Hifisonix kx-Amplifier

[maty tinman]

It’s 50 W per channel with the original sx amp supplies - about 60 watts on the slightly higher rails for class A

page 21

Output power: >28 W peak class A into 8 Ωs = 15 W RMS into 8 Ωs class A; 50 W RMS into 4 Ωs class AB; 95W RMS class AB into 2 Ωs;

Standing current Class A mode: 1.2 amps (600 mA per output pair); standing current class AAB mode: 600 mA (300 mA per pair) +-20%

Distortion (measured): typically 0.006% at 15W into 8 Ωs; 0.015% at 50 W class AB into 4 Ωs; <0.1% at 90W into 2 Ωs

Slew Rate: 140 V/us (10%~90%, symmetrical)

If the standing current is the half in class AAB, the dissipated power should not be 30 watts by channel?

[maty tinman]

http://www.doctorproaudio.com/doctor...n.htm#calc_spl

Calculators / Audio / Acoustics / SPL


SPL: KX-amplifier-KEF-LS50-83dB-15watts



with KEF Q100 (85 dB) -> 90.2 dB. In phase + 3dB: 93.2 dB.

SPL: KX-amplifier-speaker-89dB-15watts

[bambadoo]

Crap - so happy with the sx.. Just have to build this.

[Vrystaat]

Bonsai, good to see you are busy again !!

[xrk971]

Welcome back Bonsai! Nice amp design, and another one for us to try out for Class A designs. I am curious how this compares to Hugh’s Alpha 20 (or 35 Omega or 55w Alpha BigBoy). Also interested to find you listen to LS50’s as I had a chance to audition their self powered and DSP “w” variant the other day when I was in Germany. They sounded very nice for 5in bookshelf speakers.

[Bonsai]

Thanks guys - I've been busy this last year!

[Bonsai]

Maty, the kx-Amp delivers 50W into 4 ohms quite easily. Also, remember the peak class A power is about 25W (same for sx-Amp BTW). So, there is plenty of power to handle crescendo's. As mentioned on the website, of you want rock concert hall levels from a class A amp like this in a large listening space, you need to use more efficient speakers, or you need to constrain your listening space appropriately. If you shop around, you can find plenty of speakers at 93dB~96dB or more efficiency. I bought my LS50's to do an audio show after auditioning them - they were driven by a 100W amp on that show. But, they sound good even with a low power amp like this one.

[Mark Johnson]

I wish the square wave tests (page 25) weren't presented with oscilloscope bandwidth limiting turned on. There might be a bit of overshoot or underdamped ringing, which BWLIMIT prevents us from seeing.

Just barely visible is a smidgen of overshoot: the smoothed, BWLIMITed yellow trace just barely overshoots enough to kiss the upper dotted line. Then it recovers from overshoot and settles down to its final asymptotic value. Click on the white "X" at lower left to see the image full size and undistorted. The overshoot is also visible in the zoomed out (20usec/div) picture on the same page.

I also wish there were 3A or 5A "catch diodes" across the Zobel networks, to protect the output transistors when clipping into crazy reactive loads. And I wish the "OMG a rail is dead" safety diodes {Cordell section 15.3, p.325} D2 and D3 had a continuous DC current rating higher than fuses F2 and F3. I personally prefer to use the 10A04 thru hole diode in those positions; I don't mind paying 2 x $0.76 to buy them.

_

[fab]

Good project Bonsai
As usual you provide a very good informative manual and I appreciate that peoples can also learn in the process of diy.
I was impressed when I built your NX amplifier with « similar » topology as the SX or KX. The depth of the soundstage and the dynamic is special. It has motivated me into continuing experimentation of the “CFA” topology..

Fab

[maty tinman]

Bonsai, trust me, my KEF Q100 with my tweaks sound very well. They have a very similar frequency response than KEF LS50, front bass-reflex and 49 Hz at -3 dB. More sensitivity (2 dB) and minimum impedance (4.7 Ohms).

KEF saved on the furniture, with a thin DM. The 5" coaxial is very good (the 6.5", at least the old, NO).

They love power. I modified the bias of my AV Marantz SR4500, now is more high -> better sound. Maybe at low volume, in near field (with the PC), it works like class A, maybe.

My idea is the ALPHA Lender preamp + very clean power amp. Wich power amp? I do not know yet.