Dumble musical instrument amplifiers are custom manufactured in very limited numbers by Alexander "Howard" Dumble of Los Angeles, California. Dumble is a one-person operation; each amp is handcrafted by Dumble himself, and Dumble amplifiers are the most expensive boutique amplifiers on the used market. These costs are rising rapidly. In 2012 the Dumble Overdrive Special was described as the most valuable, with used amplifiers fetching on average between $70,000 and $150,000 apiece. Other examples have sold for more. 
Dumble still builds amplifiers at the rate of about 2 or 3 per year, and primarily builds for celebrity musicians and studios. He asks similar prices to the used market rates in order to dissuade resale. Dumble will service and refurbish his original amplifiers for a fee, and many players will buy used Dumble amplifiers in order to have them refurbished by Dumble. Carlos Santana and Ben Harper have both said that they bought their first Dumble used, and had Dumble refurbish the amp for their particular playing styles. 
Howard Dumble began modifying Fender tweed and blackface amplifiers in 1963  in Santa Cruz. Dumble was hired by Mosrite to build a special line of Amplifiers for The Ventures before he was 21. By the late 1970s he was modifying and building high-gain amps in the way that Randall Smith of Mesa Boogie, and others did. Unlike his contemporaries, however, Dumble was not really interested in the business of selling amplifiers in greater numbers. Dumble focused solely on getting the best possible sound/tone from an amp. Building on order only (even building his own speaker cabinets by hand), his amps were regularly called the best by high end professional musicians. Howard soon became known as an electronics master, and his high end clientele gained him a reputation as the "reclusive amp tech to the stars".
Much of the company's PR over the years has been word of mouth. Although Dumble did some interviews and advertisements in the 80s, few people ever heard of Dumble, even in the professional music community. Carlos Santana, for instance, only heard of Dumble in reference to Stevie Ray Vaughan in the late 90's. After he was lent an amplifier (it wasn't for sale) he "was hooked for life." He subsequently contacted Howard Dumble, and was able to buy one used and have it refurbished. Reportedly he has since bought more.
Since the 1980s, Dumble has covered the preamp circuitry of his amps with a thick layer of usually opaque epoxy, presumably protecting his schematic's exact design from prying eyes. There are practical reasons for covering circuits in epoxy as well, as it holds the parts together and keeps them in place. One such application of this was in the 1971 Urei 1176LN version C. Bill Putnam covered the additional "Low Noise" portion he developed for the 1176 in version C with black epoxy.
Howard Dumble legally changed his name to Alexander, and prefers to be referred to as "Alex".
Models and circuitry
Since Dumble's models are individually tailored, no two amps are exactly the same. However, most of Dumble's amplifiers will fall within a few known models. These models amount to general circuit styles and chassis layouts:
The Overdrive Special is a two channel amplifier, with a clean channel and a second "overdrive" channel. This overdrive channel is described as "cascading" from the first channel into at least one additional gain stage in the overdrive channel. This means that the clean channel tone stack and gain stages "cascade" into the gain stage of the overdrive channel, causing the clean channel to become "overdriven". In a sense, the overdrive channel sits "on top" of the clean channel. This is easily Dumble's most popular model, and subsequently is the most frequently seen. That said, the ODS (Overdrive Special) varies considerably from decade to decade, and serial number to serial number. For example, although most ODS amplifiers use 6L6 tubes in the power section (commonly associated with Fender amps), some have EL34 tubes (commonly associated with Marshall amps). On the other hand, even among the many 6L6 versions of the ODS, there are considerable variations. For example, some have a clean channel that stays clean "all the way up to 10" (referencing a gain potentiometer ranging from 1 - 10). Others have a clean channel that will start to "break up" around 3. Some overdrive channels can only reach a minimal amount of breakup, even when dialed up. However, most ODS overdrive channels have a large amount of tube distortion available if so desired. Along these same lines, many later versions of the ODS have "HRM" controls on the inside of the amplifier, which is a "Hot Rodded Marshall" tone stack that sits "on top" of the overdrive channel, or in other words comes after the Overdrive channel tube gain stage.
There are certain commonalities across all ODS amplifiers. Firstly, the ODS amps are known for their harmonic richness in the overdrive channel breakup, and transparent "open-ness" in the clean channel. The overdrive channel is often described as "sustaining", "blooming", and "musical". The clean channel is often described as "fast", "huge", and "responsive". Robben Ford describes the tone of the ODS as having "a perfect sonic curve, the lows are deep and rich but not unclear, it doesn't mush out like some amps will. You have the frequencies there for your use. The mid range [is] punchy and clear and the high end, bright, clear but doesn’t hurt your ears. It’s loud but it sounds good […]."
In an interview with Premier Guitar, Robben Ford claims that Dumble told Ford that the original inspiration for the Overdrive Special came while watching Ford play live in the 70s at a bar in Santa Cruz. Ford was using a mid-60s blackface Fender Bassman, and running a tube screamer in front of it to overdrive the tubes to breakup. Supposedly, Dumble thought Ford sounded so good, and while contemplating his sound had the revelations that led him down the path that eventually birthed the original Overdrive Special. Since buying his ODS, Ford has almost exclusively used his original Dumble or an exact clone of it live.
An Overdrive Special amplifier with an internal Reverb Circuit.
Steel String Singer
The Steel String Singer is best described as an extremely adjustable single channel "clean" amplifier with reverb.. Fewer than 12 of the original Steel String Singers have been accounted for.
As is typical with the Dumble brand, the SSS (Steel String Singer) can vary drastically from serial number to serial number. For example, The first SSS (made for Henry Kaiser) has a built-in vibrato circuit. Also, despite its reputation as a "clean machine", the earlier SSS (and possibly #7) would break up when their input gain was turned up or pushed by a loud input signal. The earlier versions also had more complicated phase inversion techniques pioneered by vintage hi fidelity amplifiers, and Fender style transformers. Starting with #4, the Phase Inversion was simplified, and the amp was given more negative feedback which cleaned up the signal even further. These updates significantly changed the sound and feel of the circuit, and became standard to the SSS model from #4 and on. The sound the Steel String Singer is most known for is a "clean feedback" effect - where the amplifier will feedback, even though the signal is audibly clean. This is most notably apparent with the later SSS models, though a balance of factors contribute to this unique response, and the earlier versions as well as other Dumble amplifiers reportedly imitate this effect under certain conditions.
Most of the aspects shared by every Steel String Singer are control oriented. Every SSS has special high and low cut filters that adjust the overall tone late in the circuit. Every SSS has reverb, and every SSS has special coupling techniques and a larger chassis style. Its sound is often characterized as an extremely clean and compressed signal with dynamic response and a lush reverb circuit. Its EQ is generally considered to be relatively flat internally, but this becomes extremely malleable through the controls provided on the front panel and its overall responsiveness. There are reportedly "higher highs" and "lower lows" that are not often heard through other amplifiers, and a significant amount of harmonic response to the strength of the input signal.
Some of the notable owners and users of the Steel String Singer include: Stevie Ray Vaughan, John Mayer, David Lindley, Jackson Browne, Eric Johnson, Kirk Hammett, and Henry Kaiser.
A single channel "no frills" combo amplifier, similar in appearance to the tweed Bassman. This was the most expensive amplifier on Dumble's amplifier price sheet in the 90s. One notable original owner of a Manzamp was Bonnie Raitt.
One of the earliest amplifiers that Dumble made, this was also the amplifier that Stevie Ray Vaughan and Double Trouble used for 80% of the guitar tracks on their debut album, Texas Flood, which was recorded at Jackson Browne's studio. Browne was a long time friend of Dumble and owned some of Dumble's earliest amplifiers (including the first Overdrive Specials). Jackson Browne's collection of amplifiers is what introduced Vaughan to Dumble's amps, and Browne introduced Vaughan to Dumble so that he could buy his first Steel String Singer.
A 300 watt Dumble bass amp made in the 70s.
Despite the variability among Dumble tonestack voicing and operation, there are certain controls that most amplifiers share:
- Bass, Middle, and High frequency potentiometers.
- Two voicings to choose from: "Jazz", and "Rock"
- Boosts for each frequency - deep, and bright (some have mid boosts).
- An EQ bypass that bypasses the tonestack entirely. (Some models have an actual "boost", rather than a bypass)
- Overall power amp "Presence" control, or a "Contour" tone cut (most have one or the other, but some amps have neither presence or contour)
Dumble also made a tube-buffered external effects loop called a Dumbleator. A few Dumble amps have a Dumbleator circuit built into them, but most have "un-buffered" input jacks that tap directly out of the pre-amp and into the power amp. This external loop was likely created because of the difficulty of fitting effects loop buffering into the chassis of the amplifier (and the limited use that effects loops serve for most players). The Dumbleator has separate "Send" and "Receive" controls for the effects, and a "Bright Switch" on at least the return. Later models also have the bright switch on the send. There are also stereo versions available. This effects loop buffering is essentially a cathode follower for the send, into a gain stage for return.
- Eric Clapton (has used various Dumble amps and Dumble modified/ refurbished Fenders over the years) 
- Sonny Landreth (Overdrive Special) 
- Stephen Bruton (had a low-watt Dumble with 4 10" speakers)
- Larry Carlton Overdrive Special
- Robben Ford (bought an Overdrive Special in 1983 and had a model custom-built in 1993/4)
- David Lindley (original owner of Overdrive Special #2, and Steel String Singer #3, and used them in stereo live)
- John Mayer (Steel String Singer - also has a large collection of used Dumble amplifiers) 
- Lowell George had an early custom Dumble head he used for most of his career.
- Carlos Santana (has at least one Overdrive Reverb and a Steel-String Singer purchased in the early 2000s, and often uses Welagen clones of his Dumbles live besides his Mesa Boogies)
- Stevie Ray Vaughan (Steel String Singers - original owner of both #7 and #8, and had an association with #9)
- Henry Kaiser (1978 Dumble Overdrive Special, original and current owner of Steel String Singer #1, original owner of SSS #4, other ODS's as well) 
- Joe Bonamassa (owned 3 Overdrive Specials) 
- Keith Urban (Overdrive Special) 
- Steve Kimock – 50 watt and 100 watt Dumble Overdrive Specials 
- Ry Cooder – (Borderline Special - an Overdrive Special made for him with Tremolo) 
- Ben Harper – 3 × Overdrive Specials (50w head + 2×12" Cabinet, 100/50w 1×12" Combo, 100/40w Head + matching 1×12" Cabinet)  In March 2016, Harper explained that Dumble had him plug his guitar directly into the oscilloscope, in order to take notes about how the frequency patterns of Harper's instruments was shaped and voice his Overdive Special accordingly.
- Eric Johnson (Steel String Singer, Overdrive Special) 
- Kirk Hammett (Steel String Singer) 
- Jason Isbell (Dumble modified Fender Pro) 
- Kenny Wayne Shepherd (Dumble modified Tweed Deluxe, nicknamed "Tweedle-Dee.") 
- Jackson Browne (Original owner of Overdrive Special #1, Dumbleland, and Steel String Singer #2) 
- Bob Rock (has Dumble service his vintage amplifiers) 
- Don Felder (uses reissue Fender Tweed Deluxe amps modified by Dumble)
- Gjika Amplification
- Bogner Amplification
- Fryette Amplification
- Carr Amplifiers
- Matchless Amplifiers
- Trainwreck Circuits
other manufacturers of boutique amplifiers
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|Wikimedia Commons has media related to Dumble amplifiers.|
- "Three Ways to Nail the Dumble Sound on a Budget". Reverb.com. Retrieved May 28, 2018.