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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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NAD 7150 Stereo Receiver/Amp Noise when Listen knob set to phono.
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? |
#2
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NAD 7150 Stereo Receiver/Amp Noise when Listen knob set to phono.
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. |
#3
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NAD 7150 Stereo Receiver/Amp Noise when Listen knob set to phono.
wrote in message ... 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 |
#4
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NAD 7150 Stereo Receiver/Amp Noise when Listen knob set to phono.
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" wrote: wrote in message .. . 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 |
#5
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NAD 7150 Stereo Receiver/Amp Noise when Listen knob set to phono.
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#6
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NAD 7150 Stereo Receiver/Amp Noise when Listen knob set to phono.
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 wrote: 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 |
#7
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NAD 7150 Stereo Receiver/Amp Noise when Listen knob set to phono.
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#8
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NAD 7150 Stereo Receiver/Amp Noise when Listen knob set to phono.
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 |
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