Am 01.09.2016 um 06:07 schrieb Bruce Griffiths:

I wonder where that relatively high noise on the LT3042 might hide.

<
https://www.flickr.com/photos/137684711@N07/24070698809/in/datetaken/lightbox/

That is maybe 3 nV/RT Hz at 10 Hz, and the limit is probably not the
LT3042 but
the GR-like noise of my old preamp below 30 Hz. (rises faster than 1/f)
Remember that 0 dB in the plot is 1 nV rt Hz, which is the equivalent
INPUT noise voltage
of an AD797 or LT1028.

The LT4042 measurement was taken from an ugly dead bug ad-hoc construction.
Deviating from the 4.7u output cap produces some noise peaks @ > 100 KHz.
(but still 30 dB better than the others)
More is less here.

regards, Gerhard

Gerhard wrote:

Nice!

The datasheet shows both NPN and PNP current multipliers.  Just curious
-- did you choose the NPN circuit for theoretical considerations, and if
so what was your reasoning -- the lower open-loop output impedance?

Thanks,

Charles

I wrote:

This should read, "I have converted a number of them by removing the
DC-DC converters and feeding the circuitry from a mains-operated linear
DC supply...."

Best regards,

Charles

It will show up if the value of the voltage setting bypass capacitor is reduced. Both the Johnson and excess noise in this resistor coupled with the current source flicker noise should become evident. The datasheet graphs indicate that the Johnson noise of the voltage setting resistor(33k2 ~22nV/rtHz) isn't significant in comparison with other sources.

Bruce

On Thursday, 1 September 2016 5:56 PM, Gerhard Hoffmann <dk4xp@arcor.de> wrote:

Am 01.09.2016 um 06:07 schrieb Bruce Griffiths:

I wonder where that relatively high noise on the LT3042 might hide.

<
https://www.flickr.com/photos/137684711@N07/24070698809/in/datetaken/lightbox/

That is maybe 3 nV/RT Hz at 10 Hz, and the limit is probably not the
LT3042 but
the GR-like noise of my old preamp below 30 Hz. (rises faster than 1/f)
Remember that 0 dB in the plot is 1 nV rt Hz, which is the equivalent
INPUT noise voltage
of an AD797 or LT1028.

The LT4042 measurement was taken from an ugly dead bug ad-hoc construction.
Deviating from the 4.7u output cap produces some noise peaks @ > 100 KHz.
(but still 30 dB better than the others)
More is less here.

regards, Gerhard

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Bruce wrote:

I have found that the voltage setting bypass capacitor can be profitably
increased to ~22uF, beyond which there is only a very small gain below
1Hz.  I would use 22uF unless that delayed reaching full voltage for too
long at start-up.  (With 22uF, it takes ~15 seconds to reach the 3042's
maximum output voltage of 15v, correspondingly less for lower output
voltages.)

With 22uF, the output noise density is ~20nV/sqrtHz at 10Hz and
~80nV/sqrtHz at 1Hz.  I believe most of the remaining noise (at least
above 0.1Hz) is being generated in the unity-gain amplifier -- the
reactance of the 22uF capacitor is only ~700 ohms at 10Hz.

Best regards,

Charles

On 2016-09-01 05:35, Charles Steinmetz wrote:

I guess that you could say that I like soldering and the following
suggestions might not appeal to everyone but it would give you a very
clean supply for your Thunderbolts.

Since I tend to ignore the the bottom line cost and do things more
complicated than necessary, you might not agree with my suggestions. On
the other hand, my designs generally work well.

In the power supply of the GPSDO that I am building right now, I have
used DC/DC converters for all voltages, but I set the output voltage
slightly over the wanted voltage. I start off with +15V input from a
AC/DC supply (purchased).

For +5V, I have used a TPS62160 (TI) with the output voltage set to +5.6V.
Then low dropout (LDO) regulators are used to get to +5V. The LDO
filters out most the switching noise. The TPS62160 delivers up to 1A and
can be fitted with all surrounding components in about 16x10mm.

In my case, I use lower currents at several points of load and use a
TPS7A4901 at each of these. The active GPS antenna LNA is one of the
consumers. It works well.

For a Thunderbolt, I guess that the TPS7A4501 could be used as the post
switch regulator.

To generate +12V, I have used TPS54332 which can deliver up to 3A. In my
case, the +12V doesn't need to be filtered, but if needed a +12V LDO
(the TPS7A4501 can used here too) is used as a follower, starting with a
switch output voltage at maybe +12.6V.

For a negative supply, I have used a LT3462A to invert the voltage. This
could be used to get -12.6V output regulated by a TPS7A3001 down to -12V.

The good thing with this approach is that it generates very little
excess heat and the output voltages could have noise levels in the order
of maybe 50uV or less.

I will try to get my act together and create a web site where I can
publish a bit about my over-complicated GPSDO design.
My problem is that I prefer soldering and programing and I am not the
best web designer.

Once it is up, I will publish a link on the list.

BR/
Joakim

Am 01.09.2016 um 07:44 schrieb Charles Steinmetz:

More belly feeling. The PNP circuit looks like the very low drop regulators
that are always good for a suprise. I did not think deeply about it.
And NPNs are more common.

regards, Gerhard

Mike wrote:

I was unfamiliar with the LPU, so I took a look at the docs.  It
develops several voltages, all from a +13.8v source.  This means that
the -12v supply necessarily is a switching supply (to get the polarity
reversal).  It is unfortunate that the power supply that needs to be
quietest for a Tbolt to perform at its best is the one that will be the
noisiest from this design.  (That will be true for any supply that uses
nothing but a positive DC input.)

Speaking of noise, none of the datasheets for the four regulators used
in the LPU gives any noise data.  It has always been my experience that
if a manufacturer fails to provide a particular specification, it is
because the part performs poorly in that respect -- so I presume the
noise performance of all of the regulators in the LPU are mediocre at
best for their type.

I have never measured an LPU, but all of the data available makes me
think it is not a promising candidate if one wants the best performance
from a Tbolt.

Best regards,

Charles

Dave wrote:

Well, yes, but that's well-known.  Ebay is what it is and ebay sellers
are what they are.  No use grousing about it, just deal with it.  The
important thing is to make sure you have a right of return.
Interestingly, after the last policy changes (at least here in the US),
it may actually be better to buy from a seller who does not offer
returns, because the "ebay money back guarantee" makes the seller refund
the bid price plus the original shipping, while an individual seller's
return policy may leave the buyer responsible for the original shipping.
Also, in some cases ebay doesn't require the buyer to return the
defective item, so you may save the return shipping and get the
defective item to play with to boot.

True, and the Power Designs supplies I mentioned all have OVP that works
very well.  If any of the supplies goes OV, it shuts all three supplies
down.  However, many electronic gizmos can be damaged if one of the
supplies falls too far below its nominal voltage while the other
supplies stay nominal, which of course would not trip the OVP.  So I
still recommend a dab of RTV on the voltage adjustment knobs when you
want the voltages to stay where they were set.

Best regards,

Charles

On 8/31/16 10:24 PM, Gerhard Hoffmann wrote:

what's the input source for these measurements? Batteries?