Thursday, April 23, 2020

"Continuum" - E88CC Gold Lion SRPP preamp

I had bought four Gold Lion E88CC gold pin tubes for another who had one of my tube preamps and wanted to upgrade it. They decided not to upgrade and I got stack with the tubes. They remained unopened  for the last 25 years until a few days back. I had most parts on hand to build a whole preamp from scratch and use these very nice tubes. And here it is. Colour is Deep Indian Red epoxy. Sound is full bodied and appears very balanced top to bottom.


  • Hammond wood cheek chassis
  • Ceramic sockets
  • Silver plated fine copper hookup wire
  • Russian PIO output caps.
  • External DC PS
  • WBT silver solder
  • Alps Blue Velvet pot
  • Vintage style Vernia gold knob
  • Two selectable inputs
  • 4uf PIO final HT cap internal to the preamp
  • Low ESR BP Ck
  • Metal film resistors
  • DC on heaters.

Monday, April 13, 2020

"Blue Wave" - CMoy style portable HP amp

It may seem odd to build yet another portable HP amp when I only recently finished the "retro-2308" compact HP amp. I have a number of Lithium batteries over from my many Oatley K272xx of the past and built this primarily to use those batteries. I happen to have a couple of genuine OPA2134 chips also and what better way to use them but in a CMoy style amp. Once I have used the Lithium batteries I may just use high quality alkaline.  

In the past my Oatley HP amps have been a little big and heavy though 100% portable. Travelling over seas a lot made  me think it was time for a lighter more compact amp. The "retro-2308" definitely fits that bill and running on 4 X 1.5V AAA batteries made it long lasting and cheap to run. Now I have a choice of two compact portable HP amp. Both sound fantastic, I'm spoilt for choice.

With space at a premium I had to build the whole chip amp and differential PS on a tiny slither of vera-brd. Two lithium batteries are held in place by glued foam strips and once more my "safe on" technique for insuring amp is not on when not in use. Only input caps are needed and I used inexpensive polies. A mil-spec chip socket, metal film resistors, quality switching phone 6.5m sockets are used and fine wire-wrap silver plated wire is used as hookup. 

With two 9V lithium batteries I should get 120hours of play between changes. The batteries are rated 1200mAh. Current draw is 9.5mA.I never use rechargeable batteries at all because they are initially dearer and generally lower capacity and lower voltage. 

The OPA2134 has distortion figures of 0.00008% with a FET frontend and a very capable drive backend. In this and other devices I have used the chip in, always sounds excellent. For $9 or so each they are good value and are recommended for audio applications with diminishing noise figures.

Monday, April 6, 2020

"MWH" - 1920s UX-171A tube preamp

I was offered the challenge of building a DHT triode preamp and offered a schematic. But there was way too much sand in the design with an active load supplied by a FET. There was also a CCS reference in the cathode cct. Any delicate suppleties in the DHT tube were to be lost and buried in all that sand. Not for me. I was shaken and a little stirred and felt a Bond to the UX-171A tube which in the past I had built a power amp around ("Intermezzo"). I have a number of 71A pairs and now the opportunity to use a pair.

Fortunately an American DIY buddy, Bruce of oddwatt fame, came up with a simple single stage designe. Using close to century old tubes I felt a Hammond retro wood cheek Al chassis was the way to go. Add to that a Hammertone blue poxy enamel paint job, a big gold retro knob and ceramic sockets and the look is there. The tubes are RCA and they use nickel plates. 

Keeping old school the output cap is a Russian military PIO 1uf metal jaket. Never done it before but this time earthed the metal (which is actually copper) jacket. Not sure any improvement but like to think it can't hurt. Due to hum issues I moved the 24 step stepper pot to after the output cap. 

There are two selectable inputs and the preamp uses my standard external PS which works with any of my 6SN7 preamps of which I am currently using two. The sound is extremely transparent and captivating. Pleased with the build, both the way it looks and sounds.