5687 in Crack

[Brillo]

I recently finished my Crack build and thought I’d share pictures and a brief write-up.  When Doc B. posted the Crack + Speedball combo sale several months back, I pulled the trigger.  I needed another project to keep busy with.  Reading through the forum posts someone (Doc maybe?) mentioned the 5687 as a solid replacement for the 12AU7 (if implementing the Speedball upgrade also), so I thought I’d do something different and give this a try.  Many thanks to Paul Birkeland and Paul Joppa for their detailed input and direction – I couldn’t come up with the technical revisions on my own.  I did learn a bit along the way, and this kit is certainly a fun build.  

Anyway, here it goes.  

The 5687 has a different pin-out, as follows:

12AU7   5687
1          1
2          2
3          3
4          4
5          5
6          9
7          7
8          6
9          8

I revised the instruction manual, in advance, to be sure I didn’t overlook making the proper connections per the pin-out changes.  The rest involved a few different parts for the two small Speedball boards, and replacing the two HLPM-6000 diodes under the 9-pin socket with a pair of 516-2275-1-ND diodes from Digikey.  
On the boards, the MJE 350s are replaced with MJE 5731As (installing them in the opposite orientation as described in the manual for the MJW 350s, metal side facing OUT).  

To keep the MJE 5731As cool, a heat sink was added (294-1115-ND).  Also, the R1 resistor on each board was replaced with a 147 ohm Dale I had in my parts box (143 ohm is the theoretical ideal per Paul and Paul).  
 
I had to trim a bit of the heat sinks off to avoid making contact with the R1 resistors, but a quick chop with the rotary tool took care of that.  I also had to rotate the boards to avoid the heat sinks making contact with the wood base.  No big deal there.

Now for the diodes, it was a simple matter of installing the 516-2275-1-NDs in place of the HLMP-6000s.  The new diodes have a short leg that represents the cathode.  This short leg is the same as the silver banded side of the HLMP-6000s.  Just connect the short leg of the 516-2275-1-ND to the center pin.  And the other leg to the 9-pin socket per the manual (but corrected for the pin-out delta as described above).  Easy.
 
That’s all there is to it.  Voltages are within spec, and everything works great.  No issues whatsoever.  I really love the bright blue light of the replacement diodes.  Pimpin’.  The photos make it look super bright, but it’s really not so much.  I did flip the top plate opposite to the manual.  Being right-handed, it seemed easier to put the volume pot on the right side.  
 
As for the sound – amazing.  I swapped out the 6080 for a WE 421a and the thing really took off.   I’m not one for audiophile jargon, but I’m enjoying the controlled bass and articulate, natural sound.  I’m running HD 600s by the way.

I have a custom-made blue pine wood base (i.e. reclaimed beetle kill lodge pole pine), but I still have to apply the lacquer finish.  I’ll post more pictures (and a link to the woodworker’s website) when that piece is complete.  

All-in-all, a really fun build and a moderate departure from the typical 12AU7 replacement.  Thanks again to Paul and Paul for their help and guidance.   Another very satisfied Bottlehead.
Chris

[Brillo]

Wow - couldn't for the life of me figure out how to include the pix in with the text.  Oh well - hopefully y'all can piece together.

[porcupunctis]

Very nice black lacquer finish.  The blue lighting really sets that off.  I like how you managed to get the attenuator and the speedball boards to co-exist.  Good work.

What sort of light did you use?

[jrihs]

What a great/elegant alternative to a power indicator lamp! Is it really bright enough to make a dependable power light? If so, I may have to copy you!!!

[Laudanum]

If I've read correctly and Im not mistaken, the different LED's were a necessary parts replacement for the red HLMP6000's used in the stock build in order to run the 5687 driver.  They are blue LED's.  So Chris gets the blue glow through the vents as a side benefit of the necessary parts change.  Also, seems that since the teflon sockets with PCB's were used, it places the new LED's in a position where their glow is more visible through the vents.  Plus, they are brigher than the little red HLMP6000's as well. 

Anyway, cool write-up and pics Chris.  I like it.

[Brillo]

Laudanum,

Yes, you are correct. The blue LEDs are a necessary parts change to maintain acceptable plate and cathode voltages.  They are much brighter than the red HLMP-6000s. Absolutely no question the amp is powered on!  It didn't show well in the photos, but the top plate and bell end are powder coated ("City Lights", it's called).  A black base with speckled clear coat - flecks of blue, orange, purple, and pink. Very subtle, but fits the aesthetic perfectly.

I'll spend some time this week paraphrasing Paul Birkeland's technical direction which supports the parts changes, then post that for the forum.

Chris

[Paul Joppa]

Just a short note here on LEDs.

The HLMP-6000 is very old technology, first or second generation, sometimes called "standard red" (but I don't think nomenclature is all that standard). It has two advantages - 1) it is quiet, and 2) it has a low dynamic impedance.

More modern LEDs - and the blue ones are very recent - are generally much more efficient light sources. Emphasis has after all been on efficient light sources! I think this is why they have a higher dynamic impedance. Having a low dynamic impedance is very important for use in a C4S, as it largely determines the power supply rejection ratio. It's less important in the cathode bias position where it even provides a slight amount of automatic bias.

[jrihs]

Absolutely no question the amp is powered on! 

Thanks...That's all I was getting at. So its required for your mod, but usable without the mod (w/ 12au7)?

Laudanum, yes they are certainly blue and not red!

[Caucasian Blackplate]

Yikes Chris, those blue LED's are way brighter than I thought they would be!

[Paul Joppa]

The voltage across the LED is used to set the tube bias, so only the comparatively dim "standard red" will give the design voltages with the 12AU7.

The design is fairly tolerant, especially with the Speedball, but at your own risk.

[Laudanum]

Absolutely no question the amp is powered on! 

Thanks...That's all I was getting at. So its required for your mod, but usable without the mod (w/ 12au7)?

Laudanum, yes they are certainly blue and not red!

Yeah, obviously blue ... but I was just trying to point out that Chris used them in place of the red HLMP-6000's due to his using a 5687 tube instead of a 12AU7 for the driver.  That the blue LED's were not used as a drop in alternative for aesthetic reasons.    Sorry if I wasnt clear.

[xcortes]

"The HLMP-6000 is very old technology, first or second generation, sometimes called "standard red" (but I don't think nomenclature is all that standard). It has two advantages - 1) it is quiet, and 2) it has a low dynamic impedance"

Is there any difference among different HLMP-6000s?

[Doc B.]

Apparently there is a high current version and a low current version available from Mouser? Maybe 50mA and 10mA? Someone was asking me about that yesterday. We use what Mouser apparently references as the 10mA version. Not at the office at the moment but I'll look up the PN when I  get there.

[jrebman]

Chris,

So9unds like a nice job -- any comments on sonics vs. 12au7?  I'd be interested in the modification directions when you get them together.

-- Jim

[Brillo]

Jim,

I know this flies in the face of the 'recommended' approach, but I skipped past the base kit, went straight to the Speedball, and implemented the 5687.  Not my typical approach, but extraneous circumstances played a factor (i.e. having to move my workspace out to the freezing cold garage).  The wiring revisions due to the pin-out delta are relatively simple, and I may give the 12AU7 a go eventually.  Then again, maybe not - the really sweeet NOS tubes are getting super expensive.  It would be great to have comparison info, but I'm over it already.

As for sonics, I love love love this amp.  I'm not a seasoned headphone listener, but I can't get enough.  I'm really enjoying the listening experience.  The balance is spot-on - just the way I expect every piece to sound.  Classical, metal, bluegrass, jazz, techno, dub, it doesn't matter.  As another Bottlehead recently posted, I'm really surprised by the soundstage and the detailed presentation - I keep hearing things in the music that, at first, I think are outside interference (verbalizations among musicians in the recording, as an example).  I'm turning my head thinking my wife is talking to me, and she's nowhere to be found.  Really fun.

How 'bout this Jim: I'll let you sample this Crack someday if you let me have a sitting in front of your Nagas.  [I'm down in Aurora.]  You can then compare against your Crack and draw your own conclusions on the 'buzz' that suits you best.  Let me know.

Chris