Sunday, November 18, 2012

Layout for circuit similar to 5F1 Champ


The Fender Champ is an iconic amplifier with roots going all the way back to 1948.   Noted for the simplicity of its circuit and controls (in many versions, just a simple volume knob), it's hard to imagine a simpler or lower-cost tube amplifier.  This perhaps explains why, over the years, many manufacturers have produced amplifiers with circuits that vary from that found in the Champ in only incidental ways, and why the circuit is of ongoing interest to DIY hobbyists.  Well, that and the great tube tone!   While a wide variety of Champ circuit variants have been produced by Fender, the 1958 Tweed-era 5F1 is perhaps the most enduring.  However, the layout employed in the 5F1 has a primitive ground scheme, and the amplifier is not particularly quiet.   I've been asked a few times how I would lay out such an amplifier with a more modern approach.  Note that while it employs a "bussed stars" approach, it has only *one* attachment point to the chassis for the audio circuit right at the input jack (although please note that any real-world circuit MUST also incorporate a completely sound safety earth connection from the third prong / ground of the mains power to the chassis).   The input and output jacks themselves should be insulated. The circuit shown here is fairly true to the original.  If I were to build one for myself, I would undoubtedly incorporate a few more changes to further modernize things to improve noise performance and reliability -- but purists would undoubtedly complain.  Please note that the suggested layout is a draught only, and should be thoroughly error-checked before using it as a launching pad.



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