BeoGram

Re: CD4 Modulator

Peter — Thu, 14 Aug 2008 06:04:38 GMT

No you can't. The Beomaster 6000 however has an input for the 4 channel record player but the Aux socket is switchable so that you can use a stereo record player. This input has a switchable RIAA built in.The BM3400 has a similar set up though one swaps between the two inputs using a button under one of the sliding lids.

If you are using a Beogram 6000 with other Beomasters, you use either the Aux or Tape input.

Re: CD4 Modulator

BenSA — Thu, 14 Aug 2008 05:10:00 GMT

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?

Re: CD4 Modulator

yachadm — Wed, 13 Aug 2008 22:12:26 GMT

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

Re: CD4 Modulator

Craig — Wed, 13 Aug 2008 12:51:42 GMT

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

Re: CD4 Modulator

camshaft — Wed, 13 Aug 2008 12:42:47 GMT

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

Re: CD4 Modulator

beoaus — Mon, 04 Aug 2008 06:08:52 GMT

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?

Re: CD4 Modulator

BenSA — Mon, 04 Aug 2008 03:43:19 GMT

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

Re: CD4 Modulator

Peter — Mon, 04 Aug 2008 03:41:48 GMT

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

Re: CD4 Modulator

camshaft — Sun, 03 Aug 2008 16:40:21 GMT

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

Re: CD4 Modulator

Peter — Sun, 03 Aug 2008 16:17:57 GMT

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

Re: CD4 Modulator

camshaft — Sun, 03 Aug 2008 16:06:36 GMT

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

Re: CD4 Modulator

BenSA — Sun, 03 Aug 2008 12:58:04 GMT

Thanks tournedos.....makes perfect sense!

Re: CD4 Modulator

tournedos — Sun, 03 Aug 2008 12:42:38 GMT

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.

Re: CD4 Modulator

BenSA — Sun, 03 Aug 2008 06:19:58 GMT

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!!

Re: CD4 Modulator

tournedos — Sun, 03 Aug 2008 06:05:14 GMT

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.