No bass sound

[Dave 47]

My NAD 3130 has developed a fault where there is no bass, (extreme treble). My speakers are the Bose acoustimass 5 and only getting sound from the tweeters. I initially thought that I had speaker problems but found this not to be the case after trying a different amp. Anyone experienced this problem that can suggest the cause?
Thanks

 

[Mooly]

Welcome to diyAudio

Two technical causes come to mind.

1/ If both channels are affected then this sounds like an 'open circuit' in the signal path whereby coupling of the signal occurs capacitively across the break.

Does the amp have preout and power in links on the rear panel that are missing???

If it doesn't have those then cracked PCB print is a possibility. Even having the wrong input selected can also give this symptom.

2/ The only components that can fail and give 'no bass' are capacitors (usually electrolytic types), however if both channels are affected then its not going to be this.

 

[JonSnell Electronic]

Both channels the same?

 

[Dave 47]

Yes, both channels are the same

 

[Dave 47]

Welcome to diyAudio

Two technical causes come to mind.

1/ If both channels are affected then this sounds like an 'open circuit' in the signal path whereby coupling of the signal occurs capacitively across the break.

Does the amp have preout and power in links on the rear panel that are missing???

If it doesn't have those then cracked PCB print is a possibility. Even having the wrong input selected can also give this symptom.

2/ The only components that can fail and give 'no bass' are capacitors (usually electrolytic types), however if both channels are affected then its not going to be this.

Both links are in place

 

[Mooly]

So your fault symptoms are pointing toward a break in the print somewhere. Bits that stick out (controls and switches) are favourite damage points.

Has this amp worked OK in the past or has it an unknown history such as E Bay.

This type of fault takes minutes to trace with a scope and signal generator or signal source such as a test CD or MP3 test tone file.

 

[Mark Tillotson]

Another possibility is the dual opamp in the preamp section might have lost one/both of its power rails - this would affect both channels and permit degraded signals to pass through the feedback networks, possibly accounting for bass attenuation.


Are the phono inputs working? - they would be affected by the same power supply rails I think.


NAD 3130 Service Manual (Page 12 of 20)

 

[Dave 47]

So your fault symptoms are pointing toward a break in the print somewhere. Bits that stick out (controls and switches) are favourite damage points.

Has this amp worked OK in the past or has it an unknown history such as E Bay.

This type of fault takes minutes to trace with a scope and signal generator or signal source such as a test CD or MP3 test tone file.

As it happens, I had considered attaching a pre-amp, if it solves the problem then this would tell me that the problem is pre-amp related but if the problem persists I could try attaching a power amp.

I did purchase from EBay, sold as faulty. I currently learning about electronics and purchased this amp as a means to give me practical experience to help me along, but I got stuck

 

[Mooly]

Fair enough

As you are learning I'm going to suggest that you first take the precaution of not connecting the amp directly to your speakers but that you either add a lowish value value series resistor to each speaker feed (say 47 ohm 0.5 watt, anything in that region really its not critical) as that will stop anything speaker/amp destructive happening if you happen to connect a full level signal directly to the power amp inputs.

The resistor might burn if you did do something like that, but that is better than the amp or speaker going pop.

The other you will se mentioned all the time is to use a DBT (dim bulb tester) which is just a mains filament bulb in series with the mains supply to the amp. The bulb will limit current in the event that something goes wrong and this can prevent major damage.

Back to your fault and yes, feeding a suitable input directly into the power amp input is a way to split the fault between pre and power sections. All you need is a volume control and a line source.

If the fault is on both channels then you can initially just concentrate on one channel... much easier.

Have a good look at the way the switches and pots are mounted on the front panel and look for damage where those parts solder to the boards.

 

[Dave 47]

Thanks for that Mooly

 

[Douglas Blake]

Sorry for the side trip... but this reminds me of a prank we played on a friend years ago...

We took the knobs off his tone controls, turned the treble all the way up and the bass all the way down then put the knobs back on in centre position. Took him about 3 days to figure out what was wrong...

... might be worth checking.

 

[korpberget]

Oh thats just evil!!

 

[Dave 47]

Sorry for the side trip... but this reminds me of a prank we played on a friend years ago...

We took the knobs off his tone controls, turned the treble all the way up and the bass all the way down then put the knobs back on in centre position. Took him about 3 days to figure out what was wrong...

... might be worth checking.

Suppose this could happen but not in this case Having a look at your link though, could be useful...thanks

 

[Douglas Blake]

Suppose this could happen but not in this case Having a look at your link though, could be useful...thanks

Have you checked for bad/cold solder joints in the area of the tone controls?
That could also cause this.

 

[Dave 47]

Have you checked for bad/cold solder joints in the area of the tone controls?
That could also cause this.

No, but I will be... thanks

 

[Mooly]

So I've finally looked at the circuit diagram and see it uses JFET series muting in the preamp output. I have an idea.

Can you measure the DC voltage on D503 anode (the end without the stripe) and report what you get.

You can also try shorting out Drain and Source of either of the FET's and see if the audio then appears normally.

Remember to have the volume turned right down first.

Edit...

Remember to have the volume turned right down first.

Actually the volume control is before the FET's and so that advice is no good. If you short the FET's as a test then do it with the amp OFF and only then power up and test. Remember not to have the speaker wired directly... use a series resistor.

 

[UserAbuser]

Um. Why has nobody suggested the obvious ?
The bose acoustimass 5 consists of a sub and two satellites.
Who says the sub itself isn't faulty ?

And while I'm at it.
Which version is this ?
1, 2, 3, Passive, or Powered ?

I'd rather think the sub has failed in some way rather than two different amplifiers.

Edit.
Did you say the fault was still there with the second amp ?

 

[Dave 47]

Um. Why has nobody suggested the obvious ?
The bose acoustimass 5 consists of a sub and two satellites.
Who says the sub itself isn't faulty ?

And while I'm at it.
Which version is this ?
1, 2, 3, Passive, or Powered ?

I'd rather think the sub has failed in some way rather than two different amplifiers.

Edit.
Did you say the fault was still there with the second amp ?

Just to clarify. My original existing amp used with the acoustimass speaker system has no fault whatsoever.

The second amp, the one in question I purchased knowing it had a fault and when hooked up, there was no bass. I then reinstated my original amp and the bass works as normal. I deduced from this that the problem was with the amp and not the speakers.

Hope that clears up any confusion.

 

[Dave 47]

So I've finally looked at the circuit diagram and see it uses JFET series muting in the preamp output. I have an idea.

Can you measure the DC voltage on D503 anode (the end without the stripe) and report what you get.

You can also try shorting out Drain and Source of either of the FET's and see if the audio then appears normally.

Remember to have the volume turned right down first.

Edit...



Actually the volume control is before the FET's and so that advice is no good. If you short the FET's as a test then do it with the amp OFF and only then power up and test. Remember not to have the speaker wired directly... use a series resistor.

Thanks for taking the time to helping me out here, it's appreciated.

Though I have learnt quite a bit on this subject recently, I've yet to get to the stage of shorting a FET, so understably I don't want to get ahead of myself.

I intend hooking up a separate preamplifier and will let you know the results that this produces. Then I need to learn more about what you suggested.

 

[Mooly]

Though I have learnt quite a bit on this subject recently, I've yet to get to the stage of shorting a FET, so understably I don't want to get ahead of myself.

My line of thought was this...

The FET is used as a simple on/off device in this application, a bit like a relay, and its function is to be 'open' circuit or more technically for a FET we say 'pinched off' meaning it is non conductive between Drain and Source.

In that off state is is used as a mute which prevents switch on and switch off thumps and noises from the preamp from passing to the power amp input, however in the off state it would also couple capacitively a tiny bit between the pins and the print which would possibly give your symptom. It's a bit like the signal jumping the gap but only the higher frequencies stand a chance of doing that.

We can easily prove/disprove the theory by simply shorting the appropriate pins together (D and S) thus linking this FET switch out.

If by chance it were related to this then the fault could actually be the mains switch, which sounds strange but it has a third contact for muting... but we would look at that depending on what you found.

Without actually hearing your fault we can only generalise, and this line of thinking of an 'open' condition somewhere would be like listening to a typical good and working amplifer fed with a loud CD disc for example, but you then turn the input selector to something else (such as tuner) and you then turn the volume and treble full up. That faint residual tinny audio you then might hear is how I'm interpreting your description of the fault.