PPM Perplexity

[cleverdick]

Good Morning Ted,

Just on the offchance, do you happen to still have details of the adjustment points for the 655-983 PPM drive card? (Just to save me a bit of time…)

Rather interestingly, in the desk they outwardly seem to have stayed set up pretty well, but on the bench, with a 0dBu differential input, they over-read by about 2dB. The proof of the pudding’s in the eating of course, and if all’s correct E-E then so be it. However, I can’t seem to find from the monitor schematic where this 2dB anomaly might be coming from. :ugeek:

Cheers,

Rich

[Ted Fletcher]

I have to say…. are you sure? How are you measuring the level? If you have an accurate RMS meter then OK, but if you are trying to measure with a digital meter switched to AC, then beware, these are generally only accurate at low frequency.

I don’t have an accurate RMS meter, but I do have a very good digital meter and checking at 200Hz my own test PPM and the 2 meters in my own 828S, sit nicely at ‘4’ when the sine wave input reads 0.775V AC.

The preset that is closest to the input terminals is the overall gain adjust. The others adjust the various break points….. and setting it up is a lengthy process that I don’t have a note of to hand

[cleverdick]

1k 0dBu tone from Minirator… gives a reading of PPM4.5. This is directly into the card on the bench, using the same movements – obviously. Through the desk, the PPMs were indeed accurate WRT main outputs. No drama, just a mild question mark. Investigation to follow on reassembly – perhaps!

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