[rsaavedra]

Quote:

Originally Posted by ayt999 thanks Raul. so since Raul is going to get a discount on his next order, by default that makes him the man that's going to do the ordering when the next PCB group buy comes around. lol thanks again.

Man coordinating a group buy is really fun, but time consuming nonetheless. I'd be glad to be the mediator of this discount in that next group buy (probably for Kevin's power supply boards? Are yours for the Dynahi Glassman?) But I'd ask that someone else be the actual hub gathering all the info and money from buyers for that other groupbuy. Then at order placement time just pass me the files and final amount, and I'd place the order gladly, indicating that coordinator's shipping address if that's possible. (For security reasons, credit card companies might object to that though).
I also wonder if this discount "token" can probably just be forwarded to someone else, if talking to PCBnet explaining our group buys.

 

[Glassman]

yes, I'm planning to do ultimate power supply for dynahi.. otherwise I wouldn't be bringing it up here

 

[intlplby]

how long until you have finished designing the ultimate PSU

isnt it going to be a revision of the second version of the jung super loop design?

if so it shouldnt be too much trouble to whip up, right?

 

[Glassman]

you're completely right, i just need some opamp that can stand way more then 30V and make shure it performs just as well as the opamps usually used in jung super reg, I also need to know if the default pass transistor will stand the current needed..

 

[hegestratos]

Quote:

Originally Posted by Glassman you're completely right, i just need some opamp that can stand way more then 30V and make shure it performs just as well as the opamps usually used in jung super reg, I also need to know if the default pass transistor will stand the current needed..

I just skimmed the datasheets of the AD825, D44H11 and D45H11. The AD825 can use a psu of at most + and - 18V, so tie it between +30 and GND and GND and -30 and you're fine. The D44H11 and D45H11 can work with 10A on the collector, so that shouldn't be a problem either.

The only thing you need to do is increase the constant current source. The D44H11 and D45H11 have Hfes of at least 60 and 40, respectively. Since you're looking for some 2A, you will need to increase the current provided to at least 0.033..A on the positive side and 0.05A on the negative side. You don't want it too high either, because that'll put strain on the feedback loop.

You'll also need plenty of heatsinks. On the output transistors alone you'll be dropping 2.5V (assuming you've got a tracking pre-reg) at 2A, so that's 5W on each side already. You'll be dissipating about 3-4 times that on the pre-regs.

Cheers,
Alfred

 

[Glassman]

actually, the AD825 can't stand the start-up of the regulator.. that's why I'd like to use OPA27, which is pretty low noise chip and can stand 44V.. you're right with the current sources.. and this thing asks for decent heatsinking..

 

[hegestratos]

Quote:

Originally Posted by Glassman actually, the AD825 can't stand the start-up of the regulator.. that's why I'd like to use OPA27, which is pretty low noise chip and can stand 44V.. you're right with the current sources.. and this thing asks for decent heatsinking..

Have you seen this thread over at diyaudio? What it lacks in SNR it makes up in sheer size. I remember there was a lot of discussion on opamps there too, especially with respect to stability. I can't say if it'll be stable with the OPA27. You will also be better off with the OPA37 because of its faster slew rate, which is still an order of magnitude behind the AD825... It does have slightly better noise figures, though.

I'm not sure why you think the AD825 can't stand the startup. I can't imagine really wild things happening. You must be loading a big capacitor somewhere, so the output should just come up nicely from zero. The feedback loop will kick in at some point, so the output should never be much above 30V. Or am I missing something? I think the ALW boards are known to work with AD825s at 30V.

Cheers,
Alfred

 

[JCTW]

Hi,
Can I orger the board this time?Tks!

 

[rsaavedra]

Quote:

Originally Posted by JCTW Can I orger the board this time?Tks!

Sorry the order was placed yesterday, and for the exact total number of boards requested by the deadline. Some of us are ordering backup boards, you might want to submit a WTB post for Dynahi boards in a few weeks, or wait for another group buy.

 

[Glassman]

Quote:

Originally Posted by hegestratos Have you seen this thread over at diyaudio? What it lacks in SNR it makes up in sheer size. I remember there was a lot of discussion on opamps there too, especially with respect to stability. I can't say if it'll be stable with the OPA27. You will also be better off with the OPA37 because of its faster slew rate, which is still an order of magnitude behind the AD825... It does have slightly better noise figures, though. I'm not sure why you think the AD825 can't stand the startup. I can't imagine really wild things happening. You must be loading a big capacitor somewhere, so the output should just come up nicely from zero. The feedback loop will kick in at some point, so the output should never be much above 30V. Or am I missing something? I think the ALW boards are known to work with AD825s at 30V. Cheers, Alfred

maybe you're right, we'll have to test it.. OPA37 is out of the question because of it being uncompensated and thus not unity gain stable.. of course it would be easier and better to use one of the usually used opamps in there.. on a second thought I think we should contact aos and ask him for a big batch of his jung reg boards and organise another group buy.. the boards are so small it shouldn't cost more then $5 for a couple of regulators.. mount them on a big heatsing and you're done.. the only shortcomming is that you'll need to mount power supply caps and rectifiers using point to point wiring, but maybe we can have aos to rework the boards a bit to include rectifiers in TO-220 packages and maybe the caps needed..

 

[strohmie]

Thought I'd bump this with regards to parts selection.

I bought almost all of the transistors from B&D Enterprises, but the 2SC3421 transistors are currently out of stock.

The resistors I went with were good ol' Vishay Dale, RN60C type (which are the 1/4W metal film variety).

The specific capacitors KG used for the .47uF are Mouser part number 75-MKT1822447014 because they fit the board (or was the board made to fit it? Chicken, meet egg.)

Not sure which op amp to pick up -- KG mentioned that they should be low-offset, and he uses the OP177G in one of his later pictures and the OPA541AM was mentioned elsewhere in the thread (though these aren't DIP, they're round-shaped). Not positive exactly how important quality is when it comes to this part.


Thoughts?

 

[Glassman]

use opa227p (not pa) as a servo opamp..

guess who bought out all the bdent's stock

 

[ayt999]

Quote:

Originally Posted by Glassman guess who bought out all the bdent's stock

lol

I better start looking for parts... at least I'll have some unpopulated ladder attenuators in a few days.

 

[strohmie]

I initially thought to buy one of those attenuators (and had myself on the list), but I dug up a pretty good Clarostat Type J 10K dual pot that I'm going to use instead. An attenuator would be better, but I'll survive. Better that than spending $80 I don't have plus resistor cost.

 

[ayt999]

what are good values to use for the volume control?

my dynamid (I guess that is what we are calling it now) uses 50k ladder attenuators but I don't know if it should be similar for the dynahi (and the balanced dynahi, whatever it is called).