SX-750 replacement filter caps

[sansevy]

Hi everyone,

I'm new to AK and to the Pioneer community. Even though I haven't been posting, I have already benefitted tremendously from the wealth of knowledge in this community. I truly appreciate it. While I've done a fair amount of soldering and tackled smaller DIY electronics kits and basic troubleshooting, working on old integrated receivers will be a step up in difficulty for me. But, I'm looking forward to it.

I just picked up an SX-750 on craigslist and I plan to tackle a recap. I've ordered replacement caps based on the list posted in the pioneer recap sticky, but I was wondering:

a) Is it advisable to replace the filter caps? I realize that this may be dependent on the current condition of the caps. They exhibit no visual signs of distress (like swelling), but I haven't had a chance to take a multimeter to them yet.
b) If replacement is advisable, can anyone point me to replacement caps that will suit and match the size of the original caps? My understanding is that, in order to match the size of the original filter caps, it is often common to increase the voltage rating of the caps. Is that correct?

Thanks!
S

 

[HVHiFI]

A) Replacement like the rest of the recap is optional if the unit is working perfectly. Personally when we are recapping a unit the filters are always done.

B) I usually start by measuring the diameter and height of the cap along with it's value. Plug the former into your search on your favorite parts house and the capacitance. You can bump capacitance slightly, I like to stay within 10-20% increase ideally. Voltage rating if increasing the value meets the diameter even better. I like Nichicon's Gold Tune series if they fit but there are many flavors. You will likely find the new caps are a bit smaller then the originals in height if diameter is the same.

 

[dlucy]

So of the things I've learned from the numerous threads here on AK:

1. The job of the power supply filter caps is to smooth the ripple coming from the full wave rectification of the diodes or bridge. The caps are storing the incoming DC and smoothing out the last remaining troughs and peaks in the converted AC. They "filter" the ripples coming from the rectifier into flatter, smoother DC.

When looking for replacements for these power supply filter capacitors you don't want or need "audio grade" caps. Instead, you should be looking for the cap series or family from your favorite brand that has the highest ripple rating and the lowest ESR rating.

The highest ripple rating tells you it has the most capacity for smoothing out ripple. The lowest ESR means it has the lowest "effective" resistance and therefore will produce as little heat as possible while dropping the voltage passing through it as little as possible. (Those of you who are actually E.E.'s please step in and correct my untrained hobbyist speak here, please).

So, don't bother with the "gold" or "audio grade" series from any manufacturer unless the datasheet for that series shows it has higher ripple current and lower ESR than all the other series of the same capacitance and voltage values.

2. Caps end up working best (lasting longer, performing better, etc.) when run at 60-70% of their rated voltage. So, if you've got 80 VDC running through your filter caps constantly and they are rated for 80 VDC, you're are going to get less life and performance from them than you would from using 100 VDC rated caps in that same spot.

3. Putting a higher capacity cap, say a 4400 uF one where the original circuit called for a 3300 uF, gives you more dynamic power available on demand (more power is stored up and ready to be delivered when the amp needs it suddenly [think crashing boom or high hat in an otherwise quiet passage]) and (usually) higher ripple, but it also strains the transformer and the components between the transformer and the filter caps when you very first turn on the unit. The filter caps "ask" the supply (rectifiers and transformer) for lots of power to fill up the cap, this happens suddenly, and the strain might be too much for the rectifiers, transformer and other bits in that same area.

Some circuits have warm up or slow start designs, but that's not common. When putting in a larger-capacity filter cap, you have to watch out for stressing the preceding components during inrush.

I have only rebuilt, recapped and upgrade five vintage stereos so far, so I'm a newbie, but I've upgraded the rectifier diodes or bridge, any resistors and other caps, in the power supply circuit that feed the filter caps and had no problem with increasing the capacitance values 50-100%. That means I've put in higher wattage resistors (e.g. 3 W here 2 W was called for) and stronger diodes (E.g. 3 A ultra-fast soft recovery ones where 1 A normal recovery ones were specificed). I've listened to the advice and warnings here, tested it out on the few units I've recapped, and had no problems yet. YMMV

Good luck! Let us know how it goes.

 

[sansevy]

Thank you to you both!

S