At 10:21 AM 7/4/2006, Rob Poretti wrote:
>Hi guys and gals,
>I'm just curious if anyone has taken stock of what bias frequencies were
>employed by the more common "professional" reel-to-reel tape recorders used
Fortunately, this has been discussed elsewhere and I can provide some
of the information:
In the early days, apparently wire recorders used bias as low as
30-40 kc, but Jay McKnight recalled in the pre-Ampex days, 60 kHz was common.
The Ampex Standard was 100 kc up to the MR-70.
With the MR-70, Ampex switched to 150 kHz bias frequency (and adopted
the Hz) [Larry Miller, ex Ampex]
Other later machines used different bias and erase frequencies.
Ampex AG-440 (A) stayed with 150 kHz [manual]
Studer A80 80 kHz erase, 240 kHz bias (1:3) [Jay McKnight]
ReVox A77 120 kHz [manual]
Ampex ATR-100 144 kHz erase, 432 kHz bias (1:3) [manual]
Studer A810 & A807 (and I think A820 2CH) 153.6 kHz [manual]
Otari MTR-10/12 II Bias 250 kHz (erase not spec'd) [manual]
Sony APR-5000, APR-24 100 kHz erase, 400 kHz bias (1:4) [manual]
MCI JH-24 Multitrack 210 kHz bias, 105 kHz erase [manual via Brian Roth]
Otari MTR-90 (original) 246 kHz bias, 123 kHz erase [manual via Brian Roth]
Here is a quick sampling of published bias frequencies for two
top-of-the line cassette recorders, a better-than-average portable,
and an early compact portable.
Nakamichi Dragon (perhaps the finest machine ever made for overall
audio quality) 105kHz (Service manual dated 1985 (scan) 1990 (Xerox))
Studer A710 (a high-end cassette recorder, without the auto-azimuth
that makes the Dragon superior) 150kHz (no date, scan on Studer ftp site)
Sony TC-D5M (a workhorse, good quality stereo portable) 85 kHz (Svc
Manual dated 1980)
Sony TC-55 (an early compact -- jacket pocket -- mono portable) 41kHz
(as low as I've ever seen) (Svc Manual dated 1972)
Richard L. Hess email: [log in to unmask]
Aurora, Ontario, Canada (905) 713 6733 1-877-TAPE-FIX
Detailed contact information: http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.