The Workbench

Re: BiPolar Capacitor on BG6000 motor

Puncher — Mon, 03 Sep 2007 07:10:03 GMT

In the case of a DC link or "bulk" capacitor the minimum value of capacitor is designed to accomodate supplying the highest dc current transients with a minimum of droop on the supply voltage. Generally in this mode the bigger the value the better although you should also try to minimise the ESR value of the cap (again to prevent modulation of the supply voltage).

Go for 105degC rather than 85 and the highest voltage rating you can within the physical size limits (although do not compromise a low ESR for a higher voltage).

Everything should work fine.

Re: BiPolar Capacitor on BG6000 motor

yachadm — Mon, 03 Sep 2007 05:53:33 GMT

Peter - thanks for your kind offer of a loaner!

I already have had experience of people sending me units for repair, and me having to fight with Customs to prevent them levying duties on the imports. I ended up having to post bonds on the equipment until it was re-exported, but it's a hassle I don't enjoy repeating.

If you could scan me the Circuit Diagram and Plan Layout pages, for the Main board, and the CD-4 board, I would certainly appreciate it.

Any comments on my previously asked question -

What about replacing 2 x 5000uF/35V Polarized, after the bridge rectifier - I can get either 4700uF or 6800uF (not 5600uF, which I thought of first)?

Re: BiPolar Capacitor on BG6000 motor

Peter — Sun, 02 Sep 2007 13:02:51 GMT

I would guess you simply need a new cartridge then. If you didn't live outside the EU, I'd lend you a good CL to try but they seem to attract import tax every time I have sent them elsewhere!!

On the capacitor front, I applaud your thoroughness but this particular capacitor is an odd one and I worry that it may well need to be a relatively special capacitor to maintain the motor working properly. It is an odd one - talking to a friend of mine, he feels that changing it could well lead to starting problems and even rumble should the replacement not be to the same spec. By all means try, but I would remove the old one with considerable care and keep it safe just in case! I do have the service manual for this deck if you don't - I think the one on site is the DC version.

Re: BiPolar Capacitor on BG6000 motor

yachadm — Sun, 02 Sep 2007 10:33:55 GMT

Hi Peter,

Thanks for your input!

Actually all my CD4 records are in pristine condition, having been bought new, and played only on my (long-time sold) BG3400 CD4 w/ MMC6000. After that was sold, the LP's were left in the cupboard for many years. I just took them out again recently, playing sparsely on my BG4500 w/ SMMC2, and now on my recently completed BG6000. So, they haven't been abused by any heavyweight cartridges.

I will certainly look into a new SMMC20CL.

I have a rule that I replace all electrolytics on any equipment I restore (the results have always proved the effort). Is this bipolar motor cap really worth leaving alone? I can't see it avoiding deterioration after 30 years.

Re: BiPolar Capacitor on BG6000 motor

Peter — Sun, 02 Sep 2007 07:14:31 GMT

Purely as a matter of interest, why are you replacing the capacitor across the motor terminals? This is a very unstressed component but is pretty critical to the smooth running of the motor. I would suggest keeping the old component just in case replacing it with something different has some undesirable side effects.

Just back from holiday so was not here at the beginning of this discussion. On the subject of the CD4 records and a MMC20EN, I have found that switching on the CD4 can make the record sound pretty awful for a few reasons.

1. The record has been played on an unsuitable deck with a heavy tracking cartridge. This simply destroys the rear channels and leads to distorted sound. I am afraid many CD4 records are like this.

2. The cartridge suspension is too stiff/worn out and the cartridge simply cannot track at 45000 Hz. My MMC6000s are not much good anymore. This gives distorted sound using CD4 though stereo is fine.

3. The stylus is worn - similar to above.

You are using a MMC20EN which must be 20 years old at least. I suspect that this as much as anything will be the problem. The footprint that the stylus puts onto the record is quite small but probably not small enough to track CD4 records. Mine certainly could not though again that could be due to age. I have not tried my SMMC20EN as my BG6000 is elsewhere at present, but I would suggest that a SMMC20CL from Soundsmith would be the most sensible cartridge to get. I have used MMC20CLs to play my CD4 records successfully but of the CLs I have, only three play them to my complete satisfaction. The others seem to produce some distortion, audible only on CD4 which I put down to a combination of 2 and 3 above.

CD4 records are in my opinion far superior to the SQ records also available but are much more fragile. They are not a patch on a modern surround sound system though.

Re: BiPolar Capacitor on BG6000 motor

yachadm — Sun, 02 Sep 2007 04:22:54 GMT

Thanks - good advice - I'll use the 220uF cap.

What about replacing 2 x 5000uF/35V Polarized, after the bridge rectifier - I can get either 4700uF or 6800uF (not 5600uF, which I thought of first)?

Re: BiPolar Capacitor on BG6000 motor

Die_Bogener — Sun, 02 Sep 2007 03:55:19 GMT

Look at the tolerance of electrolyt capacitors... +50% / -10%. Some have also +100%...

Usually the industry uses the smaller and cheaper part, so dont care about a 220uF cap. It will work.

Re: BiPolar Capacitor on BG6000 motor

ProGram — Sun, 02 Sep 2007 02:20:13 GMT

Hi! I would prefer Option 2 , but you should easily get 47 and 100 uF in bipolar (for speaker frequency-networks) and and connect them parallel, that would be the better version. Regards Chris

BiPolar Capacitor on BG6000 motor

yachadm — Sat, 01 Sep 2007 15:33:26 GMT

My BG6000 has a BiPolar 150uF 10V capacitor across the Platter Motor terminals.

There are no 150uF Bipolar caps available.

I have 3 options available:

1. Use a 220uF BiPolar - how will this affect the original requirement for only 150uF? Usually I have no problem uprating a required capacitance, if it's a small amount, but here we are looking at a 50% upward deviation from 150uF to 220uF.

2. Make my own 165uF BiPolar using the standard method of connecting in series the -ve leads of 2 x 330uF Polarized caps.

3. Or another method I just thought of - any comments - take a 47uF and a 100uF in parallel, but with each's +ve lead connected to the other caps -ve lead. See picture.

Any comments from the more electronically educated here?

Regards

M Yachad