The DACmini CX is my new 24bit 192khz source. So far the sound is excellent… all it needs is a little tube love 😉 It may be too tight inside for an all in one source / tube amp, but there is plenty of room to make it into an optocoupler volume control LC 26 tube preamp.
After using the CEntrance DAC for a while I am convinced it is an outstanding value. Not just because of its excellent sound, ability to play 24/192 files via optical or coax and 24/96 files via USB, but because of its stability and isolation from noise. Now it’s time to see just how transparent the Asahi Kasei AK4396 DAC chip really is. Bypass everything and run the balanced DAC output right from the AK chip, into high quality 1:4 step up transformers, then directly to the Hornshoppe Truth buffered preamp. This sounds astonishing! Even better than directly coupling the DAC to the grid of a preamp or driver tube. The dynamics feel decompressed, headroom limitless. It must be the synergy of the interstage transformers being given what they love and the exponential expanding dynamics from the step up transformers creating the most exciting, real and dynamic presentation I have ever heard. Yes, maybe even better than vinyl. 😉 Pictures of the mod follow:
Introducing the True Green DAC. 😉 The final product has all the conveniences of a modern DAC. It is amazingly quiet, has a remote volume control, balance control, and plenty of gain. It is the perfect source for my powerful SMPS GM70 amp.
This post may not seem too interesting, but trust me… you will enjoy listening to this source at Hornfest.
This thing REALLY rocks!
In the teaser photo: My modified Eastern Electric MiniMax Sabre32 DAC with RCA 210 tubes, transformer output, and Optocoupler / Light Dependent Resistor (LDR) Volume control. Used to drive all IT coupled 10 > 45 > GM70 monoblocks with Onetics Output transformers. Although my favorite music is from vinyl, this DAC sounds incredibly natural with 24/96 files.
Having breadboarded a few GM70 amp ideas, I was still looking for an inexpensive tube to drive the GM70. The problem is that a low impedance supply is necessary to drive the grid of the GM70. Into the hole of cathode followers I fell, until Jim Dowdy mentioned that he likes the the 6EM7. Hmmm, wow this is the ticket! An inexpensive dissimilar dual triode with half the tube looking amazingly similar to a 2A3! The 6EM7 is identical to the 10EM7 except the 10V heater requirement. www.surplussales.com has a great deal on the 10EM7’s so I bought a bunch. The schematic shows voltage tap off the 30V filament supply for 10V heaters. 6EM7 or 13EM7 tubes could easily be used since the filament resistor provides enough regulation for any of these tubes. And yes, this circuit is screaming for an interstage transformer off the 2nd plate of the 10EM7, allowing it to drive the GM70 a little into A2. I am looking for good interstage transformers. DIY HiFi Supply has some Silk 3K:3K that would work well, but they are too expensive. I will update the schematic if I find something that works, and is priced in line with this ‘economy’ project 😉
UPDATE: OK! I don’t know why I didn’t think of Hammond interstage, but a Hammond 126B should work very well. It is only rated to 30ma, so I will probably bias the tube for less current.
… For your enjoyment, here is a few links to other GM70 builds…
Audio Design Guide
Audio Talk GM70 SET
Kevin Carter of K&K Audio
Fikus the Lampizator
Dr. Z Lab
Sampleaccurate’s GM70 Build
Polish GM70 Build
Thai GM70 Build
Yahoo Boat Anchor Group
A Russian response to Ongaku
A Japanese 6AS7 2A3 GM70 version
A scary system I would love to hear.
And the schematic for my 10:IT:45:IT:GM70 Amp: