I used the Hewlett-Packard 8903B and QuantAsylum QA403 again as I did with the Hameg equipment but used the Tektronix TAS 485 scope instead of the Hameg since those were back on the shelf.
The biggest wrench in the works in terms of using the Amber is how the 331 unit interacts and can supersede the regular front panel operator controls. And, since the manual only describes the regular controls and I haven't been able to find any documentation on the 331 or the 330 version that doesn't include the counter, this involved some amount of educated guesswork and some amount of trial and error.
Basically, the Input and Output selections need to be on NOR which apparently stands for Normal, to have the input signal handled as one would expect from the front panel and the signal generator output one would expect on the front panel. It isn't a boolean NOR applied to the signals which threw me at first because I've run into some audio processing equipment where the front panel control buttons were labelled with logic gate symbols and I thought this was another application of that at first.
For the signal generator, the VAR button needs to be pushed to use the front panel frequency control knob instead of the presets on the 331. Interestingly, this also applies to the tuning of the notch filter when it's measuring distortion. The frequency of the notch filter and the oscillator are both controlled by the same front panel knob that turns a ganged potentiometer so my suspicion is that the preset buttons on the 331 switch in a resistor matrix where they've picked the resistance values that correspond to the values of the potentiometer at those frequencies.
It looks like the left and right inputs and L, R, sum and difference signals are only applied to the rear panel jacks on the 331 and regular output is disabled on the front panel when those are selected instead of NOR for the output. I couldn't test what comes in and out of the back panel jacks because I don't have any 3/4 inch connectors suitable on hand.
Level, THD+N and frequency off the 8903B's generator all looked reasonable at first glance.
And the output of the Amber's signal generator.
I was a bit pressed for time so I want to double check this to be certain but I'm pretty sure this Amber doesn't have the option for IMD testing which is unfortunate. I also suspect that it even though it looks like the 331 can generate L, R, sum and difference matrix signals from the front panel controls, that it probably can't build up the complete FM stereo multiplex composite signal the way things like the HP 8904A with the correct option and serial number level or Sound Technology ST-1000A or other FM stereo alignment generator can.
My first thoughts are this is a nice machine and I can see why they're well regarded. It's unfortunate that there's so little documentation on them out there though which is why I was hoping the ring-bound book this one came with would contain a more recent revision of the manual than the 1988 version that's already online in several locations and include the manual for the 331. The only added documentation that was included was an addenda for a power supply change.