NAD 304 integrated amp one channel fading problem - diyAudio
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Old 11th December 2008, 01:47 PM   #1
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Default NAD 304 integrated amp one channel fading problem

I have an old, old NAD 304 integrated amp which I bought on my grad student budget years ago and guess what, I am still using it with a NAD 512 CD player.

A while ago the 304 started loosing signal at low levels. It fades one channel at a time, at first it was just the left channel, now it's both. The fading in two channels isn't simultaneous. It occurs more often after a few minutes of playing, rather than when the amp's just turned on.

Sometimes I hear intermittent problem that sounds like a bad wire contact, i.e. "scratchy".

Checked all wire connections, headphone output doesn't have the same problem. What could it be and what should I check/replace?
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Old 11th December 2008, 10:23 PM   #2
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Hi Dima, Sounds to me like dirty pots / switches, If it is, you have to either clean them, Or replace, You can buy contact cleaner, but you can never really get them clean unless you take them to bits, Dont know if you can do that with nad gear? then you need a thin smear of conductive grease in the tracks...

Try some judicious twiddling of the vol, bal, tone, etc and wiggle the buttons to see if it kicks back in to life!

Had a 3020 yonkers ago, good amps as I remember!
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Old 12th December 2008, 07:54 PM   #3
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Thanks Rocco. Yes, I like the sound a lot. It's supposed to be "like" tube sound, even though it's solid state.

I tried changing bass and treble while the problem occurs and it didn't do a thing to the fading. What does have an effect on it is changing balance or volume. I assume that's because it has to do with voltage on those bad contact surfaces.

My next step is taking the baby apart and trying to clean moving parts.
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Old 12th December 2008, 08:49 PM   #4
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The NAD304 has 4 resistors that always drift high in value causing all kinds of problems.

I don't remember the numbers but it's one in each power amp, 47k supplying the zener references for the folded cascodes. Replace these with a 2W or so resistor so it won't happen again.

There are also 2 in the preamp power supply. They are in series with the collectors of the lowest voltage regulators. About 150-200 ohms or something I believe, check the schematic. Use a higher wattage resistor for the replacement here too.
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Old 15th January 2009, 10:16 PM   #5
kbook is offline kbook  United States
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I also have the same problem with my NAD 304. I am trying to change the volume but I couldn't find parts. Also, when I turn balance pot to the left channel, the right channel still has sound coming out. This is weird. I am not sure if it is caused by the 4 resistors also?
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Old 15th January 2009, 10:51 PM   #6
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Hi Dima2000

I am repairing Nad for years now.

Replace the output relay and your 304 will be OK.

Good Luck!
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Old 21st January 2009, 02:05 PM   #7
SAUDADE is offline SAUDADE  France
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Are you talking about the Speaker Relay TAIKO DGX2-24M?(RLY701 on the schematic diagram of the service manual)
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Old 21st January 2009, 02:05 PM   #8
SAUDADE is offline SAUDADE  France
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Here's an image of the area located near the speaker connection PCB. The big black square component is the DGX2 relay.
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File Type: jpg dgx2-24m rly701.jpg (89.3 KB, 744 views)
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Old 21st January 2009, 08:21 PM   #9
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Default Relay

Hi Saudage

Yes

Replace this DGX2-24M relay.

Clean the switches and controls too.

Good Luck!
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Old 22nd January 2009, 04:42 PM   #10
bmmach is offline bmmach  United Kingdom
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Hi Dima,

Did replacing the relay rectifier the problem? I have a similar model and my right channel is faded; would like to find out if this resolved your problem.

Thanks
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