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Review of my 5 DIY amplifiers. 2012/03/21: Bottlehead Smack and new analyses - Page 4

post #46 of 67

fantastic thread wyldrage..

 

you really ought to move to BJT outputs on the EHHA...much more involving than the MOSFET output devices.

 

Also for more midrange warmth try the Valvo 6GM8s. Upscale AUdio still has some stock of these.

 

Of course my go to choice is still the telefunkens of which i have a pair. Drop me a PM if you want to buy them.

post #47 of 67

Hah, you should throw a Bottlehead S.E.X. into the mix as well tongue_smile.gif It's similar to the crack, but a little "bubblier" and handles the low impedance cans better. I would be curious to see if it could handle the HE5-LE.

post #48 of 67
Thread Starter 

I may try BJT, but not now. I am pretty happy with what I have right now, and I'll wait until upgraditis strikes. Plus I have spent a bit too much recently, so I'll slow down and probably wait until sumer.

 

In other news, I have nearly finished the CTH, but I made a few mistakes ordering parts so it won't be ready until next week at the earliest.

 

As for the S.E.X., I was pretty interested in it last year, but I finally chose the Castanet for the transformer-coupled amp. The fact that Bottlehead came out with the Crack helped a bit in the decision: it allowed me to try out the different designers, while getting a very different amplifier. As for orthodynamic and the Bottlehead S.E.X., check here: http://www.bottlehead.com/smf/index.php/topic,1477.0.html . It's about the LCD-2, but the results with the HifiMAN should be close.

 

However, I know they are teasing a possible new headphone amp on their forums, as well as an actual headphone kit. The Crack will not be the last time I do business with Bottlehead.

post #49 of 67
Thread Starter 

Another small edit: I've added measures for the Speedball Crack with the 5998A tube, both as a fourth measure for all headphones and as a separate pdf. There is a better frequency response and a decrease in THD, but it still sound "off" to me.

post #50 of 67
Thread Starter 

I have been asking myself: why does the frequency response of the Speedball Crack varies so much from one headphone to the other. I finally found my answer: the variation in impedance of the headphone in function of the frequency.

 

Check the headroom graph for the Sennheiser HD 600: the same peak at 100 Hz is present in its frequency response with the Speedball Crack in my pdf. Unfortunately, the AKG k601 graph is no longer available, but I would bet it was tilted towards the higher frequencies (like the k701 slightly is).

 

graphCompare.php?graphType=7&graphID[]=573

post #51 of 67

It's also why some folk like OTL and the tube rolling that goes with it.  It's a late stage EQ, effectively.

 

OTL also has a higher output impedance than a SS output or transformer coupled.

 

Output impedance measurement is easy.  Set your amp to be the loudest it can get without clipping (for larger scale voltage, it's easier on the DMM).  Play a 0dBFs file, something like a 1kHz sine.

 

1) Read the voltage with no load,

2) Put a resistor from output to ground, measure the voltage.

3) Zout = Resistor * ((Vunloaded / Vloaded) - 1)

 

Another way is to pick a resistor so that Vloaded = Vunloaded / 2.  The resistor value is the output impedance.

 

Higher Zout changes the sound.  In this aspect, I like Beyer headphones with 120ohm, as I believe that is what they design for (IEC suggested standard).  Many people say Beyer headphones sound better with tube amps.  it's no wonder why, with OTL tube amps, which is the most popular, the Zout is rather high.

post #52 of 67
Quote:
Originally Posted by holland View Post

It's also why some folk like OTL and the tube rolling that goes with it.  It's a late stage EQ, effectively.

 

OTL also has a higher output impedance than a SS output or transformer coupled.

 

Output impedance measurement is easy.  Set your amp to be the loudest it can get without clipping (for larger scale voltage, it's easier on the DMM).  Play a 0dBFs file, something like a 1kHz sine.

 

1) Read the voltage with no load,

2) Put a resistor from output to ground, measure the voltage.

3) Zout = Resistor * ((Vunloaded / Vloaded) - 1)

 

Another way is to pick a resistor so that Vloaded = Vunloaded / 2.  The resistor value is the output impedance.

 

Higher Zout changes the sound.  In this aspect, I like Beyer headphones with 120ohm, as I believe that is what they design for (IEC suggested standard).  Many people say Beyer headphones sound better with tube amps.  it's no wonder why, with OTL tube amps, which is the most popular, the Zout is rather high.


Right now I am really enjoying my HD600 with the crack+speedball.  The crack does a great job driving higher impedance cans which is why I decided to get the HD600 again.  I also have the 250 ohm DT880 which is nice but im just not a big fan of their sound sig.  The AKG K400 and K500 are great with the crack and 6AS7G tubes.  I found that with a 5998 in the amp the AKGs would start to distort and when I turned the volume up past halfway.  

post #53 of 67
Thread Starter 

Added the Bottlehead Smack today. It's a great choice for any dynamic headphones, from Grados to Sennheisers. Enjoy.

post #54 of 67

Excellent. I was one of the pre-orders as well (technically even earlier), but life has been so ridiculously busy that I haven't even opened up the box yet. I'm eager to compare it against the Crack/Speedball I built. Maybe I should finish up the half-built b22 sitting there too eh?

post #55 of 67
Quote:
Originally Posted by WyldRage View Post

Added the Bottlehead Smack today. It's a great choice for any dynamic headphones, from Grados to Sennheisers. Enjoy.


Great review WR!  And also - a big thank you for posting those measurements!  I've been curious as to how the crack measures for quite some time (although I understand from the nwavguy article that RMAA will vary from machine to machine and may have some irregularities).  In one of his January 2012 posts, Tyll also indicated that he will be posting, as time allows, measurements for the crack on innerfidelity.  I'm eager to see them.  For purposes of you 5 amp comparison though, do you think you might have an opportunity to measure the smack at some point in the future?

 

Also, if you have an opportunity, I'd love to hear more about how you took your measurements.  I would like to try measuring my modded speedball crack, with a 5998 [as opposed to 5998a], and to compare it to the results you obtained (assuming my soundcard is adequate).  Is there a reasonably user friendly tutorial posted somewhere on how to set this test up? 

 


Edited by skeptic - 3/21/12 at 11:29am
post #56 of 67
Thread Starter 

I've measured the Smack, and re-done the others: when you change something in the chain, they are no longer comparable. For my case, I've replaced my Presonus with a E-MU 0404 USB, which has a sharp drop-off at 20 KHz and lower noise. You will not be able to compare your results to mine.

 

I've included a picture of my testing set-up, that shows how I do it.

 

Cheers.

post #57 of 67

Thanks so much for the new measurements WR, and the for the photo and explanation of your testing rig!  The use of a splitter at the headphone jack to test the various impedances was the part I just wasn't wrapping my mind around.

 

Although I don't have anything as solid as a 0404 to use for testing purposes (my options are a couple of X-fi's or various on board options), I'm going to have to give this a go sometime soon to compare my Woo 3 and modded Crack w/ Speedball.  Woo suggest that the WA3 has extremely low THD measurements, of <.08% (see: http://www.wooaudio.com/products/wa3.html ), but the Crack sounds like the better, more dynamic and detailed amp to me with my HD800s/650's and DT880's.  Maybe I just like coloration at the end of the day /shrug.  

 

In any event, this is an extremely valuable thread to anyone contemplating a DIY tube kit.  Thank you again for all of your work and thoughtful impressions!  

post #58 of 67

Out of curiosity, are you normalizing the input voltage to be the same for every amp and every headphone for the RMAA tests, say by checking the levels with a multimeter for every combination?  Somehow I get the feeling like the higher noise figures on the low-impedance headphones may at least in part be because the signal level you're measuring just changed by plugging in different headphones (because a different percentage of the signal is lost across the amp output impedance).  i.e. the reference signal level changed, not so much the noise floor

 

Thanks.  Interesting stuff.


Edited by mikeaj - 3/23/12 at 12:17pm
post #59 of 67
Thread Starter 

Every time I plug in a new headphone I play a tune and set the volume to my normal listening level. I also have to adjust the input volume on the E-MU itself.

 

That may or may not be the right way to do this, but the results is similar to my experience: I can much more easily hear the noise coming from an amplifier on Grados than on the Audez'e and the Senns. 

post #60 of 67

Good stuff here. The Bottle Head amps always look impressive.

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