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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 18th Dec 2016, 2:42 pm   #61
paulsherwin
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Default Re: NAD 7020 weak channel on FM stereo

That switch was a bit of a NAD gimmick in the early 80s. The only real benefit is that you can use a wider range of the volume control at normal listening volumes. My NAD 3030 amp (bought in 1979) had one.
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Old 18th Dec 2016, 4:14 pm   #62
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Default Re: NAD 7020 weak channel on FM stereo

One more thing to consider - NAD amps of this era tended to pick up all sorts of electrical and RF interference. My 3030 could pick up SW broadcasts on the phono input at night, and it produced a very intrusive electrical click whenever the fridge thermostat switched. The RFI sensitivity was one of the main reasons I stopped using it.

It would be worth checking that this noise isn't coming from a nearby piece of digital equipment.
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Old 18th Dec 2016, 4:45 pm   #63
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Default Re: NAD 7020 weak channel on FM stereo

Thanks for your further thoughts Paul. The strange thing about that Low Level switch is that it does completely remove the oscillation/put-put noise, on all inputs, even when the volume pot is turned to max. So, in a strange way, I have a fix already, but I'm puzzled by the normal operation.

Goldie, I'll keep you posted too. I have a NAD 3120 which was professsionally restored about 10 years ago. I gave it to a family member, but it's just come back to me as 'needing attention'. I thought I'd get my bearings on this 7020 first.
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Old 23rd Dec 2016, 7:33 pm   #64
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Default Re: NAD 7020 weak channel on FM stereo

I'm glad to report a happy ending. After replacing all the electrolytic capacitors, checking many solder connections to components and wiring, and replacing the chassis base and cover, I have a quiet amplifier. All the capacitors measured okay, except for the one I had to replace to get the FM stereo working. Many were a bit high though.

I conclude that the oscillation was caused by a marginal capacitor or solder joint...

Here's a pic of most of the capacitors that I replaced.

Thanks to all who gave advice with this, especially Paul Sherwin and Radio Wrangler.
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Old 23rd Dec 2016, 7:49 pm   #65
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Default Re: NAD 7020 weak channel on FM stereo

Good result.

NAD build quality was very variable at this time. They were having the amps contract built in Taiwan and some examples are real shockers. They do sound nice when sorted out though.
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Old 27th Dec 2016, 11:41 pm   #66
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Default Re: NAD 7020 weak channel on FM stereo

Reviewing the information I assembled before working on the 7020, I found some enthusiastic references to replacing the diodes in the power supply. Users report sonic benefits from replacing the bridge diode (KBL02) beside the four power supply caps in the unregulated power supply with four 8A FRED soft recovery diodes, and also from replacing the 22V 500MW zener diode in the regulated power supply with such diodes. These are BD801 and ZD801 on the circuit diagram.

I know the view on this board is, don't fix it if it ain't broken, but I'd be interested to hear any views on replacing older diodes with such newer types.
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Old 27th Dec 2016, 11:45 pm   #67
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Default Re: NAD 7020 weak channel on FM stereo

I would be astonished if this made a measurable (as opposed to a subjective) difference to anything. It's a simple and cheap mod if you feel like trying it though.

There are all sorts of dubious hifi 'mods' and 'upgrades' on forums. This is basically just technogossip.
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Old 30th Dec 2016, 11:52 am   #68
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Default Re: NAD 7020 weak channel on FM stereo

Thanks Paul. Excellent bit of perspective! Technogossip is fun, but just that.
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Old 1st Jan 2017, 7:22 pm   #69
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Default Re: NAD 7020 weak channel on FM stereo

I bought a NAD 7020e from new. I subsequently got an 80's Japanese class A amp from freecycle (said to be faulty but turned out to be missing the pre-amp links) which showed up just how muddy the bass was and how badly the frequency response was manipulated with both treble and bass boost. It served me well but was not exactly state of the art.
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Old 5th Jan 2017, 11:37 am   #70
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Default Re: NAD 7020 weak channel on FM stereo

I think the 7020e circuit may be different from the original 7020, as well as having a different tuner. I had an 7020e for a while in early 2014 and gave it away because it sounded very flat and dull. I've not had time to compare the two circuits, but this does not sound the same, when listened to via the same pair of Sennheiser HD414 headphones.

My subjective evidence for the sonic difference is that I don't want to give this one away yet! This is not to claim sonic genius for it though. I suspect such amplifier circuits were voiced to be used to small bookshelf speakers such as the popular Wharfedale Diamonds of that era.
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Old 5th Jan 2017, 11:45 am   #71
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Default Re: NAD 7020 weak channel on FM stereo

The original analogue 4020 tuner is certainly very good - it's the best sounding of all my tuners, and particularly impressive on female speech sibilance.
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Old 16th Jan 2017, 11:59 pm   #72
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Default Re: NAD 7020 weak channel on FM stereo

A quick update on the oscillation sound. I discovered by chance that it only occurs when the receiver is plugged into a multiple socket which is also supplying other parts of the hifi system, e.g. a CD player. The volume of the oscillation increases as more components are plugged in, even if all of them are switched off. When the receiver is plugged into the socket on its own, there is no put-put noise at all.
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