Friday, June 19, 2020

“Rosso” - E88CC SRPP Preamp





After building an excellent sounding preamp ("Continuum") based on the same Gold Lion E88CC gold pin tubes I thought I would build another. Main reason is I have another pair of perfectly matched tubes. Too make this a visually standout preamp I painted this one red and thus the name "Rosso". 

As with Continuum it has two selectable inputs. Rosso has an Alps pot and 4oz solid brass gold plated knob. Similar componentry under the bonnet. Russian PIO output caps but this time snubbed with a 0.1uf poly. Metal film resistors and silver plated wire-warp wire as hookup. My universal external PS just plugs straight into this one also via an XLR socket.

Where this one does vary from Continuum is it has been redesigned. Bruce Heran of American oddwatt fame, who provided the original design, re-tweaked the whole preamp. Much lower HT and lower value resistors. I'm sure this one sounds even better than Continuum which sold. It must be the redesign as so much of Rosso is similar to Continuum.

Treble has lifted here and transparency has taken a big step forward. Gian is high in both preamps because the original design was for a lower gain tube. In operation I have found this not to be a problem, just bloody great sounding. Combined with my DIY 300W SS power amp these two are truly a matched made in sonic heaven. 

Tuesday, May 5, 2020

Pass F5 turbo extreme build







I was commissioned to build this F5 Turbo for another. The kit is from Diyaudio shop and comprises a 5U extra heavy enclosure with steel subchassis, two 300VA trannies and double PSs. This allows the construction of a dual mono amp. There is a total 192,000uf of filtering audio grade caps and 16 dual high performance diode bridges all on their own heat sinks. Each diode bridge is capable of 15As.

The F5 boards looked first class. The components were all high-end and selected by the owner. Riedon resistors featured strongly and a few other resistors were beefed up to bring the amp to turbo specs. Also large power thermistors are placed on both legs of the mains to allow for a soft start. Matched power FETs and matched high performance driver FETs were also chosen.

To push the amp to turbo the idle current is raised to 1.6A across each power FET. Though the heat sinks are massive they still get to 50c and can only be touch briefly. This high current mode was requested by the owner. Bias is fiddley and a little vague but with persistence you can get the current up and the DC offset down.

The amp is extremely quiet and has no sound at all when on. It is beyond any of the quietest amps I have ever built. It has a dead back background. From this back hole of nothingness leaps extreme dynamics with a sweet and detailed mid and treble. Bass is deep and swings a little to the bloomy side but not unpleasantly so. This is amp is to drive 100db sensitive Zu Druids. I wish I could be there to hear it. In my system is was an expensive but extreme giant killer. May build one myself. 




“Zeus” - Holton inspired power amp




"Zeus" is named by the owner who commissioned me to make the amp. He wanted the more expensive 4U enclosure but with a silver face plate. So that's what he got. Inside is 1KW tranni and 80,000uf of 100V filter caps. The Holton amp modules are special in as much as they are 200W modules with upgraded dual die power FETs to produce 300/500W.

As usual a RFI/EFI power filter is included and a 240V speaker protection module. Amp weighs a ton and looks real pro. And what's more sounds excellent. Heavy as this amp delivers better than it looks. The owner and I are both happy with the result. 

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.

Comprises:

  • 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.




Wednesday, February 5, 2020

"Image" - Low Profile 100W Class D amp



"Image" started off as a low profile 150W Class D amp but though it sounded very good I could not remove a very low level buzz. I changed the amp to a 25W chip amp but that played no music regardless of all voltages being correct and no cct. errors. 

Wanting to make my own Devailet right from the start I found a very inexpensive, extremely compact 100W Class D module using some newer Class D chips - TDA7498. The amp will produce 80W into 8ohms and works from the original PS I built in this chassis. A 36V single rail well filtered (19,000uf) PS supplies dead quiet current to this power amp. As with most of my builds the amp includes a RFI/EMI power filter and a ferrite choke on the power cord. Part of the supply filtering is a 10uf poly and two 0.1uf polies. These are to provide a better mid and high frequency signal path and reduce bridge (35A) and filter cap noise.

The amp looks super smart in its ash black stippled 1U 19" rack mount enclosure with handles. It sits on rubber feet and has quality gold plated RCAs and solid brass three way binding post. A retro-thermionic amber "ON" LED and power switch are upfront for easy access. The amp in operation is dead quiet has excellent bass extension and sounds balanced over the rest of the frequency range. It sounds much bigger than its 100W rating and appears to drive all my speakers very well. Even after hours of use it is cold to the touch above the heatsink. Very pleased with he compact build and overall sound.