I just did some calculations on how much power the NAD will deliver in class A into 8 Ohms, with a bias current of 100mA. It seems it is a whooping 0,08W peak! I may try, over a period, increasing the bias current to 500mA to give about 1W class A. I did add to the cooling after all.
Note: I tried upping the bias current to 250mA, but the heat sinks were warmer than I liked, and I have backed down to 125mA.
In the 3020i there a two thermal fuses (E401, E402) in the output circuit, you can take these out if you are certain, that you will never short circuit the output. On the earlier original model I believe this protection is done using a relay, and an integrated circuit, I think you will be able to rip out the relay in these versions.
I just ripped out these thermal fuses and replaced them with a piece of SILVER (you have to shout that word to make sure it's stays audiophile) wire, that my good friend Peter gave me.
I do believe this further cleaned up the bass output, of the thing, so much that I will have to find means to reconnect my sub woofers soon. This means that the bass output is now at "normal" and acceptable levels. I'm not working at optimal listening conditions as a friend of mine is playing Battlefield right beside me, but I do believe these thermal fuses had a higher sonic impact, than I would have thought, then maybe again it's the SILVER.
I replaced the PSU capacitors for the power amplifier (C508/C509) with some 15000uF/50V parts I had salvaged somewhere else. This may be a little overboard, since the value of the capacitors in the original may very well, serve as protection against overheating the amp. The big idea being, that as the current draw rises, as the amp is turned up, the capacitors can not maintain their charge, thus lowering the supply voltage to power amp (and adding distortion). There is a possibility, that the amp can now overheat at high volumes, due to the larger reserve.
While I had the amp opened, I adjusted the bias (idle current) as well I upped it to 100mA, measuring 100mV across (R455/R456). This means the amp delivers a little more power before leaving class A, and heats up a bit more. I therefore added an extra heat sink, to the one already installed.
The bass of the amp now sound more controlled, and thereby somewhat less excessive, leaving a little more room for the midrange and treble to shine. This is consistent with what others have heard, changing the PSU capacitors. The increased bias current probably does not improve things to the same degree as the capacitors, and I will not recommend this mod unless you are prepared to keep an eye on the amp, checking it is not overheating. But change those capacitors.
All in all this is a really nice amplifier, and due to the simplicity of the circuit very mod-able. I won't regret the money I spend for a nanosecond.
Generated on 2018-05-03 01:14:21.926339