My Take on X-BOSOZ

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#764
chipco3434 said:
OK, this might seem like a dumb question, but with -20.2 on the DC rail, why do I even need regulation ? That's what the 9610 is doing, eh?
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If your talking about the 27r power resistor in the crc, I know what you mean. I was losing a LOT across that under load. So much in fact that I was starving my zener stack (my neg trafo secs are comparatively low compared to what most are using). I stuck a 1r power resistor in there to replace the 27 and am losing a LOT less now (why not try jumpering that 27r and see what happens. Do we REALLY need such a high value there). That, different zener values, and using a pnp bipolar instead of the 9610 got me a regulated voltage I could live with..~-14.5v under load. It struck me that I was going to have to be a little creative 'cause I wasn't following the EXACT recipe. This, with some guidance from 🙂 .

my pre still isn't done but my psu's and boards 'seem' to warm up OK.

OT: Finally got to do some comparison between my mini and my A30. The mini sounds better in all respects(except level)...no question about it. I'm thinking of converting my A30 to a higher voltage mini and really get some fets toasty 🙂
 
#767
promitheus said:
Russ White
Die you read post http://www.diyaudio.com/forums/showthread.php?postid=855641#post855641

Is there a difference in the 2 voltages?
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I actually do not claim to know enough to answer your question, remember it is not really my circuit design, just my layout. 🙂 But I am trying to understand it as much as possible.

Here is what I think,

I think the higher negative rail gives better regulation for the CCS on preamp. Thats prettty much it.

What I can tell you for certain, is it sounds excellent.

Cheers!
Russ White
 
#769
To go back and pick up on something from Chipco. I also noticed that the supplies do not regulate when two are hooked up to the same tranny's. Hook either one up alone and they are fine. 70V and 20 V. Hook them both up and the voltages start growing upward until I shut it off.

Has anyone confirmed the current draw from the transformers? I am running no load so far, just the power boards. Will make more measurements tonight, but have to go to paying job now.

Craig
 
#770
I also noticed that the supplies do not regulate when two are hooked up to the same tranny's. Hook either one up alone and they are fine. 70V and 20 V. Hook them both up and the voltages start growing upward until I shut it off.
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Thanks hayenc, I've been thinking about giving up on this stuff. Unlike my real job, I work carefully on this hobby.

Glad you were able to duplicate my observation!

Did you also notice that the tranny groans a little on power up when both supplies are connected?

Did you also notice that if you pull off one of the 16VAC connections, all else seems normal?
 
#772
chipco3434 said:


Thanks hayenc, I've been thinking about giving up on this stuff. Unlike my real job, I work carefully on this stuff.

Glad you were able to duplicate my observation!
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Keep in mnd, you are using a PE buyout trafo, which is a pretty big unknown. Those of us who have used discrete (toroid in my case) trafos for the rails have had no issues, even with two PS at the same time.
 
#779
Real quick since I am at work, but for my setup I have two separate toroids, an Avel 30 VA for the 60 and and Amveco 15 VA for the lower voltage. The initial published current draws indicated these would work, but if they won't even supply two power supply boards, I have to wonder.

I will do some more measurements when I get home tonight.
 
#780
To answer Promethius' earlier question, the reason for the negative voltage is thats what value of convenient transformer I had laying around when I built my preamp project. However, Russ is also correct that the CCS improves its behaviour with additional voltage acros the FET until you have about 10V Drain to Source. As the Drain sits at about -5V, and there is a small drop across the Source resistor, for best behaviour you want the negative rail at a minimum of -16 or -17 volts. Having -20 volts was simply convenient for my original build.

As to using the same tranformers for two channels, that's exactly what I have been doing from the very beginning with no problems, and at first glance I don't understand why it is behaving that way for some. I'll see if I can figure out what might be happening.

Cheers, Terry
 
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