Hafler Transnova 9500 power amplifier Relax and float downstream...

Sidebar 1: Relax and float downstream...

The Transnova idea is conceptually elegant and not dissimilar to a push-pull tube output stage. In a conventional output stage (diagram A), the "positive" or "hot" load terminal is connected to the junction between the emitters or sources of the complementary output transistors and the ground load terminal to the junction between the ±V reservoir capacitors. In general, this point defines the ground potential or 0V and is used as the amplifier's fundamental or "star" grounding reference. The output devices therefore act as emitter or source followers; they amplify current but their voltage gain is unity or less. The previous stages have therefore to provide all the amplifier's voltage gain as well as having sufficient output current ability to drive the output stage.

Diagram A conventional power amplifier output stage and power supply connections.

The Hafler, however, has the junction between the devices connected to ground, the drive to the load being taken from the junction between the capacitors (diagram B). You might think that nothing will happen, but the trick is that the common capacitor connection is not tied to ground, meaning that the power supply "floats" with respect to ground potential. When the output devices amplify the signal present on their gates, therefore, the entire power supply—capacitors, rectifiers, and transformer secondaries—is swung up and down by the FETs' sources. The common point is swept up and down with the power supply and therefore delivers current into the load. As the Transnova output FETS amplify both voltage and current, this greatly simplifies the task for the upstream circuitry.—John Atkinson

Diagram B Transnova output stage and power supply connections.

Hafler, A Division of Rockford Corporation
546 South Rockford Drive
Tempe, AZ 85281
(602) 967-3565

Anon2's picture

All these walks down memory lane make me think that, perchance, the state of the art in audio has not advanced too much. I get growing hints with these articles that perhaps I should look on eBay and elsewhere for pennies-on-the-dollar bargains (and someone to install new capacitors), instead of paying thousands, if not tens of thousands, more for successor "new gear."

Capacitors can be replaced if one finds a competent technician--and we have them in large metros. Speaker drivers can be replaced.

Are we not being told that only the Nissan 280Z, or post-1984 Corvettes, were classics that merit refurbishment, for a huge bargain, rather than paying thousands more for products that are "newer," but offer not much else on the performance front?

Worse, perhaps these articles tell us that not much has changed at all? Is the 1980s, 1990s CRT TV but still a CRT TV in new trappings in its audio, 2016 equivalent? Meanwhile, we have phones that outshine their Assembler Language counterparts of the Apollo age. We have 50" LED TVs that on a good day cost a fraction at a big-box retailer, and offer multiples of performance of their CRT 110-pound predecessors of 10-15 years ago.

Keep the articles coming. I keep thinking. Based on a recent article a significant musician, interviewed in this publication, has also thought, and opted for keeping 20-year old gear in favor of "mortgaging a house" on the latest and greatest.

jeffdyer's picture

I am sure that you are correct.

Analogue power electronics achieved almost perfect levels of realism in the 1970s, certainly since the end of the 1980s there has been little change in amplifier technology.

I'm sure you could pick up just about any 1980s quality stereo amplifier and plug it straight into your system. However, I doubt it would satisfy the AC power cable upgrade freaks out there.

Now the sources though, that's where the improvements have been made.

Herb Reichert's picture

and I always wanted one of these

Anon2's picture

I am glad that someone shares my views. I do concur that sources is where the action has occurred. It is also the one rare area of audio with a plausible better-performance-at-lower-prices that we see with TVs, computers, phones, etc. Improvement in sources also tend to re-validate the hi-fi hierarchy of old--we don't hear much of that one anymore either. Optimize the source (where the cost savings and big improvements are). Then go to amplification (again, go used and it's a bonus if you have a good technician in your locale to inspect of refurbish). Then optimize your speakers (an area where performance improvements seem spotty while prices march upward, with some exceptions).