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Crack;Bottlehead OTL - Page 205

post #3061 of 7977
Quote:
Originally Posted by HolyCheese View Post

I have a feeling that it's best that average listening level is around 50% of volume on the knob.

 

My opinion is that the best listening level is just around 30-35% of volume ( the knob is at about 9-10 o' clock position )

 

50% of volume to reach preferable listening level is too much for me.

post #3062 of 7977
Yes. Sort of. Use these: http://www.amazon.com/Harrison-Labs-Line-Level-Attenuator/dp/B0006N41B0/ref=sr_1_1?ie=UTF8&qid=1383060429&sr=8-1&keywords=harrison+labs+12db+attenuators

Don't bother going for anything less than 12dB, you won't notice the difference.
post #3063 of 7977
Quote:
Originally Posted by HolyCheese View Post

Is there anyway to lower the gain on this amp? It's hard to set it at low levels without volume imbalance.

I really wonder why they make all amps so extremely powerfull. I also have an O2 with the lowest gain possible and it doesn't get past 15%.
I have a feeling that it's best that average listening level is around 50% of volume on the knob.

A lot of folks will recommend the inline attenuators you can buy on amazon. A nice alternative is the addition of 4 resisters in series with, and then shunting from the input of your pot to ground, as explained here:http://www.goldpt.com/mods.html

For your o2, stock is set to 2.5x/6.5x gain. If you want to be able to use it with iems, you can easily alter one of these to unity gain by snipping 2 resisters. Also helps avoid the known clipping issues with the o2. Hope this helps!
post #3064 of 7977
Quote:
Originally Posted by HolyCheese View Post
 

Is there anyway to lower the gain on this amp? It's hard to set it at low levels without volume imbalance.

 

I really wonder why they make all amps so extremely powerfull. I also have an O2 with the lowest gain possible and it doesn't get past 15%.

I have a feeling that it's best that average listening level is around 50% of volume on the knob.

Why not do this taken from the Crack FAQ over at BH forums 

********************

3.  I can barely turn my Crack up at all before it's far too loud, what do I do?

Remove the white wire from the left RCA jack at the rear of the chassis.  Solder in a 270K resistor to the solder cup on that jack, solder the white wire to the other end.  Repeat this for the red wire with another 270K resistor.  This will give you about a -10dB pad at the input.  If you still have the issue, try 470K instead.  The wattage of these resistors isn't all that important, anything between 1/16 Watt and 1/2 Watt is reasonable, with metal film and carbon film types being most recommended.

********************

post #3065 of 7977
resisters in series will pad volume but the goldpoint method does the same while preserving the input impedance.
post #3066 of 7977

Just ordered my first Crack kit. Had a question -- I would like to use braided/shielded RCA cables to reduce the possibility of "hum" that many users reported. Unfortunately since I'm totally new at this, not 100% what to buy. Can someone send me a link to some cheap shielded RCA cables that will replace that braided one in the Crack?

 

Also, any suggestions on easy, cheap first-built improvements?

post #3067 of 7977
Quote:
Originally Posted by drizek View Post
 

On the subject of not having the headphones plugged in, on the Bottlehead forum there is a recommendation that the two unused prongs on the headphone jacks be wired to ground (picture in the link) to keep startup voltage at 0 (with no headphones plugged in). 

 

http://www.bottlehead.com/smf/index.php/topic,2946.0.html


That is very interesting and makes sense. After added a Speedball the startup voltage will actually go upwards of 10-20 volts before it quickly drops back down to 0v. I have verified this on two Cracks with Speedball and seen other experience it as well around the net. What I also found interesting is that post you found on the Bottlehead forum is from the middle of 2012, and now were sitting at the end of 2013 and as far as I know the Crack manual still has not been modified to include the grounding of the left and right channels at the TRS jack. This "mod" is even a sticky in their Crack forum section. I wonder why they havent done that yet.

 

Has anyone out there tried grounding them?

 


Edited by ben_r_ - 10/29/13 at 9:55am
post #3068 of 7977
Quote:
Originally Posted by Simanick View Post
 

Just ordered my first Crack kit. Had a question -- I would like to use braided/shielded RCA cables to reduce the possibility of "hum" that many users reported. Unfortunately since I'm totally new at this, not 100% what to buy. Can someone send me a link to some cheap shielded RCA cables that will replace that braided one in the Crack?

 

Also, any suggestions on easy, cheap first-built improvements?

 

If you correctly braid the three wires from the RCA inputs to the volume pot, you won't have any kind of hum. The noise rejection from correctly braided wires is in fact quite astounding.

post #3069 of 7977
Quote:
Originally Posted by Simanick View Post
 

Just ordered my first Crack kit. Had a question -- I would like to use braided/shielded RCA cables to reduce the possibility of "hum" that many users reported. Unfortunately since I'm totally new at this, not 100% what to buy. Can someone send me a link to some cheap shielded RCA cables that will replace that braided one in the Crack?

 

Also, any suggestions on easy, cheap first-built improvements?

 

Welcome to the thread Simanick!  There have been very occasional reports of hum, but these are almost always due to: (i) an imperfect tube, (ii) use of tube adapters to run 6sn7's (which I personally recommend against) or (iii) an attempt to use stranded hookup wire or some other such misguided departure from the stock build.   

 

When you say RCA cables - are you talking about the internal hookup wire that runs from the rca inputs to the pot?  If so, I would echo ffivaz and encourage you to just follow the directions and use the solid core wire provided.  A properly built crack has no hum whatsoever...  Prior to adding a speedball, the only mod I would suggest is installing your output caps on fly leads so that you can easily upgrade to film caps at some point down the road should you so chose.  [Search the thread for Beefy's explanation and photos illustrating this.]  Once the speedball is in, it is difficult to access the terminals to which those leads need to connect.

 

If you are buying the speedball along with the stock kit, screwing in the nylon standoffs before you wire up the a-socket can also help avoid possible damage to the fragile led's on that socket when you do get around to the speedball.  


Edited by skeptic - 10/29/13 at 10:46am
post #3070 of 7977
Quote:
Originally Posted by ben_r_ View Post
 

Has anyone out there tried grounding them?

 

 

I grounded mine a while back but never actually measured to see whether it eliminated the small spike in start-up or shut-down voltage.  Although I didn't do so for the first year or so with my crack, my practice these days, out of an abundance of caution, is just to power up before plugging in my phones, and to unplug them before powering down.  

post #3071 of 7977

Any Crack we have had around here (I dunno maybe 20 or 30 over the years?) has been dead quiet. I would suggest not trying to fix stuff until you know it's broken. The few (not many) people who reported noise may have had bad solder joints, bad braiding, or an excessively noisy environment.

post #3072 of 7977
Quote:
Originally Posted by Doc B. View Post
 

Any Crack we have had around here (I dunno maybe 20 or 30 over the years?) has been dead quiet. I would suggest not trying to fix stuff until you know it's broken. The few (not many) people who reported noise may have had bad solder joints, bad braiding, or an excessively noisy environment.


We arent discussing fixing any noise issues Doc, just dealing with the voltage spike on power up at the output and why on Bottlehead's own forum there is a sticky thread talking about how it should have been added to the manual to ground the tip and ring connectors on the TRS jack and why that wasnt added to the manual. Seems it would just be a safer way to further ensure no ones headphones ever get damaged.

post #3073 of 7977

Re discussion of noise issues, I was addressing Simanick's post.

 

I think that blown up headphones from a voltage spike are more legend than reality. Is anyone measuring the spike with headphones plugged in? If you consider the value of the output bleeder resistor and do the math you will see that the spike you are measuring with no headphone plugged in would be about 10 times higher than when you have a 300 ohm can plugged in in parallel with the resistor. In other words the impedance of the headphone itself creates a benign startup. We added that unloaded startup voltage measurement to the checkout to help confirm that one hasn't screwed up some part of the build that would leave a high DC voltage on the output after warm up (e.g., a shorted output coupling cap), not to freak anyone out about blowing s**t up. We leave headphones plugged into Cracks when we fire them up all the time.

post #3074 of 7977
Quote:
Any Crack we have had around here (I dunno maybe 20 or 30 over the years?) has been dead quiet. I would suggest not trying to fix stuff until you know it's broken. The few (not many) people who reported noise may have had bad solder joints, bad braiding, or an excessively noisy environment.

 

I might have been one of those!

 

I did use the a shielded coaxial cable to "solve the problem", but I changed so many things at the same time that I can't be completely confident that the shielded signal path was the solution. In hindsight (and from experience on other kits, etc.) I'd recommend just building it right and ensuring all your solder joints are good. It's quite likely mine was a ground loop issue or similar as a result of it being my first ever build.


Edited by Loquah - 10/29/13 at 4:07pm
post #3075 of 7977

Righty-O, I won't try to troubleshoot before any trouble.

Secretly looking forward to varnishing and painting the Crack to look classy (as many of you on here have already done). I imagine the stuff in a can is not very good (miniwax, I think?), so does anyone have any quick recommendations for the exterior coating?

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