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NAD C340

Stereo Integrated Amplifier (1998)

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NAD C340

Specifications

Power output: 50 watts per channel into 8Ω (stereo)

Frequency response: 20Hz to 20kHz

Total harmonic distortion: 0.03%

Damping factor: 60

Input sensitivity: 165mV (line)

Signal to noise ratio: 104dB (line)

Speaker load impedance: 4Ω to 16Ω

Dimensions: 435 x 110 x 290mm

Weight: 7.5kg

Accessories: remote control

Year: 1998

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Comments

re: C340

I have one of these amps with a fault in the preamp stage. The unit outputs almost no volume from the right channel. The power amp stage is working as normal. This is consistent across all inputs. I've pulled the main board out and looked for band solder joints or broken connections and all looks OK. Anmy ideas on the next thing to look at?

re: C340

Preamp
Smal PCB U15 can replace NE5532 - upgrade OPA to 2604 BurrBrown

re: C340

Apologize . wrong spec reading . U15 this is only RC board.

re: C340

Just did a bit more testing using headphone output.

Left channel works on all inputs, is loud with significant crackly distortion.
Right channel much quieter (volume level seems about right using headphones) and clear, but only works on tape and aux inputs.
When both inputs are connected the crackling in left channel disappears.
When I check the inputs with a multimeter, with the amp on and no input signal, there is around 11.3v on the right channel to ground on those inputs that are working on the right channel. 0v on the others and on all left channel inputs. When an input signal is connected the 12v state goes to 0v.

Is this symptomatic of a fault in the preamp you mention? Or possibly with the TC927310-010 switch array IC?

re: C340

A bit more prodding with the meter and I'm thinking its got to be the TC927310-010. According to the schematic it should read +/-17v on the VSS and VDD pins and 0v on the others. Its definitely not doing that as its outputting near 12v on half the right side pins. The VSS and VDD voltages are correct so I don't think the problem is elsewhere.
Not too bad a result if that's the case as they're pretty cheap on eBay.

I might as well have a go at upgrading that preamp too as they cost nothing- what benefits will that give me? A bit of a google tells me its a newer design and generally considered top be more "musical", right?

re: C340

removed the switching IC today and bridged the aux input to the output pins, amp now running perfectly. Will source a replacement switching IC and this one will be a win. Will upgrade the preamp when I do that too.

re: C340

Hi,

The input switching IC is controlled from the microprocessor using three lines, CLK (clock), DATA and STB (Strobe). The problem could be with the microprocessor. The best way to verify is with a scope and observe the three signals to see if there is any data being sent when switched. Also verify that the IC is receiving both the VDD and -17 volt supplies.

The most common problem with ALL NAD's is poor solder. Their designs were solid, but they seemed to outsource the actual assembly to the lowest bidder. My acronym for NAD was Nearly Always Defective. I worked on a lot of NAD's in warranty and out.

-bob

re: C340

I ended up replacing the switching IC today and it seems to be working fine now. Also upgraded the preamp DAC and fine tuned all the idle and offset voltages and it’s sounding very good indeed. Chalk this one up as a win and a few lessons learned in the process, not bad for $15 in parts.

re: C340

Hello.
I have one here i think needs the same treatment. Anybody want to take a shot at it. I think this is a bit over my head.
Tom

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