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spritzer

The Multi Amp aka Dynalo Mk2

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Yes, I had considered doing this (insert DMM in amps mode in place of fuse) in order to estimate bias (@15mA should be 4 * (4 * 15) or ~240mA + a bit for the other circuitry). I thought this way I might be able to estimate the bias with heatsinks attached. Sound reasonable?


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3 hours ago, rumina said:

my smd dynalo starts at 27 watt and gets stable at around 30 watt, near the max wattage of the two trafos. But its nice that the trafos are protected, i think bevor the amps overheats/runs away the trafos shut down at 115% (~35 watt). So no need for a thermal saftey switch i used in some pass amps i made.

 

Very interesting this "protection" system.

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Sounds ok, i use 20-30 % efficiency for class a amp after power supply. but that is a crude gess, good to take the magic appart from 20 watt class a amps with a mini powerbrick.

the two mean well irm-15-24 trafos have a build in protection for short, overload and over voltage http://www.meanwellusa.com/productPdf.aspx?i=681#1

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Ran a test after taking one amp back to its original config (402R, LTST-C170CKT and 255R bias resistors). I placed an ammeter in place of the fuse, and ran it for 30 minutes when it was no longer increasing. It showed a max of 245mA AC (is that RMS?). I checked the bias on this one and it was right around 15mA (300-315mV). I then installed the heatsinks and did the same test. Current draw had dropped to 235mA at a stable condition. So my theory: having the heatsinks on seems to reduce the transistor temperature a bit, resulting in lower current draw (a bit). For these two tests I was not able to have the top in place but did set it there as best I could.

Edited by Pars
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Thanks for the measurements - similar then mine ~26 watt with open lid, will rise a little with closed lid but i thinks thats should work fine as mine (i use the group buy case).

do you mean rms in terms of pmpo (or pure mystic power output 😉 )? then no - it's simply the overall power consumption of the amp.

rms would go something like= max watt out transformer - powerloss transformer (here 18%)  - powerloss regulator  (how efficiency are those regulators?) - powerloss transistors/cricuit design.

i don't like these rms values, take a big switched power supply, add some beefy mosfet and you get big fat rms values, sounds like shit and do to boooooommmmmm

 

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Yeah, just seems like the AC voltage measurements on the Fluke 89 at least are RMS. I used my bench HP 3269 or whatever it is for this though.
I was just trying to correlate the AC current draw with the DC biasing conditions but I can see that would get into a fairly complex calculation involving factors you mentioned and more probably.
Just knowing the current dropped with the heatsinks in place was enough confirmation. And 10mA AC is probably more significant that it seems.


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Something I noticed in the mini BOM was that the power switch listed (8161SH9AV2BE2) isn't rated for AC power duty. Instead, use either the "G" or "Q", which are both rated for 120/250VAC.

Use 8161SH9AV2GE2 or 8161SH9AV2QE2 instead. Mouser stocks the "Q".image.png.bcc7bf3263726ec99df4ece7832143c1.pngimage.png.c860df35c2d7f6c298bc5079b6f92fae.png

Edited by Pars
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