Discussion in 'DIY' started by z-adamson, Jul 5, 2017.
Is this ok to do?
This is just slightly less un-specific than asking us if the stuff in the red tupperware in your refrigerator is OK to eat.
An hk citation 16a uses 4 10,000uf filter caps. Replacements of the same values and physical shape and size are pricy.
Bump it up to 22,000uf and they become much more economical.
I read a thread here about a guy doing this and since I am in the middle of a rebuild of this amp, I figured I would gather some opinions about this before pulling the trigger.
Doubling to this extent could potentially run you into longer term issues such as eventual breakdown of your power switch contacts due to increased current there, plus you need to be sure that your bridge/rectifier diodes can handle the increased in-rush current on start up.
I wouldn't personally go up this much. Maybe to 15000 would be fine.
^^^ What he said
FYI, some might do this type of mod and never think twice. But potential harm would likely not happen immediately. Any potential benefits from increases in main filter capacitance come with trade-offs as mentioned above. Consider that there is likely some degree of damage to the contacts in your power switch already, and finding a replacement for that switch would be a chore (if doable at all).
There is a triac based modification for power switches that you could look into, as well as other options for increasing lifespan of the switch. I have not done the triac mod myself. And I don't know whether more stout rectifiers are available, or the capabilities of the originals, but you could research. Look at the parameter Ifsm (and others, of course) if you do any research. I have studied lots of rectifier diode spec sheets and have replaced a few sets of those in order to accommodate larger filter caps. But having gone through this process more than once, I am now coming around to an attitude of thinking the benefits are not worth the trouble and long term risks. YMMV
Another thing to consider is that there is a decent chance that any new, large value caps could be at the lower end of their tolerance range for uF. For example, if you find 15k uF caps with +/- 20% tolerance, their actual uF value could be something like 15k -15%, or around 12.75k uF. Can't promise that every case will work out like this, but it does happen enough that it has been discussed by others here (most notably, ConradH), and I have experienced it myself more than once.
Bottom line, if I was doing those amps, I definitely would not install the 22k uF caps. As for the 15k uF caps, I would be researching the rectifiers and also investigating the current health of the power switch (a good thing to do regardless possible filter cap increases). Do you have a means of measuring capacitance values in the range of 15k?
Well, in light of the opinions above I will go for the expensive nichicon 10,000uf filter caps.
And yes I can measure up to 15,000uf. Fluke 289 is up to the task I beleive.
As you already have 2x10,000uF per rail you can go for single 22,000uF per rail but doing this you degrade ESR, charging/discharging speed etc. However, replacing lower quality caps with higher quality caps will not necessarily give you audible improvement. It depends on your PS design and amplifier PS requirements.
If it is for filter caps and have the right voltage, I don't see why not. Far as I concern, power supply rail filter caps is the bigger the better.
Now don't replace 2 of the 10,000uF with one 22000uF. You put two to increase the capacitance. This is to keep ESR and ESL low.
Why not? Because this is an older amp that could very possibly already have some damage to power switch contacts due to arcing on power up/down over many years. I have opened up several switches from vintage era amps, and have yet to see one in pristine condition, some are worse than others of course. Others have reported about and posted pics of damaged power switches. This is a well known vulnerability of older gear that has been discussed many times. Increasing capacitance of main filters increases inrush current. When the switch was new the engineers intended it to be used with 10k uF filter caps. Now the switch is old, and you would advise going up to 22k uF?
That, and the rectifier diodes as mentioned by slimecity. Their ability to handle the additional inrush current resulting from more than doubling main filter capacitance is an unknown, especially when considering long term service.
I would simply change the switch, increase the capacitance improve the performance of the amp for sure.
If switch is hard to find, add a series inrush current limiter. It's definitely worth the extra trouble.
Here are the 2.5ohm 7A and 8A inrush current limiter:http://www.mouser.com/Circuit-Protection/Thermistors/Inrush-Current-Limiters/_/N-axfxj?P=1z0x878Z1z0x8glZ1z0x6um
Don't forget about the extra load on the transformer at startup.
Just eat it.
Not likely that it would be a simple matter to locate a replacement power switch with correct physical dimensions and electrical characteristics.
As for the NTC thermistor to protect the power switch, this idea has been given the thumbs-down by both EchoWars and BinaryMike in this thread (see posts 7 & 11) http://www.audiokarma.org/forums/index.php?threads/ntc-thermistor-for-inrush-current.298575/.
Wrong, In rush current limiter limit the peak current. That's what any good amp would do. I looked at my Acurus, they did exactly that.
In what world limiting the in rush current is a bad thing? You have to know the electronics, not just listen to other people. A 2.5ohm inrush limit the peak current to about 40A. You listen to people's opinion and think. This is common engineering sense.
If you want to, go back to my thread and we can debate instead of hijacking the thread here. I stand by my suggestion that inrush limiter WILL protect the switch, can handle more capacitance. I stand by more caps will make the amp sounds better. THAT if you are tinkering with changing caps, it's should be very easy adding an inrush limiter along the AC main input line.
If you worry about the rectifier, change to a bigger one!!! Again, if you dare to change the cap, why stop there...... If you want a better amp.
Your opinion apparently does not mesh with the opinions of some highly regarded members. That is OK. Just wanted to make that point so that the OP can judge for himself.
As I said, you don't just listen, listen and think, this is engineering.
The inrush works, I have close to 200,000uF of caps in my amp and I have a huge transformer that can draw more current, it's working like a champ. The frst switch lasted 3 days, and now it's lasting.
Here's what I'd do...
You have 65 x 105mm
New 65mm diameter caps are expensive. You could either get new clamps or get a pvc pipe 2" ID and cut clamp spacers. Place the cap in the pvc spacer ring and then the whole thing into the existing clamp.
But Alan, that is YOUR design. The OP is working within the limits of other engineers' designs. So, he has a fixed amount of space, a transformer that is already set, rectifiers that are already designed for the amp in question, and engineers that decided 40,000uF of capacitance was adequate for the design. Were they limited by the bean counters somewhat? Perhaps. But you're suggesting to just throw out what other engineers decided was right for their circuits and do whatever you feel is best. Have you even studied the scat in question?
Conservatively increasing capacitance is one thing, but doubling it without checking things is another. Some designs actually list what's allowable such as -10% +50%. But I don't recall one recently saying +100% is ok.
About the switch in your amp you say "...now it's lasting". I would point out that you installed the replacement switch in your amp just 2 weeks ago, on June 23. It would seem that your standard for durability is measured in weeks.
Guys, You don't want to do it, It's fine with me. If you are so worry, don't even change the value of the caps. You are monkeying with the EXISTING amp already, why not make it better. You value your amp, I would put inrush limiter and arc protector even if I use the same cap just to protect the original switch.
Study how inrush current limiter works before just listen to others opinion. Inrush limiter is for protecting the switch. It works. I would do anything to increase the value of the caps just to improve the sound.
Putting in the inrush and arc protection is so easy compare to recap that if you can do recap, do the protection regardless.
BTW, if the amp has screw mount caps, it's higher quality amp, what make you think there's no already inrush limiter and arc protection built in? Study the schematic and see.
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