Manley TAPE HEAD PREAMPLIFIERS - Manual (Page 10)

ALIGNMENT, CONTinued
8) Verify that each vernier freely adjusts from “0” to “100”. Hopefully they
should. If one doesn’t its because the pot is at the end of its travel. If this is the case either
decide that a number other than ”50” is OK or that it is unlikely that the extreme setting is
will ever be needed.
9) Power off, Wait a few minutes, Slide the top back on. The front panel has a notch to
accept the perf panel and it is sometimes a bit tricky to get it in right. If the panel is nicely
seated screw the 4-40 machine screw back in to lock the top.
10) Power on again and check that all is well and that the verniers are where you want them.
The only potential problems with this procedure is the possibility that the pots are now set so
that the maximum adjustment range is less than optimum. It would be wise to verify that one
can align to a variety of tapes including, at least, 15 and 30 IPS both NAB and CCIR tapes.
This is not a likely problem with Manley heads. It is wise to check these scenarios before a
client hands you a tape that is now a bit difficult to align. Sometimes the best answer is just
to use the original head and electronics for the unusual tape if it will solve that problem for
those rare tapes.
OTHER LITTLE HINTS
One last point worth mentioning to those that will be using these preamps with AMPEX
machines. They are factory wired for “Pin 3 HOT”. The Manley is “Pin 2 HOT”. If you
intend to typically just swap OUTPUT cables from one to the other you are going to be
probably introducing a polarity reversal. If the console input is unbalanced - only one set of
electronics will seem to pass audio. You could build a set of short polarity reverse cables for
this. Note that because the VU meter pick-off points are directly on the XLR outputs that a
shorted cable will cause the VU meter to also show little or no signal.
Keep in mind that a likely hook-up will be from preamp to DOLBY cards. Balanced inputs -
fine. Balanced inputs will provide hum rejection with balanced or unbalanced sources. The
point is that you should plan your wiring carefully to anticipate various set-ups and that it
may be smart to build a few extra cables - especially, if you use expensive wire. Plan it now.
At the factory we have found that some heat-shrink over the 12AX7WA’s helps dampen
microphonics. While we don’t usually recommend this, in this situation, the benefits out-
weigh the potential shorter tube life or potential slightly higher thermal noise. We select
these tubes for very, very low noise and minimum microphonics. Sometimes the
microphonic level changes over time or particularly over shipping . It does not seem possible
to predict that change. The shrink also shields from light hitting these 12AX7WA’s. We
found that even photons can affect the noise level here - very rare. These are the kind of
obstacles involved when a product has 90 dB of available gain at 20 Hz. That translates to a
power gain of 1 Billion. We do that with tubes......
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