Can we expect 300B/2A3 Bottlehead headphone amp someday?

[ipetruk]

Hi dear Bottlehead team,

Does it make sense to build a 300B/2A3 headphone amplifier? Have you ever considered this?

What niche, benefits or drawbacks will it have? Tube price is one drawback for sure, this . Or is it just an overkill to put a tube like that just for headphones?

Some manufacturers produce really luxury amps with 300B/2A3: Cayin HA-300 300B, Eddie Current – Studio, Manley Labs – Neo-Classic, Woo Audio WA5-LE and WA-33, Ampsandsound Agartha 2.0.

I can see traces of this discussion on other topics, but I cannot find a dedicated discussion.

Thanks,
Igor.

[Paul Birkeland]

You can use a speaker to headphone adapter with either a Stereomour or a Kaiju provided you also install the DC filament upgrade.

Drilling a hole in the base of a Stereomour to add a headphone jack is a pretty simple process, so developing a separate kit to fill this niche doesn't seem necessary.  You may also find that the Mainline offers a bit more overall performance if you don't need the extra power from the big speaker amps.

[ipetruk]

Thank you for a quick response!

As I understand Mainline is not SET. What would you say be the main reason Mainline beats SETs? I guess "better performance" is hard to quantify and are in tubes for something extra tubes provide. 300B/2A3 are described as very pleasant tubes to listen to.

Additional question, have you considered shipping Kaiju/Stereomour with that jack? From your side it is only extra hole, extra component, extra wire. It should not drive the cost meaningfully, probably extra $50 max. But it may boost sales as people will see higher value and versatility in the product. I mean people can search for the mod on the forums if they really seek it, but this feature is easier discoverable on the shop pages.

[Paul Birkeland]

As I understand Mainline is not SET.

The Mainline definitely is a SET headphone amp.

What would you say be the main reason Mainline beats SETs? I guess "better performance" is hard to quantify and are in tubes for something extra tubes provide.

The Mainline offers a much simpler circuit with a single gain stage and has a power supply that's fully shunt regulated.  It's also very quiet. 

Additional question, have you considered shipping Kaiju/Stereomour with that jack

The extra hole means keeping another two different pieces of wood in our inventory.  We would have to use the kind of jacks on the Mainline to ensure that the wood thickness doesn't present an issue, then we'd need appropriate screws to go into the wood, then we'd need to write instructions for balanced vs. unbalanced HP jacks, etc. etc.  All of these extra instructions and customizations are unnecessary if a simple adapter cable is used instead and the resale value of the amplifier is maintained with this approach.   

[ipetruk]

The Mainline definitely is a SET headphone amp.

My facts were fake news, sorry. I did not realize those are triodes... You are right.

The extra hole means keeping another two different pieces of wood in our inventory.

Ah, wait, I assumed the jack will be on metal chassis with the rest of the stuff, not on the wood. Your argument about more complex manual is valid, but I've also provided some advantages of this approach. Resale value would be fine if this was a part of a stock model

[Paul Birkeland]

Yeah, doing it on the chassis plate then means we have an extra chassis plate, kit assembly manual, and upgrade manuals.  If we do this for the Kaiju and the Stereomnour, that's five new manuals and two chassis plates added to the inventory that would be very easy to mix up with the normal versions and send people on accident.  We would also need to stock another attenuator overlay for the Stereomour. 

Here's an example of an adapter cable that accomplishes the same goal:
https://www.zynsonix.com/Speaker-Output-to-Headphone-Balanced-Adapter_p_16.html

For people who want a factory built kit, I can customize stuff like this into a custom enclosure too.

[ipetruk]

Yeah, I guess this covers the use case of very power-hungry headphones - Susvara.

But those high end amps I've mentioned above are using for 300B/2A3 for normal headphones. These tube are there not for power, but for some specific sound signatures, which is considered very "high end". I personally don't any gear with those tubes, I am only noticing that those tube are often seen in very high end amps. So it is just marketing, e.g. "This tube costs like a car, so... so... it must sound good for everything, including headphones"?

Use for speakers on another hand is well justified, that's clear

[ipetruk]

Also on a more general question, do you see any benefit of 300b/2A3 for headphone amps vs say 6C45pi?

Say, if you did provide the right shunt power regulator for 300b/2A3 amp too.

[ipetruk]

The Mainline definitely is a SET headphone amp.

I am still processing this answer. It is triode based, true. So it is a "Single Ended Triode" amp with... balanced output? This terminology is confusing

[Paul Joppa]

Balanced is not push-pull; they are completely different concepts. Single ended and push pull are internal circuit topologies; balanced lines are a interconnect protocol. In the case of Mainline, the output transformer connects the single-ended amplifier circuit to the balanced-line interconnect.

[Paul Birkeland]

I am only noticing that those tube are often seen in very high end amps. So it is just marketing, e.g. "This tube costs like a car, so... so... it must sound good for everything, including headphones"?

Yes, I would agree with that.  You'll also see a lot of 5K:600 ohm "headphone" output transformers that are useless when used in that way, but people buy them anyway...

[skygazer]

I just built a Stereomour, and I'm really enjoying playing through a pair of Buschorn Mk II's (Fostex FE83) that I originally built for my Dad 20 years ago.  8 ohm taps on the output work great for these speakers.  Note that this also works great through a Stax SRD-7/SR-Lambda (not pro) cans!  I have the DC heater upgrade kit, but haven't installed it yet.... on the to-do list.

I tried hooking up Hifiman HE400se cans (25 ohm) direct to the output, but it caused the amp to have really bad microphonics. Definitely not good!  I've ordered a pair of 12 ohm 10W resistors to parallel with the HE400se to bring the impedance down to 8 ohms at the terminals.  I should loose about 6db of gain at the headphones, but hopefully have better response & stability.  We'll see what happens.

I suspect that using this amp with 300 ohm cans is a non-starter.

[Paul Birkeland]

I just built a Stereomour, and I'm really enjoying playing through a pair of Buschorn Mk II's (Fostex FE83) that I originally built for my Dad 20 years ago.  8 ohm taps on the output work great for these speakers.  Note that this also works great through a Stax SRD-7/SR-Lambda (not pro) cans!  I have the DC heater upgrade kit, but haven't installed it yet.... on the to-do list.

I tried hooking up Hifiman HE400se cans (25 ohm) direct to the output, but it caused the amp to have really bad microphonics.  I've ordered a pair of 12 ohm 10W resistors to parallel with the HE400se to bring the impedance down to 8 ohms at the terminals.  I should loose about 6db of gain at the headphones

No, you won't lose 6dB of gain from that, and you may not notice a whole lot of difference to be honest.  You might try rewiring the output transformers for 2 ohm operation to decrease the output of the amp a bit and make things less sensitive.  You could also try an 8 ohm resistor connected to speaker + in series with a 1 ohm resistor connected to speaker - on each channel, then take the headphone output from each 1 ohm resistor.  That will pad down the output a bit for more sensitive headphones.

[skygazer]

The 12Ω resistors in parallel with the H400se's seems to work well for me.  Gain wasn't the issue... without the resistors, there seemed to be a lot of high frequency energy, with maybe some distortion.  Plus the microphonic of the stock 12AT7's were very noticeable... a kind of ringing.    By presenting an 8Ω load to the 8Ω taps on the OT, it seems more stable now.

[ipetruk]

A related question that would benefit this topic: why 300b is not noisy for the BeePre preamp, but too noisy for headphones?

Eventually BeePre 2 could be connected to the headphone amp too. If it was and that amp was super clean, would the noise of BeePre 2 be exposed? Is it expected to be used with speaker amps like Kaiju?