Taking it off list was inadvertent...
> -----Original Message-----
> From: Association for Recorded Sound Discussion List
> [mailto:[log in to unmask]] On Behalf Of Richard L. Hess
> Sent: July 4, 2006 12:13 PM
> To: [log in to unmask]
> Subject: Re: [ARSCLIST] Bias Frequencies of tape recorders
> Rob wrote me off-list to enquire about the Revox B77 and B67. I don't
> know these, but the manuals are available at
> They are huge files (100-200 MB each) but you can check out any
> non-currently supported Studer product there. (The A807 is still
> supported through 2010 and is not available there).
> At 10:58 AM 7/4/2006, Richard L. Hess wrote:
> >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 through history...
> >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:
> >Quality tape transfers -- even from hard-to-play tapes.
> Richard L. Hess email: [log in to unmask]
> Aurora, Ontario, Canada (905) 713 6733 1-877-TAPE-FIX
> Detailed contact information:
> Quality tape transfers -- even from hard-to-play tapes.