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). 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)
At $699US (April 2014) the new Elekit TU-8200 tube amplifier kit looks quite tempting.  What I like 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.  Additional information and details of the tube amplifier kit and sample building instructions are available on the Elekit TU-8200 page at TubeDepot.  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

28 March 2014

300B Single-Ended-Triode Amplifier

300B Single-Ended-Triode (SET) Amplifier Project

The DIY 300B triode amplifier shown below was completed by Stamou Tasos (Greece).  The 300B triode amplifier was built following the 300B single-ended (SE) tube amplifier schematic by J.C. Morrison.


DIY 300B Single-Ended-Triode Hi-Fi Amplifier

DIY 300B Single-Ended-Triode Hi-Fi Amplifier

For this single-ended (SE) 300B triode amplifier build Stamou has used premium parts, Lundahl audio output transformers and a DIY chassis. The 300B Single-Ended-Triode (SET) amplifier circuit uses a direct coupled 6SN7 driver stage. The output stage is a SE 300B triode and the maximum power output is about 8 Watts per channel. A pair of reasonably sensitive (~91 dB+) loudspeakers will be required with this 300B SET amplifier. 


300B Single-Ended-Triode Amplifier - Point-to-Point Construction

300B Single-Ended-Triode Amplifier - Point-to-Point Construction

The 300B SET amplifier was built using point-to-point construction.  The chassis for the 300B triode amplifier was also built by Stamou.  The frame is made from 20 mm thick MDF wood which was finished with spray primer and paint. The top plate is made from a 4 mm thick aluminum plate and the bottom plate from a 2 mm thick aluminum plate.   Your enclosure will require good ventilation.  "This is a great sounding 300B triode amplifier that I am sure DIYers will find to be very rewarding."  For the full 300B SET amplifier project details see the DIY 300B Single-Ended-Triode (SET) Hi-Fi Amplifier project page.


More 300B Triode Amplifiers


15 December 2013

4S Universal Preamplifier for 12A_7 Tubes

The 4S Universal preamp is a Super Simple Single Stage (4S) line stage preamp that works well with the entire range of 12A_7 tubes - 12AU7, 12AV7, 12AY7, 12AT7, 12AZ7, and 12AX7. You can change the tube type to vary the gain of the preamplifier by quite a large margin. 

4S Universal Preamp for 12A_7 Tubes
4S Universal Preamp for 12A_7 Tubes
The preamp uses a 6CA4 tube rectified power supply which is very quiet. The preamplifier is built using point-to-point construction techniques and into a die cast aluminum enclosure from Pomona.  The attenuation control is on the output of the preamp.

4S Universal Preamp with 6V6 Lacewood Amp
4S Universal Preamp with 6V6 Lacewood Amp
The 4S Universal is a preamp that can be adapted to the task at hand simply by swapping tubes. It also allows some tube rolling to compare various tubes in your stash. The 4S Universal preamp is a great little unit to really bring out the most in your power amps.  For full details see the 4S Universal Preamplifier Project pageComments and questions about this project are welcome in the 4S Universal Tube Preamp Project (12A*7) thread.

Super Simple Single Stage (4S) preamp with Genalex Gold Lion 12AU7
Super Simple Single Stage (4S) preamp with Genalex Gold Lion 12AU7
The photo above is one of Mark's Super Simple Single Stage (4S) preamplifier builds.  For more information see Mark's 4S Universal Preamplifier for 12A?7 Valves.

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