Beta22!

School is almost over for the winter semester and i can get back to working on my beta22 amp! WOO!

Excited!!

SCHOOOOOL'S OUT FOR SUMMER!! I've been busy and I'm ready to run a test.

Quick Q: what fuse rating should I use for a three-board setup running at 30V? Fuse will go at the primary of the power traffo.

Thanks!

Right, okay, so I built my supply to +/-30VDC. At first I fired it up, the LED didn't light, so I flipped it around and re-tested--a-okay! Light lit up and I measured roughly +/-20VDC (+/-18.75VDC~ish each rail), which was weird.

AH! R10 is 10K, oops! Okay, so I swapped out R10 for a 6.81K resistor (which is weird, because one is missing from the five I ordered already). Retest--still roughly +/-20VDC. Maybe it needs a load?

Loaded up each rail with a 50R/50W resistor. Still, I'm reading roughly +/-20VDC.

All the other parts are good. I've flipped one of the secondaries around (with minimized my VAC to the spec) and still the output isn't near the designed +/-30VDC.

My transformer puts out 38VAC unloaded on the secondaries, they're spec'd for 30VAC. (it's a Plitron 077017201 traffo, 300VA rating)

Thoughts??

Morning! For some reason I couldn't reply last night: I'll get to testing later on today, I was just curious if anyone else had come across this problem before.

KnightOfAwesome: I saw that on the AMB website, I'll get to that later today.

johnwmclean: According to the PDF KnightOfAwesome posted, I should be seeing 11.98V; I'll check that after breakfast.

Well, now, it looks like my negative rectified voltage is -0V--that can't be terribly good!!! Bad diode? Bad wire clamp? Bad solder joint? I measured the voltage off of the tabs of the diodes; two read +42VDC and two read zero; the secondaries are okay, which logically means that it's the wire clamp or the joint at the clamp. It's not some weird phase-interactions (unless I'm looking at the modial interaction of magneto-reluctance and capacitive directance going on)* because I reversed one secondary and retested to find the same results.

*edit* This is what happens when I don't get my morning Shreddies (I had frozen waffles)--alright, two diode tabs are ground and two are the rails, + and - 42VDC (actually, +/-45.4VDC) (further edit: other other two are the + input rail; maybe I need to make myself some coffee, I'm thoroughly embarrassed at this point.), which means it's all good in the hood up until the small signal diodes start to play with the signal. Ignore the "-0" on the negative input rail in the picture, it's early in the morning. Stay tuned!

I'm mapping out which points under the board I have to tap to get the other voltages that I haven't circled.

I guess it makes sense now why it's outputting 20V--it's taking all the voltage it's being given (~40V) and making the best of it! sigh. At least nothing's blown up, but those load resistors are getting toasty; I should find a heatsink to mount them on.

Thanks for the eyes, guys.

*http://en.wikipedia.org/wiki/Turboencabulator

Quote:

Originally Posted by amb 

Since your negative side unregulated voltage is 0, somehow the transformer secondary voltage isn't coming through.  Check the electricals contact at the terminal block where the transformer wires are connected to the board.  Some transformers have wires that are enamel-coated, and need to have the stripped ends scraped and tinned in order to make proper contact.  What transformer are you using (link to datasheet, if possible), and what color wires went where?  Post a pic of your board if possible.

That was an error on my part, the unregulated voltage was going through, I just made a bad assumption while not in the right frame of mind. I was reading the voltages at the tabs of the diodes and assumed that two tabs were (+) and the other two were (-), which turned out to not be the case, since what I took to be the (-) rail was actually the ground rail. Testing the legs of the diodes confirmed that I was incorrect initially.

All fixed! Found a backwards lytic cap (C9; a stubby amongst giants, too). I flipped it back around the right way and everything's peachy, look at +29.83/-29.89 rails. :D

Here's an early photo of my board--you can just see the gold line indicating the negative leg, and that it's facing the wrong way relative to it's taller mate in front of it.