+/- 18V Low Noise Fast Transient Supply???

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safesphere

Member
Joined 2014
#1
Hello friends,

I need your expert help and guidance to point me in the right direction. 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. I would be happy to buy it or build one from a kit (or at least a circuit board), but I don't have the expertise to design it myself (not from scratch anyway). Could someone please point me to a product or project or something to start from?

Input: 120V 60Hz
Output: +/- 18V (about 0.3A)
Speed and ultra-low output impedance over a broad bandwidth (ideally 3mOhm up to 100KHz)

I would appreciate any help. Thank you!
 
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#6
safesphere said:
It looks fantastic, thank you! That thread is 237 pages... Do you know if the board is available for purchase? Thanks again!
Click to expand...

If you contact member Tea Bag he is the one to ask. Be aware that there are some tricky ro source components but Teabag can supply you with those.

The Ubib is a shunt regulator. I dont know if you know what that means, I know I certainly didn't when I joined this forum! It means they require some planning and heat management is/ can be a factor to consider. Also by design they are not 'green' so depending on your personal circumstances that may also be a factor.

But having said that they are thought of very highly and are amongst one of the best psus I believe.

Edit...here is the group buy link

GB For Salas SSLV1.3 Ultra-BIB

I think if you contacted Teabag and asked nicely he will fix you up.
 
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#8
jan.didden said:
The lowest output impedance and fastest regulator is in the diyaudio store:

Super Regulator – diyAudio Store

Jan
Click to expand...

Superb. Thank you Jan! So, do I just put AD797 in place of AD825? What changes, if any, do I need to make for +/-18V instead of +/-15V? Also, the link says, "The regulator boards accept a DC input from your favorite transformer/rectifier/reservoir cap". Where can I get any help on this? Such as at least the schematics and BOM?

Thanks so much!
 
#9
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
 

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#12
jan.didden said:
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
Click to expand...

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
 
#13
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/ON-Semiconductor/MSRD620CTT4G?qs=ZpPixqFcBtxVfHzz/hqSiQ== will do.

Jan
 
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#14
safesphere said:
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.
Click to expand...
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:
https://www.diyaudio.com/forums/ana...vs-bjt-input-phono-preamp-19.html#post6361921
https://www.diyaudio.com/forums/power-supplies/359652-fine-ic-voltage-regulators-25.html#post6348373

https://www.diyaudio.com/forums/ana...vs-bjt-input-phono-preamp-10.html#post6298286
https://www.diyaudio.com/forums/power-supplies/359652-fine-ic-voltage-regulators-2.html#post6329472
https://www.diyaudio.com/forums/power-supplies/359652-fine-ic-voltage-regulators-9.html#post6331727
https://www.diyaudio.com/forums/power-supplies/359652-fine-ic-voltage-regulators-15.html#post6335611
https://www.diyaudio.com/forums/power-supplies/359652-fine-ic-voltage-regulators-18.html#post6336611


But if you really want something fast, this is fast and easy to build with readily available components around you:
https://www.diyaudio.com/forums/power-supplies/359652-fine-ic-voltage-regulators-28.html#post6353344
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.
 
#16
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.
 
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#19
amplidude said:
I power a buffer amp with lm49720 lme49600 with the sigma22 works perfect for me
Click to expand...
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.
 
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