[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?