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Here are my impressions of the 1101 Audio "V6" custom headphone amp.

I was looking for a custom OTL amp that would sound at least as good as my Glenn 300B custom headphone amp, but with a vast range of tube rolling possibilities. In April of this year I decided to start contacting custom tube amp builders. Mischa was the only person who I connected with straight away, and from his first emails I could tell this guy understood what I was trying to do (even if he thought I was a little crazy!) and from the outset he provided a detailed design.

The amp arrived last week and I've had a few extensive listening sessions since then. The amp is huge! Here are a couple of pictures showing the amp on it's own and also with other pieces to provide some perspective:

 

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I've only rolled in a few tubes so far, but initial impressions are the 6J5's are like very, very good 6SN7's with similar qualities. Thunderous base when paired with the TS 5998. Superb depth with a hint of warmth. The C3g make the amp sound more like the Glenn 300B with superb clarity, detail and "airiness". The C3g also give the amp greater power than the 6J5 or 6SN7. It's quite the combo with 4 or 6 TS 5998. The TS 12SN7 BGRP sound about the same as their 6SN7 counterpart - which is a very good thing! But, for much cheaper.

Some say the LCD4 is a slightly dark headphone (not me). That's simple to adjust by using the C3g tubes. For an extended listening session (more than 2-3 hours), I can see myself starting with a bassier tube(s) early on, and then moving to the C3g later.

A similar bass level, perhaps even more so, is with the early Mullard ECC31/6N7 foil getters in the two 6J5 sockets. First time I've heard these running without adapters. Very nice.

 

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Here are some technical details about the amp:

- OTL topology
- Up to 6 power tubes (5998/6080/6AS7) or 4 6336.
- Switch for 6AS7G/5998 power tubes on the front of the power supply chassis
- Selector switch for 6SN7/12SN7/6SL7/12SL7 (same single socket) and C3g (two sockets) and 6J5 (two sockets). ECC31/6N7 can also be used in the 6J5 sockets.
- All driver tubes can be plugged in at the same time. Selector switch indicates which are "active".
- 2 piece amp with power supply and amp as separate pieces and connected by an umbilical cord.
- Vu meters on the amp chassis
- Volt meter to measure/display voltage (obviously) and Millamperes meter to show/display milliamperes DC. This value goes up with more power tubes used - each pair of power tubes takes about 95-105 ma, plus an extra 5-10 ma for the biasing and these values are recorded/displayed on this milliamperes meter.

- Using 6SN7, 12SN7 or 6J5 as driver approx. 4.5 watts into 100 ohm, and 3.05 watts into 200 ohm. (Mischa to confirm)
- With C3G as driver it gives slightly more power output: up to 5-6 watts into 200 ohm. (Mischa to confirm)

- Hammond heater transformers for the power tubes (all indirectly heated tubes run on regulated DC).
- Lundahl LL1651 for the high voltage. Power taken from the LL1651 to supply the low voltage for generating regulated DC
for the driver tubes (6SN7/12SN7/6SL7/12SL7/C3g/6J5).
- LT3081 DC regulators to generate super low noise DC for the driver tubes. Driver tubes are also indirectly heated.
- 21st century Maida style regulator for high voltage regulation. Uses a slow start, so allows the heaters to warm up
before full high voltage is applied to the tubes.

- Solid state rectification for high voltage supply.

- Jupiter 0.22uF copper foil paper & wax coupling capacitors: Sit between the driver tube and the output tubes. One for each channel.
- ClarityCap Output capacitors link the cathodes of the power tubes to the headphone jacks. One for every power tube.

All the tubes are employing constant current sources/sinks (CCS) meaning the current going through the high voltage line does not vary over time.

All of the signal circuitry stays inside the amplifier chassis, and all of the unfiltered power stays within the power supply chassis, with only highly filtered DC being sent from the power supply chassis to the amplifier chassis.

The resistors, caps and other components chosen for the build have all been overspec'd to make sure everything is extremely long lived and stable for many decades (Mischa provides a 10 year warranty with the amps because of this). 2% silver leaded solder used as it is the most robust long term.

Most critical resistors have been chosen as very low noise military rated Vishay/Dale resistors. Military rated resistors are overspec'd for their dissipation and long term stability as they have to remain stable and functioning in critical applications within the field (people's lives quite literally depend on it at times). Reviews for the RN55/RN60 series of resistors online are very good.

Notes on impedance:
The LCD-4 would work well with an OTL amp, and even one 6BL7/6080/5998/6AS7G/6336 per sidewould provide enough power to fully drive them to ear splitting levels (you could hit 120+ db levels from the power from one tube per side).

A typical amplifier using one 6080 per channel gives an output impedance of about 50-60 ohm. Using 3 tubes per side could bring theoutput impedance down to 15 ohms or so.

 

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A tremendous amount of effort went into this amp. The exterior design and idea for features were mainly mine, but obviously the internals of the amp design were from Mischa. I did insist on a few parts though, such as the Jupiter caps.

I took photos such as these to give Mischa an idea of how I'd like the tubes positioned:

And he'd reply with a sketch like the following:

 

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Lot's of design diagrams and various ideas were produced along the way, like this initial design:

 

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Early internal build of the power chassis:

Completed:

 

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Lazering of front panels:

 

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I did well for the first day just using the GE 6AS7GA power tubes, and even with cheaper tubes the amp sounds great. But today, I couldn't resist rolling in 6 TS 5998 with TS 12SN7 BGRP and TS 6SN7 BGRP:

And TS 5998 with Mullard ECC31/6N7 and Mullard ECC32:

 

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The amp sounds fantastic. It's great to hear fairly significant differences with the C3g vs the 6SN7 and related family of tubes. I still have a LOT of power and driver tubes to roll/try out...

Any downsides? The amp does run a little warm with 6 power tubes! I certainly won't need the radiator turned on in the room during the winter when running the amp with 6 power tubes. 2 power tubes also sound very good though.

Feel free to ask and questions. I'm sure I or Mischa will do our best to reply.

 

[Sound Trooper]

Oh my... this amp looks totally bad-ass! I'm sure it sounds fantastic as well. @leftside congrats!!

 

[Monsterzero]

Feel free to ask and questions. I'm sure I or Mischa will do our best to reply

Well,yeah,how much does it cost,and how does it stack up vs. your Glenn?

 

[L0rdGwyn]

Beautiful! Love all the detailed info, looks to be a killer amp. Very nice you can keep all of your driver tubes in place. Do they receive power even though they are not "activated"?

Given the highly filtered power and DC on the heaters, is the noise floor quite low?

 

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Well,yeah,how much does it cost,and how does it stack up vs. your Glenn?

You'll have to ask Mischa regarding cost. I'm not sure he'll ever want to build a complex beast like this again lol. He assures me a simpler amp with 2 or 4 power tubes will sound just as good.

Initial impressions are the amp sounds very similar to the Glenn 300B when using the C3g tubes (which is a good thing). It starts to sound quite different when using the 6SN7 and related family of tubes. With tubes like the TS BGRP (6 or 12 volt), Mullard ECC32 or ECC31 there is thunderous bass, and fantastic depth with a hint of warmth. I still have a whole bunch of power and driver tubes to roll.

The Glenn 300B acts as a great baseline. I run both amps at the same time (with the windows open... even in the winter...), swap tubes in the "V6" and then compare sound signatures by simply moving the headphones from one amp to another. I'll also want extended listening sessions with some of my favorite tubes to give further impressions.

 

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Beautiful! Love all the detailed info, looks to be a killer amp. Very nice you can keep all of your driver tubes in place. Do they receive power even though they are not "activated"?

Given the highly filtered power and DC on the heaters, is the noise floor quite low?

The tubes do not receive power if not activated. No "triplets"

The noise floor is amazingly low considering how many tubes are in my system. I'll try vinyl tomorrow. Just been using the DAC so far.

I've also used the amp with the high sensitive Focal Stellia - and even with those the amp has a very black background. You can only hear the slightest hiss at ear destroying volume levels. It really shines with harder to drive (like planars) with higher ohm ratings (which is what it was designed for).

 

[L0rdGwyn]

Very much undermining the old adage that planars cannot be effectively run on an OTL, very cool. Well I am sure Mischa will attract some more interested parties based on what you two have created here, well done, will be very interested to see what other projects head his way.

You have a lot of tube rolling to do