[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.

 

[13405]

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.

 

[13405]

[deleted]

 

[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?