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.

14 July 2013

Cheap Open Baffle Speakers (COBIES)

Bruce has put together a pair of Cheap Open Baffle Speakers - the COBIES.  Relative to most DIY speakers this open baffle project will be quite easy to build.  One of the main design goals for Bruce was to keep the total parts cost under $150US.  The open baffle speaker project was inspired by the "Big Air" open baffle system by Jim Strasser.  

Cheap Open Baffle Speakers
COBIES - Cheap Open Baffle Speakers
Each open baffle uses a GRS 12PF-8 woofer and two Goldwood GT-25 paper cone tweeters.  One tweeter is mounted on the rear of the baffle pointed upwards about 45 degrees.

Rear Mounted Goldwood GT-25 Tweeter
Rear Mounted Goldwood GT-25 Tweeter
Bruce experimented with various crossover points settling on 3.6 kHz finding that lower crossover points put too much of a demand on the GT-25 tweeters.  Using a calibrated microphone and RTA the in-room response from 100 Hz to 10 kHz was quite smooth and free of any large irregularities. Response below 100 Hz was affected by room nodes but quite good down to 40 Hz.  Above 10 kHz was certainly excellent (up to about 18 kHz).  The overall speaker system sensitivity is estimated at 93 dB / 1 watt at one meter. Bruce uses a pair of 5 watt (each) tube mono block amplifiers (EL84 PP) with the open baffle speakers. 

"The sound is something you will either love or hate. As I said earlier open baffle speaker systems are bi-polar. I really like it, some individuals will not. The speakers have an excellent overall sound. They have a lot of ambiance and provide a good listening experience. Bass is quite clean and robust ..."

Full details are available on the  COBIES (Cheap Open Baffle Speakers) project page.  Comments and questions about this project are welcome in the Open Baffle Speaker Project thread.

15 April 2013

DIY Nearfield Monitor Speakers with Fostex FE103En

Fostex FE103En DIY Bass Reflex Bookshelf Speakers

These small computer desktop speakers were built using the in-expensive Fostex FE103En fullrange speaker drivers following the bass reflex enclosure box plans that were provided with the FE103En datasheet.  The enclosure volume is noted as 6 L and tuned to 95 Hz but the the gross volume was calculated to be 6.9 L and the box tuning frequency to be about 97 Hz.  The Fostex FE103En drivers are 100 mm in diameter and have a rated sensitivity of about 89 dB / 1 W / 1 m.  There are a couple of easy modifications that can be made to improve the FE103En drivers which are described in detail on the modifications and tweaks for the small Fostex fullrange speaker drivers information page.  A photograph of the stock Fostex FE103En drivers is shown below.

Fostex FE103En Fullrange Speaker Driver
The speaker cabinets are built from 15 mm thick Baltic birch (11 ply multiplex) plywood.  Acousta-Stuf fiber fill is used inside the speaker enclosure to dampen the rear wave from the driver and to reduce standing waves and internal reflections.  The finished speakers are shown below with the computer.  Since this position the speakers are used in the nearfield, there is no need for a baffle step compensation filter.  The  Fostex FE103En DIY Bass Reflex Bookshelf Speakers project page has full details regarding baffle step compensation for farfield use and pairing the speakers with a subwoofer.

DIY Bass Reflex Monitor Speakers with Fostex FE103En  
These little speakers have bee in use with the desktop computer in the office for a few months now and I am quite pleased with the end results.  With no crossover or filters the speakers deliver wonderful playback full with rich details.  For full project details see the Fostex FE103En DIY Bass Reflex Bookshelf Speakers (Nearfield Monitor) project page.