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SongBird : Block Diagram

May 30th, 2011 · No Comments · Design, Songbird

Getting started designing an Amp means making quite a few taste decisions up front. The only thing you really know about the amp is there is going to be a guitar plugged into it. The next few moves are up to you before you can start with circuit design.

The Bedroom Blaster.

My goal here is that creamy SE distortion at low bedroom volumes. I want low watt output, preferably even lower than the 5 Watt Skylarks and Champs. But maybe.. in the back of my mind.. I might want to boost that a bit sometimes. I also want a lot of flexibility in the amp topology. Basically, anything that can be switched, will.

Here is what most small SE amps look like :

Basic SE Topology

Basic SE Topology

Input to preamp to power amp to speaker. Just about as basic as it gets. Very little changes between the various SE amps (at least the ones that I fool with).

Amp Preamp
Champ 5C1 6SJ7 6V6 Pentode Preamp
Champ 5E1 12AX7 6V6
Champ 5F1 12AX7 6V6
Gibson Skylark (50’s) 12AX7 6V6
Gibson Skylark (Medalist) 12AX7 6BQ5

Because I want to drive it hard, and I know a bit about SE amp topologies, I know that I want to add a second preamp stage to my amp. A single 12AX7 with its two triodes is easily capable of blasting past the limits of a 6V6 output tube, so we know we will have to find a way to contain two full stages.

Now if I want to double the output, I could, in theory have a second output tube in parallel and maintain Class A1 amplification. This is not the same as Push-Pull, which most two tube amps do, and is Class AB1 (usually). I think the GA-6 ‘Gibsonette’ used parallel output tubes in Class A SE config.

Here is a slightly expanded block diagram :

Songbird Block Diagram

Songbird Block Diagram

No decisions yet about that second output tube, but I have an extra tube socket..


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