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+/- 18V Low Noise Fast Transient Supply???
+/- 18V Low Noise Fast Transient Supply???
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Old 10th October 2020, 11:56 AM   #11
Kovax is online now Kovax  Croatia
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Quote:
Originally Posted by jan.didden View Post
You should not use the 797 in this design; the 797, while superb in signal chains, has a tendency to instability in regulators.
Both Walt Jung and myself recommend the AD825 for maximum performance.
Jan
Hi,

Any newer opamps to recommend? Perhaps OPA828 from TI? Less noise and bigger slew rate.

Best regards, Domagoj
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Old 10th October 2020, 08:35 PM   #12
safesphere is offline safesphere  United States
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Quote:
Originally Posted by jan.didden View Post
You should not use the 797 in this design; the 797, while superb in signal chains, has a tendency to instability in regulators.
Both Walt Jung and myself recommend the AD825 for maximum performance.

For the transformer/rectifier/reservoir capacitor, there are many designs here, and it is not critical at all. Even Google 'full wave rectifier' will show you lots of examples. To keep the two regs fully independent, with no shared grounds, it is best to use a transformer with two separate secondary windings. For +/-18VDC, secondaries of 18VAC on a 100VA transformer is fine.
Use fast, soft recovery rectifier diodes, and don't overdo the capacitor value; it has no performance advantage and might generate fast current transients that propagate into the circuit. Something like 4700uF/35V would be fine.

Jan
Thank you Jan, this is super helpful! Could you please clarify a few points?

1. So, Schottky diodes are OK (fast and soft) right?

2. Do I need a 100VA transformer (my maximum power consumption is 10W)?

3. If I can't find the 18VAC secondary, would 17VAC or 20VAC be better? Or does it have tobe 18?

4. The preamp has a common ground, do I still need separate secondaries?

Thanks so much for your help!
Alex
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Old 10th October 2020, 09:11 PM   #13
jan.didden is offline jan.didden  Europe
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Two separate secondaries means that you can make two fully separate DC inputs for each reg (pos and neg) and only connect their grounds at the reg outputs. No common ground returns = cleaner outputs. You will have two rectifier bridges so two capacitors.

If you need only 10W you can do with a 30 or 50VA transformer, yes. If you can't find a an 18VAC xformer I would go for 20VAC, 17VAC is cutting it close especially with low mains voltages.

Schottly diodes: not sure they are fast and soft recovery. They may be fast and they have low drop voltage, but look for soft recovery diodes. They switch off softly which lowers spikes. If you go to Mouser you can select diodes and progressively narrow it down to say 100V, 1A continuously. Probably https://www.mouser.be/ProductDetail/...%2FhqSiQ%3D%3D will do.

Jan

Last edited by jan.didden; 10th October 2020 at 09:14 PM.
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Old 10th October 2020, 09:36 PM   #14
Temaad is offline Temaad  Australia
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Another option is to use the Omishra P/S from the A/K thread & the board (or completely populated) is available from Sachu888, the P/S was originally developed for the A/K AD797 MC phono amp & is very, very quiet.
Few more PCbs for AD797 HQMC phonostage for LOMc

I also use the SilentSwitcher on my P/Amp at it's normal voltage, but the only way I can get it quiet enough for a Phono Stage is to feed it with a lithium 5v phone pack battery back up devise, Used like that it is quieter than the Omishra, but used in another 5V supply configuration it is louder.

I have also used the Studer units & while they are very quiet, they are very unreliable. Had two fail within a year & neither Chinese vendor would replace the units or refund & E/bay also did not want to know!!

Cheers
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Old 10th October 2020, 09:37 PM   #15
dreamth is offline dreamth  Romania
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Quote:
Originally Posted by safesphere View Post
Hello friends,

I need a super low noise and fast transient response +/- 18V power supply for my phono preamp, but I am having a hard time finding any.
that is exactly what you DON'T need with a phono preamp.None of the best phono preamps ever made have a fast transient regulator because all phono preamps run in class A.Most of the time a simple capacitor multiplier will do.
here you have a collection of regulators used in some of the best phono gear ever made:
FET vs BJT input phono preamp
Are you really fine with IC voltage regulators ?

FET vs BJT input phono preamp
Are you really fine with IC voltage regulators ?
Are you really fine with IC voltage regulators ?
Are you really fine with IC voltage regulators ?
Are you really fine with IC voltage regulators ?


But if you really want something fast, this is fast and easy to build with readily available components around you:
Are you really fine with IC voltage regulators ?
you choose different zenner values so that you have a final +-18v if that's what you wish or simpler , use a 7808 /7908 as te original Technics denoiser and two 5v1 series zenners for the lowest tempco and best precision. although a 10v zenner can be used too.
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Old 10th October 2020, 09:38 PM   #16
amplidude is offline amplidude  Denmark
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Is sigma22 from amb.org not a candidate?
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Old 10th October 2020, 09:43 PM   #17
dreamth is offline dreamth  Romania
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May be, but a few good decades ago they started to manufacture op-amps for differential action...
This highendish trend for "fast transient power supply for class A phono circuits" needs to be put to rest as it's ridiculous.
Even if we could claim that we need to supply fast phono preamps , which is a real nonsense as there's no fast phono preamp, its slew rate being determined by the cartridge itself which is an electromechanical transducer, thus slower than you might think, we never had in our history as good low esr , high ripple capacitors as we have today, and high value lower esr caps work best with slow regulators...
The mere definition of "fast transients" put next to a amplifier for electromechanic transducers, tells you that these transients may be encountered from time to time and they can be easily supplied from a low esr cap accumulating the energy and releasing it fast just for those short fast transients.
Simple truth is that we don't need that even with the fastest and highest energy eating phono preamps as they are class A.

Last edited by dreamth; 10th October 2020 at 09:53 PM.
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Old 10th October 2020, 09:47 PM   #18
amplidude is offline amplidude  Denmark
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I power a buffer amp with lm49720 lme49600 with the sigma22 works perfect for me
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Old 10th October 2020, 09:53 PM   #19
tubemax is offline tubemax  Netherlands
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Hi safesphere,

Maybe I'm too late to recommend - but read this DIY Audio link first, I build it twice and it sounds more natural than any other PS for low power pre-amps...

Another look at the LM317 and LM337 regulators

Last edited by tubemax; 10th October 2020 at 09:58 PM.
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Old 10th October 2020, 09:57 PM   #20
dreamth is offline dreamth  Romania
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Quote:
Originally Posted by amplidude View Post
I power a buffer amp with lm49720 lme49600 with the sigma22 works perfect for me
lme49600 is a very fast hungry buffer, but nothing will push it to the limit in a phono preamp while the slew rate of the whole circuit driven by a phono cartridge is even lower than the max slew rate of lme49720,being determined by the cartridge itself.
By the way...if a phono preamp really needs a fast regulator, that is a poor phono preamp right from the start.
A good phono preamp won't allow for fast transients to be felt by the power supply.

Last edited by dreamth; 10th October 2020 at 10:01 PM.
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