Crack;Bottlehead OTL
Sep 18, 2014 at 3:30 PM Post #5,986 of 12,335
Ah - my apologies then. I misunderstood some things about the topology. Thanks for the correction, Doc. 
 
Sep 19, 2014 at 7:29 AM Post #5,987 of 12,335
I've just tried Bottlehead Crack (Speedball, 5998) -> Audio GD SA-31 -> HE-500, and it sounds excellent, with a little bit of a bass increase, added warmth, and generally just very pleasant. .
 
It's not a very efficient use of equipment, though, and not the chain I'm looking for. I hope to sell the SA-31 and replace it with something without input selection, volume control and all of that, just plain amplification - a headphone power amp - but there doesn't seem to be such a product category..
tongue.gif
 
 
Sep 19, 2014 at 8:20 AM Post #5,988 of 12,335
  I've just tried Bottlehead Crack (Speedball, 5998) -> Audio GD SA-31 -> HE-500, and it sounds excellent, with a little bit of a bass increase, added warmth, and generally just very pleasant. .
 
It's not a very efficient use of equipment, though, and not the chain I'm looking for. I hope to sell the SA-31 and replace it with something without input selection, volume control and all of that, just plain amplification - a headphone power amp - but there doesn't seem to be such a product category..
tongue.gif
 

 
You'll find the HE-500s will sound better with other amps because the Crack is designed for higher impedance, but in the meantime, you could always keep the SA-31 and simply bypass the Crack's volume control to make it a pure power amp and use the SA-31 for volume control.
 
Sep 19, 2014 at 10:54 AM Post #5,989 of 12,335
  I've just tried Bottlehead Crack (Speedball, 5998) -> Audio GD SA-31 -> HE-500, and it sounds excellent, with a little bit of a bass increase, added warmth, and generally just very pleasant. .
 
It's not a very efficient use of equipment, though, and not the chain I'm looking for. I hope to sell the SA-31 and replace it with something without input selection, volume control and all of that, just plain amplification - a headphone power amp - but there doesn't seem to be such a product category..
tongue.gif
 

you would be better served to use a different amp.  the crack is actually the opposite of what you need in an amp for the 500.  you'd be amazed at the difference in switching that amp.  
 
Sep 20, 2014 at 7:04 PM Post #5,993 of 12,335
  Guys, what are the very basic skills needed to DIY Crack aside from soldering and wire stripping?

 
That's pretty much it other than following instructions, turning a screw driver, gluing pre-cut pieces of wood together and using a test meter (by following clear instructions)
 
Sep 21, 2014 at 12:33 PM Post #5,994 of 12,335
I would add a degree of patience and the urge to be thorough. A successful build is mostly about taking your time and enjoying the process. A functional result just kind of follows naturally. If you rush it you can miss steps, have to figure out what you skipped, go back and fix the error and in the end you will spend just as much time on the build.
 
Sep 21, 2014 at 11:43 PM Post #5,995 of 12,335
The first time I built a Crack, I marathoned it in a single session then spent half a week debugging it.
 
The second and third time I built one, I spent one day laying everything out and pre-cutting/stripping/tinning the wires and terminals, then two days with the actual build (plus a third for Speedball). Both worked without a hitch the first time I fired them up.
 
Total effective build time was the same, but my second and third times were far more enjoyable and my workmanship was much better.
 
Sep 22, 2014 at 1:36 PM Post #5,996 of 12,335
So... my soldering iron has been idle for too long and I want to build a Bottlehead crack.
 
For my cans (HD700) the output impedance of the Crack is probably borderline high (cans are 150ohm at 1000Hz with higher impedance at lower frequencies), but I already own a good SS amp and prefer to build an OTL rather than a hybrid. 
 
I'm adding a DC offset protection circuit (AMB ε12) for peace of mind and a tube guard for the preamp tube which seems a little close to the volume knob and headphone cord:
 

 
Question: Can anyone recommend film caps for the output stage that will still fit comfortably in the case?
 
Thanks!
 
Sep 22, 2014 at 5:30 PM Post #5,997 of 12,335
  So... my soldering iron has been idle for too long and I want to build a Bottlehead crack.
 
For my cans (HD700) the output impedance of the Crack is probably borderline high (cans are 150ohm at 1000Hz with higher impedance at lower frequencies), but I already own a good SS amp and prefer to build an OTL rather than a hybrid. 
 
I'm adding a DC offset protection circuit (AMB ε12) for peace of mind and a tube guard for the preamp tube which seems a little close to the volume knob and headphone cord:
 

 
Question: Can anyone recommend film caps for the output stage that will still fit comfortably in the case?
 
Thanks!

 
The 100uf Solen and JFX both fit in easily, Mundorfs and Obbligato are a lot tighter
 
Sep 22, 2014 at 6:05 PM Post #5,998 of 12,335
My obbligatos are longer than the axons I replaced with them, but I didn't find it at all difficult to fit them in. There are photos of both configurations in my profile gallery if you want to see the spacing.

AdamCTs use of 100uf claritycaps are the only build I can recall seeing that required risers to accommodate a single pair of output caps.
 
Sep 23, 2014 at 3:50 AM Post #5,999 of 12,335
Thanks JamieMcC & Skepic! I will make a choice based on your suggestions. Don't want to spend a fortune on boutique caps, those look reasonably priced.
 
Also contemplating adding a USB port with a GrubDAC with an metal input toggle switch (if it ain't broke, it doesn't have enough features yet haha), but still on the fence about adding a digital input to a "retro" amp. 
 
Sep 23, 2014 at 6:27 PM Post #6,000 of 12,335
Thanks JamieMcC & Skepic! I will make a choice based on your suggestions. Don't want to spend a fortune on boutique caps, those look reasonably priced.

Also contemplating adding a USB port with a GrubDAC with an metal input toggle switch (if it ain't broke, it doesn't have enough features yet haha), but still on the fence about adding a digital input to a "retro" amp. 


Be careful with interference and noise putting a DAC under the hood.
 

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