Manley TAPE HEAD PREAMPLIFIERS - Manual (Page 8)

Playback Heads
Manley Playback Heads are custom manufactured new heads of a better quality than can
be obtained in any stock tape machine of any vintage. They are manufactured by JRF
Magnetics. We strongly recommend that you only use playback heads supplied by
Manley Labs or those under licence from Manley Labs. The reason for this is that these
are vacuum tube based units designed for "high impedance" playback heads typically
500mH (mili-Henrys). Most playback heads are low impedance varieties (2mH to
10mH) designed for transistor or transformer input stages and will certainly not be
optimally "matched" or "loaded". Older heads designed for vacuum tube inputs will
almost always be worn away and out of "spec" even if relapped. We cannot guarantee
that customer supplied heads will provide satisfactory performance.
Manley Labs is manufactuing a replacement "Head Block" for Ampex ATR style
machines. This is a precision milled assembly that provides easy adjustment of
"azimuth", "height", "zenith" and "wrap".
We generally also recommend that mounting of the head be performed by Manley Labs
or JRF Electronics in New Jersey. Correct "height", "wrap", "zenith" adjustments are
usually performed by professional tape machine technicians. These procedures will be
covered in the technical manuals of your machine. However, if you will be mounting the
head, a single 6-32 machine screw attaches the head to the original plate.
High impedance playback heads can be significantly affected by the cable between the
head and the preamp. The requirements call for extreme low capacitance and best
quality shielding. The shortest possible length of wire is also important. We use Van
Den Hull MCD 102 Mark III. These two cables have to be soldered to the original
head block connector and generally run thru the machine. We generally use either
unused pins on the connector or pins normally used for tracks 3 & 4. This allows the
original heads to be used with the original electronics if or when the engineer would
desire that option. The other end of the cable should be a 3 pin male XLR with :
pin 1 = Shield
(ground at machine)
pin 2 = Positive phase (brown wire on head)
pin 3 = Negative phase (black wire on head)
There are two common locations for the preamps to be mounted. Considering the
requirement for a short "head to preamp" cable this narrows the options to directly
below the deck or above the meter bridge.
Usually above the bridge allows easier alignments but with a slightly longer cable.
A second but rarely used option is to have a 4P2T switch that routes the high impedance
head to either the Manley tube electronics or to the original electronics. Though the
impedance matching will likely be wrong there is a possibility that the the original
electronics will have enough adjustment range to compensate for the mismatch.
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