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Old 7th April 2016, 01:54 PM   #1
KanedaK is offline KanedaK  Belgium
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Default Post regulator caps... old or new?

Still recapping my ReVox B226

next caps that are going to be replaced include the post regulator decoupling caps;

Concerning those I've had contradictory advice... replace or leave the old ones? Brand new low ESR caps would perform bad in that position? I'm confused.
The old caps are Frako, they are 30 years old, it seems to me logical to replace them. But the circuit itself has been conceived 30 years ago, and the regulator chips are from stone age. so there might be some truth in the assumption that high ESR caps would perform better, for what reason I don't know.

So, leave the old, dried out caps? Change for good caps? Change for brand new, low quality caps?

(caps are C2, C6, C8, C9, C13, C15)
here's schematics of the B226 PSU.
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Last edited by KanedaK; 7th April 2016 at 01:56 PM.
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Old 7th April 2016, 01:57 PM   #2
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Change the caps! Use whatever caps you prefer. I recommend Panasonic FC series for the regulator.
If you are afraid the regulator chips are too old why not replace them with LM317/LM337 ?
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Old 7th April 2016, 02:00 PM   #3
KanedaK is offline KanedaK  Belgium
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Quote:
Originally Posted by rrrremus View Post
Change the caps! Use whatever caps you prefer. I recommend Panasonic FC series for the regulator.
If you are afraid the regulator chips are too old why not replace them with LM317/LM337 ?
That's what they are: LM317, LM337. Are those subject to aging?
When I said "they're from the stone age" it's because I assumed (?) that there are better regulator chips now, but I don't know...
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Old 7th April 2016, 02:23 PM   #4
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I'm not an expert but I read that low ESR are not good after old regulator (78xx/79xx/lm317/337 ...).

I would change them to new high quality but not low ESR electro in 22-100uF range: silmic 2, nichicon kg/kz, etc
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Old 7th April 2016, 02:23 PM   #5
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Quote:
Originally Posted by KanedaK View Post
That's what they are: LM317, LM337. Are those subject to aging?
When I said "they're from the stone age" it's because I assumed (?) that there are better regulator chips now, but I don't know...
A lot of manufacturers produce the LM317 chips. I am not aware how the performance has improved over the years, but do not worry about it. They do not need to be changed.
Change all electro caps with suitable replacements. Use film caps in the signal path where possible (for values under 4,7uF usually) and also make sure that all contacts are clean. Relays used in the signal path should also be replaced as they also have a limited lifetime.
Op-amps ( if used in this machine ) are going to be an improvement if you use modern day low noise like OPA1612A or OPA2132
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Old 7th April 2016, 07:45 PM   #6
KanedaK is offline KanedaK  Belgium
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Quote:
Originally Posted by Albusine View Post
I'm not an expert but I read that low ESR are not good after old regulator (78xx/79xx/lm317/337 ...).

I would change them to new high quality but not low ESR electro in 22-100uF range: silmic 2, nichicon kg/kz, etc
So I can use the Silmic II that I planned to use there? that's good to know...

thanks for ur answer!
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Old 8th April 2016, 10:22 AM   #7
DF96 is offline DF96  England
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A capacitor at the output or a regulator interacts directly with the regulator output impedance, which is likely to be inductive and possibly resistively negative too in some frequency regions. A cap with sufficiently high ESR will damp any problems.

If you must change the caps (and this is probably unnecessary) then change like for like. If the cap was an ordinary cheap electrolytic then replace with an ordinary cheap electrolytic.

As I always say, in order to improve a circuit you need to understand it even better than the original designer.
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Old 8th April 2016, 10:59 AM   #8
dazzz is offline dazzz  Israel
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Output capacitor in the LM317
Beware of capacitor with low ESR.

But my experience is easy to solve the problem
At the out leg of the LM317 add low-value resistors 0.47 to 1 ohm
Then the output capacitor can be valued at up to 1000UF .
That way you solve the problem of modern capacitors with low ESR.
Just dont forget to add a protection diode -if the output capacitor are big value
220-1000uf
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Last edited by dazzz; 8th April 2016 at 11:12 AM.
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Old 8th April 2016, 01:02 PM   #9
Eldam is offline Eldam  France
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some inputs here as well: Simple Voltage Regulators Part 1: Noise - [English]
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Old 8th April 2016, 02:25 PM   #10
KanedaK is offline KanedaK  Belgium
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Quote:
Originally Posted by DF96 View Post
A capacitor at the output or a regulator interacts directly with the regulator output impedance, which is likely to be inductive and possibly resistively negative too in some frequency regions. A cap with sufficiently high ESR will damp any problems.

If you must change the caps (and this is probably unnecessary) then change like for like. If the cap was an ordinary cheap electrolytic then replace with an ordinary cheap electrolytic.

As I always say, in order to improve a circuit you need to understand it even better than the original designer.
What kind of problems can it create?
This morning I replaced the original 47uF 10V with silmic II same value, same rating.
I don't hear any noise or "nasties", but the sound seems to be less mellow and more upfront. Less "bloom".
That said, I will wait a bit for the caps to settle in. So far they only played around 45 minutes!
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