I have most of them on this site "somewhere".....the DIY ones..
I dont have pix of my Schitt Asgard (ss) or Schitt Lyr (tube).
AGDR's Inverting Version of the O2....ODAC on the side.
Marvelous and "rare" amp for sure...only a few of them out there...
The design thought here was to build an O2 like amp that used inverting amplifier stages for the gain and output stages.
The result was a cancellation of the higher-order even harmonics by the inverting stages at a cost of slightly higher background noise.
The Bottlehead Crack with Speedball.
I should say the "legandary" BH Crack....its touted by many as the OTL amp for high impedance amps.
I have to say its a great simple design that just works and works very well.
If I had only high impedance cans this could be the amp to have.
Its tempermental with tubes, or I should say the tubes are tempermental at times...noises, pinging, microphonic etc
but once it settles in its a stellar amp.
Schitt Vahalla 2
A great OTL amp that has morphed somewhat from the original Vahalla 2
Valhalla 2 is a complete re-imaging of Valhalla, with improved performance, higher output capability, lower distortion and output impedance
I can use this OTL amp with both high and lower impedances...drives the T90 and T1's very well and even the DT1350's at 80 ohms...
The DT 1350's on this amp with low impedance setting has bass that thinks its a big as anything else out there!! LOL.
The main reason for buying this amp was to see if the powere available at 600 ohms made any difference over the Bottlehead Crack.
It has the highest RMS power rating than any other head amp that I am aware of.
AGDR Desktop "O2" or what we call the "ODA"
After "rocket Scientist" disappeared many wondered what the desktop version would have been like...
he has a few design thoughts on that on his still up website...
So AGDR took the liberty of putting one swipe at this "ODA" and here is what he came up with.
Its a very demanding DIY build, many parts and costs over $200+.
It can be built wiht a few options and customizations...which cause some folks to not want to do DIY or have to think about what
are the trade-offs and parts etc...
Its the best SS amp I have heard and works with most any headphone except the electrostatics etc.
The front panel is not engraved "yet"...
The two jacks on the front right are for 1/4" and 3.5mm and this amp can run both at the same time, makes comparing really nice.
THe phone jacks are for a unity gain pre-amp output...I use it to drive a AVR at times for my pc.
Volume knob, two power rail leds, 4 position gain switch, clipping led, a front/back input selection swithc and a 3.5 mm DAC input jack.
On the back there is power, DAC input for internal ODAC, and DAC phono inputs (for USB input from PC).
The big thing is this amp has twice the current sourcing capability than the O2.
OPA1622 Integrated Headamp Project:
The next head amp was built from a friend in France who was enamored with the latest new Op Amps made by TI. These were designed for audio use and fit very well with low power head amps. (relative to the norm 2ch power amps!). Its simple to implement and has fantastic specs. The op amp is the OPA1622. It leads the way for a high performance spec wise and LOW cost head amp and its rather small, but with a wall wort. IT eveb has a cross feed circuit, that after testing I wired out and added selectable gain instead. The BIG thing here is that the OPA1688 only comes in "TINY" form factors and is very difficult to install or solder on a pc board! These chips are installed by the big boys with re-flow ovens etc...I had to learn to use a hot air gun to install these chips as well as using flip up binocular magnifiers...they are that small.
• DT1350 (80R, 109dB/mW), OPA1622 with +/-5V supply should be ok, it even can reach the max SPL of the can : 129dB
• T1 (600R, 102dB/mW), max SPL with OPA1622 with +/-5V (clipping at 4.1V) is 113dB. Certainly too short, it should be better with +/- 10 V supply, allowing 120dB SPL max.
• T90 (250R, 102dB/mW), OPA1622 with +/-5V supply should be ok, max reachable SPL : 117dB
So thats "5" of the amps at present...
Number 6 and 7 are the original O2 amps but with modifications:
One has an AGDR Booster board and the other has different op amps..."1688's"....
The booster board replaces the original NJM4556A chips, you remove them and the board plugs into their sockets, plus some wiring. Different Op Amps are used, OPA827's with a LME49600 current buffer. It lowers the DC offset voltage to the cans down to 50uvolts, has a relay for turn on/off thump. A slew rate improvement and a lower distortion specs.
Ever wanted to build a CMOY using modern parts?
Amps 8 and 9 are Two variants of the cMoy design with the new TI Super audio chips.....OPA1688.
I never built a cMoy and stayed away for objective reasons but with the new TI high perf chips
and AGDR's dogged determination he came up with several iterarions, of which I built all three!
THe neat thing here is the actual TI engineer came online to help and see how "his" new chips perfromed
in the real world.
I actually have more than 9 amps!! I have three AVR's that I use on occasion as well...
So I guess its time to build that Mainline!!