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  1. #1
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    Headphone amp as good as Crack

    Maybe it's a stretch to put this in a guitar forum, but I do intend on playing a lot through headphones, so... I built the Bottlehead Crack headphone amp. It's an Output Transformerless (OTL) class A, all tube amplifier. It's great for headphones with higher impedance. I have Sennheiser HD650 and they're a match made in heaven.

    I guess this is my first real electronics project. It came out really great. I've just been using it for music as my guitars aren't built yet, but honestly I can't stop thinking about it and can't wait to get home every day to listen to more music. It's so good I bought another one for work. And it's so good I bought a slightly different version to use with my AKG headphones (the Bottlehead S.E.X. which has output transformer for lower impedance headphones.)

    Click image for larger version. 

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    https://bottlehead.com/product/crack...amplifier-kit/

    Bottlehead has a great forum, similar to this one, with great support for building and modifying kits.
    Last edited by Joe Garfield; 15-08-2020 at 01:12 PM.
    *Pictures may be rotated due to my proximity to the equator.

  2. #2
    GAStronomist DrNomis_44's Avatar
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    Cool, I've always been fascinated by OTL Headphone amps, I definitely want to build one using a couple of spare 6SN7 twin triode tubes I've got in my stash of spare tubes.

    There's a website called Headwize, I think, that has some great designs and schematics for OTL Headphone amps.

    https://headwizememorial.wordpress.c...one-amplifier/

    https://headwizememorial.wordpress.c.../diy-projects/
    Last edited by DrNomis_44; 19-08-2020 at 12:56 PM.

  3. Liked by: Joe Garfield

  4. #3
    Quote Originally Posted by Joe Garfield View Post
    Maybe it's a stretch to put this in a guitar forum, but I do intend on playing a lot through headphones, so... I built the Bottlehead Crack headphone amp. It's an Output Transformerless (OTL) class A, all tube amplifier. It's great for headphones with higher impedance. I have Sennheiser HD650 and they're a match made in heaven.

    I guess this is my first real electronics project. It came out really great. I've just been using it for music as my guitars aren't built yet, but honestly I can't stop thinking about it and can't wait to get home every day to listen to more music. It's so good I bought another one for work. And it's so good I bought a slightly different version to use with my AKG headphones (the Bottlehead S.E.X. which has output transformer for lower impedance headphones.)

    Click image for larger version. 

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Views:	279 
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ID:	36995Click image for larger version. 

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Views:	142 
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    https://bottlehead.com/product/crack...amplifier-kit/

    Bottlehead has a great forum, similar to this one, with great support for building and modifying kits.
    Very cool project, but it seems to cost more than a decent crack habit...

  5. #4
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    I think the 6SN7 can work with this amp with the change of a couple resistors.

    There aren’t many commercially available OTL headphone amps around for a lower price. There’s a Darkvoice and a Little Dot made in China, but the parts are inferior as is the assembly work. I looked at sourcing all the parts separately and it wasn’t that much less.

    The SEX kit I bought is transformer coupled so I can use my lower impedance headphones (AKG). My gut feels is they’ll be the ones I’ll like for guitar, but we’ll see. Sennheiser has a nice rich, warm tone that’s great for listening to music but idk if that color is what I’ll want with guitar tone.
    *Pictures may be rotated due to my proximity to the equator.

  6. #5
    GAStronomist DrNomis_44's Avatar
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    Quote Originally Posted by Joe Garfield View Post
    I think the 6SN7 can work with this amp with the change of a couple resistors.

    There aren’t many commercially available OTL headphone amps around for a lower price. There’s a Darkvoice and a Little Dot made in China, but the parts are inferior as is the assembly work. I looked at sourcing all the parts separately and it wasn’t that much less.

    The SEX kit I bought is transformer coupled so I can use my lower impedance headphones (AKG). My gut feels is they’ll be the ones I’ll like for guitar, but we’ll see. Sennheiser has a nice rich, warm tone that’s great for listening to music but idk if that color is what I’ll want with guitar tone.

    Which two resistors do you think will need changing?, I'm thinking of using my two 6SN7 tubes for the two output stages (V2), and maybe a 12AX7 for the two voltage-amplifier sections (V1) in this design using three 6N1P tubes:

    https://headwizememorial.wordpress.c...one-amplifier/


    I may actually build the 6N1P OTL Headphone amp circuit as-is, but will need to order a suitable power transformer and three 6N1P tubes and three 9-pin sockets from Evatco, I think they do have some 6N1P tubes in stock, would be an interesting build project.


    As it turns-out, Evatco do indeed stock 6N1P tubes, Sovtek brand and Svetlana brand, they also stock a suitable power transformer, the one I chose had a 260-0-260 @104mA HT secondary winding and a 6.3V@3A Heater secondary winding, should be perfect for use in the 6N1P OTL Headphone amp.
    Last edited by DrNomis_44; 20-08-2020 at 01:54 PM.

  7. #6
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    I was mistaken - it’s not a matter of changing resistors, just making sure the heater voltage is correct. The Crack in stock form ties a few 6v leads together to heat the 12AU7 with 6v. You just have to use an adapter or wire the socket correctly.

    Yeah I have AKG K712s. They seem nice but I have a feeling they’ll really open up with a tube amp and particularly with more power. To my ears the Sennheisers have a ‘low mid bump’ and the AKGs have an ‘upper mid bump’. Usually when i play guitar I turn the mids all the way up so it should fit my preferences

    I’d actually missed a glue joint when I put the base together. I just fixed that last nigh and filled it today, so hopefully I’ll get to dying and grain filling and stuff. It will be good practice before getting back to my guitars.
    Last edited by Joe Garfield; 20-08-2020 at 03:02 PM.
    *Pictures may be rotated due to my proximity to the equator.

  8. #7
    GAStronomist Simon Barden's Avatar
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    The HD650s have about as flat a frequency response as you can get from headphones. AKGs like the 701/2s and 712s have a greater bass extension but are nowhere near as flat. That's only part of the story in the overall sound and feel, but a large part in the colour of the cans. AKGs tend to be more mid-forward, which can help when mixing on them, as you are presented with more sound in the areas the ear is most sensitive at and picks up most detail in. But they can slightly over-emphasize an already mid-rich sound like a Marshall amp/emulator, whilst a more scooped Fender amp sound can benefit.

    But in the end, you'll either like the sound or you won't.

  9. #8
    Only replaced mine recently due to the cord finally wearing out.
    Still, better than wireless, just like the mouse.
    Click image for larger version. 

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    cheers, Mark.

  10. #9
    GAStronomist DrNomis_44's Avatar
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    My main pair of headphones is an Audio Technica ATH-M30X, nice sounding pair of headphones, but I think it's about 32 Ohms impedance or something like it, AKGs are supposed to be the bee's knees.
    Last edited by DrNomis_44; 20-08-2020 at 12:22 PM.

  11. #10
    GAStronomist Simon Barden's Avatar
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    The HD650s don't have any bump or dip worth talking about. I have the Sonarworks headphone frequency response levelling plug-in, and the compensating curve for the HD650s is almost flat, with no more than ±1dB adjustment from flat. Whereas the one for my K712s is a lot more pronounced. Of course that's the generic 'averaged' response correction, and individual headphones will be slightly different, but I know Hrudolf from Sonarworks said that the HD650s didn't very by much at all between samples.

    So what you are hearing is pretty much what's being produced. Headphones take out any room influences, so if you are comparing the headphone sound with the sound from hi-fi or monitor speakers, the HD650 sound will be a truer response, without the dips and peaks in frequency response caused by room reflections (unless you have a very well acoustically treated room).

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