Increasing gain on the Crack

W

wullymc

New member
Hi everyone,

I am very much enjoying my Crack.  Currently I am using it with a face and thought my computer to my DT880 600ohms.

For most of my music I have to have the volume between 12 and 2 o'clock.  Would this be normal?  I know that 600 ohm headphones are hard to drive.

I have just now ordered a turn table - project debut carbon and a phono box.  I have read that lps playback quieter than cds.  I haven't received the tt yet but am worried that I won't have enough volume.  The phono box can deliver 40 or 43db of gain.

I am wondering if it is possible to increase the gain on the Crack?  I have a 6as7 power tube and have read that kf I go with a 5998 it will increase the gain by 3db.

Also, I don't have the speedball.  Would this increase the gain?

I guess another option is to go with 250ohm dt880s bot I really enjoy the 600ohm ones.

Thanks very much for any feedback. 
 
Most people have too much gain -- even for 300/600 ohm cans, but the Crack is designed for these high impedance loads and should have no problem driving them.  The important question here is what is the output voltage of your source?  I don't know what a "face" is, but any normal digital source, even the lowish output level of an iDevice should be fine.

Changing the output tube won't change the gain -- this is configured as a cathode follower so gain is always just a bit under 1, or no voltage gain, just current gain.  The only thing that will change here is the output impedance, and that should not be an issue with 600 ohm cans.

As for levels of CD vs vinyl, it all depends on the cartridge type, the level of any given recording, the gain and thus, output voltage of the source gear, but most of today's gear should deliver somewhere around the 2v output voltage standard, which is more than enough to drive the crack to ear damaging levels. I am guessing that your current source is very low output and/or there is something else wrong with the amp, or cables, or something.  More gain from the Crack is probably not what you need, just a higher output source, and again, any standard dac or phono stage should be plenty sufficient.  Though you will need to use a moving magnet cartridge with that preamp with 40 dB gain for best results -- again, that may or may not be true depending on the level of the source material, etc.  It will probably be fine with some of the high output mc carts as well.

If you're needing to turn the Crack up that high with your current source, it must be putting out a very low output signal.

HTH,

Jim
 
Thanks for the reply Jim

The fact that I am using is the jdslabs odac.  On their specs Page it indicates the the Maximum output Line out 100K: 2Vrms.  I take it that this is 2 volts.

I tried my ipod classic to the Crack and still the volume was not affect.  It still had to be up.

When I finished the Crack itested all the voltages and everything was ok

I'm confused.  What headphones are you using and where is your volume?

 
I would suggest waiting until you have actually tried the turntable before you decide there is a problem. You really shouldn't worry about where the knob is set if the amp is playing loud enough. There is no industry standard for where the knob should be set.
 
As long as you get satisfying volume without having to put the volume at maximum things are good.  An often misunderstood relationship is between gain and volume.  Gain is how much the signal, at whatever level reaches the amplifying device, is increased.  

The volume control takes the input, in your case a standard 2V CD input, and cuts it down.  Then the gain of the amp makes the voltage swing bigger.  So the more of the source you feed the amp the more power it produces, the more physical volume you get from your headsets.  

Do you ever run out of the volume pot before you reach the volume you want from your headsets?  If not, you are fine.  Which is what I see Dan just posted while I was typing.
 
Dave,

I have the hd-8000s and MB Quart QP-400s -- both 300 ohms.  I don't remember ever having to turn things up past 10:00 with a 2v source -- which is what the odac says it is, so I guess I didn't expect the 600 ohm cans to be that much more.

BTW, I myself will be using a preattenuator on the volume pot so I can get my comfortable listening level to around 12:00 give or take -- pots sound better in this range and as Grainger says, if you haven't run out of steam, you're listening in the best place pot and where you have the most fine control.  I'm one of those folks who find that every reccording has a level that is just-so for my comfort (and this actually the way engineers (good ones) tend to do things as well).

What a tube like the 5998 will do is lower the output impedance somewhat, but not having any experience with 600 ohm cans, I couldn't tell you how much of a difference it makes vs the 300 ohm ones.

Doc's absolutely right though -- don't psych yourself out  it looks like the phono stage you are getting should be fine -- as will most but a few exotic and passive ones, and without trying one of those I couldn't even make any sort of prediction on how well they would work with the crack  It's all a matter of gain, load, and output of your cartride.

Are you getting the new Debut Carbon?  If so, I'd like to hear what you think of it -- got that in mind as a recommendation for a frriend as a reasonably priced, but good performing table.

-- Jim
 
Hello Wully,

Yes, you can increase the gain of the Crack, and the Speedball is one way to do it.

The 6080, 6AS7, and 5998 will all have approximately the same gain in the cathode follower position (a bit less than unity), so that will not help you.

The Crack drives high impedance headphones very well, there should be no need to switch headphones on that account, and you could potentially end up with less output by doing so.

I would get the vinyl system setup and verify that you have this issue.  Most users find that the amp is a little bit too sensitive for their likes, so you would really want to be extra sure that you need significantly more gain before performing these modifications.

You should get about .5V out of your vinyl setup, I think you'll find that this is more than enough for your setup.
 
I see the OP is currently using the ODAC as a source. I'm listening to the ODAC right now myself, and I assure you that the Crack has no problem driving 300 or 600 Ohm headphones to ear-splitting levels. I can't even get to 10 o'clock and I have 7 o'clock as zero volume. I wonder...do you have the digital volume control on your computer set at full volume? I think that must be the issue. The ODAC and Crack cannot be the bottleneck here. If you have to set  the Crack to 2 o'clock to get an adequate signal with your 600 Ohm headphones then...it's time to get your hearing checked!  :P  (Just kidding.)

Best regards,
Adam
 
Thanks everyone for your replies. I truly appreciate it!

I agree that it shouldn't matter what position the volume is at as long as it is giving enough volume to satisfy my needs.  I actually can put the Crack to maximum volume without distortion and it doesn't provide ear hurting distortion. 

I have verified that it just isn't the ODAC because I have gone directly from my iPod and also used my DVD player through a different set of cables.

I will wait until I get the turntable and will report back. 

Dave

PS: maybe I will get my ears checked.  My wife says I miss a lot of things she says...ha ha


 
Dave,

Many modern DVD players put out 300-400mV of output, and some modern portable devices aren't much better (my HTC phone has the same issue).

The ODAC has a 2.0V output, and I would use every bit of that (IE - crank the volume up on the software side).

2.0V going into the Crack, then feeding HD-800's should make more SPL than you can stand!
 
Yes, that's what I was trying to say, but I think Adam hit the nail on the head -- it's probably a software setting in whatever software application the op is using to feed the ODac.

-- Jim
 
wullymc said:
  .  .  .  PS: maybe I will get my ears checked.  My wife says I miss a lot of things she says...ha ha
Click to expand...

That is not just you.  My wife says the same thing.  I think it is a guy thing.  Deb, do you have this problem?
 
Thanks guys,

I have reviewed my software side of this.  I am using Windows 7.  24 bit 44.1.  The sound is maxed out on the computer.

I don't know what else it could be.

I usually use Foobar.  I have tried iTunes and Windows Media player to see if it was a setting in Foobar.  The was no change with a change of application.

I am happy with the sound between 12 and 2 but think I should have a lot more power (volume).  I will try when I get the turntable and see what volume I will require.

Maybe eventually I will go with the Speedball upgrade....maybe I will send in my Crack to get it installed and have Bottlehead review my work!

Take care...Dave
 
I am in Ottawa.

I don't know if it would be a good idea to recheck the voltages?  What component would possibly cause the volume problem if there is one?

Thanks!
 
I'm still a bit lost here. "12 and 2" doesn't really translate to anything when we don't know how the knob was oriented when installed. The knob can turn through 3/4 of a clock face. Some people have the knob at its lowest setting at 7:30, some at 6:00 and some at 12:00.  Is the knob at lowest volume at 7:30 and between 12 and 2 is like turned up halfway to 2/3 of the way, or is the lowest volume setting point of reference something else?
 
I have confirmed on my crack, with 600 ohm phones, the volume turned to 12:00-01:00 is where I normally listen. I never looked closely at the stock pot, is it log tapered? I know that the alps I have in there now is. I wonder if this is the situation, the attenuation decreasing at a log rate as it is turned up? (meaning there is no problem).
 
Thanks.

Sorry, I have the volume pot installed so that 0 is at 7 o'clock.  It is the stock pot that came with the kit.

 
Dave,

You have your volume control installed as I would.  That is pretty much standard.  But Dan had to ask because who knows where the screw gets set on the knob.

Your situation is odd.  Maybe a recheck of the voltages and posting anything over 15% high or low would help clarify it.

The stock pot is log or audio taper.  Linear tapers act really funny in an audio application.  

Oh, I'm in Knoxville TN, so I'm no help.  We do have a number of Canadian Bottleheads.
 
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