Next up: Balanced JISBOS
Dec 10, 2007 at 5:33 AM Thread Starter Post #1 of 23

doobooloo

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It was winter, it was cold, it was a cold winter... (giggles)

OK so it's cold outside and I'm sitting here wondering why I have a fantastic sound card (Echo MIA MIDI) that is capable of balanced outputs and I'm only using it as a single ended card, despite my HD580s being terminated to a 5-pin XLR (my choice AND the official standard for dual balanced signals).

And, my sound card, with AD8620 opamps and BlackGates caps, is more than capable of powering my HD580s beautifully (and loud!) in single ended mode without an amp. Balanced technically doubles the power, and should power my phones even more beautifully, but this configuration has that 2% missing from a truly capable amplification and a lossy digital volume control controlled via Windows.

Right now I'm quite content with my GS-1 with SA in single ended mode but I know I can do better by going balanced and going simpler... by building a balanced JISBOS!

So here's my thought. Since quality 4-channel stepped attenuators are rather expensive, I'm going to build a separate passive preamp box (perhaps with multiple selectable inputs/outputs) that can be used with various other future DIY amps, and have a standalone "amp" box with just audio in, and audio out, no volume control. This amp box, of course, will merely be a buffer box as there's enough quality voltage amplification going on at the sound card level.

I'm going to put the four JISBOS boards on a FPE designed sheet acting as a motherboard and heatsink for the output transistors. This board is going to slide into one of those nice extruded aluminum cases, and with nice thick custom panels from FPE for front and back, and I'm good to go.

Progress is going to be slow as I'll have to work little bit by bit but it's surely going to be exciting! I'll post updates as I get preliminary details up... but right now I've only ordered about half the parts needed...

Oh, and power supply recommendations? Since I'm not feeling particularly motivated, I'm thinking of starting off with the +/-15V Elpac power supply that is bundled with the HeadAmp Gilmore Lites, and upgrading to maybe a sigma 22 built in similar fashion later on...
 
Dec 10, 2007 at 8:31 AM Post #3 of 23

~n00beR

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I will be watching your progress closely
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I am currently working on a balanced cmoy, and have a couple of deisgns I want to prototype.

Heheh this could be my next step
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I checked out your thread on the balanced TPA6120 however the schematics have gone
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Good luck with your endevour and keep us posted
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Apr 10, 2008 at 1:38 AM Post #9 of 23

Killercrush

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I'm also interested in your project, mostly due to the high price/performance ratio of this design. I would love to own a 3-channel standalone amp version.

Here's what I found on Headwize :



It looks like you're not the only one : P
 
Apr 10, 2008 at 1:46 AM Post #10 of 23

luvdunhill

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Quote:

Originally Posted by fierce_freak /img/forum/go_quote.gif
I'm considering using balanced jisbos standalone as an "amp." I'm just wondering what it might compare with if voltage gain isn't taken into consideration.


ah..well, my sources are rather wimpy. around 2vrms (this is even balanced) is my most manly source. I'm sure it would sound fantastic. I played around with various transistors and pretty much disagreed with all the opinions on the JISBOS website ... the 2sc2344/2sa1011 and the 2sc2238/2sa968 are the only combinations I can really recommend, the rest were an order of magnitude worse IMHO.
 
Apr 10, 2008 at 6:37 AM Post #12 of 23

akione

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Quote:

Originally Posted by fierce_freak /img/forum/go_quote.gif
Cool, thanks for the tip, Marc. Of course, those have to be the most expensive
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....... and very hard to find outside the US.
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It's a nice idea this, though. One I've been considering for a while.

It should make a good, cheap, balanced amp, I'd have thought.
 
Apr 10, 2008 at 6:30 PM Post #13 of 23

Ferrari

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Quote:

Originally Posted by Killercrush /img/forum/go_quote.gif
I'm also interested in your project, mostly due to the high price/performance ratio of this design. I would love to own a 3-channel standalone amp version.

Here's what I found on Headwize :



It looks like you're not the only one : P



Hee, it's my pic. That little balanced amp is up and running for almost 5 months now, still need to be cased up.
It was nice to experiment with those tiny JISBOS buffers. They sound BIG unless they are small !!!
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Keep in mind that the effective voltage gain in a balanced configuration is 2x (with unity-gain JISBOS buffers).
 

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