This amp first debuted in May of 2015. At that time I wanted to convert a design that had been gathering dust in my projects folder into a
real amplifier. And, I just happened to have a suitable chassis available that wasn't being used. Since then, I have had several questions from various people about using the Edcor GXSE transformers for maybe a little bit better low end response.
Well, I have finally revisited the design and have made some modifications which make the schematic better suited to the GXSEs and which I think should yield some interesting results. Here is the modified schematic:
Attachment:
Schematic_V2.jpg
In addition to the output transformer change, I have increased the cathode bypass on the power stage (to support better low end response) and increased the interstage coupling capacitance (also to support low end response).
When I first designed this circuit, I was playing with some budget output transformers that get very mushy at the low end. Some of my design decisions at that time were compromises for those output transformers; and they persisted in the original schematic. I have also changed up the power supply a little bit for better channel separation. And finally, I chose to use an Edcor power transformer for this build as it stays much cooler than the Hammond. I wanted this characteristic because the transformers will be in a wood alcove and I didn't want to thermally stress the wood any more than necessary. Additionally, the added filament winding capacity will allow me to use a jeweled indicator on the front of the amp.
And just so people don't think this is merely an academic exercise, here is the chassis in dry fit, sitting on my workbench.
Attachment:
V2_Dry_Fit.jpg
When I get a little further on with the project I'll post an update. I intend to give this amp a full set of testing for frequency response and distortion. I am shooting for marginally better performance than the original and better channel to channel separation performance.
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