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Intermittent dropouts on phono input

F

FearlessFerret

Jan 1, 1970
0
I'm in the middle of a multi-year project to digitize my vinyl collection and
I've got a reucrring problem that's driving me up a wall.

I have a Dual CS 528 turntable hooked to a Pioneer SX-201 which is functioning
as preamp. My homebrew PC (a dual-CPU 1 GHz Intel server board) sound card (a
late-model low-end SoundBlaster) is wired to the tape in/out jacks. A cassette
deck is connected to the CD inputs.

Most of the time, the setup works fine. It's not audiophile quality by a long
stretch, but it works well enough that I hear the music and not the technology.

The problem is that without warning, one or the other channel will drop out
partially or entirely, with a 60-cycle hum appearing noticeably (but not at full
volume). If I pull and reinsert the turntable inputs, it goes back to normal,
and pulling and reversing the turntable's power cord also clears it.

Thinking that this looks like an intermittent ground loop, I took care to plug
the amp, TT and the PC into the same (battery backed-up circuit of the) UPS.
Didn't help.

One other thing I noticed is that sometimes the signal will drop out when there
is a spike on the line (like when the dehumidifier turns off) but I can't say
I've noticed that since I put everything on the UPS. I have even replaced both
the turntable and the amp and get the same problem.

Over the course of the summer the setup was not giving me much trouble, but in
the past couple of weeks I have difficulties several times a day.

Now I'm wondering if there is some kind of diode effect somewhere that is
causing a charge buildup, but at this point I'm just veering into wild
speculation because I'm all out of ideas.

/ff
 
C

clifto

Jan 1, 1970
0
FearlessFerret said:
The problem is that without warning, one or the other channel will drop out
partially or entirely, with a 60-cycle hum appearing noticeably (but not at full
volume). If I pull and reinsert the turntable inputs, it goes back to normal,
and pulling and reversing the turntable's power cord also clears it.

I'm betting the ground connections on your turntable cables aren't good.
Could be corrosion or intermittent cables.
 
M

Mark D. Zacharias

Jan 1, 1970
0
FearlessFerret said:
I'm in the middle of a multi-year project to digitize my vinyl collection
and I've got a reucrring problem that's driving me up a wall.

I have a Dual CS 528 turntable hooked to a Pioneer SX-201 which is
functioning as preamp. My homebrew PC (a dual-CPU 1 GHz Intel server
board) sound card (a late-model low-end SoundBlaster) is wired to the tape
in/out jacks. A cassette deck is connected to the CD inputs.

Most of the time, the setup works fine. It's not audiophile quality by a
long stretch, but it works well enough that I hear the music and not the
technology.

The problem is that without warning, one or the other channel will drop
out partially or entirely, with a 60-cycle hum appearing noticeably (but
not at full volume). If I pull and reinsert the turntable inputs, it goes
back to normal, and pulling and reversing the turntable's power cord also
clears it.

Thinking that this looks like an intermittent ground loop, I took care to
plug the amp, TT and the PC into the same (battery backed-up circuit of
the) UPS. Didn't help.

One other thing I noticed is that sometimes the signal will drop out when
there is a spike on the line (like when the dehumidifier turns off) but I
can't say I've noticed that since I put everything on the UPS. I have
even replaced both the turntable and the amp and get the same problem.

Over the course of the summer the setup was not giving me much trouble,
but in the past couple of weeks I have difficulties several times a day.

Now I'm wondering if there is some kind of diode effect somewhere that is
causing a charge buildup, but at this point I'm just veering into wild
speculation because I'm all out of ideas.

/ff

Duals are notorious for output cables going bad. That's my guess.

Especially the white and black pairs.


Mark Z.
 
R

Ron(UK)

Jan 1, 1970
0
FearlessFerret said:
I'm in the middle of a multi-year project to digitize my vinyl
collection and I've got a reucrring problem that's driving me up a wall.

I have a Dual CS 528 turntable hooked to a Pioneer SX-201 which is
functioning as preamp. My homebrew PC (a dual-CPU 1 GHz Intel server
board) sound card (a late-model low-end SoundBlaster) is wired to the
tape in/out jacks. A cassette deck is connected to the CD inputs.

Most of the time, the setup works fine. It's not audiophile quality by
a long stretch, but it works well enough that I hear the music and not
the technology.

The problem is that without warning, one or the other channel will drop
out partially or entirely, with a 60-cycle hum appearing noticeably (but
not at full volume). If I pull and reinsert the turntable inputs, it
goes back to normal, and pulling and reversing the turntable's power
cord also clears it.

Thinking that this looks like an intermittent ground loop, I took care
to plug the amp, TT and the PC into the same (battery backed-up circuit
of the) UPS. Didn't help.

One other thing I noticed is that sometimes the signal will drop out
when there is a spike on the line (like when the dehumidifier turns off)
but I can't say I've noticed that since I put everything on the UPS. I
have even replaced both the turntable and the amp and get the same problem.

Over the course of the summer the setup was not giving me much trouble,
but in the past couple of weeks I have difficulties several times a day.

Now I'm wondering if there is some kind of diode effect somewhere that
is causing a charge buildup, but at this point I'm just veering into
wild speculation because I'm all out of ideas.

/ff


I had a similar problem on my Dual 505. It turned out to be tarnished
contacts on the removable cartridge carrier. No amount of cleaning cured
it for long so I solved it by pulling the loom through the arm a little
and wiring directly onto the cartridge.

HTH
Ron(UK)
 
T

Tim Schwartz

Jan 1, 1970
0
Hello,

I have to agree with Mark Z., the most likely problem is the awful RCA
cables that Dual used for years. If the turntable is one of the ones
where there are RCA plugs at both ends, simply replace them. If they
are soldered at the turntable, or have the slip on lugs, then you can
change the RCA plugs, but be careful to get decent quality plugs (I like
the Switchcraft 3502) and you have to do a good soldering job. Crimp or
screw terminals will be problematic on phono signals.

Cleaning head shell contacts might also be a good idea, and Dual
headshells sometimes have awful crimps as well. I'd use isopropyl
(rubbing) alcohol on a q-tip to clean the contacts.


Regards,
Tim Schwartz
Bristol Electronics
 
A

Asimov

Jan 1, 1970
0
"FearlessFerret" bravely wrote to "All" (09 Oct 05 10:48:26)
--- on the heady topic of "Intermittent dropouts on phono input"

Fe> From: FearlessFerret <[email protected]>
Fe> Xref: core-easynews sci.electronics.repair:344542

Fe> I'm in the middle of a multi-year project to digitize my vinyl
Fe> collection and I've got a reucrring problem that's driving me up a
Fe> wall.
Fe> I have a Dual CS 528 turntable hooked to a Pioneer SX-201 which is
Fe> functioning as preamp. My homebrew PC (a dual-CPU 1 GHz Intel server
Fe> board) sound card (a late-model low-end SoundBlaster) is wired to the
Fe> tape in/out jacks. A cassette deck is connected to the CD inputs.

Fe> Most of the time, the setup works fine. It's not audiophile quality
Fe> by a long stretch, but it works well enough that I hear the music and
Fe> not the technology.
Fe> The problem is that without warning, one or the other channel will
Fe> drop out partially or entirely, with a 60-cycle hum appearing
Fe> noticeably (but not at full volume). If I pull and reinsert the
Fe> turntable inputs, it goes back to normal, and pulling and reversing
Fe> the turntable's power cord also clears it.
Fe> Thinking that this looks like an intermittent ground loop, I took care
Fe> to plug the amp, TT and the PC into the same (battery backed-up
Fe> circuit of the) UPS. Didn't help.

Fe> One other thing I noticed is that sometimes the signal will drop out
Fe> when there is a spike on the line (like when the dehumidifier turns
Fe> off) but I can't say I've noticed that since I put everything on the
Fe> UPS. I have even replaced both the turntable and the amp and get the
Fe> same problem.
Fe> Over the course of the summer the setup was not giving me much
Fe> trouble, but in the past couple of weeks I have difficulties several
Fe> times a day.
Fe> Now I'm wondering if there is some kind of diode effect somewhere that
Fe> is causing a charge buildup, but at this point I'm just veering into
Fe> wild speculation because I'm all out of ideas.


From the description of the sudden mysterious hum behaviour it gets my
antennas up for some type of parasitic oscillation. When dealing with
parasitics, there has to be enough gain at some frequency. The stage
with the most gain is probably the phono input and this narrows the
search area.

My theory is that the phono cable you are using adds just the right
amount of stray capacitance to make the phono input oscillate at VHF.
The quick fix is to add a small value resistor (100 ohms to 1K) in
series with the input or a ferrite bead through the center conductor
of the socket (or cable if impossible but closest to amp). However,
the root cause of the hyper-sensitivity to parasitics may be a dried
up decoupling electro in the receiver's phono preamp stage.

Of course, this theory may be totally out to lunch and it really is
simply a dirty connection or broken solder.

A*s*i*m*o*v

.... A stereo system is the altar to the god of music.
 
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