"Just needs a squirt of switch cleaner, one of the volume controls doesn't work"
Sadly not.... and I can see marks on the PCB where someone had been liberally spraying the stuff at the poor innocent volume control!
What happens is the joints break up between the volume pots and the PCB... leading to an intermittent or non-existent connection.
A quick solder up of these joints provides a long lasting repair.... if only it was a quick job. Most amplifiers of this design require a considerable amount of disassembly to get to the joints. Joints to and from the phono connectors on back panels present a similar problem.
Just to show you how long this sort of thing takes, here's a time-lapse video I made (and I wanted an excuse to try some sort of overhead camera thing!). This repair took an hour!
... still better than a "soundbar" or other hideous self contained speaker.
Been there... Whe working at the college I repaired one for the HOD, it came back the following day, in this instance it was a blown output stage. After the third time I insisted on visiting his house. The fault was soon found, on the insistance of the "other half" the decent speaker wires were replaced with bell wire which was "NEATLY" stapled to the skirting board and painted white. The staples making a perfect S/C evry 300mm or so. Brilliant!!! I never did like the sound of NAD amplifiers, too laid back and lacking detail. And that started with the dreaded NAD320.
ReplyDeleteI repaired one of these today and the issue was indeed broken solder connections on one of the volume pots. It's a long double shaft (left inside the right) and any lateral force applied to the volume knobs while adjusting places a lot more force than a short shafted pot would on the solid soldered pot to main board connections. Factory soldering is pretty thin, so resoldering with a generous hand makes nice strong repairs that will last long, as Doz states. Hopefully at least another 25 years, in this case. My patient had some liquid ingress and the cleanup took more than half of the 3 hours to complete the repair which included testing all signal switching paths, tone sweep, output power and signal balance checks and bias adjustment. I hooked the unit up to my "go to" pair of Arcam Delta 2s and I was impressed with the soundstaging and bass control of this FET equipped NAD, vs the earlier 3020i of my wife's, which uses older and slower 2N3055 transistors for the output and lacked solid bass with tight control. It comes close to my FET based Arcam Alpha 6+ amp from the same era, which set me back GBP600 in '96 vs the 310's launch price of GBP100 in '95. The frequency response is really impressive for an amp in this price range. At 20Hz, everything in my workshop was shaking like an old Vauxhall with extra batteries and two oversized subs with the EQ set to +12dB; and with the volume set high enough, even my semi deaf ears could make out the lower frequency portions at the 20kHz tone test limit. A great amp if you have one or can pick one up for a bargain. Thanks for the helpful blog article Doz, you have saved both my client and I extra time and cash!
ReplyDeleteI bought one of these in February of this year (2020). It was an ebay "special". Supposedly one channel was low power. This chassis was in poor health needless to say. Power caps and output coupling caps were incorrect form factor, wrong size and lower working voltage than spec. I replaced these caps plus all the original WENDELL caps with nichicon 105C. Replaced the bias trim pots with sealed multi turn pots. Also the reason one channel was low power was due to the crimping (not soldered) secondary leads from the transformer to posts of the power supply. These are now soldered. Lastly the volume control: this was broken inside the pot at the right channel terminal. I had to add a conductive adhesive to bridge the fracture and now works. Probably stress on the face-plate connection to the control can either weaken the solder connection and/or the actual pot (as in my case). Overall, I'm quite pleased with the performance of this little 20W chassis.
ReplyDeleteExcellent work Joe... another saved from landfill !
DeleteIt is quite a beast for only a 20W amplifier. I see a review criticism that it's "lacking in bass" which I somewhat understand - though if they were listening to secondhand devices it's likely the primary or secondary filter caps were toast. It's a fairly neutral sounding amp compared to the bombast many prefer and lacks a "loudness" button and has a touch of stereo widening built in. But... When the music contains bass - secure your finest china - it'll be rattled loose of those shelves! The first time we watched The Lego Movie Part II, Catchy Song caught us by surprise :D
DeleteThe only concerning aspect about this amp are the BUK555 mosfets. If those die the closest functional equivalent is a little off spec.
Hi Doz and Joe,
ReplyDeleteThanks for the sharing, i owned one of this NAD 310, it sounded great with the KEF Coda 7. I've not powered it up for almost a year plus ever since it produce a thump sound every time i switch it on, do you have any idea on how to reduce or eliminate it?
i have also plan to change the power and output coupling cap with either Nichicon/Panasonic of the same grade and specs, hoping it will sound better. Any advice?
Rgds
It's getting on now. Certainly changing ~40 year old caps will probably help *if* the existing ones are out of spec. I don't buy into all this audiofool cap bull, but both panasonic and nichicon make quality components. Worth checking out the two large PSU caps too. You'll need to trace your thump. Turning the volume down before switching on. Still thumps? It's not the pre amp. There's not really any "anti-thump" circuit in these, but if one rail is coming up before the other, that will not be helping. The service manual's on hifi engine, so tracing it through won't be difficult.
DeleteHi Doz,
ReplyDeleteThanks for the reply.
Yeah, i still love and miss the warm nice sound from it.
The thump exist even if i turned the volume down to zero, and switch on the amp. I've downloaded the manual, but i'm not sure what to trace, hence the plan of changing the CAPs first.
I've read in some other blog suggesting to place a 1k resistor across the speaker's terminal for 30s upon power up, and later take it out, and connect the speaker.
https://www.ecoustics.com/electronics/forum/home-audio/695581.html
Any idea if that would work in your opinion?
Rgds
Lal
Hi Lal, What you're essentially doing is making a speaker delay circuit. There's no reason that won't work, the 1K will bleed away the charge on the output capacitor in a few tens of seconds. You could use a timer circuit and a relay to automatically achieve this... change those caps out first, and see what gives.
DeleteHi Doz,
ReplyDeleteSuch an informative blog u have, i read it for 2 days browsing repairing topics, help me in understanding electronic repairing.
Hope i can repair my Nad310 :-)
Rgds
Lal
Good luck Lal!
Delete