Hi-Fi problem.

[CAMRAMan]

Having dug out my ancient hi-fi system, I'm having a problem getting it to play in stereo.


NAD 3020 amp.
Sherwood CD player
Wharfdale speakers


When I play a CD the RH channel comes through fine, but nothing comes out of the LH channel. If I press the mono button, both speakers play. Moving the balance button to and fro in mono makes the requisite difference in volume on either side.


Any ideas what's up?

[PaulF]

Can you try a different cable? Or reverse the cable so that the L output of the CD player goes to the R input of the amp.

That should help identify which component if faulty.

[Diver300]

It could be
1) The LH output of the CD player
2) The LH parts of the cable
3) The LH input of the amplifier

I think that the amplifier has phono input, and swapping left and right should therefore be easy. If the problem swaps sides, you've eliminated 3). If the problem stays on the left, then you've narrowed it down to 3)

PaulF's suggestions are good.

You could also try a different input on the amplifier. "Phono", "CD/Aux" and "Tuner" are just names so that one pair of inputs on the back of the amplifier is used when the button with the same name on the front is pressed.

From what I can tell, the amplified has main amplifier input sockets. I'm not sure how the main amplifier input is switched from running from those sockets of from the preamplifier. If there is a switch, that could have become unreliable during storage.

[The_Mikey]

Also be mindful of dirty relays, if the tape loop function has been activated (assuming it has a tape loop) then the switch or relay associated with that could be dirty and causing a loss of audio.  Some amp's have jumper cables across tape loops, if one is missing this might result in a dead channel until a bypassing jumper is reinstalled. 

[Feanor]

From what I can tell, the amplified has main amplifier input sockets. I'm not sure how the main amplifier input is switched from running from those sockets of from the preamplifier. If there is a switch, that could have become unreliable during storage.

On the ones I've dealt with, theres no switch.
The preamp outs are on a pair of RCA phono jacks mounted next the power amp in jacks.
There's a pair of U-shaped links that jumper them.

<peers at schematic>

The mono switch is early in the pre-amp stage: There are no active components prior to this switch on any of the line inputs ( just the phono preamp stage for the phono input ).
For all the line level inputs, all there is prior to the Mono switch are the input sockets and the input selector switch.
The signal daisy-chains it's way through each switch stage in this order:
Phono, tuner, aux/cd, tape Play.

If you determine that there is indeed signal present at both inputs by reversing the L/R inputs, and the fault is in the amp, then there's not much it can be.

It seems likely to be dirty switch contacts.
Try using the tape Play input, as it avoids the switch contacts.

Switch inputs back and forth repeatedly to try to clean the contacts.

[Diver300]

The schematic that I've found shows the phono input as going through the equaliser, while the other inputs are equivalent.

I agree that there's little between the inputs and the stereo/mono switch, so the connection to the main amplifier must be OK.

There are quite a few contacts in the selector switch.

[pcolbeck]

Do not use the phone input with the CD player. You can use any of the others as they are all exactly the same just with different labels for convenience of identifying what's plugged in. The phono input on the other hand expects a much lower level signal than the others and runs it through an extra pre amp that both boosts it and compensates for a record players riaa compression before feeding it to the standard amplifier section.,

[CAMRAMan]

Thanks all. I'll give those ideas a shot in the morning.

[CAMRAMan]

Right; one problem solved - I think - another's arisen.

I hooked up my 1982-vintage Dual CS-505 and it played stereo through both channels. Not the amp, then. On examining the CD player leads, the central male pin on one channel has no metal, just plastic. Replacement ordered.

Now, is the varying speed on the Dual a belt problem, or the motor objecting to not being used since the summer of 2000? Only a new belt will answer that one...

[robgul]

Right; one problem solved - I think - another's arisen.

I hooked up my 1982-vintage Dual CS-505 and it played stereo through both channels. Not the amp, then. On examining the CD player leads, the central male pin on one channel has no metal, just plastic. Replacement ordered.

Now, is the varying speed on the Dual a belt problem, or the motor objecting to not being used since the summer of 2000? Only a new belt will answer that one...

I have visions of a small dog sitting beside a horn on your record player!

[CAMRAMan]

Oi! I said 1982, not 1892! 😀

[tiermat]

I'd be tempted to try cleaning the belt and wheels with IPA (not the craft beer type) as there will be a good chance that both have got shiny/dirty in storage.

Or buy a direct drive deck.

[aidan.f]

Add gun or sewing machine oil for the bearings.

[pcolbeck]

Add gun or sewing machine oil for the bearings.

Hypoid gear oil was what a few turntable manufacturers used to recommend. I have just purchased a bottle of Comma EP80W-90 Gear Oil for a couple of turntables on my "sort em out" shelf.

[Feanor]

Right; one problem solved - I think - another's arisen.

I hooked up my 1982-vintage Dual CS-505 and it played stereo through both channels. Not the amp, then. On examining the CD player leads, the central male pin on one channel has no metal, just plastic. Replacement ordered.

Now, is the varying speed on the Dual a belt problem, or the motor objecting to not being used since the summer of 2000? Only a new belt will answer that one...

If the speed is varying, it's almost certainly the belt has perished and lost it's sproing after sitting for so long.
If you remove the belt, it will probably not spring back like a happy rubber band; it will sit there in the shape is has taken up, like saggy old knicker elastic.
Basically, after it's lost it's elasticity, there's not enough belt tension to transmit the drive.

The motor itself is synchronous, so it can't really go at the wrong speed.
The only electronic parts IIRC were a capacitor and resistor to provide a phase-shifted supply for a second winding.
If the motor starts and runs, these are fine.

Bearings can get a bit rumbly, but not to the point it's varying the speed.
It will manifest as rumble in the audio.

So yes, replace the Main Drive belt, I'd say.

(And whilst you are at it, replace the Pitch Control belt too; they are quite brittle and it may well have disintegrated too. Not that it is critical to the turntable's operation, it just means the pitch control knob doesn't do anything any more.)

A couple of tutorial videos..
https://www.youtube.com/watch?v=qMyGKXlJL4E
https://www.youtube.com/watch?v=tlEHLvlQ3Uw

Incidentally, if anyone's curious as to how you do pitch control on a synchronous motor (It does not have Variable Frequency Drive! )...
It's mechanical; a Continuously Variable Transmission.
If you look at either of the videos I linked to above, look at where the main drive belt goes round the motor pulley.
Notice a couple of things about the motor pulley:

- It is stepped, this is the 33-1/3 vs 45 rpm adjustment. A derailleur arm guides the belt up and down between these.

- It has vertical slots cut in it: it is 'segmented'. It is expandable! There is a conical wedge do-hicky on the motor spindle which can be pushed up and down, expanding or contracting the pulley diameter by a small amount.  It's not visible on the video, but the pitch control pulley on the motor assembly is raising and lowering this conical wedge.

[CAMRAMan]

Thanks for that, Feanor; great advice. I'm still waiting for the new drive belt, but I did have trouble adjusting the speed years ago.

[CAMRAMan]

So, an update:

The CD/stereo issue turned out to be the NAD inputs. Once I put the CD through the Tuner input, stereo was restored. Job done on that front.

The Dual issue is yet to be resolved. I've got a new belt to put on it, but in the meantime, I bought a new turntable and that works fine. I'm not sure what I'll do with the Dual yet.

Thanks for all the tips and advice.

[Feanor]

The CD/stereo issue turned out to be the NAD inputs. Once I put the CD through the Tuner input, stereo was restored. Job done on that front.

Oddly enough, that input is the one that has to go through the most contacts on the input selector switch!
I expect half a can of servisol and a bit of vigorous switching might fix the Aux/CD input.

The Dual issue is yet to be resolved. I've got a new belt to put on it, but in the meantime, I bought a new turntable and that works fine. I'm not sure what I'll do with the Dual yet.

Just fix it because it's the Right Thing to Do, obv....

[CAMRAMan]

Yebbut, I'm afraid it'll sound better than the new one...

[pcolbeck]

Yebbut, I'm afraid it'll sound better than the new one...

Probably will unless you spent quite a bit on a new one. The Dual 505 was a pretty good turntable, budget in it its day (compared to a Linn Sondek) but the proper HiFi end of budget.

[Mr Larrington]

Standard package for discerning Penniless Student Oaves in the 1980s was Dual CS-505/NAD 3020/Mission 700s

[Thor]

I thought I was high-end cos I had a CS505 deluxe, a NAD 3130 and Mordaunt Short 25tis.

[CAMRAMan]

I couldn't justify a Sonndek, but I still hanker after a Rega Planar 3. I've just not got the space to situate it correctly.

[nicknack]

You don't want any of this belt drive rubbish. My direct drive Dual 604 that's 40 odd years old is still going strong. 

[rafletcher]

I had a Sansui SR222, NAD 3020 and some flavour of Wharfedale speakers, later replaced with Mission 700’s.