Single Ended Tube Amplifiers

Listener Impressions by Francesco Pintavalle

 March 2000

0. Intro

Andrea Ciuffoli Single ended amplifiers (published on Audio Design Guide) are the last creation of this world renowned audio designer, in search of definitive sound for its system. The technicalities are best described in the project pages, nevetheless I would like to recall some of the important aspects of those two amplifiers.

The topology chosen for both of the devices resembled a bit the Sakuma style. It works in pure A1 class, the power stage is coupled to the driver tube with a 1:2 transformer - good decision but only for a null grid current setup - the bias is fixed for the power stage (even if there was an automatic bias setup made for testing purposes). The power supply is very very strong with a double L filer fed by a couple of good GZ34.

  1. Tubes: 2x Rytheon 5842, 4x Svetlana 300B, 2x Mullard GZ34.
  2. Magnetics: Lundhal for all the magnetic devices.
  3. Passive: Caddock resistors everywhere, all caps are Elna Cerafine.
The Listening test has been performed in a rather small room, with a system setup ...

Reference Equipment

  1. Transport source: CD player Philips CD723
  2. DAC: Andrea Ciuffoli DAC 2.0 (see the project pages)
  3. Preamplifier: None, direct connection to the Power Amplifier
  4. Speakers: 2 ways self made with a TQWT low frequency unit with 20W75 Esotec Dynaudio driver (200mm) and a HD14D34HR Audax dome tweeter (34mm). Crossover point @1550 Hz 20dB/dec (1st order)
  1. J.S. Bach: die Kunst der Fuge, Experion XX, Astree
  2. L. van Beethoven, 5th/7th/8th Symphony, ..., ...
  3. Pink Floyd, ..., ...
  4. Bruce Springsteen, Tunnel of Love, ...
  5. many CD by Fonè

1. PSE listening session

Due to the usage of a fully transformer coupled system, the amplifier seems to disappear, especially when set up with a fixed bias for the power tubes.

The Soundstage is really impressive, stable, clean, open, wide. Instruments are perfectly positioned in the acoustic scene. The depth of the musical event is really stunning, as well as its elevation. I can 'see' the natural dimensions for each instrument.

Power is more than what can be required for a good level of pressure. In particular with complex musical events, like orchestras, there are no compression effects at any volume.

Low level details are unmatched.

2. SE listening session

Lower power has its effects, considering that the loudspeakers userd for this test are 84dB spl @2.83V it is not a problem!

The image is something less stable than the PSE, but such an effect could be generated by the usage at the power limit of the amplifier itself.