Sony TA-N900

The second ESPRIT unit and a Stereo Sound Best Product in the winter of 1981, alongwith the TA-E900 companion.
Also a bestseller for Sony - probably the most common ESPRIT unit and an excellent amplifier.


Its 1978 origins were named TA-N89 : inside the enclosure of a TA-N88B, in Class A or B like a TA-N86B... so it is normal the final TA-N900 took from both : 20Khz PLPS power-supply and Class A operation.
What changed was the absence of NFb, the entrance of MOS-FETs and of a Heat-Pipe with a wheel cooling fan added and a strict monoblock use : a renewed TA-N9 of sorts.


The circuit starts with a bootstrapped double cascode FET differential input with current-mirror output (1st stage), bootstrapped cascode inverted amp (2nd stage) and ends with an emitter follower SEPP output (3rd stage).

The output is made by a pure complementary SEPP output in Class A operation (sans NFb), with four pairs of high Gm enhancement type MOS-FETs (Sony 2SK173 / 2SJ54).

The power-supply is Sony's Pulse Locked Power Supply, chopping the AC at 20Khz ; heat regulation is done with a Heat Pipe attached to a BSL wheel fan for accelerated air flow 200W in Class A oblige.


Low-TIM design, 27dB open loop gain, 2x 22,000µF ELNA For Audio smoothing caps and 99,99% pure copper wiring are also inside this very slim box which didn't need to be that slim but Sony, in 1979/1980, still was on to the slim profile inaugurated in 1976 with the 88s and 86s.

Unlike the TA-E900 or TA-E901, there is ony one sealed blue module inside the N900 : it is the Class A input amp, placed between the input and the pre-driver stage.

The Heat-Pipe of the N900 is a bit different than those used in the TA-N9, TA-F80 or TA-P7F : its heat-dissipating area is made of thick diecast aluminium fins painted in black. More like a regular heatsink - but it's a Freon-filled Heat-pipe.

The way the power transistors are hooked to the pipe itself is also very diffrent : the aluminium clamping block see its thickness multiplied by around 4 when compared to the TA-N9 !

As time has proven, the main crux of the TA-N900 is the PLPS box which, sealed as it is, heats up like mad : the T701 iron core inverter and caps end up fried or failing at best.
Said inverter is NLA since long and is not a kind of easy-to-swap part.


The ESPRIT TA-N900 nevertheless sold very well, despite its Sony origins : like the TA-N86B, it was and still is that good.