# dynahi power supply!



## kevin gilmore

OK, so i'm a little busy...

 Here is the power supply board REV ZERO. I have not checked this
 yet, someone else should. I don't even have all the parts to make
 sure they fit in the boards. The board is tight to keep it inside the
 20 square inches...

http://gilmore.chem.northwestern.edu/dynahips.zip

 you will need a gerber viewer to look at this.
 I would not have boards made on this just yet...

 not the turkey present i was planning on...


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## randytsuch

Is there a schematic to look at?

 Randy


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## kevin gilmore

Same thing as the dynalo schematic with lm338's replacing the
 pre-regulators, and opa541's replacing the opa548's. And a few
 resistor changes...


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## bg4533

Do you have a rough estimate as to how much this PSU will cost?


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## kevin gilmore

6 caps at about $8 each
 2 caddock power resistors at $5 each
 2 opa548's at $17 each 
 2 lm338 at $2 each
 board at $10 in quantity
 ref02 at $9
 8 fast recovery diodes at $1

 few other parts...

 NOTE: there are definitely some problems with this layout.
 The opamps and the power resistors are too close. So don't
 go making boards just yet.

 Note2: Board now at rev 1. Everything fits. Very tight however.
 Just barely under 20sq. Same file same name.


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## dgardner

For those without a gerber file viewer... 
 Here is the topside, bottomside, and silkscreen so far

View a jpeg of artwork = 471KB


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## Talonz

This is great 
	

	
	
		
		

		
			





 We only need one power supply then, correct?


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## strohmie

One power supply board and likely a heat sink as well, along with the other parts. Hopefully Kevin organized the board such that the regulators can be cooled using the same heat sink, a la Dynahi's output transistors.


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## sft

You need a large heatsink .


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## kevin gilmore

Yep, same heatsink. That is the idea.
 Yes it gets hot.


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## dgardner

So... the question remains... does this puppy put out 4A per rail? or 2A per rail? It looks like if the transformer is beefy enough and the heatsinks are big enough, one unit could power the dynamite configuration. Am I right?


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## kevin gilmore

with the .2 ohm current limit resistors, the maximum current is about
 3 amps. Certainly enough to run a dynomite, but not enough to run
 speakers. But if you are going to run a dynomite, you really want
 2 power supplys for dual mono...


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## eweitzman

Where'd the trick 5uF caps go -- no more overkill? 
	

	
	
		
		

		
		
	


	



 - Eric


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## sft

4700uF + 470uF + 1uF(PP, if you want) is absolutey enough for small power amp.


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## kevin gilmore

quote
 Where'd the trick 5uF caps go -- no more overkill? 
 - Eric

 You are kidding right?? If i make room for the caps the board
 gets a whole lot bigger. So for the people who want them
 (which includes me) they go in between the power board and
 the amp boards.


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## eweitzman

Quote:


  Originally Posted by *kevin gilmore* 
_You are kidding right??_

 

Nah, I wasn't kidding. I just hadn't looked into the sizes 
	

	
	
		
		

		
			





 So I just checked out the CDE type 930 MPP line. The highest dV/dt is 74V/mS, it's a 0.063uF/630V cap. The 5uF/100V cap is 6V/mS and is pretty big (0.6" x 1.75"). What particular 5uF cap do you use that has 200V/mS? Photoflash? 
	

	
	
		
		

		
		
	


	




 Unobtainium? 
	

	
	
		
		

		
		
	


	




 - Eric


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## kevin gilmore

illinois capacitor part numbers 395ppr630kj or 475phc850k


 Unavailable in small quantites anymore, there are distributors out there
 that sell these. The exact cap i use is no longer available.


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## JohnFerrier

Percy Audio carries a nice selection passive audio components.

http://www.percyaudio.com/
http://www.percyaudio.com/Catalog.pdf


 JF


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## dgardner

Quote:


  Originally Posted by *kevin gilmore* 
_illinois capacitor part numbers 395ppr630kj or 475phc850k


 Unavailable in small quantites anymore, there are distributors out there
 that sell these. The exact cap i use is no longer available._

 


 Kevin's broken links are:
395ppr630kj
475phc850k


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## eweitzman

Thanks. I noticed that Allied has some 1uF Illinois snubbers for about $8, amazing dV/dt of 1200. Big suckers too. 

 About the caps at Michael Percy: he carries lots of film caps, but I don't believe they're these crazy fast snubbers.

 I long for the days of 0.1uF bypasses... Like Kevin says in the dynalo article, this is "over the top and unnecessary". But I'll probably do it anyways


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## dgardner

Can some of the folks who have already shopped around for nice looking, large, torroidal transformers post some of their suggestions to this thread... What VA rating and secondary voltage makes sense?


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## strohmie

Quote:


  Originally Posted by *dgardner* 
_Can some of the folks who have already shopped around for nice looking, large, torroidal transformers post some of their suggestions to this thread... What VA rating and secondary voltage makes sense?_

 

I'd say you're going to want a toroid with dual secondaries at around 40Vrms (thus giving about 50 volts post-rectification, depending on the transformer)...may as well give yourself plenty of headroom and aim for at least three amps per secondary, so about 250VA or more.

 A couple common recommendations I've seen around here for toroids are Toroid Corp of Maryland (www.toroid.com) or Plitron (www.plitron.com). The Toroid Corp's 732.382 (320VA, post-rectified 48.8V at 4.4amps) may work for this.


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## kevin gilmore

Actually 36 volt secondaries is about right unless you want it to get
 REALLY hot.

 updated file, same name and place. Would appreciate it if someone
 would check it over. There was one glaring mistake that i just found.


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## Pars

Quote:


  Originally Posted by *kevin gilmore* 
_illinois capacitor part numbers 395ppr630kj or 475phc850k

 Unavailable in small quantites anymore, there are distributors out there
 that sell these. The exact cap i use is no longer available._

 

Digikey has some BC MMKP 383 snubbers that go up to 2.7uf and aren't huge, that have a dV/dt of 130 at that capacitance. Not as fast as the ones Kevin uses, but I don't know that anyone other than Kevin has successfully gotten their hands on the Illinois ones. Illinois still lists the original 505PHC850K in their catalog... these aren't available anymore?


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## strohmie

Quote:


  Originally Posted by *kevin gilmore* 
_Actually 36 volt secondaries is about right unless you want it to get REALLY hot._

 

Are we talking 36vrms here? I think the one I referenced was dual 38vrms secondaries and only gets up to 49 after rectification and filtering.


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## kevin gilmore

36 volt RMS. 38 volt rms would work too...


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## bg4533

This PSU will be similar in price to the 2 Condors people are using, maybe a bit more expensive. How will it perform in comparison?


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## TrevorNetwork

I would expect it to perform much better. The Condors/PowerOne are not that good.


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## tiberian

Quote:


  Originally Posted by *TrevorNetwork* 
_I would expect it to perform much better. The Condors/PowerOne are not that good._

 

they generate a huge amount of heat that's for sure, quality wise i think they are much better than those cheap wall warts (mine are heavy and well constructed), but of course one can build an expensive power supply for a dynahi with very expensive caps etc.


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## TrevorNetwork

This is exactly what I mean. They are heavy, and hot. I would expect the Kevin-designed PSU to run much cooler, be lighter, be easier to mount, and have better performance. The performance issue is of course an assumption until we see some numbers. All considered though, the PowerOne / Condor are quite good sonically. I was thoroughly impressed with the sound of the Dynahi using the PowerOne PSUs. I am not sure it could be much better, but, leave it to KG to come up with something better!


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## Garbz

Quote:


  Originally Posted by *Pars* 
_Digikey has some BC MMKP 383 snubbers that go up to 2.7uf and aren't huge, that have a dV/dt of 130 at that capacitance. Not as fast as the ones Kevin uses, but I don't know that anyone other than Kevin has successfully gotten their hands on the Illinois ones. Illinois still lists the original 505PHC850K in their catalog... these aren't available anymore?_

 

I used very similar ones in my Dynalo's PSU. Mine were Epocs 4.7uf, not Visheys. However they seem to work pretty well. Not that I did a blind test though. However they are uncoated and can't be used where topside traces run around the copper.


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## strohmie

Given the heatsinking requirement for the dynahi supply, I wouldn't expect it to run cool. The basic idea with Kevin's supply is a design with high-quality components -- it should hypothetically be better than the Condors and be relatively easy to build given the small number of components.


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## eweitzman

Quote:


  Originally Posted by *Garbz* 
_Mine were Epocs 4.7uf .. they are uncoated and can't be used where topside traces run around the copper._

 

Uncoated capacitors? Are these electrolytics with the plastic jacket removed from the can?

 - Eric


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## bg4533

What free viewer will open the files for this board? I have tried GC-Prevue, Eagle and a few others and can't open them.


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## Garbz

no they are uncoated film caps. See the big metal boxes below:


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## aos

Wouldn't it be a massive overkill to go for a 3-4A transformer? From what I remember Kevin said that the amp uses about 300mA per channel. That's 600mA total. I'd go for 1A transformer unless you want balanced amp in which case I'd go for 2A.


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## sft

Yes, 1A transformer is enough for two channels. I use a high quality transformer. The temperature of the transformer is about 40~45 C.


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## strohmie

Quote:


  Originally Posted by *aos* 
_Wouldn't it be a massive overkill to go for a 3-4A transformer? From what I remember Kevin said that the amp uses about 300mA per channel. That's 600mA total. I'd go for 1A transformer unless you want balanced amp in which case I'd go for 2A._

 

That depends on your intended purpose. I believe some are thinking about using the Dynahi to power efficient speakers, so there will be a higher current requirement there. That Toroid of Maryland recommendation I mentioned was for these more extreme cases.

 sft, what brand/type of transformer do you use?


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## SHLim

Quote:


  Originally Posted by *strohmie* 
_That depends on your intended purpose. I believe some are thinking about using the Dynahi to power efficient speakers, so there will be a higher current requirement there. That Toroid of Maryland recommendation I mentioned was for these more extreme cases._

 

That is interesting. High end pre-power amp in one. Don't mind some newbi questions on this. How many watt does the Dynahi put out? How efficient does the speaker needs to be? Will 92db be enough or it need something like 96db? Can it haddle speaker/driver with low impedance like - 3 Ohm? 

 TIA,
 Sam


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## sft

Quote:


  Originally Posted by *strohmie* 
_sft, what brand/type of transformer do you use?_

 

type:toroidal

 brand:OEM

 I like PLITRON......


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## MisterX

Does anyone have any comments, thoughts, or suggestions on the current layout?


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## dgardner

It seems a shame not include some 1uF or 10uF tantalum decoupling caps for the OPA541's. These are going to be needed no matter how you slice it. If they aren't in the layout then you will likely need to tack them onto the bottom of the power at the power pins of the 541's, which is a little messy.

 Also, it looks like a small silkscreen error on the -50V cap. It's labeled +12. Silkscreen on the first stage regulators looks wrong to me too. Weren't these Linear Tech parts?

 /EDIT = Ooops. I was looking for the old circuit topology with the positive and negtive regulator setup. I see what's going now...


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## dgardner

BTW, who's going to be the guinea pig for the first pass PCBs? I'm interested in paying for the first 10 or so, if everything gets cleaned up to everyone's satisfaction.


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## amb

Quote:


  Originally Posted by *dgardner* 
_it looks like a small silkscreen error on the -50V cap. It's labeled +12. Silkscreen on the first stage regulators looks wrong to me too. Weren't these Linear Tech parts?_

 

No, the silkscreen is correct. Kevin is using two positive regulators instead of one positive and one negative, and as such it is connected in a way that the voltage at the "negative" regulator's input pin would measure +12V relative to ground (50V - 38V = 12V). The LM338 regulators are from National Semiconductor, but you should be able to substitute with the Linear Technology LT1084.


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## amb

Since no one has posted a schematic diagram of the dynahi PSU, I went ahead and drew one. It is shown below. Please let me know if you see anything wrong. This is based on the PCB artwork although I have not extensively checked the PCB layout for errors.






http://www.amb.org/ti/audio/dynahi_psu_20041128c.gif

 Edit: Added power opamp bypass capacitors per Kevin Gilmore.
 Edit2: Fixed locations of 0.1uF capacitors.


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## MisterX

Quote:


 Since no one has posted a schematic diagram of the dynahi PSU, I went ahead and drew one. 
 

I love you man! 
	

	
	
		
		

		
			






  Quote:


 BTW, who's going to be the guinea pig for the first pass PCBs? 
 

YGPM.


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## amb

About those snubber capacitors across the rectifier diodes... Kevin labels them "0.33" on the board, and I assume they're 0.33 microfarad. That's much larger than I'm used to seeing for this application. More often these are in the order of several hundred _picofarads_ instead. Any comments?


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## kevin gilmore

There are a pair of .1's near the power opamps. The layout is bigger
 however, so you can certainly stuff 1uf tantalum caps in there instead.
 Same thing with the diode snubbers, you can put anything you want
 in there too. The big caps are very close to the power opamps anyway
 so i don't think there will be any trouble. The protoboard design works
 just fine. With a few 3 resistor changes and a smaller transformer it
 can be used for a dynalo and just about anything else too. It is very
 quiet.

 This is a very tight design to keep the board size under 20 sq inches.
 (19.8275)

 3 oz copper is also a good idea.


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## MisterX

What Windows based Gerber viewer would you "guys" suggest? 
 Every one of the free viewers I have tried so far has had some type of a problem with the files.


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## dgardner

I got Viewplot to work. It's free.
http://www.roneda.nl/info_files/vpl_download.html


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## dgardner

Putting the BOM together...

 Dynahi Power Supply - Bill of Materials:
Dynahips BOM (pdf) - Updated 11-28-04 2:32pm
 (items highlighted in yellow seem solid to me)
Dynahips BOM (excel).

 Dynahi Datasheets directory:
Datasheets (pdf)

 Supplier Links:
Surplus Sales Heatsink (HSK) HS-TWS

Remaining Questions:
 1) Need part numbers for caps on rectifiers.
 2) Need at least one suitable Plitron part number for the transformer.


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## kevin gilmore

actually i was thinking mp930 which is half the price
 mouser number 684-mp930-0.2 $4.15 ea (2 needed)

 electrolytic caps are digikey p7485-nd $5.84 ea (6 needed)
 digikey ref02bp-nd $5.04 (1 needed)
 digikey lm338 (to220) $2.10 ea (2 needed)
 digikey mur860 $1.14 ea (power diodes, need 8)
 digikey opa541ap-nd $16.65 ea (2 needed)


 Added 4 tantalum caps right on top of the opamps.
http://gilmore.chem.northwestern.edu/dynahips.zip


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## dgardner

Artwork now looks like this:

 EDIT:/ See Post #55

 PDF of TOP, BOT, and Silk:
Artwork layers(pdf)


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## amb

I edited the schematic diagram (posted earlier) to match. You may have to Reload or Refresh your browser to get the new image.


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## kevin gilmore

here is what is should look like...

http://gilmore.chem.northwestern.edu/dynahips.gif

 caps still don't show in the schematic after multiple reloads...???


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## amb

Quote:


  Originally Posted by *kevin gilmore* 
_caps still don't show in the schematic after multiple reloads...???_

 

Fixed.
 Edit: See post #45.


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## kevin gilmore

that one works 
	

	
	
		
		

		
		
	


	




 but there is one too many .1 cap, and one of the .1 caps is
 on the reference.

 close enough for goverment work.
 the gif i posted makes everything clearer.
 (only took me an hour to remember how i did this the last time)


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## amb

Quote:


  Originally Posted by *kevin gilmore* 
_there is one too many .1 cap, and one of the .1 caps is on the reference._

 

OK, fixed.


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## amb

One thing I noticed is that the OPA541 op amps' pin number designations on the PCB silkscreen does not match that of the manufacturer's datasheet. They are physically correct, however. The schematic diagram I drew has pin numbers based on the datasheet. This is just a heads-up in case anyone gets confused.


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## kevin gilmore

the pin numbers on the opamps on the layout are in fact wrong.
 And come from the fact that the pins are .067 apart from each
 other. So to get it exact, i started in the middle, then go .067 to
 the left, then .067 to the right... Same thing with the pins on
 the blue hawaii tubes.

 Those numbers don't ever print on the boards anyway as there are
 holes there...


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## eweitzman

The two sets of resistors on the inverting inputs of the two OPA541 (10K+10K, 10K+50K) have to be well matched and have very low temperature coefficients to maintain precisely +/- 30V, don't they?

 - Eric


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## kevin gilmore

.05% ultra low tc resistors like the vishay precision resistive products
 are what i use. PRI is a company vishay bought out about 4 years ago.

 Actually only the 2 x 10k resistors for the minus supply have to be
 really good, because the minus supply tracks the plus supply. The
 voltage does not have to be exactly 30v the supplys just have to
 track so that the servo does minimal work.


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## strohmie

Quote:


  Originally Posted by *dgardner* 
_Remaining Questions:
 1) Need part numbers for caps on rectifiers.
 2) Need at least one suitable Plitron part number for the transformer._

 

The Plitron toroids don't have 36Vrms versions, so the 38Vrms, 1.05A toroid's part number (normal headphone operation) is 037035201.

 To increase the VA rating, just change the first "3" to anywhere from 4-7 to get the part number:

 047035201 - 120VA, 1.58A
 057035201 - 160VA, 2.10A
 067035201 - 225VA, 2.96A
 077035201 - 300VA, 3.95A


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## eweitzman

Quote:


  Originally Posted by *strohmie* 
_The Plitron toroids don't have 36Vrms versions, so the 38Vrms, 1.05A toroid's part number (normal headphone operation) is 037035201._

 

This tranny's regulation is 12% and the 38V is at full load (ie, 1A). So if the PS draws much less, than the voltage will be even higher (ie, at 500mA, the voltage will be about 40V). It might make more sense to go with a 35V transformer, possibly with an even higher current rating.

 Kevin, can you tell us what the current draw is?

 - Eric


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## strohmie

Quote:


  Originally Posted by *eweitzman* 
_This tranny's regulation is 12% and the 38V is at full load (ie, 1A). So if the PS draws much less, than the voltage will be even higher (ie, at 500mA, the voltage will be about 40V). It might make more sense to go with a 35V transformer, possibly with an even higher current rating._

 

Kevin had mentioned that a 36Vrms is preferable, 38Vrms is acceptable. 35Vrms should work fine too -- for that matter, if each channel draws 300mA during normal operation (as aos had mentioned) then a 40VA, 35V or 38V, ~.5A per secondary transformer might even be fine.

 I just tend to give myself more headroom that I need sometimes, just to make sure the toroid won't get too hot, hence the 38Vrms, 80VA suggestion.


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## TrevorNetwork

I am willing to orchestrate a group buy for the power supply boards once they are finalised.


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## dgardner

I would suggest a first pass debug prototype run to make sure the artwork is acceptable befor a production and group buy run. Too much risk otherwise, IMHO.


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## dgardner

The deed is done. 25 first pass protos are officially on order with an 8 day turn. About four member-debuggers are lined up. Kevin will be one of them. Once we get through this phase, TrevorNetwork can fireup the group buy.


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## strohmie

If you need any more guinea pigs, I'll help out. I was planning to buy parts for the power boards plus some items for my CD player, so let me know (PM or otherwise).


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## MisterX

dgardner: 
 How many boards did you end up ordering? 
 And more importantly how much do we owe you for them? 
	

	
	
		
		

		
			





 Thanks a bunch for the awesome effort as well.


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## dgardner

25 total boards from PCBNet. After my second time order credit, boards are about $6ea. In group buy volumes we should do better I hope. I have already paid the tooling charge on this as part of the order. So if the tooling is good, we can simply re-order without a tooling charge. 
	

	
	
		
		

		
		
	


	




 Cross your fingers.


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## MisterX

Do they do that with the tooling? 
 I thought they smacked you for it everytime you ordered something (for the expendable stuffs) but I have only placed one order so......


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## dgardner

I checked out the re-order feature on their site for one of my previous orders and it showed $0 for tooling to re-order. You and I might need to collaborate to avoid the tooling charge on the next buy. If so, that's fine. They don't seem to charge a setup fee.


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## MisterX

OK, that makes sense. 
 Since I did not have a return order we got dinged for tooling but at the same time we got the discount from the first group buy so I guess it all worked out.


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## strohmie

Quote:


  Originally Posted by *kevin gilmore* 
_.05% ultra low tc resistors like the vishay precision resistive products are what i use. PRI is a company vishay bought out about 4 years ago._

 

For the 10k resistors (1/4W, .05%), the part number from Mouser is 71-PTF6510K000AXBF (I'm assuming these are the ones Kevin was talking about). The length of these is .475" for reference...may be too large for the board but I'm not certain. I think the Dales are about .05" smaller.

 Hypothetically the rest can be Vishay-Dale type.


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## skyskraper

any chance we could get the BOM in excel format?

 would be nice to modify it for those of us who arent stateside


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## Pars

Quote:


  Originally Posted by *dgardner* 
_25 total boards from PCBNet. After my second time order credit, boards are about $6ea. In group buy volumes we should do better I hope. I have already paid the tooling charge on this as part of the order. So if the tooling is good, we can simply re-order without a tooling charge. 
	

	
	
		
		

		
		
	


	




 Cross your fingers._

 

Any way in the group buy that the members of that buy could reimburse dgardner for the tooling charge? After all the work etc. that he has done, I would think that would be the least we could do....

 Chris


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## sft

agree!


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## skyskraper

i agreee!~


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## catweasel

Hi Kevin,
 May I ask:
 Why a dual tracking regulator?. Why such an expensive chipamp as there are much cheaper available from National, or simply an opamp and a pass transistor. No frequency compensation on the opamp? No noise filtering on the reference?. Why such huge caps on the output?

 You operate the REF02 pretty close to the safe powersupply limit. See also:
http://www.diyaudio.com/forums/showt...451&highlight=


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## FredD

I am curious about the selection of a DC and more importantly AC gain of 6 for the OPA541. This means the output impedance and noise is 6 times than using the device at unity gain. Most regulator designs filter the noise from the voltage reference has well. A REF01 could be tiered with REF02 or a couple of LM329s in series to get about 15 volts and gain a factor of 3 improvement. A TL431 could be used to get the full 30 volts. Operating the LM338 with a 50 volt input is not a good idea since the part is specified for a maximun differential voltage of 40 volts and will see the 50 volt difference between Vin and Vout at startup before the output cap for the LM338 is charged. I wonder the design is if it is really fleshed out enough to go fab enough PCBs yet since we are talking about an pretty expensive design. Some might be more comfortable with a bit more development time before plunking down their money. The voltage margin on the LM 338
 is very worrisome to me.


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## walangalam

I'm not sure if it applies to LM338, but LM317 are known to dislike low impedance capacitors in its output, so that tantalum cap might not be appropriate.

 There is an interesting set of experiments on different regulators over at TNT-Audio: 
Crash Course on Voltage Regulators - 1 
Crash Course on Voltage Regulators - 2 
Crash Course on Voltage Regulators - 3 
Crash Course on Voltage Regulators - 4 

 where the author looked into regulator noise performance and plotted the effect of different capacitor impedance.

 The conclusion is that low impedance is bad for LM317, so a less expensive part than the specified $5 tantalum might even be better.


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## kevin gilmore

The prototype power supply works perfect.

 The dynahi boards you all got were the 3rd revision. I ate the
 first 2 prototype revisions myself. I would have done so on the
 power supply board too but someone else offered to do it.

 Will it work, who knows. There is only one way to find out.
 The reference will be on a socket anyway, so replacing it with
 a tl431 and changing one resistor is very easy.

 I like dual tracking regulators. I also like power supply rails that
 are push pull. So large inductive loads can't throw the dc levels
 out of whack.

 You can certainly do what sft has done which is a jung style regulator
 with a pass transistor. Just make sure you pick a high voltage opamp.

 I don't see any national semiconductor parts that are rated for 80 volt
 rails that are any cheaper than the opa541's.

 Did i ever say this was going to be cheap??


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## flecom

by the design it appears that its one power supply board for both amp boards...

 but...

 should one of these boards be able to power 4x dynahi boards (in a balanced configuration) ?


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## kevin gilmore

It is good for several amperes with a big enough heatsink.


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## flecom

ok cool 
	

	
	
		
		

		
		
	


	




 yay less money to spend 
	

	
	
		
		

		
		
	


	




 im going to probably aircool the whole thing with a pair of nice and quiet 80mm Panflow L1A's or somethign like that...of you run them at 7~8v (they are 12v fans) they are dead silent...

 as the power supply and 4x dynahi boards are going to generate quite a bit of heat!


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## FredD

There are at least two........ the very well known and well regarded LM3886 and the LM3875 come to mind. As far as high cost goes......don't confuse good engineering with parts cost. A $20 savings in the cost of the regulator chips (and for even better performance on top of it) buys better caps, resistors, and rectifiers.


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## dgardner

The Excel verision of the BOM is here.


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## skyskraper

thanks


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## sft

LM3886, 3875 are not unit-gain stable.


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## randytsuch

Quote:


  Originally Posted by *FredD* 
_There are at least two........ the very well known and well regarded LM3886 and the LM3875 come to mind. As far as high cost goes......don't confuse good engineering with parts cost. A $20 savings in the cost of the regulator chips (and for even better performance on top of it) buys better caps, resistors, and rectifiers. 






_

 

Off topic, but wondering if this is Fred Dieckmann from diyaudio? I profited (mentally) from your posts (if this is the same Fred) over there.

 Randy


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## FredD

It doesn't matter with the right out output network. Go read the data sheets about driving large capacitive loads. Many three terminal regulators require minumum capacitance values for stability. The original Sulzer op amp based regulator used an uncompensated NE5534 in a unity gain circuit. I've built rock stable regulators with gain of minmum gain of ten "chip amps" before.


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## sft

Hi FredD, 

 Try, lose nothig, maybe it works, who knows? Pay more attention on the negative voltage output. 
	

	
	
		
		

		
		
	


	





 I'm sure this one works very well.

 PCB is made in Taiwan, 2Oz.

 use LT1085 as preregulator. 
 preregulator ouput : 38.7V(100R, 3K)
 voltage ref: REF102BP
 Current limit resistor=0.1R
 Temp. of HS: 75 ~80 C, I need a bigger HS.


----------



## steel

WoW...how fast ...

 you made the PCB....great


----------



## FredD

I know.... I have built several. I used tiered positive regulators with separate secondaries and bridges. The negative three terminal three terminal regulators are not as good as positive regulators. I have used the LT108x parts. The chip amp is better in every parameter and much cheaper. I got interested in the chip amps as regulators after hearing some excellent LM378 amps from Scott Nixon. All a regulator is an amplifier with a big DC offset and most of the chip amps have much better PSRR (good enough that a preregulator is not required) gain band width (over 5 times that typical three terminal regulator), and much lower noise. Why even bother with three terminal regulators when you can build simple and inexpensive chip amp based regulators with far better performance for the same money.


----------



## sft

I mean for dual tracking(gain= -1), you may encounter some troubles. Maybe not , who knows?

 Soryy for my poor english.


----------



## kevin gilmore

sft is now building my stuff faster than i can build my stuff.
 If he would have waited a couple of days he would have had the
 final board with the 4 extra tantalum caps. Which he can certainly
 solder on the bottom. His prices on boards are so much cheaper
 and faster than the usa its not even funny.

 Maybe i can get sft to build me a couple of uberamps. The monster
 heatsinks are killing me time wise.

 At least all the parts fit 
	

	
	
		
		

		
		
	


	




 Need to find a place for the bigger heatsink insulators for the opa541's.


----------



## sft

Quote:


  Originally Posted by *kevin gilmore* 
_If he would have waited a couple of days he would have had the final board with the 4 extra tantalum caps. Which he can certainly solder on the bottom._

 

I've done. 
	

	
	
		
		

		
		
	


	




 I enjoy your design in these years.Thank you very much.

 Expect your new design. It's exciting always.


----------



## eweitzman

Quote:


  Originally Posted by *FredD* 
_Why even bother with three terminal regulators when you can build simple and inexpensive chip amp based regulators with far better performance for the same money._

 

Let me take a crack at this question ... because you haven't posted a schematic yet? 
	

	
	
		
		

		
		
	


	




 - Eric


----------



## flecom

Quote:


  Originally Posted by *kevin gilmore* 
_Need to find a place for the bigger heatsink insulators for the opa541's._

 

well SFT's dosent appear to have any insulators, im guessing they are not nessicary? isnt the tab on those v-?


----------



## kevin gilmore

OH yes they do have insulators, look closer. The metal part of a
 opa541 is tied to V-. The screw that holds it to the heatsink also
 has the insulator.


----------



## doobooloo

Any updates?

 So, is the board layout pretty much finalized?


----------



## dgardner

First pass proto boards came in today. I'll be sending them out tomorrow for debug. I'll post some more info then...


----------



## doobooloo

That's great news! Keeps us posted!


----------



## eweitzman

I've been operating under an assumpation: this power supply design is adequate for one amp with two channels, there's no need for dual supplies unless you really wanted a true dual mono amp. Can someone confirm?

 - Eric


----------



## sft

1)Yes.

 2)true dual mono amp. is fine since the amp. pcb is mono.


----------



## MisterX

Quote:


  Originally Posted by *dgardner* 
_First pass proto boards came in today. I'll be sending them out tomorrow for debug. I'll post some more info then..._

 

You think Monday is a good day to announce a group buy for them then?


----------



## dgardner

Getting shipments ready... There are five pieces left that are unspoken for at $6ea + shipping. Interested debuggers can PM me.


----------



## MisterX

Payment sent. 
 Thanks a ton for handling the "beta test" group buy for these boards.


----------



## skyskraper

will i be ok using: Toroidal Transformer 37+37,15+15 160VA, with this psu? 

 anyone had luck building the first run boards?

 so excited


----------



## kevin gilmore

Got the boards finally, partially stuffed one, will stuff more tomorrow.
 Everything definitely fits. Still missing the .2 ohm resistors.
 Pictures tomorrow.


----------



## doobooloo

ooOOOOoohh. Patiently waiting for results!


----------



## eweitzman

I won three Acopian A030MX250 power supplies in a chassis with some other stuff on eBay on Monday. 0-30V, 2.5A, 0.005% or 2mV regulation, 0.25mV ripple. These list for $295 new. Sure hope at least two of them are working properly. I might build the amp in the case. It'll be heavy: each Acopian unit weight 11 lbs.


----------



## kevin gilmore

Just 2 more parts to go which should be here tomorrow.

 Old camera pictures

http://gilmore.chem.northwestern.edu/dynahips1.jpg

http://gilmore.chem.northwestern.edu/dynahips2.jpg

 The 3 10k resistors are the .05% ultra low drift pri resistors.


----------



## Dreamslacker

Quote:


  Originally Posted by *kevin gilmore* 
_Just 2 more parts to go which should be here tomorrow.

 Old camera pictures

http://gilmore.chem.northwestern.edu/dynahips1.jpg

http://gilmore.chem.northwestern.edu/dynahips2.jpg

 The 3 10k resistors are the .05% ultra low drift pri resistors._

 

Hi. May i know what brand & model are those ultra low drift resistors?


----------



## kevin gilmore

I use the pr1/10 tc5 .05%
http://www.prpinc.com/pdf/PRSeries.pdf


----------



## Pars

Quote:


  Originally Posted by *kevin gilmore* 
_I use the pr1/10 tc5 .05%
http://www.prpinc.com/pdf/PRSeries.pdf_

 

Kevin,

 Do you buy direct from PRP? Or is there a distributor you know of who sells small quantities? 

 Michael Percy has the PR9372 audio resistors for replacements filling in his stock of Roederstein and Holco. Buying direct from PRP will get you pricing of $5-$10 apiece in quantities of 20+ per value (IIRC)... not exactly conducive to small volumes... hehe.


----------



## dip16amp

I found these at Mouser and they actually measure to 0.05% tolerance and I can match up pairs to better than 0.01% with a 5.5 digit meter. I got eight of them and matched 4 pairs to within half an ohm of each other.

 PTF5610K000BZBF
 10k ohm
 1/8w
 0.1%
 5 ppm/c
 $1.42

 Here is the 50k ohm to go with them.

 PTF5650K000BZBF
 50k ohm
 1/8w
 0.1%
 5 ppm/c
 $1.42

 They also have this more expensive one for those without access to a good meter and want better than 0.01%.

 PTF5610K000TZBF
 10k ohm
 1/8w
 0.01%
 5 ppm/c
 $8.40

 Also found this at digikey for the capacitor that should fit.
 493-1133-ND
 Nichicon
 UVR1J472MRD
 4700µF
 63V
 22x50
 10mm lead spacing
 4.40 each
 10 for 33.34


----------



## Talonz

Considering the capacitors are $6 a pop and we need 6, I did some searching and found an alternative:

http://cgi.ebay.com/ws/eBayISAPI.dll...tem=3858985692

 4700uF 63v capacitor for $1.99 each + $6 shipping. I asked the seller for more information regarding the history (listed as excellent condition) and the branding. I suspect that they are new since there are 512 available.

 Size as listed is: 40x25mm which is smaller then the Panasonics, 50x25mm

 I checked the Nichicon datasheets and the size could not be matched to their line either. Of course, the labeling looks like the Panasonic line though.

 What do you guys think? It would save us $15 on the price of the power supply. At least I know that it would be a meaningful saving to me 
	

	
	
		
		

		
		
	


	




 Edit: Did some more looking around and I'm wondering if the cheaper caps that mouser carries would be okay (Cornell Dubilier andUnited Chemi-Con) since they are only half the price of the panas. The UCC caps are $3 and rated for 105 degrees. The Max EST at 120ohms is 40% better then the Pana line. The ripple current is 30% worse though (at 105 degrees, which we won't be at). Is this a plausible replacement?


----------



## doobooloo

Dr Gilmore,

 Is the PSU board using the same heatsink assembly as the dynahi amp board? Are the regulator and opamp holes aligned with those on the dynahi amp, and the mounting holes as well?

 If so, that would be just great.


----------



## eweitzman

They're probably cheap because they're over 11 years old.
 Elco caps have a fixed life (like 25 years in use?) and a fixed shelf life.


----------



## doobooloo

Quote:


  Originally Posted by *Talonz* 
_Considering the capacitors are $6 a pop and we need 6, I did some searching and found an alternative:

http://cgi.ebay.com/ws/eBayISAPI.dll...tem=3858985692

 4700uF 63v capacitor for $1.99 each + $6 shipping. I asked the seller for more information regarding the history (listed as excellent condition) and the branding. I suspect that they are new since there are 512 available.

 Size as listed is: 40x25mm which is smaller then the Panasonics, 50x25mm

 I checked the Nichicon datasheets and the size could not be matched to their line either. Of course, the labeling looks like the Panasonic line though.

 What do you guys think? It would save us $15 on the price of the power supply. At least I know that it would be a meaningful saving to me 
	

	
	
		
		

		
			





 Edit: Did some more looking around and I'm wondering if the cheaper caps that mouser carries would be okay (Cornell Dubilier andUnited Chemi-Con) since they are only half the price of the panas. The UCC caps are $3 and rated for 105 degrees. The Max EST at 120ohms is 40% better then the Pana line. The ripple current is 30% worse though (at 105 degrees, which we won't be at). Is this a plausible replacement? 
	

	
	
		
		

		
		
	


	


_

 

Never mind. Sorry.


----------



## kevin gilmore

Same heat sink, yes. Same holes in the same place for the angle
 bracket, NO. Believe me i tried but just could not get the holes
 in the right place. Besides which you don't want extra holes under
 the opamps anyway.


----------



## dip16amp

Will those 3500 ohm resistors get a little warm because they will have over 36 volts across them and almost 0.4 watts? They just look kind of small there.


----------



## kevin gilmore

The ones i'm using are .5 watt metal film resistors. I know they
 don't look like it, but they are rated for .5 watt.


----------



## MattN

I'd like to thank Dan for the proto boards. I've put one together today and it works nicely, though I've only tested it at half load because I'm waiting for a bigger heatsink.

 I'm using a 30v transformer and have set the preregs to about 35v: I hope that will be enough for the OPA541s when I connnect both dynahi boards. 

 Matt


----------



## sft

If the spec. of the transformer is (30V,1A), (30V,1A), I think the voltage is too low. 2A or 3A is OK. for 30V. 35~37V is the best IMHO.


----------



## MattN

It's 30v rms, 160VA, which gives me about 39v after the rectifiers. The PS output is +-30.50v I've cobbled together some heatsinks and got it running now. I'll let it settle down a bit before getting out my good headphones.
 Matt


----------



## dgardner

One suggestion on the layout might be to increase the hole diameter for the 1n400x diodes. They are really tight. Another 3-5 thousandths should do it. Everything else seems to fit nicely, but Kevin was right, it is tightly spaced. Should have mine up and running by the end of the day...


----------



## intlplby

is anyone going to release a finalized Bill of Materials for the PSU soon..... i wouldn't mind having one before I place my next orders from digikey and mouser


 btw, what is the estimated cost per PSU we are looking at?


 will the HSK 260 found at 
http://www.surplussales.com/Heatsinks/HeatSink1.html
 work for both the Dynahi and DynahiPS (3 total)


 also as far as heatsinks would it be possible to use a bunch of CPU heatsinks such as:

http://www.newegg.com/app/ViewProduc...118-202&depa=0

 or

http://www.newegg.com/app/viewproduc...106-044&DEPA=0

 or

http://www.newegg.com/app/ViewProduc...106-045&depa=0

 i don't know a lot about the heat dissipating requirements and if these things can meet them so that's why i am asking


----------



## dgardner

I got my four Dynahi boards running & trweaked individually today with a lab supply. Hooked up two and started listening to stereo. WOW. Right now is running at 27+27=54 watts per stereo pair after a warmup period of about 10 minutes. (900ma at +30v and 900ma at-30v). I think I have this right... That's a fair chuck of heat. I'm using the Surplus sale heatsinks and a thick bracket. It is HOT, but easily touchable.


----------



## kevin gilmore

I'm aware of the hole size on the 1n400x diodes. Does definitely
 fit. Definitely tight too. Before more boards are made i will change
 to the next hole size up.

 changed the diode holes from 30 to 40 thousands. Same file name
 same place.


----------



## sft

I wish just a little bigger board.
 There are a bunch of wonderful capacitors with 30mm diameter like Black Gate FK, Nichicon KG Golden Tune, Rifa PEH, ...


----------



## kevin gilmore

I'll make a bigger board next week.


----------



## sft

Yeh!
 A beautiful Sunday!


----------



## kevin gilmore

what size are the caps you want, and what is the pin to pin spacing?


----------



## intlplby

wouldn't it be possible to use a Peltier element to cool these better (hehe... i'm just looking for ways to add to the power consumption even more)


----------



## bg4533

Quote:


  Originally Posted by *intlplby* 
_wouldn't it be possible to use a Peltier element to cool these better (hehe... i'm just looking for ways to add to the power consumption even more)_

 

What would the peltier help? It would likely make cooling even more of an issue.


----------



## intlplby

the peltier helps pump the heat to the heatsinks faster...

 i found some other heatsinks places

http://www.alphanovatech.com/

www.thermaflo.com


----------



## bg4533

Yeah, but doesn't the peltier need a heatsink to handle the heat it creates as well as the heat it pumps out?


----------



## Talonz

A peltier isn't going to be a good option. It's useful in overclocking computers because you want your CPU to be at a low temperature. Here, a lower temperature does not benefit you. The only goal is to maintain a safe stable temperature. The peltier will create an even larger heat output, so much that you will probably need active cooling. Not a good thing in this situation.


----------



## sft

Quote:


  Originally Posted by *kevin gilmore* 
_what size are the caps you want, and what is the pin to pin spacing?_

 

Pin to pin spaceing: 10mm, snap in
 diameter: 30mm. I've tried.The board will just "grow up" a little 
	

	
	
		
		

		
			





 Thanks a lot !


----------



## skyskraper

you guys going to run this revision thru proto stage again? or just send straight to print for people when the layout works?


----------



## skyskraper

also seeing as this is a power supply, will i see benefits of using vishay dale's matched over generic 1% metal films hand matched? 

 if the vishays are the go, do any of you guys with more experience using them have any advice u can give me on quantities i need to order to get matches. i find the generics i have match one in every 4, i'd be hoping the vishays are way more accurate then that for 50x the price (for my prices)


----------



## kevin gilmore

here is the layout with the bigger caps.
 Someone needs to check this for errors.

http://gilmore.chem.northwestern.edu/dynahipsbig.zip


----------



## sft

It seems missing four 10uF caps.


----------



## kevin gilmore

yep you are right. I started with the wrong file again...

 fixed now. Same file name same place.

 Sure enough there is a SLIGHT error in the first batch of
 power supply boards. Fixed real easy. The 10uf cap on the
 minus rail on the left opa541 is not connected to anything.
 It needs a .1 inch wire soldered to the .1 right next to it.

 Board layout for this version will be fixed shortly.


----------



## kevin gilmore

I finally got around to measuring the production power supply and
 it comes out as about 4 microvolts rms of noise at 1 ampere.
 I'm very happy with this.

 updated dynahiprototype with production power supply, lindberg
 transformers (UK) top line wbt connectors, and Penny & Giles
 volume knob.

http://gilmore.chem.northwestern.edu/dynahiproto.jpg

 should make a great portable to bring to headphone meets 
	

	
	
		
		

		
		
	


	




 (3600 grams)

 time for another production unit with ultra high end resistors


----------



## intlplby

so that's it? we're ready for a group buy already and the BOM is finalized?

 drew


----------



## kevin gilmore

There are 2 versions of the boards, both of which are ready as
 far as i can tell. One is the version already prototyped with the
 one wire that was missing added. The other board is a bit bigger
 and accomidates the 30mm electrolytic caps.


----------



## MisterX

The board specs are: 3 ounce copper,134 holes, and how big is the new board? 
 I used 5.15 X 4" and got a quote of $3 each (before tooling and shipping) with a two week lead time for 450 boards. 
 Sound about right?


----------



## Edwood

Woohoo, here we go again! 
	

	
	
		
		

		
		
	


	




 -Ed


----------



## Dreamslacker

Quote:


  Originally Posted by *kevin gilmore* 
_I use the pr1/10 tc5 .05%
http://www.prpinc.com/pdf/PRSeries.pdf_

 

Thank you for enlightening me. =)


----------



## bg4533

Quote:


  Originally Posted by *MisterX* 
_The board specs are: 3 ounce copper,134 holes, and how big is the new board? 
 I used 5.15 X 4" and got a quote of $3 each (before tooling and shipping) with a two week lead time for 450 boards. 
 Sound about right? 
	

	
	
		
		

		
		
	


	


_

 

You going to run this groupbuy too MisterX?

 Hmmm...4 microvolts of noise. Seems low, but I don't know anything. What do batteries usually have?


----------



## kevin gilmore

Both boards are 142 holes

 The smaller board is 5.15 x 3.85 inches

 The bigger board is 6.15 x 4.30 inches

 On the bench due to fluorescent lights and other floating crap the
 noise is actually 15 microvolts. But inside a screenroom with a 7.5
 digit voltmeter with the shielded cable the actual power supply noise
 when running the amplifier with no input signal is below 5 microvolts.
 I very much doubt a jung regulator can do this, plus it is not dual
 tracking.

 With appropriate resistor and transformer changes this power board
 can run just about anything. +/-15, +/-18, +/-24 ...


 If you are going to a board run with the bigger board, then i need a few.


----------



## MisterX

It helps if I actually look at the current board revision. 
	

	
	
		
		

		
		
	


	



 450 pieces, Two week fab time, 3 ounce copper: 
 The small one= approximately $2.91 each. 
 The large one- approximately $3.69 each.


----------



## Woody

Quote:


  Originally Posted by *FredD* 
_I am curious about the selection of a DC and more importantly AC gain of 6 for the OPA541. This means the output impedance and noise is 6 times than using the device at unity gain. Most regulator designs filter the noise from the voltage reference has well..... Operating the LM338 with a 50 volt input is not a good idea since the part is specified for a maximun differential voltage of 40 volts and will see the 50 volt difference between Vin and Vout at startup....._

 

Has there been a separate dicussion of these points ? On the face of it they seem logical and valid. 

 Halving the gain seems sensible and only appears to add the cost of a couple more voltage references. To my mind the Dynahi + PSU must be challenging for the "Audiophiles Headphone Amp" crown, so why compromise ? Cost cant be a factor ? Am I missing a good technical reason ? Apologies if I've missed this debate.

 Perhaps the point relating to the 50Vin differential will not be relevant if the PSU remains switched on, but if not, I could imagine this leading to premature failure, perhaps even critically so with some expensive headphones attached ?

 Please dont shoot me down, I dont want to be negative, I just dont have enough knowledge to be constructive 
	

	
	
		
		

		
		
	


	




 I already have the amp boards and transistors and idolise the design goals for this amp, I just want to be sure I'm not compromising the amp I build at the last hurdle with the PSU.


----------



## dip16amp

Quote:


  Originally Posted by *Woody* 
_Has there been a seperate dicussion of these points ? On the face of it they seem logical and valid. 

 Halving the gain seems sensible and only appears to add the cost of a couple more voltage references. To my mind the Dynahi + PSU must be challenging for the "Audiophiles Headphone Amp" crown, so why compromise ? Cost cant be a factor ? Am I missing a good technical reason ? Apologies if I've missed this debate.

 Perhaps the point relating to the 50Vin differential will not be relevant if the PSU remains switched on, but if not, I could imagine this leading to premature failure, perhaps even critically so with some expensive headphones attached ?

 Please dont shoot me down, I dont want to be negative, I just dont have enough knowledge to be constructive 
	

	
	
		
		

		
		
	


	




 I already have the amp boards and transistors and idolise the design goals for this amp, I just want to be sure I'm not compromising the amp I build at the last hurdle with the PSU._

 

From his noise measurements, it doesn't seem like noise is a problem and trying to double up on the REF02 may add more noise.

 The 50 volt input could be reduced to 40 volts by using 28 volt transformers and setting the LM338 outputs to 35 volts. Since the amps are class A, current draw is fairly constant. The power supply would also run much cooler.


----------



## kevin gilmore

33 volts rms at the primary under load is the minimum requirement at
 1 ampere of output current. There is loss across the diode bridges.


----------



## Ozymand

MisterX, was the last Dynahi amplifier board group buy about 900 modules? Only curious, since you really only need one Dynahi power module per two Dynahi amplifier modules. When this comes around, I'm all for it. My friends are salivating at the opportunity to try a $600 headphone amplifier for "free" (so they think, I'll charge them by the hour!).


----------



## Woody

Quote:


  Originally Posted by *dip16amp* 
_From his noise measurements, it doesn't seem like noise is a problem and trying to double up on the REF02 may add more noise.

 The 50 volt input could be reduced to 40 volts by using 28 volt transformers and setting the LM338 outputs to 35 volts. Since the amps are class A, current draw is fairly constant. The power supply would also run much cooler._

 

I can see your point about the 28v transformers, although I wonder if there is then a risk of not enough voltage headroom for guaranteed regulation or to power the amps ?

 On the noise, I'm not sure it would increade as a percentage of the total Vref or even Vout (Ignoring the point FredD makes about filtering noise on Vref), but isnt a lower output impedance desirable ? Or does a lower output impedance come at the expense of something else ?

 Looking at the way KG designs all of his stuff I'm sure there is good reason, compromise doesnt feature in his vocabulary, as I say I'm just curious.


----------



## MisterX

Quote:


  Originally Posted by *Ozymand* 
_MisterX, was the last Dynahi amplifier board group buy about 900 modules?_

 

174 for the first group buy and 640 for the second.... throw in the gain clone guys that may want to jump on a good psu and I figured 450 was a good estimate.


----------



## bg4533

Quote:


  Originally Posted by *MisterX* 
_174 for the first group buy and 640 for the second.... throw in the gain clone guys that may want to jump on a good psu and I figured 450 was a good estimate. 
	

	
	
		
		

		
		
	


	


_

 

Interesting...I never thought of using this as a gainclone PSU. I was going to build one in the next month or so here. Would this PSU be a good choice? Worth the money for something like a gainclone?


----------



## dip16amp

Looking at the datasheets, the OPA541 needs three volts input to output difference for a one ampere load so it needs at least 33 volts.
 The LM338 needs a two volt difference for one ampere, so thats 35 volts.
 The MUR860 has a one volt drop for one ampere and two diode drops brings it up to 37 volts.
 Divided by 1.414, that equals a 26.2 VAC transformer.
 Thats what I see as the absolute minimum so a 28 VAC transformer does give a margin for two to three amperes of current.
 The six 4700 uf caps along with the four 470 uf caps on the amp boards does provide over 30,000 uf of power reserve so voltage overhead would not be a problem.


----------



## kevin gilmore

Real measurements.
 All under 1 amp load!

 33.6 volts rms AC at the inputs of the diodes.
 40 volts DC on the first stage rectification cap.
 36 volts DC after the lm338 regulators.
 30 volts DC after the opa541's.


----------



## dip16amp

Quote:


  Originally Posted by *kevin gilmore* 
_Real measurements.
 All under 1 amp load!

 33.6 volts rms AC at the inputs of the diodes.
 40 volts DC on the first stage rectification cap.
 36 volts DC after the lm338 regulators.
 30 volts DC after the opa541's._

 

Good to see that you got the LM338 input voltage down to 40 vdc but that diode drop is quite large. The schottky barrier rectifiers like the MBR1060 have much less voltage drop and I'll have to measure them to compare.


----------



## kevin gilmore

I have decided to add the trimpot to the reference, you can
 choose not to populate it if you want.

 Both boards will be updated within an hour or two.


----------



## intlplby

Is someone going to start the groupbuy thread?


----------



## Edwood

Calling Mister X................................
	

	
	
		
		

		
			





 OK, after the holidays.

 -Ed


----------



## MisterX

Quote:


  Originally Posted by *Edwood* 
_Calling Mister X................................
	

	
	
		
		

		
		
	


	




 OK, after the holidays.

 -Ed_

 

Monday Monday Monday.


----------



## dgardner

We should update the BOM for the two boards and put a some general pricing in for folks.

 Here's what I have to far from the BOM listed above:
 1) Change 3.57K resistor from 1/4w to 1/2w.
 2) Pick a final part number the snubber caps on the rectifier diodes.
 3) Put in alternate electroylic caps for both boards.
 4) Add precision resistor options.

 Any others?


----------



## kevin gilmore

Increased the mounting holes for the 3.5k resistors to make sure
 they will take a .5 watt. If the length needs to change too, let
 me know. Both boards now updated. The optional trimpot is a 10k.
http://gilmore.chem.northwestern.edu/dynahips.zip
http://gilmore.chem.northwestern.edu/dynahipsbig.zip

 I would like 4 of the bigger boards if that is what you are going to
 have made please.


----------



## dip16amp

The 3.5k ohm resistors would change to 3.32k ohm for a LM338 output of 36 volts. Maybe change the board silkscreen to say 40 volts on the LM338 inputs and 36 volts on the OPA541 inputs. Those would be the minimum voltages that you are currently running.


----------



## ble0t

Unfortunately, Mouser doesn't have the RN65D (1/2W) series in stock for 3.57k, but I found the KOA Speer (50ppm) with part #MF1/2CL3571F.

 As for the snubber caps, the biggest voltage I have been able to find at Mouser in ceramic caps is 50V, which correct me if I'm wrong, seems a bit on the low side? They are Kemet .33uf 50V 10% with part #80-CK06BX334K. There are some 100V film caps made by AVX also...those are part #BF074E0334J. Anyone find anything else?

 As for the precision 10k resistors, the part number listed earlier in the thread is also at Mouser and is part #PTF6510K000AXBF. These seem to be just what the doctor ordered


----------



## dip16amp

Quote:


  Originally Posted by *ble0t* 
_Unfortunately, Mouser doesn't have the RN65D (1/2W) series in stock for 3.57k, but I found the KOA Speer (50ppm) with part #MF1/2CL3571F.

 As for the snubber caps, the biggest voltage I have been able to find at Mouser in ceramic caps is 50V, which correct me if I'm wrong, seems a bit on the low side? They are Kemet .33uf 50V 10% with part #80-CK06BX334K. There are some 100V film caps made by AVX also...those are part #BF074E0334J. Anyone find anything else?

 As for the precision 10k resistors, the part number listed earlier in the thread is also at Mouser and is part #PTF6510K000AXBF. These seem to be just what the doctor ordered 
	

	
	
		
		

		
		
	


	


_

 

The temperature coefficient is the main reason for using the precision resistors and the PTF5610K000BZBF and PTF5610K000TZBF does have three times better stability of 5 ppm/c than the PTF6510K000AXBF of 15 ppm/c.


----------



## Edwood

Is it adviseable to use one PSU per Dynahi board for dual mono? Or is it a waste, and not necessary? Or is it only necessary for a DynaMite with four Dynahi boards?

 -Ed


----------



## kevin gilmore

picture of the current big board

http://gilmore.chem.northwestern.edu/dynahipsbig.bmp


 There is no such thing as excessive. Two transformers, 2 power
 supply boards, dual mono... Very nice.


----------



## sft

a wonderful thing:

 2 transformers + 2 psu pcbs + 4 amp pcbs + switch
 = a full bal. dynamight *AND* two dual mono dynahies


----------



## skyskraper

christ almighty !¬¬!¬


----------



## bg4533

Quote:


  Originally Posted by *kevin gilmore* 
_with the .2 ohm current limit resistors, the maximum current is about
 3 amps. Certainly enough to run a dynomite, but not enough to run
 speakers. But if you are going to run a dynomite, you really want
 2 power supplys for dual mono..._

 

What is the point of a current limiting resistor? Wouldn't it be best to just let the PSU be limited by the OPA541?

 If the resistor was lowered to .1ohm would the max current be doubled? Are there any problems with doing this?

 Since current is limited it seems logical that the PSU can only take advantage of a certain sized transformer. Is this true? What is the max size that can be taken advantage of given the .2ohm resistors? How about .1ohm resistors? If I am to use a transformer with a current rating of 5A does this mean that without the current limiting resistor the PSU could output 5V?

 I am considering integrating the Dynahi with a Gainclone or even using the Dynahi to power speakers directly and think I need more than 3A power.


----------



## amb

Quote:


  Originally Posted by *bg4533* 
_What is the point of a current limiting resistor? Wouldn't it be best to just let the PSU be limited by the OPA541?_

 

The current limit resistor is a part of the OPA541 design. The resistor, in conjunction with circuitry inside the opamp, prevents the OPA541 from self-destructing in case of short circuit or other overcurrent conditions. Have a look at the OPA541 datasheet and answers to your questions are all in there.

  Quote:


 Since current is limited it seems logical that the PSU can only take advantage of a certain sized transformer. Is this true? 
 

For the most part, yes.

  Quote:


 What is the max size that can be taken advantage of given the .2ohm resistors? How about .1ohm resistors? If I am to use a transformer with a current rating of 5A does this mean that without the current limiting resistor the PSU could output 5V? 
 

The OPA541 is rated for continuous 5A current maximum, but you must also take into account the power dissipation and heatsinking requirements, etc., so in practice, current-limiting to a value less than the maximum with a bit of margin is the prudent thing to do.

  Quote:


 I am considering integrating the Dynahi with a Gainclone or even using the Dynahi to power speakers directly and think I need more than 3A power. 
 

The dynahi's PSU is really not designed to be a speaker amp power supply. You should either consider using a separate PSU for the gainclone, or go with a PSU that could supply much more current.


----------



## intlplby

i know Raul found it necessary to mount the PSU in a separate enclosure from the Dynhahi when using the Condor PSUs...... is it the same for these PSUs or can they be mounted in the same case as the Dynahi with no problems?


----------



## kevin gilmore

depends on the quality of the power transformer. Some leak magnetic
 fields pretty bad. Some are fully shielded. My current unit has the
 powersupply inside the box and a higher power transformer external.


----------



## Earwax

Quote:


  Originally Posted by *kevin gilmore* 
_There are a pair of .1's near the power opamps. The layout is bigger
 however, so you can certainly stuff 1uf tantalum caps in there instead.
 Same thing with the diode snubbers, you can put anything you want
 in there too. The big caps are very close to the power opamps anyway
 so i don't think there will be any trouble. The protoboard design works
 just fine. With a few 3 resistor changes and a smaller transformer it
 can be used for a dynalo and just about anything else too. It is very
 quiet._

 

What size transformer would you recommend for a Dynalo? 

 And could someone provide more specifics on what else needs to change to use this board for a dynalo PS?


----------



## sft

3K5->2K2
 50K->22K8


----------



## dip16amp

Quote:


  Originally Posted by *Earwax* 
_What size transformer would you recommend for a Dynalo? 

 And could someone provide more specifics on what else needs to change to use this board for a dynalo PS?_

 

The TE62084 at digikey works well. Set the output of the LM338 to 21 volts with a 1.91k in place of the 3.5k resistors and a 22.6k in place of the 50k to get +/-16.3 volts output.


----------



## Garbz

Basically any 50VA torroid will do. The 18v one dip16amp recomends will probably cut it close but save you a lot of heatsinking. I use one with 25v secondaries and it gets HOT.


----------



## mustang

So what transformer do you guys reccommend without changing any resistor values? Since the maximum load on the transformer from the amplifier is 125VA. Plitron carries a 160VA toroid transformer with a 38V RMS each winding with a 2.1A (part number 057035201). Will this transformer work?

 Thanks


----------



## bg4533

Quote:


  Originally Posted by *mustang* 
_So what transformer do you guys reccommend without changing any resistor values? Since the maximum load on the transformer from the amplifier is 125VA. Plitron carries a 160VA toroid transformer with a 38V RMS each winding with a 2.1A (part number 057035201). Will this transformer work?

 Thanks_

 

Did you calculate 125VA or read it somewhere? If so how did you calculate it? I figured it would be a bit higher than that.

 I am thinking the 35V Plitrons might be better if you go over the max since there would be a little less heat.


----------



## mustang

Quote:


  Originally Posted by *bg4533* 
_Did you calculate 125VA or read it somewhere? If so how did you calculate it? I figured it would be a bit higher than that.

 I am thinking the 35V Plitrons might be better if you go over the max since there would be a little less heat._

 

According to this BOM:

http://djgardner.com/headphone/gilmore/dynahips/BOM.pdf

 The output voltage of each winding is 38V at 1.5A which comes to 38 * 1.5 = 57VA for each of the two windings. So 57 * 2 = 114VA + 10% (to account for core loss) which = ~125VA. 

 The closest VA I can get from the Plitron site is 160VA (38VRMS @ 2.1A) for each winding.

 Note: I am assuming the load is 1.5A for each channel.

 Please someone correct me if I'm wrong somewhere.


----------



## ble0t

You can't go wrong with a larger transformer (within reason of course). Anyways, the larger they are, the better regulation they have. I'd say a 160VA is a good choice


----------



## dgardner

Don't pay too much attention to the VA rating I put in the BOM listed above. It's overkill high for a channel setup. It was a place holder until there was a consensus on the transformer. Personally, I order the 160VA one a few weeks ago. They're due in a couple of weeks.


----------



## mustang

Well if it was overkill then why did you order a 160VA one? How much current does the Dynahi exactly draw? Sorry, I'm just a bit confused. 

 Thanks for the help everyone


----------



## dgardner

Sorry for the confusion. I should have said "the 250VA rating" thats showing the BOM is overkill for a two channel unit. I need to update the BOM to show something around 160VA. 

 The dynahi board pair I'm running right now (combined) draw about 850mA on each power rail of a lab supply at +30V and -30V. So it seems to me that the transformer spec would be two secondaries at 35-38V at about 1 to 1.5 amps each.


----------



## bg4533

If you are going Plitron might as well go overkill. In the standard transformers there is only an $8 difference between the 120VA and 300VA model. That is nothing considering the overall cost of the Dynahi. Personally I am going to get the 35V secondary 300VA model. 

 Did people order the Plitrons directly from Plitron? Is there anywhere else online that carries them and ships to the US?


----------



## bg4533

Quote:


  Originally Posted by *mustang* 
_Well if it was overkill then why did you order a 160VA one? How much current does the Dynahi exactly draw? Sorry, I'm just a bit confused. 

 Thanks for the help everyone_

 

I PMd KG about driving speakers with the Dynahi a bit back and this is one of his PMs:
 "The 2 amp channels at idle pull about .75 amp.
 So a 2 amp supply would be able to put about
 1.25 amps more out before it reaches its limit.
 That would be only a few watts into the speakers."

 Originally people were using 2x1A 30V Condor PSUs and that worked but got overly hot.


----------



## strohmie

Quote:


  Originally Posted by *mustang* 
_Well if it was overkill then why did you order a 160VA one? How much current does the Dynahi exactly draw? Sorry, I'm just a bit confused._

 

It sucks not having an internet connection...

 The base current draw of the Dynahi is ~300mA per channel, thus ~600mA total with a transformer voltage around 30V. Thus the approximate absolute minimum VA rating on the transformer you buy would be around 30VA (round up to 1A max operation at 30V). But it's stupid to get something that low, IMO. Reason being, the closer to the required VA rating your transformer is, the more likely it is to hum/buzz/vibrate. Basically, you don't want to have your transformer running at full load for this application. Thus a higher VA rating is preferable.

 Now, if you're using your Dynahi for more testing purposes (very low impedance headphones, small efficient speakers, etc.) your current draw is going to jump. Think a few amps total. So in that case you want a higher transformer rating, again above the actual usage.

 Me? I haven't bought a transformer for my Dynahi yet (still haven't matched transistors again or figured out how I'm going to case it) but I plan to use a 120VA transformer. And as mentioned, the price difference between a lower VA rating and a higher one is relatively low.


----------



## mustang

Thank you for the clarifications dgardner, bg4533, and strohmie.

 One more...does anyone know how many amps the 2SC3421 & 2SA1358 draw per channel at full load?

 Thank you


----------



## ble0t

Datasheets tell all... 
	

	
	
		
		

		
			





2SC3421 

2SA1358


----------



## amb

Quote:


  Originally Posted by *mustang* 
_does anyone know how many amps the 2SC3421 & 2SA1358 draw per channel at full load?_

 

 Quote:


  Originally Posted by *ble0t* 
_Datasheets tell all..._

 

Actually the datasheet doesn't give you an answer to mustang's question. The question was not about the max current capability of the transistor. It's how much current the transistor will pass in this particular application (the dynahi) under full load.

 Now, the term "full load" is nebulous unless you specify what the load impedance is. At any rate, as long as the load impedance is not too low as to cause the amp to drop out of class-A operation at maximum output voltage swing, then the quiescent current is the full load current (the definition of class A). In this case it's around 80mA or so per output transistor.

 Now, at what impedance will the amp drop out of class A at full output voltage swing? With tightly regulated +/-30V power rails, the theoretical peak swing is 60V / 1.4142 = 42V. Actual swing will be a bit less due to internal losses in the transistor. At any rate, if we just round down to 40V peak, then the peak current delivered into the load would be I = 40V / R (where R is the load impedance). To remain in class-A operation for a push-pull emitter-follower output stage, the peak current must not exceed twice the total output stage quiescent current. Since there are four parallel pairs of output transistors, the total quiescent current is about 320mA. Solving for R, gives R = 40V / 640mA = 63 ohms.

 What this means is that with a 63 ohm or higher load impedance, the amp will remain fully class-A all the way up to clipping threshold. With a 32 ohm load, the amp will drop out of class A at about half the max voltage swing, and operate at class-AB above that. Still, even 20V peak is A LOT (much more than any sane person is likely to use on a 32 ohm can). So, for headphones loads, this amp can be called "class A" for any realistic listening volume and then some.

 When the amp goes into class-AB mode, and the current that would pass through the output transistors will vary with the output voltage swing, the actual current depends on the load impedance.


----------



## Oli

not wanting to be critical -

 surely the 5v reference could be replaced with a 10v reference (and the gain halved), such as TI's REF102 - the reference has approx half the noise too. Anybody want to try it?


----------



## sft

I've tried. It works well. compare it to ref02 not yet...


----------



## kevin gilmore

Same pinout, so its plug and play. Just change one resistor, and
 make absolutely sure the intermediate voltage stays at 36 or below.


----------



## stackofhay

I found a unit at AVEL in CT that seems to suit the bill for the Dynahi PS.

 2 x 35VRMS, 160VA toroidal, $35.26 plus UPS including mounting hardware.

 Model Y236507 Web link for Y23 series data . I spoke with Melanie at x41.

 It is not as sexy looking as the Plitron, but I'm not sure the electrons or magnetic fields know the difference. Besides that, it's about $20 cheaper.


----------



## TrevorNetwork

I think the 2 x 30v is probably better.


----------



## Oli

sft, if we could have some noise measurements, that would be excellent!!

 my primary concern was sourcing too much current from the reference, therefore potentially making the ref unsuitable.


----------



## kevin gilmore

the only current pulled from the reference is the input bias of the
 opa541. 50 picoamps worst case.


----------



## Woody

Stackofhay, I've yet to build or even purchase the transformer but 2x 35Vrms, 160VA looks a little excessive, I'm guessing that your unregulated voltage will be high resulting in even more heat. Judging from others results, 2x 35Vrms 80VA would be more appropriate. A previous poster suggested that when he used 2x 30Vrms, 160VA , that he ended up with an unregulated 39V, so you'd be up around the 44v mark or higher.

 I'm in the same boat, looking for an alternative to the Plitron and Avel are available in the U.K., so if I'm spouting rubbish someone please shootme down.

  Quote:


  Originally Posted by *stackofhay* 
_I found a unit at AVEL in CT that seems to suit the bill for the Dynahi PS.

 2 x 35VRMS, 160VA toroidal,_


----------



## stackofhay

Thank you and others for your notes


 Regarding the 35+35 unit I recommended...

 Here's my thinking -- fire away!

 In an earlier message, Mr. Gilmore stated "33 volts rms at the primary under load is the minimum requirement at 1 ampere of output current. There is loss across the diode bridges."

 According to AVEL, the regulation on the 120VA units is 9% and the regulation on the 160VA units is 8.3%.

  PHP Code:

    RATED AT...                  OUTPUT (V) at LOAD (VA) 

Voltage     VA   Reg         0VA     60VA    90VA   120VA 
  
30         120   9%          32.70V 31.35   30.68   30.00 
30         160   8.3%        32.49  31.56   31.09   30.62 

35         160   8.3%        37.91  36.82   36.27   35.73  
 ​



 There is no 35+35 unit available at 80VA, 100VA or 120VA, so I took the conservative approach.

 IMHO it is RMS that delivers VA to the load and all the excess will just come out in the form of PS heat. The amp boards are receiving regulated voltage, so they're fine, and If I'm reading the schematic right, I should not fry anything, so I'm stickin' with it!

 p.s. I called AVEL -- they will tool a 100VA 33+33 unit if there is demand for 50 units or more -- individuals would be able to order this directly from AVEL so no group-buy logistics are required.

 p.p.s. I would APPRECIATE it if someone would tell me how to put neat tables into posts...


----------



## ble0t

Perhaps a 'group buy' of a good transformer for this project is in order? Is there enough interest to get an order of 50? Would they do it for any lesser #, perhaps something like 25?


----------



## mustang

Quote:


  Originally Posted by *ble0t* 
_Perhaps a 'group buy' of a good transformer for this project is in order? Is there enough interest to get an order of 50? Would they do it for any lesser #, perhaps something like 25?_

 

I think that'd be a good idea granted we get a consensus on what VA rating PS to buy.


----------



## Turing

Judging from the amount of people buying the boards, I'm sure there would be at least enough interest to make an order of 50.

 The only problem would be getting people to agree on the optimum transformer to use.

 I'd be down for at least one.


----------



## stackofhay

Based on my call -- a formal group buy is not required. If there is sufficient demand, they'll wind up some units for this application and probably include them in their standard products catalog.

 The person with whom I spoke indicated that 50 is a minimum run for them, and they'd need "assurances" of the demand -- otherwise AND THAT THEY WOULD accept orders directly from individuals. 

 I suggest we run a poll somehow -- I'm no expert on HTML or this forum, so I'd appreciate some guidance, or for somone else to run the poll.

 I believe the price for a 100VA unit is around $31 plus shipping -- with mounting hardware included.

 There would be no NRE charge if we'd provide a confident assurance that we'd collectively take 50 of them. 

 Perhaps Mr. Gilmore could help us determine a definitive spec for a unit appropriate to single PS, dual AMP configuration?

 MY SUGGESTION IS 100VA 33+33 WITH DUAL PRIMARY FOR 115/230 50/60Hz

 (Edited -- deletes in silver and inserts in ALL CAPS)


----------



## ble0t

Yep, I saw that we don't need to do a traditional group buy...I put it in quotes because we need to at least get the # of people who want one down. As soon as we nail down the correct specs that everyone can live with, we can start up a poll/group interest thread to guage how many we would need.

 Sound like a plan?


----------



## stackofhay

Exactly!


----------



## intlplby

i'd be down for 6, but i would want something with a higher VA rating so i could use the dynahi to power small efficient speakers as well.....


 i don't know what the general concensus is on what VA rating is necessary to power small speakers


----------



## Woody

Quote:


  Originally Posted by *stackofhay* 
_MY SUGGESTION IS 100VA 33+33 WITH DUAL PRIMARY FOR 115/230 50/60Hz_

 

If this gets the nod from everyone then it gets my vote. After my last post I've been finding out just how anything between 25+25 60VA and 55+55 100VA is rarer than hens teeth !

 Not sure what the complications for me would be in the U.K. Presumably Avel would manufacture them in the states, so I'd have to check with them what the cost would be to ship to the U.K.

 If there is anyone else interested from the U.K, let me know, we may have some options, either buying from the Avel U.K. branch as a "group" or buying from another U.K. company. I did find one company that could supply a 35+35 80VA toroidal for a min order qty of 10.


----------



## stackofhay

Quote:


  Originally Posted by *Woody* 
_If this gets the nod from everyone then it gets my vote. After my last post I've been finding out just how anything between 25+25 60VA and 55+55 100VA is rarer than hens teeth !

 Not sure what the complications for me would be in the U.K. Presumably Avel would manufacture them in the states, so I'd have to check with them what the cost would be to ship to the U.K.

 If there is anyone else interested from the U.K, let me know, we may have some options, either buying from the Avel U.K. branch as a "group" or buying from another U.K. company. I did find one company that could supply a 35+35 80VA toroidal for a min order qty of 10._

 

The issue is creating a spec with which everyone can live. I'm trying to find something that will work for the single supply, 2 amp board folks. I'm figuring that if someone is going to go differential, then they'll use two of everything, and if they want to go dual mono with two PS boards, a single 100VA transformer should have sufficient headroom.

 (I'm not sure about the folks who want to drive speakers though, as I would think that there would be work required to tweak up the power supply in many places to handle the increased output stage bias and the greater dynamic load presented by speakers.)


----------



## ble0t

I think 100VA per channel (assuming you would go dual mono) for an efficient speaker setup would be plenty, especially considering the fairly generous amount of capacitance in the power supply. I think that 100VA might be a good size for the headphone amp (assuming one PS board for both channels) because it is not excessive, but does provide for some headroom.


----------



## amb

Quote:


  Originally Posted by *ble0t* 
_I think 100VA per channel (assuming you would go dual mono) for an efficient speaker setup would be plenty, especially considering the fairly generous amount of capacitance in the power supply. I think that 100VA might be a good size for the headphone amp (assuming one PS board for both channels) because it is not excessive, but does provide for some headroom._

 

IMHO that's massive overkill. The regulator output is current limited to 3A. Even though the rail capacitors could provide some transient current bursts, they cannot do so in a sustained manner. Thus, all those extra VAs in the power transformer will go wasted.


----------



## intlplby

so is it basically not worth trying to drive efficient speakers with the dynahi and instead just build an amp specifically for speakers?


 if that's the case then i can live with it and i'll go with whatever transformer everyone else is thinks works fine


----------



## drubrew

My Avel 30v + 30v 2.67A 160VA just arrived. I will let everyone know how it turns out. I have also designed a second power supply to also try that will run off the same transformer. The part number was Y236505 @ $35.26 and $8.50 shipping. I might be able to get a good deal on Quantity orders since I am a Dealer. Let me know if you guys want to pursue the option.
 Drew


----------



## ble0t

After looking at things a bit closer, I think AMB is right. The Dynahi is around 30W (15W/channel) if I'm not mistaken. To provide a very stiff power supply, I've always used 2X the power rating, which would be approx 60VA. Looking at Avel's specs, they have a 63VA and 80VA range as well that might be more appropriate sizes. That is, if I'm thinking about this correctly


----------



## dgardner

Quote:


  Originally Posted by *dgardner* 
_Don't pay too much attention to the VA rating I put in the BOM listed above. It's overkill high for a channel setup. It was a place holder until there was a consensus on the transformer. Personally, I order the 160VA one a few weeks ago. They're due in a couple of weeks._

 

Actually, I mispoke here. I ordered this from Plitron:
 037035201 TOROIDAL XFMR 2 X 38VAC @ 80VA


----------



## ble0t

I thought I'd drop in another place to possibly inquire about the transformers...

Victoria Magnetics

 I've heard nothing but good things, and they are used to doing things in small quantities. I don't think their prices are bad either...possibly only a couple $ more per toroid.


----------



## stackofhay

Quote:


  Originally Posted by *dgardner* 
_Actually, I mispoke here. I ordered this from Plitron:
 037035201 TOROIDAL XFMR 2 X 38VAC @ 80VA_

 

I completely agree that the 160VA I mentioned earlier is waaaay overkill for a simple stereo unit, and even more overkill for a dual mono setup. 

 I bought it because it was the smallest model available at 35+35. I would strongly prefer something with about 1/2 the VA rating at 33-35VRMS per winding.

 I saw the Plitron unit, and figured I'd look for something local... 

 Please let us all know how things turn out with the Plitron!


----------



## bg4533

Quote:


  Originally Posted by *kevin gilmore* 
_with the .2 ohm current limit resistors, the maximum current is about
 3 amps. Certainly enough to run a dynomite, but not enough to run
 speakers. But if you are going to run a dynomite, you really want
 2 power supplys for dual mono..._

 

I am still trying to figure out this PSU... I just looked at the PSU schematic, but still don't fully understand it. Both OPA541s seem to be linked together. What is accomplished by this? Each OPA541 is capable of putting out 5A of current. Is the max current of the PSU 3A per DC out or total? How much is each OPA541 limited to here? If a PSU is only used to power one channel is the PSU still capable of the same max output or only half?


----------



## stackofhay

Take a close look at how they are hooked up.

 The 5V voltage reference is multiplied by +6 by the first op amp, thus generating 30V for V+.

 The second op amp uses the +V rail as an input. The second's gain is set to -1 so its output is -30V. Each rail is driven by a separate op amp.

 This way, they both track as complements as components warm up etc... and theoretically, the servo won't have to do much work maintaining DC offset.

 Kevin Gilmore mentioned in an earlier post that matched, low temp coefficient resistors for "the second op amp" are important.




  Quote:


  Originally Posted by *bg4533* 
_I am still trying to figure out this PSU... I just looked at the PSU schematic, but still don't fully understand it. Both OPA541s seem to be linked together. What is accomplished by this? Each OPA541 is capable of putting out 5A of current. Is the max current of the PSU 3A per DC out or total? How much is each OPA541 limited to here? If a PSU is only used to power one channel is the PSU still capable of the same max output or only half?_


----------



## ble0t

The first OPA541 is setup to have a gain of 6 with an precise input of 5V from the REF02, thus producing the +30V rail. The second OPA541 has negative unity gain and is setup to follow the first OPA541, but produce a negative -30V rail. The 0.2R resistors limit the current to 3A in each case. The supply voltage for both OPA541's is supplied by the LM338's.

 Hopefully, I'm looking at it correctly myself 
	

	
	
		
		

		
			





 EDIT: that stack of hay beat me to it


----------



## stackofhay

Quote:


  Originally Posted by *ble0t* 
_
 EDIT: that stack of hay beat me to it 
	

	
	
		
		

		
		
	


	


_


----------



## ble0t

I've sent quotation requests to 4 different companies (Victoria Magnetics, Avel Lindberg, Amveco and Toroid Corp) for 10, 25 and 50 piece orders of a transformer with the following specs:

 80VA
 115V/230V dual primary
 35V - 35V dual secondary @ greater than 1A

 I've kept everything bare minimum on the quotes thus far (standard plate mounting, no shielding, etc.) to get an idea of the base cost. Hopefully I'll get some replies back by early next week.


----------



## dip16amp

Here's a couple of transformers that I tested on the power supply. Both are used with the output wiring in series so two transformers are needed per power supply. I use four transformers for my balanced dual mono dynahi. I used a couple of 5k bourns pots in place of the 3.5k resistors to adjust the LM output.
 Measurements are: transformer output vac rms, diode output, LM output, OPA output.

 Radio Shack 273-1512 25.2 VAC 2 amp 50 VA $10.49 each
 no load: 27.9 vac, 37 vdc, 33 vdc, 30 vdc
 with load: 26.9 vac, 33 vdc, 31 vdc, 28 vdc


 Digikey PL56-28 28 VAC 2 amp 56 VA $18.14 each
 no load: 34 vac, 45 vdc, 35 vdc, 30 vdc
 with load: 33 vac, 39 vdc, 35 vdc, 30 vdc

 The 25.2 volt transformer clearly does not have enough voltage under load and shows what the minimum volts that the LM (two volts) and OPA (three volts) need. 

 The 28 transformer under load shows a two volt margin on the LM regulator and a two volt margin on the OPA541. The diode output of 39 vdc is also under the maximum limit of the LM338 (40 vdc) that it will see on power up. The 35 vdc is under the 36 vdc operating range if the REF102 10 volt reference is used. I will change the 50k resistor to 20k and try the REF102CP next week.

 Digikey and Mouser also sell the VPP28-2000 from Triad Magnetics that has the same specs (28 vdc, 2 amp, 56 VA) which should work. Mounting brackets or standoffs are needed for mounting on both of the 28 volt transformers.
 I was also considering the digikey TE62083 toroidal with series output 30 vac 1.66 amps, 50 VA but I don't really need the higher voltage.


----------



## sft

What's the real value of AC-voltage(wall wallet) in California?Thanks in advance.


----------



## amb

Quote:


  Originally Posted by *sft* 
_What's the real value of AC-voltage(wall wallet) in California?Thanks in advance._

 

The US standard is 117V AC 60Hz.


----------



## dip16amp

My wall outlet currently measures 119 vac.


----------



## sft

Thank you everybody.


----------



## Woody

Quote:


  Originally Posted by *ble0t* 
_I've sent quotation requests .... a transformer with the following specs:

 80VA
 115V/230V dual primary
 35V - 35V dual secondary @ greater than 1A
 ._

 

Just noticed that this is a standard part for Plitron, P/N 037018201.


----------



## kevin gilmore

quote
 The US standard is 117V AC 60Hz.

 That may be the standard, but it is completely useless especially
 around large cities with significant manufacturing areas.
 In the summer i have seen my electricity as low as 105 and in the
 winter as high as 122.


----------



## Woody

There is an amount of conflicting info in this thread, I'd dearly love to clarify some of it as it could help with sourcing a transformer. The current favourite seems to be a 2x35v 80VA transformer, which of course is not readily available in the UK !

 Firstly, dip16amp has calculated minimum required voltages at each point in the PSU circuit, based on data sheets allowing for 30Vdc out @ 1A, 

 26.2 Vrms before diodes/ Output of transformer (Too low ?)
 35Vdc before LM338
 33Vdc after LM338 (And into OPA541)

 Now here are some real world measurements of the Dynahi amp:

 KG: 300mA per amp board
 dgardner: 450mA per amp board

 Now here are some real world measurements of the PSU:

 Dip16amp , using 2x 28Vrms 100VA sees 33Vrms before diodes, 39Vdc before LM338 and 35Vdc into OPA541

 KG, using an Avel ?????, sees 33.6Vrms before diodes, 40Vdc before LM338 and 36Vdc into OPA541.

 MattN using a 30Vrms 160VA transformer, sees 39Vdc before LM338.

 Observations:

 1) KGs boards use 50% less power than dgardners.

 2) Dip16amps 28Vrms (Digikey) transformer puts out 34rms with no load. So it either should be sold as a 33Vrms transformer or its regulation is appalling ? [edit] Or the line voltage was high ?

 3) All 3 transformers end up with the desired 39/40 Vdc before the LM338, although this doesnt necessarily make sense. Now in both Dip16amps and KGs measurements there is perhaps a large voltage drop across the rectifier diodes, where as MattNs drop is smaller (closer to expected ?) The other possibility is that all three measurements were taken under different conditions !

 This is all suggesting to me that a 30Vrms >100VA transformer may well be the way to go and if there is any problem with too low a voltage into the LM338, then adjust its output as required to maintain the necessary headroom (>2v), so long as >=35Vdc is maintained before LM338 and >=33VDC is maintained after it.

 The good news is that 30VA 160VA transformers are readily available. 

 Can anyone else chip in with some more real world measurements ? Perhaps measuring with a fixed 1A load on both 30Vdc rails ?


----------



## kevin gilmore

The amount of power the amp boards pull are directly related to
 the led voltages. I designed it such that with the bag of led's i have
 (about 500 left) i get each board to pull 300ma which is 600ma total.
 dgardner's boards are pulling more than that. Nothing wrong with that
 either as long as you have the required amount of heatsinking.
 The transformers i'm using are avel-lindberg. Because that is what
 i have a number of laying around. I have ordered custom transformers
 which should finally be here next week. My measurements were with
 a true rms voltmeter. I did not measure my line voltage at the time.


----------



## dgardner

Quote:


  Originally Posted by *Woody* 
_
 dgardner: 450mA per amp board
_

 

I dropped the 100 ohm resistor in the VAS stage down to about 90 ohms and this dropped the idle current of the board pair down to about 620mA cold and about 750mA all warmed up. On mine, 85 ohms might have been even better. If the design goal is about 85mA through each output stage transistor, I am right about there; maybe a smidge higher.

 So the point is:
 1) you can easily control/scale your total current consumption at idle.
 2) transistor gains play a part in this, so depending on what you get an adjust might be needed.


----------



## dgardner

Quote:


  Originally Posted by *kevin gilmore* 
_The amount of power the amp boards pull are directly related to the led voltages._

 

Said another way: The LEDs set the magnitude of the contant current sources through the FETs, which set the magnitude of the VAS stage voltage, which sets the current value of the output Stage. The idle currents are all related to each other by design. TRUE - I could have selected different LEDs and got the same effect.

 One other note: if you use the trim pots to lower the DC offset, you are in essense increasing one (or both) of the constant current sources, which makes the total current consumption of the board go UP slightly.


----------



## Woody

Thanks KG and dgardner, hopefully you can see I'm not trying to catch anyone out. 

 I havent worked in the electronics field for over 20 years now and while trying to fathom this stuff out for myself I'm discovering just how rusty I am.

 Could someone validate my thinking ?

 Using a 30Vrms 160VA transformer, it would be reasonable to assume that the Vrms out would be approx 31.5Vrms, allowing for the fact its rated at 10% regulation and it would only be about 20% loaded (0.5A per Dynahi board). However for the purposes of the calculation I'll assume transformer secondary outputs of 30Vrms @230Vrms primary. This will help to offset the possibility that the transformer is on the low side of its output tolerance spec.

 Minimum UK mains voltage is 216Vrms, which equates to a worst case 28.17Vrms secondary output.

 28.17Vrms=39.83Vpk at input of rectifier diodes.

 Allowing for a 3v ((There is big discrepency here in peoples measured voltage drops ??? - See below !) drop across the two diodes, gives a rectified 36.83Vpk. 

 Calculating the Vripple at the input of the LM338, as Vrip=Iloadx(dt/c), gives a ripple voltage of ~100mV.

 So worst case voltage at input of LM338 is 36.73Vdc.

 LM338 has a dropout of 2v @ 1A, but allow 2.43V, although should be less than 2v because we are only drawing 0.5A.

 So this would require the LM338 to be set for 34.3v using 3500ohms and 133ohms. 

 The OPA541 needs (Vsupply - Vout) >3v @ 1A and >2.5v @0.5A, so there would be >1.3v of headroom in the supply voltage of the OPA541. Its tight but OK I think ?

 BUT, and its a big BUT, what is the voltage drop across those rectifier diodes ? I've allowed 3v but both dip16amp and KG are seeing about 7v. The spec says less than 1v, so what the hell is that all about ?... I suspect my calculations ! 
	

	
	
		
		

		
			





 If it was closer to 2v for both I'd get another 1v of headroom, but if it really is 7v then I'm completely stuffed and a 30V transformer is a big NO-GO regardless of VA rating.


 Rgds


----------



## Nisbeth

Woody, two things:

 1) If you're getting a quote for a custom transformer, why not get some "semi-exotic" voltage like 2 x 33V?

 2) Couldn't the LM338 be substituted with the LM/LT1084 which has a lower dropout voltage?


 /U.


----------



## dip16amp

Quote:


  Originally Posted by *Woody* 
_Thanks KG and dgardner, hopefully you can see I'm not trying to catch anyone out. 

 I havent worked in the electronics field for over 20 years now and while trying to fathom this stuff out for myself I'm discovering just how rusty I am.

 Could someone validate my thinking ?

 Using a 30Vrms 160VA transformer, it would be reasonable to assume that the Vrms out would be approx 31.5Vrms, allowing for the fact its rated at 10% regulation and it would only be about 20% loaded (0.5A per Dynahi board). However for the purposes of the calculation I'll assume transformer secondary outputs of 30Vrms @230Vrms primary. This will help to offset the possibility that the transformer is on the low side of its output tolerance spec.

 Minimum UK mains voltage is 216Vrms, which equates to a worst case 28.17Vrms secondary output.

 28.17Vrms=39.83Vpk at input of rectifier diodes.

 Allowing for a 3v ((There is big discrepency here in peoples measured voltage drops ??? - See below !) drop across the two diodes, gives a rectified 36.83Vpk. 

 Calculating the Vripple at the input of the LM338, as Vrip=Iloadx(dt/c), gives a ripple voltage of ~100mV.

 So worst case voltage at input of LM338 is 36.73Vdc.

 LM338 has a dropout of 2v @ 1A, but allow 2.43V, although should be less than 2v because we are only drawing 0.5A.

 So this would require the LM338 to be set for 34.3v using 3500ohms and 133ohms. 

 The OPA541 needs (Vsupply - Vout) >3v @ 1A and >2.5v @0.5A, so there would be >1.3v of headroom in the supply voltage of the OPA541. Its tight but OK I think ?

 BUT, and its a big BUT, what is the voltage drop across those rectifier diodes ? I've allowed 3v but both dip16amp and KG are seeing about 7v. The spec says less than 1v, so what the hell is that all about ?... I suspect my calculations ! 
	

	
	
		
		

		
		
	


	




 If it was closer to 2v for both I'd get another 1v of headroom, but if it really is 7v then I'm completely stuffed and a 30V transformer is a big NO-GO regardless of VA rating.


 Rgds_

 

The 30 vac rating is at full load which for a 160 VA tranny would be over 5 amperes. The no load voltage will be 10 percent higher which would be 33 vac. Your actual load will be no where near max and will not drop much from that. Even with a 7 volt diode drop there will be 39.7 vdc to the LM regulator.
 Hopefully, someone will provide their measurements for a 30 vac 160 VA or 100 VA transformer.
 The 28 vac transformer has 18 percent regulation so it's no load voltage is higher.


----------



## Woody

Thanks dip16amp. 

 The other option I hadnt given any thought to, I go with two smaller transformers, a 0-15,0-15 Vrms 50VA and a 0-18,0-18Vrms 50VA, (observing phase 
	

	
	
		
		

		
		
	


	




 ) , connect the secondaries in series to get 2x 33Vrms.

 The cost is about the same as a single 30Vrms 160VA.

 I was planning on housing the transformers externally, and two separate transformers should run cooler than 1 big one ... I think ?

 Either way, Im still struggling to see how the MUR860 are dropping 3.5v each, I've just looked at the spec again ,even at 30A they shouldnt drop more than 1.1v each !


----------



## dip16amp

Quote:


  Originally Posted by *Woody* 
_Thanks dip16amp. 

 The other option I hadnt given any thought to, I go with two smaller transformers, a 0-15,0-15 Vrms 50VA and a 0-18,0-18Vrms 50VA, (observing phase 
	

	
	
		
		

		
		
	


	




 ) , connect the secondaries in series to get 2x 33Vrms.

 The cost is about the same as a single 30Vrms 160VA.

 I was planning on housing the transformers externally, and two separate transformers should run cooler than 1 big one ... I think ?

 Either way, Im still struggling to see how the MUR860 are dropping 3.5v each, I've just looked at the spec again ,even at 30A they shouldnt drop more than 1.1v each !_

 

They would drop 1.1 volts if it was DC but because it is AC ripple, it's average is about 3.5 volts per diode.


----------



## Woody

Quote:


  Originally Posted by *dip16amp* 
_They would drop 1.1 volts if it was DC but because it is AC ripple, it's average is about 3.5 volts per diode._

 

Now you've got me. I can see that the current will flow through the diodes only for a short period of time during each cycle and that instantaneous current will be high as the 4700uF caps are charged, but even then its surely not going to be as high as 30A is it ?


----------



## dip16amp

Quote:


  Originally Posted by *Woody* 
_Now you've got me. I can see that the current will flow through the diodes only for a short period of time during each cycle and that instantaneous current will be high as the 4700uF caps are charged, but even then its surely not going to be as high as 30A is it ?_

 

It isn't that the diodes are actually dropping more than 1.1 volts, but that they aren't seeing the peak input voltage as DC. The input ripple averages to the lower diode input DC value.


----------



## Woody

Quote:


  Originally Posted by *dip16amp* 
_It isn't that the diodes are actually dropping more than 1.1 volts, but that they aren't seeing the peak input voltage as DC. The input ripple averages to the lower diode input DC value._

 

Of course I see what you mean now. Because the anode only sees the peak for an instant during the period its actually conducting, its the rms (or avg ?)value of the full wave rectified signal that it sees Doh ! I feel pretty stupid for not seeing that, it seems so obvious now


----------



## Woody

After much recalculation, allowing for worst case scenarios, I'm opting for a 2x30Vrms 160VA, transformer. 

 And hey if its wrong its wrong, I've spent hours deliberating over a 15 GBP part !


----------



## ble0t

Well, Avel Lindberg got back to me today...here's the scoop:

 Primary: Y23 type 115 + 115V 50/60 Hz
 Secondary: 35 + 35V @ approx 1A
 Size: approx 3.4" x 1.6"
 Finish: polyester tape, stranded leads, dish mounting hardware

 10: $28.36 each
 25: $23.53 each
 50: $20.75 each

 Delivery: If ordered soon, 10-12 weeks, after that up to 16 weeks

 Obviously, the delivery time is a tad high...I am going to e-mail her back and see if that could be decreased at all.

 BTW...is there still any interest in doing this? It seems that doing a larger order would in fact save a significant amount of $$$


----------



## walangalam

How about the encapsulated ones? Seeing that the dynahi is sensitive to stray fields I think we should consider the low-magnetic field transformers.


----------



## ble0t

Yes...this is a possibility for any of the places that I have requested quotes from. My goal was to just get a baseline idea as to what the price would be and then take it from there.


----------



## intlplby

not for that time frame.... i was looking to getting mine when the PSU boards arrived


----------



## ble0t

Well, I meant in general...from the limited response, I might just scrap the idea completely


----------



## eweitzman

I would love to have the minimum tranny for heat reasons as long as the voltage under load doesn't get too low. 

 I would buy one, perhaps two. The wait is not a concern for me.

 - Eric


----------



## intlplby

maybe it would be best to look into a group rate for a transformer model that is already manufactured.....


 i.e. we figure out what transformer and from what manufacturer and then get that manufacturer to commit to a competitive price and then we can just say we are using a head-fi referral to get the better rate when ordering directly

 drew.... i think a lead time that long is not going to be popular because by the time you get the buy organized and numbers figured out.... it will be 2 weeks to a month and then add the lead time that is 3-4 months.... i know a lot of people are now just waiting on the PSU boards to complete the dynahi and i'm sure they don't want to wait on transformers


 i may be wrong though


----------



## Earwax

Quote:


  Originally Posted by *eweitzman* 
_I would love to have the minimum tranny for heat reasons as long as the voltage under load doesn't get too low. 

 I would buy one, perhaps two. The wait is not a concern for me.

 - Eric_

 

Me too, on the heat issue. I'd be intersted at least 1, when we're sure it's the right size.


----------



## ble0t

Well...here's the reply from Victoria Magnetics:

 "We can make the transformer you are inquiring about. Cost would be $58.00
 each for 10-25 pieces, for a 50 piece order the cost would be $54.00 each.
 That price includes mounting washers. We can add magnetic shielding to them
 for an additional $2.00 each, that should shield any nearby components from
 the magnetic field of the transformer."

 This is obviously a little expensive, although I guess these guys make some good toroids.

 As for Plitron (and as stated above), they do have a part # for the stated specs and the pricing is $49.03 for 10 - 24 pieces and $47.73 for 25 - 49 pieces.

 Again, this may be higher than what some are looking for...what do you guys think? I'm still waiting for a response from one of the places (Toroid Corp.), so maybe they will be the dark horse and surprise us


----------



## ble0t

Got a response back from Avel Lindberg about bumping up the order...

  Quote:


 We should be able to slip some in to production at one of our other
 locations and have a delivery of units to you by mid February. We would need
 to know fairly quickly if you would like for us to squeeze these in. Pricing
 would be as follows:

 Primary: Y23 type 115 + 115V 50/60 Hz
 Secondary: 35 + 35V @ 1A
 Size: approx 3.4" x 1.6"
 Finish: polyester tape, stranded leads, dish mounting
 hardware

 10-49 $35.45 each
 50: $30.44 each 
 

Seeing as how the boards won't be arriving at our doorsteps for another couple weeks, this lead time isn't all too bad. It's a jump in price, but still cheaper than the off the shelf Plitron model. I'm waiting to hear from one more place to see if that price/time frame can be beaten. As stated in an earlier post, Avel could possibly do individual shipping if we requested it. What does everyone think? Is there enough interest to get at least 10 of these?


----------



## walangalam

I would be interested for 1 if its shielded.


----------



## Woody

Quote:


  Originally Posted by *Oli* 
_not wanting to be critical -

 surely the 5v reference could be replaced with a 10v reference (and the gain halved), such as TI's REF102 - the reference has approx half the noise too. Anybody want to try it?_

 

Just a warning that the REF102s I've looked at all specify max input voltage of 36v, where as the REF02s seem to be universally specified for 40v max input. So without adjusting the output of the LM338, the REF102 is not a drop in replacement.

 There are some Linear Tecnology parts LT1019-10 and LT1021-10 that are specified for max input of 40v, but you need to choose spec carefully as some are worse than REF02BP in respect of noise and temp coef, although that said most appear better (Check LT1019A and LT1021A). The LT devices are more expensive and harder to come by though in the UK.

 So on the face of it a 10v REF102 looks good, the reality is not.


----------



## ble0t

Quote:


 I would be interested for 1 if its shielded. 
 

Well, this would increase the cost, depending on what you would want to do. I guess I was hoping more people would be interested in this so we could take advantage of the savings and maybe even get them encapsulated if there was enough interest in doing that.

 I think Avel is going to end up being the best bet out of the 6 manufacturers I've contacted. Two of them haven't even gotten back to me, so I'll rule them out 
	

	
	
		
		

		
		
	


	




 I'm going to need to put this together quickly if we want to get in with Avel and get them here by mid Feb. I think I will start a group buy thread to guage things a bit better.


----------



## Woody

Any recommendations for the MUR860 snubber capacitors ?

 They're specified for 0.33uF, although KG says anything will do (Within reason I guess 
	

	
	
		
		

		
		
	


	




 ) 

 I looked at the formula for calculating the correct capacitance, taking into account the diode capacitance and secondary winding inductance etc.....but gave up a thought I'd just assume something between 0.1uF and 0.33uF 
	

	
	
		
		

		
		
	


	




 I'm assuming the peak voltage across the snubber cap will be just under the Peak-to-peak secondary output of the transformer, so it has to be rated for 100v as a minimum ? 

 Is there a recommended type of cap for this application ?

 Can someone tell me the hole pitch/mounting space on the current PSU board ?

 Thanks in advance


----------



## ble0t

I'd say use a ceramic capacitor around 100pF. The one I plan on ordering is this.


----------



## Woody

OK, thanks Ble0t.

 Has anyone looked at the On Semi/MotorolaMS8860 as an alternative to the MUR860 ? 

 The MSR860 are marginally slower but appear be ultra soft recovery, theoretically atleast reducing the potential for RFI.

 [Edit] Only thing I can see which needs to be allowed for is the fact that the forward voltage drop is a little higher, so you'd potentially need a secondary output a couple of volts higher than with the MUR860. 

 Any comments ?


----------



## Pars

I thought that in Hagerman's article on calculating snubber values that using solely a cap as a snubber was a waste of time? That you really needed to use a resistor in series with the cap? Perhaps this info is outdated?


----------



## Woody

Quote:


  Originally Posted by *Pars* 
_I thought that in Hagerman's article on calculating snubber values that using solely a cap as a snubber was a waste of time? That you really needed to use a resistor in series with the cap? Perhaps this info is outdated?_

 

Its a good point. There seems to be various ways to do it, from what I've read the caps in parallel with the diodes may not be the best but it seems accepted that it works.

 In addition there seems to be more focus on the use of soft recovery diodes now, to reduce the problem to start with. That is stop, any ringing when the diode stops conducting. Hence my suggestion of the MSR860.

 Just in case though, I'm going to leave myself the option of using an RC snubber before the rectifier, as you mention, by using a slightly higher output secondary (Allowing for a drop across the snubber resistors), this should also allow me to use the soft recovery diodes which have larger forward voltage drops. 

 I'd love to be able to put the PSU and Dynahi amp boards in the same case, but I need to satisfy myself first that the PSU is not emitting any RFI.


----------



## Woody

Quote:


  Originally Posted by *Nisbeth* 
_...
 2) Couldn't the LM338 be substituted with the LM/LT1084 which has a lower dropout voltage ? /U._

 

Sorry Nisbeth I hadnt noticed your reply before. I've just looked through various specs, albeit only a cursory one but there doesnt seem to be anything else with the right combination of max Vin (>=38v), max Vout (>=34v), Max Iout (~1A) etc.


----------



## Edwood

What is the largest diameter possible for the electrolytic caps in the latest board (the group buy one going on right now)?

 I'm having a hard time finding 4700uF 50V in more exotic varieties, would 10,000uF 63V be too much overkill?

 -Ed


----------



## Nisbeth

Quote:


  Originally Posted by *Edwood* 
_What is the largest diameter possible for the electrolytic caps in the latest board (the group buy one going on right now)?_

 

No sure, but I believe it's 30 mm diameter with 10 mm lead spacing (snap-in)


 /U.


----------



## ble0t

Cornell Dubilier has a good selection of the snap-in type caps (which Mouser does stock quite a few of). Here's a link to the datasheet. I even found a 4700uf 63V version that is 30mm x 30mm (which I needed for my intended case size).


----------



## Edwood

What is the voltage rating required for the *Monolithic Ceramic, 0.33uf caps* which are close to the Power Rectifier, Ultrafast, 600V 8A parts?

 Anyone have a Mouser or Digikey part number for the 0.33 caps?

 -Ed


----------



## stackofhay

I'm using Mouser # MKT1818433064,  a .33uF nice poly film cap with 7.5mm spacing and a 63V rating.


----------



## Edwood

So, has a definitive toroidal transformer been decided upon?

 -Ed


----------



## ble0t

A number of us decided on these specs...

Dynahi Transformer Group Buy


----------



## Edwood

Is it just me, or is anyone else having problems finding any place that stocks a toroid in those specs.

 Seems every place has to custom order it. 
	

	
	
		
		

		
			





 -Ed


----------



## dip16amp

Quote:


  Originally Posted by *Edwood* 
_Is it just me, or is anyone else having problems finding any place that stocks a toroid in those specs.

 Seems every place has to custom order it. 
	

	
	
		
		

		
		
	


	




 -Ed_

 

If you use two of these toroidal trannies from digikey: TE62083 50VA 2X15 and wire each for 30VAC then you have a 30V + 30V 100VA.

 Or use two TE62084 50 VA 2X18 for a 36V + 36V 100VA.

 Or use one TE62083 50VA 2x15 and one TE62084 50VA 2x18 and wire them for 33V + 33V 100VA.


----------



## strohmie

Toroid of Maryland has a 2x30V toroid at 100VA (I think) that I bought for the purpose. We'll see how well it works.


----------



## Woody

Quote:


  Originally Posted by *Edwood* 
_Is it just me, or is anyone else having problems finding any place that stocks a toroid in those specs.

 Seems every place has to custom order it. 
	

	
	
		
		

		
		
	


	




 -Ed_

 

In the UK I can get a custom 1off toroidal, with electrostatic and electromagnetic screens for just over £30. This isnt too outrageous in view of the overall cost of the Dynahi 
	

	
	
		
		

		
		
	


	




 If you go back through the posts, Plitron do a standard 2x35V 80VA. This should be fine for a standard two board (non-balanced Stereo) Dynahi.

 Not sure if there are minimum order quantities though.

 2x30V secondaries will probably work, although you may need to adjust down the output of the regulator to maintain the min reg input for a regulated output.

 I did some calculations, based on the UK mains tolerance, The output of a 30V secondary was borderline at the minimum specified mains line level. 

 You also need to make sure that you dont choose a secondary voltage that is too high (or too large a VA rating) that the unregulated voltage exceeds 40V (i.e input to the regulator). This is especially true if you plan to power the PSU on and off a lot as the max regulator differential (in to out) is 40V.


----------



## doobooloo

I don't know if this question has been asked before but here I go:

 I recently purchased some 1000uF/200V Nichicon caps (30mm dia.) to use for the Dynahi PSU. They were $1 each, so I thought, what the heck. 
	

	
	
		
		

		
		
	


	




 Now I'm wondering if using these smaller value caps instead of the default 4700uF caps will hurt performance in any noticeable way. I thought 4700uF x 6 = 28200uF was kind of overkill and that 6000uF should be plenty.

 FYI, the caps are these from Electronic Goldmine:

http://www.goldmine-elec-products.co...em=12&mitem=17


----------



## Woody

Quote:


  Originally Posted by *doobooloo* 
_I don't know if this question has been asked before but here I go:

 I recently purchased some 1000uF/200V Nichicon caps (30mm dia.) to use for the Dynahi PSU. They were $1 each, so I thought, what the heck. 
	

	
	
		
		

		
		
	


	




 Now I'm wondering if using these smaller value caps instead of the default 4700uF caps will hurt performance in any noticeable way. ....._

 

Well ripple before the regulator is obviously going to be higher, but whether it'll be high enough to cause a noticeable problem is another matter.

 Depending on how good they are, they might even be better than the 4700uF on the fully regulated 38V side in this particular application, as the current draw is relatively low and constant.

 However, I seem to recall that running electrolytics at a voltage substantially lower than their rated voltage reduced their life considerably. Normal life expectancy is in the region of 5 years. 50VDC is the highest you are going to see in the Dynahi PSU.


 I'm sure I'll be shot down in flames now for my ignorance 
	

	
	
		
		

		
		
	


	




 ......


----------



## doobooloo

So is it safe to use 50V caps instead of 63V and higher caps?


----------



## dgardner

I am unaware of any problem with electrolytics running at *lower* than rated voltage. One thing I know is true: look at the temperature rating. 105C caps have a much longer life than 85C caps and are less prone to losing their capacitance rating as they can "literally dry out" over very long periods of time. (years).


----------



## doobooloo

I vaguely remember something similar about running caps at lower voltage, but it wasn't related to long-term reliability, but more in line with effective capacitance (lower than rated voltage -> less effective capacitance).

 Well the LQs have a pretty standard life of 2000 hours at 85 degrees:

http://ece-www.colorado.edu/~ecen451...eets/lq_98.pdf


----------



## Pars

I remember Tangent and/or someone else posted a reply once about running electrolytics below their rated voltage. Something to do with the chemical reaction of the electrolyte depending upon the cap running close (but not above) the rated voltage. I think I had replied to someone modding a DVD player or something to replace the caps with the next higher voltage rating (and 105 degree) rated caps, and was summarily shown the error of my ways 
	

	
	
		
		

		
			





 However, you will have an initial surge upon power up, so the transformer running at 30V will probably surge to 38-40V initially. 50V caps would probably be the minimum you would want to use, with 63V being safe, I would guess.


----------



## steinchen

quoting tangent and morsel:

 1. Bigger is better, within a particular line of capacitors.
 2. It's usually better to use a lower-capacitance part from a better line of capacitors than a higher-capacitance part from a poorer-performing line of caps.
 3. using many smaller value caps will probably provide lower ESR than fewer larger value caps
 4. picking voltage rating high above the needed voltage rating is a waste of space and money


----------



## Woody

dgardner said:
			
		

> I am unaware of any problem with electrolytics running at *lower* than rated voltage. QUOTE]
> 
> I'm confident I've seen the problem quoted in a number of places, manufacturers data sheets amongst others. I'll admit though I personally dont see the logic. I'm nearly as confident it was to do with a chemical degradation, as opposed to anything else and that it was performance/age that was impacted.
> 
> Unfortunately the chances of me finding those references would be nil. I guess we'll just have to rely on the body of evidence in the following posts to prove or disprove the assertion


----------



## doobooloo

Another question...

 From the board layout pic, it seems like that out of the six large caps:

 1 @ 50V
 1 @ 12V
 2 @ 38V
 2 @ 30V

 Looks like the 50V and 12V caps feed into the two LM338s and the 38V and 30V feed into the OPA541s.

 So... I was wondering if I could use different caps of varying voltage levels for the six big cap spots. Specifically:

 8200uF/16V/105C or 22000uF/25V/85C for the 12V position
 2200uF/63V/85C for the 50V position
 8200uF/50V/85C or 4700uF/50V/105C for the 30/38V positions

 I couldn't find suitable 35V caps but those would work for the 30V positions, right?

 Any opinions on this would be greatly appreciated! Thanks in advance!


----------



## jogor

yes, e-caps should not be operated way below the rated voltage. operation at low voltages causes the aluminum oxide dielectric to thin (reform), which alters the capacitance and break down voltage. This has the same effest as storage without any dc bias (for years), although much slower. This is the reason why e-caps have limited shelf life.

 One good question would be how low is low for an application. For Component stress derating you could start off with a rule that e-caps should not be operated below 20% of rated dc voltage.

 for inrush currents concern, you could use thermistor for limiting. cheap and effective.

 for surge voltage concerns, e-caps are also rated for this (check the specs). although such condition is only allowed for a short duration of time.


----------



## Woody

Quote:


  Originally Posted by *jogor* 
_yes, e-caps should not be operated way below the rated voltage. operation at low voltages causes the aluminum oxide dielectric to thin (reform), ...._

 

Thats good enough for me. I've been vindicated


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## dip16amp

Quote:


  Originally Posted by *doobooloo* 
_Another question...

 From the board layout pic, it seems like that out of the six large caps:

 1 @ 50V
 1 @ 12V
 2 @ 38V
 2 @ 30V

 Looks like the 50V and 12V caps feed into the two LM338s and the 38V and 30V feed into the OPA541s.

 So... I was wondering if I could use different caps of varying voltage levels for the six big cap spots. Specifically:

 8200uF/16V/105C or 22000uF/25V/85C for the 12V position
 2200uF/63V/85C for the 50V position
 8200uF/50V/85C or 4700uF/50V/105C for the 30/38V positions

 I couldn't find suitable 35V caps but those would work for the 30V positions, right?

 Any opinions on this would be greatly appreciated! Thanks in advance!_

 


 One cap is connected between +12V and -38V so there is actually:
 2 @ 50V 2200uF/63V/85C
 2 @ 38V 4700uF/50V/105C
 2 @ 30V 4700uF/50V/105C


----------



## Woody

Quote:


  Originally Posted by *doobooloo* 
_Another question... ....
 So... I was wondering if I could use different caps of varying voltage levels for the six big cap spots. Specifically:

 8200uF/16V/105C or 22000uF/25V/85C for the 12V position
 2200uF/63V/85C for the 50V position
 8200uF/50V/85C or 4700uF/50V/105C for the 30/38V positions
_

 

The other thing I'd say is check the spec, in the RIFA range I was looking at the 63V variant had better specs (ESR, Iripple etc) than the smaller volt (same uF) rated caps in the same range, for marginal extra cost. I had similar ideas until I saw this and decided to go for all 63V.


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## doobooloo

Interesting read regarding temperature ratings and large can caps:

http://lists.contesting.com/archives.../msg00085.html

 Don't know if this still applies to lower-voltage caps, but what the heck 
	

	
	
		
		

		
		
	


	




 Oh, I just secured a bunch of 30mm dia 50V/10,000uF Nichicon LK caps for less than $2 a pop, so I'm going to use them for the five <50V spots and get some 63V or 80V Nichicon LK caps for the 50V spot. 
	

	
	
		
		

		
		
	


	




 Hopefully I'll be able to return the 12 200V/1000uF caps I purchased by impulse...


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## dgardner

Here's another transformer question. Instead of using one big torroid with two secondaries, couldn't two smaller ones be used?

 The AMVECO 70084 is 50VA with 2x18 @ 1388mA. Could the two secondaries be wired in series to get 1x36 @ 1388mA. Then just use two? Wouldn't this work? These are fairly nice looking and readily available off-the-shelf.


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## dip16amp

Quote:


  Originally Posted by *dgardner* 
_Here's another transformer question. Instead of using one big torroid with two secondaries, couldn't two smaller ones be used?

 The AMVECO 70084 is 50VA with 2x18 @ 1388mA. Could the two secondaries be wired in series to get 1x36 @ 1388mA. Then just use two? Wouldn't this work? These are fairly nice looking and readily available off-the-shelf._

 

Yes, you can use two of these toroidal trannies from digikey: 

 Two TE70083 or TE62083 50VA 2X15 and wire each for 30VAC then you have a 30V + 30V 100VA.

 Or use two TE70084 or TE62084 50 VA 2X18 for a 36V + 36V 100VA.

 Or use one TE70083 or TE62083 50VA 2x15 and one TE70084 or TE62084 50VA 2x18 and wire them for 33V + 33V 100VA.

 The TE70083 and TE70084 are PC board mount (solder pins) and are encapsulated and more expensive.

 The TE62083 and TE62084 are chassis mount (wire leads) with a single bolt.


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## Edwood

Available off the shelf, yes.

 Cheaper solution, no.

 Better solution, ?

 -Ed


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## catweasel

Toroids have high interwinding capacity passing all the crap on the mains. Better use a R-Core or a dual-chamber transformer fo audio.


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## dip16amp

Quote:


  Originally Posted by *Edwood* 
_Available off the shelf, yes.

 Cheaper solution, no.

 Better solution, ?

 -Ed_

 

The TE62083 and TE62084 are only $18.83 each but if you buy ten of them, they are only $16.74 each.


----------



## Edwood

Quote:


  Originally Posted by *dip16amp* 
_The TE62083 and TE62084 are only $18.83 each but if you buy ten of them, they are only $16.74 each._

 

Ah, I see.

 Nice.

 What are the Pros and Cons of using two smaller transformers in series vs. one large transformer?

 -Ed


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## digi01

here is my simple power supply for dynahi,I have remove the opa549 parts.


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## ble0t

Reminds me of your LM3886 supply...


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## z2trillion

If this is really off topic, I apoligize in advance. If I wanted to reduce the voltage on this power supply, what should I do? [Edit]Do I just change the values of the feedback resistors on the opamps? [/Edit] I assume I would also need to order different transformers than the ones being used for +/-30V.


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## dgardner

OK. So I built one of the MisterX Group Buy PSU boards up tonight and hooked it up to two dynahi amp boards. Did a few rough thermal calcs:

 PowerDis-regulator (each) = (Vin - Vout) * Iout
 PowerDis-opamp (each) = (Vin - Vout) * Iout

 So for each rail this means:

 I-input-ampboard = .350A each board on each rail * 2 boards for stereo.
 PowerDis-regulator = (50 - 38) * .700 = *8.4W* (each rail)
 PowerDis-opamp = (38 - 30) * .700 = *5.6W* (each rail)
 PowerDis-total = 2 * (8.4 + 5.6) = *28W*

 This puppy gets pretty hot. Using the angle bracket and one piece of the Surplus Sales heatsink that's been popular is probably not going to cut it without some help from the side panel.

 Popped a thermal couple on the LM338 tab and got a reading of *80C*. Anyone else have any results and measurements to post?


----------



## Edwood

Quote:


  Originally Posted by *dgardner* 
_OK. So I built one of the MisterX Group Buy PSU boards up tonight and hooked it up to two dynahi amp boards. Did a few rough thermal calcs:

 PowerDis-regulator (each) = (Vin - Vout) * Iout
 PowerDis-opamp (each) = (Vin - Vout) * Iout

 So for each rail this means:

 I-input-ampboard = .350A each board on each rail * 2 boards for stereo.
 PowerDis-regulator = (50 - 38) * .700 = *8.4W* (each rail)
 PowerDis-opamp = (38 - 30) * .700 = *5.6W* (each rail)
 PowerDis-total = 2 * (8.4 + 5.6) = *28W*

 This puppy gets pretty hot. Using the angle bracket and one piece of the Surplus Sales heatsink that's been popular is probably not going to cut it without some help from the side panel.

 Popped a thermal couple on the LM338 tab and got a reading of *80C*. Anyone else have any results and measurements to post?_

 

You think *two* of those Surplus Sales using an angle bracket would suffice?

 -Ed


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## drubrew

Here are some pics of what I have done. I bypassed using an angle/bracket to hold the heatsink. I had to trim the pc board to get this to work. But the result is less heat transfer loss. I have not hooked this up yet as I am currently hooked up to an alternate power supply design. So I'm not sure it is the perfect solution yet.


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## Edwood

dubrew: What electrolytic caps and value did you use for the amp board there?

 -Ed


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## Nisbeth

EDIT: Wrong board 
	

	
	
		
		

		
		
	


	





 /U.


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## dgardner

Here is my attempt at thermal analysis. No fancy tools. It looks like the PSU design's weakest point is thermal management on the LM338's. Correct me if I'm wrong, but you'll need to be very careful about heatsink selection. A sink with something less than 1 degree C / watt is definitely required to avoid maximum junction temperatures. Comments and abuse welcome... 
	

	
	
		
		

		
		
	


	




LM338 Worksheet (pdf)
LM338 Worksheet (excel)

 EDIT: Anyone using 38VAC secondaries is going to have a lot of heat to get rid of. (like me, doh!)


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## Nisbeth

Good work Dan 
	

	
	
		
		

		
		
	


	




 Did you (or someone else) calculate the minimum acceptable voltage that should be fed to the regulators. Playing around with the spreadsheet yields much more practical results if the 50VDC is reduced, but I'm not sure of how low I can go? Would it perhaps be possible to use an LDO regulator instead of the LM338 (such as the LM/LT1084)? 
	

	
	
		
		

		
		
	


	





 /U.


----------



## dgardner

Quote:


  Originally Posted by *Nisbeth* 
_Playing around with the spreadsheet yields much more practical results if the 50VDC is reduced, but I'm not sure of how low I can go? Would it perhaps be possible to use an LDO regulator instead of the LM338 (such as the LM/LT1084)? 
	

	
	
		
		

		
		
	


	


_

 

Funny you mention that. I looked around on the LM338 datasheet looking for the minimum dropout voltage, like you would see on a fixed output regulator. It really goes to show you that you should spec the transformer as *low* as possible. Try popping something like 42-45V input the spreadsheet instead of 50-55V and look at the favorable impact to thermal management. I'm working on the transformer, rectifier, filter math now...


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## dip16amp

Quote:


  Originally Posted by *dgardner* 
_Funny you mention that. I looked around on the LM338 datasheet looking for the minimum dropout voltage, like you would see on a fixed output regulator. It really goes to show you that you should spec the transformer as *low* as possible. Try popping something like 42-45V input the spreadsheet instead of 50-55V and look at the favorable impact to thermal management. I'm working on the transformer, rectifier, filter math now..._

 

The LM338 needs aleast two volts across it and the OPA541 needs at least three volts. A 30 VAC transformer will get about 40 volts DC to the LM338 and set the voltage to output 35 volts into the OPA541.


----------



## Nisbeth

Quote:


  Originally Posted by *dip16amp* 
_The LM338 needs aleast two volts across it and the OPA541 needs at least three volts. A 30 VAC transformer will get about 40 volts DC to the LM338 and set the voltage to output 35 volts into the OPA541._

 

With 40V to the regulator, the heat looks a bit more manageable 
	

	
	
		
		

		
		
	


	




 Additionally, 40V to the regulator (=30VAC transformer) would make it possible to use 50V electrolytics all round, right? (got a box of those lying around 
	

	
	
		
		

		
		
	


	




)


 /U.


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## dgardner

Here's the rest of the analysis. Hopefully, this is helpful to someone. I'm confident now that I did not waste my money on this board. I'm also confident I know how to use it with a dynalo as well.

 My Plitron 38Vrms scenario (bad!):
My 38V Plitron scenario (pdf)
My 38V Plitron scenario (excel)

 dip16amp - your scenario plays out quite nice. thanks for the help:
Best dynahi scenario (pdf)
Best dynahi scenario (excel)

 Dynalo 16.4v scenario (a cinch!):
Dynalo scenario (pdf)
Dyanlo scenario (excel)

 Please report bugs and errors via PM.

 EDIT:/
 still need to factor in partial loading on transformer based on percent regulation.
 still need to get a theta-jc for plastic power (guessed 4)
 still need to confirm power-diss equation for opa541. (guessed)


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## dgardner

Fixed a few errors and typos.
dynahi & dynalo applications (pdf)
dynahi & dynalo applications (excel)


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## Earwax

Quote:


  Originally Posted by *dgardner* 
_dynahi & dynalo applications (pdf)
dynahi & dynalo applications (excel)_

 

Thanks for posting your analysis. I think that's going to help me quite a bit.


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## drubrew

Here is the alternate Power Supply to try. Same torroid can be used in both the Gilmore design and this one.


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## drubrew

Here are some pics:




 The rest Are big so here are the downloadlinks:
http://www.moon-audio.com/Images/Dynahi/Dynahi1.jpg 
http://www.moon-audio.com/Images/Dynahi/Dynahi2.jpg 
http://www.moon-audio.com/Images/Dynahi/Dynahi3.jpg 
http://www.moon-audio.com/Images/Dynahi/Dynahi4.jpg 
http://www.moon-audio.com/Images/Dynahi/Dynahi5.jpg 
http://www.moon-audio.com/Images/Dynahi/Dynahi6.jpg 
 Enjoy Drew


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## amb

Sorry about reviving an old thread, but if anyone is still building a dynahi PSU, I found another vendor for a suitable toroidal power transformer:

 Sumner Technology: http://www.sumr.com
 Specifically, they have 80VA toroidal power transformers with 2x35V secondaries, available with a single 117VAC primary, dual primaries for 117/230V, or a multi-tapped "universal" primary that allows it to be used in a variety of countries.

 Check it out.


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## MisterX

You planning on ordering one T... err amb?


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## amb

Quote:


  Originally Posted by *MisterX* 
_You planning on ordering one T... err amb?_

 

I might... just sent them an email for a price quote.


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## DigiPete

Quote:


  Originally Posted by *amb* 
_I might... just sent them an email for a price quote._

 

Thanks for the link. I'd be looking into the 2x30V for the dynahi as well.

 I sent in for a quote on that one.

 DigiPete


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## Edwood

Will this toroid run a lot cooler?

 -Ed


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## amb

Quote:


  Originally Posted by *Edwood* 
_Will this toroid run a lot cooler?_

 

I doubt that this toroid itself will run cooler than others of comparable specs.


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## dgardner

I think the question is: Are you thinking about 35Vx2 or 30Vx2?


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## MisterX

Quote:


  Originally Posted by *amb* 
_I might... just sent them an email for a price quote._

 

Cool... let us know what you find out. [size=xx-small]♥[/size][size=x-small]♥[/size][size=small]♥[/size][size=medium]♥[/size][size=large]♥[/size][size=x-large]♥[/size][size=xx-large]♥[/size]


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## skyskraper

Quote:


  Originally Posted by *MisterX* 
_Cool... let us know what you find out. ♥♥♥♥♥♥♥ 
	

	
	
		
		

		
		
	


	


_

 

mickey mouse dots?


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## amb

OK, I got a response from SumR. The single-quantity price for the 80VA, single-primary 117V, 2x 35V secondary toroid is $34 USD. Seems very reasonable. It's going to cost $20 to ship to California, though. 
	

	
	
		
		

		
		
	


	




 I think I'm going to go the SumR route rather than the usual Plitron or a custom Avel-Lindberg.


----------



## DigiPete

Quote:


  Originally Posted by *dgardner* 
_I think the question is: Are you thinking about 35Vx2 or 30Vx2?_

 

Is there any concensus on whether or not a 30v 80VA torroid can power the Dynahi properly? Dgardner's spreadsheet says yes; has anyone actually used a 30v transformer sucessfully?

 Thanks
 Pete


----------



## DigiPete

Quote:


  Originally Posted by *DigiPete* 
_Is there any concensus on whether or not a 30v 80VA torroid can power the Dynahi properly? Dgardner's spreadsheet says yes; has anyone actually used a 30v transformer sucessfully?

 Thanks
 Pete_

 

Any thoughts? Anyone?


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## dgardner

Of course it works. I've built several with 30VAC transformers. All you really need to do is make sure that, under load, the input-output dropout is above the minumum on the LM338's and the OP541 power rails are a few volts above the output pin. As long as these minumums are met with some margin of safety, the PSU will run fine. If you put in the higher voltage transformers, it will only serve to lower the efficiency and raise the thermal dissipation on the 338's and 541's. The TO-220 and Plastic Power packages for these parts do not support unlimited thermal dissipation. If you keep the power dissipation for each part at around 4 watts each or less, life gets a whole lot easier. Try to make these part survive with 6-8 watts eachs gets real close to the edge. If you fry one of the LM338's you will likely fry your expensive OP541's.


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## amb

Digipete, for 30V secondaries, the post-rectified voltage is around 42V before taking diode drops, transformer load loss and AC line voltage variation into consideration. This doesn't leave much margin if you're going with the original Gilmore design where the first stage LM338 regulator's output is 38V.

 If you change the LM338 voltage setting resistors to make it output 35V then a 2x30V transformer would probably be fine. In this configuration the power dissipation of the LM338s and the OPA541s will be all reduced considerably.

 I am going with 2x35V secondaries and the original Gilmore voltage settings because I will have _plenty_ of heatsinking.


----------



## DigiPete

Dan and AMB,

 Thanks for your insights!

 Just started the Dynalo/mid. But I am thinking ahead to the Dynahi.

 Next challenge is the transistor matching... slightly off topic

 Should I match the Dynalo PNP and NPNs using the 2, 4.4 and 16 ma currents as would be found in the actual amp, and just tweak Rb to get those currents? Also, is a 16v supply the way to go (a must?), or would 9v be acceptable? Looks like I need some sort of bench supply.

 Thanks
 Pete


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## amb

http://www4.head-fi.org/forums/showthread.php?t=93115


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## DigiPete

Quote:


  Originally Posted by *amb* 
_http://www4.head-fi.org/forums/showthread.php?t=93115_

 

Thanks Amb,

 After re-reading that post, matching at the expected Ic seems to be the way to go, though it seems the hfe didn't change too much as a function of Ic.

 Would using the amp itself as the test rig for fine tuning work (measure the Ic's in circuit, and swap trannies until the Ic's are matched)?

 Pete


----------



## amb

Pete, I am replying to your questions in the transistor matching thread instead of here to stay on-topic, and also to keep the info easier to search.


----------



## amb

An update re: post #320 and #329 above, SumR has notified me two days ago that my toroid has been shipped (with UPS tracking number included). Each of my email inquiry to them were promptly and personally answered by the president Mr. Richard Sumner himself.

 I previously sent price inquiries to SumR and Plitron at the same time, and only yesterday did Plitron reply with their price quote: $61.61 USD each for the 80VA 2x35V model. Heh, this compared to SumR's price of $34 USD. Also, Plitron's lead-time is 4-5 weeks, whereas SumR was able to build my toroid as soon as my payment was received.

 Needless to say, I am very happy with SumR's service and price, compared to Plitron.


----------



## Tril

Quote:


  Originally Posted by *amb* 
_ Each of my email inquiry to them were promptly and personally answered by the president Mr. Richard Sumner himself._

 

 The same thing happened to me. Every email I sent was answered by Mr. Richard Sumner the day I sent them or the next day. I ordered a transformer last week and received it this week. That's fast. I'm very satisfied with the service I received from Richard Sumner Technology Inc.


----------



## DigiPete

Here is a question on tranformers for a Dynamite(might?) and grounding:

 Problem #1 I am using two Dynahi PSU's, I can get one 30x30V 250VA for $43 from partsexpress +ship ($10?)

 or two 30x30V 80VA for $34 ea + $25 shippping from Sumr

 Is the extra expense of using two smaller xformers worth it? What is the downside of using just one larger xformer to power both PSUs?

 --UPDATE-- Problem #1 solved. 2 @ 30x30V 80VA for $22.53 ea +10.5 ship from Avel 

 Problem #2 In the Dynamight, since there are 4 amp boards, what ground are each of them supposed to reference to? If the two left boards supposed to reference to the left PSU ground, and the right amp boards to the right PSU ground, should left boards be isolated from right boards ground wise?

 Are the amp boards supposed to be grounded to the chassis as well (this would mean losing independent L, R grounds)?

 Thanks in advance for any insights 
	

	
	
		
		

		
		
	


	




 Cheers
 DigiPete


----------



## dip16amp

Balanced headphones will not connect to ground so it doesn't make any difference. If you want to be able to to also use TRS unbalanced headphones then the left and right grounds must be connected together. The input grounds will be connected together at the source anyways.

 The chassis should be VAC safety ground and isolated from signal ground.


----------



## DigiPete

Quote:


  Originally Posted by *dip16amp* 
_Balanced headphones will not connect to ground so it doesn't make any difference. If you want to be able to to also use TRS unbalanced headphones then the left and right grounds must be connected together. The input grounds will be connected together at the source anyways.

 The chassis should be VAC safety ground and isolated from signal ground._

 


 OK. So... the input and output connectors (XLR and/or RCA) are isolated from the chassis (PSU and amp boards grounds float), and the A/C main ground is connected to the chassis.


----------



## dip16amp

Quote:


  Originally Posted by *DigiPete* 
_OK. So... the input and output connectors (XLR and/or RCA) are isolated from the chassis (PSU and amp boards grounds float), and the A/C main ground is connected to the chassis._

 

The PSU grounds have to be connected to the amp board grounds. They are just not connected to the chassis.


----------



## DigiPete

Quote:


  Originally Posted by *dip16amp* 
_The PSU grounds have to be connected to the amp board grounds. They are just not connected to the chassis._

 

Of course 
	

	
	
		
		

		
		
	


	




 , just trying to find out how the other grounding connections should be made.

 Thanks for your help 
	

	
	
		
		

		
		
	


	




 Pete


----------



## Tril

In the BOM, it's written :
 SINK PAD - 11 Pin Plastic Power - DIY

 That's for the 2 OPA541AP. I want to know if that size of pads exist or if it does not and you have to buy a big pad and cut it to the correct dimension.

 I've looked in digikey and mouser catalogs and I haven't found any pads big enough. There are probably at least some but I must have missed them.

 If someone knows parts numbers for this, please share them with me.


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## amb

Tril, you can use Digikey part number BER107-ND which is pre-cut, or buy a big sheet of the stuff and cut to size yourself.


----------

