Re: [ARSCLIST] Setting bias and EQ on Technics 1520

[Jim Long <JJimLong@xxxxxx>]

In a message dated 2/1/2008 12:04:23 AM Eastern Standard Time, 
LISTSERV@xxxxxxx writes:


> > -----Original Message-----
> > From: Sammy Jones [mailto:sjones69@xxxxxxxxxxxxx]
> > Sent: Sunday, January 27, 2008 3:08 AM
> > To: 'ARSCLIST@xxxxxxxxxxxxxxxx'
> > Subject: Setting bias and EQ on Technics 1520
> > 
> > Hello listmembers,
> > 
> > I mentioned several months ago that I have a Technics RS 1520 reel to
> > reel tape recorder in excellent condition.  I have recently bought some
> > new-old stock Ampex 631 reels to make test recordings.
> > 
> > The main function of this deck is to playback pre-recorded reels and
> > transfer to CD, but I'd like to make some recordings on it just for
> > fun.
> > 
> > My problem is in setting the EQ and bias properly to record on this
> > tape.  This is my first time recording tape on a machine with settable
> > bias and EQ, and the Technics service manual does not specify how to do
> > this.  I've found some information on the web for bias setup, but not
> > EQ.
> > 
> > Could any listmembers who know how to set EQ and bias on Technics 1520s
> > please respond with directions?
> > 
> > Thanks,
> > Sammy Jones




Hi Sammy,

I will defer to the tape-recorder gurus who frequent the ARSC listserv, but I 
do have two RS-1520's along with the original operating instructions and a 
service manual, which appears (as suggested by Steve Koto), to be made of two 
sections glued together: adjustments and schematics (74 pages) and a parts list 
(23 pages).

Because the 1520 has bias and EQ adjustments on the front panel and an 
internal 1-kHz and 10-kHz signal generator (one of the reasons I purchased the first 
one new, in 1988), the operating instructions on page 8 contain a procedure 
for bias and EQ adjustment using the front-panel meters.  Basically, one first 
adjusts the bias current (the graph shows stopping at the peak output point as 
one increases the bias current, though I distantly recall other general 
recommendations to go beyond the peak by a dB or so for lower distortion) and then 
adjusts the record EQ to get equal levels at 1 kHz and 10 kHz.

Page 8 includes a table that lists the rough (switched on the front panel) 
bias and EQ settings for various tapes.  Ampex 631 is not listed but all you 
need to do is find the settings that let you find the bias peak and get equal 
level at 1 kHz and 10 kHz.  As an aside, I recall getting amazingly flat R/P 
response at 3.75 IPS with Ampex 407 tape, which I used years ago to make long 
background music compilation tapes before CD changers killed the need.

I will be happy to scan and send to you this page of the instruction manual.

The 74-page service manual looks to be super complete.  I'm not certain I am 
even capable of going through all the mechanical and electrical adjustments 
noted.  The section on bias does not tell one how to adjust it for a particular 
tape but rather how to get the proper nominal values for the three click 
positions.

Please feel free to contact me offline, including by phone.  I am on Eastern 
time.

Jim Long
Senior Sales Support Engineer
Bosch Communications Systems
Electro-Voice
Michigan remote

Home office: 269-422-5207   </HTML>