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Some LME49600 implementations - Page 14

post #196 of 291
Thread Starter 
Quote:
Originally Posted by Avro_Arrow View Post

Just for reference, "The Wire" runs at +- 15 volts and the LME49600 in wide band.

 

I wonder how hot they run?

 

That's kind of irrelevant. I was suggesting that changing the BW might have an effect greater than would be expected on the basis of the current in the BW pin, which would be a clue that it was oscillating.

 

You have to consider then in what configuration it might run OK, say with a LME49710 or, dare I say it, an NE5532. There's nothing to suggest that the OPA211 is any more likely to be the cause. I'll check the math on the servo. 

 

I've got 4 more 49600s arrived. I guess I'll have to build another one before I respin the board.

 

w

post #197 of 291

you know it doesnt have to be all or nothing right? you can connect to the rail via a resistor to calculate a bandwidth somewhere between the low iQ mode and wide BW mode

post #198 of 291
Thread Starter 
Quote:
Originally Posted by qusp View Post

you know it doesnt have to be all or nothing right? you can connect to the rail via a resistor to calculate a bandwidth somewhere between the low iQ mode and wide BW mode

 

For the moment I've just suggested this as an experiment which might affect the amplifier's propensity to oscillate, which hasn't been demonstrated yet. Avro_Arrow's build seems to be running hot, but we don't know why. Mine isn't running hot and doesn't look unstable within the limits of tests I have been able to apply, my scope only runs to 60MHz.The current drawn by mine corresponds closely to expectations, Avro_Arrow's is ~ +15mA. A more reliable indication of oscillation would be a drop in current draw when the loop is broken by lifting a pin, e.g the input pins on one or both of the 49600s, but obviously this will only have an effect if the amp is oscillating.

 

w

post #199 of 291

I removed the jumpers and put the LME49600 into low Iq mode.

As expected, they run cooler, however, the LME49990s still run hot.

 

Current draw on each rail (relay energized) is 85 mA

post #200 of 291

I ordered an infrared thermometer so maybe in a few days I will be able to give you an exact temperature...

 

Just for laughs I put my meter on AC and tested across the output with no signal.

It read zero. Even if it is oscillating, I doubt the frequency response of my meter

would pick it up anyway.

post #201 of 291

I put a little work into the amp yesterday, hoping to get more done next weekend.

post #202 of 291

I got all the smd parts on.  Just need another evening to finish it up.

post #203 of 291

Missed a few parts on my first order, but I'm slowly but surely getting there on my board.

post #204 of 291
Quote:
Originally Posted by tcpoint View Post

I got all the smd parts on.  Just need another evening to finish it up.

 

Quote:
Originally Posted by Nebby View Post

Missed a few parts on my first order, but I'm slowly but surely getting there on my board.

 

What are you guys using for a power supply?

post #205 of 291
Thread Starter 
Quote:
Originally Posted by J-Pak View Post

 

 

What are you guys using for a power supply?

 

I have a selection of AC wallwarts, 12, 15 and 16V. The 12V is just sufficient to get 13.75V after the regulators because it is good for 1A and probably runs a bit above the 16.95V peak that it should produce when loaded. (In my case) there is 1.7V lost in the 2 10R resistors in the CRCRC filter in the onboard PSU, and the regulators require 2V to maintain regulation. For a loaded 12V wallwart this would be 16.95 - 1.7 - 2 = 13.25V, half a volt below what the regulators are set to, but as I said, a lightly-loaded wallwart probably runs at least 0.5V hot.

 

The 16V wallwart still works, but the regulators run pretty hot. One of the things I thought of doing is dismounting the regs from the board and mounting them to the case and bringing wandering leads to the board. Insulating kits (washers) would be required and 3-pin headers on the board with mating plugs would simplify assembly. That said, I've run the amp on 16VAC, boxed up, for several hours. The box gets warm, but it didn't kill the amp.

 

post #206 of 291

I have some of these laying around in various voltages. They are pretty common...their normal use is to power security systems and fire alarms.

 

Quote:
Originally Posted by J-Pak View Post

 

 

What are you guys using for a power supply?

post #207 of 291

OK, here are some numbers.

 

Ambient temperature 28c.

 

After about ten minutes at idle (volume control zero),

LME49990: 51c

LME49600: 54c

LM3x reg  : 55c

 

OPA211   : 45c (probably being heated by the LME next to it.)

post #208 of 291
Thread Starter 

OK, ~25 over ambient is not unreasonable, obviously lower would be better but it doesn't indicate that the devices are likely to fail. The 49990 is rated for continuous short circuit and the 49600 has thermal limiting. The layout is compact and some compromise in terms of running temperature is inevitable.

 

The principal concern remains that the amplifier as a whole is oscillating, so anything you can do to clarify the situation one way or another would be welcome.

 

w

post #209 of 291

I tried disabling the servo by removing R4, 5 and 6.

No change.

Offset without the servo was 0.5 mV.

 

I tried bypassing the LME49600 by lifting pin 2 and 4.

Jumper from Pin 2 to R14 to maintain the feedback loop.

No change.

 

I would have to conclude by this point that it just gets hot.

Live with it.

 

It will be interesting to hear other peoples results.

post #210 of 291
Thread Starter 

Thanks for making the effort. It seems the amp is working correctly, if running a bit hot.

 

I'm certainly not unhappy with the SQ of mine.

 

Hopefully someone else will complete one soon.

 

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