Re: signal leads that pick up less ambient noise?

On 20/02/2025 22:41, Christopher Howard wrote:

>
If you make your signals balanced differential drive then you can
withstand a lot of ambient common mode noise without problems. The way
that instrumentation amplifiers do it.
>

 I'm interested in this idea, though I'm not sure how to apply this in
any practical way to the connections inside the analog computer, i.e.,
the patches between the different integrators and such.
 As far as the connection from the signal generator to the analog
computer input, that doesn't sound too hard. But with a quick search on
the Internet, it seems that balanced cables are not made with BNC
connectors on one end, to match the signal generator. Do you know of an
adapter that would work for this?

At the low frequencies you are using you don't need BNC or coax. Twisted signal pair inside a grounded at signal source end screen might actually be better for what you want here.

For the differential receiver, do I need anything special for this, or
can I just feed the conductors into an LF356 op amp (unity gain
configuration...?)
 

>
IOW rather than coax you have two signal lines v+ and v- inside a
passive conductive outer shield that plays no part in the signal
transmission. It is there only as a Faraday shield against external
interference.
>

 Any particular cable you recommend?

At the low frequencies you are talking about some of the cables intended for broadcast quality microphones have the right sort of screening.

I think there is something funny going on with your setup.

 I don't know of anything "funny" but am still learning. This is
certainly a DIY, learn-as-you-go project. For the analog computer, I'm
largely following the Grappendorf schematics, though building it on a
breadboard instead of printing the PCBs, which I can't afford right now.
 https://www.grappendorf.net/projects/analog-computer/

Those boards don't look at all sophisticated. When you say building it on breadboards do you mean Vero board or some other soldered prototyping medium or do you mean literally on a plug in patchboard?
Layout and signal screening will be important if you want to build an analogue computer that will actually behave itself. As a beginner you might be better off buying the kit of bits with the working PCBs.
It is incredibly easy to make small but important mistakes on prototype breadboards and the push fit ones can quickly become a rats nest. You can learn to etch and drill your own PCBs (no solder mask). That is how I got started as a teenager. The chemicals are a bit harder to buy now. OTOH laser printed masks are way quicker than by hand felt pen resist.

Some other substitutions I have made: I haven't built a PS as I happen
to have access to a bipolar 15V supply already, though admittedly it is
a rather old unit. I also haven't built the reference voltage module but
am hoping to have parts for that in the next few weeks.

Have you checked that your bipolar 15v supply isn't the noise source?
The noise you are describing at around 40kHz looks awfully like an old school switched mode PSU sort of frequency.
--
Martin Brown