[time-nuts] Buffer amplifier, OP Amp, vs MMIC, vs discrete?

[Bob kb8tq]

Hi

The file you reference is showing a rather complex single mixer setup.
It simply omits the mixer from the schematic.  The audio amplifier that is
part of that setup is going to improve the measurement floor by a couple
of db. 

With most people saying that it’s way to complex to set up to measure 
this stuff, I’d suggest that a “get it going” rig that is within a couple db
(but wires up in an afternoon) is the better approach.

The main issue of doing it in an afternoon is that it needs to be done
from the small parts you have on hand. What sort of bypass caps do 
you stock? Which voltage regulators are already at hand? Do you do
your breadboards with 1206 parts? Any real design will need to be 
adapted to “fit” that part of things. 

Some examples:

+/- 18V is a nice supply for some of this. 79L18’s are “uncommon”. 
If you have them then this or that op amp makes a lot of sense. If 
the highest you want to play with is +/- 12V then a very different 
set of op amps make sense.

The RPD series of mixers are much better at this than other parts.
Maybe you don’t want to use them. Since they are 500 ohm output
and most other mixers are 50 ohm, the circuit changes more than 
just a little bit. 

Lots of variables. 

Bob

> On Apr 4, 2020, at 7:36 AM, Tobias Pluess <tpluess at ieee.org> wrote:
> 
> Hi Dana
> 
> No I don't have insight into the Wenzel stuff.
> The Wenzel amp I mentioned is this:
> 
> http://www.techlib.com/files/lowamp.pdf
> 
> 
> Tobias
> 
> On Sat., 4 Apr. 2020, 12:25 Dana Whitlow, <k8yumdoober at gmail.com> wrote:
> 
>> What is a "Wenzel amp"?  Are you referring to the broad line of amplifiers
>> made by Wenzel Assoc?
>> You sound like you've got some insight into what is inside these things,
>> that is not available from
>> the datasheets from Wenzel, but I don't even know if these are what you
>> refer to.
>> 
>> Please elucidate.
>> 
>> Thanks,
>> 
>> Dana
>> 
>> 
>> On Fri, Apr 3, 2020 at 6:55 PM Tobias Pluess <tpluess at ieee.org> wrote:
>> 
>>> Hi Taka
>>> 
>>> what are those discrete amp designs you mention? I have seen some, but
>> not
>>> those you mention. These which I have seen seem to be quite dated, use
>>> strange or old parts (selected 2SC... transistors which are not so easy
>> to
>>> obtain here) or have other issues.
>>> There is also the Wenzel amp, but building it seems to involve some black
>>> magic as it works only with some very sophisticated, selected, exotic
>> parts
>>> and I have never seen a proper explanation about how it really works and
>>> how the part values are calculated (for example if you want to change the
>>> gain).
>>> As I am (mostly) not afraid of discrete circuits it would be interesting
>> to
>>> which designs you mean.
>>> 
>>> Best
>>> Tobias
>>> HB9FSX
>>> 
>>> 
>>> On Sat., 4 Apr. 2020, 00:07 Taka Kamiya via time-nuts, <
>>> time-nuts at lists.febo.com> wrote:
>>> 
>>>> I'm seeing a fairly obvious trend on this list.  When it comes to
>> buffer
>>>> amplifiers, many people, in fact, most I've seen recommends fast OP
>> Amp.
>>>> Discrete Amp, such as ones from K5FX design, NIST design, Clifton amp,
>>> and
>>>> others are mentioned only sometimes.  Trends are similar for
>> distribution
>>>> amps.  Video amps are generally not recommended.
>>>> 
>>>> But I have never seen a suggestion of MMIC like ones from
>> Mini-circuits.
>>>> There are few that work from DC, fairly good NF, but often too high of
>>>> gain.  Other than high gain, are there reason NOT to use MMIC?
>>>> 
>>>> ---------------------------------------
>>>> (Mr.) Taka Kamiya
>>>> KB4EMF / ex JF2DKG
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