Unfortunately mine when biased at 21mV did suffer a lot, at high levels of output power it was getting realy hot and it would go into protection mode after half an hour of hard pushing but my speakers are not an easy load as they dive to 3ohm @2.5kHZ plus that I am using it in bridged mode as I use one amp for each speaker's mids/tweeters so I had to readjust the bias to normal levels.
I think that it hasn't got to do so much with speaker's sensitivity as with speakers's inpedance, for example here is the impedance diagram of my speakers where you can see that @2.5kHz impedance dives to 3ohms so in my case the bridged nad 216 suffers a lot when cranked up, when normal biased it gets hot but at least it's not going into protection mode.
Another thing that helped a lot in my case is the extra 4 X 4700uF electrolytic caps I've added at the rectifier filter and the bigger rectifier bridge I've put.
The 218 has 8 X 4700uF caps which is just two more than the 216 and these might not be enough.
Another thing that helped a lot in my case is the extra 4 X 4700uF electrolytic caps I've added at the rectifier filter and the bigger rectifier bridge I've put.
The 218 has 8 X 4700uF caps which is just two more than the 216 and these might not be enough.
I think that it hasn't got to do so much with speaker's sensitivity as with speakers's inpedance, for example here is the impedance diagram of my speakers where you can see that @2.5kHz impedance dives to 3ohms so in my case the bridged nad 216 suffers a lot when cranked up, when normal biased it gets hot but at least it's not going into protection mode.
Another thing that helped a lot in my case is the extra 4 X 4700uF electrolytic caps I've added at the rectifier filter and the bigger rectifier bridge I've put.
The 218 has 8 X 4700uF caps which is just two more than the 216 and these might not be enough.
Yes, i do understand the impedanceprofile means a lot but this was a ”light load, never under 6 ohm anywhere. I should’ve mentiones that too.
What bridgerectifier did you change too? I use the orginal with 4x12000uF/ 80v Nippon SMG. Plan of changing the smaller diodes from 1n4003 to byv27/200 and the bigger 5402 to byv28/200.
In combination with the extra 4X4700uf caps on the filter there was an improvement -you see I made these changes at the same time- but I don't think it came from the bridge rectifier but from the extra caps.
At the same time I replaced every electrolytic cap in the amp with Nichicons as after 20 years I think they needed to be renewed.
At the same time I replaced every electrolytic cap in the amp with Nichicons as after 20 years I think they needed to be renewed.
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I've now changed the 4 pcs "IN5402" to Vishay BYV-28-200 with positive results. Sound became more fluent and cleaner. Not as much as in the bridge in my S100 but that was expected.
Next is to change all those IN4007 or was it 4003 to BYV-27-200 (or BYV 26-600) like in my Nad S100..
Btw, giaspyr; can you check your values on R203 and R 204? They suppose to be 330 ohm but my R203 read (in curcuit) 183 ohm...hmmm
They are located just near voltage regulator, beside the 4x 220uf/160v caps.
To be continued...
I did a lot of things recently with this amp.
Replaced the diodes as i said to BYV-227-200 in the regulator section... faster and cleaner sound. Recommend it.
While doing this also replaced a few resistors that were out of spec like 2x330R... didn't find any fusible in that size/resistance so went with metal films Panasonic that looks solid with 3W rating.. (still getting hot though)
And there was a 22k 1% res that was out of spec (23.5K) and at the same time the trannies, 2sd631K/600K and sc2240/970..these are going very hot in this construction, temp like 70 degress..
Measured voltage to +68.9 vs -68.6v and that good enough. Dc on output to 2.7-3.0mv on both ch.
On output/input ive replaced almost all res to Dale RN or CMF 60 or 55. also Halcro some places where Mouser didn't have Dale.. all this "mods" makes a sound that is very detailed and efortless with huge transparent sound.. this is far from orginal hehe =)
Replaced the diodes as i said to BYV-227-200 in the regulator section... faster and cleaner sound. Recommend it.
While doing this also replaced a few resistors that were out of spec like 2x330R... didn't find any fusible in that size/resistance so went with metal films Panasonic that looks solid with 3W rating.. (still getting hot though)
And there was a 22k 1% res that was out of spec (23.5K) and at the same time the trannies, 2sd631K/600K and sc2240/970..these are going very hot in this construction, temp like 70 degress..
Measured voltage to +68.9 vs -68.6v and that good enough. Dc on output to 2.7-3.0mv on both ch.
On output/input ive replaced almost all res to Dale RN or CMF 60 or 55. also Halcro some places where Mouser didn't have Dale.. all this "mods" makes a sound that is very detailed and efortless with huge transparent sound.. this is far from orginal hehe =)
Hi Martin, today I've checked R203/R204 in circuit and I get reading of about 270Ω for both, maybe it is best to replace them.
Replace also the R212, R217 (both 22K) and the R243/244 (5,6K) to 1W. I've seen and heard many NAD 214/&216 with problems involving these incl mine.
If you can (highly recommended) replace also the trannies on heatsinks plus the 2xto-92s.. in the regulator.
-They run superhot and if they have never been replaced they will soon go. Obsolete trannies but you can find from ebay (CDIL brand for SD631/600 and Tayda has good 2240 and 970/1015's if i remember correct.
If you can (highly recommended) replace also the trannies on heatsinks plus the 2xto-92s.. in the regulator.
-They run superhot and if they have never been replaced they will soon go. Obsolete trannies but you can find from ebay (CDIL brand for SD631/600 and Tayda has good 2240 and 970/1015's if i remember correct.
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Best caps to change are the ones that are out of spec. 25 years old amp, may be a lot of low hanging fruit. Electrolytics age due to the water held in by a rubber seal. Plastic film & ceramic disc caps don't. Electrolytics have a plus near one lead, a minus near the other lead, or the legend "NP" after the voltage for non-polar. I determine mains cap deterioration by measuring voltage on speaker at max volume. Use an analog voltmeter, not a DVM. P=(V^2)/Z where z is speaker impedance. P less than rating, mains e-caps are dried up.
Personally, audio grade caps from nichicon are good, but not 4x superior. The way the price is. I buy industrial long life caps, so I don't have to change caps 4 times again as I had to do to the ST70. You buy a cap rated 3000 hours service life up from nichicon, panasonic, rubicon, vishay, you're not buying any ****.
Per Mr antoine comment, a lot of overpriced roc's eggs out there in the audio market.
This thread had some psycho-acoustics in previous posts, IMHO. Power supply rectifiers, the faster more expensive ones can be more of a RF problem than the cheap ones, unless snubbed with proper ceramic disk series a damper resistor. Read long thread about snubber design. No 120 hz or 100 hz (double power line frequency) buzz in your amp, not a problem. NAD schematic shows no snubber across diode bridge. A cheap improvement is a .01 uf ceramic cap across the + - 52 supplies. An additional improvement might be a 1 uf poly cap across each 4700 e-cap, although sometimes you get oscillation out of that configuration.
Personally, audio grade caps from nichicon are good, but not 4x superior. The way the price is. I buy industrial long life caps, so I don't have to change caps 4 times again as I had to do to the ST70. You buy a cap rated 3000 hours service life up from nichicon, panasonic, rubicon, vishay, you're not buying any ****.
Per Mr antoine comment, a lot of overpriced roc's eggs out there in the audio market.
This thread had some psycho-acoustics in previous posts, IMHO. Power supply rectifiers, the faster more expensive ones can be more of a RF problem than the cheap ones, unless snubbed with proper ceramic disk series a damper resistor. Read long thread about snubber design. No 120 hz or 100 hz (double power line frequency) buzz in your amp, not a problem. NAD schematic shows no snubber across diode bridge. A cheap improvement is a .01 uf ceramic cap across the + - 52 supplies. An additional improvement might be a 1 uf poly cap across each 4700 e-cap, although sometimes you get oscillation out of that configuration.