parnass@THINK.COM> (01/11/90)
I think those reporting "hum" problems when the CTR-82 is
powered by the AC wall adapter are experiencing a "ground
loop" condition. This is not a fault of the recorder itself,
rather a system problem that can happen whenever an AC powered
recorder is connected to an AC powered radio.
It happened with my CTR-75s until I connected them properly.
Perhaps a repost of this older article will help you
interface the CTR-82. Since the time it was last
posted, the Uniden 760XLT has been upgraded with a TAPE
jack.
x
TIPS ON CONNECTING THE
CTR-75 CASSETTE RECORDER
by Bob Parnass, AJ9S
When available on sale, the Radio Shack CTR-75 voice
operated (VOX) cassette tape recorder is a good choice for
scanner and shortwave listeners. The CTR-75 has been sold
since 1985 and was reviewed in a previous article.1
Another article described a simple modification to shorten
the 4 second post recording delay in order to conserve
tape.2 Dan Doyle, Tony Sarni, and I applied this modifica-
tion to our CTR-75s with excellent results.
Since those articles, some readers have reported difficulty
in connecting the CTR-75 to their scanners, and I hope the
information presented here will help.
As mentioned in the initial review, the CTR-75 has 2 input
jacks: AUX and MIC. They are not the same. The MIC input
is more sensitive than the AUX input, and performance can
vary depending on which jack you connect to your scanner.
Some scanners, like the Radio Shack PRO-2004 and Icom R-
7000 have REC or TAPE OUT jacks, which are specifically
designed for connection to a tape recorder. The output
levels at these jacks are fixed at low levels -- enough to
drive a recorder but too weak to drive a speaker. Since
the levels are fixed, adjusting the volume control has no
effect on the "loudness" of the signal fed to the tape
recorder.
Other scanners, like the Uniden/Bearcat 760XLT, lack
recording jacks, so audio must be taken from the EXT SP
(external speaker) jack. The signal level at this jack is
much higher than it would be at a TAPE OUT jack. It is not
at a fixed level, and varies with the setting of the volume
control.
The CTR-75 won't work if its MIC jack is connected directly
to the EXT SP jack of a 760XLT scanner. There are at least
two ways to connect the 760XLT to the CTR-75:
1. Connect the 760XLT directly to the CTR-75's AUX
input, although the radio's volume control has to be
slightly increased.
2. Connect the 760XLT through an attenuator ("signal
reducer") to the CTR-75's MIC input. I used an old
Radio Shack 51 dB attenuator, model #274-301, which
last appeared in the 1983 Radio Shack catalog. The
closest Radio Shack substitute is the 40 dB attenua-
tor found in the 1989 catalog, #274-300 priced at
$2.79.
Connections to various radios are summarized in the table
that follows. In each case, set the VOX SENSITIVITY switch
on the CTR-75 to HIGH.
__________________________________________________________________
| CTR-75 Tape Recorder Connection |
| for Various Scanners |
|Scanner Scanner Jack CTR-75 Jack Remarks |
|________|_______________________________________________________|
|PRO-2004| TAPE OUT AUX TAPE OUT jack is located|
| | on rear of radio |
|R-7000 | REC MIC REC jack is located |
| | on front of radio |
|R-71A | REC MIC REC jack is located |
| | on front of radio |
|760XLT | EXT SP AUX radio volume control may|
| | have to be increased |
| | EXT SP MIC attenuator pad must |
| | be used between radio |
| | and recorder, e.g., |
| | Radio Shack #274-301 or |
| | #274-300 |
|________|_______________________________________________________|
__________
1. See "The Radio Shack CTR-75 VOX Cassette Recorder," by
Bob Parnass, AJ9S, in The RCMA Newsletter, April 1988,
page 46.
2. See "Technical Topics," in The RCMA Newsletter, July
1988, page 76.
--
============================================================================
Bob Parnass, AJ9S - AT&T Bell Laboratories - att!ihuxz!parnass (708)979-5414levin@BBN.COM> (01/11/90)
In article <12520@cbnewse.ATT.COM> parnass@cbnewse.ATT.COM (Bob Parnass, AJ9S) writes: | |I think those reporting "hum" problems when the CTR-82 is |powered by the AC wall adapter are experiencing a "ground |loop" condition. This is not a fault of the recorder itself, |rather a system problem that can happen whenever an AC powered |recorder is connected to an AC powered radio. | |It happened with my CTR-75s until I connected them properly. | |Perhaps a repost of this older article will help you |interface the CTR-82. . . . I didn't see anything that would say how to correctly eliminate the ground loop. Anyhow, I think I'm having a different problem. I saw the note about the sale on CTR-82s and went out and got one. I get power from an old Archer (R.Shack) universal adapter set to 6 volts. I connect its AUX jack (chosen after experimenting) to the earphone jack on my old Regency scanner (I don't recall the model, it was maybe the first 10-channel programmable they sold, at least 7 years old). So far, so good. But after recording maybe half a cassette (a C-90 if it matters), the cutout stopped cutting out; or rather the machine would sort of half-stop, and run at variable speeds 1/4 to 1/2 normal, operating normally whenever a real signal from the scanner came in. This behavior seemed to get worse, and also occurred even with a dummy plug in the mic jack! I took the machine back to RS the next day and swapped it for a new one. The new one shows the same behavior. The design of the think may be half-assed. It seems as if the cut-out mechanism is analog in some sense -- the machine seems to fade off instead of being switched off. Before I take this one back, either for one more exchange or for a refund, I'll make sure my 6 volts is exactly that, and see if there is anything else obviously wrong. If anyone knows what's going on please let me know. /JBL (Bob, I'd love to get hold of the information about reducing the cutoff time from ~5 seconds to <2, if there's a convenient way for that to happen. Thanks) = Nets: levin@bbn.com | "There were sweetheart roses on Yancey Wilmerding's or {...}!bbn!levin | bureau that morning. Wide-eyed and distraught, she POTS: (617)873-3463 | stood with all her faculties rooted to the floor."
postmaster@CUVMB.CC.COLUMBIA.EDU (01/12/90)
To overcome a ground loop problem with my Panasonic recorder, I disconnected the shield at one end of the shielded cable between the recorder and scanner. -- ============================================================================ Bob Parnass, AJ9S - AT&T Bell Laboratories - att!ihuxz!parnass (708)979-5414