History of the Dumble Overdrive Special
A little background on the Overdrive Special, and which configuration is right for me?
It’s hard to describe the characteristics of the various Sebago amps without exploring a little history regarding all Dumble Overdrive Special amplifiers, so here is a attempt to put some words to the tonal magic: No two Overdrive Specials were ever built exactly the same, but the basic circuit topology is what gives the Dumble amps their special qualities, and all Overdrive Special amps share this basic topology. The very open and uncompressed feel, overdrive without fuzz, warm sustaining cleans, and of course that saxophone -like midrange and sing that these amps are famous for all come from the cascaded four gain stage preamp and unique Dumble "tone stack". The power amp (Phase Inverter and power tubes) do have some variations, but most are a direct copy of the early Bassman (50W) and Twin (100W) style 6L6 power amps.
The major differences in Dumble circuits can be grouped by the decades in which they appeared. While not a strictly linear progression, it helps simplify the lineage to group the configurations as “70’s”, “80’s” and “90’s”. The early amps built throughout the 1970’s show the most variations as the circuit was quickly evolved and enhanced. The 70’s amps are characterized by their slightly lower gain overdrive resulting in a more “raw” overdriven tone, and not quite as much of that classic Dumble lower midrange frequency content. The 70’s clean channel is very much like a “fat” Fender Blackface Twin, very warm with that classic 6L6 sparkle but much rounder and fatter by comparison. Players that made this generation of amps famous include Lowell George, David Lindley (primarily playing slide guitar with Jackson Browne), and Carlos Santana.
Many of the 70’s amps have been upgraded and incorporate pieces of the later 80’s style circuits, mainly the “Skyliner” tone stack (more on this in a bit). The most famous Dumble players (Robben and Larry) were using later 80’s and 90’s configurations, but if you know what you are looking for and want that raw, classic rock or “edgy country” sound, then the 70’s amps can be a good choice. Sebago Sound has experimented with KT77 power tubes in the 70’s circuit with great results. The KT77’s give the clean channel a bit of that Vox like slightly overdriven clean when pushed, and a nice aggressive Overdrive breakup when pushed as well. Clips are available on the right side of the web pages.
Most of the Overdrive Special amps built in the 80’s amps are known as “non-HRM” Skyliner amps. The “non-HRM” refers to the extra tone-stack that HRM amps have after the second OverDrive stages. The non-HRM amps don’t have this tone stack and as a result the overdrive is bit more open and full sounding. The Skyliner tone stack is very balanced for both the clean and overdrive channels. There are quite a few variations on the 80’s circuit, some more appropriate for jazz/fusion playing and some more for country or blues playing. The most popular amp is the jazz voicing, which is based on Robben’s Dumble #102 circuit. The country/blues voicing is based on the #124 circuit, if you are following along with all the Dumble amp serial number discussions on the forums. Both are wonderful sounding amps, the differences are fairly subtle. The jazz voicing is a bit higher gain with some more compression on the overdrive. Terry Hait’s amp in the videos on this site is a jazz voiced amp.
If you still have questions about which amp is right for you, please contact us and we'll be able to give you all the information that will help you choose the right amp for your playing style and to reach your tonal nirvana.
