The first post in this series developed into a design manifesto – a retrospective on everything I’ve learned both as a designer and music lover.
Never lacking something to say, it quickly became apparent that this would be a multi-part series.
In this post, I’m going to cover my breadboarding approach: selecting the basic architecture, defining/refining the layout along with initial parts selection.
For those of you unfamiliar with the breadboarding concept, think of it as rapid prototyping. The idea is to have a system which allows you to quickly change parts, layout, and architecture.
As your design evolves, you can settle into something that approximates the look of a production amplifier. Bear in mind that moving to this next stage means that the implementation will be less flexible, and it will discourage you from exploring design options and making changes. It’s best to let the design sit a bit before moving to this stage.
Not shown in any of the photos are two filament transformers. They were introduced at about the 6th iteration, while still prototyping on this MDF base.
Many of my respected friends claim that your breadboard amplifier will be the best sounding amp, and that packaging it into its final chassis will result in unavoidable compromises (eddy currents and such).
I have not found this to be the case, and I’ll discuss in a later post.
Breadboarding is a means of testing your circuit and component layout. I’ll use many high quality parts (i.e transformers, resistors and capacitors), but in the initial iterations, there’s no attempt to optimize this. In my humble opinion, a good circuit should benefit from good parts but it should not require them in order to sound good.
I had a pair of amplifiers from a well-known manufacturer in my house and they weren’t working for me. When I quizzed him about this, his first question was “what power cord are you using?” That would not be the first question I asked if I were in his shoes. An amplifier should sound fine with a garden variety power cord. Yes, it will improve with a good one, but if it’s a capable design, it should not require it.
In the photos, you’ll see gray, rectangular tube sockets. These are relay sockets and they allow you to easily change the layout. Better sockets sound better, but again … at this point, the object is to flesh out the design/architecture, and the design flexibility conferred by these sockets is beneficial.
There were a few other parts compromises in the early stages – specifically, the hookup wire, input jacks and the binding posts. Capacitors had yet to be experimented with as well.
As the design evolved into the pre-production prototype, a copper ground plane was added, the layout matured (shorter signal path), and parts improvements were implemented.
In part 3 of this series, the design has matured, and we cover some design changes implemented to clean up the layout and improve serviceability.