Harmonic Convergence: the Effect of Component Tweaking Further Reading

Sidebar 1: Further Reading

• Ben Duncan, "Analog Equipment Design," Parts 1–5, Home Studio Recording, 1985–86.

• Ben Duncan, "Amplifiers—So You Thought You Could Just Change the Amp?," Line Up (Institute of Broadcast Sound, UK), April 1992.

• Martin Colloms, "Some Observations on the Results of Objective and Subjective Technical Reviewing Practice in High Fidelity," Proc. IOA (UK), Vol.13 Pt.7 (1991).

Anton's picture

Thanks for uploading this.

A truly fun read.

Bogolu Haranath's picture

As a side note ....... The Mark Levinson No.20 models mentioned in the 'Footnote 12' have very low output impedance ... between 0.01 and 0.05 Ohms ........ In the current models, Mark Levinson makes one such model, with very low output impedance, the No.534 stereo-amp (Stereophile Class-A) ...... See Hi-Fi News measurements of ML No.534 :-) ........

jeffhenning's picture

Very interesting article.

A few thoughts:

• Not that you had to mention it, but switch mode power supplies seem to have advanced to the point that, when done well, they seem to have some big advantages over the standard types. They're used to tremendous effect by Benchmark and Devialet.

• Both Benchmark's and Devialet's amps, which are radically different designs, outperform any Class A amp I've ever heard of. The Benchmark AHB-2 AAA circuit designed by THX uses some type of crazy Class A, A/B and B voodoo to get the advantages of all those types as well as feed-forward correction.

• Reading a transcript of a town hall with Bruno Putzeys and Peter Lyngdorf of Purifi Audio (between them they have around 60 years experience creating groundbreaking Class D amps), their latest design uses something like 85dB of feedback to eek as much out of the amps as possible. While in classical designs that would be insane, in the world of Class D it's apparently a great thing.

• In the end, I don't care how a piece of audio gear gives me perfect linearity, bullet-proof operation and a total absence of noise & distortion as long as it does that... or something imperceptibly close to it!

Graham Luke's picture

I would imagine that the roll of lavatory paper is the most pertinent item in the photograph above...

Archimago's picture

Or maybe 5W or 10W into that 8-ohm load pre- and post- modification rather than slightly below clipping for a 200W amp!?

Let's see the difference in harmonic structure at actual real useful power output levels!

Ortofan's picture


Ortofan's picture

... performed and analyzed independently, so that it could be determined which modification might have made the most difference, between the resistor replacements, the electrolytic capacitor substitutions, the op-amp rolling or the redressing of the wiring harness.

johnny p.'s picture

...until the last few years. Power-supply regulation and circuit-stage design remained the same, with high noise and distortion to boot.

I think the Sanders amp in 2008 was the first that used Thermal-Trak transistors and an IC-regulated power supply.

Since then, few have done the research as no (designers) seem to care.

But all-A circuits, like Valvet and Pass, have paved an alternate but scientifically-legitimate method of amplification. If used w/ highly-sensitive speakers.

adrianwu's picture

The necessity of class A/B with all the attendent power supply modulation and crossover distortion only serves the purpose of increasing the power output to beyond 20W. But a 300W amplifier only plays 12 dB louder than a 20W one, and all the extra power is often just converted to heat by over complicated crossover networks and inefficient drivers. The high end industry has been focussing on the wrong problem, which is to produce high power amplifiers that can drive complex impedance loads, when what they really should be doing is try to produce high sensitivity drivers and using active crossovers. High sensitivity drivers have distortion levels orders of magnitude lower than low sensitivity drivers, and TDH of drivers are measured in percents or even tens of percents levels, not 0.1% percent level of amplifiers. By reducing power output to 20W or less, power supply design can be simplified, and negative feedback often becomes unnecessary, which avoids instability problems and the generation of unpleasant harmonics.

Don Whittle's picture

Great article by Ben Duncan that shows how better quality components and thoughtful wiring layout produce a clearer sound.

I am a civil engineer with a lifelong interest in audio and
particularly appreciate articles such as Harmonic Convergence that use
observation along with engineering and science to improve audio performance.

Over the years I have owned and listened to many home audio and professional amplifiers including Krell, Kelvin Labs, Electrocompaniet, Pass Labs, C Audio, TOA, EMC, Bryston, Carver, HH, QSC, Turner, Turbosound etc, etc.

But learning to use a soldering iron and scope has led to some amazing aural places just like the article suggests. As my best power amps for everyday listening today are modified Rauch DVT250s & 50s, which I found were designed by Jerry Mead, Ben Duncan and team for recording studios and touring artistes.

Over several years I've bought a number of battered old Rauch amps online. They'd come out of London's clubs and venues, all closing down. Even after just a clean-up, they produced surprisingly realistic sound. Then I came across Ben's upgrade path much as mentioned in the article. This article on component quality and wiring layout is showing graphically the musical improvements that I'm now hearing. It's great when musicality and solid engineering combine.

This article seems to be a continuation of the concept in Ben Duncan's book on power amplifiers and his numerous articles on audio that focus not simply on circuit design but on all aspects of the audio system out to subtle distortions, mains and RF, and looking at how every tiny part can affect the final sound.