Walk into the lounge of any keen Audio Enthusiast and you'll see a Valve Amplifier at the heart of their system. Why? Quite simply because the old fashioned Valve Amplifiers gave the best sound. So what if there was a pocket size valve amp that would give us back the rich audio quality our smartphones so badly lack?
The Hybrid Valve Headphone Amplifier gives us back the warm rich quality sound that was lost when valves when transistors took over from valves. Plug it in between your phone or MP3 player and your headphones. Your music now passes though real glass tubes valves resulting in vastly improved sound quality. It will also boost the volume so you'll now have enough power to drive your headphones.
Although the sound is big, the amplifier is small- about the profile of an iphone 4, and smaller than many new phones. With a long life rechargable Lithium battery you will be able to listen to your favorite music for hours on the go.
How to Connect
The Valves- made by Rocket Scientists
Made by USA company Raytheon, makers of the patriot missile and Apollo's guidance computers. These glass tube valves are special: You'll find these same valves in some of the best studio microphones such as the Audio Technica's AT3060.
When designing the Valve Amplifier our first priority was to get the best sound possible to make up for the poor sound from most portable devices. Right down to the individual resistors, we've chosen components to give the lowest noise and distortion and best construction quality:
- Laser cut front and back
- CNC milled case from solid block of Aluminium
- Anodized case
- Laser engraved graphics
- Stainless steel fasteners
- Raytheon 6418 Valves- Military Specifications
- Metal Film Resistors
- 2 OZ Copper Tracks
- Bur Brown series OPA2134 amplifier 0.0008% distortion
- Low ESR Capacitors
- Surface Mount Components
Read the M2 Magazine Review
When your music enters the Amplifer the left and right channels pass into two Raytheon 6418 Valve as a stream of electrons. It then gets boosted in volume thanks to the world class Bur Brown series OPA2134 chip. This device has an unbelievable low distortion of just 0.00008%. These active components are supported by metal film resistors and thick two ounce copper tracks. We've shielded the amplifier in an aluminium case which is CNC machined from a solid block. The anodized front and back panels are laser cut and secured with marine grade stainless steel screws. The graphics are laser engraved onto the front and back. The valves are displayed behind a strong plexiglass window.
What's in the Box:
Military Spec quality case
Choose your color:
Kickstarter funding for Automated Assembly
Update 4 May; Now on www.hifipig.com
Update 15 May
Some backers have ask what the Output Impedance of the Valve Amplifier is. This is an important parameter as if affects the way the amplifier drives your headphones and the overall quality of sound and frequency response. Generally a low impedance is preferred and this is seen with many high end amplifiers. So here's how I did the measurements:
A sine wave signal is fed into the Valve Amp and the output voltage is measured by an oscilloscope. I ran the test twice with a 400 Hz signal for the first test and a 2000 Hz for the second. I read the output voltage first with no load and then I switched in the 33 Ohm load resistor and recorded the output voltage again. It will be lower. Here's the 400 Hz, no load with the result of 542 mV shown at the bottom of the oscilloscope:
And here is the screen shot for 400 Hz with load resistor with a result of 536 mV:
If we apply the formula below we can calculate the output impedance:
Ro = Output impedance and RL = 33 Ohm resistor. The result is 0.369 Ohms. I tried the same test again, this time with a 2000 Hz signal and a high drive level. Vopen this time was 825mV and VLoad was 821mV, resulting in 0.16 Ohm's impedance. The variation is due to many factors and the average impedance is 0.265 Ohms.
FREQUENCY RESPONSE CURVE
Frequency response was measured by running a signal generator into the amp at fixed amplitude and varying the frequency from DC through to 20kHz. The output was then measured on an oscilloscope for RMS volatge readings over the entire frequency domain. These were then entered into a spreadsheet and plotted on a graph. The results show a completely flat frequency response from 50Hz through to 17700Hz.. Through this range the output did not vary be even a millivolt. There was some roll of above 17700 Hz and a little below 50 Hz, with most of the low frequency roll of occuring below 20Hz. This result show and amplifier with an extremely flat frequency response.
Project backed by:
We've been asked for more colours- so in addition to Red, Blue and Black, we're adding Kickstarter Orange, and Green. These colours are anodized into the aluminium for extra durability. The graphics are then laser engraved.
UPDATE: VOLUME CONTROL
I've had many requests to add a volume control, mostly from those that want to run a DAC or DAP into the Valve Amp The purpose built 1Meg Ohm Potentiometers arrived today, I've added one to the PCB. Here's how it looks:
Now there are 2 places in the circuit when I could have added the volume control pot. Most amplifiers place the volume pot right at the input. Here's a circuit of a common Amp with the volume pot at the input (dotted area):
There are 2 good reasons why not to place the potentiometer here:
#1 Reason: The volume pot resistor & capacitor combination acts as a high pass filter so as the volume setting changes so does the frequency response.
Here's what a high pass filter looks like( looks familiar?):
#2 Reason: If the volume pot adjusts the volume at the input, this leaves the output stage set at full gain. Now as quiet as the OPA3124 is, there's always some noise (hiss) in all amplifiers at full gain. To negate problems #1 and #2 the volume pot has been placed right at the gain control circuitry of the OPA2314, the output amplifier. Now we have no filtering and a very quiet amp. As a result you can plug in your sensitive IEM type earplugs and play your music loud. If you leave all the settings as they are, and pull out the input cable the music stops- and is replaced by: nothing. Not even a hint of noise.
Risks and challenges
I have over 25 years of manufacturing and export experience in designing and producing medical products and electronics devices. I have designed, produced and marketed electronic telemetry products globally and therefore already have the knowledge and experience required to take an audio product to market. I will use my existing suppliers to provide the assembled PCB's.
While the PCB assembly of surface mount components will be out sourced, we will still hand solder the valves and switch as I have found in the past that hand assembly of these critical components gives the best quality results.
The Hybrid Headphone Valve Amplifier is fully designed and tested and already selling in High-End Audio stores in New Zealand and we have received outstanding feedback.
So far our amplifiers have been assembled by hand using a 20x power microscope to place and solder the surface mount components. The process is time consuming and tedious. Our next step is to have the circuit boards assembled by machine. We will still use exactly the same high end components and still hand solder and assemble the valves and cases.Learn about accountability on Kickstarter
- (30 days)