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SV101673.JPGOPA2134 Preamp II with selectable inputs3674 viewsOP amp based preamp, that provides two pairs of selectable inputs, volume and balance control and 6dB of gain. A compact cct. with the only links on the cct. brd. being silver earth links, packs a lot of performance into a solid cast aluminum case. With distortion figures as low as .00008%, solid pure silver wire throughout, WBT silver solder and each of the the two circuit boards having their own virtual +/- power supply plus additional tar and aluminum damping/shielding internally this preamp can deliver. I hope the new owner enjoys listen through it as much as I have enjoyed building it. See the DIY OPA2134 Preamplifier page for more build details.
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IMG_1423.JPGMaking the chassis3672 viewsBefore bending the sheet metal.
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OatleyPhonoPreInsideS.jpgMongrel Dog Audio JAN6 418 valve phono preamp3668 viewsThis is the new tube phono preamp kit for MM cartridges from Oatley Electronics. The small tube preamp kit comes with all components required, including NOS JAN 6418 sub-miniature tubes and a wall wart for the switch mode power supply. The wall wart PS has multi-outlet adapters to fit most mains power outlets worldwide. The PS auto-switches to the correct mains voltage to provide 5V DC to the kit. There are two tube stages with each stage supporting a FET buffer to the next. The PCB is plated through and screen printed.
See the 6418 Tube RIAA Stereo Phono Preamplifier Kit project page for more details and a review of this kit.
Mark Houston
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6EM7-Tube-Power-Amp-Arabella.jpgArabell - 6EM7 Tube Power Amp3658 viewsInspired by a beautiful Acacia, heavy, chopping board I fashioned this excellent sounding single-ended 6EM7 tube power amp (Arabella). To hide wiring a shallow aluminum skirt is tucked up underneath. Smaller components also reside here. Larger power supply caps are housed in a “trunk†at the back where the RCAs and gold plated speaker binding posts are also located. Tubes are Dutch made AWA NOS and Sovtek 5Y3. A large Hammond power transformer (370EX) and Hammond 20H 100mA choke (193C) grace the gorgeous wooden top plate. Edcor GXSE (GXSE10-6-5K) audio output transformers stand proud and blue to give this build a striking look and super clean pure sound. I love the amp for its looks and sound, all 2.5W of it.
Mark Houston – retro-thermionic
UPDATE - June 2015 - see the 6EM7 Single-Ended Triode (SET) Vertical Amplifier project page for the latest revision of this amplifier.
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TwiningsRear.JPGWooden boxed 12AX7 Tube Preamplifier3644 viewsThis is my fourth of these 12AX7 valve preamp kits in which I built it in a wooden tea box and used Cardas Capacitors. The connections to the timber box are made by a 3mm think aluminum strip.The remote power supply is hard wired to the preamp via a short cord. This preamp has brought an element of focus to my 6T9 Tube Amplifier, Fostex speakers and from early listening, greater detail across the board.
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50year-old-tube-amp.jpg50 year old triode tubes single ended 3.5 WPC3644 viewsThis amp uses all triode tubes in single ended configuration and thus the circuit as short and sweet as possible. The result was 3.5 watts per channel, with 0.07% distortion at 1kHz, 1 watt and not much worse at the extremes. We also did not have the deep pockets to try the more exotic transformers and coupling capacitors available. I'd like to, though, and set up my A/B switch box to see if I could discern any difference. The A/B test with myself and others paired with a high end solid state amp with 0.007% distortion, or ten times less did not reveal any discernible difference. I have a notion that some high end speakers might make the biggest difference of all. The row of LED's are a clever circuit we designed which indicate 3 decibel increments of sound pressure level (SPL). Each 3 decibel increase in loudness requires a doubling of wattage, as many of you know. These light up in sequence , e.g. 0.04 watts, 0.08, 0.16, 0.30, 0.7, and so on to 8 watts total.
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Electros.jpgElectrostatic Speakers3636 viewsThese Electrostatic speakers are made by a company which does not make speakers but develops new technologies in electrostatics. The best way to demonstrate these technologies is to build speakers to showcase them. They also have developed acoustic filtering which is applied to their sub-woofers which are based around two 5" drivers firing on opposite directions.
The tall black panels have two 100W amps built in the base made from discrete components, one for the panel array and the other to drive the sub-woofer in the base. The black speakers have a RRP of $AU12,000. Small black panels on the table are $AU1000 a pair. The tall silver panels produced clear live sounding mids and highs but seriously lacked base. These were demonstrated at a GM of The Melbourne Audio Club, Victoria Australia.
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DIY-50EH5-25EH5-Tube-Amp.jpgDIY 50EH5 / 25EH5 Tube Amplifier3634 viewsThis tube amplifier project uses the parts from a junked Fleetwood console stereo. It uses a 6AX4 full wave bridge rectifier two 5A 400V fast recovery diodes. The preamp tube is a 12AX7 and the power tubes are 50EH5. I followed the basic ideas from Gio's DIY 50EH5 Tube Amplifier Project. This is my super sized version of the amp with all DC regulated filament supplies and even does a lower frequency response than usual because of larger output transformers (underneath the chassis).
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Jordan-JX92S-Speakers.jpgJordan JX92S Fullrange Speaker Drivers3631 viewsA pair of Jordan JX92S Fullrange Speaker Drivers.
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IMG_1412.JPGAluminium and mate3622 viewsThe aluminum sheets used for the dissipater and a "Mate".
"Mate" is the Argentinian equivalent of "Tea" for a British.
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Amp1.jpgPush-Pull 6P3S-E & 6N2P (OddWatt)3622 viewsUL, cl.A /Ia=51 mA for each 6P3S-E tube. Schematic follows the idea of the KT88 push-pull Oddwatt design. /thanks Bruce/. Audio Output transformers are Hammond 1650, with triode and UL modes and output for 8 and 4 ohms, rated "HiFi" bandwith 20-20000Hz +/ - 0 dB!!
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MongrelChamp.jpgFender Champ 5F1 valve guitar amp.3617 viewsMy build of the Fender Champ 5F1. It is a SE three stage tube amp based on the 6V6 power valve and 12AX7 triode. The amps were first made in the late 40's up to early 80's. And re-issued in 2006. The original schematic had valve rectification. I added a 10H open choke. There are only two inter-stage caps and one by-pass cap on the 6V6 cathode resistor (not counting PS caps). I went for a Classic Champ sound by using cotton covered, single core, tinned copper wire as the hook-up wire, bees wax (Jupiter originals) inter-stage caps, an original Ozzie made 12AX7, Ozzie 5Y3 and 6V6 Black Glass (original). PS caps were increased from 8uf to 47uf and an effects loop added (between stage one and stage two). I didn't install the NFB loop from the OPT secondary to stage two. Instead I made the output stage UL (Edcor tranny). The amp is stable even when over-driven heavily. When hooked-up to a Pioneer PA 12" driver (4" Al/vented dust cover) it sounds excellent. Very clean highs and gutsy lows.
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KT88-Push-Pull-Tube-Amplifier.jpgMonoblock KT88 Push-Pull Tube Amplifier3587 viewsPhoto of a KT88 Odd Block without the protective cage. This tube amp design will work with a number of octal tubes (KT77, 6CA7, EL34, 6L6GC, KT88, KT90 and 6550). SRPP driver stage using a 12SL7 tube. Output stage is a Class A Ultra-Linear SIPP with 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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Finished.JPG"not another chip amp" - Enclosure3577 viewsThis is where most new amps end up for a few weeks burn in, sitting atop the NAD C542. This is my latest chip amp which I promised I would never build. I started and completed the amp in one day. The amp modules had been built a some time before so most of the hard work was marking and drilling then assembly. On start-up it had a bad hum which I have managed to reduce to a low level. See the other image ("not another chip amp") for the inside shot. This amp feels like it has the power to deliver big time and it certainly sounds nice enough. Will I make another chip amp? Stay tuned.
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DSCN0061_M1~2.jpgMy Black Velvet OTL headphones amplifier 3572 views6AS7G RCA & Rare RV200/600 Tungsram-Germany & PCC88 Siemens /golden pins/
OTL for headphones 200 and more ohms. Loftin-white, only 1 cap ELNA between output stage and headphones.
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IMG_1479.JPGChassis and plastic3566 viewsBending the plastic was a pain, i did it with a hair dryer and a LOT of patience... i don't recommend you to try to do it, it takes a lot of effort and time.
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KT88-Monoblock-Tube-Amplifiers.jpgDIY Monoblock KT88 Push-Pull Tube Amplifier Kits3565 viewsShown in the photograph are a pair of DIY Monoblock KT88 Push-Pull Tube Amplifier Kits. See the review for additional details of this great sounding tube amp kit. Also shown in the photo is a NAD C521i CDP used a transport and a Behringer SRC2496 which is being used as an up-converting DAC. The little black box is a DIY Lightspeed (optocoupler) Attenuator.
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IMG_1480.JPGMaking the chassis, bottom view3550 viewsHere are the two pieces that make the chassis put together. Bottom view.
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Rear.JPGOPA2134 Opamp Preamp - Bees Wax Paper Capacitor3529 viewsThis is the third of these diy opamp preamplifiers I have made using the Burr-Brown OPA2134 chip. In this build as with my last (which was sold to an audio buff in Denver) I included two switchable inputs. I used 1uF Bees Wax and Paper Jupiter caps (see other photos) which have increased the bass depth a lot. A lot of resonance dampening has been employed. This is a smart looking and very smart sounding preamp. The stereo focus has increased dramatically.
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12AX7-Tube-Preamp-5AR4-Power-Supply.jpg12AX7 Tube Preamp with 5AR4 Tube Power Supply3524 viewsTwinings Tea Box preamp with external valve rec. PS
Another Tea Box valve preamp but this time with a valve rec. remote PS. The rectifier valve is a 5AR4. The iron consists of a Hammond power transformer and 10H choke. Golden Dragon tubes are used in the 12AX7 Tube Preamp . The preamp uses silver hook-up wire, Alps Blue Velvet attenuator, brass cones and 4oz brass knob. Jupiter hand made beeswax caps are used in the amp modules and silver solder throughout. The sound stage has gained greater dimension and detail has improved over my SS preamp.
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