[PAGE 1]
Progross Report on the Desien and Construction of Side Tone Lelay Apperatus on Subcontract under Contrsot

The first epparatus built was designed on the principlo of a constsnt tspo speed of about 40" per second with a veriablo distanco between the recording ond plsybaek heads. The recording hoad was fixed in position snd the playback head wes movable on a track which was designed to proserve the elignment. The tape in the form of an endless loop was carried overtivo light low inertia pulleys, one of which was fixed and the other having o spring mounting whioh meintainod a constant tension on the tape." The sound quslity was fair. Tho loop of tepe of overall length about 2 feet appearod to givo adequate rosults for poriods up to one-half hour. The ovorsll quality, however, was not by any means equal to the Maenecord equipment. Although lower quality amplifiers (Pentron) wers used in thia work, the mein difforence in quality was noise inherent in tho tapo and hoad system used.

Consequently, a variablo speed constent heod separation device vas designed ond built. The hoads were fixed in position et the minimum distance (1"). The endless loop of tapo was driven by a variable speed LC motor, using a 6 volt storsge battery. Sinco an overall speed rangc of at lesst l0-l wsa desired with good torque over the range, the use of s resistance in the field was found to be inadequate. The desired conditions were mode by varying tha srmoturo resistanco and tho field resistonce simultaneously, but in opposite direotions. Ihis was accomplished by s modified potentlometer, fixod rosistenco combination between the field and the armoture. In this way, a 25-l speod rsnge was obtained with cood torquo.

Tho renge of delay with this oquipment was from sbout O.02 to 0.4 seconds. Tie noiso level of the machino wes fairly high, apparently due to inadequate alignment and traoking of tho tepe.

It becamo opparont that construotion of a higher ordor of sccuraoy was necessary. It was decided to modify the ilagnocord rocording unit by keoping a fixed rolstionship botween the heads ond a constant tepe spoed by ineluding meens for varying the longth of tapo botween the fixed rooord and playback hoads. This can be done by an arrangement of amall pulleys, the middle one of which cen be variod in diatenco from the heads. In using this method, thc amount of tope betweon the heads is twioe the separation of tho middlc roller from the heads. hen this apcaretus was conatruoted and tested, it was. found thet the introduotion of the auziliary cquipmont

A19,I,47,30

B

[PAGE 2]
Poge 2

2/24/53