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.

More Single Driver DIY Speaker Projects

• Zigmahornet Speakers with Fostex FE103E / FE103En
• Fostex FX120 DIY ML-TQWT Speakers
• Fostex FX120 DIY Bass Reflex Bookshelf Speakers
• Fostex FE206En Double Bass-Reflex Speakers

6DJ8 Tube Headphone Amp

We are always on the lookout for good headphone amplifiers and here is a great simple tube design that will work with a wide range of headphones.  This tube headphone amplifier design comes to us from Bruce Heran.  The tube headphone amplifier is designed along the lines of the Oddwatt power amplifiers with the exception that this headamp does not require a driver stage. The headphone amplifier uses only one 6DJ8 tube per channel in a push-pull configuration.  All the circuit gain is in the single output stage. A constant current source (CCS) is used on the cathodes to force class-A operation. The headphone amplifier circuit has no coupling capacitors and no feedback loops.  There are a total of only 7 components including the tube in each channel.  The output stage is transformer coupled and the two transformer choices will accommodate most headphones with an impedance between 32 and 600 ohms.

6DJ8 (ECC88) Valve Headphone Amplifier - Inside

6DJ8 (ECC88) Tube Headphone Amplifier - Finished

The frequency response at the 50 mW level is from 20 Hz to 28 kHz within 0.5 dB and the wide band signal-to-noise is at -84 dB. Power consumption of the headphone amplifier is approximately 20 Watts (W).  Bruce reports excellent results with his Koss Pro4AAT (250 ohms) and Sennheiser HD-280 PRO (64 ohms) headphones.  "there was no audible noise or hum and the response was rich and clean"  For full project details, see the DIY 6DJ8 (ECC88) Tube Hi-Fi Headphone Amplifier Project page.

More DIY Headphone Amplifier Projects:

• IRF610 MOSFET Class-A Headphone Amplifier
• DIY CMoy (Grado RA-1 clone) Headphone Amplifier
• 12AU7 (ECC82) Tube / IRF510 MOSFET Headphone Amp

Push-Pull EL84 Mono Block Amps

 Mono Block Ultra-Linear Class-A Push-Pull EL84 Tube Amplifier Project

Recently Bruce has been enjoying his PoddWatt amplifier and the EL84 tube sound that he has revisited the original OddWatt amplifier project, tweaked it and put together an improved EL84 push-pull amplifier.  Like the previous EL84 projects the Mini Block amplifiers use a EL84 self-inverting push-pull output stage that is biased into class-A operation.  The big difference is that the amplifiers are built as mono blocks.

Mini Block Push-Pull EL84 (6BQ5) Valve Amplifiers

Interior - Mini Block EL84 Push-Pull Amplifiers

The input circuit is a 5751 SRPP.  The ouput uses the ultra-linear connection and output power was 5.8 W @ 2% distortion and less than 0.25%  at 1 W.  The measured frequency response was 10 Hz to 44 kHz within 0.2 dB.   Bruce reports that the Mini Blocks have slightly more output power than the Poddwatts and seem to have more detail while retaining all the good characteristics of the stereo Poddwatt amps.  Full details are available on the Mini Block Ultra-Linear Class-A Push-Pull EL84 (6BQ5) Valve (Tube) Amplifier Project page.

More Mono Block Tube Amplifier Projects

• Push-Pull KT88 Tube Mono Block Amplifier Kit
• KT88 Push-Pull Mono Block Tube Amp Project 

Fostex FE206En Double Bass-Reflex Speakers

Fostex FE206En Double Bass-Reflex Speakers

Fans of low power tube amps love high-sensitivity full-range drivers like the 200 mm Fostex FE206En and with good reason.  The drivers are relatively inexpensive, they sound good and they do not require a crossover.  The main reason for the fan fare is because of their high sensitivity (96 dB / 1 W / 1m), which makes them ideal for use with very low power amplifiers.  However, the high sensitivity and wide frequency bandwidth of the driver come at a cost - a very low mass paper cone and a tiny excursion (Xmax=0.8 mm).  This adds up to mean that extracting bass from the Fostex FE206En is often a challenge.  The common solution to this challenge is a large back-loaded horn type enclosure.

Fostex FE206En Back-Loaded Horn Speaker Enclosures 

The problem is that these elaborate back-loaded horn type enclosures often require a skilled woodworker to construct.  The Fostex FE206En driver datasheet also include a recommended enclosure plan for a suitable bass-reflex type enclosure which is far easier to construct.  Mark has built a couple sets of the Fostex FE206En double bass-reflex speakers and reports that the simple enclosure works well with the FE206En full-range driver.

Fostex FE206En Double Bass-Reflex Speakers 

Since Mark will be using the speakers as part of his home theater setup, undercoating paint was used for a stipple like flat black and non-reflective finish.  Mark reports that the speakers are an excellent mate for use with his 6EM7 SET amp.  Full details are available on the Fostex FE206En Double Bass-Reflex Speaker project page.

More Single Driver DIY Speaker Projects

• Fostex FE103En Bass-Reflex Monitor Speakers
• Zigmahornet Speakers with Fostex FE103E / FE103En
• Fostex FX120 DIY ML-TQWT Speakers
• Fostex FX120 DIY Bass Reflex Bookshelf Speakers