No Sound from NAD 7240PE

[ramair02]

Simple test: just set the input selector to CD (with nothing connected to the CD jacks on the rear panel) and start turning up the volume. If no or much less buzz or hum, your power supply is ok, and your cartridge/turntable is the source.

I'm not familiar with your turntable and the lack of ground, but it sounds like a potential problem to me. The phono section of the receiver has much higher gain than the other inputs, making it more susceptible to buzz or hum. You may also have a ground loop; best way to help avoid that is to make sure the receiver and turntable are plugged into the same outlet. If the turntable has a 2-prong AC plug that is not polarized, you can try flipping that to see if you get more or less buzz one way over the other.

Another simple test: turn the input selector to something other than phono, disconnect the turntable RCAs from the back panel of the receiver (never connect or disconnect inputs while the receiver is powered on and those inputs are selected), and then set the input selector back to phono and start turning up the volume. If you hear less buzz at a given volume level that way, I'd be suspicious it is a ground problem from the cartridge.

I think you will find the 3.5mm to RCA cable a good investment. You can play internet radio into the receiver that way as well. Another way is way ChromeCast Audio if you have an android device or chromebook handy, where the stream is set up from your wifi router to the CCA; I really like this way because as once you set up the stream, you can turn your device off and the streaming continues.

Sorry for the delay.

When I set the input to CD and turn up the volume, there is no buzz or feedback. IT remains silent.

I do have the receiver and turntable plugged into the same surge protector.

I still have to run the test with the turntable disconnected. Haven't gotten to that yet.

I have a 1st gen Chromecast, but I'll definitely look into picking up the Chromecast Audio device. That seems like a great way to stream through the amp & speakers! I've always done it through th eTV soundbar, which leaves me quite longing.

 

[northpaw]

Having them in the same outlet should be good enough; but you can also try plugging the turntable into one of the receptacles on the back the 7240PE for even less chance of issue. However, it may be that you will not be able to eliminate the residual hum or buzz you are hearing without actually tying the grounds together.

On the NAD itself, don't be surprised if you have brief episodes of sound cutting out, etc. before you do the deoxit treatment. After that, it should be pretty consistent for a good while, i.e., a few years.

One other thing you should consider doing is checking and adjusting the DC offset and amplifier bias (also called centering and idle adjustment, respectively). Fortunately, the NAD permits both to be adjusted (many receivers in its price class do not). They are very simple to do, but it does require a simple digital multimeter and, for the idle ajustment, a soldering iron). Instructions for making these adjustments are given in page 5 of the service manual (called "center voltage" and "idle current" there) , and more info about DC offset is given in the first page of the sticky post by Echowars at the top of the Solid State section that this thread is in. There are a few cautions to be aware of before you tackle these, due to oxidation on the interior pots (because they have not be exercised since the factory) and the need to go in small increments, but we can cover that when you are ready to make the adjustments.

Adequate multimeters are available from Amazon and many other suppliers for $15-$25; you can use Amazon reviews or you can search here for recommendations. You will find it useful for things far beyond stereo equipment; actually, given that you build computers, etc., I'm surprised you don't already have one in your toolbox. Personally, I don't know what I would do about figuring out what state of depletion my batteries in (not only AA and AAA, but coin batteries, etc.), or checking things for continuity, etc.

 

[ramair02]

My DeOxit kit finally came in and I redid everything I had previously done with the other contact cleaner. The hum/buzz is WAY down (although still audible if I turn up the volume). I also plugged the turntable into the back of the NAD, which may have helped.

I haven't yet dived into adjusting DC offset / amplifier bias. I'll do some reading about that, get myself a multimeter and get going on that, but it may be a few months. I'm really enjoying the setup as is and am incredibly happy that it all works as well as it does!

Thanks again for everything.

 

[ramair02]

One last question about my NAD 7240PE:

On the back is a switch for either 4 ohm or 8 ohm. I'm currently running it on the 4 ohm setting with my Pioneer BS22s. Is there any reason I should switch it to 8 ohm? Or am I fine the way it's setup now?

 

[northpaw]

I don't know what kind of impedance the Pioneer's present, but you are fine and safest to leave it at 4 ohms even if they are 8 ohm speakers. As I recall, the 4 ohm setting simply lowers the voltage on the higher voltage rail as a safety factor when driven hard. So it might cut the ultimate volume a tad, but you would be hard pressed to notice.

That switch, though, should get deoxit too, if you haven't already. As a precaution, just remember to turn the unit off first before either switching it or cleaning it, as I remember someone reporting failures when they moved the switch while the unit was on. That switch is also supposed to be set to 8 ohms when any DC offset or bias adjustments are made, but then returned to 4 ohm.

 

[ramair02]

I don't know what kind of impedance the Pioneer's present, but you are fine and safest to leave it at 4 ohms even if they are 8 ohm speakers. As I recall, the 4 ohm setting simply lowers the voltage on the higher voltage rail as a safety factor when driven hard. So it might cut the ultimate volume a tad, but you would be hard pressed to notice.

That switch, though, should get deoxit too, if you haven't already. As a precaution, just remember to turn the unit off first before either switching it or cleaning it, as I remember someone reporting failures when they moved the switch while the unit was on. That switch is also supposed to be set to 8 ohms when any DC offset or bias adjustments are made, but then returned to 4 ohm.

Great info. I totally ignored this switch when using Deoxit to clean up the amp. I'll make sure I spray some Deoxit in there and work the switch back and forth. It's been screwed down in the 4 ohm position probably all of the amp's life!

The BS22's are rated at a nominal impedance / input impedance of 6 ohms. This analysis (http://www.stereophile.com/content/pioneer-sp-bs22-lr-loudspeaker-measurements#zPIr6vJDw4VBHg1r.97) states that this rating is on the conservative side, but I'm not sure how best to interpret that.

I'm happy with the performance leaving the switch on 4 ohms, as I rarely turn the volume up past a 1/4 turn (approximately 9 o'clock). So, I suppose with that being the case, there's no sense setting it to 8 ohms.

 

[ramair02]

Ok, now that the receiver is working great, I need to start addressing the buzzing sound I'm getting. It's noticeable with my speakers and much more noticeable with headphones on. The buzz increases steadily as I increase the volume. Do I need to adjust DC offset and amplifier bias? Or are there other things I can try first?

 

[northpaw]

DC offset and amp bias should be checked and adjusted, if needed, to get the best sound from your system, but is unlikely to be the source of the hum issue.

Since you don't have the hum on other inputs, the amp itself seems fine. It could be something in the phono preamp circuit, or an issue with how the TT grounds.

Did you fully clean up the oxidation on the phono jacks and any affected internal connections/wiring? No more green? You might need to do a more aggressive job there, as it appears your TT grounds through the shields on one of the RCA jacks (see a post on page 2 of this thread: https://www.vinylengine.com/turntable_forum/viewtopic.php?t=81330).

If you search for your TT model and "hum", you will see quite a few have the same issue. No clear resolution I saw, but my suspicion is that the TT is not being effectively grounded at present. That may be a fault of the connections, or with the TT itself. I would suggest that you try to verify you are grounding through the shield on one of the RCA jacks, as suggested in the thread above. An additional cross check on just the phono preamp in the receiver is to connect a different TT to it (one that has a ground wire) and see if the problem persists; take your unit to a friend's system with a TT if you have to.

 

[Drum]

Firstly, get a copy of the service manual from hifiengine. You need to register (to prevent robot attacks) it is safe
No mention of your skill level and tools available.
Do you have a digital multimeter?
Are you comfortable taking voltage measurements with the amp "live"/powered up?


The amp has joining links at the rear that allow you to separate it into the preamp stage and the power stage.
This allows you to use other pre and power stages. Do you have other equipment with similiar links or a
seperate pre or power amp. By running tests you can isolate the problem as being in pre or power stage.

Many reasons for no sound. Since both channels are affected the power supply would be a good starting point.
As a guess I would say the power supply to the preamp is down. Can you measure the dc voltage at R311 and 312
as shown in the pic, either leg is fine

You should also visually check for any leaking capacitors, NAD has bad history in this area.

View attachment 865914

I have a similar problem with my 7240. I get very low volume. The amp section puts out much more volume if I use a different preamp so it must be the pre-amp. I measured the voltage at R311 and R312 and it is 1.5 volts at each across the resistor. It is 7.5 volts between the two. Are these what they should be?

Thanks in advance.

 

[Drum]

Just checked the voltage at R311 and R312 on my other 7240 and it is at nearly 5 volts, so it seems like that may be the problem. Does this mean that the small transformer for the pre-amp side is bad, or is there some other possible check. What about the yellow and blue wires that actually go over to the pre-amp side - what voltage should those be at?

Even though the two are the same model the layout inside is somewhat different.

 

[mbz]

R311, 312 carry the +/- power supply to the OPAMP (NJM2043) a critical
component in the preamp. Measure the voltage at R311 red probe with
black probe connected to the chassis. Repeat for R312. Expect about
+/-14V as per the service manual. A significantly lower voltage indicates
a problem with the power supply. If the voltages are about OK then follow
the deoxit treatment mentioned above.

 

[Drum]

I got 20V on one side of 312 and 18V on the other side. For 311 I got 1V and 2.5V.

So it seems like one is too high and one too low.

My working 7240 shows 20V and 15V for both 311 and 312.

Also I had to connect the red probe to the chassis to get a positive reading on my multimeter for both 311 and 312. On my working 7240 one was positive and one was negative.

Thanks.

 

[mbz]

R312 carries the negative supply, R311 the positive.
The positive supply is down so the OPAMP is not
working correctly, this will affect the sound.

Fix the positive supply and the opamp will work
and draw the required current, R312 voltages will
drop.

Pic of power supply attached. The likely candidate
is Q501, you should test and replace (KSC1815 or
KSC1845??) if necessary. Try to confirm that there
is about 28Vdc at R507/Q501 collector. You should
also measure the resistance of R507(68), R511(1k)
and R505(1k). In circuit will be close enough. You
should also inspect caps C513,4,5,6,7,8. NAD were
notorious for using budget caps and then pushing
them to the limits.

 

[SoCal Sam]

NAD gear has switches on the back panel. Not sure with your receiver but the switches usually are for Bridging and Soft Clipping. Clean both of them thoroughly.

 

[Drum]

There is 28V at R507/Q501
R507 infinity Might be 0 - the labeling isn't clear I could be measuring 510
R505 800 ohm
R511 800 ohm

Caps in question are not bulging or leaking.

Thanks

 

[Drum]

NAD gear has switches on the back panel. Not sure with your receiver but the switches usually are for Bridging and Soft Clipping. Clean both of them thoroughly.

Just cleaned that - no difference.

Also took some measurements of output. I can get 64db at 1 meter at full volume. If I depress the bass eq button I can get 70 db. Loudness button does nothing. Volume seems normal if I use my other 7240 as the pre-amp.

 

[mbz]

With correct 28V at Q501 collector and Q501 emmitter only showing 2.5V I would have
to say that Q501 is suspect faulty. You can probably test with the diode function on
your multimeter, red probe on base, black probe on emitter, should read about 700mV.
Regardless of the result, I've seen enough to say replace the transistor, use KSC1815
(preferred) or KSC1845 from a relioable source.

 

[Drum]

Thanks mbz. I will pick up the transistor and replace it. I'll let you know how it turns out. May take a week or more - nothing like that available in town.

 

[Drum]

Well - the transistor/s arrived and I installed one. The good news is I didn't destroy the receiver, but the bad news is that it didn't fix the problem. I supposed I need to redo my tests to make sure I got everything right. I also need to test the new transistor - unfortunately did not test it before I put it in.

I did fiddle with the receiver a little more and found that it takes about 15-20 seconds to get some sound when turned on, and sometimes it keeps playing for about 10 seconds after it is turned off. As it is warming up the sound is crackly and extremely low and gradually builds volume - though never getting very loud. After about a minute it seems to be stabilized.

I checked all speaker outputs and they are all the same. I double checked the volume / balance and they are extremely smooth without a hint of crackling. Everything works as it should just low volume and then the loudness does nothing and the BassEQ increases the volume by about 10 db

I retested the output and now I can get about 70 db and about 82 db (with Bass EQ engaged) at max volume Not sure if that is because it has been on for a few hours warming up or I made an improvement. Also possible I used A weighting instead of C the first time I measured the volume. Either way 80 db max is not great (speakers are fine and play loudly with other amps). I will retest it as a power amp just to see how it acts when it is turned on.

 

[Drum]

Reset the receiver up as an amp - my other 7240 was the pre-amp. Now the sound is normal and comes on instantly when I turn on the broken receiver. I did time it for how long it plays after I turn it off. 15 seconds. Maybe this is just what the older NAD's did as there is clearly an age difference between the two units.