QRX-9001 restoration question

Sansuiman

I like big amps and I can not lie!
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Hi all,

I have a couple of questions stemming from the restoration of a QRX-9001 and would welcome any input, especially from Quad Bob, since he has first hand knowledge of reworking this beast.

First off, I am fully recapping this unit (first of four that I own) and have hit a snag - there are eight 4.7uF bi-polar electrolytics with a rating of 80(!!)WVDC on the power supply board.

A search of the usual suspects (Digikey, Allied, Mouser, MCM) shows that nobody stocks bi-polar 'lytics rated over 50WVDC. MCM and Mouser have non-polar rated at 100VDC, but (and I must admit my ignorance here) I'm unsure if a non-polar can be subbed for a bi-polar. Anybody here have a definate anwer to this one, or a source for bi-polar caps rated at >80WVDC?

Ok, second question. As far as the decoder boards, I am contemplating replacing all the electrolytics with polypropylene caps, so I don't ever have to worry about the caps going south again.

As well, I've heard (although I'm not yet convinced) that poly caps improve the audio quality over electrolytics. I would be interested in any comments on whether this claim holds water, and if there is a particular brand of cap I should consider for it's superior characteristics.

TIA for any input

Kevin / The Sansuiman
 
Bi-polar, non-polar... 6 of one, half-dozen of the other. Same deal.

Mouser carries the Nichicon jobs, but to make the order worthwhile you'll have to come up with more than those four caps. Skip the Xicon caps...seen to many of 'em leaking after only a year or two or service.

Unless the electrolytics on the decoder are all very small values, you're never going to be able to do this. For one, the polypropylene caps are unusual in values larger than .47µf, and they are huge compared to the original electrolytic parts. Metalized polypro are available up to values around 4.7µf, but larger ones are tough to locate, and begin to get real expensive. I'm not familiar with the unit, but I'd venture to guess that there are but a few places in the signal path where the film cap is an option (but if you can squeeze one in, by all means).

Any film cap is superior to an electrolytic in the signal path, but the cost, size, and available values limit the places where you can use them. For DC filtering however, it's probably going to be a while before anything replaces the electrolytic cap.
 
First off, I am fully recapping this unit (first of four that I own) and have hit a snag - there are eight 4.7uF bi-polar electrolytics with a rating of 80(!!)WVDC on the power supply board.

A search of the usual suspects (Digikey, Allied, Mouser, MCM) shows that nobody stocks bi-polar 'lytics rated over 50WVDC. MCM and Mouser have non-polar rated at 100VDC, but (and I must admit my ignorance here) I'm unsure if a non-polar can be subbed for a bi-polar. Anybody here have a definate anwer to this one, or a source for bi-polar caps rated at >80WVDC?

I use Nichicon 100V 4.7uf Bipolar from Mouser. You'll also find Bipolars on the protection pcb. So, look a little harder.

Ok, second question. As far as the decoder boards, I am contemplating replacing all the electrolytics with polypropylene caps, so I don't ever have to worry about the caps going south again.

Replacing them all with polys is a waste (been there, done that).
I replace only the signal path electrolytics with polys. Values are 3.3uf and 1uf...........trace the paths and replace accordingly. They are much larger.......but will fit with a little planning.

As to their audible performance........I like to describe it as 85% of the improvement results just from getting new caps in there, the other 15% is the extended range and detail if polys are used.

As far as:
As well, I've heard (although I'm not yet convinced) that poly caps improve the audio quality over electrolytics. I would be interested in any comments on whether this claim holds water, and if there is a particular brand of cap I should consider for it's superior characteristics.

I've only restored about 70 Vario-Matrix decoders now for over 60 owners.....not one of which has ever asked that the polys be removed or been less than totally thrilled with the performance. As to the "claim"...........its pretty basic science/engineering. Sansui themselves used strictly signal path polys in the QSD-1000 (the "cost is no object" ultimate Vario-matrix decoder) which is what started me down the path of upgrading the receivers, QSD-1 and QSD-2.

Good luck, you'll soon find that a real restoration of a QRX-9001 involves a lot more than simply replacing the caps!
 
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