I love old and vintage amps. And this amp is no exception.
Davoli Krundaal is a company that started in 1957 in Parma, Italy. The main designer, Athos Davoli, was an electronic engineer that worked on the Savoia Marchetti fighter planes during WWII and later started his own workshop after the war. There, in Parma, he started to develop designs based upon vacuum tubes for instrument amplification. From the 60's his fame rose and most Italian bands (and foreign bands that toured Italy) used Davoli amps for their instrument amplification and PA. The peak time of Davoli was between 1969 and 1972 in which he had 220 people working full time on his amps. Around this time Davoli also released the Davolisint, a synthesizer that was completely designed by Davoli. From 1965 Davoli issued competitions on who was/ were the best music bands through the whole of Italy in which these bands could win Davoli products. His oldest son started Davoli UK Ltd in London but moved a year later back home to Parma. There he started Wilder: Willy Davoli Equipment rental, a company that would rent PA's for bigger and smaller shows.
Davoli started a partnership in 1960 with Antonio 'Wandre' Poli (1926 - 2004), a visionary electric guitar designer where Davoli would deliver the amps that were sold with the Wandre guitars. This Davoli Blue Jeans amp was one of these collaborations. This Davoli amp was usually sold together with a Wandre Blue Jeans guitar. Sadly, this amp did not came with the guitar. The Davoli Blue Jeans amp was released in numerous different coloured enclosures all with the same internal circuit. The amp as depicted here is in the white on white colour scheme.
The circuit
The amp is housed in a beautiful plastic enclosure that bears the Davoli name etched on the sides. The back of the amp is used to connect to the amp and to control the amp. The amp was issued with two DIN input connectors as was common in Italy in the 50's. Also apparent are the Banana plug inputs that one could use to connect an instrument. Two separate inputs are available for this amp in which the DIN and the Banana plug inputs are placed parallel. Both inputs have their own volume controls but both share a common tone knob. A switch is located on the back to increase the speed of the tremolo and a single remote switch is permanently connected to the amp to turn the tremolo effect on and off.
With the cardboard removed you can spot inside the amp. Inside is a metal H-frame that holds the speaker, the controls and the circuit. The H frame is connected to the plastic enclosure with four nuts and bolts securing it from movement. On one leg of the 'H' the PSU is located and on the other leg is the audio circuit. On the inside of the H the two tubes are present: a 12AX7 preamp tube and a ECL82 preamp / poweramp tube. The amp was delivered with a two prong power cable and a death cap.
A schematic can be found online here. I also traced this unit for some extra information.
This amp is a fine example of a single ended amp with the use of an ECL82 tube that houses both a preamp tube as well as a poweramp tube. The extra 12AX7 is used as another preamp stage but also to make the tremolo work. The design of the amp is pretty standard with minimal ways to control volume and tone. The tremolo circuit is also pretty common and uses some clever ways to turn this effect on as well as double the tremolo speed.
The fix
The amp came in with a two prong power cable and electrolyte caps that were pretty old and dry. I replaced the power cord and all electrolyte caps. After this change the amp worked well except for the tremolo effect. I tested most signal caps which were dry and leaky so in the end I replaced all caps in the amp. With this change the amp became stable and good sounding.
One big issue was a hum sound that was as loud as the input signal. It sounded like an instrument cable that was left connected to the amp with no instrument connected to it. Grounding the input didn't make the problem go away. After I replaced the power cable, all electrolyte caps, signal caps and the power supply (making it use silicon diodes instead of the selenium rectifier) the problem still remained. In the end the problem turned out the physical location of the power cables going to the tone knob (which houses a switch) that caused all hum and noise. By removing the power cables from this location to the PSU location all noise went away. I also tried to place the on/off switch more to the left of the right by replacing the volume knobs AND tried to replace the tone knob with a new switching tone knob. Both had no effect on the noise issues.
Presumably the death cap and the two prong power cable filter out the noise of the AC input. By replacing the cable and removing the death cap I added the noise to the circuit. I can highly recommend to replace the two prong power cable with a three prong power cable and to remove the death-cap to prevent harm to the player. This means though that you lose the ability to turn the amp on and off with the switch as you have too little free space to add an new power switch to the amp. I simply accepted it that you turn the amp on by plugging it in a power socket.
The sound
The amp sounds absolutely lovely! With it being a 1959 amp the controls are limited and the whole setup of the amp further limits the use of it. Yet, the sound is full, big and throaty considering it comes from a single 8" speaker. The sound is full of mids and therefor really apparent in a live situation. The volume it produces is enough and does sound well in a bandformat. The tremolo effect is limited with only a speed switch, yet the speeds they chose do fit the effect this little amp has. The tone control knob has a really broad range and does compliment your tone beautiful. It interacts well with the plugged in instrument; by adding pedals you'll lose this connection.
On the negative side the noise factor on this amp is pretty high. With all controls set to 0 the amp still produces white noise. And although it is easily drowned out by playing you instrument on volume, on lower volumes the noise gets noticeable. As it is fitting the design of the amp (volume / gain knob on the beginning of the amp) this noise simply fits the amp and no real adjustments can be made to lower it.
This amp is an amp that needs to be played! And after some work it sounds even better! A great little amp for that 50's vibe tones! And just looking amazing!
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