Built one 30 years ago ...



In those days (audio days) I had to use a B77 to 'record' the diff files.
Now that could be done digitally and would be easy to analyse supersonic frequencies (I could not hear above 18.5kHz in those days)

There are also much better devices to make something like this.
Schematics everywhere...
Just google 'differential amplifier' and the rest is peanuts to add.


Unfortunately such a device mixes FR (amplitude), phase and time and translates them all to amplitude.
With modern ways of analysing it should be possible to 'extract' aspects by viewing more signals at the same time.

Now I understand why my remarks were interpreted the wrong way and were seen as an attack instead of the (wished for) expansion of tests.

Basically a lot of us who were earnestly trying to mesh out the standards saw it as you thread-crapping.

--

On the comparator:

If the argument that tube amps do certain things better than solid-state amps is true, than it seems that a comparator (using solid-state parts or opamps) might not yield any meaningful results.

What I'd like to see is a method that can capture and present dynamic / transient behavior differences of amps - namely in amount of feedback. Feedback does wonderful things like tighten up the bass and extend FR, but it closes the soundstage and makes everything flatter and duller sounding.

I would use transformer summing instead of opamps At least if this were going to be a real time sort of difference test

Basically a lot of us who were earnestly trying to mesh out the standards saw it as you thread-crapping.

Get it now.... shouldn't have used the cheeky emoticons....

On the comparator:

If the argument that tube amps do certain things better than solid-state amps is true, than it seems that a comparator (using solid-state parts or opamps) might not yield any meaningful results.

Why ?
rethorical question as I understand where it comes from.
It comes from the notion/conviction/idea that transistors/opamps can't do what tubes can.
Let's just say I don't share your P.O.V. and see why you will probably not test this way, assuming an opamp cannot capture the effect.

Here is an idea for you to experiment with.
Play music on the tube amp and load with a headphone (or speaker)
record it using a PC (24bit many kHz) and play it back on an amp like the Rag.
Listen if 'the sound' is recorded and captured.
IF it has ... opamps can accurately follow it.
Can't do those tests myself. No access ... no time.

Yes... I also tested a (crappy, not high end) tube amp.
Was interesting to do.
Would like to do this again once with real tube amps.
Not in the business anymore nor access to high-end gear.

What I'd like to see is a method that can capture and present dynamic / transient behavior differences of amps - namely in amount of feedback. Feedback does wonderful things like tighten up the bass and extend FR, but it closes the soundstage and makes everything flatter and duller sounding.

You will need to create a signal that jumps from 0dB to say -70dB (which appears to me my limit when listening to loud extremely resolving speakers)
The signal needs to jump in level exactly around the '0'.
Reproduce it and look with a scope (not a digital recording) and see IF there is overshoot or the signal behaves other than the source.
Easy to see with 2 channnel scope and overlay.

That'll tell you which amp has problems.
Sort of a monotonicity test but with a much larger dynamic difference.
DC shifts will play a role as well, perhaps use a suitable high pass.
Certainly with non-balanced and coupled stages.

I would use transformer summing instead of opamps At least if this were going to be a real time sort of difference test

Trafo's may introduce higher distortions (hysteresis of the core), and won't do as well in frequency and phase response but the idea is intriguing.
When you have dual input windings you can easily change the phase if needed.
That would be a neat feature.
perhaps you could test it with the same signal on both input windings and see what it does.

You need to attenuate the input signal sligthly and match the other signal in amplitude to see how it nulls.
Would be elegant and fiully passive though.

Make sure there is NO DC present.