“Piccolo” - 5654W compact tube preamplifier

 

This smart looking and compact tube preamp uses (matched) JAN GE 5654W tubes. The kit is sold with lesser performing 6J2 but here they have been upgraded. The enclosure is Hammond extruded anodised Al smart looking enclosure. Three inputs are selected by two front switches. The black knob is a large anodised Al type with a good feel. All internal components are of very good quality. 
 

Power is via a 12VAC 1A plug pack and connects to the preamp via a two pin locking connection. Internally HT is generated to produce a dead quiet preamp. Under test up to 90% max volume there is 0.0mV of noise. At 100% volume, 0.4mV of noise. Input impedance is 100K. The blue colour when on is a pleasant glow and the filaments fire is also easily seen. Tube rolling is possible. 
 

From such small tubes I didn’t expect how good sounding this preamp could be.

“Iron Stone” - OPAMP based MM RIAA phono preamp

 

I bought the last six Jaycar LM833 dual OPAMP based MM phono stage kits. This is the very last. Two were resold and four assembled and three sold so far. Where the previous “Player” was enclosed in an expensive Hammond extruded anodised Al enclosure this one cleverly hides in a strayed plastic enclosure. Colour is Iron Stone and thus the name for this final build. The paint is durable epoxy enamel on an etching primer. 

The last two builds are powered by an external 12VAC wall wart. There is excellent power filtering and +/- 12V regulators on board to ensure a dead quiet MM phono stage. The RIAA EQ is a mix of passive and active plus there us a buffer gain stage. The front knob controls gain not volume though more gain means more volume. Input impedance is 47K. Internal components are most NP caps and metal film resistors. The inside of the enclosure is heavily lined with bituminised Al foil which is earthed. The foil shields the inside from stray electrical interference and the bitumen damps any resonances. 

Overall the sound is transit quick, very clean and extremely detailed. The LM833 OPAMPs have bipolars transistors throughout which provides a rich warm tone though any similar OPAMP can be used. For example an OPA2134 can be dropped in. I find this FET/bipolar OPAMP not as warm and the bass not as full. Im staying with the LM833. 

“Horizon” - Custom SRPP preamplifier

This build centres around the 12AX7 tube and a SRPP schematic I have used a number of times. The custom part is a remote control which I have never used before. The motorised Alps Blue Velvet pot comes as a single unit with motor and control circuitry smartly attached on the rear. The remote is small with only volume usable. It works well but the steps are a little large and the preamp has a lot of gain.

To fix both issues I have some Tung-Sol 12AU7s coming which have a much lower gain and will allow the remote pot to be better controlled. If you pair this preamp with a power amp of low gain the X7s are a better selection. I’m very pleased with the finish which is Gun Metal epoxy hammertone. The chassis has wood cheeks and the whole appearance is understated and vintage industrial looking. 

Two inputs selected from the front switch, silver plated fine copper wire for hookup and 1uf of PIO output caps makes for a good sounding preamp. The PS is external and has a Hammond 5H choke in a double Pi configuration. Also there is 300uf of snubbed high voltage caps for filtration. A 4uf PIO snubbed cap is the final cap and situated in the preamp. This always improves overall sound. Filament voltage is DC and the preamp is dead quiet, fast and detailed sounding. 

French EL3N pentodes in a wine box amp

 

Bought a matched pair of French EL3Ns from eBay - NOS NIB but no amp to listen to them. Also bought ceramic bases and adapters. The adapters will allow you to insert the tubes into most pentode amps but ensure voltages and currents are correct. I was lucky both were close enough. 

From what I have read you should run the tubes in triode strap but for me who loves UL I left them as the amp had been wired for 6L6. In UL you get a little more power and I feel extra drive. Whatever, they sound extremely good and with one of my wine box 6L6 amps the tubes hissed but in the other (same schematic and parts values) dead quiet. You can get these tubes quite cheap but I paid a premium and again "whatever" a very pleasing audio result. 

"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.