maybe these were made later than the others.

Martin

My first 4002 was like that, with no switch.

 

Craig

Well I must have th AC one as there are like 4 huge grey capacitors. Isn't it a lot more rare then the DC model. Excuse my lack of knowledge but what is the difference between an AC motor and a DC motor? (I know I learn't it at school   )

I might be wrong, but I think the AC motor version has a similar motor to the original Beogram 4000 - a very well built and engineered unit. The DC version came along later when the accountants got to work on the design spec!

francoisvl:

Excuse my lack of knowledge but what is the difference between an AC motor and a DC motor? (I know I learn't it at school   )

Just as the name implies, AC motors are run with alternating current. The frequency of the AC directly governs the motor rotation, and up to a certain limit, the physical load on the motor will not affect the rotational speed. The AC Beograms have an oscillator (frequency controlled by speed selection & fine adjustment) and a power output stage which then supplies the motor itself. One of the large caps provides a phase shift for this current, so that the two coils in the motor produce a rotating magnetic field which turns the rotor.

DC motors on the other hand are just supplied with a voltage (or more correctly, current) which directly affects the torque that is output by the motor. The physical load then tries to brake the rotation. Once at balance, the rotation speed will be stable, but it has to be monitored and regulated by some other means. This can be just a physical device (working by centrifugal force, for example) or a complex electronic feedback system.

In theory, the AC version can be more stable, but as always, there can be good and bad implementations of both. I don't believe the AC Beograms have any significant advantage over the DC versions of same models.

Thank you for your reply tournedos.

 sory but another confusing part of this Beogram is that it has wires attached to al 6 pins unlike the other 4002 that has only three!!

francoisvl:

 sory but another confusing part of this Beogram is that it has wires attached to al 6 pins unlike the other 4002 that has only three!!

Perhaps near the end of the lifetime, the CD4 demodulator was not a practical option anymore (i.e nobody ordered it), so the now unnecessary rear channels were left out of the output cord, just like the CD4 switch was left out of the chassis. These later machines would have been DC models as well. 

Thanks tournedos.....makes perfect sense!

Durban, I recently learned the hard way that although the CD4 can replace your need for an RIAA amp it doesn't amplify the sound to full line level power anyway.  I normally listen to my pentas at about 35 to 45 in volume level.  At first I thought the CD4 on my 4002 wasn't working.  I had the 4002 connected directly to the aux input of my 4500 system and was hearing nothing, until I dared to turn the pentas up to 80, and that's when I could begin to hear the record!  Even then the quality wasn't too great.  When I get the time I'm just going to switch to a standard RIAA preamp and forget about the CD4.  I can't say I'm really disappointed though.  It's a white 4002 with CD4 that I picked up more for the beauty and rarity as a collector.  It wasn't until after I bought it that I learned from Peter the CD4 could replicate the RIAA in a way.

Austin 

My Beogram 6000 amplifies up to line level. It sounds as though yours has a fault.

A fault that just makes it quieter?  Talk about something that'll be a pain to trouble shoot lol.

I imagine that it just was not working! If it sounded rotten (possibly tinny) then the RIAA might be inoperative.

Camshaft...mine does the same as yours, does not amplify to line level either. Maybe the 4002 works differently to the 6000?

My BG6000 plays rather loud at line level. Certainly louder than the BG4500 or the BG1202 both with internal RIAA's. Are you sure the module has not been removed?

 

Hmm, I just tried mine again and there's no difference regardless of whether I have the cd4 switched on or not.  I suppose either it's faulty or I have one of the empty ones.  Thing is, when I picked it up from the seller, he still had the 4-channel RCA adapter plug on.  I guess I'll have to open it up when I get a chance and look inside.

 Austin
 

camshaft:

Hmm, I just tried mine again and there's no difference regardless of whether I have the cd4 switched on or not.  

Is that not the correct way it should work? If the position of the switch made a difference to the output level. It would mean that stereo recordings would play at a different volume to quad ones. If that makes sense?

 

Craig

 There appear to be misconceptions about this fine piece of equipment! I'll try to shed some light on the subject.

1. What is the CD4 Demodulator?

It is a 4-Channel RIAA amplifier, and IMHO, one of the best in the world, even compared with all the fancy new digital op-amps available today. Its transparency and clarity is surpassed by only the best Tube amps. B&O pulled out all the stops when they came up with this one.

The CD4 Demodulator provides full line-level output to all 4 channels, all the time (even if only 2 channels are recorded on your LP).

The choice of your BeoMaster (or other) Receiver/Amplifier will determine whether you hear all 4 channels (Quadraphonic) or only 2 channels (Stereo).

 

2. What the CD4 switch does: 

The switch changes only the Upper Limit of the Frequency Response (Low-Pass Filter) of the output signal from the BeoGram Turntable.

With the CD4 switch OFF, the Upper Limit of the frequency response of the output signal is limited to about 20kHz.

With the CD4 switch ON, the Upper Limit of the frequency response of the output signal is extended to about 50kHz.

That's the only function of this CD4 switch.

The switch position makes NO difference to the output volume level, EVER!

The switch does not switch the RIAA amplifier ON or OFF, EVER!  The RIAA amplifier is permanently ON (as long as you have AC power to the BeoGram).

 

3. Why is the CD4 switch required? 

The switch is required because the Quadraphonic CD4 signal is encoded in a special track, recorded at approximately 44kHz.

A regular stylus is incapable of picking up this signal, and the BG4002/6000 needs a MMC5000, MMC6000, or MMC20CL to pick up this high-frequency 44kHz signal.

If you play a regular stereo LP (non-Quadraphonic) on this turntable, you may hear high-frequency distortion. Switching the CD4 switch OFF, lowers the Low-Pass Filter's upper limit to 20kHz, thus eliminating this high-level distortion.

4. Rebuilding this CD4 demodulator.

I have now rebuilt 4 of these, and I can state with confidence that its sound quality as an RIAA amplifier is absolutely superb. If anyone is not satisfied with their CD4 Demodulator's performance as an RIAA amplifier, feel free to contact me, and I will rebuild it for you. It is easily disconnected from the Chassis, and sent by mail.  Absolutely, do not throw it away - Please!!!!

Regards

Menahem

Thanks Menahem!!

 The mystery has been solved and I finally understand what a CD4 switch and modulator is for. I unfortunately then only have the switch : (

 So I'm presuming that since the beogram will at full line level you would not be able to use the phono input on a Beomaster?