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 NEW    Bruce Heran outlines the details and construction of his simple DIY 6DJ8 (ECC88) Tube Hi-Fi Headphone Amplifier Project.

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KT88-OddWatt-and-ForeWatt-Preamp.jpg
KT88-OddWatt-and-ForeWatt-Preamp.jpgKT88 OddWatt Tube Amp and 5751 ForeWatt Tube Preamp2814 viewsWooden enclosures for a pair of Bruce's KT88 OddWatt Tube MonoBloc Amplifiers. Between the two mono amps is a new project - a 5751 (SRPP) ForeWatt tube preamplifier. The KT88 tubes are JJ / Tesla KT88 Blue Glass.
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PDC400s.JPG$50 Teac PDC400, as good as a $700 NAD C5422811 viewsOf course in its day this five CD player with four times oversampling and dual DACs would have cost a lot more than $50. But from a secondhand store, in a sleepy fishing village in southern Australia, this was a real steal! It has removable cover and hinges. No remote. And it works 100% flawlessly and is in excellent condition. Seen here with my headphone driver and ATH-AD700 headphones. I obtained two identical CDs and identical cables and put both the NAD and Teac through an A/B switch.Queued both CDs perfectly and switched from NAD to Teac repeatedly to try to resolve which played better. There was absolutely nothing between the two. The Teac performed as well as the NAD in every area. I have been told that if Teac went to the trouble of installing dual DACs it would definitely be a good player. I have about thirty hours of play on it in a very short time and it delivers clear and detailed music and works very well with my 2N3055 based headphone driver. Yes, a real steal!
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IMG_1960.JPGMini 12AU7 Tube Preamp2803 viewsAnother picture of the 12AU7 tube preamp close up showing the input/output plugs on the side. The preamp got its name from being nearly impossible to wire the internal parts because of the small case.
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12AU7-IRF630-LM317-headphone-amplifier.JPG12Au7 / irf510 Headphone Amp2795 viewsThis is the final amplifier. Takman metal film resistors everywhere except for the pink ones (cathode resistors) which are carbon film. Elna Silmic II Electrolitic capacitors and Solen film capacitors. The sound is great!

Project Link - DIY 12AU7 (ECC82) / IRF510 Headphone Amplifier
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KT88-Push-Pull-Tube-Amplifier-Cover.jpgKT88 Push-Pull Tube Amplifier (monoblock)2783 viewsThe third of the "OddWatt" tube amp projects. This one is the Odd Blocks which will work with a number of octal tubes (KT77, 6CA7, EL34, 6L6GC, KT88, KT90, 6550). The driver stage is an SRPP using a 12SL7 tube. For the amp shown above, the output stage is a Class A UL SIPP using Gold Lion KT88 vacuum tubes. LM317 Regulators are used to provide the cathode CCS.

For more information, see the 12SL7 SRPP / KT88 Push-Pull DIY Tube Amp project page.
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EL84-Push-Pull-Tube-Amplifier-OddWatt.jpgEL84 Push-Pull Tube Amp after OddWatt2759 viewsEL84 Push-Pull Tube Amplifier built following the concepts of the OddWatt EL84 Push Pull Tube Amplifier Project.
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OPA2134-opamp-Headphone-Amplifier.jpgOPA2134 CMoy Style Portable Headphone Amplifier2738 viewsThis simple headphone amplifier is based on the high performance OPA2134 opamp chip. This headphone amp\driver is good sounding and portable. The schematic is based on the very popular CMoy headphone amp design with some changes in passive parts values. For the power supply I elected to power the amp from two 9V batteries (18V) which provides longer playback time and greater dynamics.

There is only 100 mm of hookup wire in the signal path and all connections are component-2-component on the protoboard. Low ESR 200uF caps and a resistive network provide the differential voltages required to operate the chip without an output capacitor. The brd. is silver soldered with Mil. spec machined chip socket and Russian PIO caps on the input. Power only comes on when both phone jacks have plugs in them and the power switch (at the back) is on. The enclosure is impact resistant and lined with heavy aluminum foil for shielding and enclosure resonance control. The sound is clean and bright with good volume and dynamics. The amp is dead quiet with no signal.
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TeaBoxII.JPGTea Box 12AX7 Valve Preamp II2730 viewsSee the previous photo for more detail. In this image you can see the solid brass cones, 4oz brass knob and another view of the preamp. The SMPS is contained inside making one very neat and attractive looking valve preamp. Golden Dragons replace standard 12AX7 valves.
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PhonoFront.JPGPhono Preamp Kit with RIAA Equalization2729 viewsAfter resurrecting the Rega TT and RB300 tone arm with a Grado Sonata wood body cartridge I went on the hunt for a phono preamp. The Pro-Ject PhonoBox SE preamp was a value for money purchase, a neat and good sounding unit. This phono premp kit cost under $AU100 to build (including AC adapter) and challenges the Pro-Ject on a the sonic level. I can find no fault musically with the kit which has no hiss or hum and a natural sound quality. It is available from Jaycar Australia. Better than the Pro-Ject by provide the facility to have three different selectable compensations including RIAA and early DECCA (ffrr) and a host of others to select from. And to go one step better again there is a gain control to balance between CD and phono input levels. The case is ABS plastic and tar and foil lined. Gold RCAs used (see other photos). A +/- 12V regulated PS is include on the one peace cct. brd. The PS is shielded. Distortion is rated at .014% and RIAA accuracy is better than 1db. Signal to noise is -84dB.
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5751-SRPP-EL84-6BQ5-Push-Pull-Tube-Amp.jpg5751 SRPP / EL84 (6BQ5) Push-Pull Tube Amp (PoddWatt)2716 viewsAnother OddWatt tube amplifier. This one uses EL84 / 6BQ5 tubes in a self-inverting push-pull topology for the output stage driven by a 5751 SRPP. The gain is sufficient to allow direct connection to a portable mp3 player. As will all the OddWatt amplifiers, it measures very well and Bruce reports that it sounds very good. See the 5751 SRPP / EL84 (6BQ5) Push-Pull DIY Tube Amplifier project page for full details.
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00005.jpg25EH5 / 50EH5 Tube Amplifier2713 viewsAnother view of the amplifier from the top. As you can see, I was using headphones as I took the effort of adding a jack with impedance matching resistors so I could listen to my music in peace. The funny thing is that I can apply just about any load to the amplifier without any audible change other than volume.
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DIY-6V6-Push-Pull-Tube-Amp.jpgDIY 6V6 Push-Pull Tube Amplifier2711 viewsA photo of a 10W 6V6 Push-Pull Tube Amplifier put together by Michael S. Holden. Michael has put together a detailed set of instructions for this tube amplifier project:

10W 6V6 Push-Pull Vacuum Tube Amplifier (Class-AB) - Michael S. Holden - (PDF 3.4MB)
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PhonoRear.JPGDIY Phono Preamplifier Kit2702 viewsThe finished kit (see other photos) can be assembled in an afternoon. I used insulated gold plated RCAs but on an ABS plastic case like this insulated RCAs are not required. Keeping all connections on the rear makes for a simple front panel with gain control and recessed red led. I used thick silicon stick-on feet to ensure vibration into the unit is kept to a minimum. Stick down computer stand-off hold the cct. brd. to the bottom of the case and also help with vibration control. The case is lined with heavy sticky tar and foil. Base, sides and lid and are lined but not earth. This helps with shielding the low voltage levels and case dampening also. Shielded wiring is used internally and silver solder used throughout.
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Jan6418JewelBoxInside.jpgInside the sub-mini Jewelery box preamp2700 viewsI have a weakness for "cute" enclosures, particularly timber ones. The mirror is just a bonus. The circuit board is part of a kit from Oatley Electronics Australia. I have replaced the carbon resistors in the kit with metal film, the 0.1uF MKT caps with 0.47uF polypropylene types, the 220uF electrolytic caps (output) with 470uF low ESR types. Also the PT2308 headphone driver chip was replaced with a Burr-Brown OPA2134 OP amp chip. 2 X 9V lithium batteries provide 9V to a L4949 regulator which controls filament current to the Raytheon JAN6418 sub-mini valves. Attenuation is trim set and volume controlled by external devices.

Three grommets are used as valve dampeners. These tiny valves can be extremely microphonic. Three grommets stops the microphonic problems dead! The amp is extremely quiet. See the JAN6418 Valve (Tube) Preamplifier Kit page for full details.
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retro-EL34-SE-UL.jpg2690 viewsThe enclosure base is made using Australian Spotted Gum and the power transformers and choke are from Hammond. The audio output transformers (OPT) are from Edcor (15W XSE open frame type series) and reside in the base and are shock mounted. The feet are filled with lead sinkers for resonance control. A CLCRC filter network ensures the amp performs dead quietly and has an extremely high head room. Frequency response is to 40kHz and power is 5W RMS into 8ohms. Russian paper in oil caps are used in the inter-stage and bipolar caps and low ESR caps are used in the cathode bypass. Silver plated wire-wrap wire hooks up the gold plated RCAs to the nearby 6N1P and connects the secondary of the OPTs to the binding post. The paint work is epoxy enamel on 2mm high grade Al plate and component-2-component wiring. This is a fast amp with a huge sound stage and a rich lush EL34 sound.

For more info, see the Pimp my tube amp thread on the discussion forum.

Mark Houston – retro-thermionic
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rectifier_tube_150_amp_6_phase.jpgMassive Rectifier Vacuum Tube (Valve)2687 viewsWhat a tube! This is a vacuum tube rectifier. 150 Amps with 6 channels.
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S-5-Electronics-K-16LS-kit-enclosure.jpg2686 viewsI'm running this stock apart from the Alps Blue volume pot which I upgraded after the original sprang a leak. I'm using quite a few components bought from: http://www.mafaudio.com/pro/propage.aspx.

There are seven LED's that light up the feet and fronts of the brushed aluminum transformer cases. The LED's are powered from a 12v mains transformer bought from Maplin in the UK. The VU meters also run from the extra transformer. The chassis is made from wood bought from the local yard. To cut the VU meter holes I used a 32mm Spade bit then used a file to open the hole up to just under 34mm. The main volume control area was drilled using a 50mm Forstner bit and the tone controls a 30mm Forstner bit. It's coated in about 5-6 coats of clear varnish and involved an awful amount of sanding.

There are more photos available in my photo library.

Luke Collings,
Wiltshire, UK
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BoydSmall.jpgJAN6418 sub-mini valve preamp kit MKII2681 viewsYet another build of the Oatley JAN6418 valve preamplifier / headphone amplifier kit. This one was built to order. An Alps blue velvet pot and 4oz brass knob and pure silver hook-up wire add to the build quality.
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KitAmpTopSmall.jpgKT88 SE UL Tube Power Amplifier2658 viewsI had put the partially finished amp in the gallery some weeks back. Now finished not a lot of difference on the outside except for the many silver colored screws on the top plate and some feet. See the other image for the underside shot. After a number of hours of careful listening and listening to it though others CD players, pre-amps and speakers I can say that most liked the sound. SE tube amps produce absolute and exquisite mid-range and silky highs and deep sound stage but this amp has a slightly narrow sound stage presentation. Bass improved and hum vanished with additional PS filter caps. With a brushed Al top plate and Mirabue timber thick timber base, Edcor XSE OPTs and component-2-component wiring on all circuit boards (including rectifier broard) this amp represents a clean and easy build with in-expensive parts. Though low powered (6W+) for a few hundred dollars you can experience the benefits of a tube SE UL design. So easy, so nice!

Here is a link to the KT88 Single-Ended (SE) Schematic I followed.
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PreProduction-Odd-Block-Tube-Amps.jpgOddWatt / OddBlock KT88 Push-Pull Tube Amp Kit2654 viewsThis is a pre-production photo of the OddWatt / OddBlock KT88 Push-Pull Tube Amplifier kits that are available from OddWattAudio.com.

Full details of the tube amplifier topology along with complete DIY instructions are available on the 12SL7 SRPP / KT88 SIPP (Push-Pull) DIY Tube Amplifier project page.
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