"Wealth will increasingly be defined by our ability to go offline whenever we want." - Fernando Gros
0 items in your cart
$0
Blog // Thoughts
May 13, 2011

The Amp Building Thing

Although I didn’t spend any time tinkering or making on my recent trip to Adelaide, I did pull some old amplifier schematics books out and cook up some ideas with my father. His background is in tube (valve) audio which, in its day, was kind of the tech/geek frontier we now associate with the web, […]

Point To Point

Although I didn’t spend any time tinkering or making on my recent trip to Adelaide, I did pull some old amplifier schematics books out and cook up some ideas with my father.

His background is in tube (valve) audio which, in its day, was kind of the tech/geek frontier we now associate with the web, apps and tech start ups. It’s always fascinating to me that the technology we might now consider old and antiquated was once cutting edge and new. Mark my words, first generation iPods and black PowerBooks will one day be “retro.”

In fact, this is a new golden age for old audio technology, especially in professional recording studios. And, audiophiles are buying back into vinyl and tube amps in a big way – even horn based speakers are back in vogue.

When I was a kid tube amplifiers were out of fashion for guitarists. Most players wanted (supposedly more reliable) transistor amplifiers, often with multiple channels, loads of tone controls and other effects. Even when tube amps started to come back into prominence, they mimicked the complexity that players had gotten accustomed to in transistor amps.

But, there is a certain kind of appeal in plugging a good guitar into a simple, one channel tube amp, with a limited number of controls. It’s a purity thing.

And, it’s also a freedom thing. Guitarists love to play simple tube amplifiers for the same sorts of reasons that draw people to vintage motorbikes, or sailing boats, or cooking from first principles. It’s just you and the open road, or the ocean, or the fresh ingredients.

So, we looked at the original Vox AC4 schematic and early 50s Supro design. I’ve never built an amp with a tube rectifier (the part of the circuit that feeds the correct voltage to the tubes) and I’m keen to build an amp with only one or two controls. Something simple and direct.

But, my eye also caught some of kits Mercury Magnetics sell, for upgrading current, mass produced tube amps. For example, although the new Fender Champ looks great, it sounds stiff and brittle. Mercury Magnetics sell a kit to upgrade the amp with a better speaker and better transformers – very tempting (and do-able in my Hong Kong apartment).

Part of the appeal of tube amps for me is that the electronics have a wonderfully physical nature to them. Although modern computerised devices can often be built smaller and cheaper with little effect on their performance (up to a point), tube amps are more subtle and sensitive.

The placement of the components effects their sound and performance. Tubes have sonic properties that come directly from the way they are manufactured. Transformers will sound different depending on the way they are wound and the metal used for their magnetic components. Speakers are the same – drivers with ceramic magnets have a different sound compared to those using AlNiCo, or other metals.

And, the electronic design is conceptually different as well. Sure, the same principles of electronics apply – there are circuits governed by rules and equations. But, there is no programming, which is striking given that code now permeates even the most basic of contemporary electronic devices.

Code-less sonic freedom in a box – I love it!

Tagged
3
Responses
Toni 12 years ago

Amp building is fun, especially when you hear your new build for the first time.

Something worth bearing in mind: if you’re building a small single ended design like an AC4 cone or similar, a valve rectifier should not make a difference, tonally speaking, than a solid state one that produces the same voltage. An SS rec will normally provide a higher voltage from a given input, and that can make the amp a little cleaner and stiffer, but this can be reduced with appropriate resistors or a zener diode.

If you’re thinking about swapping transformers on a champ then it’s well worth looking at Heyboer for a nicely custom designed one. MM did (do?) an upgrade kit for the Epi valve Junior that was inappropriate (a choke for an amp using 1 EL84!) and cost around 2.5X the original amp cost. You could probably reduce stiffness by dropping smoothing cap capacitance and rebiasing the 12AX7 a little warmer.

If OTOH you’re thinking about a custom build then I’d love to see and hear the results.

Toni 12 years ago

BTW I didn’t say it before, but that’s a nice PTP build in the image. Is that one of yours or your dad’s?

    Fernando Gros 12 years ago

    Toni, thanks for your comments. That’s one I soldered under my dad’s supervision. His ones looks neater!

    I will document anything we build for the blog.

Leave a comment

Enter your and your to join the mailing list.