Bottlehead Forum

Bottlehead Kits => Crack-a-two-a => Topic started by: L0rdGwyn on March 28, 2018, 03:40:41 AM

Title: Crack-a-two-a Build Log
Post by: L0rdGwyn on March 28, 2018, 03:40:41 AM
I am starting a build log for my recently purchased Crack-a-two-a and TwoQuiet attenuator.  This will be my second Bottlehead build, the first being the Crack + Speedball.  I was really happy with the Crack, loved it actually, so I decided to sell it and upgrade  8) FYI I'm no engineer, just a guy who likes to build stuff and knows how to use a soldering iron.

I'm going to be adding some boutique parts to the build, mostly for aesthetics, including new RCA jacks, tube sockets, isolation feet, and volume knobs.  Going to be about a month until I get my hands on the kit, so everything will be planned to a T by the time it arrives.  If it goes as planned, should be pretty sleek!  Also going to add some film output caps after getting used to the stock sound.  Never did this on my original Crack, so curious to see what impact it actually has.  I have a large selection of input and output tubes to roll when it is complete, as well as some Sylvania Gold Brand 6005 shunt tubes to try.

One aesthetic choice I am considering is tube shields for the 6AQ5's.  For the engineering-inclined, will tube shields have any benefit on the shunt tubes besides heat dissipation?  I know they are also used for RF isolation in driver tubes.

Thanks for checking out my build, I will post here as I go along!


Title: Re: Crack-a-two-a Build Log
Post by: Paul Birkeland on March 28, 2018, 04:47:49 AM
The 6AQ5s aren't particularly sensitive to noise pickup in this circuit, but there's no harm in shielding them.  Some of the anodized tube shields look pretty cool.

If you're buying different sockets, I'd recommend staying away from the teflon ones.

-PB
Title: Re: Crack-a-two-a Build Log
Post by: L0rdGwyn on March 28, 2018, 05:12:38 AM
Thanks, PB.  I'm picking up some vintage shields made for 6AQ5's, gonna polish 'em up nice and shiny :) and I've heard the horror stories with the teflon sockets, I'm staying away, most likely going with Audio Note ceramic sockets.
Title: Re: Crack-a-two-a Build Log
Post by: L0rdGwyn on March 31, 2018, 09:36:50 AM
So, while waiting for the Crack-a-two-a kit to arrive, I thought I'd work on another project in preparation for its arrival :)

Since I am moving from the Crack to the Crack-a-two-a, I decided its time to turn over a new leaf and roll some 6SN7's alongside my 12AU7's.  So, I needed an adapter.  I picked up a Garage1217 6SN7 to 9-pin adapter, having read they are the highest quality around.  I wasn't a fan of the exposed look of it though or the lack of insulation.  So, I decided to fashion a new base.

I used a rotary tool and diamond burr attachment to shave down the ceramic on the sides of the adapter.  I picked up a red phenolic octal tube base, cut out the base pins, and sanded the interior.  I then used some thin cyanoacrylate adhesive to bond the base to the adapter.  Voila!

A simple project but really happy with the results.
Title: Re: Crack-a-two-a Build Log
Post by: adeep42 on March 31, 2018, 10:52:00 AM
NICE
Title: Re: Crack-a-two-a Build Log
Post by: Paul Birkeland on March 31, 2018, 01:04:44 PM
Yeah, not sure if it was you or someone else who posted a photo of that base elsewhere, but I was surprised to see exposed metal that one would assume connects to socket pins.  The voltages in the Crack aren't that spectacularly high, but that's certainly not always the case!

For a less labor intensive approach, silicone RTV from your autoparts store will cover that up and is non corrosive, but what you did looks a whole heck of a lot better.
Title: Re: Crack-a-two-a Build Log
Post by: L0rdGwyn on March 31, 2018, 02:04:11 PM
Thanks, was going for functionality and aesthetics, so the extra effort was worth it I think.  With the materials in place, only took 30-45 minutes.
Title: Re: Crack-a-two-a Build Log
Post by: JamieMcC on March 31, 2018, 11:03:27 PM
Nice idea maybe a circle of thin clear plastic like from a cd jewel case could be used to cover the exposed metal bits on the base.
Title: Re: Crack-a-two-a Build Log
Post by: L0rdGwyn on April 02, 2018, 03:31:23 PM
Received my vintage EBY 6AQ5 tube shields today, these are nickel-plated brass, going to attempt to polish them to a mirror for the final build using a Jeweler's Rouge compound.

Edit: added a pic after 20 minutes of polishing.

Edit 2: pic after polishing to chrome-like finish.
Title: Re: Crack-a-two-a Build Log
Post by: xcoolhandx on April 19, 2018, 03:57:30 PM
Well done Sir,subbed  ;D
Title: Re: Crack-a-two-a Build Log
Post by: 2wo on April 19, 2018, 04:57:44 PM
Nice....John
Title: Re: Crack-a-two-a Build Log
Post by: L0rdGwyn on April 21, 2018, 10:13:33 AM
We're getting close to Crack-a-two-a ship day!  To fill some time, thought I'd post here some of the components I'm planning on putting in this build.  As I said before, I recognize many of these "upgrades" are unnecessary and likely will not significantly improve performance of the amp, but I wanted to make this feel like a real statement OTL amp, so some premium parts are going in regardless.

Sockets - took me a while to get these together, but I am using Japanese Azuma gold-plated ceramic sockets.

RCA's - Audio Note silver-plated RCA jacks.  This was an aesthetic choice really, realized after the fact that getting nickel plated would have saved me the trouble of cleaning the sockets when they oxidize, but what's done is done!  Audio Note claims silver jacks have magical audio properties, so I'm gonna go with that.

Output capacitors - Mundorf MCap EVO Aluminum Foil and Oil.  Fitting these bad boys may take some effort, especially when the TwoQuiet attenuator is installed, but from my measurements it is doable.  I'll be building the amp stock and giving it some time before these go in.

RC filter capacitor on driver C4S board - Mundorf SUPREME EVO Silver and Gold.  Again, gonna build stock then put these puppies in at a later time.

Shunt tubes - picked up another relatively cheap set of shunt regulator tubes to roll in, General Electric 5-star 6005's.  As of right now, I'll have the stock tubes, the Sylvania Gold Brands, and these to roll through and compare.

Volume knobs - Audio Note 25mm Polished Chrome.  The top plate of the amp is going to wet-sanded and polished to a mirror finish, so I thought having matching chrome knobs would give the amp a real premium look.

Feet - Cardas Golden Cuboids with Dayton Audio spiked feet.  For the sake of convenience, picked up these myrtle wood cubes from Cardas, sold as audio component standoffs/risers.  I am going to sand them, stain them with the base, glue them inside the four corners of the amp, and install the spiked feet.

I'm also reconsidering the socket shields on the 6005's.  While they might look cool, they aren't going to really serve a functional purpose and might take the look of the amp a little over the top.

Will post again when the kit arrives and I start some test staining.  Yup, I am going to do a test board first, have a few different colors I'm considering  :))
Title: Re: Crack-a-two-a Build Log
Post by: L0rdGwyn on May 15, 2018, 11:38:09 AM
Time to update the ol' build log!

Been pretty busy these past few weeks (grad school and all that), so I wasn't able to make any meaningful progress until these past few days.

I was working on polishing the top plate to a mirror finish, got it 90% of the way there but was not satisfied with the result, so that has been put on hold while I gather some materials.  In the meantime, I've put together the base and started the stain.

Pictured you'll see my test board.  I really like General Finishes' gel stains and was deciding between either Georgian Cherry or Antique Walnut.  Decided to go with the walnut.  The base was assembled and I added my spiked feet combined with Cardas "Golden Cuboids" myrtle wood blocks as substrates.  Hopefully they hold up, putting Elmer's Wood Glue to the test, that transformer is no joke.

Finished the staining, really pleased with the look.  I was originally planning a second coat but with these gel stains it won't get substantially darker (in my experience), so just one will do.  Going to let it cure for two days then add the top coat!  I'll post pictures of the top plate when I get it right :)

Title: Re: Crack-a-two-a Build Log
Post by: L0rdGwyn on May 17, 2018, 07:58:05 AM
Well, I got my mirror finish.  It isn't perfect, but the imperfections aren't noticeable at a distance and I'm not sure it ever could be.

Here are some photos with the parts mounted to the chassis.  Had to sand the interior of the octal cutout to fit my Azuma socket.  All of the sockets are bottom-mounted.  Also subbed in some shiny hardware.  Base still needs its top coat.

Title: Re: Crack-a-two-a Build Log
Post by: Paul Birkeland on May 17, 2018, 08:24:43 AM
It sure is coming along nicely!
Title: Re: Crack-a-two-a Build Log
Post by: Doc B. on May 17, 2018, 09:32:49 AM
Looks nice!
Title: Re: Crack-a-two-a Build Log
Post by: Karl5150 on May 17, 2018, 01:10:20 PM
Button caps, acorn nuts and all that polishing. It's all in the details. Good work.
Title: Re: Crack-a-two-a Build Log
Post by: JamieMcC on May 17, 2018, 08:41:37 PM
Nice work looks great
Title: Re: Crack-a-two-a Build Log
Post by: L0rdGwyn on May 19, 2018, 08:45:08 AM
Thanks for the compliments!  The circuit is coming along nicely, should finish it in the next two days.

Question for Doc/PB - how crucial is it that the 220 Ohm resistor bodies be flush with the the A socket leads?  Because I am using non-stock sockets, the resistor body between A2 and 12U is about 1cm away from A2, as close as I could get it with the leads.  Just so happens that A2 is about as far away as it could possibly be from 12U with the socket orientation the way it is.
Title: Re: Crack-a-two-a Build Log
Post by: Paul Birkeland on May 19, 2018, 11:23:37 AM
It's always a tough call to make without having it sitting in front of me.  Do your best to get them as close as possible. 
Title: Re: Crack-a-two-a Build Log
Post by: L0rdGwyn on May 19, 2018, 01:02:25 PM
Uh oh, hope it won't cause problems. Here is a picture, for both A2 and A7 the resistor body is about 8-9mm away.  If necessary I could desolder everything and flip the socket, might get me another few mm.

UPDATE: I am reorienting the socket 180 degrees, should solve the issue.  Thanks for the help, PB.
Title: Re: Crack-a-two-a Build Log
Post by: Doc B. on May 19, 2018, 05:49:48 PM
Quote
UPDATE: I am reorienting the socket 180 degrees, should solve the issue.

Using the stock socket in the as designed position will solve the issue. Rotating the socket 180 degrees is begging for a miswire.
Title: Re: Crack-a-two-a Build Log
Post by: L0rdGwyn on May 20, 2018, 06:27:21 AM
Thanks, I checked and double checked the wiring of the 9-pin, rotating it 180 got the resistors where they needed to be.

Here is a picture of the stock circuit.

I am having a weird issue with my resistance checks, in that I cannot measure them at all.  I have my negative lead on the #8 near the IEC, I get a 0 Ohm reading at the power transformer screw, then cannot measure anything across the transformer.  Checking for continuity also gives no result at any transformer terminal.  This is consistent across two different multimeters and they are set to the correct range for each reading.  Fuse is not blown, all tests up to this point were passed, reflowed all of the joints at the transformer, power switch, ground bus, IEC.  Feel pretty dumb like I'm missing something obvious here, any suggestions?  I've been staring at this circuit too long.
Title: Re: Crack-a-two-a Build Log
Post by: Paul Birkeland on May 20, 2018, 07:44:38 AM
I have my negative lead on the #8 near the IEC, I get a 0 Ohm reading at the power transformer screw, then cannot measure anything across the transformer. 
Only the transformer screw with the ground tab has to be 0 ohms.

I checked the resistance readings in the manual and I do not see any resistance checks for any power transformer terminals.
Title: Re: Crack-a-two-a Build Log
Post by: L0rdGwyn on May 20, 2018, 08:40:32 AM
Only the transformer screw with the ground tab has to be 0 ohms.

I checked the resistance readings in the manual and I do not see any resistance checks for any power transformer terminals.

Ah yes, knew it had to be something dumb on my part, this is what happens when you are working night shifts and build this circuit in two sittings.  Thanks for humoring my stupid question regardless, PB.

All resistances and voltages are within spec - time to give this baby some head-time!

Here are some beauty shots, really pleased with how it came out aesthetically.

COMING SOON: TwoQuiet attenuator upgrade, Bottlehead Power Cord, and ridiculously large output caps :)
Title: Re: Crack-a-two-a Build Log
Post by: faskenite on May 20, 2018, 01:19:31 PM
I’m in the middle of a tricked out Stereomour build - maybe i’ll follow your example!  I’m planning on keeping the brushed aluminium top plate as is, but could you share as to how you got the mirror finish?
Title: Re: Crack-a-two-a Build Log
Post by: L0rdGwyn on May 20, 2018, 03:24:04 PM
I’m in the middle of a tricked out Stereomour build - maybe i’ll follow your example!  I’m planning on keeping the brushed aluminium top plate as is, but could you share as to how you got the mirror finish?

Certainly!  First off, it was a lot of work.  Took some serious trial and error, had to start over multiple times.  I first sanded down the top to remove the machined texturing, started with 180 grit, then 240, 320, then 400.  This step is really important, if you don't get it all the way down, you will see the grooves in your final finish.  I then used a benchtop buffing tool and buffed with Brown Tripoli compound, a good once over the whole plate.  From there, I did a full once over with white diamond buffing compound, then went back around and spot buffed with the white diamond.  After all of that, I polished the top with White Diamond liquid metal polish to finish.  Also had to clean in between each round to remove buffing compound.  Ultimately I am happy with the result, but getting it to a perfect mirror just isn't feasible, the aluminum is very prone to scratching so there are imperfections (even wiping with microfiber can leave visible micro-scratches).  I would only recommend doing it if you have a lot of patience, it definitely tested mine.
Title: Re: Crack-a-two-a Build Log
Post by: L0rdGwyn on May 21, 2018, 02:27:05 PM
Added the Mundorf caps and TwoQuiet attenuator.  Here are some pics of the final circuit.

Title: Re: Crack-a-two-a Build Log
Post by: Paul Joppa on May 21, 2018, 05:39:50 PM
I know that PB worked hard to make sure there was a ton of room for special caps and other such things - looks like you used up all the space with those Mundorfs! Looks good!
Title: Re: Crack-a-two-a Build Log
Post by: L0rdGwyn on May 23, 2018, 05:54:25 PM
I know that PB worked hard to make sure there was a ton of room for special caps and other such things - looks like you used up all the space with those Mundorfs! Looks good!

Thanks Paul!  They just fit, had to change the orientation of two terminals in the TwoQuiet, but hey it works!
Title: Re: Crack-a-two-a Build Log
Post by: L0rdGwyn on May 26, 2018, 02:55:28 PM
Alright, final entry in the build log.

Finished my Bottlehead Power Cord.  Had a little mishap with the adhesive heat shrink included in the kit, so I had to replace the shrink and the tubing.  Since the plugs were both goopy, and everything else on this build has been customized, decided to go ahead a pimp out my cord a little bit: got some nice fabric woven tubing, 4:1 heat shrink, and a Wattgate AC plug.

After finishing the top coat on the base, I buffed it to a high gloss (not sure if it comes across in the pics with the lighting).

Well that's it!  Build complete.  Below are some pics of the cord and some shots of the final build.  Also has the 6SN7 adapter I put together.

Thanks for checking out my log!  Happy listening.
Title: Re: Crack-a-two-a Build Log
Post by: Raymond P. on May 26, 2018, 07:09:23 PM
LOrdGwyn, thanks for documenting your build. Really enjoyed your pictures. Would you mind describing the sound of the Crack-a-two-a compared to your Crack+Speedball? Also please state the headphones and tubes used for the comparison. Thanks in advance.


-Raymond
Title: Re: Crack-a-two-a Build Log
Post by: L0rdGwyn on May 31, 2018, 09:39:27 AM
LOrdGwyn, thanks for documenting your build. Really enjoyed your pictures. Would you mind describing the sound of the Crack-a-two-a compared to your Crack+Speedball? Also please state the headphones and tubes used for the comparison. Thanks in advance.


-Raymond

Hey Ray!  Thanks for checking it out.  And absolutely.  Keep in mind this is from memory (I no longer have my BHC+SB), so I can't give you a true A-B comparison.  My standard setup on my BHC+SB was a Western Electric 421A power tube with a Mullard CV4003 driver.  Here are my thoughts while listening with the same configuration on the Crack-a-two-a but with General Electric 5-star 6005 shunt tubes.  My two main sets of headphones are my Beyerdynamic DT1990 Pros and my Sennheiser HD660S.  I would say the things that stick out with the Crack-a-two-a is an increase in clarity, better bass definition, and wider sound-staging.  I think there is also better separation between sounds/notes, which may be what Doc is referring to when he says the power supply gives a blacker background.  I feel that the presentation is also more detailed, more microdetails, but its hard to say without a direct comparison.

Hope that helps!  Sorry I can't be more specific without the Crack to do a side-by-side, I don't want to be misleading, but let me know if you have any questions.
Title: Re: Crack-a-two-a Build Log
Post by: Jimb0 on June 01, 2018, 03:04:28 PM
LOrdGwyn, I think you gave a perfect A-B comparison between the Crack+Speedball and Crackatwoa. I currently have both amps and a pair of HD 650's with the Crack being fully modded. I think you were spot on. Although the Crack+Speedball is very nice, the Crackatwoa offers a lot more. Music sounds like real life, like you're in the studio or concert with the artists. I can only imagine what these sound like with HD 800S's. Definitely worth every penny. To my ears they sound and look like a $1500+ amp.

Very nice amp btw. I love what you did with the chassis! Awesome work :)
Title: Re: Crack-a-two-a Build Log
Post by: L0rdGwyn on June 05, 2018, 01:38:28 PM
LOrdGwyn, I think you gave a perfect A-B comparison between the Crack+Speedball and Crackatwoa. I currently have both amps and a pair of HD 650's with the Crack being fully modded. I think you were spot on. Although the Crack+Speedball is very nice, the Crackatwoa offers a lot more. Music sounds like real life, like you're in the studio or concert with the artists. I can only imagine what these sound like with HD 800S's. Definitely worth every penny. To my ears they sound and look like a $1500+ amp.

Very nice amp btw. I love what you did with the chassis! Awesome work :)

Thanks, Jimb0!  Glad you agree and I appreciate the compliment :) really loving this amp so far, having a lot of fun rolling tubes and headphones.  Just purchased my first true TOTL headphone to pair with it, ZMF Auteur, can't wait.