[cgrums]

Quick question:

I'm about to pull the trigger on an Avel Lindberg 50 VA 2x25V Toroidal. I've read the Dynamid doesn't draw more than 800 mA...am I alright with this X-Former?

http://www.avellindberg.com/transfor...ange_specs.htm

(I'm looking at the Y236206)

 

[amb]

2x25V secondary is too high for a dynamid/dynalo. 2x15V or 2x18V is more like it (depending on which PSU you use). Any higher and the PSU regulators will dissipate too much unneeded heat.

50VA is quite sufficient.

 

[cgrums]

Quote:

Originally Posted by amb /img/forum/go_quote.gif 2x25V secondary is too high for a dynamid/dynalo. 2x15V or 2x18V is more like it (depending on which PSU you use). Any higher and the PSU regulators will dissipate too much unneeded heat. 50VA is quite sufficient.

Thanks AMB! I'm actually thinking of using your sigma 22...so should I be looking at more along the lines of the Y236204 (50 VA 2x18V)?

 

[amb]

Quote:

Originally Posted by cgrums /img/forum/go_quote.gif Thanks AMB! I'm actually thinking of using your sigma 22...so should I be looking at more along the lines of the Y236204 (50 VA 2x18V)?

Yes, that'll work nicely.

 

[cgrums]

Quote:

Originally Posted by amb /img/forum/go_quote.gif Yes, that'll work nicely.

Great. I've come up with yet another question (what would I do without you guys?

)

I've been reading AMBs instructions for building the sigma 22: http://www.amb.org/audio/sigma22/

R9 and R10 together set the positive output voltage which the negative rail in turn tracks. I understand why R9 has to be left alone and so I've settled on R10 = 5.76K and I'll use the 6.0V diode. This should give me ~ +-16.38V which is as close as I can get to the 16.4V I see people dialing the Dynahi PS down to for use with the Dynalo/mid.

In choosing the transformer I originally went with my 2x25V secondary rating after reading this paragraph off AMBs site:

"For other output voltages, a rule of thumb for this PSU is that approximately 9V-10V drop should be maintained across the pass MOSFETs under load. This allows for the 4V Vgs of the MOSFETs plus about 5V of headroom to allow for line voltage fluctuations. Using the ±15V output as an example, the pre-regulator voltage should be 24V. Accounting for a couple of volts drop across the rectifier diodes, that figure goes up to 26V. The transformer voltage should be 0.707 times that of the rectified DC voltage, so 26V * 0.707 ~= 18V. Thus, a dual 18V or a 36VCT transformer should work well."

My math goes like this:

16.4V + 9V (MOSFETs) + 2V (recitifier drop) = 27.4V

To get AC: 27.4V*.707 = 19.37V

Taking all this into account, is the 50VA 2x18V transformer going to be able to supply enough of a potential for each rail?

Edit: I notice that Plitron makes a nice 50VA 2x20V which would seem to work better here...is that still going to be too much for the PSU circuit?

 

[amb]

Considering that you won't be operating the transformer at its full load rating, the actual secondary voltage will be higher than the spec, so you'll still have plenty of "headroom" left for line fluctuations, so the 2x18V secondaries will be fine.

While your calculation for ±16.4V is fine, there is no requirement that you run the amp exactly at that voltage. ±15V is also good, and that is what Headamp uses for its Gilmore Lite (same circuit as dynalo).

 

[Paragon]

A 35VA 22V 1.59A torroid will output almost 35VDC at idle hooked up to the original Dynalo PS that Kevin designed. This is on 117V mains. I might possibly change to a lower transformer depending on voltages and heat when running an amp.