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OTL/OCL Triode Headphone Amp

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ships in 1-3 days.





Want to hear what your headphones sound like when directly connected to the tubes? Are you also a bit crazy and heat-tolerant? Then Folkvangr—our completely bonkers, limited-production, 10-tube OTL/OCL tube amp with impedance multiplier—may be for you. 

Connect Directly to the Tubes
Folkvangr goes beyond output transformerless tube amps, and also eliminates the output coupling capacitor. With Folkvangr, your headphones are literally connected directly to eight 6N6P output tubes, with nothing at all in-between. An advanced 8-servo DC stabilization system with DC sensing and relay protection ensures the safety of your headphones.

Change Your Lows to Highs 
Tubes will never be the equal of transistors with low impedance loads, so we added a switchable, integrated impedance multiplier that makes your low-impedance headphones look like high-impedance headphones. Switch on the multiplier, and your 32 ohm headphones look like 256 ohms to the amp, so you can use a wider variety of headphones.

Roll, Switch, Connect, and More
With Folkvangr, you can “roll” the 6N1P input tubes for 6922, ECC88, and many other tube types, so you’re assured of a wide variety of options. Choose low or high gain, switch between two inputs, and connect to the provided preamp outputs to create an entire system. 
Designed and Built in California
By “designed and built in California" this is what we mean: the vast majority of the total production cost of Folkvangr—chassis, boards, transformers, assembly, etc—goes to US companies manufacturing in the US. Our chassis are made minutes from our facility. Our PCBs are done just over the hill from us. Our transformers are also made in California. You get the picture. 
5-Year Warranty and Easy Return Policy
Folkvangr is covered by a 5-year limited warranty that covers parts and labor. And if you don’t like your Folkvangr, you can send it back for a refund, minus 5% restocking fee, within 15 days of receiving it.  One exception: the tubes. Those we cover for 3 months.

Without Impedance Multiplier
Maximum Power, 32 ohms: 300mW RMS per channel at less than 10% THD
Maximum Power, 300 ohms: 1.2W RMS per channel at less than 10% THD

With Impedance Multiplier
Maximum Power, 32 ohms: 1.4W RMS per channel at less than 10% THD
Maximum Power, 300 ohms: 1.5W RMS per channel at less than 10% THD
Frequency Response: 20Hz-20Khz, +/-0.5db (worst case, high gain, 32 ohms, impedance multiplier off)
THD: < 0.5%, 20Hz-20KHz, at 1V RMS, low gain, 300 ohms
IMD: < 0.4%, CCIF at 1V RMS low gain, 300 ohms
SNR: > 100db, unweighted, referenced to 1V RMS, low gain; >90dB, unweighted, referenced to 1V RMS, high gain
Crosstalk: < -60dB, 20Hz-20KHz
Output Impedance:  18 ohms (hi gain), 7 ohms (low gain), 8/3.5 ohms with impedance multiplier hi/low gain
Input Impedance: 100K ohms
Gain: 6.5 (16.3dB) or 1.5 (3.5dB), via front switch
Topology: Output transformerless (OTL) and output capacitorless (OCL) Class-A triode headphone amplifier with White cathode follower (WCF) output; switchable gain and 8x impedance multiplier.
Protection: analog computer style oversight for high DC with turn-on delay and muting relay. 
Power Supply: 400VA transformer with secondaries for discrete regulated 200V and +/-100V supplies, plus secondaries for regulated +/-12V oversight and impedance multiplier supplies, plus 6.3VAC at 7.2A for tube heaters, more than 10,000uF filter capacitance on HV supplies
Power Consumption: 100W
Size: 16 x 8 x 2.875” (total height with tubes 4.5")
Weight: 15 lbs

Are you kidding me? 

No, seriously. How do you justify the existence of this amp?
We don’t. Same as lots of other companies don’t justify the existence of their $1.5 million supercars with single-digit gas mileage, 168-core computers that need 20A AC sockets to run, $450,000 watches, $10,000 espresso machines, or anything else that’s completely bonkers.
Well, then, can you at least sell me on it?
No, we don’t do sales pitches. You either want it or not. Simple as that.
Then can you tell me why you might want such a thing?
Again, no. You either want it or you don’t. You understand it or you don’t. There’s no judgement here—I mean, we say pretty much every time we’re asked that you don’t need anything more than a Magni as a headphone amp, and we’re 100% serious about that. 
At least tell me it’s super-powerful.
Nope, not really. 
Then it measures really good?
Again, ah, no.
Or it’s super-convenient and easy to live with?
Nope, it gets really hot and we wouldn’t use it with IEMs.

Some people like tubes. Some people like lots of tubes. Some people want the most tubes we ever put into a product, plus the complete insanity of an OTL and OCL tube amp—as in, your headphones are connected directly to the cathodes (and anodes) of the 8 output tubes, with absolutely nothing in-between.
Why is OTL and OCL important?
OTL, or output transformerless, is an approach to tube amps that eliminates the usual output coupling transformer. This sounds neat in theory, but to make it work, you need some very unusual tubes—tubes that can do relatively high current. “Relatively,” because even the stoutest tubes are laughable in the context of, say, MOSFETs. Folkvangr gets higher output into low impedances by simply using a whole lot (8) of these relatively high-current tubes. But Folkvangr goes a step farther and also eliminates the output coupling capacitor that is usually used in an OTL amp, so your headphones are literally connected to the tubes. 
That sounds…terrifying.
Yes. Which is why, even though we have 8 separate DC servos to stabilize the output pairs, and even though we have DC sensing and protection, we don’t recommend you use this amp with sensitive IEMs. 
So why did you do this at all?
First because it was interesting. What would an OTL/OCL tube amp sound like? I mean, it’s not like there are a ton of them out there. So we built one to see how it went. And it turned out we really, really liked the way it sounded. And so we decided to build it. Fun fact: we didn’t measure it until near the end of the development, so that wouldn’t influence the sound. So if you’re looking for a measurement amp, this ain’t it. 
And what is this Impedance Multiplier you’re talking about?
The impedance multiplier is a way to make the headphone load look like 8X its actual impedance, so if you’re using, say, a 32 ohm headphone, it looks more like 256 ohms to the amp. It’s a lot like a transformer, but instead of a hunk of iron, it’s a simple electronic circuit using an integrated buffer. 
Eeek! You’re mixing ICs with tubes! Heresy!
Yes, ho ho.
Oh I don’t want this now, this is evil, this is—
Then leave the Impedance Multiplier turned off. Turning it off takes it completely out of the circuit. When it’s off, there’s nothing IC-like between you and the tubes. Fun fact: even when it’s on, there’s technically nothing between you and the tubes, since the output of the impedance multiplier is taken in parallel, and the reference is the tube output, so the distortion profile is exactly the same.
Why no balanced inputs or outputs?
Because this isn’t a balanced amp, and we don’t add connectors to fake you out. 
Why isn’t it balanced?
Because it magnifies the tubes’ inherent weaknesses—current output and output impedance. Balanced amps have to deliver twice the current into the same load, which ain’t a great idea with tubes. Also, balanced amps have double the output impedance. So, as a balanced amp it would be an inferior amp.
I hear that tubes ain’t gonna be available anymore. How does this affect this crazy-ass tube amp?
Well, the death of the tube may be a bit overblown. As of the time of this writing, the 6N1P and 6N6P used in Folkvangr are still readily available, and we have large stocks of each. We expect that you’ll be able to find these tubes for a long, long time.
Do the tubes need to be matched?
The two input tubes, yes. The 8 output tubes, nope. 
Does this amp run warm?
No, not at all. 7.2A of heater current, plus 120mA across 200V doesn’t dissipate any power, thanks to our special zero-point Tesseract Cooling Technology.

You’re kidding!
Yes, of course we are. It runs plenty hot. This is fine. It’s designed to run this hot for a long, long time.
What is Folkvangr?
In Norse mythology, Folkvangr is kinda like, well, a “better” Valhalla. As in, you needed to be personally chosen by Freya to enjoy that afterlife, whereas Valhalla just required you to die in battle. Since we’re simple, we chose Folkvangr as the name for this much bigger, crazier tube amp.