[patricklang]

After running through multiple sets of 9v's in the first month after adding additional buffers to my meta42, I decided it was time for a power supply.

I'm using a surplus +24v dc brick I found, followed by an extra regulation stage based around an LM317, nominal output of 19.4v after regulation.

When I built this last week, it tested fine and was playing great for 10 mins or so. I did not have time to enclose it, so I let it sit until this weekend. I plugged it in this weekend, and no sound. My power rails are stable, 19.4v as expected, the LM317 is cool to the touch, so the current is low. My power LED is on, but I get no sound. As I power the amp off, I get a split second of sound.

My first guess was that I was using too much voltage for the AD8066. According to the specs, Vcc-Vee <= 24 v, so my 19.4 should be just fine. My power caps on the meta are panasonic fc, 10v electrolytic, so within proper bounds. While powered on, no chips heat up, I do not see anything strange anywhere.

My next thought was that my power brick may not be isolated. If this was the case, I would expect that my power LED on the meta would be off, but on second thought, this may not be the case since it is not powered by the TLE2426. So I tried my battery powered portable cd. I get the same results - no sound except as its powering down.

I'm boggled - what should I check next? The amp is not fried, it still works off a pair of 9v's in series.

 

[patricklang]

Well, I know exactly what's wrong, just not whats causing it. I have no source hooked up, just the amp and a pair of cheapo headphones.

With my power supply connected, I'm seeing +19.4v at vs+ on the 8066, and 0 at vs-. Definitely a problem.

With the voltage correct at the LED, my polarity is correct (plus I'm not hitting the crowbar diode, otherwise I'd have some heat at the lm317).

 

[amb]

Seems like your power supply's V- is shorted to signal ground.

 

[aeriyn]

Quote:

Originally Posted by amb Seems like your power supply's V- is shorted to signal ground.

Solution? Isolate the power jack so it doesn't let the metal case go to V-. =P

 

[robzy]

Quote:

Originally Posted by aeriyn Solution? Isolate the power jack so it doesn't let the metal case go to V-. =P

Hehe.... does this fix it?

Rob.

 

[aeriyn]

Well signal ground shorts across V- when the output jacks or the power jack is not isolated because power jacks tend to ground to the case (touching the metal). If he were to isolate either the output or the power jack, it would probably fix this. Unless he has something hooked up totally whacked, this is the only way I can think that V- would get tied to the signal ground, especially since it works with batteries just fine.

 

[patricklang]

Yep, that's it. Makes sense. When I tested it, the jack was not yet mounted. I've spent the last hour studying the PCB and schematic, when the problem was the case

Ok, now to isolate the power jack. Both my input and output jacks are grounded to the case.

Anyone know of isolated power jacks?

 

[MisterX]

Got a pair of plastic washers around the house?

If not try this---> http://www.mouser.com/index.cfm?hand..._pcodeid=01603

 

[patricklang]

Found some thin mylar washers at Lowe's, its working great. I knew I was missing something stupid.