5687 in Crack

[Brillo]

I recently finished my Crack build and thought I

[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!

[Paul Birkeland]

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.

[Jim R.]

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