Bottlehead Forum

Bottlehead Kits => Crack-a-two-a => Topic started by: Happy Ghost on December 25, 2021, 04:36:43 AM

Title: Merry Christmas everyone!! (pics of new build)
Post by: Happy Ghost on December 25, 2021, 04:36:43 AM
Hello All,

Just like the elves at the N. Pole, I was toiling away in my basement working on the C2A. Still burning it in, but so far it sounds wonderful :) I am attaching a few shots of the amp.. I plan to add the attenuator upgrade early next year.. Want to enjoy it in the stock form for a bit..

Best wishes!
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: Mucker on December 25, 2021, 10:48:10 AM
Looks great! I'd love to have a C2A but my Crack/SB is so good, I can't really justify it. I just finished building an S3X and it's incredible. Enjoy!
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: johnsonad on December 26, 2021, 01:27:20 AM
Nice looking build!  I hope you enjoy it as much as I enjoy mine.  It's the one kit I wish I would have bought years earlier.
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: Karl5150 on December 27, 2021, 04:38:12 AM
Very nice, the brass/gold tone on the transformer sets off nicely against the bright red plate.
Enjoy,
 Karl
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: Happy Ghost on December 27, 2021, 10:59:53 AM
Looks great! I'd love to have a C2A but my Crack/SB is so good, I can't really justify it. I just finished building an S3X and it's incredible. Enjoy!

I was using a S3X for so long. I listened to my HifiMan's and Grado's with it and it was fantastic.. (side note: the S3X was my Covid project and it saved my sanity :) )
But the C2A is in a diff league when I paired it with my new HD 8xx.. The same phones on the S3X sounded a bit metallic and for lack of a better word... restrained.. still good, mind you...
However when it hooked it up with the C2A, the music was so natural sounding and effortless... the combo is so so good.. this is the summary of what I discovered so far..  :)  can barely contain myself not to install the 2quiet upgrade immediately
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: Happy Ghost on December 27, 2021, 11:08:59 AM
Very nice, the brass/gold tone on the transformer sets off nicely against the bright red plate.
Enjoy,
 Karl

Thanks Karl! for this one kit, almost everything clicked during the build process (well.. there is a solder joint in the C4S board which still worries me a bit :) )
the wood base always used to be a major challenge for me in terms of the final finish. I used a wipe-on poly this time and it worked wonders.. the margin for error is considerably reduced and the final result is quite good.. It took 3 coats for me to get a good finish..
for the chassis work, I plan to try powder coating next time.. I see pics of the build others have done, and powder coating looks so amazing..
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: Happy Ghost on January 30, 2022, 03:45:28 PM
All done!! The stepped attenuator brought the vocals slightly forward. But I need to crank the coarse dial to -18dB setting most of the time. Which seems a tad high.. Anyways.. I'm guessing the Moreplay sitting around waiting to get assembled should fix that :)
I tried my Sennheiser headphones (6xx/8xx) on the Crack,SEX 3.0 and C2A. And IMHO the C2A wins by a huge margin.. Especially on the 8xx, music sounds so natural.. Amazing! Love it when listening to jazz especially.. If someone has tried this same experiment (esp. with 8xx) on the Mainline, then can you please let me know your thoughts. I am too deep in the rabbit hole now.. Might as well enjoy the journey :)
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: Paul Birkeland on January 30, 2022, 04:11:51 PM
The red looks great!

The position of the volume controls will depend both on the headphones you're using as well as the output level of the source you have connected.  A dedicated DAC will often have about 10x the output of something like the headphone jack on a phone.
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: Happy Ghost on January 30, 2022, 05:57:01 PM
Thanks PB! This is getting interesting..

I am using an ANK DAC 2.1... I think it outputs 2.0 V or thereabouts.. ..
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: Paul Birkeland on January 30, 2022, 06:00:06 PM
You can always play a 60Hz tone through it at full source level and measure the AC voltage across an RCA jack with your meter.
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: Happy Ghost on January 31, 2022, 02:12:10 AM
I tried changing the DAC from ANK to a Khadas Tone Control.. I still need the volume to be cranked up.. So I am assuming the 8XX needs more juice than most other headphones I guess.. It's either that or my hearing is shot  ;D

Anybody else experience something similar with the HD 8xx series in general?
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: Paul Birkeland on January 31, 2022, 04:20:53 AM
Well if you're at -18dB and using the fine control to adjust volume with a 2V DAC, then you still have that 18dB of headroom which is tons (almost 10x the voltage output).  Technically you could turn the C2A all the way up on a 2V DAC and it will play undistorted.  Your headphones won't appreciate that though.
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: johnsonad on January 31, 2022, 05:02:53 AM
Anybody else experience something similar with the HD 8xx series in general?

Not at all. I'm using the pot attenuator and it sits at about 7 o'clock with HD800. Driven by an iDac2, normal 2v output. I don't listen at high volumes though.
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: Happy Ghost on January 31, 2022, 06:43:50 AM
Interesting.. So for me with the HD8xx, I use almost all the volume at the -18dB region.. The fine control is almost near the max. For couple of records, I might even go up a little bit.. -9DB but with the fine control down.. With the 6xx though, I am at the -18 db region, but not using most of it i.e. the fine control is near the middle region.. The funny thing is prior to the upgrade to the stepped attenuator, the volume on the C2A hardly every crossed the 9 'o clock region...
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: Paul Birkeland on January 31, 2022, 06:55:06 AM
Interesting.. So for me with the HD8xx, I use almost all the volume at the -18dB region..
But again, 20dB is 10x voltage.

To put it another way, when the coarse control is all the way up and fine is at -6dB, you can still double the output voltage from there.
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: Happy Ghost on January 31, 2022, 08:09:37 AM
I think I finally get it.. Assuming a gain of ~ 53 DB, and with the controls set for -20 (Coarse+ fine), I am getting 33DB out.. And before the stepped attenuator, with the logarithmic volume pot at ~ 8 'o clock region, gain must be ~ 36dB. So quite close and i guess it was a false alarm :( Hope my math is alright..
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: Paul Birkeland on January 31, 2022, 09:20:09 AM
The attenuator takes away from what comes into the C2A.  Gain is what the circuit adds. 

If you have an extra step or two on the coarse attenuator you are miles from running out of gas.
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: Sp33ls on February 02, 2022, 02:16:43 PM
I'm at about -27dB right now using a Dragonfly Red (my workstation DAC) into my HD800S. I run the Dragonfly at max volume into the C2A, which is supposedly around 2.1V.

I don't think I want to really go any louder than this except for some classical tracks which are mastered with more dynamic range.

The -18dB mark would likely cause acute hearing damage when combined with this DAC lol.

But my goodness does this amp sound great with the 800S.

How much THD would you guesstimate is present with a Bendix 6080 & Telefunken 12AU7 @ 1mW? Think it's somewhere in the 1-3% range?
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: Paul Birkeland on February 02, 2022, 03:12:46 PM
I could take some measurements sometime of the C2A I have here.  I think I have that particular tube set as well. 
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: Sp33ls on February 02, 2022, 03:42:51 PM
I could take some measurements sometime of the C2A I have here.  I think I have that particular tube set as well.

Would be really interesting to know!

From a selfish perspective, it'd be interesting to get a rough feel on "okay, so this is what about 1% THD sounds like"... Of course, the distortion profiles vary, even from tube to the tube.

I'm assuming something like the BeePree 2 has a bit less of the tube sound than the C2A, but still shares the typical sonic benefits associated to tubes?
Title: Re: Merry Christmas everyone!! (pics of new build)
Post by: Paul Birkeland on February 03, 2022, 05:14:57 AM
The sonic signature of a 300B is a fair bit different than a 12AU7.  The 12AU7 somewhat intentionally a tubey sounding choice, as there's a reasonable amount of non-linearity, especially with the stock plate loading resistors.

The 300B is definitely not as tubey, as it's a very linear device.  It has a notable amount of weight and punch that I can't seem to get out of any indirectly heated tubes.  I wouldn't really want the 300B in front of the 6080 in a headphone amp though, as they aren't super duper quiet, and that's very important in a headphone amp.