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Sunday, October 23rd, 2005
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3:45 pm - Worklog: Balanced Amplifier for the AKG K340
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This thread is for a few people that I am working with in designing a new amplifier specifically designed for the AKG K340 headphones. Feel free to post if you have any suggestions, but this is primarily for the explicit use of Renato, Eaphan, Ori and myself. All content is copyrighted and may not be used for commercial purposes. If you wish to build the design personally for your own use it is at your own risk.
Thanks,
Jason [philodox]
Here is the most current version of the amp, using one 6H30 tube per channel.
Tubes are biased at: -3.9V grid, 100V/31mA (each). Voltage gain is 6.2, sufficient for 95 mW from 1.0V RMS input.
Note: Matched pairs of 6H30 sold here: http://store.triodestore.com/6h30pirussiamp.html
[I ended up getting my matched pairs from parts connexion... matched quad plus triode matching for only $5 total!!!]
Here is the head-fi thread that started the whole idea... and here are a few more I started for advice:
Tube Questions - http://www6.head-fi.org/forums/showthread.php?t=145200
Parts Selection - http://www6.head-fi.org/forums/showthread.php?t=145206
The Family Tree
I've linked some of the designs that led up to this amp in case there is anything that we may want to incorporate into our circuit. ;)
[The new circuit shares very little with the KG designs though]
bamaslama [starting point]: http://home.cogeco.ca/~philodox/bamaslama.JPG
PSU: http://home.cogeco.ca/~philodox/bamaslamaPSU.JPG
dynatoob [brother]: http://gilmore.chem.northwestern.edu/dynatoob.gif
minimig [father]: http://gilmore.chem.northwestern.edu/migmini.gif
mig [grandfather]:
http://gilmore.chem.northwestern.edu/kgdt1.gif
http://gilmore.chem.northwestern.edu/kgdt2.gif
mig2 [great uncle]: The same as mig, but replace the solid state current source with a 6c33.
Kevin Gilmore on Balanced amplifiers...
As far as balanced removing 2nd harmonics, this is certainly true. It really depends on what you want from your amplifier. Everything I do is to make the natural distortion absolutely as low as possible, and make rise and fall slew rates also to be identical.
My stuff certainly is not single ended dht triode and does not sound like it either. Some people like the kind of sound that RS or SP produce. I don't happen to like that kind of sound. When I go to the symphony or opera I know what it is supposed to sound like. That is the sound I'm after. Not something with a harmonic balance that is way out of whack.
Renato’s input
“Ok... so... let me see if I can make sense of this. You were happy with the Dynahi, so we have to find out it's voltage output (peak to peak) and it's current capabilities, as this is probably close to what you need to drive the K340's appropriately. Then we could match a tube amp with similar capabilities. You have to remember that when it's balanced, the voltage will be twice as much, not sure about the current. You can go whole hog and build the most powerful amp out there but the cost will probably be astronomic, especially if you want to use the best parts available. So the moral is, build to suit your needs.”
“Rather than do a complete build lets do the amp first as a 2 channel. The reason for this is so we can test and decide on parts selection for the final balanced build. Once we decide on parts selection then we can build the 2nd 2 channel for the final 4 channel (balanced build). The reason I'm suggesting this is because it would be crazy (and more costly) to change parts on 4 channels. We have to build, listen and be happy with the voicing of the amp before we continue. It's considerably easier to change out 2 caps than 4, (or resistors) and considerably cheaper. Also I think we should build with the ECC40's up front. The input stage and output stage are capacitor coupled so one stage should not affect the other. This will affect the power supply section though, just so that you are aware.”
Eaphan’s input
“In the interest of tube life and saving power, it's going to need a standby mode. What I'm thinking is a 4 position rotary switch (similar to the one on Ray Samuels' tube amps), but with a turn-on mode.
Position 1: Off. No power goes anywhere.
Positinn 2: Low power standby. Resistors in series with tube heaters. High voltage section off.
Position 3: Standby. Full power to tube heaters. High voltage section off.
Position 4: On. Full power to everything.
Position 2 warms up the tubes slowly and prevents turn-on surge which can damage the tube heaters and kill the tube. It also lets you keep the tubes kinda warm without sucking too much power. So if you had to step out for 2-4 hours you don't have to turn the amp off. Position 3 keeps the tubes warmer but uses more power. Use it if you need to eat dinner or do something that takes only an hour or 2.
I have something setup on my own amp but with a series of switches instead of a nice neat rotary switch.”
Ori’s input
“The design was getting complex without much sonic return on investment, so I hinted at the output cap direction. I think that's a simple approach to a simple amp and it adds a level of protection that many OTL amps lack. If you decide to complicate the design and go for the "best" you can do, then I'd consider a complex direction - without guarantees. It may be a flop! But logically, I'd move in the direction of a balanced/bridged output - to avoid DC offset on the load without a servo. Then try to "massage" the design so it is DC-coupled. Last, increase current bias on both drivers and finals, so the peak load current is only a fraction of the final's bias. This gives you headroom and minimal distortion, at the cost of a 6336 and a big supply...”
Ori's first revised version for reference [12B4A/6AS7] - http://home.cogeco.ca/~philodox/otl_hd_2.jpg
current mood:  geeky
current music: david bowie - can you hear me
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(46 comments | comment on this)
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| Tuesday, October 4th, 2005
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9:00 pm - Well, it's my 2 year anniversary and my Wife bought me a CD.
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I've been loving this song that they played on the OC 'imogen heap - hide and seek' for a long time and my Wife just bought me the CD for our 2 year anniversary [along with a few other things]. So I'm going to go give it a listen now.
No more crappy quality MP3 with weird skips. Yeah! 
current mood:  satisfied
current music: james brown
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(5 comments | comment on this)
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| Wednesday, September 28th, 2005
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1:00 pm - Review: 21 hertz - Ocean of time [swedish/french trip hop]
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Well, I'm not too sure what to write about yet as I am new at this livejournal stuff, but I wrote this review a while back and would be interested if anyone has any comments. It hasn't been published yet, but may appear on tripofagia or landlost magazine shortly. If you want to read one of my older reviews, go have a look at the reviews page on Tripofagia. My review of Microbunny's 'Dead Stars' is the third one down on that page.
Anyways, on to the review...
21 hertz | Ocean of time
Life is full of surprises and sometimes they come from where you least expect it. A few months ago I received an email asking that I review an album based on the write-up I did for Microbunny last year. I agreed but, being busy with moving into my new condo, I didn’t get a chance to look at the artist’s website or listen to any of their music. Then Ocean of time arrived and, while I have still been busy, it seems to be what I reach for when I want to lay back and relax. The band, 21 hertz, consists of Karin Steneby 1 on vocals, Christian Hörkkö on guitar and keyboards, Christian Ricci 2 on bass and pads, and Sylvain Brochard on turntables.
Outside starts things off like many Trip Hop albums with a dirty beat overlaid with scratches. It takes a while to get used to what turns out to be, in the end, a very expressive voice with an impressive range. The bass is quite fluid while still having good definition and their integration of live instruments and synthetic sounds is striking. Karin’s voice has very some interesting qualities and is almost holographic at times. I wonder if they are using some creative studio enhancements here.
The first thing that comes to mind when hearing Sparrow is “Now, this is more like it!” I’m not implying that the first track is in any way lacking, but this is when I really start smiling. Again the quality of the recording strikes me. The placement of the instruments or imaging is really quite good. This is definitely not what you’d expect from such places as “Christian’s closet” or “Sylvain’s rat hole” [where the recordings were made]. I think they are being just a little modest.
The vocals cut through the smooth deep bass like a knife in Wave of time, seeming to sculpt the music with their cadence. There is something quite attractive about Karin’s accent when singing “I just want to stay, here with you…” The laidback and sometimes lazy-sounding voice carries with it a marvelous emotional range. There are some nice jazzy beats near the end that neatly finish things off.
The song Ever is very familiar. In fact, I checked the CD to make sure that it’s not a cover song, but as far as I can tell, all of their material is 100% original. The tone of the album changes significantly here and this track would not be out of place on an alternative rock station. That said, it is one of my favorites on the album. The epic quality that her voice and the accompanying music take on is just the kind of thing that I like. Whoever said that Trip Hop has to be boring?
A slower pace is set with some very pleasing guitar work in My time. Karin’s voice is melancholic but retains its purity of sound. The rolling bass fleshes out the mood nicely. All in all, it is a simple song that comes together in such a way that it is very unique.
Silence is a darker song and the tempo is once again quite fitting for the mood. Her voice is overlaid multiple times to create a chilling effect. You almost expect this song to erupt at times, but they keep pulling you back to the creeping beat and forcing you to give yourself over to it.
The rhythm in Still I do is rather catchy and I’ve caught myself humming it many times. There is perhaps too much scratching for my taste, but it does not impede the song in any way. Although it doesn’t necessarily sound like Jazz, it seems to evoke the same response in me and I find myself snapping my fingers and looking for a Cuban cigar.
Tired is another example of how well they have integrated her voice into their music. As with any great group it is just another instrument in the composition. The pace and buildup in this track is spot on - nice and slow with an occasional explosive burst of energy that carries you away.
The album ends with a dark song that is brightened by Karin Steneby’s sweet voice. Ocean ends up getting fairly abstract near the end, but that is the best way to close off a Trip Hop album. Unless it’s with “hookers and gin” 3 that is…
This album has really impressed me. As I wrote this I listened to it again and I think the hardest thing for me to decide was which track I liked most. The music is incredibly varied while still fitting within a common mold and not loosing you with sharp turns. I would have a hard time guessing how many times I listened to Ocean of time before finally sitting down and writing, but it was no small number. I can only think of a few albums in my collection that I would not grow tired of after this much exposure. I can’t wait to see where this group goes in the future. Wherever it is, I will be there waiting for their next release.
Review written while listening on an Eastsound CD-E5 CD player, DiMarzio M-Path interconnects, a Veda Audio Dynahi headphone amplifier, and a pair of AKG K340 Electrostat-Dynamic Headphones modified by Headphile and re-cabled in BlackSilver.
album: Ocean of time
artist: 21 hertz
year: 2005
label: Independent
website: 21hz.org
review by philodox
august 2005
1. Karin Steneby is also an impressive painter/sculptor and
her work can be viewed on their website.
2. The photography and music of Christian Ricci can also be
found on the site and is worth checking out.
3. If you are not getting this Portishead reference, you need
to listen to their self-titled album again. :)
current mood:  working
current music: silent poets
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