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

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.

Hah, you should throw a Bottlehead S.E.X. into the mix as well 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.

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.

Quote:

Originally Posted by holland 

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.  

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?

Quote:

Originally Posted by WyldRage 

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? 

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!  

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.

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