Öogliibox is OddAudio's "house brand" of DIY projects, named because I built my first battery powered phono preamp inside a thrift store cutlery box (E.G. a butt ugly box). Add some phony Euro flair, an umlaut, and bam: Öogliibox. Having access to a resin 3D printer means I can even make my own badges!
Generally these are components built for my own reference system but I have sold a few of my phono preamps. Given that I obsessively include the best and most expensive components possible it makes no sense financially to sell these designs commercially - plus they are based on open source designs so making profit off of other people's explicitly free work is frowned upon.
ÖogliiBlocks Triple Chassis Tube Monoblock Amplifiers
The design of the ÖogliiBlocks described below has been extensively updated, so much so I'm including updated schematics. I call this the Mark I, Mod I revision given it's built off the Mod 0 framework but it could really be considered a new design.
The biggest update was ditching cathode bias for AB-Qi autobias modules and the associated bias supply rail, which came with a switch to Edcor power transformers (the Hammonds were just too damned buzzy, and lacked bias voltage taps).
Refinements were made to the NFB to lower the feedback and adjust the compensation to improve high frequency response.
Some small tweaks to component values were made to optimize the circuit but the architecture is still the same. Adding a basic AC balance circuit to the driver stage (just varying the plate resistance on each triode) proved to be a useful addition to optimize the performance. Anyone who thinks a 6SL7 can't drive a quad of EL34s is very, very wrong. It works and it works extremely well.
Power is now 70W/ch in Ultralinear and 35W/ch in Triode.
The results are spectacular, the best tube amp I've heard in my system to date.
I’ve been on a tube kick recently, the combination of a fine tube amp with Magnepans is a magical one that needs to be heard to be believed. Expansive soundstage, incredible depth, remarkable holography... I’m less than concerned about ruler-flat response and nerdy distortion measurements when I can create a mesmerizing 3D soundstage that fills the room.
Tube amps are simple creatures that are a pleasure to build, but settling on a design is tricky. With so many options and opinions even deciding what to build is a challenge.
I had a few key parameters in mind when I chose my base design:
Seperate power supply (dual mono in a single chassis feeding the pair of blocks)
At least 50W per channel, the more the better
EL34 outputs as I have a selection of them on hand and I like the character of Gold Lion KT77s
Push pull ultralinear, with the option to wire in triode
Based on a proven design as I’m not knowledgeable enough to start from scratch.
Feedback design as I already have a no-feedback tube amp (Cary Audio V12R) and want to try something different
After some research I settled on Maple Tree Audio Designs Super Stealth + monoblock as my jumping off point. Maple Tree is a highly regarded Canadian builder of tube gear that is known for their exceptional value and quality, providing superb bang for buck. And they kindly include full schematics for all their designs in their owner's manuals, encouraging DIY noodling. They were even kind enough to give me some help when I encountered some issues – even though I was merely building a clone of their design, not an actual customer!
The SS+ is a nice tidy design using 2 EL34s in Class AB configuration with cathode biasing to put out 30W/ch. Negative feedback is employed. A 6SJ7 is used for input voltage gain and a 6SL7 for phase splitting. Importantly for my taste there are no coupling caps in the input section, only in the usual spot between the phase splitter and the outputs. The fewer things in the signal path the better. Plus I was curious about using oddball input stage tubes rather than the boring usual suspects (bonus: using weird tubes means you can score really good NOS examples for way cheaper than common options).
However my target for power would not be met with a mere 2 output tubes... so tack on an extra pair and we should be good! With tube designs this is easy, just mirror all the component values with a few minor tweaks and run the extra tubes in parallel... you can add as many as your heart desires and your power supply can support.
To that end I redesigned the power supply section to suit more modern practices and up the power to suit the extra output. Each channel is fed by a Hammond 710 for B+ and a Hammond 167R6 for the heaters. A DC section is added in each block to run the input tube heaters, with AC for the outputs. All rectification is done with HiperFred fast recovery diodes. Most importantly I cranked up the capacitance: 2700uf per channel on the B+ bypassed at each stage with Solen film capacitors. Separate switches control the B+ and heater power, so I can preheat the tubes before applying B+ (basically the “standy/operate” mode you see on some amps).
I left well enough alone in the amplifier section and stuck to Maple Tree’s values, except for increasing the coupling caps from 0.1 to 0.47uf to bring the bass response down a bit lower (and suit 220K grid leak resistors for the extra output tubes). I also bypassed all the cathode capacitors with Wima film caps. And of course I spec’d a more suitable output transformer, in this case Edcor CXPPs rated for 100W with 3.3K primary impedance (going off the Maple Tree value of 6.6K primary for 2 tubes, halving the value for an extra pair). A note, the Hammond output transformer spec’d by Maple Tree is not a great choice for audiophile use and is easily bested by anything from Edcor’s catalog, which often ends up being cheaper pound for pound and one of the best performers this side of an exotic (read: expensive) OPT.
By default the Maple Tree design is configured for ultralinear operation only. I prefer the clarity and punch of ultralinear in my system but I always like to have the option for triode (which is handy for taming a harsh recording) so I added a switch and the appropriate wiring to accomplish this.
Everything is installed in eBay’s finest Chinesium chassis - though I’ll admit I absolutely SUCK at machining work, with only hand tools at my disposal, and nothing is lined up straight or true... As I have buddies in the engineering field I’ll be outsourcing machining for future builds, or for anything I build for a customer.
As usual I resin printed all of the badges and labels, including all the tube positions and ultra/triode switch indicators.
The result is clipping power at 55W in ultralinear and 27W in triode. I don’t currently have a distortion analyzer so can’t provide these measurements – yet (I’m working on it).
Here are my schematics for the power supply and amplifier (one channel shown for each). Note that I am not a designer, just a dumb technician who has enough knowledge to be dangerous. There are likely areas for improvement and I would welcome suggestions. Build it at your own risk!
For tubes I installed NOS Amperex 6SJ7s and Tung Sol 6SL7s and new Gold Lion KT77s.
The results are superb. These are very transparent amps that lean towards the neutral side of the tube spectrum, with great treble extension and clarity. Overall it’s very balanced without noticeable emphasis on any one part of the spectrum – so no, it doesn’t have obviously tube-y tone but it images like tubes should, which is exactly how I like my tube amps to perform. Soundstage width and depth are excellent. Noise floor is extremely low, inaudible on my Magnepans. Triode mode softens the highs just a touch but honestly it’s surprising how close both modes sound, with only very subtle differences between them aside from the peak power.
Öogliibox Tube Phono Mark IV/Tube Power Supply Mark I. The more I listen the more I like tubes, at least on the front end (I still like solid state power with the tube magic on the source/pre side to liven up the sound). The next illogical step in the Öoglii line was thus a tube phono stage. And why not go all in and use a seperate tube rectified power supply? Why the hell not indeed. This beast is based on D. Klimo LAR Gold Plus PCBs the Chinese have been selling out the backdoor on eBay. And I can assure you these are not "inspired" by Klimo, they are identical and high enough quality that I suspect they come from the same factory making their boards. What a time to be alive and take advantage of lax Chinese copyright rules so us filthy peasants can build our own knockoffs of equipment we couldn't otherwise afford.Not that this was cheap to build, at least to build my way. Top-tier hand-selected components throughout are driven by new JJ gold pin tubes (Power: EZ81 rectifier, 12AT7 voltage regulators. Phono: E88CC MC gain stage, E88CC+12AT7 MM/output stage).
The result is shockingly good. Extremely low noise, in fact a lower noise floor than my solid state Phono Mark I-III builds. Huge soundstage. Smooth and rich leaning towards the neutral side of tube tone with the JJs I'm using.
My only gripe is the MM stage only has 35db of gain and for some reason it has more noise than the 60db MC input, despite them running the same output stage. I run my Ortofon 2M Bronze through the MC input with the loading adjusted accordingly and it works perfectly - in fact during bench testing I saw over 40V output without clipping, so this thing is STOUT and has an absurd amount of headroom. I was so happy with the quality of this design that I also ordered the line stage PCBs, which I'll be building soon.
Öogliibox Tube Preamp Mark I. I've always wanted to build a pure tube component with point to point wiring, and I like the flavour that tube preamplifiers can give a solid state system on the front end. So after doing some cursory research I decided to build a SRPP push-pull class A preamp based on Bruce Heran's (OddWatt, no affiliation!) Forewatt design. I essentially had to build this unit twice. The first iteration crammed everything into a single chassis and I had significant power supply noise getting into the signal path. I rebuilt it with a remote power supply which solved most of the noise problems, but I found it still had too much background hiss with the tubes I had on hand (it should be quiet, but tube selection and matching is critical for this). The final version incorporates a -10db voltage divider on the output which gives a dead silent background and brings the gain down to a more reasonable level. I also went with some teeny 0.022uF cathode bypass caps to give a slight (1db) boost to the 10khz+ upper frequencies to compliment the slightly rolled off highs of my Magnepans. While the design recommends ECC802S variant of the 12AU7 I had awful hiss with a set of new JJs I bought for the project- while I wait for those to get exchanged I'm currently running a set of vintage Telefunken ECC83s (12AX7) which while not specifically recommended actually sound quite good. I'll experiment with tube rolling but even with these old tubes tossed in it sounds fantastic - clean and smooth with superb soundstage and imaging. It beats my previous benchmark Schiit Saga + by a significant margin, particularly in front to back depth. The bass is a bit tubby with the ECC83s so I look forward to hearing how it sounds with the 12AU7 variants it's designed for.
Öogliibox Mellivora Capensis Power Amp Mark I. Based on the DIYAudio Honey Badger with DIYAudioStore power supply, soft start and speaker protection boards installed in an AliExpress chassis. With a 1000VA Antek transformer and 80,000uF of filter capacitors this beast was built specifically to drive my Magnepan LRSs with as much headroom as possible - a measured 140 watts into 8 ohms and 270 watts into 4 ohms, both channels driven. A sweet sounding class AB amp that has tons of drive, tight bass, and a huge soundstage.
Öogliibox Phono Stage Mark II. My current phono stage which has seen many revisions, it currently resides in a die cast Hammond enclosure with seperate power supply. I intend to build a top spec remote dual rail power supply using a spare 300VA toroidal transformer I have. The stage itself is built upon a Muffsy PP4 board running on +-15V with Burr Brown opamps. You won't find a better sounding or fully configurable solid state phono stage for less money than what Muffsy offers. Put good parts into it and you'll be blown away with the performance for the money.
Öogliibox Phono Mark III. I built this one from spare parts I had lying around and sold it to a local hifi guy. Hopefully it's still running sweetly in someone's system!
Öogliibox Phono Mark I. The genesis of my DIY obsession and the origin of the "Ugly Box". I built this circuit from scratch with point to point wiring on a perfboard using the Audiokarma CNC phono stage schematic. Runs off 9V batteries for around 15-20 hours. Ugly though it may be it was a revelation how much better this was than my NAD PP2e and I never looked back.