What is scrape flutter?

[Tom B.]

Here's an Ampex 350 head assembly I had JRF Magnetics modify a few years back. It started as one of those play-only units where a dummy idler was factory-installed in position 1 and a PB head in position 3. John reversed the orientation, putting the PB head first, machined the center to accept a 440-type scrape-flutter idler (not installed in this photo) and moved the dummy head to the last position. The static guides on the transport idler roller and takeup tension arm were also replaced with hand-picked ABEC-7 bearings.

The idea was to have the tape pass over the playback head first before encountering any static guides that would introduce additional flutter.

It was a good idea but I wasn't able to prove that the net results were better than the standard head configuration. A few people thought the playback was characteristically 'different' between the two setups but we couldn't agree if the concept worked as intended.

Swapping between this unit and a stock assembly took time, perhaps a half-hour to do the swap and do a quick alignment/azimuth check. And, the head in this unit is a Flux Std replacement unit, not Ampex. Since we were listening to older recordings in which some scrape flutter was already present (that we previously identified), we would continue to hear that artifact but weren't able to distinguish if the modified unit didn't add additional S/F on playback. The ability to record new material onto new tape probably would have been a better test but obviously we weren't set up to do that (the machine was built as a repro-only).

Tom

 

[DexterMiller]

Didn't Crown address a similar issue to this on their 700 and 800 Series decks way-back-when(?): by having all the guide posts made of glass and, also, having the shortest tape travel path of all 10 1/2" machines (then) being produced(?).

I've always found, that, once the tape stocks of the '70s changed into the problematic/SSS base formulas with the dull black backcoating...the spring loaded tension arms (not the backtension inertia idler) were the obvious part(s) of the transport which would get hung-up by scrape/squeal/etc. before it made its way near the heads and register as an artifact in the output signal. [The worse than (usually) known old stock --- so dried-out by this point, that, it can drag even a three (AC!) motor deck to a grinding halt is Sony PR-150 and Ampex 291, 292...aside from the documented offenders: Ampex "20/20", 456; Scotch 206; Capitol/Audio Devices "The Music Tape"; and the infamous Radio Shack "Concertape".]

This is one of the reasons I, personally, avoid the latter-era Teac/Tascam machines with DC motors. They have much weaker drive torque and the slightest hiccup of resistance anywhere along the tape path renders a tape unplayable on them.