New 200 watt Kit amp features ultra low distortion and Thermaltrak devices

[snoopy]

Check it out

http://www.siliconchip.com.au/cms/A_110797/article.html

Specifications & Performance

Output Power: 200 watts RMS into 4W; 135 watts RMS into 8W
Frequency Response at 1W: -3dB at 4Hz, -1dB at 50kHz (see Fig.4)
Input Sensitivity: 1.26V RMS for 135W into 8W
Input Impedance: ~12kW
Rated Harmonic Distortion: < .008% from 20Hz to 20kHz for 8W operation; typically < .001% (see Figs.5-8)
Signal-to-Noise Ratio: 122dB unweighted with respect to 135W into 8W (22Hz to 22kHz)
Damping Factor: <170 with respect to 8W at 100Hz; <50 at 10kHz
Stability: Unconditional

The Ultra-LD Mk.2 Amplifier Module uses the new On Semiconductor ThermalTrak power transistors in a circuit which is largely based on our high-performance Class-A amplifier which was featured in SILICON CHIP during 2007. The ThermalTrak transistors are a new version of the premium MJL3281A & MJL1302A and have an integral diode for bias compensation. As a result, the circuit has no need for a quiescent current adjustment or a "Vbe multiplier" transistor.

This is also our first amplifier module to use a double-sided PC board. Ostensibly, there is no reason to use a double-sided board for a relatively simple circuit such as this, especially as our previous single-sided amplifier boards have had few links. In fact, we have used the double-sided design to refine and simplify the external wiring to the PC board which has been arranged to largely cancel the magnetic fields produced by the asymmetric currents drawn by each half of the class-B output stage. We provide more detail on this aspect later in this article.

Power output of the new module is on a par with the above-mentioned Plastic Power module and significantly more than the original Ultra-LD module. As well, it uses a considerably simpler power supply than the Ultra-LD module.

Power output is 135 watts RMS into an 8-ohm load and 200 watts into a 4-ohm load for a typical harmonic distortion of less than .001%. The new module also has slightly higher gain than the Ultra-LD module but still manages to produce an improved signal-to-noise ratio of -122dB (unweighted) with respect to 135W into 8W. This is extremely quiet.

A look at the accompanying performance panel and the performance graphs will show that this is a truly exceptional amplifier, bettered only by the Class-A amplifier described during 2007. In fact, some of the distortion figures we have obtained are so low, around .0007% for operation into 8-ohm loads, that we were amazed. We had expected this Class-AB amplifier to be better than anything we had published before – but not this good!

[Spasticteapot]

What output transistors are those?
What voltage does it need?

[snoopy]

Originally posted by Spasticteapot
What output transistors are those?
What voltage does it need?

ThermalTrak equivalent of On Semi MJL3281/MJL1302 or Toshiba 2SC3281/2SA1302 but with higher ratings.

Vceo = 260V
Pdiss = 200 watts
Icmax = 15 Amps

http://www.onsemi.com/PowerSolutions...do?id=NJL3281D

Data Sheet:-

http://www.onsemi.com/pub_link/Colla...NJL3281D-D.PDF

[Samuel Jayaraj]

It is NJL and not MJL. MJL and 2SC/2SA are not thermaltrak types

[smithy666]

This is classic Silicon Chip - put a 47uF bipolar electro (what they specify) right at the start of the signal path. Yep, that won't affect the sound one bit....

[AKSA]

Snoopy,

Leo believes that an amp with zero measureable distortion sounds the best, and that topology is everything. I believe components make a difference, too.

Hugh

[Greg Erskine]

Hey Hugh,

I bet YOU could take this amp, tweak a few parts (I reckon it would be only a half dozen or so) and this amp would sound as good as any and better than most.

I think you would find the prototype will sound reasonable good because Leo knows about matching components etc, but the production kits (cheap $90 per amp) will need some close attention.

regards

[roender]

This amp has two major problems:
1. The OPS is way overbiased (70...100mV over Re, normally should be 18...25mV) and will suffer from GM doubling when will switch from classA to classB.
2. The OPS is thermally undercompensated. The diode inside ThermalTrack devices has different TC than a silicon BE junction, -1.66mV/grdC compared with -2.1mV/grdC

[snoopy]

Originally posted by AKSA
Snoopy,

Leo believes that an amp with zero measureable distortion sounds the best, and that topology is everything. I believe components make a difference, too.

Hugh

So do Halcro and a lot of other amp designers !! But then again I suppose if you don't have the means or the money to measure it then you won't know if an amp does measure well so you will always make an excuse as to why it is not important

[snoopy]

Originally posted by smithy666
This is classic Silicon Chip - put a 47uF bipolar electro (what they specify) right at the start of the signal path. Yep, that won't affect the sound one bit....

My loudspeakers have quite a few large value bipolar caps in the crossover that have to handle large amounts of current. Should I be worried about this one lowly capacitor that only has to handle a fraction of the current ??