NAD 7150 Stereo Receiver/Amp Noise when Listen knob set to

Hi
I'm not a tech in any way, but before I take this for repair, I want
to make sure it's not a simple connection/hookup issue.

I got this and a Technics turntable on Ebay, and I'm very happy with
them so far. The receiver is hooked up, radio works great, audio from
DVD/TV works great.

When I select Listen/Phono, I get a loud rumble through the speakers,
whether the TT is on or not, and whether it is plugged into the back
of the REC or not.

The noise goes up and down when the volume is turned.

The TT does work and play records, but the rumbling is underneath.

Also, the ( I assume) ground lead from the back of the TT, where does
that get connected?

 

[William Sommerwerck]

When I select Listen/Phono, I get a loud rumble through
the speakers, whether the TT is on or not, and whether
it is plugged into the back of the REC or not.

I don't know what you mean by "rumble", but I assume you mean "hum".

Yes, if the TT is not properly grounded to the amplifier, there's a good
chance of getting loud and annoying hum.

On the other hand, the fact you get this noise even when the TT is not
connected suggests there might be something wrong with the amplifier's phono
preamp.

I'd suggest starting your troubleshooting by making sure the TT is properly
grounded to the amp. Check the ground wire to be sure it isn't broken.

 

[Arfa Daily]

<nukemedtc99m@yahoo.com> wrote in message
news:fafbo41jsoucm6rk11poqc3hh6qso5h4l5@4ax.com...

Hi
I'm not a tech in any way, but before I take this for repair, I want
to make sure it's not a simple connection/hookup issue.

I got this and a Technics turntable on Ebay, and I'm very happy with
them so far. The receiver is hooked up, radio works great, audio from
DVD/TV works great.

When I select Listen/Phono, I get a loud rumble through the speakers,
whether the TT is on or not, and whether it is plugged into the back
of the REC or not.

The noise goes up and down when the volume is turned.

The TT does work and play records, but the rumbling is underneath.

Also, the ( I assume) ground lead from the back of the TT, where does
that get connected?

The fact that the rumble goes up and down with the volume control, coupled
with the fact that it is not present on other input selections, indicates a
fault with the phono input preamp, which is usually a fairly conventional
opamp stage. As you say "speakers" in the plural, I assume that the problem
is present on both stereo channels. I have heard this sort of problem being
caused by the opamp itself being faulty on a number of occasions over the
years, but other causes could be a power supply issue - such as a bad
decoupling cap on one of the opamp rails, or even a noisy regulator, that
only shows when you are switched to a very high sensitivity input such as
"phono".

As far as fixing this problem goes, it should be a simple matter for an
experienced engineer, but if you have no personal experience of electronic
service work, it may be beyond your capabilities. I wouldn't expect it to be
expensive.

Any separate ground wire from the turntable, just needs to be connected to
the amp's rear panel metalwork. Most amps which have a specific phono input,
usually have a knurled screw to accommodate this ground wire. Depending on
the overall configuration of the system, the effect of attaching this wire
can be anything from un-noticable to profound.

Arfa

 

Thank you to both William and Arfa I'll be looking for a service
establishment.
Thanks again



On Sun, 1 Feb 2009 16:23:01 -0000, "Arfa Daily"
<arfa.daily@ntlworld.com> wrote:

nukemedtc99m@yahoo.com> wrote in message
news:fafbo41jsoucm6rk11poqc3hh6qso5h4l5@4ax.com...
Hi
I'm not a tech in any way, but before I take this for repair, I want
to make sure it's not a simple connection/hookup issue.

I got this and a Technics turntable on Ebay, and I'm very happy with
them so far. The receiver is hooked up, radio works great, audio from
DVD/TV works great.

When I select Listen/Phono, I get a loud rumble through the speakers,
whether the TT is on or not, and whether it is plugged into the back
of the REC or not.

The noise goes up and down when the volume is turned.

The TT does work and play records, but the rumbling is underneath.

Also, the ( I assume) ground lead from the back of the TT, where does
that get connected?



The fact that the rumble goes up and down with the volume control, coupled
with the fact that it is not present on other input selections, indicates a
fault with the phono input preamp, which is usually a fairly conventional
opamp stage. As you say "speakers" in the plural, I assume that the problem
is present on both stereo channels. I have heard this sort of problem being
caused by the opamp itself being faulty on a number of occasions over the
years, but other causes could be a power supply issue - such as a bad
decoupling cap on one of the opamp rails, or even a noisy regulator, that
only shows when you are switched to a very high sensitivity input such as
"phono".

As far as fixing this problem goes, it should be a simple matter for an
experienced engineer, but if you have no personal experience of electronic
service work, it may be beyond your capabilities. I wouldn't expect it to be
expensive.

Any separate ground wire from the turntable, just needs to be connected to
the amp's rear panel metalwork. Most amps which have a specific phono input,
usually have a knurled screw to accommodate this ground wire. Depending on
the overall configuration of the system, the effect of attaching this wire
can be anything from un-noticable to profound.

Arfa

 

[Tim Schwartz]

nukemedtc99m@yahoo.com wrote:

Hi
I'm not a tech in any way, but before I take this for repair, I want
to make sure it's not a simple connection/hookup issue.

I got this and a Technics turntable on Ebay, and I'm very happy with
them so far. The receiver is hooked up, radio works great, audio from
DVD/TV works great.

When I select Listen/Phono, I get a loud rumble through the speakers,
whether the TT is on or not, and whether it is plugged into the back
of the REC or not.

The noise goes up and down when the volume is turned.

The TT does work and play records, but the rumbling is underneath.

Also, the ( I assume) ground lead from the back of the TT, where does
that get connected?

Good morning,

On the back of your NAD 7150 to the left of the phono input jacks are 3
items that require your attention. On top is a switch marked "MC MM"
to set the phono preamp for Moving Coil or Moving Magnet type
cartridges. Moving Magnet are more common, so that is where I'd try
setting the switch first. Just below that is the ground screw where you
can attach your turntable's ground wire. The lowest item of the 3 is
the phono capacitance switch, which I would leave in the center position
for now.

I suggest moving both of the switches back and forth a few times to
clean up their contacts, as that could be your entire problem. Try the
MM position first. The MC position will give more gain, but overload
more easily. As for the phono capacitance, I'm not sure what setting to
suggest, as it depends on your cartridge, so try the middle first, and
see how it sounds. You won't hurt anything by trying the other
positions for a sound you like.

The phono stage in this receiver does not use a common op amp, it uses
discrete (separate) transistors, and uses an FET input differential
pair. I'd agree with the other posters that if both channels have the
same problem, then the power supply could be the cause too.

Lastly, there are 3 other switches on the rear of your receiver and I'd
suggest you set the as follows (for normal stereo use):

Bridging: Off

Soft Clipping: On

Speaker Impedance: Normal


Regards,
Tim Schwartz
Bristol Electronics

 

Thanks Tim
I switched to MM and cut the sound down by half or more.
I have confirmed that the sound is only on the left channel, and I
would descibe it not so much as hum as the sound of wind blowing on a
vocal microphone. Anyway........
The other settings you recommended have no real effect, but I have
them where you suggested.

Where from here?

Thanks again.
Gene









On Mon, 02 Feb 2009 12:01:20 GMT, Tim Schwartz <timhhk@verizon.net>
wrote:

nukemedtc99m@yahoo.com wrote:
Hi
I'm not a tech in any way, but before I take this for repair, I want
to make sure it's not a simple connection/hookup issue.

I got this and a Technics turntable on Ebay, and I'm very happy with
them so far. The receiver is hooked up, radio works great, audio from
DVD/TV works great.

When I select Listen/Phono, I get a loud rumble through the speakers,
whether the TT is on or not, and whether it is plugged into the back
of the REC or not.

The noise goes up and down when the volume is turned.

The TT does work and play records, but the rumbling is underneath.

Also, the ( I assume) ground lead from the back of the TT, where does
that get connected?

Good morning,

On the back of your NAD 7150 to the left of the phono input jacks are 3
items that require your attention. On top is a switch marked "MC MM"
to set the phono preamp for Moving Coil or Moving Magnet type
cartridges. Moving Magnet are more common, so that is where I'd try
setting the switch first. Just below that is the ground screw where you
can attach your turntable's ground wire. The lowest item of the 3 is
the phono capacitance switch, which I would leave in the center position
for now.

I suggest moving both of the switches back and forth a few times to
clean up their contacts, as that could be your entire problem. Try the
MM position first. The MC position will give more gain, but overload
more easily. As for the phono capacitance, I'm not sure what setting to
suggest, as it depends on your cartridge, so try the middle first, and
see how it sounds. You won't hurt anything by trying the other
positions for a sound you like.

The phono stage in this receiver does not use a common op amp, it uses
discrete (separate) transistors, and uses an FET input differential
pair. I'd agree with the other posters that if both channels have the
same problem, then the power supply could be the cause too.

Lastly, there are 3 other switches on the rear of your receiver and I'd
suggest you set the as follows (for normal stereo use):

Bridging: Off

Soft Clipping: On

Speaker Impedance: Normal


Regards,
Tim Schwartz
Bristol Electronics

 

Whoops, make that the right channel, I replugged the spkr wires bkwds



On Tue, 03 Feb 2009 15:45:27 -0500, nukemedtc99m@yahoo.com wrote:

Thanks Tim
I switched to MM and cut the sound down by half or more.
I have confirmed that the sound is only on the left channel, and I
would descibe it not so much as hum as the sound of wind blowing on a
vocal microphone. Anyway........
The other settings you recommended have no real effect, but I have
them where you suggested.

Where from here?

Thanks again.
Gene









On Mon, 02 Feb 2009 12:01:20 GMT, Tim Schwartz <timhhk@verizon.net
wrote:

nukemedtc99m@yahoo.com wrote:
Hi
I'm not a tech in any way, but before I take this for repair, I want
to make sure it's not a simple connection/hookup issue.

I got this and a Technics turntable on Ebay, and I'm very happy with
them so far. The receiver is hooked up, radio works great, audio from
DVD/TV works great.

When I select Listen/Phono, I get a loud rumble through the speakers,
whether the TT is on or not, and whether it is plugged into the back
of the REC or not.

The noise goes up and down when the volume is turned.

The TT does work and play records, but the rumbling is underneath.

Also, the ( I assume) ground lead from the back of the TT, where does
that get connected?

Good morning,

On the back of your NAD 7150 to the left of the phono input jacks are 3
items that require your attention. On top is a switch marked "MC MM"
to set the phono preamp for Moving Coil or Moving Magnet type
cartridges. Moving Magnet are more common, so that is where I'd try
setting the switch first. Just below that is the ground screw where you
can attach your turntable's ground wire. The lowest item of the 3 is
the phono capacitance switch, which I would leave in the center position
for now.

I suggest moving both of the switches back and forth a few times to
clean up their contacts, as that could be your entire problem. Try the
MM position first. The MC position will give more gain, but overload
more easily. As for the phono capacitance, I'm not sure what setting to
suggest, as it depends on your cartridge, so try the middle first, and
see how it sounds. You won't hurt anything by trying the other
positions for a sound you like.

The phono stage in this receiver does not use a common op amp, it uses
discrete (separate) transistors, and uses an FET input differential
pair. I'd agree with the other posters that if both channels have the
same problem, then the power supply could be the cause too.

Lastly, there are 3 other switches on the rear of your receiver and I'd
suggest you set the as follows (for normal stereo use):

Bridging: Off

Soft Clipping: On

Speaker Impedance: Normal


Regards,
Tim Schwartz
Bristol Electronics

 

[Dave Platt]

When I select Listen/Phono, I get a loud rumble through the speakers,
whether the TT is on or not, and whether it is plugged into the back
of the REC or not.

I switched to MM and cut the sound down by half or more.
I have confirmed that the sound is only on the left channel, and I
would descibe it not so much as hum as the sound of wind blowing on a
vocal microphone. Anyway........

Since it occurs even if the turntable is plugged in or not, it must be
a fault in the receiver.

Since the level of the noise changes with the volume control, it's
prior to that point in the circuitry.

Since you say it occurs when you select Listen/Phono, and don't say
that it occurs in other settings of the input control, it's probably
in the part of the circuitry which is specific to the phono stage.

Since it's only in one channel, rather than in both, it's probably not
in any circuitry common to both channels (e.g. the power supply).

Since you say it's a wind-like noise and rumble rather than a hum,
it sounds like it's of a broad-band origin rather than being from
60-cycle powerline noise pickup.

Based on all of the above, I suspect that the fault may be a failed
transistor (or op-amp) in the phono preamp circuitry - the "RIAA amp"
stage. This is the low-level circuitry which boosts the phono input
signal up to "line level" voltage, and also apply the RIAA
equalization curve (which boosts the low frequencies and rolls off the
highs). It's located between (in the electrical sense, and perhaps
physically as well) the phono input jacks and the program-selector
switch.

The fact that it's a wind-like rumbling lends a bit of additional
evidence to the suspicion that it's in the RIAA stage, because this
stage boosts the lows. If it was just a white-noise source after the
RIAA stage it would sound more like a hiss than a rumble.

RIAA phono preamp stages often use op amps (ideally low-noise ones)
and/or low-noise discrete transistors (e.g. 2N4401/2N4403). The use
of low-noise parts is even more important in preamps that have a
moving-coil operating mode, since MC cartridges have low output
voltages and require more gain from the preamp (and are thus more
subject to noise problems). I suspect that one such transistor or
op-amp has gone noisy in your receiver.

I don't know what the 7150's input stage looks like, as I wasn't able
to find a schematic or manual for free download.

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[David Nebenzahl]

On 2/3/2009 2:25 PM Dave Platt spake thus:

The fact that it's a wind-like rumbling lends a bit of additional
evidence to the suspicion that it's in the RIAA stage, because this
stage boosts the lows. If it was just a white-noise source after the
RIAA stage it would sound more like a hiss than a rumble.

I had exactly this problem with a receiver years ago, and it turned out
to be a bad transistor somewhere in the preamp stages.

In my case, I was easily able to find the offending part by tapping on
the transistors, as the bad one had gone microphonic. You might try
this; turn the receiver on, turn the volume up just a little ways until
you can hear the noise (not too high, now), then tap on all the
transistors you can see in the preamp section (near the input
connectors, probably). If you hear a big "thump!" when you hit one, it
needs to be replaced.

In the case of my receiver, I was able to get a NTE replacement that was
close enough. The thing still works fine 15 years later.


--
Personally, I like Vista, but I probably won't use it. I like it
because it generates considerable business for me in consulting and
upgrades. As long as there is hardware and software out there that
doesn't work, I stay in business. Incidentally, my company motto is
"If this stuff worked, you wouldn't need me".

- lifted from sci.electronics.repair