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Bottlehead Amplifier Discussion / Comparison Thread: Crack, SEX & Mainline

Discussion in 'Headphone Amps (full-size)' started by loquah, Sep 24, 2013.
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  1. dmhenley
    I've got a stepped attenuator on the way - last mod for the SEX amp. Have an Alps in there now. I'm curious.
  2. gab840
    Great ...Provide impressions post-upgrade !!! :)
  3. gab840
    Guys, Can you recommend a good power cable as my Sex Amp is of 240V and cant get the same from Bottlehead directly as they have for 120v only. 
  4. DavidA
    Got a question on OTL amps, saw this posted in another thread in relation to the Crack, does this make sense?
  5. Loquah
    That sounds like someone who's misinformed. OTL designs are popular because of their simplicity which gives excellent performance for the price. The zero feedback design actually does leave the signal unaltered as far as I understand it, but obviously the week influence the overall tonality of the sound.

    The Crack has a well earned reputation as one of the best amps around for the price and with high impedance cans
    smitty1110 likes this.
  6. DavidA
    Thanks for the reply, I was thinking that the OTL design was one of the simplest based on my very limited electrical engineering knowledge and why would there be so many OTL amps out there if the design was inferior?
  7. Loquah
  8. dmhenley
    Stepped attenuator installed in the SEX amp today. $50 part from Ebay.

    Driving 'phones: Higher resolution and wider listenable volume range are initially apparent, and in comparison to the Alps blue I had in prior. Sounds fantastic. I feel the low end is tighter too - maybe just more texture across the entire spectrum. 

    One note: I definitely have to turn the volume up higher - even with the Nighthawks. It's not subtle. And, when I first tried driving my Lore (98db speaker), the difference was more dramatic. Example: with the Alps blue, and depending on source material - 10 o'clock on the dial was loud. I've a small listening space. With this new part, I'm going to 12 o'clock plus.  

    Is this expected, or might I have created a problem during the install?
    I can head over to the BH forums if this gets technical, but thought I'd throw it out there. I should add there is no distortion and I'm finally using the full power of the amp. No complaints.

    What were your experiences going from the standard or an Alps pot to a stepped attenuator?
    Did you experience any kind of break in with this type?
    jodgey4 likes this.
  9. JamieMcC
    Hi I'm pleased you like the new stepper I have a stepped attenuator in my Sex it was fitted from the get go so thats not much help so cant really comment on how the stock pot sounded in the Sex I guess its exactly the same as fitted in a number of the BH kits.
    Its pretty sad to hear that the production of such a versatile and great sounding amp has come to a end. I enjoy mine both with headphones and speakers (Fostex FX120 full range drivers)
    However getting back on track here is an old post of some previous impressions of changing from the stock pot on the Crack to the Valab stepped attenuator. You will see they are generally in line with your own impressions.

    "Initial impressions with a few hours listening.
    Tubes, Mullard 12au7 and Tung-sol 5998, Phones Beyer T1 and HD 650's
    Most noticeable is an improvement in clarity particularly to the mids and top end.  Music seems to have more of a crispness and openness to it.
    Placement within the soundstage seems a little more precise. Instruments have a little more attack and bite to the leading edges of notes.
    I can hear some woodiness texture to certain wind instruments I had not noticed before.
    Listening as I type to Fleetwood Mac, Lindsey Buckingham’s I' so afraid one of my favourite tracks, is more forceful, darker the bass is tighter and has a touch of presence to it rather than just hearing it.
    My low level volume channel imbalance has gone.
    I was not sure how I would like the volume steps compared to the Cracks standard smooth action pot which I was familiar with in contrast the Valab seemed notchy when trying it before fitting and not very nice at all from a tactile point of operating (I came close to not fitting because of this and had an Alps Blue pot at the ready). This impression improved once fitted and I was adjusting the Valab with the knob fitted.
    I am really pleased with the Valab I have had it in my draw for a while and had been a little daunted as to fitting it because of the amount of de-soldering and rewiring that was required in my case and not wanting to wreck my perfectly working Crack in the process.
    IMHO the Valab has taken my BHC+Speedball +Tung-sol 5998 to a level of refinement above which I had been experiencing when running with the 6AS7G GEC brown base without the Valab fitted. My perception of performance of the GEC is likewise improved."
  10. dmhenley
    Hey Jamie - thanks for the details!
    I am very happy with the upgrade. Was thinking last night, that this was my final mod for the SEX. The Jupiter caps and attenuator are enough.
    It is too bad that they had to retire it. On that note - going to try and grab some more 6DN7's soon. 
    Now, onto the next project!
  11. dmhenley
    Alright, so....I was enjoying the new attenuator, and a couple days later the right channel went out. Being new to building, I assumed it was error on my part, and checked, re-checked and then re-wired one section in an attempt to correct the issue. after a couple three hours of total work over two days, I pulled the tubes and swapped them right for left. Right channel is back. Should've checked the tubes first.

    Now, this is what Grandpa Rudy would've called goin' round your elbow to get to your thumb.
  12. Loquah
    LOL. Done that myself! :wink:
  13. dmhenley
    I wanted to update a comment we shared on the Nighthawk thread re: noise with the SEX and Nighthawks.
    I'm updating my analog chain, and picked up a tube (6922) phono pre this week. It sounds fantastic, and I've been doing some listening with the Nighthawks. There's almost no hum....so, the hum is worse when the Gungnir mb is plugged into the SEX. At least, that's my assumption. I've not yet tested this, but it was a surprise. Assumed it was the SEX, but perhaps not. The vinyl sounds ridiculously good through the NH, and in part because the noise floor is lowered. 
  14. rbc3
    I use my Mainline at the office.  Yes it gets occasional stares and questions about what kind of weird science kit I have going on.  
    A recent post in another thread about TheBit Opus 1 DAP has me wondering what people over here think about double amping.  The Opus 1 does not have a line out and so I'm listening to music using the 3.5mm headphone out plug through the Mainline in to my headphones.  Does anyone else use a portable or other audio source that doesn't have a line out with your Mainline?  What have you done to avoid any double amping effect?  I'm not even sure I understand what double amping is because most home audio systems have a preamp with gain in addition to an amp...
  15. Loquah
    Double amping isn't the end of the world. As I understand it, the biggest issue is that you are placing more potential influence on the signal in the signal path and therefore may be degrading the sound quality. If you're happy with the sound though you should stick with it.

    I use the Shozy Alien with an external amp sometimes because the external amp has better control over the drivers in the earphones / headphones so it does sound better than using the Alien alone.

    In general, it seems to be common practice to raise the volume on the source quite high (often to max), but make sure you don't introduce any clipping and distortion into the signal. If you hear distortion, pull the source volume back until the distortion is gone and then a few more just to be safe.
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