Replacing Filtersupply large can capacitors

[BrianEno]

I've had a large quantity of US made poweramplifiers from the eighties and nineties like Krell, Levinson, Threshold and Rowland.
Although they differ over circuittopology one thing they had in commen: a big powersupply.
My amps had toroids ranging from 1 to 2.5 kVA per channel and large can capacitors from Mallory, Sprague and CDE.
Designers like Nelson Pass all stated that those capacitors would last approx. 20 to 30 years. So Threshold Stasis(1,2 & 3, S/1000, SA/1 S/500) Krell KSA and KMA series, Levinson ML series (ML-2, 3, 9 & 11) and Rowland Model 5 & 7) all or almost are qualified for having a capreplacement. John Soderbergh performs those operations for Threshold amps standardly.
My question is as follows:
With todays capacitortechniques (better dielectrum I suppose) one can buy in the same size (length and diameter) and Voltage a much higher capacitance rating.
I now operate a pair of Threshold SA/1 from 1984 that had a capacitorbank with 4 Mallory's 80 Volt with 29,000 uF capacitance each.
They measure 6 3/4 Inch and have a diameter of 3 Inch.
The substitude I opted for was a CDE 75 Volts (Railvoltage is 60 Volt) 82,000 uF same diameter (so it fits in the clamps) and even a lower height of 5 5/6 Inch.
At the picture you can see that the Mallory is bigger and produced in last week of 1983. The CDE was produced in week 22 in 1998. So I gained less the nine years her ;-). With a variac I reformed the capacitors before I really start to use them in the amps.
I know that the bridges in the amp will be taxed more but are there any other disadvantages or advantages you can come up with.
All owners of the amps I summoned plus all I did not mention (Sumo, SAE, GAS, Bedini's, Belles, McIntosh, Pass Alephs, NRG, Classe etc..) will face this dilemma to stick with the same size and getting a much larger capacitance or just downsize to volume or increase the Voltage.
What is the best practice here not counting availability and cost.
Thanks.

[huibert34]

The higher the voltage with the same capacitance you get a lower ESR, so for transient response you get a smaller voltage drop.When you increase the capacitance you get les riple but a larger peak current in the diode bridge and transformer ( shorter time the diode bridge is conducting). Goldmund use in his Mimesis 9 only 2 x 4700uF.

[BrianEno]

Originally Posted by huibert34

The higher the voltage with the same capacitance you get a lower ESR, so for transient response you get a smaller voltage drop.When you increase the capacitance you get les riple but a larger peak current in the diode bridge and transformer ( shorter time the diode bridge is conducting). Goldmund use in his Mimesis 9 only 2 x 4700uF.

What would you prefer and why?

[TheLaw117]

Originally Posted by BrianEno

What would you prefer and why?

Somewhere in between? I think more capacitance is probably better overall, but I have no justification for that. ESR is also important...Hmmph

[huibert34]

Originally Posted by BrianEno

What would you prefer and why?

I should prefer the old capacitance , so the diode bridge is not overloaded and the same for the transformer.I do not know the quality of the old American capacitors but there is a big difference between some types, not in capacitance but in ESR.

If you want good quality you can try the 4 pole of Jensen if it is possible to use them . They give a exellent separation between input and output.
I think the 4 pole capacitors give a major upgrade in sound quality.And I think you are looking for a upgrade

[BrianEno]

Originally Posted by huibert34

I should prefer the old capacitance , so the diode bridge is not overloaded and the same for the transformer.I do not know the quality of the old American capacitors but there is a big difference between some types, not in capacitance but in ESR.

If you want good quality you can try the 4 pole of Jensen if it is possible to use them . They give a exellent separation between input and output.
I think the 4 pole capacitors give a major upgrade in sound quality.And I think you are looking for a upgrade

The 4 pole of Jensen is a Snap-in type of capacitor.
I'm was referring to those large can capacitors like Nippon Chemicon (Sprague), Mallory's and Cornell Dublier (CDE). They're outfitted with screw terminals high or low post and mostly a diameter of 3 Inches. Most manufactures use clamps to fit them to the chassis. I found those in all old Threshold (mostly Mallory) Krell (first Mallory the Sprague) Levinson (Sprague) and Rowland (CDE) amps. There still must be thousands out there in those old amps that were to expensive (no one throws away a Threshold S/500 or Levinson ML-3 after 30 years of service) to disregard. So according to all the designers they need at least a capreplacement. Question remains what is wise if you choose to reatin the physical dimensions of the caps: an increase in capacitance or Voltage?

[huibert34]

If you look at the side of CDE :
Aluminum Electrolytic Capacitors - Capacitors by Dielectric - CDE.com you can see the different lifetime and temperture (and quality )of the different capacitors. I Think every brand have there own list . So I should chose for a high temperture and long lifetime,and not which have the most capacitance.

I have the old goldmund mimesis 9 , also with very old capacitors from Philips, but stil no problem. I agree those old amps were very expensive but very good quality

[YellowWorm]

Originally Posted by BrianEno

I now operate a pair of Threshold SA/1 from 1984 that had a capacitorbank with 4 Mallory's 80 Volt with 29,000 uF capacitance each.

I know that the bridges in the amp will be taxed more but are there any other disadvantages or advantages you can come up with.

What is the best practice here not counting availability and cost.
Thanks.

You have a capacity of 58,000uF per rail voltage (or is it 2 different capacitor banks, one for each channel?) which should be OK.

Replacing the 29,000 with 82,000 will incur a very large inrush current which can blow your fuses unless your amps have a soft start circuit built in. In addition at this level of capacitance there probably is some resistor for discharging the caps when you switch off the amp. The wattage of this resistor must be increased otherwise it would not last much. Naturally, you must also change the bridge to a high current FAST bridge.

Moreover your choice of reducing the voltage is wrong. Electrolytic capacitors exhibit leakage, and the smaller the voltage rating - the higher the leakage. This effectively will reduce clarity in the bass performance.

My choice would be to replace the caps with slightly bigger ones i.e 40,000 max. (at 100V or more if space allows) and bypass them (i.e connected parallel to them) with 470uf film capacitors to reduce higher frequency interference. Low ESR is mandatory. To the best of my knowledge best smoothing capacitors for audio are ELNA SILMIC II. I would also change the bridge to a fast one of higher amperage.

If you are not sure how to select your bridge, stick at 30,000uF and simply increase capacitor's voltage and bypass them with film capacitors as stated above

[Conrad Hoffman]

I'd stop listening to the designers, who have no special ability to predict how specific capacitors age, and test the damn capacitors for value, dissipation factor, leakage and HF ESR. Replace the ones that are starting to degrade (way fewer than you probably think) with at least equal voltage and temperature ratings. Test those too, since it's kinda dumb to install parts that aren't any better than the originals- they often aren't, especially if the size has been reduced. The value should probably be between rated and 2X, but no hard and fast rule.

[canvas]

I think Rifa 169 33000uf/100V is probably the best option for you. Paralleled with big film (100uf+) is also a good way to improve the sound, but the type of the film is important.