If at first you think that this is a DRD amp, look again. It is not. The output impedance of the SMPS supply is less than 10 ohms and is voltage regulated. The same low impedance supply that is feeding the plate choke of the 841, and driving the grid of the 300B is also directly connected to its cathode. No slow, giant heat inducing cathode resistor found here! In fact the stacked SMPS supply can easily deliver over 300mA of current to any of its voltage taps, instantaneously and continuously, while maintaining voltage to +/-1V! The ultra low impedance supply means the SMPS filtering capacitors are essentially out of the signal path. This gives incredibly good low frequency coupling… better bass than any electrolytic or oil capacitor could provide. Bias protection for over-current of the 300B is provided by the multiple voltage regulated taps that the stacked SMPS supply offers, not just the current draw of the 841 driver tube. Additionally, the thoriated filament 841 tube will begin drawing current before the oxide filament 300B tube. A large sonic improvement would be found by using a true audio rated low DCR plate choke, wound by Bud at Onetics, to load the 841 plate. A low DCR plate choke would improve dynamics and recovery of both tubes better than the inexpensive 200H chinese choke I had laying around. Even-so, listening tests show that this breadboard amp destroys my Welborne Terraplane DRD monoblocks in every audible way that matters, putting out more wattage while dissipating less wasted heat.
Latest
10 IT 801A
Practical application of the SMPS B+ idea upon a tested amp design. Here is the very simple schematic:
YouTube videos of my experiments. Wear headphones 
SMPS for B+?
People hate SMPS. “Too noisy”, “All that hash will kill the music”. It is time to see if they are right. Show me another supply that can provide over 300mA of current at 800V+ all while having an output impedance of less than 10 ohms!
Here is a video of the SMPS supplying 770V B+ and -96V bias for my 826 IT GM70 breadboard amp. YouTube Video
EDIT: Well, once again I am late to the party. Way back in 2009 Ed Brown of diytube.com had the same idea. He didn’t stack as many, but the concept was proven valid with just six units in series. See more HERE.
The future?
This 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.
Inspired by Parker Audio
Over the years I have listened to some very good speakers, and Daves speakers always stuck in my mind as doing things better than most. (Actually, doing less wrong than most) Here is what I have been listening to lately…
I fell in love with these ultra light paper cone vintage drivers made by Grundig. Loose interpretation of the Parker Audio configuration but adding the baffle-less Grundig drivers is what you see here. Other than a single cap protecting the Heil tweeters, the speakers are crossoverless. Flat response is possible by wiring the dipole Grundigs in series which brought down the midrange sensitivity to match the bass output of the single 5ohm Grundig driver in the sealed box, and the 4ohm Heil. Putting the Grundigs back to back in dipole arrangement, along with the Heil tweeters sounds very real. My big JBL horns can’t come close to the presence these speakers have.
Compare my video to your own system… here is the Hi-Rez digital download from Reference Recordings. Free HRx 24/176.4 Music Download And two more HERE.
Perpetuum Jazzile – Africa
Have you seen this yet? Awesome!
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A worthy digital source!
Eastern Electric MiniMax DAC / JBL Horn Speakers
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 Level 3 Onetics Output transformers. Although my favorite music is from vinyl, this DAC sounds incredibly natural with 24/96 or 24/192 files… More info soon!
Hot New Music!
Music with my highest recommendation can be found at www.waveformhq.com
Check out “Sub Conscious” by Phutureprimitive
March 15th… The newest release can be downloaded here!!! It is time to get out the BIG amps .
A low voltage GM70 / гм70 amp
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
Nicholas’ baby/monster
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:
Hornfest 2010
As always, Ed Schillings ‘Hornfest’ is a delight to the ears (if not the eyes). This year I took my Behringer 2496 DEQ along for the ride. When we measured Ed’s listening room I was shocked how different it was from my own. I was even more surprised that my open baffle speakers needed NO digital equalization in Eds room. This was disconcerting, since I had spent so much time and energy pursuing a digital solution.
We ended up running Joels tubed Jolida CD player directly into Ed’s ‘Truth’ buffered LDR preamp and finally into the awesome Dowdy Llama 826 / GM-70 amp. This resulted in stunning presence, incredible speed and dynamics on the baffle-less speakers. How can digital equalization sap so much life from music? Certainly, more research is needed.
Here is a link to a video of that setup…
Open baffle speaker by Greenvalve Audio at Hornshoppe Hornfest 2010 Dowdy GM-70 Amp
