"Clarity" - 70W Class AB power amp

From some inexpensive pre-assembled 120W SS power boards I constructed this good looking and extremely good sounding power amp. The brds are by LJM and purchased through eBay. The amp modules can deliver 120W each but because I used parts on-hand the max power possible is 70Wpc. The power tranni is from another project the 88,000uf of Mundorf MLytic audio grade caps from another but never got used. Diode bridge is 10A and the filter assembly is fully snubbed. A charcoal black 2U 19" rack mount enclosure I had to source new including other minor parts. 

Looks cool and runs dead quiet. Lots of gain, around 31db, where 24db is the norm. The chassis and amp are earthed and fused and the amp an understated look. This amp doesn't appear to run out of power even when played very loud. The bass is deep and very well controlled and extremely tuneful, mids to treble are absolutely crystal clear thus the name. Clarity and transparence are definitely the signature of this amp which runs dead cold. A very high efficiency Class AB and one I have been enjoying daily. 

"Xfi" - Garber inspired X-amp

 

If Don Garber hadn't built the X-amp all those years ago neither would I. Don passed in 2017 so I can't image too many new X-amps under the fi audio name. So Don, thanks, this is not a turning point for me but a milestone in 52+ years of audio electronics and my homage to a man who thought outside of a timber base and top plate with tubes exposed. Not sure of any sonic or electrical advantages from the cramped X space design but for looks - it's a killer!

Sonic improvement will come with parts selection and layout. How does my "Xfi" sound - incredible! Due to - Mundorf EVO interstage caps, Hammond over speced power tranni, Edor 10W OPTs, Russian NOS/NIB 6H5C (6AS7) power tube (stunning sounding and by far the best 6AS7 I have very heard), modern Tung-Sol driver tube, ceramic sockets all carbon film 1W resistors, Sylvania NOS/NIB 5U4GB rec tube, double Pi filtration and DC on heaters. 

Over the last few years I've got friendly with local metal suppliers - KK Metals - who cut and bent my four plates to my specs - 200mm square, 3mm Al and right angle bend in the middle. Not hard. Drilling all the assembly holes was done with plates clamped together to ensure perfect assembly alignment and it worked. An external PS allowed a little more room in the amp but it still got crapped and smaller parts had to swapped for larger ones. Still a very good result.

Colour is Gun Metal Epoxy and apart from a few artistic runs looks industrial purposeful. Right now this is the best sounding amp I have ever built and through my 93db sensitive woofer and horn speakers displays very detailed, transparent mids, solid bass and crisp treble. Plays loud! Piano and voice are right in the room or be transported to the studio. That good. Already thinking a 1622 (6L6) amp but it will need to be a little larger. 

"Oceans" - 6SN7 single stage preamp

 

This build is very similar to the original Ocean but the tube is a new JJ 6SN7GT.  Nice so far but all parts need a 50 hour break-in. Choked PS double Pi with 5H choke. Cast Al enclosure, Alps Blue Velvet pot gold vernier knob, snubbed NP Cks, silver plated fine wire for hookup. HT=260V, Bias=3.8V. All metal film Rs. Three inputs on this one. And Ocean Blue Hammertone finish.

Reference - EAR834p MM phono stage

 

This the third of the EAR834p builds but only the second of this high-end kit. The PCB for both the preamp and PS are heavier duty 2oz copper and beautifully made. Plated through, silk screened and solder masked. The board is partially assembled but for me all the tall parts on the bottom so the ceramic tubes sockets poke through the top plate. The quality of the passive parts is exotic and extreme some I have never seen before.

I wanted this to be the very best build of this phono stage I have ever made so Psvane new "S" gold pin 12AX7s and Tung-Sol 12AU7s were ordered. Enclosure is a larger than normal Hammond wood cheek. Paint is gloss black Epoxy Enamel with an etching primer. Tough when dry. Cheeks are finished with bee's wax. RCAs are high-end Teflon, rhodium and copper. 

PS is external and uses a 24V 1A wall wart to supply low voltage AC to be rectified and smoothed. Filaments are on DC in a single Pi config and HT a doubled Pi. HT smoothing is CLCRC with a 5H Hammon choke. Supper quiet PS supplying 12VDC and 260VDC. No shielded wire is used internally but heavily twisted fine silver plated copper wire for all audio path hookup. WBT silver based solder used and heavier multi-strand wire supplies filament current and HT voltage. I cut traks and modified the PCB to work with 12V for the filaments and not 6.3V. Silicon rubber tube dampers help control micro-vibrations in the new tubes. 

The sound is very transparent with excellent sound-stage depth and well extended solid bass. The presentation is grounded and feels real! The best EAR I have ever made, yes have to agree, looks very good sound even better? A real keeper though not cheap. 

External Xovers with high-end inductors

 

I was asked to make some external Xovers for another's expensive big speakers. Initially it was to be an electronic Xover which I have built before but we ended up with passives. Inductors were copper foil and "C" core. Neither of these I have used before but were easy to work with. The caps were simple 100V NPs Xover caps and the Xover was symmetrical. 

Hookup wire was double pairs of solid core Cat5. Boxes were plastic and jammed with Dacron. this  provides a non-magnetic resonance suppressed enclosure. Binding posts were solid brass gold plated three-ways. The mids and woofers were different impedances but that just meant careful selection of parts. Limiting resistors matched driver sensitivity. The tweeters feed of the mid-range and are internal. 

Word from the owner is they sound about right with no fine tuning required. I had to make some guesses how to voice the Xovers to give balance across frequencies. Looks like I made some good guesses. 

"Ocean" - RCA 6SN7 preamp

 

Once more drawing from vintage tubes I've had for years here is another fabulous sounding super simple preamp. On a compact cast Al enclosure and sprayed Ocean Blue Hammertone with large vernier gold knob. Two inputs and external PS which uses electronic smoothing on the HT (DC heater voltage also) with also PIO output caps and carbon film resistors. Solder is WBT silver solder.

An alps pot controls level out as it is on the output rather than the input to ensure an extremely quiet preamp. Wiring is point-2-point and componenet-2-component wiring, no PCBs and no shielded wire to dull the sound. Signal wire is all silver plated, mill-spec. fine copper wire. Gold plated RCAs. 

I have stated on the past I'm a lover of modern high-end Chinese tubes but the last few preamps with vintage Radiotron and now RCA tubes has made me re-consider tube selection in the future. There is an abundance of detail, transparency, warmth and extreme naturalism in the last two builds not sure I have felt in newer expensive tubes. Another gem built mainly from parts on hand. 

"Mirage" - 6H3N-EB preamp

There are many strange and wonderful tubes you can build preamps and power amps with. When repairing an Asian made 300B I thought the driver tubes (6H3B) may have been faulty. Accidently I ordered two triplets of 6H3 tubes one triplet 6H3N-EB Russian tubes. The 6H3Ns ended up in a headphone amp and the "EB" tubes in this two-stage preamp. Thankfully both builds perform beautifully and are as pleasing to the eye as to the ear.

"Mirage" is another example where a solid plastic enclosure looks like a metal one. This trick I have performed a few times in the past with good results. Also to add to the look this one is sprayed two-tone in Epoxy Enamel. Inside there is a mix of carbon film resistors, metal film and wire wound. Caps are a mix of polies, X2, and low ESR electrolytic. Further HT filtering is carried out at the front-end. This preamp is dead quiet. But the interesting component is the output cap. This is a vintage Australian PMG made NP 1uF cap. The PMG is where I started work in 1970 and was Australia's fledgling telecommunication government owned company. Evidently, they made a lot of their own components and that's where I picked-up the rare cap fifty years ago.

The PS is external and there is another external box with the stepdown tranni and power filter. The PS is choked in a double Pi configuration (300uf of filter caps) and there is DC on the heaters. The AC PS plugs into the PS and the PS plugs into the preamp. Two inputs are provided and hookup wire is fine silver plated copper wire. The knob is custom-made of American Oak on a black Al base. 

The topology is simple plate follower front-end followed by an SRPP backend. This combines good gain with very low output impedance. The sound is very clear almost SS like. Bass extends to 30hZ and mids upfront and very clearly and very cleanly presented. I've heard greater transparence in my other tube preamps but not the clarity this preamp presents. From cheap tubes and a plastic enclosure comes a true treasure of a beautiful simple preamp.