05 July 2015

DIY 6EM7 Single-Ended Triode (SET) Amplifier

This unique looking hi-fi amplifier was put together by Matt in a vertical wooden chassis that has been styled after early vacuum tube equipment of the 1920s.  The amplifier uses a single 6EM7 tube per channel.  

 6EM7 Single-Ended Triode (SET) Amplifier
 6EM7 Single-Ended Triode (SET) Amplifier

The 6EM7 tube has two dissimilar triodes in one envelope.  One is a high gain, low power unit intended as an amplifier or oscillator, and the other is a higher power unit originally intended to drive the magnetic deflection coils on the back of a CRT.  Together the tube sections are well suited to create a nice little audio amplifier with just one 6EM7 tube per channel.  The clean output power from the 6EM7 SET amplifier is 2.2 Watts per channel and the frequency response is consistent with the advertised performance of the Edcor audio output transformer (40Hz to 18kHz).

Matt reports that the single-ended 6EM7 amplifier sounds wonderful!  Bass is well articulated without being boomy, mid-tones are clear and even, and the highs are crystal clear. The amp has exceptional transient response; reproducing my favorite classical recorder piece ("Frederick The Great : Sonata in B-Flat - Allegro" performed by Michala Petri) with clarity, lightness, and vibrancy.

For full details, see the 6EM7 Single-Ended Triode (SET) amplifier project page.

01 September 2014

Fostex FE206En Rear-Loaded Horn Speakers

Once again Mark tries on the Fostex FE206En high sensitivity fullrange driver, but this time in large rear-loaded horn loudspeaker cabinets. The horn speaker cabinet plans are from the FE206En driver datasheet.
Fostex FE206En Rear-Loaded Horn Speaker Cabinet
Fostex FE206En Rear-Loaded Horn Speaker Cabinet
Each horn speaker cabinet is made up from thirty-six pieces of 21 mm thick pine plywood.  Australian beeswax is used on the outside of the horn cabinet and heavy cedar oil was applied to the mouth of the horn.

The sensitivity of the FE206En driver is greater than 96 dB / 1W / 1m, so the rear-loaded horn speakers are very well suited for use with very low power tube amplifiers.
Fostex FE206En Back-Loaded Horn Speakers with 6EM7 SET Amplifier
Fostex FE206En Back-Loaded Horn Speakers with 6EM7 SET Amplifier
Mark reports very good performance from the back-loaded horn speaker cabinets.

"Where this type of single driver loudspeaker system does shine is in it's ability to image. The back-loaded horn speakers can draw an extremely accurate soundstage. This is due to the fact the all the music is coming from a single point and is not smearing the sound over multiple drivers." 

"Big, bold and made of pine they are. Excellent sounding they are also. For me, with my Paris amplifier (dual mono SE 6EM7 integrated with 4S tube preamp) in triode mode, the combination of a high sensitivity speaker, razor sharp sound stage and extended and very clean mid-range, can lead to a whole new listening experience." 

Full project details are available on the Fostex FE206En Back-Loaded Horn Speaker page.

27 July 2014

Gobo LM1875 Amplifier Kit

The sharp looking amplifier below is the Gobo Stereo Audio Amplifier from boxkedkitamps.com which is sold as DIY kit.  We have completed a review of the Gobo LM1875 stereo amplifier kit which is available on the main site.  The Gobo kit is a class-AB chip amplifier kit that uses the LM1875 IC. The LM1875 amplifier kit includes all the required parts and enclosure to build a complete stereo amplifier. 

Gobo LM1875 Stereo Amplifier Kit
Completed Gobo LM1875 Stereo Amplifier Kit

The kit comes with a very detailed step-by-step instructions that make it possible for a first time amp builder with only soldering skills to complete the kit.  The amplifier kit comes with good quality parts like audio-grade capacitors from Nichicon Muse, Panasonic and WIMA.  The linear power supply for the amplifier kit makes use of a audio-grade toroidal transformer from Antek.

LM1875 Amplifier PCB modules
Assembled LM1875 Amplifier PCB Modules

LM1875 Amplifier Kit
Assembly - Gobo LM1875 Amplifier Kit

The completed kit really looks great.  The enclosure of the LM1875 amplifier kit is made from translucent blue acrylic plastic.  The rounded sides of the enclosure are very precisely laser cut hinges that allow you to bend and fold the plastic over to form the enclosure.

Gobo LM1875 Amp Kit + NAD C516BEE + Fostex FE206E BLH Speakers
Gobo LM1875 Amp Kit + NAD C516BEE + Fostex FE206E BLH

Above, the finished Gobo LM1875 is matched up with a pair of Fostex FE206E back-loaded horn (BLH) speakers and a NAD C516BEE CD player.  The amplifier is very accurate and  neutral with strong and accurate bass response.  The midrange and top end response is extended and sounds natural and detailed with no coloration.  Coupled with sensitive single-driver loudspeaker systems the combination is very revealing of recordings.  For the full details of the DIY kit, see our review of the Gobo LM1875 stereo amplifier kit

More Chip Amp / Gainclone Amplifier Projects

22 April 2014

Elekit TU-8200 Tube Amplifier Kit (SE 6L6)

Over the past several years I have been enjoying an Elekit TU-879S Stereo Tube Amplifier Kit paired up along side of Fostex FE206E high sensitivity speaker drivers in Dallas rear-loaded horn enclosures.  I put a number of hours on the Elekit TU-879S, enough to fully consume the stock EH 6L6 tubes and to cycle through a number of power tube sets before deciding on JJ EL34 blue glass tubes.  Throughout this time the Elekit TU-879S amplifier has been reliable and a good performer sonically so it was disappointing to hear that the popular TU-879S tube amp kit had been discontinued. 

Elekit TU-879S with Fostex FE206E Rear-Loaded Horn Speakers
Elekit TU-879S with Fostex FE206E Rear-Loaded Horn Speakers

However, there is good news - the follow-up tube amplifier kit to the Elekit TU-879S, the Elekit TU-8200 is now available from TubeDepot (USA) and VK Music (Canada).  The renowned Elekit designer, Mr. Fujita, has gone back to the drawing board to design a superior tube amplifier kit from top to bottom. The Elekit TU-8200 will allow the kit builder to enjoy fine tube audio sound in just a few evenings.

Elekit TU-8200 - 6L6 Tube Amplifier Kit - Parts
Parts - Elekit TU-8200 Tube Amp Kit

Some of the improvements over the Elekit TU-879S tube amplifier kit include:
  • Three Selectable output modes - Ultra-linear, Triode, or Pentode by changing a jumper on PCB.
  • TU-8200 kit ships with a R-core power transformer that supports 100V, 115V, 200V, and 230V mains. 
  • Improvements to the audio and power supply circuitry.
  • Headphone output.
  • Optional Elekit PS-3249 DAC to decode audio from computer USB source.
The Elekit TU-8200 tube amplifier kit ships with Electro-Harmonix 6L6GC power tubes, but will also accept a wide range of other power tubes such as 6CA7, EL34, KT66, KT77, KT88, 6550 (and more) with no modifications and no need to re-bias.

Elekit TU-8200 - 6L6 Tube Amplifier Kit - Rear
Elekit TU-8200 - 6L6 Tube Amplifier Kit - Rear

Elekit TU-8200 Main Specifications
  • 2 X 12AU7, 2 X 6L6GC (can also use 6CA7, EL34, KT66, KT77, KT88, 6550)
  • Output Modes: Ultra-linear, Pentode or Triode mode
  • 6L6GC (Ultra Linear) 8W + 8W  (8 ohms)
  • 6L6GC (Pentode) 8.2W + 8.2W  (8 ohms)
  • 6L6GC (Triode) 4W + 4W  (8 ohms) 
  • Speaker Impedance: 4-6.3 ohm and 8-16 ohm
  • Headphone: Standard jack (6.4mm DIA)
  • Power Consumption: 60W (with 6L6GC)
  • Weight: 14.55lbs (6.6 kg)
  • Dimensions: Width 9.92" (252mm) x Height 6.22" (158mm) x Depth 11.22" (285mm)
The new Elekit TU-8200 tube amplifier kit looks quite tempting.  What I liked most about the TU-879S tube amplifier was the seemingly endless amount of tube combinations that were possible.  With the TU-8200 tube amp kit and the ability to select between Ultra-linear, Pentode or Triode output modes, the number of possible tube combinations are endless.  We are planning to take a closer look at one of the Elekit TU-8200 tube amp kits soon so please stay tuned for more updates.

Elekit TU-8200 - 6L6 Tube Amplifier Kit
Elekit TU-8200 - 6L6 Tube Amplifier Kit