[blueworm]

mini^3 powa

 

[morsel]

175mA is definitely too high. Typical current draw using 2 9V batteries is around 50mA. Something must be getting warm.

 

[Filburt]

I'd check for DC offset and mild oscillation.

 

[amb]

Quote:

Originally Posted by Cedman What I would like to find out is how I fired it, did I fired it by pluging it in or by turning it on? I guess the real question is, can I turn on the Mini³fy PINT while the wallwart is plug in? or is that straightly for changing only when I uses the W+ and W- connection?

The opamp was damaged when you turned on the power with all un-isolated jacks. That configuration short circuits the output of the rail splitter (virtual ground) to its V-, which, when power is applied, means a rather quick AD8397-death.

If the jacks are properly isolated, then yes, you can use the PINT while it's charging. The wallwart supplies power to the amp via D1 rather than the batteries when it's plugged in (D2 is reverse-biased at this point because the wallwart's voltage is higher than the batteries').

Quote:

Another problem I was having was that my led doesnot work, it only flashes once when I turn on, but never stayed on, maybe I need a different size RLED? I'm only using a single 9V NIMH. the led does stay on when my groud chip is toasted ...

The Rled + LED combination spans the rails, and has nothing to do with the ground chip... something is weird.

Quote:

Originally Posted by Heady I have just finished a mini3-fied PINT and it sounds great. Only thing is that its current draw seems to be high, at about 175mA.

That's too high. A properly functioning amp with two AD8397s should draw in the neighborhood of 50mA (plus and minus a few). Is your DMM accurate?

 

[Heady]

Quote:

Originally Posted by Teerawit What are your DC offset readings?

That's the strange thing, they are in the range of 0.1 mV, isn't that in the good range? And the opamps are not hot, I have an infra-red thermometer which I used to measure the temperature, the opamps are only 38degrees at the most.

Edit - ok, the amp is oscillating. With no music playing, the opamps get warm in a couple of minutes, about 48 degrees celcius.

Quote:

Originally Posted by amb That's too high. A properly functioning amp with two AD8397s should draw in the neighborhood of 50mA (plus and minus a few). Is your DMM accurate?

How would I test a DMM for accuracy? I have absolutely no idea.

Thanks to all for the replies, hopefully will find the cause soon.

 

[nysulli]

first off, thanks to tangent, amd, and morsel for their replies to everyone and the instructions on how to minify the pint, with the help of this thread i just finished up my first amp, a minified pint, which sounds amazing, everything worked great without any fidling, amp has a gain of 3, powered with 2 8.4v NiMH 270mah batteries, dc offsets for IG to OG, OG to OR, and OG to OL are all under 1mv with a 50000 count DMM (high end extech, its nice to work in a lab

)

when i'm done enjoying my new amp, maybe i'll post some pictures, but for now, back to the music, i can hear my HF-1's calling for me

 

[amb]

Quote:

Originally Posted by Heady How would I test a DMM for accuracy? I have absolutely no idea.

Here is one way. First, get a known, good 9V battery, measure its voltage so you know whether the DC volts function of your DMM works. This doesn't tell you whether your DMM is dead-on accurate, but at least you'll know it's within ballpark.

Then, switch your DMM to DC mA mode and connect it in series with a 180Ω 1/2W resistor, then power the meter + resistor combo with that 9V battery. You should read approximately 50mA on your DMM. (9V / 180Ω = 0.05A)

The resistor will get warm and your battery will begin to drain, so don't do this for too long.

 

[Filburt]

Okay, so I did a mini3'd PINT...

I'm getting about 4,0mw on IG to OL and 6,0mw on IG to OR...this seems a bit high. IG to OG is 0,8mw.

The ground amp gets pretty hot. It hurts my finger to hold it on there.

I tried playing audio through it, and it sounds okay to me. I don't hear distortion. I'm wondering if maybe it's some mild oscillation. Maybe I should get some different ferrites...

 

[amb]

Quote:

Originally Posted by Filburt I'm getting about 4,0mw on IG to OL and 6,0mw on IG to OR...this seems a bit high. IG to OG is 0,8mw.

You mean mV of DC offset, right? Those are reasonable figures.

Quote:

The ground amp gets pretty hot. It hurts my finger to hold it on there. I tried playing audio through it, and it sounds okay to me. I don't hear distortion. I'm wondering if maybe it's some mild oscillation. Maybe I should get some different ferrites...

Measure the current draw of your amp. If it's around the expected ~50mA, then it's ok. If it's much more than that, then you do have an oscillation somewhere. Did you do the cut/jumper pcb modification at the ground opamp output to take the ferrite out of the feedback loop?

 

[Heady]

Quote:

Originally Posted by amb Here is one way. First, get a known, good 9V battery, measure its voltage so you know whether the DC volts function of your DMM works. This doesn't tell you whether your DMM is dead-on accurate, but at least you'll know it's within ballpark. Then, switch your DMM to DC mA mode and connect it in series with a 180Ω 1/2W resistor, then power the meter + resistor combo with that 9V battery. You should read approximately 50mA on your DMM. (9V / 180Ω = 0.05A) The resistor will get warm and your battery will begin to drain, so don't do this for too long.

Thanks amb, now I've got to look for and buy a 180ohm 1/2w resistor.

 

[Filburt]

Quote:

Originally Posted by amb You mean mV of DC offset, right? Those are reasonable figures. Measure the current draw of your amp. If it's around the expected ~50mA, then it's ok. If it's much more than that, then you do have an oscillation somewhere. Did you do the cut/jumper pcb modification at the ground opamp output to take the ferrite out of the feedback loop?

Yep, I did exactly as you instructed, and used my multimeter to check if the connection had been cut.

And yes, I meant mV. Sorry, I'm a bit fuzzy headed today

 

[Filburt]

Okay, drain is at ~85mA, so I guess some oscillation is present. How shall I tame it? I only have one type of ferrite, but maybe I should try a fresh one? Note that the L/R op-amp doesn't get particularly warm.

 

[amb]

Quote:

Originally Posted by Filburt Okay, drain is at ~85mA, so I guess some oscillation is present. How shall I tame it? I only have one type of ferrite, but maybe I should try a fresh one? Note that the L/R op-amp doesn't get particularly warm.

Is your headphone cable connected when you checked the quiescent current? If so try unplugging it. If that makes the current go down, then the cable capacitance is too high and causing the instability. You will either have to use beefier ferrites, reduce the headphone cable length, or both.

If the cable is not connected when you checked the current, then the ferrite shouldn't be the issue. Perhaps take some good pics of your build, with clear images of the top and bottom of the pcb and the wiring to the jacks and post them here?

 

[Filburt]

Quote:

Originally Posted by amb Is your headphone cable connected when you checked the quiescent current? If so try unplugging it. If that makes the current go down, then the cable capacitance is too high and causing the instability. You will either have to use beefier ferrites, reduce the headphone cable length, or both. If the cable is not connected when you checked the current, then the ferrite shouldn't be the issue. Perhaps take some good pics of your build, with clear images of the top and bottom of the pcb and the wiring to the jacks and post them here?

No cable was connected. It did occur to me that capacitance may be an issue, so I didn't connect it.

I'm not sure what would be objectionable on the build. If anything, it's the cleanest one I've done thus far, even cleaner than the one I did for my perfectly working 8397/6172 hybrid. What should I look out for? I used a very small piece of resistor lead to connect the two pins on the ground op-amp, but it is the one messier portion of the build. Should I just bridge them with some solder?

 

[amb]

Quote:

Originally Posted by Filburt I'm not sure what would be objectionable on the build. If anything, it's the cleanest one I've done thus far, even cleaner than the one I did for my perfectly working 8397/6172 hybrid. What should I look out for? I used a very small piece of resistor lead to connect the two pins on the ground op-amp, but it is the one messier portion of the build. Should I just bridge them with some solder?

It's ok to use a small piece of resistor lead for the jumpering.

I am not certain what might be the problem either, but having more eyes to look at the board is never a bad idea...

Btw, what ferrites did you use?