scope preamp...

S

server

Guest
I want to measure the noise of a voltage regulator, probably an LM2941
making 5 volts out. So I need a low noise high gain preamp for a
scope.

Looks like this would work:

https://www.alphalabinc.com/product/lna10/

Any other suggestions?

I could make something, but it\'s marginal on time/cost and this looks
pretty cool.

Maybe I can bypass the upper feedback resistor to reduce noise, and
massively bypass the output to ground, if all that is atable.

I want 5 volts at a few hundred mA and wideband noise well below 100
uV RMS. I could make my own regulator if I had to, but LM2941 is easy.
This is going to power a bunch of cmos logic, about 20 ns worth total,
and Vcc noise becomes jitter.

I have an old TM500 thing in the dungeon, but I doubt it still works.
I guess I\'ll dust it off and see.
 
On Sun, 11 Sep 2022 11:11:05 -0400, Joe Gwinn <joegwinn@comcast.net>
wrote:

On Sat, 10 Sep 2022 16:23:41 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 10 Sep 2022 19:19:24 -0400, Joe Gwinn <joegwinn@comcast.net
wrote:

On Sat, 10 Sep 2022 15:55:47 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 10 Sep 2022 14:49:02 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

lørdag den 10. september 2022 kl. 23.34.00 UTC+2 skrev jla...@highlandsniptechnology.com:
I want to measure the noise of a voltage regulator, probably an LM2941
making 5 volts out. So I need a low noise high gain preamp for a
scope.

Looks like this would work:

https://www.alphalabinc.com/product/lna10/

Any other suggestions?

I could make something, but it\'s marginal on time/cost and this looks
pretty cool.

Maybe I can bypass the upper feedback resistor to reduce noise, and
massively bypass the output to ground, if all that is atable.

I want 5 volts at a few hundred mA and wideband noise well below 100
uV RMS. I could make my own regulator if I had to, but LM2941 is easy.
This is going to power a bunch of cmos logic, about 20 ns worth total,
and Vcc noise becomes jitter.

I my math adds up the LM2941 is 150uV typical at 5V, the ancient LM7805 is 40uV

I do want low dropout to minimize dissipation. We\'ll probably switch
down to +6.25 maybe and then LDO to make a very quiet +5.

This is important so maybe I\'ll make my own regulator, which would
likely be lower noise than an IC reg.

The classic dodge is a switcher driving a linear regulator, followed
by Phil H\'s favorite capacitance multiplier, with RC filters all
along.


Joe Gwinn

That adds a lot of dissipation.

That\'s the reason to start with a switcher - most of the voltage drop
is there.

But dissipation be damned - we want low noise.


This looks pretty good. It\'s actually not bad without R5+C3, kinda
surprising. Using a quiet 3 volt reference helps a lot.

Interesting, but I won\'t get to this SPICE for a while.


Joe Gwinn
Click to expand...

This is better. The mosfet was basically ohmic, but an NPN still acts
like a follower.

No comp on the opamp is weird but seems to work. I\'d better breadboard
this.



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John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:

This is better. The mosfet was basically ohmic, but an NPN still acts
like a follower.

No comp on the opamp is weird but seems to work. I\'d better breadboard
this.
Click to expand...

Not bad. -189dB to 10 Hz, then rises to about -100 dB.

Noise is ~7.5nV/root(Hz) with a slight hump around 10.5 KHz, then falls off
to 1nV/root(Hz) at 100 KHz.

No need for a fancy NPN. A 2N3055 is fine at these low frequencies.

https://tinyurl.com/438bb8a7

Are you going to be able to measure noise?




--
MRM
 
On Mon, 12 Sep 2022 09:11:45 -0000 (UTC), Mike Monett VE3BTI
<spamme@not.com> wrote:

John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:

This is better. The mosfet was basically ohmic, but an NPN still acts
like a follower.

No comp on the opamp is weird but seems to work. I\'d better breadboard
this.

Not bad. -189dB to 10 Hz, then rises to about -100 dB.
Click to expand...

Much better than the mosfet version. At low drop, a fet is basically a
couple-of-ohms resistor from the unreg input to the output.

Noise is ~7.5nV/root(Hz) with a slight hump around 10.5 KHz, then falls off
to 1nV/root(Hz) at 100 KHz.

No need for a fancy NPN. A 2N3055 is fine at these low frequencies.

https://tinyurl.com/438bb8a7
Click to expand...

I want a surfacemount high-beta NPN. It\'s impressive how many
different fets we have in stock and how few classic bipolar
transistors.

We do have FZT692 in SOT-223. It looks perfect for this regulator.
Beta is 500 min (!) at 2v and 100 mA. Its Early voltage must be
insane.

Are you going to be able to measure noise?
Click to expand...

I will, somehow. I\'m especially concerned about low frequency, 1/f,
noise, which will modulate my prop delays. LDOs aren\'t usually
specified for 1/f but opamps are. Putting the voltage ref on the power
chip, apologies to Bob Widlar, isn\'t always the best idea.
 
On Mon, 12 Sep 2022 07:12:23 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

On Mon, 12 Sep 2022 09:11:45 -0000 (UTC), Mike Monett VE3BTI
spamme@not.com> wrote:

John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:

This is better. The mosfet was basically ohmic, but an NPN still acts
like a follower.

No comp on the opamp is weird but seems to work. I\'d better breadboard
this.

Not bad. -189dB to 10 Hz, then rises to about -100 dB.


Much better than the mosfet version. At low drop, a fet is basically a
couple-of-ohms resistor from the unreg input to the output.


Noise is ~7.5nV/root(Hz) with a slight hump around 10.5 KHz, then falls off
to 1nV/root(Hz) at 100 KHz.

No need for a fancy NPN. A 2N3055 is fine at these low frequencies.

https://tinyurl.com/438bb8a7


I want a surfacemount high-beta NPN. It\'s impressive how many
different fets we have in stock and how few classic bipolar
transistors.

We do have FZT692 in SOT-223. It looks perfect for this regulator.
Beta is 500 min (!) at 2v and 100 mA. Its Early voltage must be
insane.


Are you going to be able to measure noise?

I will, somehow. I\'m especially concerned about low frequency, 1/f,
noise, which will modulate my prop delays. LDOs aren\'t usually
specified for 1/f but opamps are. Putting the voltage ref on the power
chip, apologies to Bob Widlar, isn\'t always the best idea.
Click to expand...

It\'s interesting that nobody seems to make a voltage reg that accepts
an external reference. Some ADCs and DACs have an internal ref with
external over-ride capability.

One can drive the ADJ pin of a 317 type from an opamp, basically use
it as a power amp.

You can stack LM1117s to get 1.25, 2.5... volt steps, like an FPGA
might want.
 
On Mon, 12 Sep 2022 08:14:47 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

On Mon, 12 Sep 2022 07:12:23 -0700, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:

On Mon, 12 Sep 2022 09:11:45 -0000 (UTC), Mike Monett VE3BTI
spamme@not.com> wrote:

John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:

This is better. The mosfet was basically ohmic, but an NPN still acts
like a follower.

No comp on the opamp is weird but seems to work. I\'d better breadboard
this.

Not bad. -189dB to 10 Hz, then rises to about -100 dB.


Much better than the mosfet version. At low drop, a fet is basically a
couple-of-ohms resistor from the unreg input to the output.


Noise is ~7.5nV/root(Hz) with a slight hump around 10.5 KHz, then falls off
to 1nV/root(Hz) at 100 KHz.

No need for a fancy NPN. A 2N3055 is fine at these low frequencies.

https://tinyurl.com/438bb8a7


I want a surfacemount high-beta NPN. It\'s impressive how many
different fets we have in stock and how few classic bipolar
transistors.

We do have FZT692 in SOT-223. It looks perfect for this regulator.
Beta is 500 min (!) at 2v and 100 mA. Its Early voltage must be
insane.


Are you going to be able to measure noise?

I will, somehow. I\'m especially concerned about low frequency, 1/f,
noise, which will modulate my prop delays. LDOs aren\'t usually
specified for 1/f but opamps are. Putting the voltage ref on the power
chip, apologies to Bob Widlar, isn\'t always the best idea.


It\'s interesting that nobody seems to make a voltage reg that accepts
an external reference. Some ADCs and DACs have an internal ref with
external over-ride capability.

One can drive the ADJ pin of a 317 type from an opamp, basically use
it as a power amp.
Click to expand...

I\'ve seen exactly this done to power LNAs, after a switched that did
the bulk of the voltage dropping.

Joe Gwinn



You can stack LM1117s to get 1.25, 2.5... volt steps, like an FPGA
might want.
Click to expand...
 
mandag den 12. september 2022 kl. 17.15.05 UTC+2 skrev John Larkin:
On Mon, 12 Sep 2022 07:12:23 -0700, John Larkin
jla...@highlandSNIPMEtechnology.com> wrote:

On Mon, 12 Sep 2022 09:11:45 -0000 (UTC), Mike Monett VE3BTI
spa...@not.com> wrote:

John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:

This is better. The mosfet was basically ohmic, but an NPN still acts
like a follower.

No comp on the opamp is weird but seems to work. I\'d better breadboard
this.

Not bad. -189dB to 10 Hz, then rises to about -100 dB.


Much better than the mosfet version. At low drop, a fet is basically a
couple-of-ohms resistor from the unreg input to the output.


Noise is ~7.5nV/root(Hz) with a slight hump around 10.5 KHz, then falls off
to 1nV/root(Hz) at 100 KHz.

No need for a fancy NPN. A 2N3055 is fine at these low frequencies.

https://tinyurl.com/438bb8a7


I want a surfacemount high-beta NPN. It\'s impressive how many
different fets we have in stock and how few classic bipolar
transistors.

We do have FZT692 in SOT-223. It looks perfect for this regulator.
Beta is 500 min (!) at 2v and 100 mA. Its Early voltage must be
insane.


Are you going to be able to measure noise?

I will, somehow. I\'m especially concerned about low frequency, 1/f,
noise, which will modulate my prop delays. LDOs aren\'t usually
specified for 1/f but opamps are. Putting the voltage ref on the power
chip, apologies to Bob Widlar, isn\'t always the best idea.

It\'s interesting that nobody seems to make a voltage reg that accepts
an external reference.
Click to expand...

LM723 ?
 
On Monday, September 12, 2022 at 7:12:37 AM UTC-7, John Larkin wrote:
On Mon, 12 Sep 2022 09:11:45 -0000 (UTC), Mike Monett VE3BTI
spa...@not.com> wrote:

John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:

This is better. The mosfet was basically ohmic, but an NPN still acts
like a follower.

No comp on the opamp is weird but seems to work. I\'d better breadboard
this.

Not bad. -189dB to 10 Hz, then rises to about -100 dB.
Much better than the mosfet version. At low drop, a fet is basically a
couple-of-ohms resistor from the unreg input to the output.
Click to expand...

I\'d say, rather, that a FET needs more slew rate from the driving op amp
than a bipolar transistor. dV/dt is a limited resource when considering
broad bandwidth types of noise. Miller capacitance in the transistor
will partly compensate the op amp...
 
Am 11.09.22 um 05:30 schrieb jlarkin@highlandsniptechnology.com:
On Sun, 11 Sep 2022 05:01:34 +0200, Gerhard Hoffmann <dk4xp@arcor.de
wrote:

Am 11.09.22 um 00:55 schrieb jlarkin@highlandsniptechnology.com:
On Sat, 10 Sep 2022 14:49:02 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

lørdag den 10. september 2022 kl. 23.34.00 UTC+2 skrev jla...@highlandsniptechnology.com:
I want to measure the noise of a voltage regulator, probably an LM2941
making 5 volts out. So I need a low noise high gain preamp for a
scope.

Looks like this would work:

https://www.alphalabinc.com/product/lna10/

Any other suggestions?

I could make something, but it\'s marginal on time/cost and this looks
pretty cool.

Maybe I can bypass the upper feedback resistor to reduce noise, and
massively bypass the output to ground, if all that is atable.

I want 5 volts at a few hundred mA and wideband noise well below 100
uV RMS. I could make my own regulator if I had to, but LM2941 is easy.
This is going to power a bunch of cmos logic, about 20 ns worth total,
and Vcc noise becomes jitter.

I my math adds up the LM2941 is 150uV typical at 5V, the ancient LM7805 is 40uV

I do want low dropout to minimize dissipation. We\'ll probably switch
down to +6.25 maybe and then LDO to make a very quiet +5.

This is important so maybe I\'ll make my own regulator, which would
likely be lower noise than an IC reg.

I did not measure the LM2941, but the Lm2940 is about the worst
choice possible.
It would require real work to be better than a LT3042. Its main
drawback is the small load current because of the tiny package.


https://www.flickr.com/photos/137684711@N07/24070698809/in/album-72157662535945536/

0 dB is 1nV/rtHz.

In the LT3042 data sheet is a a circuit with an external NPN
to take the heat. It measures about the same as the 3042 alone.
The noise peak climbs to 100 KHz but does not grow in size.

Adding more output C increases peaking. Cset may be increased
at the cost of larger startup time. Cset=100u can make sense and
lowers the 1/f corner to a few Hz. It is not really 1/f but
1/f**2 or 3. More than 100u seems not to help.


https://www.flickr.com/photos/137684711@N07/24070698809/in/album-72157662535945536/


Some empty boardlets are left over. 1.5A@5V from a 6.6V raw
source is ok. The transistor costs a diode drop vs. bare 3042.

I think I\'ll make my own LDO with an opamp and an n-fet. By the time I
have a dpak fet and some giant caps, the opamp and a few passives add
not much more board area.

If I use a good 3 volt reference (which I\'ll have) I expect much less
low frequency noise than using the 1.25v bandgap and feedback point of
a regulator.
Click to expand...

LT3042 uses a precision current source to develop the output voltage
over a resistor. That is easily filtered.

They even have a proposal of using a post-filtered LT6555
reference with the *1 output stage of the LT3042.

None of that stuff will be on the same die as the big hot pass
transistor.
Click to expand...

Like their external cheap D44H10 NPN

I\'ll prowl the dungeon and see if I have a AM503 amplifier, and see if
it still works, to measure the LDO noise. Or maybe just trust Spice.
Click to expand...

You can trust spice, but you cannot trust the models.
Few have 1/f noise, or even correct data.
Many transistor models have been made with the Orcad parts
program. You recognize them since all have the same RBB.

Gerhard
 
Am 11.09.22 um 05:30 schrieb jlarkin@highlandsniptechnology.com:

I\'ll prowl the dungeon and see if I have a AM503 amplifier, and see if
it still works, to measure the LDO noise. Or maybe just trust Spice.
Click to expand...

The current probe amplifier?
 
On Tue, 13 Sep 2022 04:33:57 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:

Am 11.09.22 um 05:30 schrieb jlarkin@highlandsniptechnology.com:

I\'ll prowl the dungeon and see if I have a AM503 amplifier, and see if
it still works, to measure the LDO noise. Or maybe just trust Spice.

The current probe amplifier?
Click to expand...

No, sorry, Am502.

https://w140.com/tekwiki/wiki/TM500_and_TM5000_plug-ins#/media/File:Tek_am502_1.jpg
 
John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:

No, sorry, Am502.

https://w140.com/tekwiki/wiki/TM500_and_TM5000_plug-ins#/media/File:Tek_a
m502_1.jpg
Click to expand...

That is a very nice variable bandwidth amplifier. It would be nice to have a
HP 3400A true RMS voltmeter, 10 Hz to 10 MHz to convert the p-p readings to
true rms. That way, you could get consistent readings to compare with various
datasheets. Or just use a scope if it has true rms conversion.




--
MRM
 
Mike Monett VE3BTI wrote:
John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:

No, sorry, Am502.

https://w140.com/tekwiki/wiki/TM500_and_TM5000_plug-ins#/media/File:Tek_a
m502_1.jpg

That is a very nice variable bandwidth amplifier. It would be nice to have a
HP 3400A true RMS voltmeter, 10 Hz to 10 MHz to convert the p-p readings to
true rms. That way, you could get consistent readings to compare with various
datasheets. Or just use a scope if it has true rms conversion.
Click to expand...

One gotcha with those 500-series modules: they look like they should be
hot-pluggable, but emphatically are not. (Ask me how I know.) ;)

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On Tue, 13 Sep 2022 05:08:56 -0000 (UTC), Mike Monett VE3BTI
<spamme@not.com> wrote:

John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:

No, sorry, Am502.

https://w140.com/tekwiki/wiki/TM500_and_TM5000_plug-ins#/media/File:Tek_a
m502_1.jpg

That is a very nice variable bandwidth amplifier. It would be nice to have a
HP 3400A true RMS voltmeter, 10 Hz to 10 MHz to convert the p-p readings to
true rms. That way, you could get consistent readings to compare with various
datasheets. Or just use a scope if it has true rms conversion.
Click to expand...

Scopes do variable-bandwidth RMS and FFTs and things, but most max out
at 5 or maybe 2 mV/div.

All that used to be extra-cost but is standard now.

Right now I could do with a gain of 10, which I could build in an
hour, but I might get some fancy preamp for future use.

My kids have a bunch of Python libraries to slurp scope data, and then
run matlab sorts of stuff on it too. We could, say, cross-correlate
something to noise on one supply.

Looks like we\'ll need very quiet supplies: +20, +5, +4, -5, all from a
wall wart that might be 12 or 24. And ugly supplies +7, -7, 3.3,
+3ref, 1.8, 1.35, 1.0. Eleven supply rails in a tiny box jammed with
stuff. It\'s a giant puzzle, either fun or a damned nuisance.

The old product ran from +12, and people occasionally blew them up by
using the wrong wart, so we\'d like the new rev to tolerate at least
24. +24 is our standard wart these days.

One discovery is the LT8603, one boost and three bucks in one chip.
 
On Tuesday, September 13, 2022 at 8:04:13 AM UTC-7, John Larkin wrote:

Looks like we\'ll need very quiet supplies: +20, +5, +4, -5, all from a
wall wart that might be 12 or 24. And ugly supplies +7, -7, 3.3,
+3ref, 1.8, 1.35, 1.0. Eleven supply rails in a tiny box jammed with
stuff. It\'s a giant puzzle, either fun or a damned nuisance.

The old product ran from +12, and people occasionally blew them up by
using the wrong wart, so we\'d like the new rev to tolerate at least
24. +24 is our standard wart these days.
Click to expand...

And 48V is the standard wart for POE, 12V is the standard wart for an
external hard disk, 19.5V is the standard for a laptop... and few
of the connectors are any kind of standard.

If you want quiet, I\'ve seen good performance from medical-grade power
supplies (but not from wallwarts). And point-of-load switchers have
been a pernicious source of pickup hash; you don\'t do low-noise next to
those.
 
On Mon, 12 Sep 2022 18:26:56 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Monday, September 12, 2022 at 7:12:37 AM UTC-7, John Larkin wrote:
On Mon, 12 Sep 2022 09:11:45 -0000 (UTC), Mike Monett VE3BTI
spa...@not.com> wrote:

John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:

This is better. The mosfet was basically ohmic, but an NPN still acts
like a follower.

No comp on the opamp is weird but seems to work. I\'d better breadboard
this.

Not bad. -189dB to 10 Hz, then rises to about -100 dB.
Much better than the mosfet version. At low drop, a fet is basically a
couple-of-ohms resistor from the unreg input to the output.

I\'d say, rather, that a FET needs more slew rate from the driving op amp
than a bipolar transistor. dV/dt is a limited resource when considering
broad bandwidth types of noise. Miller capacitance in the transistor
will partly compensate the op amp...
Click to expand...

The best closed-loop systems are good open-loop at the start.

A 2 volt drop emitter follower is good; a 2 volt drop fet follower is
terrible.
 
tirsdag den 13. september 2022 kl. 19.56.02 UTC+2 skrev whit3rd:
On Tuesday, September 13, 2022 at 8:04:13 AM UTC-7, John Larkin wrote:

Looks like we\'ll need very quiet supplies: +20, +5, +4, -5, all from a
wall wart that might be 12 or 24. And ugly supplies +7, -7, 3.3,
+3ref, 1.8, 1.35, 1.0. Eleven supply rails in a tiny box jammed with
stuff. It\'s a giant puzzle, either fun or a damned nuisance.

The old product ran from +12, and people occasionally blew them up by
using the wrong wart, so we\'d like the new rev to tolerate at least
24. +24 is our standard wart these days.
And 48V is the standard wart for POE, 12V is the standard wart for an
external hard disk, 19.5V is the standard for a laptop... and few
of the connectors are any kind of standard.
Click to expand...

and USB-C PD is 5-9-12-20V at upto 5A

since EU is mandating that a lot stuff with batteries will be required
to charge from USB-C PD there\'s going to be a lot of that around
 
On Sat, 10 Sep 2022 14:33:49 -0700, jlarkin@highlandsniptechnology.com
wrote:

I want to measure the noise of a voltage regulator, probably an LM2941
making 5 volts out. So I need a low noise high gain preamp for a
scope.

Looks like this would work:

https://www.alphalabinc.com/product/lna10/

Any other suggestions?

I could make something, but it\'s marginal on time/cost and this looks
pretty cool.

Maybe I can bypass the upper feedback resistor to reduce noise, and
massively bypass the output to ground, if all that is atable.

I want 5 volts at a few hundred mA and wideband noise well below 100
uV RMS. I could make my own regulator if I had to, but LM2941 is easy.
This is going to power a bunch of cmos logic, about 20 ns worth total,
and Vcc noise becomes jitter.

I have an old TM500 thing in the dungeon, but I doubt it still works.
I guess I\'ll dust it off and see.
Click to expand...

Turns out we had one of these tucked away in the lab.

https://www.ee-quipment.com/products/differential-preamplifier?variant=35410631368

Measures 5 uV RMS noise into my scope at 1k gain and 1 MHz bandwidth.
Not bad.

There is a little spikey stuff from the USB power wart, about 10 uV.
 
lørdag den 10. september 2022 kl. 23.34.00 UTC+2 skrev jla...@highlandsniptechnology.com:
I want to measure the noise of a voltage regulator, probably an LM2941
making 5 volts out. So I need a low noise high gain preamp for a
scope.

Looks like this would work:

https://www.alphalabinc.com/product/lna10/

Any other suggestions?

I could make something, but it\'s marginal on time/cost and this looks
pretty cool.

Maybe I can bypass the upper feedback resistor to reduce noise, and
massively bypass the output to ground, if all that is atable.

I want 5 volts at a few hundred mA and wideband noise well below 100
uV RMS. I could make my own regulator if I had to, but LM2941 is easy.
This is going to power a bunch of cmos logic, about 20 ns worth total,
and Vcc noise becomes jitter.
Click to expand...

I my math adds up the LM2941 is 150uV typical at 5V, the ancient LM7805 is 40uV
 
jla...@highlandsniptechnology.com wrote:

====================================
I want to measure the noise of a voltage regulator, probably an LM2941
making 5 volts out. So I need a low noise high gain preamp for a
scope.

Looks like this would work:

https://www.alphalabinc.com/product/lna10/

Any other suggestions?

I could make something, but it\'s marginal on time/cost and this looks
pretty cool.

Maybe I can bypass the upper feedback resistor to reduce noise, and
massively bypass the output to ground, if all that is atable.
Click to expand...

** An L/C or even RC filter after the reg will do the job.
Trim the output to make up for any voltage drop.


..... Phil
 
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