NAD 304 integrated amp one channel fading problem

dima2ooo · 11th December 2008, 01:47 PM

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?

rocco gibralter · 11th December 2008, 10:23 PM

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!

dima2ooo · 12th December 2008, 07:54 PM

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.

megajocke · 12th December 2008, 08:49 PM

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.

kbook · 15th January 2009, 10:16 PM

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?

Highspeed · 15th January 2009, 10:51 PM

Hi Dima2000

I am repairing Nad for years now.

Replace the output relay and your 304 will be OK.

Good Luck!

SAUDADE · 21st January 2009, 02:05 PM

Are you talking about the Speaker Relay TAIKO DGX2-24M?(RLY701 on the schematic diagram of the service manual)

SAUDADE · 21st January 2009, 02:05 PM

Here's an image of the area located near the speaker connection PCB. The big black square component is the DGX2 relay.

Highspeed · 21st January 2009, 08:21 PM

Hi Saudage

Yes

Replace this DGX2-24M relay.

Clean the switches and controls too.

Good Luck!

bmmach · 22nd January 2009, 04:42 PM

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

11th December 2008, 01:47 PM	#1
dima2ooo diyAudio Member Join Date: Dec 2008	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?

15th January 2009, 10:51 PM	#6
Highspeed diyAudio Member Join Date: Jul 2006	Hi Dima2000 I am repairing Nad for years now. Replace the output relay and your 304 will be OK. Good Luck! __________________ Highspeed

21st January 2009, 08:21 PM	#9
Highspeed diyAudio Member Join Date: Jul 2006	Relay Hi Saudage Yes Replace this DGX2-24M relay. Clean the switches and controls too. Good Luck! __________________ Highspeed

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11th December 2008, 10:23 PM	#2
rocco gibralter Account disabled at member's request Join Date: Aug 2008	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!

12th December 2008, 07:54 PM	#3
dima2ooo diyAudio Member Join Date: Dec 2008	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.

12th December 2008, 08:49 PM	#4
megajocke diyAudio Member Join Date: Jan 2003	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.

15th January 2009, 10:16 PM	#5
kbook diyAudio Member Join Date: Feb 2006 Location: Michigan	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?

21st January 2009, 02:05 PM	#7
SAUDADE diyAudio Member Join Date: Jan 2009	Are you talking about the Speaker Relay TAIKO DGX2-24M?(RLY701 on the schematic diagram of the service manual)

22nd January 2009, 04:42 PM	#10
bmmach diyAudio Member Join Date: Mar 2008	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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