[ Home TNT-Audio | Staff & Contacts | HiFi Playground | Listening tests | DIY & Tweakings | Music & Books ]

Zen and the art of learning from building

Building a 6080 SET amplifier Part 1

Product: DIY SET6080 Amplifier
Manufacturer: You dear reader
Price: Your mileage WILL vary - it's all up to you
Author: Mark Wheeler - TNT UK
When: Created, modified, modified again & again, & again and continually reviewed: 1997- Spring 2025

The most valuable curve in audio is the learning curve

Because it is really about the learning curve we can all undertake that will deepen our relationship with our audio experience. Building a kit is a great way to start that journey. Modifying a kit or commercial product will take us on the next steps. Scratch building from a published design is one step further. Then designing and building from scratch puts us on the bus showing the destination blind FURTHER.

Once on that FURTHER bus, we end up modifying loudspeaker drivers, ordering transformers to our own spec or winding our own inductors. We are now deeply immersed in our own counterculture loitering with fellow audiophiles on the lunatic fringes of what starts from the gateway drug of consumer electronics.

We are now in the nether world of audio madness, served in the past by specialist magazines like the wonderfully eclectic and beautifully illustrated Sound Practices and their ilk. Your Old Scribe has a complete set of Sound Practices (among other DIY audio comics), every one of which has been read cover to cover at least once and some issues several times. The build described here was the step across the threshold from casual indulgence to Class A commitment.

A First Full Amplifier Build

Building from scratch allows us to experiment with ideas promoted by manufacturers and to know exactly how it works or whether it makes any difference at all. Scratchbuilding enables us to experiment with concepts for which commentators often take positions of certainty with little evidence offered. From this point forward we are in a position to test whether there is any validity in the marketing blether about bypass capacitors, negative feedback, triodes Vs pentodes, valves vs transistors, output transformer taps...

This amplifier design was my first foray into some new audio frontiers. Your Old Scribe had previously modified or restored commercial valve amplifiers. Your old scribe had previously updated commercial transistor amplifies with better parts. Your old scribe had modified and then scratch built power supplies for amplifiers and active crossovers. Your Old Scribe had specced a custom built amplifier built in exchange for some commercial photography work. Despite this, I'd never bought sundry parts from diverse sources and made them work in a published design, let alone had the temerity to change that design while building it.

This single ended triode (SET) amplifier design was published in a diy supplement with Hi-Fi World in December 1993. The late Tim de Paravicini had designed this circuit for HFW as a low-cost introduction into the world of single ended triode amplifiers. Tim's circuit is clever enough to tolerate experiments with negative feedback. The gain is high enough for this to be an integrated amplifier with an input selector and volume potentiometer. The gain could even be pushed higher with less feedback.

Your old scribe had been conducting experiments with different cases for amplifiers and crossovers (active and passive), so this design was an opportunity to experiment with a power amplifier. Your old scribe intended for this amplifier to be integrated into an active loudspeaker system.

“How could the old scribe work the word integrated into a sentence about an amplifier that he is intending to “disintegrate” as a power amplifier?” Ask Plebs, stage left

The decision to integrate this circuit as a power amplifier in an active loudspeaker system immediately creates certain design priorities. This single ended valve amplifier being only 4 W per channel will serve treble or mid range & treble. Therefore big reserves of current for bass duties are less important than low noise and clean treble.

Knowing that this amplifier will have to harmonise with at least two, if not four other channels of amplification means that it might as well be built with similar brands of passive devices as the other channels. I have spent an inordinate amount of time testing and auditioning passive components to establish whether or not there is any audibility. This arcane knowledge might as well get used. Some ridiculously expensive Couture brands didn't seem much better, then some more modest brands with audiophile, or highly selective pretensions. Tim de Paravicini has been noticeably sceptical about the claims for certain passive components. These two positions seem to coincide for this build.

The mid-treble role affects decisions about size and type of smoothing/storage capacitors in the power supply. This design uses a solid state rectifier in an unregulated power supply. The choice of rectifier device and the first capacitor can be guided by this role as a treble only amplifier. There is a choke in the power supply pi filter, but being after the first capacitor, this is not a choke regulated supply. It is a true Pi filter. This inductor is a great advantage over a resistor at both ends of the frequency spectrum.

Fortunately, Hi-Fi World's side hustle World Audio Design, sold the transformer/choke sets separately. This enabled your old scribe to source the case work, and other components elsewhere. “The glass is only there to drive the iron” and the supplied transformers are suitably over specced and downrated. If you want to build one now, companies like Sowter and Hammond would be able to supply suitable transformers and chokes. The valve world still uses this quaint nomenclature and even the word condenser occasionally crops up.

Conclusion

Your Old Scribe has been building loudspeakers since childhood. Here in part 1 of this build, I've explored some of the reasons that we might want to build our own amplifiers too. These reasons fall into two main categories. The first is the pure joy of delving deeper into our hobby. Every new activity we try to learn kindles new neural pathways. The more neural pathways we have, the better protected we are from brain degeneration and the more able we are to apply critical thinking in other areas of our life. The second category is that of “I built that!” pride and ability to make the amplifier without compromise. We have built ourselves an amplifier that contains exactly our preferred group of features.

In this build such features include copper lined wooden casework, remote mains transformer, variable levels of negative feedback, various output impedance matches, all triode single-ended operation, good quality connectors, point-to-point hard wiring and an unusual output valve. In Part 2 we will look at the circuit design, in Part 3 it is power supply and case evolution and in Part 4 building, testing and auditioning.

Having said all the stuff about this being aimed at mid-treble application and ability, on connecting it full range to the modified Hammer Dynamics TQWP 97dB/2.83V loudspeakers, it made great sounds in all but the lowest three octaves (20-160Hz). Another two octaves down were improved with the 4Ω tap so this amplifier could achieve full range duties, especially in a single driver set up like Lowthers.

Here is the audio circuit:

Did you enjoy this article? You can support our free, advertising-free magazine with a small Paypal donation using the button below. Thank you!

© Copyright 2025 Mark Wheeler - mark@tnt-audio.com - www.tnt-audio.com.

[ Home TNT-Audio | Staff & Contacts | HiFi Playground | Listening tests | DIY & Tweakings | Music & Books ]