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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. JamieMcC
    I would be mindful of the size of some of the capacitors especially if going above 10uf .

    fwiw I had some 10uF 800Vdc Audyn Cap MKP Plus in my Mainline for a while and thought they sounded pretty good a plus is they are a nice fit and have decent size stiff solid lead outs which are a help with securing adding some sticky back Velcro makes doubly sure they will not move until you want them to.

    Just keep a check on ebay for 10uf caps used as you might be surprised what turns up there was a load of the 10uf Mundorf supreme Silver gold oil last year for something like £20 each!
    Last edited: May 29, 2019
  2. L0rdGwyn
    Just wanted to comment Re the Telefunken 6005 I mentioned before - there is a noticeable improvement in clarity when going from the Telefunken EL90 (that I was using previously) to the Telefunken 6005 in the Crackatwoa. Will do a comparison between the General Electric and Telefunken 6005 at some point soon.
  3. L0rdGwyn
    And by soon, I meant right now. WOW, definitely the best clarity, space, and bass definition I have heard via shunt regulator tubes. After doing an A-B, bests the General Electric 6005 easily. Listening with a Tung Sol 6SN7GT round plate input, MOV A1834 output.

    Wes S likes this.
  4. SmashBruh
    I don't really have any soldering experience and that does make me a little nervous, but the capacitors aren't on the board, so I figure I can't cause too much damage, right?

    I think the Mainline can take between 10uf-20uf with a minimum of 200V; but I've been having a hard time determining whether a higher UF is beneficial or if it would be fine to stick to 10UF which comes stock on the Mainline. Some people say it increases the base response (which I would like) however Loquah reported not much change in base response when upgrading to 18uf.

    And that's good to hear about Capacitors sounding more similar than different!
  5. itsikhefez
    I built the Mainline a while back so forgot which value I used... it was a 10uf 400V Auricap XO.
    Due to the point-to-point construction of the Mainline there is less risk of ruining something when you swap that part out. Only thing to consider is that there are other leads going to the same terminal block as the cap, so make sure to be careful around those.

    Do you have a soldering iron ? A DMM can also help to measure the voltage there after the change (not a must though)
    I buy caps from pcX as they often have 25% off their entire stock which makes the prices more reasonable.
  6. SmashBruh
    Good call! I ended up buying some 10uf MSSGO caps on ebay just now for less than half price! :D

    I have a DMM and I have a soldering iron coming along with some Cardas silver solder. It doesn't seem like much else is soldered to the points where the Daytons are, only a wire on each end. Which I guess begs the question- once I remove the solder from the points will I be able to resolder the same wire back to the same point with the new caps, or will I need to replace all the wire that's desoldered??
  7. SmashBruh
    Just put in the 10UF Mundorf SSGOs in. They only juuuust fit in my mainline where the old capacitors were. I've only had a few minutes with them but I do notice that they seem to be anywhere between 6-9 db less loud than the Daytons for some reason? Is that normal? I kind of expected them to be louder since they have such a higher VDC rating. Overall I find them to be more like the Daytons than they are different tbh. They excel at imaging just like the daytons and everything seems to still be very neutral. They also seem to be a good amount more detailed as well. I think they might also be a liiiittle more musical but that's sort of a hard thing to quantify.

    I'm a little disappointed. I mean, they sound great, but so did the original Daytons. They failed in giving the amp more slam like I wanted; but I will say that the treble at least definitely has more energy now! :)

    Edit: Just found out the capacitors only had 10 hours of use into them... Looks like they do need to be broken in!
    Last edited: Jun 1, 2019
  8. JamieMcC
    Caps never sound partially good straight after they have been soldered in give it a couple of weeks and then stick the Daytons back in again you might be surprised.

    Going back the other way the difference always seems more easily discernible.
    Tom-s likes this.
  9. Tom-s
    While i'm fully aware it's not a standard BH headphone amp, i'm building my Stereomour II to serve that purpose mostly.
    I got it in two days ago and plan to build it this weekend.
    Here's a small build log. Just to show how easy it is to DIY a BH amp.

    First step. Painting the plate and bell end.
    Needed: Cleaner ( i use 1€ brake cleaner), sand paper, primer, paint and patience.
    I first sand all surfaces, then clean after each time sanding and before every layer, sand again, clean again etc. First layer of primer, sand again, second layer, sand again, paint in 3-4 very thin coats. Allow sufficient time between steps.
    This process took me one night. (the paint will now cure for 24-48 hours)

    Tonight i'll do the same for the chokes and build the wooden base.

    Before (note, the amount of grease on the bell end)
    Primer (first layer)
    Paint (done)
    JamieMcC and itsikhefez like this.
  10. itsikhefez
    Nice paint job! I had the Mainline and I didn't do too much cleaning on the plate. I really regretted it later because it would get dirty easily and was hard to get looking clean.

    Good luck on your build.... 2A3 should be a wonderful headphone amp.
    One issue you may have is hum. I am also building a Single-ended triode amp with 45 tubes for headphones.
    The amp is built usually for speakers where users typically report that the amp is dead silent, but I have some hum with HD650 that I'm trying to work out.
    Since the Stereomour is generally intended for speakers, once HP's in the 32-300 range are connected to the output-transformer, the reflected load on the 2A3 will be much higher (i.e. less hard to drive).
    Whether that is an issue doesn't seem to be clear cut. To my understanding, generally as you put a lighter load on the tube, you lose power but distortion is also better. Losing power in this case is not a problem because there is still much more than needed for HP's.
    Some say distortion decreases only to a certain point, and that there may also be frequency roll-off.
    Either way, putting a 12ohm resistor across the output will put the ideal load on the 2A3, and you won't notice the loss of power because 3-4W is much more than anyone would need for headphones.

    Perhaps you already know all this... just putting it here in case it turns out to be helpful.
    Last edited: Jul 12, 2019
    Tom-s likes this.
  11. Tom-s
    Small write up.

    Friday i finished the chokes with the same procedure as the top plate (only black paint) and i glued the wood base.
    On saturday it was moving day (finally out of the student dorm (15m2) and into a house!), so no amplifiers were build.


    Yesterday morning i could finally start the build. All paint had dried by then. But i've left the wood unfinished as it wouldn't have been dry by yesterday.
    With the whole amplifier painted in honors of the AKG K1000 headphone, the wood will be finished ebony just like the AKG K1000 holtzbox.


    First step was to connect everything to the top plate, without damaging the paintwork. For this reason, i work on a towel when the amp is upside down.


    Next here's a picture of the heater wiring (always comes in an amp first) and ground path (oh, and a bit of the input).


    On the input i've made my first change from the normal SII. I wired the input for a standard volume control. I've included a closeup picture if anyone is planning on the same in the future. I hope it shows the wiring scheme in a clear manner.


    Next to the input it was time to wire the driver stage. With the CCS board as most important step. Like with all my amps, the only change i made was the R1 resistor (higher quality; Dale). Another resistor that is very important in this stage is the cathode resistor. But BH already uses a high quality Dale resistor to serve this purpose.


    After that it was just the output stage needed to be wired (forgot to take pictures).

    All resistances and voltages checked out so i've been pumping up the jams via speakers last night.
    It has a very spatial sound with the Heresy III's. With a lot of details. It's like listening to headphones that are speakers.
    Anyway, that was what i build it for, for the K1000 earspeakers.


    With the 1-day building manner, i lost track of time and other stuff around me (and forgot to take more pictures (Don't mind the beers ^^)).
    In total, it took me +-12 hours to get it done.

    For now, no upgrades were installed. The Shunt Regulator upgrade will follow the next coming weeks. Although i'm kind of scared to install it, as it will make me buy a Crack-a-two...
    After a few months i'll review it for headphone use.

  12. Tom-s
    The Stereomour II with headphones?

    For headphones with an AC filament supply (on the 2A3's) you need some very quiet 2a3's with most headphones.
    My SII was build for the AKG K1000's headphones and for now it's performing very good with these (no DC filament needed).
    It is absolutely 100% silent with them, no hum, no nothing (104db/w/m). So the DC supply will be left out for now (same with AKG K340's).
    The EML 2A3 solid/mesh are supposed to be very quiet tubes, these can be tried with more sensitive headphones in an AC filament SII (starts hammering the piggy bank).

    The K1K's are very very transparant headphones with a gorgeous soundstage!
    Some find them lacking in bass, but even with the driver angle's as wide as possible, i'm enjoying them with the SII.
    The sound is rich, warm, full, and yet unbelievably detailed. This combination bests even the HD800/Mainline, loving it.

    How about upgrades?

    The SII has the biggest advantage over Stereomour I, in that it was designed to incorporate new BH upgrades and making the essential caps more accessible.
    The first and foremost Shunt Regulator upgrade is a big upgrade with this amp!! C2A calling..
    The DC filament supply and Mourquiet (a shunt / series stepped attenuator) are the other official upgrades (and i have no plan to install these for now).
    Capacitors to upgrade: interstage coupling cap, outputstage/parafeed coupling cap, cathode bypass cap (2A3) and the PS caps.
    Resistors to upgrade: attenuator (Mourquiet), cathode resistor (driver stage, output stage) and CCS current setting (R1) resistor.

    The most important capacitor is the interstage coupling cap and i soon replaced the stock with K40y-9 Ruskie's.
    The soundstage sized up, details came out but the tonal balance is not my preference. There's a loosening of the bass, with an unnatural tone to piano/strings from time to time.
    I'll leave these in for now to give them time to set-in a bit and change them with Mundorf Silver Oil somewhere in the next coming weeks.
    In the PS the last 100uf cap before the 2a3 parafeed choke was replaced with 470uf because i had the room for it, with little effect (beware the DC filament supply won't fit any longer).
    For the output stage some Jupiter parafeed caps are planned. Can't wait to install these.
    For the bypass cap on the 2a3 cathode (conveniently located at the front of the amp), four leftover MBGO's from the Crack will be used (if i can get them to fit, another reason Mourquiet wasn't installed). This can only be done after my coupling cap journey is complete.


    Tube rolling is a very worthwhile activity with this amp. Driver tubes are readily available and cheap to try with a good influence on the sonic character of the amp.
    The supplied Sylvania's were changed with Philips ECC81 (1957 TK1's D foil getter), Telefunken ECC81's and GEC A2900's.
    All three lived up to the expectation to be an upgrade from stock. The GEC's and Philipses were magical with both headphones and speakers.
    The Tele's (unexpected) were less preferred with the speakers / room because voices were placed so far back, they sounded muddled.

    I can definitely see the SII as an astonishing amp for most headphones (DC filament required).

    On the Bottlehead forum you can read all about @Deke609 's adventures with the SII and Audeze LCD 4's.
    JamieMcC and cddc like this.
  13. cobyatch
    Has anyone encountered a tube that produces a really loud static noise when the volume pot is turned all the way down? Currently having this problem with my RCA 6F8G, does not happen with any of my other 6F8G's using the same adapter or with my 12AU7's. Sucks because it's probably my favorite sounding tube right now with the Crack, but have been rarely using it out of safety for my ears and headphones lol.
  14. cddc
    haven't tried 6F8G myself yet, but I heard 6F8G is noisier than 12AU7 and prone to radio interference from wi-fi router, PC, or cellphone, etc.

    if i cannot hear static at normal volume, i normally do not mind the static at volume 0,

    try to clean the pins on your 6F8G or move your amp away from wifi router to see if it helps.
    Last edited: Jul 25, 2019
    cobyatch likes this.
  15. cddc
    btw, i think static or microphony is okay, but arcing could be dangerous
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