Double Cross Pilot Run Part II

by James Brown

The final step of the Double Cross electronic assembly is to curve the amplifiers against a standard.  This ensures that all the parts are correct and that the pot tapers are right, etc.  This may seem a little extravagent, but I like the fact that every amp that goes out is the same.

Here’s George McKale, a fellow amp engineer helping out with the testing.

This is a 100% quality check on each chassis assembly, and I receive a set of curves for each serial number amp that goes out.   Here’s the QA inspector performing the curve tests:

The frequency response curve that comes to me shows 3 different curves, one for each channel, and they match reasonably close.  These curves show the result of a very small signal going through the amp, with the effects of all the various eq points in the circuit, both pre and post eq.  If the curve is off more than a couple of dB, then there are bound to be wrong values accidently placed, a solder bridge, or some other variance.  Variation within a couple of dB is usually caused by the knob settings being off a tiny bit, so they’re acceptable.

Now if we’re lucky enough to get the rest of the parts in time, we should be finishing up the pilot run later this week……