sx-Amp and nx-Amp


Paid Member
2003-07-25 10:44 pm
Updated January 15 2016

I've put the complete write-ups for the nx-Amplifier and sx-Amplifier up on my website

If you want to make 'em, including where to buy PCB's, everything is there - look under the respective amplifier posts.


100W RMS into 8 Ohms CFA class AB Amplifier featuring DC-570 kHz bandwidth, <1us rise times, ~200 V/us slew rate. Uses +-45 to +-50V Power Supply. PSU +Protection board with Mosfet SSR provides overcurrent, DC offset and on/off muting.

The new V2.0 nx-Amplifier PCB incorporates all of the errata changes and suggestions made by builders over the last year: Ovation nx-Amplifier: A 100 W class AB Current Feedback Amplifier

Download the nx-Amp V2.09 build document here The Ovation nx-Amplifier V2.0_9 |

You can also buy a set of very high quality double sided through hole plated, silk screened gold flashed V2.0 boards from Jim's Audio here:


15W RMS into 8 Ohms current feedback class A amplifier, 28 Watts peak class A into 8 Ohms. DC-530 kHz (-3 dB) bandwidth, 140 V/us slew rate and rise times <1 us. Uses +-20V to +- 22V DC power supply . You can download the full amplifier write-up and build document here: (updated March 2016, and BOM updated 18th September 2016))

You can buy a set of very high quality double sided, through hole plated gold flashed sx-Amplifier PCB's from Jim's Audio here:

Notes About Components

The BC547 and BC557 have been discontinued by a number of suppliers and this has lead to problems in both the sx-Amp and the nx-Amp for some builders.

In place of the BC547(C) NPN devices you can use the BC550(C) - data sheet here

For the originally specified BC557(c) PNP devices you can use the BC560(c) - data sheet here

You can use either the C suffix with an hFE range of ~400 to 800 or the B suffix with an hFE range of ~200 to 450. I suggest if you can use the C suffix, then that should be the first option. However, note that you should use the same hFE suffix for both the NPN and the PNP small signal transistors.


Here is the nx-Amplifier December 2021 BOM updated to cater for obsoleted parts:-


  • nx-Amp BOM December
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I've put the complete Gerbers and drill files for these amplifiers up on my website Audio Amplifer Design and Music Reviews. If you want to make 'em, everything is there - look under the respective amplifier posts.

Any questions, feel free to ask me

Just finished reading the NX amp documentation... seems like a tempting proposition, I am surprised nobody has jumped at the offer yet! I know I would be interested in giving the NX a try. Anyone else?

I had high hopes of selling boards via a web shop, but too busy at work for now and at least the next 6-12 months - many projects. Quite a few people PM'd me asking for boards, so that's why I put them up. Please feel free to do a group buy. Same for sx-Amp.
I can give it a shot, since I am ordering boards in small q. anyway, both for this hobby, and some unrelated reasons, but TBH, someone would have to help a bit.

The most obvious questions would be which board or boards to start with. I noticed that the nx Amp has a few surface mounted parts on the bottom side, and that tends to discourage people from wanting to solder them. Others have solved that by having those parts professionally assembled, but that raises the cost somewhat. Making bare boards is very inexpensive, but any time a small-ish quantity goes into assembly with SMDs, the cost rises.

I had a few boards made for the through-hole version of the VSSA (details in the Pee-Cee-Bee thread), and those turned out to be about $10 each double-sided with solder mask and silk in quantity of a dozen-or-so. Q. 100, probably half that, not sure.

So, some discussion would be in order, regardless of who decides to take it on.

To anyone else reading this - This is a very generous offer, and it would be a shame to let it pass!