PINT Problem

[FallenAngel]

Thanks, I'll install the ELNA 25V when it gets in, for now I'll try using a single 9V and see if that works, hopefully didn't burn the Cap up. But that's exactly what I'm thinking happened to my second one since the opamp in that one gets to like burning hot in 1 second flat.

Well, I tried running the PINT with a single 9V battery and the results are still very similar. The DC offset on both channels is 1mV at low volume and goes up to around 9mV at full blast.

The oscillation is still there though, current draw starts with 35mA but jumps to over 100mA within a second or two and steadily increases. Running lower and lower on ideas, but we'll see what happens after changing Caps and yet again checking all solder joints. Oh the joys of DIY.

 

[SubRosa]

I did up a PINT tonight and I ran into some problems. Firstly, I was getting a large amount of DC Offset, 2.5V on L/R, but then I realized I forgot to jumper the two pins on the ground op-amp (my PINT is Mini^3'fied) and that fixed that problem. DC Offset went down to 1mv on both channels, woohoo -- not quite. I tested some cheap headphones and used my iPod as the source and everything sounded OK, no distortion, no hissing or crackling...until I turned the volume up. The sound cut right out and then returned in cracks. Have any suggestions as to what the problem may be? Chips stay relatively cool and I have an AD8397 for L/R and an LM6172 in ground, gain set to 4.

PS: I cannot measure current draw with my DMM for some reason so I'm in the dark on that.

 

[mb3k]

Quote:

Originally Posted by SubRosa I did up a PINT tonight and I ran into some problems. Firstly, I was getting a large amount of DC Offset, 2.5V on L/R, but then I realized I forgot to jumper the two pins on the ground op-amp (my PINT is Mini^3'fied) and that fixed that problem. DC Offset went down to 1mv on both channels, woohoo -- not quite. I tested some cheap headphones and used my iPod as the source and everything sounded OK, no distortion, no hissing or crackling...until I turned the volume up. The sound cut right out and then returned in cracks. Have any suggestions as to what the problem may be? Chips stay relatively cool and I have an AD8397 for L/R and an LM6172 in ground, gain set to 4. PS: I cannot measure current draw with my DMM for some reason so I'm in the dark on that.

Maybe it's as simple as replacing the battery?

 

[SubRosa]

Quote:

Originally Posted by mb3k Maybe it's as simple as replacing the battery?

I tried a rechargeable and three different alkalines, all checked with my DMM at around 8.6V, which I would think would be fine. I'll add another battery.

 

[[AK]Zip]

Quote:

Originally Posted by SubRosa I tried a rechargeable and three different alkalines, all checked with my DMM at around 8.6V, which I would think would be fine. I'll add another battery.

8.6v is ok. I would look elsewhere for your problem.

-Alex-

 

[Filburt]

Quote:

Originally Posted by SubRosa I did up a PINT tonight and I ran into some problems. Firstly, I was getting a large amount of DC Offset, 2.5V on L/R, but then I realized I forgot to jumper the two pins on the ground op-amp (my PINT is Mini^3'fied) and that fixed that problem. DC Offset went down to 1mv on both channels, woohoo -- not quite. I tested some cheap headphones and used my iPod as the source and everything sounded OK, no distortion, no hissing or crackling...until I turned the volume up. The sound cut right out and then returned in cracks. Have any suggestions as to what the problem may be? Chips stay relatively cool and I have an AD8397 for L/R and an LM6172 in ground, gain set to 4. PS: I cannot measure current draw with my DMM for some reason so I'm in the dark on that.

Do you still get sound OK when you have the volume low again, or is it now permanently distorted/crackled?

When I built up my AD8397/LM6172 hybrid, I _did not_ do the mini^3 mod, so I don't know how the 6172 takes to the mod, though I wouldn't have necessarily expected ill effects. If I had an extra 6172, I'd throw it into my mini^3 PINT and test it, but I can't...oh well.

Try this...check your DC offset with the volume turned up this time to beyond the point it starts crackling at. That might help me diagnose the problem more effectively.

 

[SubRosa]

I added a second 9V battery and am now unable to reproduce the lock-up and crackle. I can turn the volume higher now, but now I get crackling that gets progressively worse.

EDIT: DC Offset at full swing of the pot shows 3mv/1mv L/R.

EDIT 2: I got brave and decided to hook up my KSC35s, crackle is greatly reduced compared to the cheap Maxell 'phones I was testing with, but it's still present at (unbearably) high volumes and it's noisey as heck.

 

[Filburt]

Hmm, I wonder if doing the mini^3 mod in combination with using the LM6172 is somehow causing a problem with the ground chip being able to source/sink enough power in some manner, which is maybe why changing to 2x9v had an effect. Or maybe the mod wasn't done properly.

 

[SubRosa]

Quote:

Originally Posted by Filburt Hmm, I wonder if doing the mini^3 mod in combination with using the LM6172 is somehow causing a problem with the ground chip being able to source/sink enough power in some manner, which is maybe why changing to 2x9v had an effect. Or maybe the mod wasn't done properly.

I can try swapping the LM6172 for an AD8397. I checked continuity when I made the cut for the Mini^3 modification and it was good. Resistor values pulled from mb3k's PDF. I'm fairly certain the modification was done properly but I'll check over things again.

 

[Filburt]

Quote:

Originally Posted by SubRosa I can try swapping the LM6172 for an AD8397. I checked continuity when I made the cut for the Mini^3 modification and it was good. Resistor values pulled from mb3k's PDF. I'm fairly certain the modification was done properly but I'll check over things again.

Well, let's see what happens when you do that...

 

[FallenAngel]

Well, I threw in the ELNA 25V cap into C4 (damn that thing is huge!) and I'm still getting the same thing. Fairly low DC offset, 1-9mV between low and full volume, but the problem regarding oscillation still exists and the current draw starts at 60mA, quickly raises to 90mA, then gradually goes up and above 110mA while the ground opamp heats up.

A couple of quick questions to help me in my investigation:
Please note this PINT is mini^3-fied

1) When the amp is on, what should the DC voltage be between IG and OG?
2) Would there be any problem using this cap for C7 Kemet SMD Tantalum Chip Capacitors 25V 1.5uF 10% "B" - RoHS: COMPLIANT
3) Stupid question: does it matter if I stick R4 on top of C4 instead of under it?
4) Would it be worth it to drop in an LM6172 (I got one lying around) for ground opamp instead of the AD8397?

Thanks guys

 

[SubRosa]

I swapped the 6172 in ground for an AD8397 and that made my problem worse, I can barely turn the pot before the sound cuts out (as it did before the second 9V). I measured DC Offset after a lock-up and it measured the same 3mv/1mv L/R.

 

[tangent]

Quote:

Originally Posted by FallenAngel what should the DC voltage be between IG and OG?

Very low. Single digit millivolts.

Quote:

Would there be any problem using this cap for C7

No.

Quote:

does it matter if I stick R4 on top of C4 instead of under it?

No.

Quote:

Would it be worth it to drop in an LM6172 (I got one lying around) for ground opamp instead of the AD8397?

It's certainly worth a try. It's a lot more tolerant of being run in unity gain.

 

[SubRosa]

I scrapped my first board and started on my spare, I used new parts all around except for some ceramics and the pot. I turned it on and C6 immediately smoked itself, I'm not sure why that is, but I just took it out. DC Offset is reading 1mv on both channels. Guess what, same symptoms as before except marginally better, I can turn it up with a single 9V battery without crackling until high volume levels and it will sometimes cut-out but I can still hear the music very faintly, rather than not at all. I'm not sure if I'm hearing distortion at normal listening levels. Is it possible that the pot has been the source of my troubles? It's the only thing that got transferred from the old board that should be able to cause this behaviour.

 

[[AK]Zip]

If C6 smoked then you have other problems.

-Alex-