Crash Course on Damping Factor: Growing Audio Systems - Part I

[Tetrode growth]

Half a Century at the Audio Crease

What can be learned from amplifiers:

What on earth is damping factor?

[Italian version here]

Parameter: Damping Factor & Bass Alignment & System Frequency Response
Interface: Amplifier with Loudspeaker with room
Price: PRaT & Boom
Author: Mark Wheeler - TNT UK
Published: September, 2023

“How come there is no web address, factory name or email address?” ask Plebs, stage left, perfectly reasonably

“So where does this fit in with the Old Scribe's pursuit of vast active systems or single-ended valves?” demand Plebs Chorus, stage left

Old Scribe's First Foray into Audio Shopping

When trying to choose how to spend a very limited amount of money, as a very Young Scribe, on a very first audio system, many hours were spent poring over catalogues & technical specifications of available gear both within and way beyond their very limited budget. Before the days of easy online dictionaries & encyclopedias, explanations of a whole new language entailed visits to public libraries and asking questions in stores.

In those days, in the developed world, every town boasted a number of competing audio stores, audio & combined TV stores and audio & vinyl record stores for LP's and singles. Department stores, from Woolworths to Harrods, also had “Radio & TV” departments that often sold surprisingly specialised brands of HiFi equipment.

The audio magazines often had a back page advertisers' index where one could check a tick box next to each advertiser name and receive copious amounts of pulped trees extolling the virtues of their wares. There would be white papers and AES preprints alongside glossy brochures of their products. Smaller manufacturers often sent Roneo or Gestetner mimeographed manually typed sheets of data and design philosophy. Among the parameters being measured in catalogues from the manufacturers was amplifier damping factor.

“Damping Factor?” Ask inquisitive plebs, stage left, ”Was this some kind of amplifier moisturiser?”

“Oh No! The puns have started, wail distressed Plebs Chorus, stage left

Among this wealth of information was the brochure for the Accuphase E202 amplifier. This looked a cut above the offerings from rivals and its rear panel included a damping control.

Accuphase boasted:
“The E-202 has a Speaker Damping Control which permits choice of three damping factors and induces maximum potential performance from any loudspeaker.
Damping factor with an 8 ohm load becomes more than 50 when this control is set to NORMAL.
Likewise, it is 5 at MEDIUM position, and 1 at SOFT position”

[Damping control]

Damping Factor and Valves

Transistor amplifiers (this is 1973, Class D only means feedforward in this era) achieve their output impedance (hence their damping factor) through the inherent low output impedance (Z) of the output devices (bipolar or MOSFET) and the feedback essential for stability, in traditional circuit design. Hence that Accuphase E202 Damping Control worked by varying global negative feedback.

Valve amplifiers (except for very rare & expensive Output Transformer-Less, or OTL circuits) do not drive the loudspeaker voice coil directly from the output devices. Perhaps Damping Factor could be controlled by choice of winding ratio between primary and secondary? Is this why some people claimed thay valve (tube) amplifiers were superior to transistor amplifiers?

In 1973 these questions were beginning to be asked in the audio press as well is a Young Scribe's schoolboy brain.


The conclusion is obvious: more investigation was needed by a young Old Scribe. In Part II the Young Scribe's experiments will be revealed with the 50 year hindsight and further experiments of an Old Scribe.

Music enjoyed while writing this review

Reference system

physical media: some vinyl, some CD

  • Can: Live In Brighton 1975
  • Little Feat: The Last Record Album
  • Miles Davis: Kind of Blue UHQR0004
  • Jaco Pastorius: Modern American Music...Period - The Criterion Sessions
  • Bob Dylan: Rough And Rowdy Ways
  • Rory Gallagher: Check Shirt Wizard

Equipment used in this review:

  • Turntable: Michell Orbe SE

  • Turntable Modification 1: Pedersen

  • Turntable Modification 2: Resin sand cast subchassis dampening

  • Turntable Modification 3: Pete's Pylons & feet isolators

  • Turntable Modification 4: Jade IsoDuo & Deflex plain sheet beneath Orbe motor pod

  • Pick-up arm 1: HadcockGH242 SE with all silver wiring from cartridge to silver Eichmann Bullet plugs

  • Turntable shelf frame support: Marble Slab on sand bed in spalted beech & plywood wall frame

  • Additional Turntable shelf isolation: 10mm laminated glass

  • Cartridges: Dynavector DV XX-2 MkII or Decca London (John Wright serviced 2020)

  • Phono pre-amplifier: Canor TP306VR+ on Brightstar Isonodes Extra Large

  • Line Pre-amplifier: Audio Research Corporation Reference 3 with steel top cover removed, casework damped by BrightStar Little Rock 5, tube rolled and vibration further controlled internally by silocone O-rings and Pearl valve cooler/dampers, on Something Solid end grain balsa plank, on kevlar sling supported by separate sand-filled steel frame support

  • Treble Amplifier: de Paravicini (HiFi World) designed SET6080 in RATA Torlyte case and outboard mains transformer; glued onto cut down ErAudio Space Harmoniser & passive components selected by Old Scribe

  • Passive Loudspeakers: TQWP loaded Hammer Dynamics 12 with upgraded outboard litz wired crossovers & Fostex tweeters on 2 adjustable Polycrystal Isolator front cone feet & rear brass spike.

Extensive and ever evolving acoustic treatment including corner bass absorption, high frequency (above 2kHz) absorption at primary tweeter reflection points, high frequency diffsorbers at critical points on solid walls.

Some wire is used to join these components together. No interconnects cost more than 10% of the device at each end, much of it made by the Old Scribe from high quality components without Pixie Dust. Old Scribe amplifier-to-loudspeaker wire (full range, mid-range, tweeter) is ultra-low impedance Black Rhodium S900, a low-Z variation (3x3mm^2 csa) on the Black Rhodium S300 & S600 cable that came out well in Ben Duncan's objective and subjective correlation tests, selected primarily to match the OPT/driver damping factor, not for any magical qualities. Bass only loudspeaker cable Naim NACA5, which remains rarely challenged below 300Hz. Mains is supplied by an audio only spur and 3kVA balanced transformer due to local noise conditions, secondary tied to technical earth (ground) with Radex earth (ground) non-inductive connections. Crossover and power amplifiers fed by a minimum connections hydra. Sources and pre-amp from terminal blocks from same transformer secondary. Crossover and power amplifiers fed by a minimum connections hydra. Sources and pre-amp from terminal blocks within the audio only ring.

DISCLAIMER. TNT-Audio is a 100% independent magazine that neither accepts advertising from companies nor requires readers to register or pay for subscriptions. If you wish, you can support our independent reviews via a PayPal donation. After publication of reviews, the authors do not retain samples other than on long-term loan for further evaluation or comparison with later-received gear. Hence, all contents are written free of any “editorial” or “advertising” influence, and all reviews in this publication, positive or negative, reflect the independent opinions of their respective authors. TNT-Audio will publish all manufacturer responses, subject to the reviewer's right to reply in turn.

[Donate with Paypal!]

[Find us on Facebook!]

© 2023 TNT-Audio Mark Wheeler - -