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Old 6th September 2017, 12:45 AM   #1301
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Richard Murdey
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It probably bears some experimentation, but by default I would leave them in.
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Old 6th September 2017, 05:22 AM   #1302
ammel68 is offline ammel68  United States
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Originally Posted by rjm View Post
It probably bears some experimentation, but by default I would leave them in.
I went ahead and retained C10-C17 on my PCB layout using a separate regulated PS like the Jung Super Regulator.
I don't own a scope to do any measurements or comparisons with, so experimentation is limited on my end.
Do you think keeping C10-C17 on the board is sufficient and/or okay?
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Old 6th September 2017, 11:07 PM   #1303
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It comes down to the interplay of the capacitance and trace inductance at high frequencies. The idea is to keep capacitance close to the amplifier circuit to provide low impedance bypass connection from the output ground to the power supply rails.

Yes, the superreg output is itself low impedance - due to the high feedback of its design - but there is separation between it and the amplifier which adds impedance and can cause other problems besides. Although the Sapphire has so far proven to be remarkably stable, I can't guarantee it will work without sufficient bypass capacitance and I have no data to guide you on how much or how little you will need with your build. The Superreg itself may or may not like to have capacitance on its outputs, so that's another consideration.

I'd suggest a few hundred uF and some ceramic 0.1 uF bypass caps as they are positioned on the existing board should keep everything copacetic. They might be unnecessary, but on the other hand I don't think you'll need more than that.
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Old 7th September 2017, 02:27 AM   #1304
ammel68 is offline ammel68  United States
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I'd suggest a few hundred uF and some ceramic 0.1 uF bypass caps as they are positioned on the existing board should keep everything copacetic. They might be unnecessary, but on the other hand I don't think you'll need more than that.
I kept three 100uF caps and one .1uF cap per rail as shown on my board above.
That's why I posted an image showing I left them in the same location as your boards.
Would that not be considered a few hundred uF?

I have other regulated supplies that I can try. The Jung is my favorite with op-amp circuits. I haven't tried it with any discrete circuits.

Most of my regulated supplies are set for around +/-12VDC.
I measure +/-11.5VDC on the boards with matched Zeners that I got from you?
So, is there a voltage range that you recommend?
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Old 7th September 2017, 09:29 AM   #1305
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Without changing any resistances, 9-15 V is probably a reasonable range for the power supply rails.

And yes, as you have the board configured above would meet what I'm arbitrarily saying is sufficient. But since you have space, you might add optional some 1000 uF just in case.
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Old 7th September 2017, 07:47 PM   #1306
bczupa is offline bczupa  Poland
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Richard, if using a separate PS like the Jung Super Regulator, can I eliminate all of the 100uF and .1uF caps or is better to leave them on the board?
Thanks.
I'm using an external power supply, and a general rule for most regulators is that large capacitance after the regulator should be avoided.

However, instead of removing the capacitors from the board I would advise to use the existing places and install lover capacitors, and mix electrolytic with some film one (which are large by design)

So instead of 2x1000uF on the input install electrolytic 47uF 50V + 4,7uF to 10uF MKP.

That is what I did and works like a charm.

Removing all capacitors from board would be very bad idea - proved in some previous projects - lesson learnt the hard way !
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Old 7th September 2017, 10:13 PM   #1307
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I'm using an external power supply, and a general rule for most regulators is that large capacitance after the regulator should be avoided.
Can you explain the reason better? And also if you can, explain how to calculate the proportion of capacitance from before regulation to after?
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Old 7th September 2017, 11:52 PM   #1308
bczupa is offline bczupa  Poland
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Can you explain the reason better? And also if you can, explain how to calculate the proportion of capacitance from before regulation to after?
There is no such thing as the right proportion. To simplify - before is good, after is bad. It just the way it is. Much depends on the regulator design, but most regulators works this way.

There is of course a point were increasing filtering capacitance make no sens, and too much could be bad as well ... but you are not likely to reach this point, unless you build a batery of caps that goes in really high number. An a few 100uF capacitors spread over the board is not a large value. Just the two 1000uF capacitors on the board input should not be mounted - these are smoothing capacitors required to 'smooth' DC pulses from the rectified AC voltage coming from the bridge.

There is much to read on the Internet, you can examine datasheet of the regulator in question, no need to break the doors that are already open, here is a good and simple explanation:

power supply - Why is a capacitor before a voltage regulator more effective than after? - Electrical Engineering Stack Exchange

And for sure uncle google can provide more.

To quote from the above source:

"The output capacitor should be as small as possible, just enough to bridge the time when the regulator responds and compensates for the increased load. Roughly speaking, if you increase the output cap you just hardening the work of the regulator."

However, you need to add (possibly low-ESR) capacitors to every utilization point to mediate the high impedance of the wire/PCB track after the regulator. For this reason you should keep small capacitors on board close to the power utilization take place.

So, don't remove the caps from the board, just make their capacitance smaller , and try lowering ESR (use right type) and use decoupling film capacitors with low dissipation factor tan δ.

I used small capacitance Rubycon ZL series caps rated for 50V.

I personally see no benefit in modifying the PCB just because you want to use a regulated power supply. If you want to make it smaller, than OK, otherwise - no.

Last edited by bczupa; 8th September 2017 at 12:09 AM. Reason: a typo correction
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Old 8th September 2017, 12:49 AM   #1309
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just enough to bridge the time when the regulator responds and compensates for the increased load.
Yes, that would be an ideal situation, but no, there is no value of capacitance, large or small, that would provide this compensation exactly. The larger the capacitance and the lower the related inductance, the less droop you will observe on the regulator output in response to a step-change in the current load.

Large capacitors on the regulator output do not make the regulator work harder - they do exactly the job you expect, make the output voltage fluctuations less for the same "work" done by the regulator.

However, there is a long list of reasons why a large capacitor on the output of a regulator is bad idea. The higher the performance of the regulator (the more feedback used to reduce output impedance) the worse of an idea it becomes.

All this talk of regulators got me thinking though: power amplifiers do not normally use regulated supplies and no one gets especially upset, there is an argument to be made that headphone amplifiers don't need heavily regulated power supplies either. Some people even suggest unregulated supplies, but I'm not convinced that's the way to go. I do wonder, though, if a relatively light touch here might be preferred.
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Last edited by rjm; 8th September 2017 at 12:55 AM.
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Old 8th September 2017, 03:24 AM   #1310
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I personally see no benefit in modifying the PCB just because you want to use a regulated power supply. If you want to make it smaller, than OK, otherwise - no.
I didn't modify the board for any "benefits" per se. If the other components of the original regulator aren't going to be used, then I'm going to eliminate them.
A few clicks of the mouse and they're gone and the board's size is also reduced as you noted.

After thinking about it, I don't think the 1kuF caps are needed if using a separate supply with its own output caps.
The Jung regulator uses 120uF output caps. Connecting the Jung's outputs directly to 1kuF caps makes no sense to me.
I agree that they're more for smoothing the DC from a rectifier.
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