Electrolytic capacitors have a wet dielectric which degrades with age and temperature. As a result the extremely thin oxide layers may become less isolating when stored over decades. Either the capacitor shorts or opens at some point, or just doesn't perform as good when it was new.
Re-capping is the usual procedure to replace (all) electrolytic caps in restoring old audio equipment.
The most common coupling capacitor value in these modules is 15uF / 40V. These smaller values might be replaceable with solid foil capacitors, though it largely depends on the space on the circuit board if this is possible and the cost involved. High-end audio nut cases (no relation to this blog) may spend top dollar/euro/yen on such things. Here it just has to be in line with the actual value of these units. So we will only use foil if the costs are limited. Otherwise just stick to cheap but good quality electrolytic caps. The likes of Nichicon, Panasonic, Vishay. Vishay bought a lot of the old European brands like Roederstein and also owns the BCcomponents that came out of Philips Electronics Components in 1999. So sadly we can't replace it with the original Philips blue ones, since they went out of passive component business at least two decades ago. I had, and maybe still have, some of them as NOS parts, but would need to test them individually to see if it's worth using them. (would be stupid to install an already faulty or near to faulty component)
Wima offers a 15uF 50V MKS foil type measuring 26.5 x 11mm and 21mm height with short radial leads with 22,5mm pitch. I used a calliper to check one of the small axial 15uF 40Volts (I think Philips blue style) and measured 13mm.
This surely fails.
Also the cost of these Wima caps is quite steep (€ 5,71 including VAT) given the amount required in the circuits.
16 in the E900, and 15 in the F760N.
Also looked at SMD foil capacitors because they tend to be smaller, but the maximum available capacitance was 6,8uF/63V WIMA with PET dielectric.
Don't know if those are any good on audio, but surely not as bad as ceramic types. These have an exotic SMD size code 6054 Note the 60 is the metric size 6.0mm.
Thus the footprint is 6.0mm by 5.4mm. The connection pitch would fit easily with some extra wire. A bit of a fiddle, but might work.
Only the stack or side by side space taken might form a problem. One could put two in parallel to reach 13,6uF and add a third 1,5uF to reach about the 15uF.
Downside: one has to buy them on roll of 500 pieces, for a whopping total of € 979,00 incl VAT.
Cheaper but surely not good for audio are the ceramic SMD capacitors, since they have non lineair properties causing distortion.
So I won't consider those, but are surely a much cheaper kind of capacitor.
Thinking it all over again: maybe recapping everything is just overkill.
Just replace them selectively by using some common sense. Maybe first measure the units with a frequency sweep and maybe a THD+N measurement to maybe locate bad performing caps. I guess mostly the 25V rated in the power supply decoupling need attention, since it is quite close to the 24Volt incoming supply voltage.
Maybe just revisit the schematic and make a new list to identify which ones probably operate close their maximum rating and just need preventive replacement.
Finally the overview of all of the electrolytic caps I found by scanning over the schematics.
E900
A board
4x 47uF 25V (approx work voltage 22.5V, replace with 40V)
8x 15uF 40V
2x 100uF 25V
B board
8x 15uF 40V
3x 100uF 25V (approx work voltage 23.5V, replace with 40V)
F760N
A board (compressor side-chain, control voltage)
2x 8uF 25V
3x 15uF 40V
2x 100uF 10V
2x 220uF 25V
B board (variloss FET controlled amp)
1x 4.7uF 10V
2x 15uF 25V
10x 15uF 40V
1x 47uF 25V
2x 100uF 10V
2x 220uF 25V
Re-capping is the usual procedure to replace (all) electrolytic caps in restoring old audio equipment.
The most common coupling capacitor value in these modules is 15uF / 40V. These smaller values might be replaceable with solid foil capacitors, though it largely depends on the space on the circuit board if this is possible and the cost involved. High-end audio nut cases (no relation to this blog) may spend top dollar/euro/yen on such things. Here it just has to be in line with the actual value of these units. So we will only use foil if the costs are limited. Otherwise just stick to cheap but good quality electrolytic caps. The likes of Nichicon, Panasonic, Vishay. Vishay bought a lot of the old European brands like Roederstein and also owns the BCcomponents that came out of Philips Electronics Components in 1999. So sadly we can't replace it with the original Philips blue ones, since they went out of passive component business at least two decades ago. I had, and maybe still have, some of them as NOS parts, but would need to test them individually to see if it's worth using them. (would be stupid to install an already faulty or near to faulty component)
Wima offers a 15uF 50V MKS foil type measuring 26.5 x 11mm and 21mm height with short radial leads with 22,5mm pitch. I used a calliper to check one of the small axial 15uF 40Volts (I think Philips blue style) and measured 13mm.
This surely fails.
Also the cost of these Wima caps is quite steep (€ 5,71 including VAT) given the amount required in the circuits.
16 in the E900, and 15 in the F760N.
Also looked at SMD foil capacitors because they tend to be smaller, but the maximum available capacitance was 6,8uF/63V WIMA with PET dielectric.
Don't know if those are any good on audio, but surely not as bad as ceramic types. These have an exotic SMD size code 6054 Note the 60 is the metric size 6.0mm.
Thus the footprint is 6.0mm by 5.4mm. The connection pitch would fit easily with some extra wire. A bit of a fiddle, but might work.
Only the stack or side by side space taken might form a problem. One could put two in parallel to reach 13,6uF and add a third 1,5uF to reach about the 15uF.
Downside: one has to buy them on roll of 500 pieces, for a whopping total of € 979,00 incl VAT.
Cheaper but surely not good for audio are the ceramic SMD capacitors, since they have non lineair properties causing distortion.
So I won't consider those, but are surely a much cheaper kind of capacitor.
Thinking it all over again: maybe recapping everything is just overkill.
Just replace them selectively by using some common sense. Maybe first measure the units with a frequency sweep and maybe a THD+N measurement to maybe locate bad performing caps. I guess mostly the 25V rated in the power supply decoupling need attention, since it is quite close to the 24Volt incoming supply voltage.
Maybe just revisit the schematic and make a new list to identify which ones probably operate close their maximum rating and just need preventive replacement.
Finally the overview of all of the electrolytic caps I found by scanning over the schematics.
E900
A board
4x 47uF 25V (approx work voltage 22.5V, replace with 40V)
8x 15uF 40V
2x 100uF 25V
B board
8x 15uF 40V
3x 100uF 25V (approx work voltage 23.5V, replace with 40V)
F760N
A board (compressor side-chain, control voltage)
2x 8uF 25V
3x 15uF 40V
2x 100uF 10V
2x 220uF 25V
B board (variloss FET controlled amp)
1x 4.7uF 10V
2x 15uF 25V
10x 15uF 40V
1x 47uF 25V
2x 100uF 10V
2x 220uF 25V
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