Why split chassis?

[Leonc]

I'm not sure I've seen this discussed here: what was the purpose of splitting the chassis into power amp and pre-amp sections? I've seen references in old Supro catalogs which seemed to imply that this translated to quieter performance...which has not been my experience with my three old Valco amps with split chassis, LOL. Of course, they are old and there are many other factors at play. But...anyone know why these sorts of designs were used for a while back in the past?

 

[teemuk]

Modularity?

 

[WaltC]

I think it has to do with the evolution of the guitar amp. If you think about it, the early amps had one chassis on the bottom with the plug and controls down there. Then they moved the plugs and controls up to where it was easier to work with them, but left the weight (Trannies and such) down low so the amp wouldn't be too top heavy, plus several different models of amps might use the same power section with different pre-amp sections, and only the upper chassis and pre-amp would have to be changed, then some folks (Leo Fender and company) moved both to the top with the Tweed stuff and decided that the trade-offs were worth it and carried on that way.

Keep in mind that lots of Valco/Supro/CMI amps were made for different companies (Gretsch, Airline, Silvertone, etc.) and they could use the common power sections and tailor the pre-amp/controls/inputs to what each company wanted.

 

[Leonc]

Good points. Another company that appears to have stuck with this approach for a while in some models was Sano and it seems like they also made amps for a few different brands.

 

[macula56]

the new Excelsior from Fender is built like that.

 

[Leonc]

Yeah, but in their case, I'd bet it was only done as an attempt to nab some of that authentic "vintage" vibe, from a marketing angle.

 

[Rambergwest]

If the original question was not historically framed you would say that it is to prevent the power supply from injecting noise into the preamp section. The idea is hifi oriented and does have the potential to lower the noise floor when used with a proper circuit design.

 

[Prairie Dawg]

That is probably the reason, to eliminate crosstalk. Some of the old Danelectro made amps were built like this and had a single preamp tube located in the upper chassis-some like my Sherwood had everything downstairs and the power switch, controls and trem stuff up in the top. probably also for ease of access.

It's not a bad way to build things if you ignore all that juice running up and down the wiring bundles.

Of course Danelectro was, at that time, into doing stuff like running the filament of the first preamp tube as part of the cathode resistance for the power tubes.