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Old 19th November 2001, 09:04 PM   #21
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kiwi,
Strictly speaking, the circuits I hung under the SOZ are current <i>sinks</i>. This is one of those annoying oddities that crops up when you start speaking about current. Once upon a time, it was believed that current went from positive to negative. That was before they discovered that there were such things as electrons. Now, it's accepted that current--in the sense of a flow of electrons--flows from negative to positive, but for historical reasons people still think in terms of a positive to negative flow. As a consequence, a current <i>source</i> is a circuit that "supplies" current in the historical sense. Think of it as being "above" the circuit, usually hanging off the positive rail. A current <i>sink</i> "accepts" current in the historical sense. Think of it being "below" the circuit, usually sitting on the negative rail or ground.
Confused yet?
Don't feel bad, so's everyone else. Just think, they had a 50/50 chance of getting it right and muffed it. If it's any consolation, electronics is not the only field afflicted with such contradictions. In chemistry, the formula for ammonia, NH3 (assume that the 3 is a subscript, I can't remember the trick to make it drop), is backwards according to current conventions. The hydrogen should be listed first. But, for historical reasons, everyone still writes it the old way.
In practice, most people just call everything a current source. Annoying, but there it is.
Yes, you could run a single current source (you're welcome to read that as sink if it makes you happier). The circuit would work just fine and should have somewhat higher gain. The heat would be ferocious in one current source, so plan accordingly if you want to build one.
Tom,
Yes, inductors would work fine. The single-ended tube folks do it all the time. It works even better without the resistor--simply replace R1&2 with really <i>big</i> inductors. The reason I haven't pursued it is that you can't just walk out and buy large value, high current inductors, and for some reason most people seem reluctant to wind their own, judging from the threads on the topic here. If enough people show interest, I'd be glad to do so.
You can use the SOZ with an unbalanced input, albeit with less gain and higher distortion. That, in turn, can be taken care of by...current sources. The more resistance under the tail of a differential, the better it functions as a phase splitter, and a current source has (at least in theory) infinite resistance.
Incidentally, I've got a dual-tracking current source that's set by a single voltage input, I just need to put the silly thing on the SOZ. The only thing lacking is hours in the day...

Grey
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Old 4th December 2001, 06:29 AM   #22
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Grey,

I noted in another post you were building your SoZ to be the HF amp to run your tweets in your 4 way system.

Are the power mods discussed in this thread /in theory/ and are the SoZ's not yet done? Or did i read that you /do/ have one completed? (i've been reading this purple forum a few too many hours today, sorry)

I ask because in this posting: power as a function of frequency, and upper x-over point i declare: "...HF Amp: to be determined... " and the SoZ is interesting me. Yet, to keep with my corresponding power levels, i'd need 37 watts/ch into a 6~8ohm load, which, due to living in Atlanta, would make summers unbearable with the stock Soz...

Also, which active x-over are you using? You own or John P's?

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Old 4th December 2001, 03:20 PM   #23
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I'm using a crossover that I designed. Nothing fancy, just JFETs and MPSA18s as followers in a Sallen-Key configuration. It's the kind of thing you can throw parts at from across the room and depend on them to settle in properly.
The SOZ isn't necessarily going to end up as my tweeter amp--that's just a possibility, depending on how it sounds. It won't have enough power for me to use it anywhere else in my system. The main reason I started fiddling with the thing is that every month or two, someone would rediscover the wheel and start another thread on,"Gee, I wonder what would happen if you used a current source with the SOZ?" or bring it up in another thread, often in a discussion on Zens. Far too many people are starting new threads about the same things over and over and over. This was just a convenient way to draw interest in the SOZ/current source idea to one place, instead of having it spread all over the state of Nevada.
There's also a great deal of curiosity about current sources, so I thought it would provide an easy example of a current source being added to a previously-existing circuit that a large number of people are already familiar with. A teaching exercise, if you will. Someone asked how a current source worked once--I ought to copy the answer into this thread so as to provide some backup for the circuit itself, but haven't taken the time to track down the other thread.
It's a low-to-mid priority with me; I work on it when I have spare time (which means: rarely--too many other irons in the fire). If I get to a point where I think it'll do a good job on the tweeters, I'll toss it in my system.

Grey
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Old 6th December 2001, 09:42 PM   #24
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I am about to make a PCB for a 'BOSOZ with current sources', I have used the variety of CCS as described by Grey in this thread (only adapted to the lower quiscent current, thanks Grey). My question is where can I find out more about different current sources and how to design them. Grey you alluded to the fact that there are many different types and the one shown on the SOZ is just a garden variety, also mentioned that I might like to try them all before I decide which one is best for me, bit like beer really. I seem to remember seeing a page at Elliot Sounds web site regarding current sources/sinks, I will chase this up in the meantime.

Cheers

Dan
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Old 6th December 2001, 10:08 PM   #25
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Dan,
I picked up what I know piecemeal as I went along. There are different ways to go at a current source. The basic way is to provide a fixed DC input to the grid/gate/base. This is sufficient to tell the device that you want some arbitrary current output, depending on what you put in. The next step is to include some error correction via a sensing resistor. The current source I used for this project is an example of this class. Things can get more complicated--you can use an opamp (or just a differential if you like) to sense a steady voltage on one side and the error on the other side. It's just a question of how far you want to push it. Like everything else, there's a limit as to how complicated you want to make the current source, at least for audio use. Commercial current sources are available that have more stuff in them than my entire system.

Grey
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Old 6th December 2001, 10:14 PM   #26
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Grey,

After reading the article at the ESP website and your response I tend to think that this style of CCS is probably as complex as it needs to be for audio applications, certainly if I am the one that has to build the circuit.

Dan
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Old 26th October 2003, 11:03 AM   #27
Tyimo is offline Tyimo  Hungary
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Grey!

Could you tell me how big inductors would need for the SOZ? I would like to try it!
Thanks
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Old 26th October 2003, 04:45 PM   #28
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Quote:
Originally posted by Tyimo
Could you tell me how big inductors would need for the SOZ? I would like to try it!
I used 1 Henry air core chokes. Worked very well.
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Old 26th October 2003, 11:21 PM   #29
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The inductance will determine the frequency response. It's a simple filter. A smaller value inductor will give you high frequencies only--perhaps good for a tweeter amplifier in a biamp system. The larger the inductor, the lower the frquencies the amplifier will reproduce. Kind of a built-in active crossover. Unfortunately, the amplifier is still trying to reproduce the lower frequencies, so you lose the benefit of less strain on the amp. Still, it will work quite nicely if you want to follow that path.
To keep track of the idea, remember two things: 1) the larger the load on a gain device, the more gain (other factors being equal), and 2) an inductor is, in a sense, a frequency dependent resistor. At DC (in other words a really, really low frequency...F=0), an inductor is close to a dead short, limited only by the resistance of the wire itself. As the frequency climbs, the impedance increases and with it, the gain. More inductance will lower the frequency at which the gain starts to climb. No inductor at all, i.e. connecting the Drains of the MOSFETs directly to the rail, will not hurt anything (as long as you don't exceed the limits of the devices) but will produce no gain.
An air core coil is a good idea because air doesn't saturate when the magnetic field gets strong. Iron core inductors are smaller but the price you pay is in performance.
A 1 Henry air core coil is a pretty large coil in every sense of the word. Hint: It'll be cheaper if you wind your own.
Go for it.

Grey
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Old 27th October 2003, 01:20 AM   #30
moe29 is offline moe29  United States
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I use the 2mH inductors Mr. Pass mentioned in the SOZ article.
They work fine. You can still get them from MCM... at least as of a
few months a go, when i ordered last. Of course i just looked and
Tyimo is in Hungary, so that info won't help him... but you cans
see a pic of them in my post in the X-SOZ thread if that helps in
making your own.
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