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Crack;Bottlehead OTL - Page 449

post #6721 of 6726
Quote:
Originally Posted by Maxhawk View Post
 

I posted this on the Bottlehead forum, but there seems to be more activity here so I thought I'd repeat it.

 

This thread (http://bottlehead.com/smf/index.php?topic=5989.131) on the Bottlehead forum describes methods to mod the Crack to optimize bias for various tube types. I had added a switch and resistors to allow use of the 12BH7 as well as E80CC/5687 but wanted something neater and consequently more reliable long-term. Here's the before shot:

 

 

 

I decided to make my own PCB, integrating a DPDT switch and resistors, and condensing the dual boards into a single PCB.

Here's the bare PCB:

 

 


And stuffed with parts:
 

 


Installed in place of the 2 separate boards:

 

 


The first try wasn't perfect, as the mounting holes needed some dremeling to allow the PCB to clear the standoff from the other PCB. Also some of the pads are on the small side and the holes for the LEDs are too large, but it did work first time.

 

After spending more time switching between the 12BH7, and 5687, I find that the 5687 excels in imaging and placement, but is down on bass compared to the 12BH7.

 

I had to buy 10 pcs minimum and I've only got one Crack, so I've got extras if anyone is interested.

 

 

May I be the first to extend a very warm welcome to Head-fi :rolleyes:

 

I very much look forward to your future contributions.

 

-Paul

post #6722 of 6726
Quote:
Originally Posted by bigfatpaulie View Post
 

 

 

May I be the first to extend a very warm welcome to Head-fi :rolleyes:

 

I very much look forward to your future contributions.

 

-Paul

Thanks!  This is my first foray into tubes and it's been a great experience so far. It's been fascinating learning about all the different tube manufacturers and all the rebranding. I ordered way too many tubes in a short amount of time trying to figure out what kind of sound I like. I've got around a dozen input tubes and 5 output tubes.

 

Finishing my Crack got me motivated to finish restoring a McIntosh MC240 that was gifted to me. It's done but I'm still tube rolling since the bass seems weak. One day I'll actually measure the frequency response to see if it's really rolling off the low end.

post #6723 of 6726
Quote:
Originally Posted by Maxhawk View Post
 

Thanks!  This is my first foray into tubes and it's been a great experience so far. It's been fascinating learning about all the different tube manufacturers and all the rebranding. I ordered way too many tubes in a short amount of time trying to figure out what kind of sound I like. I've got around a dozen input tubes and 5 output tubes.

 

Finishing my Crack got me motivated to finish restoring a McIntosh MC240 that was gifted to me. It's done but I'm still tube rolling since the bass seems weak. One day I'll actually measure the frequency response to see if it's really rolling off the low end.

Welcome.

 

The Crack makes a great amp for the Sennheiser HD600 / HD800 and Beyerdyamic T90 / T1. I prefer using an RCA clear top 12AU7 and Tung-Sol 6AS7g, though I have begun to experiment with E80CC and have acquired a few. The Tungsram seems to work well with the Tung-Sol. I managed to acquire the Western Electric 421a. It is a silent, non-microphonic tube providing a sonic delight to the ears, though expensive and hard to find.

post #6724 of 6726

For the folks who find Crack gets too loud too fast, would putting something like Schitt Sys (passive preamp) between the source and Crack be a good possible solution?  Thoughts?

post #6725 of 6726
Quote:
Originally Posted by peanuthead View Post
 

For the folks who find Crack gets too loud too fast, would putting something like Schitt Sys (passive preamp) between the source and Crack be a good possible solution?  Thoughts?

 

A lot of people use: http://www.amazon.com/Harrison-Labs-Line-Level-Attenuator/dp/B0006N41B0/ref=sr_1_6?ie=UTF8&qid=1427595458&sr=8-6&keywords=Line+Level+Attenuator

 

The DIY option involves adding 2 resisters in series with your inputs, and two more shunting from your pot to ground, which preserves input impedance: http://www.goldpt.com/mods.html

post #6726 of 6726
Quote:
Originally Posted by skeptic View Post
 

 

A lot of people use: http://www.amazon.com/Harrison-Labs-Line-Level-Attenuator/dp/B0006N41B0/ref=sr_1_6?ie=UTF8&qid=1427595458&sr=8-6&keywords=Line+Level+Attenuator

 

The DIY option involves adding 2 resisters in series with your inputs, and two more shunting from your pot to ground, which preserves input impedance: http://www.goldpt.com/mods.html

 

The resistors work perfectly for this they are a quick easy and inexpensive solution that can be reversed later if required.

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