Using the QuantAsylum QA401 for accurate Audio Measurements

The QA 401 from QuantAsylum (superseded by a newer, improved QA 402 and now the QA403) has emerged as a popular, comprehensive audio test instrument in the DIY audio fraternity and the go to instrument in many cases for commercial production testing in the audio industry. It combines a first rate DAC and ADC with […]

Read more →

So Just How Quiet is Your Phono Stage?

You may be in for a surprise: actually not that quiet! The reason of course is that the cartridge inductance and resistance dominate the noise in any decent phono amp. To get the best in terms of noise performance, you really need to keep the input referred noise voltage and noise current to a minimum. […]

Read more →

Class A Buffering the Correct Way

Here’s a simple way to force an opamp output stage to run in class A when used with a discrete buffer output stage – it takes just 1 resistor to provide a near constant current source load. Operating the opamp (and the output buffer stage) in class A dramatically reduces harmonics on the power rail […]

Read more →

Hifisonix ‘Symphony’ Line Preamplifier

I designed and built this preamplifier while living in Taiwan a few years ago. The Symphony preamp features Baxandall tone controls, up to 7 inputs,  a class A 2 W headphone amplifier and a Goldpoint 24 position attenuator.  The write-up describes the design process and choices in some detail and my listening impressions: Part 1 […]

Read more →

Baxandall’s Original Tone Control Article from Wireless World 1952

This article was published in October of 1952, when Baxandall was 31 years old, the design having already won him a prize 2 years earlier in a competition. His design basically relegated other tone control circuits to the scrap heap, although cheap passive, or non-inverting circuits still persisted well into the 1980’s, especially in low […]

Read more →

Hifisonix UBx Universal JFET Buffer

A while back, one of the diyAudio forum members who was building the nx-Amp (here’s the thread on DIYaudio.com) enquired about either reducing the amplifier’s overall gain, or providing a volume control facility. Since both the 15 W class A  sx-Amplifier and its bigger 100W sibling the nx-Amplifier, are Current Feedback Amplifiers, performance is quite […]

Read more →