I murdered my ICEpower module -- AGAIN!

[xtian]

*bad words*

ICEpower 50ASX2BTL: https://www.parts-express.com/icepower- ... w--326-214

I'm building out a PR chassis with a 170w ICEpower amp module for my buddy who plays cello. I tested it successfully with guitar > ICEpower > 8 ohm speaker. This worked fine, though the guitar needs a preamp to push the power amp hard enough. So I added a tiny preamp module, at first attempting to power it with the 24vDC accessory output from the ICEpower module--this caused the preamp module to malfunction. But I didn't burn it up, so I tried again by powering it with a 9v battery, and this all worked very nicely. Good, strong signal going into the ICEpower.

OK, days later, I finally received some DC-DC buck converters, so I can drop the 24v accessory power down to 9v for the preamp module. I connected the DC converter to the ICEpower 24v first, and set the output voltage to 9v via the trimmer, measuring with my meter. All good. Then I wired in the preamp board, plugged in the speaker, and powered up. POP, pop. No more output. My 24v supply is now dead, though the -24 supply is still working.

I checked and rechecked my wiring--no errors, no poliarity reversed. What the heck did I do?

The only thing useful I can find in the ICEpower PDF is the 24v supply is protected by 400mA fuses--those fuses measure OK. There is NO other information about test points, and I know better than to poke around blindly in a switch mode PSU.

[xtian]

I got out my bench power supply and hooked up the DC buck converter and the preamp board. They draw 20mA at idle. So, current draw is not the issue.

I swear I didn't short anything out! I hate an expensive mystery.

[JazzGuitarGimp]

Let that be a lesson to ya, sonny! We’re here to build TUBE amps, from input to output! I wish I had some advice for you, though. It does seem weird that the 24V supply fuse is good, but the power supply itself seems to have died. Let us know what happened when you get it sorted out, please.

Ciao,
Lou

[pompeiisneaks]

sometimes it can be about where you make the common connections, and they need to be isolated from other parts of the circuit.. if that makes sense...

If it's dead, you can send it my way and I can try to do a post mortem... I've played with and fixed a few SMPS.

~Phil

[xtian]

Phil, I was very careful about not ganging grounds. Nothing is connected except as required by the modules.

Lou, I found an open fuse, I think. I'll carry on tomorrow, but only if the sun shines. What am I saying. It's August in California.

[pompeiisneaks]

Sorry just throwing something out there. Glad you found a fuse. Hope it's all well. (I was only kidding about sending it my way )

~Phil

[pdf64]

Dc to dc converter to drop a few Vdc? You do like a high tech solution!
Is a dc blocking cap between pre and power modules required?

[R.G.]

As PDF says - a buck converter for 20ma??? Why not use a 7809?

[xtian]

I bypassed the burned fuse and powered up with variac. All went smoothly. I have my 24v accessory voltage back, and the ICEpower module is working again.

@PDF: Something caused a hard current draw. Blocking cap sounds like a good idea. The largest non-polar cap I have is 3u3. Will that work? Do I just need to block the +signal and not the signal ground?

@RG: Buck converter costs $3, looks tidy and professional, allows me to vary voltage (I haven't settled on a preamp module yet).

To avoid blowing the fuse (or the circuit!) again, I can add series resistance to limit current, right? 27v = 200mA x 135 ohms (5.4w)

[pdf64]

p26 of the data sheet indicates that there’s a dc blocking cap built in.

[R.G.]

@RG: Buck converter costs $3, looks tidy and professional, allows me to vary voltage (I haven't settled on a preamp module yet).

OK. I understand wanting to look tidy and professional. I'm always messing up and going for "works good" first, then finding I have to redo it.

Of course, you could use an LM317, TO-220 package, programmed with two resistors for any voltage between 1.25V and the max voltage for the device, 30+ volts. It internally current limits to ~1A, and can be rigged to current limit below that.

[drew]

I'm building out a PR chassis with a 170w ICEpower amp module for my buddy who plays cello.

Don’t tell me, let me guess, this is one of those string quartets where the viola player trades up from a Super Reverb to a Dual Showman, then the cellist just *has* to get something even louder? How many times have we all seen this play out.

[xtian]

You jest. And yet... I played acoustic guitar thru a pair of Mackie SRM450s, and my buddy played his cello (piezo pickup, also mixed thru Mackies). I had to turn him off. I coudn't compete with the acoustic volume from the cello. Those classical instrument makers already fought the volume war!

[xtian]

In our last episode, I popped the onboard 400mA fuse protecting the 24v aux supply. I replaced the fuse, installed a different preamp module (one that's happy with 24v), and all was well.

In THIS episode, I tried to implement the Enable (mute) function by grounding the Enable pin. Now the amp is silent even with Enable function back to normal, and amp is drawing 90+ watts, getting very hot, with no signal applied (normally, it draws, like, 6 watts at idle). Damn!

From the datasheet, p.23: "The enable pin can enable/disable the amplifier. If the pin is left unconnected, then the level is high (+5V) and the amplifier is enabled. If the pin is pulled low (0V) externally, the amplifier will be disabled."

Did I mess up? Should I have used a pulldown resistor instead of grounding the pin directly?

[pompeiisneaks]

I know I've seen quite a few controllers requires a pulldown, but I think it's stupid of the manuf to not specify that in the directions. I know I've burned up an arduino because I didn't have a pulldown resistor, I think some later versions of the arduino have them built into the chip, but it's not always the case.

~Phil