Jeff Chan's Audio Page -- DIY Amplifier Comparison

DIY Amplifier Comparison

Here's a scorecard to keep track of the design features of various modern solid-state Do-It-Yourself (DIY) Audio Amplifiers. These are very clean, thoughtful designs that likely sound better than many commercial amps. It's also cool that they follow in the footsteps of the original Hi-Fi generation when, if you wanted good-sounding equipment, you built it yourself.

I'm focusing mostly on Nelson Pass' published plans because they're simple and therefore somewhat easier to build. Design elegance also tends to lead to better sound, since there are fewer elements corrupting the signal. Still, building an amp requires mechanical and electronic aptitude and usually a lot of time and effort finding parts. It's certainly easier to buy a commercial amp, but it's perhaps not as rewarding as building your own. All amps run pure Class A or heavily Class A biased Class AB. All plans have appeared in Audio Amateur magazine or it's successor audioXpress.

Name Stages Topology Devices Feedback Power Efficiency Features

Zen 1 Single-Ended MOSFET Moderate 10W 20% Very Simple, Active Current Source, Capacitors on input and output

Son of Zen 1 Balanced Single-Ended MOSFET None 10-50W 5% Balanced Power Differential Pair, no coupling capacitors, resistor current sources

Hoffman 2 Balanced Input, Single-Ended Output MOSFET Moderate 35W 20% Current Sources for both stages, Split Power Supplies, No Capacitors on output

A40 4 Single-Ended Differential Pair Input, Voltage Gain Stage, Darlington Push-Pull Output Bipolar Moderate 40W 40% No coupling capacitors, Current sourced input and voltage gain stages

A75 2 to 3 Balanced Input, Variable-to-none Cascode Driver, Push-Pull Output MOSFET Adjustable to None 75W (into 8 Ohms, 150W into 4 Ohms) 45% Gain contribution of Cascode driver stage adjustable down to none, resulting in adjustable feedback and distortion characteristics ranging from a 2 to 3 stage design. Current sourced differential input.

Name	Stages	Topology	Devices	Feedback	Power	Efficiency	Features
Zen	1	Single-Ended	MOSFET	Moderate	10W	20%	Very Simple, Active Current Source, Capacitors on input and output
Son of Zen	1	Balanced Single-Ended	MOSFET	None	10-50W	5%	Balanced Power Differential Pair, no coupling capacitors, resistor current sources
Hoffman	2	Balanced Input, Single-Ended Output	MOSFET	Moderate	35W	20%	Current Sources for both stages, Split Power Supplies, No Capacitors on output
A40	4	Single-Ended Differential Pair Input, Voltage Gain Stage, Darlington Push-Pull Output	Bipolar	Moderate	40W	40%	No coupling capacitors, Current sourced input and voltage gain stages
A75	2 to 3	Balanced Input, Variable-to-none Cascode Driver, Push-Pull Output	MOSFET	Adjustable to None	75W (into 8 Ohms, 150W into 4 Ohms)	45%	Gain contribution of Cascode driver stage adjustable down to none, resulting in adjustable feedback and distortion characteristics ranging from a 2 to 3 stage design. Current sourced differential input.