[PETEREK]

My left channel sounds like a fart. I cannot figure out what is wrong with it, but it is giving the effect of a badly blown driver (the headphones are fine). Is anyone up for checking it out and hopefully fixing it for me? I can send along some nucleotide RCA interconnects for whomever does it, and return shipping money. Only people in the US and who have positive feedback OR a lot of posts please. 
 
I've been losing my mind trying to isolate the problem, but have not made any progress. Desolder, resolder, repeat..
 
PM me if interested, thanks.

 

[ZachPtheDude]

My left channel sounds like a fart. I cannot figure out what is wrong with it, but it is giving the effect of a badly blown driver (the headphones are fine). Is anyone up for checking it out and hopefully fixing it for me? I can send along some nucleotide RCA interconnects for whomever does it, and return shipping money. Only people in the US and who have positive feedback OR a lot of posts please. 

I've been losing my mind trying to isolate the problem, but have not made any progress. Desolder, resolder, repeat..

PM me if interested, thanks.

Did you post about your issue on the Bottlehead forum?

 

[Mich4lle]

It seems that the 5998 is everyone's preferred power tube, so I'll pick up one of those at some point. I'm curious about what people find to be the most realistic and natural sounding input tube, though? Other mods I plan on doing soon are replacing the output capacitors with Dayton polyproylene caps (2 x $24, not bad), and a stepped attenuator--any recommendations below $50? I'm trying to keep this as cheap as possible.

I may have to place the order for the tubes soon since I think I might have busted my power tube when it rolled off the table onto the floor maybe 1.5 ft while installing Speedball. The amp is really quiet and the left channel barely comes through at all. It could also be an issue with the Speedball but I've double and triple checked all the connections and everything is in the right place.

Well you were asking about an input tube, I have done a lot of research and I am also pretty interested if anyone else here agrees with me, but I read that the Amperex Bugleboys are very realistic sounding tubes and are a great match with the 5998. So that might be a good place to start, but they are pretty pricey at around 75 dollars a tube. So if anyone has hands on experience with this tube please do chime in.

 

[FunyunBreath]

  Well you were asking about an input tube, I have done a lot of research and I am also pretty interested if anyone else here agrees with me, but I read that the Amperex Bugleboys are very realistic sounding tubes and are a great match with the 5998. So that might be a good place to start, but they are pretty pricey at around 75 dollars a tube. So if anyone has hands on experience with this tube please do chime in.

 
+1
 
Thats the exact tube combo i've been using and it sounds fantastic. The bugle boys are indeed expensive but look for "Hewlett Packard by Amperex" labeled 12au7's. They can be had for around $20 and a lot of them are just rebranded Bugle Boys.
 

 

[Maxhawk]

For folks who don't frequent the Bottlehead forum, I posted a bunch of measurements I took with an Audio Precision...

 

[PETEREK]

Did you post about your issue on the Bottlehead forum?

No I haven't.

 

[Maxhawk]

  Still, this is a better cap, and is on sale for 25 dollars (the 100uf, 250V one):
http://www.partsconnexion.com/capacitor_film_claritycap_px.html

Nice cap, but they're quite large at 60x81mm. The ones I used were only 42x51mm (http://www.ebay.com/itm/2pcs-250V-100uF-MKP-Crossover-Metallized-Polypropylene-Non-Polarized-Capacitor-/331366732405?pt=LH_DefaultDomain_0&hash=item4d26ff1275). Sure it's a cheap poly from China, but I figured even the cheapest ones are probably better than an electrolytic.

 

[nailbunny7]

  Nice cap, but they're quite large at 60x81mm. The ones I used were only 42x51mm (http://www.ebay.com/itm/2pcs-250V-100uF-MKP-Crossover-Metallized-Polypropylene-Non-Polarized-Capacitor-/331366732405?pt=LH_DefaultDomain_0&hash=item4d26ff1275). Sure it's a cheap poly from China, but I figured even the cheapest ones are probably better than an electrolytic.

That's true, any film will be better than a standard electrolytic. I've seen people make the Obbligato 100uf caps fit, and those are 65x135mm, so the Clarity cap would be easy by comparison
What I personally did was leave the electrolytic in there and bypassed it with a 47uf Obbligato Gold capacitor for a combined total of 147uf.

 

[skeptic]

  For folks who don't frequent the Bottlehead forum, I posted a bunch of measurements I took with an Audio Precision...

 
Well done and thanks for sharing!  I've always wanted to see these sorts of measurements for the crack.  The 5998 at 600 ohms looks really good.  Now I want a T1 for my office rig 

 
 
[Also - quick question, do you have the resister mod in place for running 12bh7's or were those measurements with a standard speedball'd crack?]

 

[Maxhawk]

   
[Also - quick question, do you have the resister mod in place for running 12bh7's or were those measurements with a standard speedball'd crack?]

 
I've got a switch to optimize bias for 12AU7, 12BH7, and E80CC.
 
http://www.head-fi.org/t/476650/crack-bottlehead-otl/6705#post_11450274

 

[skeptic]

   
I've got a switch to optimize bias for 12AU7, 12BH7, and E80CC.
 
http://www.head-fi.org/t/476650/crack-bottlehead-otl/6705#post_11450274

 
Ah, of course!  Forgot you were the one who designed the cool speedball mod/switch board.  Don't suppose you still have an extra floating around that you might be convinced to part with?

 

[ohcrapgorillas]

I found the issue with my Speedball--I had switched a couple of the tiny resistors around between the small and Speedball boards. Listening to live Radiohead with the HD600 right now and I'll leave my review short: whoa. nice. 

 

[atomicbob]

  I found the issue with my Speedball--I had switched a couple of the tiny resistors around between the small and Speedball boards. Listening to live Radiohead with the HD600 right now and I'll leave my review short: whoa. nice. 

Nice. You have increased your trouble shooting skills. HD600 and any variant of Crack is a nice combination. I have tailored my mods to suit my tastes at this time, though I have prepared for other mods as I feel venturesome.

 

[ohcrapgorillas]

  Nice. You have increased your trouble shooting skills. HD600 and any variant of Crack is a nice combination. I have tailored my mods to suit my tastes at this time, though I have prepared for other mods as I feel venturesome.

Thanks! My mods are going to be as follows (in order):
 
* Amperex HP-branded input tube
* Dayton polypropylene caps
* 5998 power tube... unless there's a more realistic sounding alternative for cheaper.... but the tube itself is also so pretty...
* stepped attenuator

 

[atomicbob]

  Thanks! My mods are going to be as follows (in order):
 
* Amperex HP-branded input tube
* Dayton polypropylene caps
* 5998 power tube... unless there's a more realistic sounding alternative for cheaper.... but the tube itself is also so pretty...
* stepped attenuator

That is a sensible order. I am quite satisfied with the stock pot at the moment. Mine seems exceptionally quiet, balanced and smooth turning. I have the Dayton caps but just put in 820 uF Nichicon Electrolytics bypassed with 1 uF polypropolene caps. Bass really kicks while snare snaps nicely.

I should point out that increasing the value of the output caps will also increase the size of the power on transient that will appear at the headphone jack. Either change the 2.49 K resistor to around 300 ohms or keep headphones disconnected during power on and wait for the amp to warm up before plugging in the headphones.