Crack;Bottlehead OTL - Page 73

Quote:

Originally Posted by lextek 

I thought soldering the lugs of the heatsink to the PCBs was a pain.  I was afraid of overheating the board.

lextek - I found that moving the iron around helps the solder flow to all areas, especially on those large lugs.  Same goes for soldering a PC board... I rarely let the iron stay still because solder just didn't want to flow to all open cavities.  But if you think about it... the heatsink is conducting most of that heat at that point so I doubt much heat was being put through the board.

Hey, really cool idea.

thanks,
 

Quote:

Originally Posted by lextek 

I put some heat shrink over the clips.  You could also use some silicone tubing I guess.

 

Warning: Spoiler! (Click to show)

 

 

Warning: Spoiler! (Click to show)

 

 

Quote:

Originally Posted by Draygonn 

Is there a way to test the LEDs to see if I've blown them out?

I damaged a diode on my A-socket while putting in the stand-offs for my speedball, and had some similar questions at the time.  

If you don't have a diode setting on your meter (like me), you can still cause a good diode to light up by measuring resistance across the diode (in the right orientation), with your meter on the most sensitive scale.  Per what I have read in various places, it is possible to damage a good diode if your meter is not set to one of its highest sensitivity resistance settings.  Also note - even when your leads are oriented correctly, causing the LED to light up, resistance will, within a second, max out on your meter.  More details are discussed in my bottlehead troubleshooting thread here: http://www.bottlehead.com/smf/index.php?topic=1825.0  

Hope this helps!

Quote:

Originally Posted by Draygonn 

Is there a way to test the LEDs to see if I've blown them out?

Sure. A diode measures very high (i.e. near infinite) resistance in one direction and the HLMP-6000 measures around 1500 ohms in the other direction. Just use your DMM on the ohms setting to measure, swapping the test leads for each direction. In some cases the battery in the meter will make the LED light up, in other cases it won't, so that is not a useful indicator.

There is a lot of tech support info for Crack kit builders on the Bottlehead Forum. 

http://www.bottlehead.com/smf/index.php/board,24.0.html

Quote:

Originally Posted by Doc B. 

Sure. A diode measures very high (i.e. near infinite) resistance in one direction and the HLMP-6000 measures around 1500 ohms in the other direction. Just use your DMM on the ohms setting to measure, swapping the test leads for each direction. In some cases the battery in the meter will make the LED light up, in other cases it won't, so that is not a useful indicator.

 

There is a lot of tech support info for Crack kit builders on the Bottlehead Forum. 

 

http://www.bottlehead.com/smf/index.php/board,24.0.html

The interesting part of this, in my experience, was that when my meter was set to a scale that would have allowed me to measure 1500 ohms, it would not cause any of my diodes (the good or the damaged) to light up.  However, if I had it set to either the highest, or second highest, sensitivity - it would light up all of my good diodes, but it would not light up the damaged one.  Sure enough, when I replaced the diode that would not light up with a new one from BH, all of the voltages in my crack + speedball were right on the mark.

There is clearly some nuance to what goes on when measuring resistance across diodes...  For example, this resource suggests that the measured resistance will "will vary substantially with the particular ohmmeter used to take the reading."  http://www.allaboutcircuits.com/vol_3/chpt_3/2.html

Edit: this thread makes for a pretty good read about measuring LED's and their non-linear nature, if anyone else finds this topic at all interesting: http://cr4.globalspec.com/thread/4943/Resistance-of-LED-s  (See in particular the posts by Masu)

That is why many DMMs have a diode checking setting. If yours has one, using that setting that is the best way to measure.

Quote:

Originally Posted by lextek 

Came across a post on the Bottlehead forum about using the Crack as a preamp. I had to ty it. Made up a cable to go from headphone jack to my little SS amp. Used some Kimber speaker cable I had. Must say the Crack/Speedball makes a nice little preamp/linestage not sure which is the correct term. Pretty cool.

A line stage is a preamp that does not include a phono-stage. 

The term preamp is commonly misused.

Does anyone else find gain on Crack to be a little too high?  Using my CDP with the typical output of 2V, I can't move the volume knob past 7-8 o'clock before it's too loud on HD650/HD800.

I've resorted to connecting Crack to the preamp output of my HeadAmp GS-1 in order to "attenuate" the source signal.  Still sounds very good...

Yep, I find the POT a bit quick for my tastes.  I set my volume knob to point at 6 o'clock when muted, and 7 or 8 is already to or beyond what I need for normal listening. I've been reading the bottlehead forums, and it seems others are either replacing the POT with different models that can help, or using resistors on the line to the POT to reduce the signal.  My pot has a bit of an imbalance at low volume. I have enough volume swing with my older tunes that have high dynamic range, but new music with 4-6 db or less of dynamic range gets loud so quick I can't make the volume low enough for my preferred listening level.

You have a few options to tame the gain, mostly involving pre-attenuation on the input.

In my case, I replaced the stock 100k pot with a 50k TCK-2CP2511 in series with a 50k resistor, giving approx 6dB of attenuation. The TKD also has excellent channel matching and sounds better than the stock pot. You can also use a resistor divider on the input, as detailed here: http://www.goldpt.com/mods.html

Thanks Beefy.  Is the TDK a drop-in replacement or did you have to make some changes to the panel?