PandorAmp V1.0 : HiFi Tube Audio for the 21st Century
PandorAmp is an open-platform tube amp, designed to be integrated seamlessly into a modern audio system, giving the warm sound of a tube amplifier, and the control of a user-customizable microcontroller. First and foremost, I have designed a really awesome sounding, low distortion stereo tube amp. On top of this, I have overlaid a control scheme with a high-end microcontroller. The overall effect is a tube amp that allows you to monitor and control bias levels, power supply voltages, tube health, gain levels, feedback levels, and a bucket full of other things. The amp is really exciting, as this is the first time people can open up the box (thus the name) and mess with hardware and write code to control their amp. We can only offer a limited run of 75 assembled amplifiers for this first project, but we will release more kits if there is interest. Any funding beyond target will fund future projects at nielltronix.com
What we plan to do:
We are going to take the current lab demo unit and turn it into a
real product you can enjoy, crack open, and hack. The project will also launch an online community at nielltronix.com/forum to provide support and share ideas and tweaks to the amp and future projects. There, members will see progress on the amp and the build. The amp, which is
sitting on my lab bench cranking out tunes right now through studio
monitor speakers, is in a fully functioning state. All the various bits
and pieces work, but we need funding to integrate them into a whole. That
entails final industrial design work, mechanical engineering work to
design sheetmetal and woodworking prints, final circuit board (PCB) layout
design, parts procurement, and software design work. Sounds like a lot,
but that's why this project is on Kickstarter!
The amp will come with an LCD screen and a rotary encoder user interface, as
well as a USB port and an onboard bootloader for uploading your own
code. The code as-shipped, will be fully documented and tested, but
released in the CC domain. www.nielltronix.com
will maintain a forum for owners to share their own modifications to
the code or hardware. This is a tube amp that embraces the DIY movement
and brings tube audio into the MAKE-sphere in both a hardware and
software domain. Once the amp is released, users will be able to log into the Nielltronix community and discuss their amp mods and experiences with others. The amp is fully developed on the bench, and with full schematics, and a USB port, you can modify it to your heart's content. It is a tube amp
both for the hackerverse and the serious audio connoisseur!
The photo at the top shows what our industrial designer has come up with for the two chassis being offered. The chassis on the left is a hand-rubbed box-joint cherry wood frame made custom by Goose Creek Woodworks. The chassis on the right is made from custom-made anodized aluminum, made in New England. The amplifier itself is a 45W per channel stereo amplifier with user-selectable XLR or RCA inputs, switch-selectable 4, 8, or 16 ohm output, and a microcontroller. The microcontroller talks to the power supply, the amp, and the LCD and rotary encoder input device. Both designs have the same guts, but both designs cost a lot of money to produce. Any additional funds will to toward more Nielltronix amps or future kits and projects on nielltronix.com/forum.
Here lies the real driving force behind this project: I know there
are people out there who are just as passionate about high-end audio
and are tired of the same old stuff. Here's a new, exciting design
with an open-source, open-hardware approach, but that costs a lot of
money to get off the ground. Lots of parts are subject to minimum
purchases, and custom metalwork and woodworking cost a lot of money
too. Tubes must be secured in large quantity beforehand to ensure users
will have replacements. All of these things add up to a daunting task.However,
with just a little help at the beginning, we can make an amplifier that
the entire DIY and high-end audio community can appreciate.
Manufacturing Plan and Details
Nielltronix's president's decade-plus-long history in the electronics business has
forged relationships with vendors and engineering partners, enabling a
very lean manufacturing process. The PandorAmp electrical schematics and layouts are all in OrCad, and mechanical parts, save for flat sheetmetal parts, are all created in SolidWorks. Once all the final details are ironed out, and the funding from kickstarter arrives, PCBs will be manufactured by Advanced Circuits in Colorado. SMT and thruhole parts kitting will be handled by Digikey's new hands-off BOM kitting service. In addition to the bare board manufacturing, Advanced Circuits' new turnkey manufacturing service will be handling the raw PCB stuffing. Additional soldering and manual wiring will be finished by Nielltronix staff, though if demand is large enough, connectors and cables will be handled through OSI Electronics in North Andover, MA. Code is being written currently to expand the amp's interface capabilities. All code is in C, compiled with the C18 compiler provided by Microchip.
Once mechanical details are finalized and SolidWorks models completed, sheetmetal and woodwork final drawings will be executed. Woodworking drawings will be sent in a build-to-print state to Goose Creek Woodworks. Bent sheetmetal drawings will be shopped to a few different sheetmetal shops in New England with whom Nielltronix has had experience on projects in the past. Machined parts will be handled primarily by Clematis Machine in Waltham, MA. Flat sheetmetal parts, such as the top, front, and rear panels will be fabricated by Front Panel Express. Artwork for the flat sheetmetal can be seen below.
Custom ferrite transformers will be supplied by Renco, while custom iron transformers will come from Edcor. Mechanical hardware will of course mostly come from McMaster-Carr, but other hard-to-find hardware will come from a number of smaller vendors.
Final assembly, programming, and test will occur at Nielltronix headquarters. The Nielltronix assembly team (Fred, Dale, Jerry, Mike, the other Mike) has access to over 1500 square feet of manufacturing space, with all the necessary tools (programmable reflow oven, several soldering rework stations, oscilloscopes, etc.) to build this hardware.
2-channel stereo amplifier, 45W/channel
Custom output transformer with 4, 8, 16 ohm taps
Push-Pull Class AB2 with novel phase splitter
Integrated silicon audio front-end with microcontroller interface
Menu-driven intuitive click-and-scroll interface
< 0.5% THD 25W, <1% THD 45W, -3dB 10Hz, 45kHz
Signal input: RCA or XLR, clipping at 3V
Power input: Universal input, 100-240VAC, 200W
Power supply: <100mV 120Hz ripple at 425V, <75mV 120Hz ripple at 300V, <50mV 120Hz ripple at -75V
DC Grids, soft start buck grid circuit for long tube life
What about this t-shirt?
Our awesome designer spent a lot of time on this t-shirt design. We are using locally-sourced t-shirt printing in Boston, MA from http://www.hemlockink.com/.
Above is the Nielltronix tshirt, available in both army green and heather gray. It captures the awesomeness of the PandorAmp project and the cool nielltronix.com online community in a single cool t-shirt. Special thanks to @derekcascio for help with design.
So where is the project now?
Good question. I'm listening to the amp right now, but that doesn't answer the question. There are a number of things that must be addressed before you can listen to this amp in your livingroom. Here's a list of the various amp systems and subcomponents that must be finished before product release.
Power Supply: We haven't made any changes to the power supply in about 4 months, during which we've been testing the amp in all kinds of situations, from techno to Bach, and shorted output to low-line input. We just have to do a final iteration of the power supply PCB.
Controller Board: The interface circuit audio parts sit on a vector-board in the prototype chassis. The digital controls sit on breadboard, as seen above, with wires going to the audio interface board. A final PCB must be designed and created for this.
Chassis: Two chassis possibilities are shown above. The wood chassis is relatively well defined, and final manufacturing drawings need to be finished and sent to the woodworkers. The inset custom anodized aluminum chassis panels for the wood amp are designed and ready to send to the custom sheetmetal shop. The custom sheetmetal amplifier chassis is in concept phase, and will need to be fleshed out, detailed, and manufactured.
Parts Acquisition: Many parts must be acquired - from nuts and bolts to vacuum tubes and microcontrollers. Custom output transformers have been designed, and must be ordered. All of the electronic components required to make these amplifiers must be ordered, sorted, and made ready for assembly.
Power Amplifier Section: The hardest part, to be certain. Luckily, this part is pretty well taken care of. The tubes all work great and most importantly, they sound great!
Q: This amp seems cool, but I've never heard of the 1625 tube. Can you make it work with other tubes?
That's the whole reason behind running this project as an open
source/open hardware project! You can modify this amplifier to use a
variety of beam-power tetrodes or even pentodes. The power supply has
enough juice and the transformer is designed around a common plate
impedance, allowing for a variety of tubes. Don't like the 6SN7?
Plenty of tubes are pin-for-pin compatible!
Q: How does it sound?
A: Insanely awesome.
Q: This sounds like a complex project and a pretty ambitious build. Have you ever done anything like this before?
A: Products Nielltronix has designed are key components in semiconductor manufacturing processes, and are installed around the world. The president, Fred Niell, has released several different nixietubeclocks before, and is comfortable with this type of project. We're confident we can get all of this hardware and software out the door in the time given.
Q: I love my amp's sound, but I found a better bias point for the tetrodes when listening to techno. I'd like to share my data with others - what's the best way to do that?
A: The Nielltronix website will go live soon with a forum specifically for the open source modification of the amps, along with future projects. PandorAmp users can share schematics, data, code, and other ideas relating to the amps, and help guide us toward new projects.
Detailed Design Brief:
The input stage is based on a professional grade differential audio line stage receiver, the INA2134. The gain is set with an ultra-low THD stereo audio attenuator chip, the PGA2311. Additional gain processing and feedback processing is handled with National's performance audio dual opamp the LM833. The input stage is on a PCB in mixed SMD and thruhole technology.
power amplifier is a push-pull class AB2 amplifier using either Russian
G-807, American 807 or 1625 tubes for the power stage (user
selectable), and 6SN7s for the phase splitter and gain stages. The
output stage uses a high-grade M6 steel based transformer with a
low-leakage-inductance bobbin, giving excellent high-frequency
response. The AB2 operation point requires a fair amount of grid
current on the output tubes. As such, cathode followers are used to
drive the grids in high-power excursions. This is a departure from many
commercial tube amps that simply use a capacitor to couple from phase
splitter to output tube grid - doing so seriously affects transient
response introduces IM distortion at high levels. Additionally, since
the cathode followers don't care about the change in grid-circuit
impedance, there is a seamless transition from A to AB2. The
phase-splitter uses a novel active-tail cathode circuit, giving
extremely flat gain and phase, as well as extraordinary bandwidth. Components are mounted on a PCB with all tube connections are made with MOLEX minifit and microfit connectors.
around the tubes and the input stage are a high voltage power supply to
power the tubes and a microcontroller and associated user interface
hardware. Both the microcontroller and the high voltage power supply
present significant departures from traditional vacuum tube amplifier
design. The microcontroller adds incredible flexibility to the design.
The high voltage supply is not the typical plate transformer, rectifier
tube, and huge capacitor bank, rather, it is a sophisticated switch
mode power supply.
The high voltage power supply is a high
efficiency current-mode flyback circuit, utilizing a UC3845 and a
custom-wound transformer. The supply achieves roughly 82-85% efficiency
depending on bias settings. The main plate voltage of the amplifier is
425VDC, the preamp tubes use 300VDC, and the fixed bias sits at
-75VDC. Each voltage is supplied by the high voltage feedback
amplifier. The supply has a hardware-programmable transient response
and loop characteristic, meaning that the supply can sag and be just as
slow and underdamped as a typical tube and cap supply, or it can be
incredibly stiff and respond to transients in less than 10microseconds.
The amplifier as shipped will be set for ultra-fast transient response,
giving incredibly tight bass response and good speaker damping factor.
Additionally, the fully regulated 300V that feeds the screens of the
power tetrodes gives excellent dynamics and stability.
microcontroller can act in "hands-off" mode, where the tubes really
and the micro just reports things, or in a more "active" mode where the
micro is in charge of controlling feedback or bias levels. The power
supply is controlled by the microcontroller, as is the soft-start of the
filaments. Bias points are reported as well as total hours for each
tube. The microcontroller has both USB functionality and a bootload
capacity, making it possible for the user to change the firmware inside
the chip. The micro also has control of the filaments of the tubes -
the tube filaments are protected from inrush current by the
microcontroller driving a buck converter that provides a controlled
current to the filaments during warmup phase.
The microcontroller implements a simple, intuitive click-and-scroll type interface through a rotary encoder plus pushbutton control on the front panel. Additionally, a USB jack is situated on the control board to allow users to bootload code from their computer.
Absolutely! The amp will sound great with the as-delivered settings and software, so you can enjoy the amp without ever cracking the lid open. However, the amp does come with all you would need to customize the interface, should you choose to do so.
You will receive our never-ending gratitude and thanks, and you will also receive membership in the online audio and electronics hacking community at nielltronix.com. There you will find updates on the progress of the project!
With your donation, you will get an awesome T-shirt (see design in description), silkscreened on high quality shirts. You will also receive membership in the online audio and electronics hacking community at nielltronix.com. Every bit helps!
This pledge amount buys a barebones, no-chassis PandorAmp kit, the complete developer's guide and schematics, all 3 PCBs and components, transformers, tube sockets, a microcontroller with pre-loaded code, and no tubes. Note that the control board is mostly SMD devices, and requires some serious soldering skill and experience to assemble. Expect more than 50 hours for experienced electronics nuts. Only for the bravest souls... :)
This pledge amount buys complete, ready to assemble PandorAmp kit, with the hand-rubbed lacquered cherry chassis. Kit includes complete developer's guide and schematics, all parts and hardware, assembled and tested circuit boards and no tubes.
This pledge amount buys complete, ready to assemble PandorAmp kit, with the black anodized aluminum chassis. Kit includes complete developer's guide and schematics, all parts and hardware, assembled and tested circuit boards and no tubes.
With this generous donation, you will receive the black anodized aluminum chassis PandorAmp kit. You will receive all boards, and your choice of matched power tubes (G-807, 1625, NOS or new-production 807), your choice of matched preamp tubes (6SN7 or 6H8C), complete documentation, and everything else.
With this donation, you will receive a fully completed, extremely limited edition metal or wood chassis PandorAmp (your choice). These will be delivered in March, and will be extensively tested in-house and fully burned-in. The amp will be hand-assembled and tested by me and my crack team of technicians. Your amp will be assembled with your choice of power tubes (G-807, 1625, NOS or new-production 807), your choice of preamp tubes (6SN7 or 6H8C), and will include all documentation, and everything else. Each assembled amp will be serialized.
With this over-the-top donation, you will receive a fully completed, extremely limited edition metal or wood chassis PandorAmp. These will be from the first production run, and will be extensively tested in-house and fully burned-in. The amp will be hand-assembled and tested by me and my crack team of technicians. Metalwork on your amp chassis will be custom-engraved with your message (50 character max). Your amp will be assembled with your choice of power tubes (G-807, 1625, or 807), your choice of preamp tubes (6SN7 or 6H8C), and will include all documentation, and everything else. Each of these early-supporter amplifiers will be hand-signed and serialized.