Frigate® (User Manual) is a high end pure class A OTL DIY tube headphone amplifier kit designed for the highest quality music reproduction with the minimum distortion. An essential part of any good sounding headphones is the amplifier that is driving them. Frigate® is capable of driving a wide range of headphones from 30 Ohm Grado to 300 Ohm Schennheiser and it will give you the best advantage in listening pleasure. The most immediately noticeable quality of Frigate® is its silent background, nearly totally devoid of hiss. With the volume turned to maximum listening levels and no music playing, there is dead silence. With matched Electro Harmonix 6922 and Sovtek 6H30Pi driver tubes, the amplifier puts out a rock and roll flavor, with that midrange and lower-treble hardness that makes rock enjoyable. The impact of percussive instruments is forceful, and it feels like air is being moved on deeper bass notes. The bass extends quite deep and is somewhat emphasized in a slightly round way. The best way to describe Frigate's sound is to say it is ORGANIC.
Do not compare this tube amplifier to the ones made somewhere in Asia from counterfeit parts and using low voltage Wal-Mart switching power supplies. Frigate® uses only the finest audiophile quality components that have been carefully selected with no expense spared. Frigate uses two 6922 and two 6H30Pi tubes for their linearity and low distortion. The 6922 and 6H30Pi tubes are matched with an aid of Amplitrex tube tester and a computer. High quality Kemet, WIMA, Nichicon capacitors are used along with an audio grade ALPS volume potentiometer. Military grade Vishay/Dale metal film resistors used throughout the kit. A high quality triple bus power supply Trident® (situated on a separate PCB) with ultra low noise characteristics delivers anode and filament voltages and a very generous amount of post and pre regulation smoothing capacitance provided by Nichicon and Kemet capacitors. The kit is assembled on Canadian made printed circuit boards that have thickness of 1.75 millimeters and 2 Oz copper traces. You have three choices for purchasing this kit: (a) headphone amplifier kit Frigate alone without power supply Trident® and without transformers; (b) headphone amplifier kit Frigate with power supply Trident® but without transformers; or (c) headphone amplifier kit Frigate with power supply Trident and transformers (filament 182L12 and B+ 182E110). The transformers are manufactured in Waterloo, Ontario, Canada and are designed for both 120V and 240V power arrangements.
Parallel tubes are commonly found in hi-fi amplifiers since they give an improvement in the Signal-to-Noise Ratio (SNR). This happens because the two tubes combined can operate at lower anode current while still achieving the same gain as a single tube. Less anode current means less flicker noise. In fact, it is a general rule of electronics that every time we double the number of amplifying devices in parallel, we get a 3 dB improvement in SNR, in theory at least. In practice the figure may be better or worse than this, depending on how other circuit parameters change.
Frigate® is using a parallel arrangement of 6H30Pi tubes and operates at 70% of the current of the single stage 6H30Pi, so the total anode noise current of both circuits is the same. But because the parallel stage 6H30Pi has a lower anode resistance Ra, its output noise voltage is lower, while its gain is higher. These two elements combine to give an overall improvement in signal to noise ratio of 4 dB. And even more importantly, the parallel stage will give lower harmonic distortion and more output swing.
Headphone amplifier kit Frigate® is also available as assembled, tested and operating headphone amplifier. Contact us if you wish us assemble headphone amplifier Frigate® for you.
Specifications of Single End Pure Class A OTL Headphone Amplifier Kit Frigate®
Frequency Response: 10Hz - 250 KHz (-1dB)
Headphone Impedance Range: 30 Ohm - 600 Ohm
Input Impedance: 100 KOhm
Output Impedance: 295 Ohm
Total Harmonic Distortion: < 0.001%@1KHz
Power Consumption (Anode): 32W@250 Volt
Power Consumption (Filament): 18W@6.3 Volt
Signal to noise ratio: 108 dBa
Crosstalk between left and right channels: -92dB
Maximum Output Power vs. Impudence:
200 mW@30 Ohm
250 mW@60 Ohm
500 mW@100 Ohm
650 mW@200 Ohm
900 mW@300 Ohm
650 mW@400 Ohm
250 mW@500 Ohm
200 mW@600 Ohm
Component Selection of Single End Pure Class A OTL Headphone Amplifier Kit Frigate®
Tubes: Two Matched Electro Harmonix 6922 and Two Matched 6H30Pi
Volume Potentiometer: ALPS RK27 also known as Blue Velvet
Resistors: Vishay/Dale Metal Film
Input Coupling Capacitors: WIMA 1 Microfarad
Interstage Coupling Capacitors: WIMA 1 Microfarad
Output Coupling Capacitors: WIMA 1 Microfarad
Decoupling Capacitors: Nichicon 100 Microfarad
Feedback Grounding Capacitors: Nichicon Muse Audio Grade 100 Microfarad
PSU Pulse Suppression Capacitors (Anode): Eight WIMA 0.047 Microfarad MKP-X2
PSU Pulse Suppression Capacitors (Filament): Eight WIMA 0.047 Microfarad MKP-X2
PSU Pre-Regulator Capacitors (Anode): Three Nichicon 100 Microfarad and One Kemet 0.22 Microfarad
PSU Post-Regulator Capacitors (Anode): One Nichicon 100 Microfarad and One Kemet 0.22 Microfarad
PSU Pre-Regulator Capacitors (Filament) Left: Three Nichicon 1000 Microfarad and One Kemet 0.22 Microfarad
PSU Post-Regulator Capacitors (Filaments) Left: One Nichicon 1000 Microfarad and One Kemet 0.22 Microfarad
PSU Pre-Regulator Capacitors (Filament) Right: Three Nichicon 1000 Microfarad and One Kemet 0.22 Microfarad
PSU Post-Regulator Capacitors (Filaments) Right: One Nichicon 1000 Microfarad and One Kemet 0.22 Microfarad
PSU Voltage Regulator (Anode): MOSFET IRF840
PSU Voltage Regulator (Filament) Left: LD1084V
PSU Voltage Regulator (Filament) Right: LD1084V
I had intended to build the kit over the Christmas break when I have a little more free time, but curiosity got the better of me, and I finished it last weekend in prototype configuration. The kit is very easy to build, and the parts quality seemed very good. I wasn't sure of the tab on the low voltage regulators was live (they often are) so I mounted them electrically isolated from the heatsinks, but perhaps that was unnecessary. The parts lists etc are helpful.
The amp has been running more or less continuously for the week, breaking itself in and breaking in the new pair of HD700's. Initial impressions are very good - very very quiet; good crisp dynamic sound and great spatial separation. Channel matching seems very good indeed. That is all with CD source - I will try it with a proper quality signal (vinyl) tonight.
Once everything seems broken in I will probably play around with it a bit - something I can't resist! The coupling caps will be first to go - I am quite fond of the Ebay Russian PIO capacitors, bypassed with some Teflons.I'll need to decide what I am finally going to keep in there before building an enclosure for it - the PIOs are quite bulky. The enclosure will almost certainly be the Christmas project.
Thanks for producing such a nice design and such a good value kit!
Brian, New Zealand, October 17, 2013