NAD 214 poweramp refurbishment
Being an audio enthusiast, a proper power amp can be a thing of beauty. Big toroidal transformers, capacitor banks and relatively easy to understand symmetrical layout. A friend of mine donated his NAD 214 after upgrading to a 200 watt, THX certified, Parasound poweramp.
The NAD wasn’t without fault. It sporadically started producing some noise and hiss. A bit of googling showed some common issues with the 214 (and his bigger brother, the 216). Issues that could be the cause of the noise:
- Bad solder joints
- Oxidized print connectors
- Fried speaker relay
- Undersized/ dried up main PSU capacitors
- Offset idle current
Bad solder joints
The NAD 214/216 are prone to bad solder joints. An explanation might be the rather thin PCB combined with the heating up and cooling down of a typical power amp. The remedy is simple, although it requires some time; resolder all critical joints. Luckily, there’s room to spare inside the housing, but the high-current cabling is soldered directly to the PCB which takes some hassling, but it’s doable.
Oxidized print connectors
Nothing new here. Where two pieces of metal meet, oxidation can degrade a proper connection, resulting in all kinds of strange issued. A small piece of steel wool or fiber optic pen and some kontakt 60 spray can do wonders.
Fried speaker relay
The speaker relay is notorious in the 214/216 series. Over time, either the contacts burn in, or the actual coil burns out. It presents problems ranging from a distorted output signal to the amp being stuck in protective mode. The relay’s housing can be removed so you could clean the contacts, but I’ll take replacement over cleaning any day.
The DEC brand is hard to come by in Holland, but with the help of the spec sheet, I quickly traced a similar relay by Omron. Critical specs are:
- 48V coil voltage
- 4170 ohms coil resistance
- 5A max switching current
- Pin spacing: 7.5mm width, 5x5x5x15mm height
- 2x normally open switch
The Omron G2R-2-48V 48 V/DC 2 matched this perfectly. So, out with the old, in with the new.
Undersized/ dried up main PSU capacitors
The main capacitor bank in the NAD 214 is known to be undersized. The 9400uF (2x 4700uF) per channel can cope with low volumes, but at higher volumes, when more power is needed, bass response can become weak. Electrolytic capacitors dry up over time, loosing capacitance. This effect is accelerated when used in warm environments. This can lead to distorted audio and other issues.
The NAD 214 uses the same PCB’s as the bigger 216. Because of this, the PSU PCB accounts for 2 additional capacitors (one per channel). These connections can be utilized to increase the capacitance in the 214, without having to resolve to more expensive higher capacitance caps. Also, because board space is limited and higher capacity caps tend to be bigger. So I decided to replace the 4 old 4700 85 degrees with 6 brand new 4700 105 degrees caps. Giving me a total of 14100uF capacitance and better temperature handling.
Offset idle current
There is talk about the idle current being set to high for certain production series. The potentiometer used to set the current can change in value as well, so resetting the idle current according to the service manual is always a good idea in the 214’s case.
The service manual’s procedure is as follows:
Ensure VR301 and VR302 are set to minimum (fully counterclockwise) before first switching on.
- Connect DVM (digital voltage meter) across TP301 and TP303, Left channel
- Adjust VR301 left channel for a reading of: 20mV +/- 1.5mV
- Connect DVM across TP302 and TP304, Right channel
- Adjust VR302 right channel for a reading of 20mV +/- 1.5mV
- Leave power on for a further 5 minutes minimum
- Repeat steps 1 to 4
After all the work, it was time for the fieldtest. I connected my 80 Watt bookshelf speakers, powered up the amp, waited for the click of the brand new relay and listened without any input. Dead silent, perfect. Playing some music, it sounds great. Effortless, defined and powerful. It’s been running for a couple of days without any fault, so it’s safe to say the issues are fixed and the NAD 214 can provide me with music for hopefully many years to come.