Re: 1A5 - Usefulness, Experience


- What are the likely uses for this plug-in?
Things when you want to "float the scope".

- Will it help me analyze audio amplifier performance?
Mainly power output, sometimes when you need it, balanced ins and outs on line or lower level equipment. Not so much on bridged outputs until they hit many watts.

- How about balanced modulators in SSB radio receivers?
Doubt it. You can pick that up at the output, single ended. (usually, at least on CBs) Though unbelievably the output is linear, it does not necessarily have a balanced input., If you have anything specific in mind, post the topology or a link. Far as I know SSB transmitters are run in the linear mode. I am sure a better one exist but I am not familiar with it. YOU know the schematic, YOU know if it would be necessary.

- Are there types of solid state circuits (digital or analog) that it will help me with?
Only a few, unless you are working on some really cool stuff. It will mostly be analog. In fact part of its usefulness would be a calibrated amplitude so that if you lock the horizontal to the carrier in SSB for example, you can see the phase shift. You can see it anyway but this thing will tell you more easily whether it leads or lags.

- One channel of my 1A1 preamp has now gain - can I use the 1A5 (in the 545 that Is also here) to diagnose this problem?
If you have to get a differential waveform off the deflection plates of a scope CRT, this is EXACTLY what that thing will excel at. A set of identical probes on a regular dual trace plugin, set to add and invert one channel will get you do so far. But if say, you are looking for noise. You are looking for like 250mV of noise riding on 130 volts DC, and there are position shifts which would be taken out by AC coupling... THAT is where a unit like this comes in handy.

If you use the two channels and null them, every time you want to switch ranges you have to switch them both and hope they match. With a differential amp if it s working right you can count on that.

Many scopes are only +/-3% on many parameters. A differential amp might be about that in the absolute sense, + to - it is much more accurate. MUCH more. I have specifically calibrated scope channels to be ABSOLUTELY equal, and ABSOLUTELY is a relative term. If you got the right generator you will find that they are not equal all the way up and down the scale.

The differential amp is SPECIFICALLY designed to be.

Take a differential probe into a differential amp and put both ends of that probe into the mains, or maybe a generator outputting 150 volts P-P. Crank the gain to something like 100mV/div. and you should see nothing.

Forget floating the scope for anything good as well, in doing that you transmit the signal, but more importantly you put a capacitive load on one side.

Yup, it is useful no doubt. You will probably find it most useful in scopes because after a certain point EVERYTHING is differential in a scope. Sure the plate drive doesn't clip exactly equally, but who cares as long as it is linear when it is on the screen ?

I cannot advise about your particular model. I am familiar with these things but not that particular one. SPECIFIC weaknesses (if any) I just do not know, but I tried to field your more general questions.

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