SHRO is Single Head Read Only, the name we gave to our tape path architecture developed for the Model One.
Our first SHRO headblock was designed after studying vinyl disk mastering "pre-listen" headblocks built by Studer. Measurement confirmed what a prominent mastering engineer had informed us: these headblocks had audibly lower scrape flutter.
We turned next to modifying headblocks for Studer A820 owners. Where tape wrap and span needed to be controlled by guidance points, we elected to use precision rolling elements, aware of the much higher costs and the possible introduction of unwanted rotational element flutter inherent in this approach. These rollers are carefully assembled and selected for lowest possible total indicated runout. ATAE SHRO A820 headblocks are prized by their owners for sonic accuracy and neutrality.
Not well understood by many is the subject of forced guidance versus precision guidance and headblock interchangeability. For a popular example, the Ampex ATR-100 series quarter and half-inch tape machines have interchangeable headblocks that rely on forced guidance in those headblocks, while the Studer A80 and A820 quarter and half-inch tape machines have interchangeable headblocks that allow precision guidance through their headblocks. Studer did this even when the construction of a tape transport permitting precision guidance with headblock interchangeability is perhaps ten times more costly to implement. Why? It comes down to whether or not one believes that scrape flutter is audible, or that the tape damage resulting from edge force guiding is of concern.
Other shops construct headblocks for Studer reproducers by replacing the erase and record heads with stationary guides (also called dummy heads) machined to a profile and radius similar to that of the original heads. Alternatively, they will install additional reproducing heads of other track formats into the same headblock, with any head selectable by a switch. While this latter scheme is popular because only a single headblock is needed, it remains a bad idea not only because the tensioned tape is pulled over three (or more) scrape-flutter-generating stationary objects, instead of only one, but also because with every tape pass, all of the installed heads are subjected to wear simultaneously.
ATAE SHRO headblocks are not sold as after-market accessories because we want to asure that our headblocks are used only on properly working and adjusted transports. It is unfortunate fact that the precision guidance in many surviving A80s and A820s has been lost either by lubricant expiration or unqualified servicing. Taking the A80 for example, if the heights of the left guide roller and the stabilizer roller are not exactly correct, the precision-guided tape path through the headblock is compromised and the precision headblock interchangeability is lost. Further, optimum tape tension settings for SHRO reproducers are not the same as found in three or four-head recorder-reproducer configurations. For all of these reasons, we need to inspect and adjust any A80 or A820 transport undergoing conversion to a reproducer with SHRO.
Analog audio circuit design engineers with small signal and tape head expertise know that placing a first stage of gain in the headblock very near the reproducing head is ideal. Studer did this, Cello did this, and ATAE's playback circuit designers continue this practice.