# PINT Problem



## Filburt

Okay, so I've a problem with my PINT. The power supply is 18v (2x9v). I've checked polarity on everything, as well as alignment of the op-amps. I've also checked all the resistor values, and the soldering job is clean.

 So the problem is, my ground channel op-amp (AD8397) heats up to burn-my-finger temperature within seconds. Presumably, this isn't normal. So, any ideas on what might be wrong? Is the chip just bad?

 I had this problem on the last board, and desoldered the op-amps and mounted it on a new board with fresh parts minus the Alps pot and the rail cap, both of which I tested before using on this board. I have no idea what the problem is, and I'm finding this rather frustrating...


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## MisterX

do you have pictures?

 do you know what the Dc-offset and current draw is?


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## Filburt

How do I measure those two things with my multimeter?

 I can try to get some pictures tommorow. However, I checked maybe 10 or 15 times against the schematic as well as tangent's tutorial that uses a PINT prototype, and I checked my soldering repeatedly. It appears to all be correct, and solder job is quite clean...


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## cire

for DC offset: set multimeter to measure millivolts and stick in the probes in parallel with the signal output ground and left (then right).

 current draw: set multimeter to measure at least 2 amps and stick probes in series with the battery to amp.


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## MisterX

The whole notion of showing us pictures is that sometimes we can see what you keep overlooking. 
 (a fresh set of eyes is always a good thing)


 To measure current draw you have to insert the meter between the amp and the power source

 maybe the picture I photochopped will help explain it? 







 To measure the DC offset:
 Connect the amp to the source and with no music playing measure between 
 out ground (+) and inground (-)
 out left (+) and inground (-)
 and
 out right (+) and inground (-)


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## BavariaBarbarian

Awesome pic, MisterX!

 Can I extrapolate, that you answered this question repeatedly?


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## NeilR

Misterx,

 Why do I care about the offset between input and output? I always measure offset between OR/OG and OL/OG. That's what the load sees.

 If there were, for example, an offset between OG and IG, why do I care?

 Regards,
 Neil


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## amb

Quote:


  Originally Posted by *NeilR* 
_Why do I care about the offset between input and output? I always measure offset between OR/OG and OL/OG. That's what the load sees.

 If there were, for example, an offset between OG and IG, why do I care?_

 

It's true that the load sees across from OL/OR and OG. However, if there is an unreasonable amount of DC offset between IG and OG, then that indicates there is something wrong with the circuit.

 The output voltage of a unity gain voltage follower (which is what the ground channel output amp is) should be identical to its input (0V, assuming ideal opamp). A large discrepancy might point to oscillation, failed opamp, or bad soldering/wiring.


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## MisterX

Quote:


 I always measure offset between OR/OG and OL/OG. That's what the load sees. 
 

Remember we are not talking about a conventional amplifier here. 
 The active ground channel complicates things just enough that measuring "what the load sees" does little to indicate if there is a problem with the ground channel 
	

	
	
		
		

		
		
	


	




  Quote:


 If there were, for example, an offset between OG and IG, why do I care? 
 


 Who am I to suggest what you should care about?


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## NeilR

Quote:


  Originally Posted by *MisterX* 
_Remember we are not talking about a conventional amplifier here. 
 The active ground channel complicates things just enough that measuring "what the load sees" does little to indicate if there is a problem with the ground channel 
	

	
	
		
		

		
		
	


	







 Who am I to suggest what you should care about? 
	

	
	
		
		

		
		
	


	


_

 

OK... I was looking at it from the perspective of damaging/degrading headphone sound. I see your points regarding a difference as indicating an issue. I've never had a problem myself so I have never paid attention to it (although I check it on my new 3 channel amps when I do my smoke test).


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## Filburt

Pictures:








 Yeah, that one resistor is a bit chewed up. I accidentally chipped off some of the covering post-build, but the problem was occurring before that happened, so that sort of isolates it from explanatory factors. The ground channel AD8397 is slightly disfigured on the top as well due to issues during its removal from the other board. It's not *too* bad, but the top part is slightly guffed up.


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## Teerawit

Are your battery connectors hooked up properly?


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## Filburt

Quote:


  Originally Posted by *Teerawit* 
_Are your battery connectors hooked up properly?_

 

Yes, and one might note the diodes are in place to provide reverse supply protection, anyhow


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## dhp

C8+ appears shorted out to the opamp's top right pin on the bottom


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## Filburt

Those two things seem to be connected on the PCB itself. I'll try to clean it up but I'm not sure it'll make a difference...


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## dhp

Quote:


  Originally Posted by *Filburt* 
_Those two things seem to be connected on the PCB itself. I'll try to clean it up but I'm not sure it'll make a difference..._

 

just clean up that one top right pin on the bottom opamp so it doesn't touch the board, just the pad


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## Teerawit

Quote:


  Originally Posted by *Filburt* 
_Yes, and one might note the diodes are in place to provide reverse supply protection, anyhow 
	

	
	
		
		

		
			



_

 

Let me clarify: 

 one battery connector has the red lead going to B+, black lead to M-
 the other battery connector has the red lead going to M+, black lead to B-


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## Filburt

Okay, I cleaned it up. It didn't make a difference. The pad for that pin is connected to that hole, which is connected to the pad for C8.


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## Teerawit

Quote:


  Originally Posted by *DieInAFire* 
_just clean up that one top right pin on the bottom opamp so it doesn't touch the board, just the pad_

 

It's a via, shouldn't be a problem.


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## Filburt

Quote:


  Originally Posted by *Teerawit* 
_Let me clarify: 

 one battery connector has the red lead going to B+, black lead to M-
 the other battery connector has the red lead going to M+, black lead to B-_

 

Yes, that is how it is connected.


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## cire

Quote:


  Originally Posted by *DieInAFire* 
_C8+ appears shorted out to the opamp's top right pin on the bottom_

 

C8 is the V+ bypass for the ground channel opamp. they are supposed to be connected.


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## JDAPJ

Your problem is probably due to oscillations.
 I have had those problems too, and for me the solution was to increase the caps 
 at each op. 10uF standard electrolyte to the l/r amp and 1uF to the ground channel.
 Now let's not get into a debate about that this doesn't make any difference because of this and that...all I know is that it worked for me and it's worth a try isn't it?

 /jdapj


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## kramer5150

Maybe you could use your multi-meter and do continuity checks across different / adjacent solder pads. Refer to the schematic, and hopefully find a short ...? Maybe this would help show any pads that are NOT supposed to be connected to each other?

 Garrett


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## cire

its possible the ground 8397 was damaged when you previously removed it. i would try sticking a new one on.


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## Filburt

It's possible that it was damaged, but the whole reason I rebuilt it was because it did this on the *other* board too. Same exact problem. I rebuilt it with fresh components other than the op-amps on a new board, and it still does it. I'm thinking maybe it's just a bad 8397 and it can't run unity gain stable. I don't have any spares, unfortunately. All I have is a couple of LM6172s.

 I ordered some new stuff from tangent, but it hasn't arrived yet for whatever reason (I'm guessing USPS-related problems).


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## Filburt

Okay, I threw a 6172 on, and didn't experience the rapid heating up. Looks like that 8397 was bad.


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## JDAPJ

U didn't try my solution?
 Or did u even bother to read it??

 /jdapj


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## cire

your solution wouldn't have fixed a damaged opamp....


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## Filburt

Okay, new problem. I'm only getting some crackling sound out of the left channel, and all I have is hiss on the right channel. It's not a loud hiss, just some hiss. I have to turn up the volume pretty far to hear anything on either side. I checked my connections for the input/output, and can't see anything wrong.

 The ground channel amp gets pretty hot when I have it turned up high enough to hear stuff.

 Any ideas on what might be wrong? Oscillation again? I didn't leave out the ferrites, as you can see from the pictures, and my installation of the LM6172 was _very_ clean, even cleaner than the 8397 installation thanks to my trusty desoldering braid and very thin silver solder.


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## tangent

Quote:


  Originally Posted by *Filburt* 
_I'm only getting some crackling sound out of the left channel_

 

Why are you testing first with headphones? I'll bet you find that DC offset is unacceptably high.

  Quote:


 Any ideas on what might be wrong? Oscillation again? 
 

Yes, that's likely. Can you try some low value resistors (10-100) in place of the L1s? If that fixes it, the ferrites aren't the right sort for the problem you're having. One problem with the ferrite solution is that it requires careful tuning: the ferrite has to match the problem, it's not a guaranteed fix. I'm having second thoughts about recommending it as a default.


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## Filburt

Quote:


  Originally Posted by *tangent* 
_Why are you testing first with headphones? I'll bet you find that DC offset is unacceptably high.

 Yes, that's likely. Can you try some low value resistors (10-100) in place of the L1s? If that fixes it, the ferrites aren't the right sort for the problem you're having. One problem with the ferrite solution is that it requires careful tuning: the ferrite has to match the problem, it's not a guaranteed fix. I'm having second thoughts about recommending it as a default._

 

I tested it first with headphones because, for some reason, it didn't occur to me that it'd have problems. Yes, it was a bit of naiveté on my part...oh well.

 Should I order different ferrites? The ones I got are the 50 ohm ones you have in your parts list from Digikey. I don't have any low value SM resistors handy, so I can't test it with those.

 I checked the DC offset...it's _gigantic_, assuming I'm testing it right. I used MisterX's instructions, and measured ~1,2v on the right and ~3,9v on the left, which is obviously atrocious levels of offset. This was with the switch just off of the on position (e.g. around the lowest volume position).

 While I don't have the spare resistors, I do have the C3 caps. Should I try those? 

 Edit: Okay, tried C3. Now I get 2,8 on the right and 0,5 on the left...


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## tangent

Quote:


  Originally Posted by *Filburt* 
_Should I order different ferrites?_

 

If you don't have a scope, you don't have the information you need to select the proper ferrite. This is one reason I'm beginning to backpedal on ferrites being the default choice. No question, ferrites are the best way to go if you can get away with it, but it's not a foolproof option. (No aspersions being cast here, really.)

  Quote:


 I don't have any low value SM resistors handy 
 

I guess you didn't plan on adding R1? The low values you'd use there would be suitable.

 You could solder-tack some 1/8W resistors to the pads instead. Even 1/4W...you'd just need to bend the leads back under the part.

  Quote:


 Okay, tried C3. Now I get 2,8 on the right and 0,5 on the left... 
 

What units? Volts? millivolts? Megavolts?


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## Filburt

Oh, duh, I totally forgot about R1. Wouldn't that be such a high value that it would seriously damage the performance?

 The units on the numbers were volts, not millivolts. Sorry about the commas, if that's being confusing. Right is 2.7v and left is 0.5v, whereas before C3 right was 1.2v and left was 3.9v. This is, admittedly, enourmous DC offset. I was surprised to see such a huge shift post-C3 installation.

 What I'm wondering is how others got ferrites to work sufficiently, then. Maybe someone could tell me which value worked for them?


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## Filburt

Okay, I replaced all L1s with 75 ohm resistors. Now I'm getting 4,8v on the right and 5,7v on the left. Still a ton of offset.


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## tangent

Quote:


  Originally Posted by *Filburt* 
_Okay, I replaced all L1s with 75 ohm resistors. Now I'm getting 4,8v on the right and 5,7v on the left. Still a ton of offset._

 

Then I wonder if we're chasing the right thing. Are the chips still getting hot? What's the amp's current draw?


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## Filburt

Quote:


  Originally Posted by *tangent* 
_Then I wonder if we're chasing the right thing. Are the chips still getting hot? What's the amp's current draw?_

 

How do I measure the current draw?

 The LM6172 is getting warmish, while the AD8397 is getting very hot.


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## Teerawit

Quote:


  Originally Posted by *Filburt* 
_How do I measure the current draw?_

 

Break the connection between the power supply and your amp. Insert your ammeter (in series) to reconnect the power supply to your amp. What does your ammeter read when the amp is powered?


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## Filburt

Quote:


  Originally Posted by *Teerawit* 
_Break the connection between the power supply and your amp. Insert your ammeter (in series) to reconnect the power supply to your amp. What does your ammeter read when the amp is powered?_

 

Er, so I pull out one of the power supply wires, like the positive lead, then what? Stick it to the positive probe on my multimeter and then poke that into the positive power-in?


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## shimage

Quote:


  Originally Posted by *Filburt* 
_Er, so I pull out one of the power supply wires, like the positive lead, then what? Stick it to the positive probe on my multimeter and then poke that into the positive power-in?_

 

I think you have it, although I'm little confused by what you're saying. MisterX posted a great picture of it the first time you asked how to measure current draw ...


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## Filburt

Quote:


  Originally Posted by *shimage* 
_I think you have it, although I'm little confused by what you're saying. MisterX posted a great picture of it the first time you asked how to measure current draw ... _

 

Oh yeah...forgot about that! Thanks MisterX!


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## Filburt

Okay, measured current draw. It's 44mA idle. This is with the AD8397/LM6172 combo. This seems like it might be a touch high, but maybe it's okay.


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## Filburt

Okay, now it's reading 5,2v on the right and 6,7v on the left...I haven't changed anything yet...


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## Filburt

Teerawit had me measure IG to OG, and that came out at basically 0v (it was fluctuating between 0,001 and 0,000v on my multimeter...mostly at 0,000).


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## Filburt

Okay, tried jumpering L1 for the hell of it after removing the resistors from L1 on the Ad8397 (still had it on the LM6172).

 Got 5,4v on the right and 6,9v on the left, which is the exact same dc offset as when 75 ohm resistors were in (1,5v) but pushed up 0,2v.


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## Filburt

Okay, forgot to put C2 in (doh). Now I get 5,55 on the right and 5,35 on the left. So now we have a reversal of offset. This is with L1s jumpered.

 Now here's something odd. I have tried putting ferrites back into L1, as well as resistors, and all they do is *increase* my dc offset by a lot. When I put ferrties in, for instance, my offset shot up to 1,2v between the two, as opposed to the 200mv jumpered. This is really strange.


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## Filburt

Okay, tried jumpering L1 on the LM6171, and it went to 5,55 and 4,95. Tried switching 75 ohm resistor back in and it's still stuck at that.

 Argh, this is just so confusing and frustrating


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## tangent

You're measuring OG to OR and OG to OL, right? DC volts?


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## Filburt

No, I was instructed to do IG to OR/OL.

 I built a new one with the parts you sent me, tangent. I get about 1mv on IG to OR, and about 0,9mv on IG to OL. For OG to OR and OL, I get ~7,0v for both.

 Problem, though. When I turn on the amp, with headphones on it, I get this winding up sound (e.g. starts lowish, goes high - starts at maybe 800hz and then goes to 4khz within a second or so). This is with new jacks in place. With the old jacks in place, I was getting some of the signal, but it sounded like a bunch of it was missing, and it was pulled to the centre and sounded hollow, and when I turned up the volume, it would start to crackle and have static. I have C3 installed, and the ferrites. The ground channel amp gets hot, while the other not so much. It doesn't get extremely hot, though, but it does hurt my finger to hold it there more than momentarily.


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## tangent

Quote:


  Originally Posted by *Filburt* 
_No, I was instructed to do IG to OR/OL._

 

That's the same thing, if IG to OG is near 0V.

  Quote:


 I get about 1mv on IG to OR, and about 0,9mv on IG to OL. For OG to OR and OL, I get ~7,0v for both. 
 

Then IG to OG must give about 7V, too. In which case, the ground channel is broken.

  Quote:


 I was getting some of the signal, but it sounded like a bunch of it was missing, and it was pulled to the centre and sounded hollow 
 

The amp isn't grounded correctly. Likely you've got IG or OG swapped with something, or there's a conduction path where one oughtn't be. Is this happening with the amp outside of a case, with the jacks flopping around on the end of hookup wires?


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## Filburt

Yes, IG to OG gives 7v. Okay, so now my ground channel is broken? *sigh*...I wonder what broke it. Do you mean the chip is broken or the connections are messed up? I have been extremely meticulous and careful in building these things...

 Does the description with the whirring sound help? Is the op-amp busted? I don't have any left 
	

	
	
		
		

		
		
	


	




 Is there a way to find where the fault is?


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## Filburt

Okay, I put a 75 ohm resistor on L1 for the ground channel, and it got rid of the squealing sound. It occured to me to do it after I removed the cable extension for my earphones and plugged them in without it, and noticed that no squealing happened. 

 However, I now once again have the messed up hollow/drawn to centre sound, which sounds like once again a problem with the ground. I don't really know what to do, though, at this point...

 Also note, I'm using the isolated jacks from mouser (Kubiconn).


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## PinkFloyd

The squealing sound and heat you mention is oscillation. From the look of the underside of the PCB the soldering is pretty iffy, go over everything with a hot tip and let it flood into the joints a bit more to form a nice mirror like finish.... feed a little dab of solder from the reel onto each joint as you melt the existing solder. It's amazing how poor soldering is attributable to 99% of the faults in an amp, double check every last pad. Haven't read the entire thread but one of those resistors doesn't look too healthy to me (the one adjacent to C1R). There's enough solder on those opamps to sink a battleship, get some desolder braid and mop it up..... you're soldering a small opamp not welding a wing onto a car. Less is more when it comes to soldering and you can actually see if the joint is ok, big wads / blobs of solder can hide a dry joint.


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## Filburt

Well I rebuilt it, so those pictures are the old amplifier. I checked all the solder joints and re-did them, with no effect. I did the second amp even more carefully than the first. I realise something has to be wrong, though...


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## PinkFloyd

Quote:


  Originally Posted by *Filburt* 
_Well I rebuilt it, so those pictures are the old amplifier. I checked all the solder joints and re-did them, with no effect. I did the second amp even more carefully than the first. I realise something has to be wrong, though..._

 

It'll be something very minor, been there many times, take a rest and then go back to it refreshed and don't look for the obvious.


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## Filburt

Alright, sounds like good advice. Maybe I'll try remounting everything.


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## kramer5150

Wow this is a GREAT thread!!! Filburt has a really good sounding cmoy, and IMHO is a competent builder... Certainly higher up the ladder than my meager skills.

 I think I'll hold off on a pint build... just too much black magic going on here for my meager skills.

 Good Luck!!
 Garrett


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## Filburt

Alright, I went and tried to improve the soldering on a variety of things, to no avail.

 I also tried installing 75 ohm resistors on the main audio amp's L1s to see if it'd have an effect...it didn't. If anything, it made it worse, so back in the ferrites go. I'll leave a resistor in the ground channel, though.

 One thing tangent didn't make clear to me is whether IG to OR/OL is supposed to be 7v also, or if it's okay that both are about 1mv. Based on what I'm hearing, it sounds like the problem is in the grounding of the input, but I can't see anything wrong with it, unless either the op-amp or the traces are screwed up in some way. I really hope it's not the op-amp, as I have no spares. I only have one board left, too, so I'm really not wanting to have to build this up yet again, especially since I'm running out of other parts.


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## Filburt

Okay, here's an update and my advice to others trying to build this -

 I figured out the problem with the sound at this point. Having a 75 ohm resistor on L1 for the ground channel causes it to basically just not work. I end up getting a weird hollow sound. However, it is _not_ stable, as far as I can tell, with the 50 ohm ferrite from DigiKey. It blew up on me when I tried to switch back to the ferrite. Wonderful.

 The other amp appears to be stable at gain 4 with the ferrites and caps on C3.

 I swapped in an LM6172 again, with ferrite, not 75 ohm resistor as, again, I end up with weird sound if I have it there. It works correctly and very stable. It sounds rather good, very similar to the Hornet, which means it's aggressive and detailed, but the soundstage is slightly collapsed and it isn't as warm as my CMoy or something like an SR-71. It's also very quiet in terms of noise floor. When I first turned it on, I checked my power to make sure it was working as I couldn't hear anything (no pop, no hiss, etc.). When I played music through, though, it became apparent that it was working 
	

	
	
		
		

		
		
	


	




 It is running very stable now, though, with all ferrites on L1, caps installed on C3, AD8397/LM6172 combo. Neither chip gets hot driving my earphones or my friend's ATH-EM7. I may try removing C3 to see what happens, if it's making much of a performance hit, but somehow I'm doubting it is.

 I'm going to order another couple AD8397 from AD, as someone pointed out to me that it's cheaper there and I am running out of money, but I have enough parts for another amplifier. Based on what I know now, I have some pretty solid ideas on how to build this successfully the first time around.

 After this great ordeal, and considering my limited college student budget, I am accepting donations 
	

	
	
		
		

		
		
	


	




 If anyone has any questions, let me know (or if you want to donate ) and I'll try my best to answer.


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## amb

Hi Filburt, as you discovered, you should not put a resistor in place of L3 (the ferrite on the ground channel output). While a resistor in place of L1 and L2 is more or less ok, it's not so with L3. This is because the ground channel is supposed to source/sink the return current from both channels, and must have very low output impedance in order to preserve stereo separation. Putting a resistor there kills the low output impedance. That's what gave you the "hollow sound".

 The ground channel amp operates in unity gain, and has a direct feedback path from the output to the non-inverting input (sans any resistor). This is probably the one place where an AD8397 is going to be very unhappy if the headphone cable has significant capacitance. The L3 ferrite isolates the output of the chip, but the way it's wired up on the PINT (where the ferrite is wrapped within the feedback loop), it offers no isolation to the inverting input. See the PINT schematic.

 On our Mini³-ized PINT, we did a small surgery to the PCB to put the ferrite outside of the feedback loop, giving isolation to both the output and the inverting input. This involves one small cut and one jumper to the PINT board. See pics below:

 Original PINT:






 Our modification:






 In addition, we also put L1 and L2 outside of the feedback loop by populating R4 on the pads for C3 (leaving the original R4 pads unused), and then stacking C3 on top of R4. This is a little frustrating to do due to the small SMD part size, but it all worked out very well.


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## tangent

Quote:


  Originally Posted by *kramer5150* 
_just too much black magic going on here for my meager skills._

 

In several ways, the PINT is the most difficult amp to build on my site. It's definitely not for everyone.

  Quote:


  Originally Posted by *Filburt* 
_here's an update and my advice to others trying to build this_

 

Thanks for the detailed report, Filburt. I'm glad you've worked out a stable configuration.

  Quote:


  Originally Posted by *amb* 
_we did a small surgery to the PCB to put the ferrite outside of the feedback loop_

 

It'd probably be simpler to just jumper L1G and use a ferrite bead around the OG wire at the board end.


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## Filburt

If I get some new 8397s in, I *might* try to perform the modification amb mentions and will take pictures so people can see how it works.

 Thanks for the explanation about LG, amb. That's what I figured was happening, but I didn't trust myself on it since my major is Philosophy, not electrical engineering 
	

	
	
		
		

		
			





 Tangent - Yeah, I thought I'd share on that one, in case someone else was having problems. It seems to be very stable in this configuration, and is very black on the background, even with the volume turned at full. Even in my quiet room, I can barely detect that it's on...in fact it's so quiet I really can't confirm that there is any noise. This particular aspect of it is amongst the best I've encountered in portable amps. It does seem to accentuate background noise on recordings more than my other amp, but it seems to be proportional to the greater degree of forwardness and slight increase in brightness, so I think it's probably okay. It's running fairly cool, too. With the lid open, it runs just above room temperature with my earphones. With the lid closed, it gets a bit warmer, but not too bad.


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## amb

Quote:


  Originally Posted by *tangent* 
_It'd probably be simpler to just jumper L1G and use a ferrite bead around the OG wire at the board end._

 

Yes, but clumsy to do with SMD parts (difficult to make a mechanically-sound wire connection to the end of a SMD ferrite. If one is to do this, then a through-hole "bead-on-lead" would be a better choice. The wire to the jack can then be twisted and spliced onto the leaded bead, and insulated with heat-shrink tubing.


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## Heady

Quote:


  Originally Posted by *amb* 
_In addition, we also put L1 and L2 outside of the feedback loop by populating R4 on the pads for C3 (leaving the original R4 pads unused), and then stacking C3 on top of R4. This is a little frustrating to do due to the small SMD part size, but it all worked out very well._

 

Hi amb, I may be wrong but I think tangent mentioned that C3 should be left out, if using the ferrite beads. In which case, there is not need for the fiddly stacking? What do you say?

 Thanks.


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## amb

Quote:


  Originally Posted by *Heady* 
_Hi amb, I may be wrong but I think tangent mentioned that C3 should be left out, if using the ferrite beads. In which case, there is not need for the fiddly stacking? What do you say?_

 

C3 can and probably should be omitted if you're using the high value feedback resistors as listed on tangent's schematic and parts list. However, when you Mini³-ize a PINT, you switch to lower resistor values, substitute a 1K resistor in place of the input coupling cap, and change the ferrites to be outside the feedback loop. With this scheme, C3 is no longer optional.


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## Teerawit

Quote:


  Originally Posted by *amb* 
_However, when you Mini3-ize a PINT, you switch to lower resistor values, substitute a 1K resistor in place of the input coupling cap, and *change the ferrites to be outside the feedback loop.*_

 

The ferrite for just the ground channel or for all three channels?


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## Heady

Quote:


  Originally Posted by *amb* 
_C3 can and probably should be omitted if you're using the high value feedback resistors as listed on tangent's schematic and parts list. However, when you Mini³-ize a PINT, you switch to lower resistor values, substitute a 1K resistor in place of the input coupling cap, and change the ferrites to be outside the feedback loop. With this scheme, C3 is no longer optional._

 

Thanks for your comments. I am planning to try both arrangements. According to your earlier post, with the pictures, does it mean that:
 1. make the cut as shown in the picture
 2. make the jumper as shown
 3. solder R4 and C3 in C3 position
 4. solder L1(L), L1(R) and L1(G) in the positions as silk-screened on PCB
 is what is required to mini3-ised the PINT?

 Thanks again for making clear your comments.


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## splaz

Quote:


  Originally Posted by *amb* 
_C3 can and probably should be omitted if you're using the high value feedback resistors as listed on tangent's schematic and parts list. However, when you Mini³-ize a PINT, you switch to lower resistor values, substitute a 1K resistor in place of the input coupling cap, and change the ferrites to be outside the feedback loop. With this scheme, C3 is no longer optional._

 

Hmmm... 

 So if you replace the input caps and then use lower value resistors like said in the other topic, then you should also do the other fiddling around you just mentioned or is it fine just without input caps and with lower resistor values ?


----------



## Filburt

Quote:


  Originally Posted by *splaz* 
_Hmmm... 

 So if you replace the input caps and then use lower value resistors like said in the other topic, then you should also do the other fiddling around you just mentioned or is it fine just without input caps and with lower resistor values ?_

 

I would have thought my findings in this thread would make it abundantly clear that you _cannot_ simply replace the input caps and resistor values and expect everything to work correctly. Modifying the design in some manner is essentially mandatory if you go this route, and amb or tangent's suggestions will work. I will probably perform these modifications on my next build and post pictures if I can (probably next week).


----------



## amb

Quote:


  Originally Posted by *Teerawit* 
_(change the ferrites to be outside of the feedback loop)
 The ferrite for just the ground channel or for all three channels?_

 

We did it for all three channels, but I think at minimum the ground channel is the one that would most benefit from this.


----------



## amb

Quote:


  Originally Posted by *Heady* 
_1. make the cut as shown in the picture
 2. make the jumper as shown
 3. solder R4 and C3 in C3 position
 4. solder L1(L), L1(R) and L1(G) in the positions as silk-screened on PCB_

 

Yes.

  Quote:


 is what is required to mini3-ised the PINT? 
 

The above, plus install 1KΩ resistors in place of the two input coupling caps, change R4 to 6.2KΩ, R3 to 1.2KΩ, and C3 to 10pF.


----------



## dsavitsk

Quote:


  Originally Posted by *Heady* 
_3. solder R4 and C3 in C3 position_

 

? What did I miss?

 edit: never mind, I looked at the schematic


----------



## splaz

I was forgetting you were trying it Filburt.

 It's just that I can't recall amb or morsel mentioning anything else apart from this new piece of information. So I thought what they said before about replacing the input caps without this new info on ferrite shifting and putting in C3, would work.

 Now bear with me, still a bit rusty on the whole theory side. This is what the schematic would now look like ?

 Same goes for the right side.

 edit: I know it probably shouldn't be called R0 I just found it easier to copy and flip a nearby 0 than put in a 5. Lazy I know...


----------



## amb

Quote:


  Originally Posted by *splaz* 
_This is what the schematic would now look like ?_

 

Yup.

  Quote:


 Same goes for the right side and similar for ground. 
 

Except, of course, there is no R0, R2, R3, R4 or C3 at the ground channel.

 Edit: I see that you added a ground channel schematic. It's right on.


----------



## morsel

I am so scatterbrained, thank goodness amb remembers these details. We Mini³ified our PINT weeks ago. I wasn't going to mention the pcb surgery, as the ferrites should also work inside the feedback loop, but perhaps not for the ground channel, since it has no feedback resistor to isolate the inverting input from the load.


----------



## Filburt

Well, after three boards and 3 dead 8397s, I certainly wouldn't take the chance again on a non-modified configuration. I did take the opportunity to experiment a bunch with other ideas while I was at it, so I ended up turning the failed ones into a self-teaching thing.


----------



## Heady

Quote:


  Originally Posted by *amb* 
_Yes.


 The above, plus install 1KΩ resistors in place of the two input coupling caps, change R4 to 6.2KΩ, R3 to 1.2KΩ, and C3 to 10pF._

 


 amb, thanks very much for your clarification. I also want to point out that in Tangent's list of parts, C3 is already 10pF. Just in case it mystify someone else beside myself.


----------



## splaz

I meant similar as in with the keeping the ferrite out of the feedback loop. But yeah I put up a ground one anyway.

 Well I have two boards so this is definitely something I'm going to try. I'll make one with input caps first though to make sure I can get one that actually works. 

 If you do it Filburt, put up a pic of the C3 stacking. Sounds interesting.


----------



## amb

Quote:


  Originally Posted by *splaz* 
_put up a pic of the C3 stacking. Sounds interesting. 
	

	
	
		
		

		
		
	


	


_

 

Here's ours. Each "C3" is actually R4 and C3 stacked together. Note that this is one of tangent's green prototype PINT pcbs.


----------



## dhp

so in addition to the normal positions of R4, you also stack an additional 2 R4's onto the C3s?


----------



## amb

Quote:


  Originally Posted by *DieInAFire* 
_so in addition to the normal positions of R4, you also stack an additional 2 R4's onto the C3s?_

 

No. Leave the original R4 position empty. The purpose of doing this is to put the output ferrite outside of the feedback loop. See the schematic.


----------



## mb3k

For the people who came into this thread a little late, I compiled a summary to Mini³fy the PINT amp:

http://www.mb3k.com/hosted/mmmpint.pdf

 Thanks to
 amb, Morsel, Tangent, Filburt, and all other contributors


----------



## Heady

Quote:


  Originally Posted by *mb3k* 
_For the people who came into this thread a little late, I compiled a summary to Mini³fy the PINT amp:

http://www.mb3k.com/hosted/mmmpint.pdf

 Thanks to
 amb, Morsel, Tangent, Filburt, and all other contributors_

 

Excellent, mb3k.


----------



## seanohue

one question about the cut: is basically what your doing there is cutting the trace that connects pin 7 to L3? How deep does the cut need to be to do this?


----------



## cire

deep enough to sever the trace. less than a millimeter would be enough


----------



## seanohue

Ok, simple enough


----------



## Teerawit

Quote:


  Originally Posted by *seanohue* 
_Ok, simple enough 
	

	
	
		
		

		
		
	


	


_

 

Remember to check for discontinuity after delivering the scalpel


----------



## Jam_Master_J

Quote:


  Originally Posted by *mb3k* 
_For the people who came into this thread a little late, I compiled a summary to Mini³fy the PINT amp:

http://www.mb3k.com/hosted/mmmpint.pdf

 Thanks to
 amb, Morsel, Tangent, Filburt, and all other contributors_

 

Good Work. I plan on Mini3ifying my PINT.


----------



## dhp

is it just me, or are the arrows in the PINT picture switched? In amb's before and after pics, the after picture has 2 arrows, but it seems like they're pointing to the opposite thing?


----------



## amb

Quote:


  Originally Posted by *DieInAFire* 
_is it just me, or are the arrows in the PINT picture switched? In amb's before and after pics, the after picture has 2 arrows, but it seems like they're pointing to the opposite thing?_

 





 If you're referring to the "cut here" and "jumper here" arrows, they are correctly oriented. Look at the before and after pics carefully -- red means "connected", black is not connected.


----------



## dhp

Quote:


  Originally Posted by *amb* 
_




 If you're referring to the "cut here" and "jumper here" arrows, they are correctly oriented. Look at the before and after pics carefully -- red means "connected", black is not connected._

 

doh, flipped the colors in my mind


----------



## Pendergast

Hello!

 I just finished a minified PINT, and although I did not have the exact values or sizes recommended, it worked pretty well!

 The differences are as follow:

 R3 and R4 = 2.37kohms 1/4 W
 C1 replaced with 1kohms 1/4 W

 R4 have been soldered to C3 but with those sizes, it is a bit ugly.

 But it works quite well!

 This is very exciting!


----------



## civilmonkey

Nice work, congrats!

 I juist finished my PINT. I used the mini'fy guide and followed it to a 'T', with a gain of 6. The amp played great before casing it, chips stayed cool, etc. Then I cased it in a mint tin, and the U1 chip gets very warm now (i'm assuming oscillation.) No sound whatsoever, DC offset 6 and 13 mV, but current draw 61 mA. 
	

	
	
		
		

		
			





 I uncased it, and it's still oscillating. The jacks were isolated, the DC jack wasn't. Maybe that had something to do with it.

 One thing is that it take 5'ish second for the chip to get very warm (just too hot to keep a finger on, but not burning hot). With other chip problems I've experienced, the chip gets hot much quicker.

 Anybody have any ideas?


----------



## amb

civilmonkey, the DC jack's body is actually the negative supply rail. If you didn't isolate it and the tin comes into contact with any part of the circuit that it shouldn't (such as the virtual ground) then you had a short circuit condition. Since the virtual ground splitter and output ground channel are all driven by AD8397s (which has no output protection) do not take kindly to short circuits and may already be blown.


----------



## civilmonkey

hmm, good point. I knew that, and thought it was a little sketchy using a non isolated DC jack, but I saw others were doing that. Perhaps I was unlucky. 

 I didn't think that was my problem, b/c with the PINT board in the tin, the only thing touching the mint tin is the PCB and the POT (and I didn't have power applied while inserting the board). Still, it's very possible. The fun thing I've learned with DIY is that sometimes you never know...


----------



## Jam_Master_J

I didn't realize tying v- to the case was such as a bad thing. Tangent seems to do it sometimes, but I guess you gotta be careful.


----------



## amb

Quote:


  Originally Posted by *civilmonkey* 
_hmm, good point. I knew that, and thought it was a little sketchy using a non isolated DC jack, but I saw others were doing that. Perhaps I was unlucky. 

 I didn't think that was my problem, b/c with the PINT board in the tin, the only thing touching the mint tin is the PCB and the POT (and I didn't have power applied while inserting the board). Still, it's very possible. The fun thing I've learned with DIY is that sometimes you never know... 
	

	
	
		
		

		
		
	


	


_

 

One thing to keep in mind, the power switch is _after_ the reservoir capacitor C4. This has the benefit that as you turn off the amp, the power goes away immediately rather than drain down with the capacitor, which removes a possible source of turn-off noise. However, this arrangement means that C4 is charged at all times (when the battery is connected). Even when the battery is removed it will still stay charged for a long time. If, while installing your board into the tin, for some reason the charged capacitor finds a temporary short circuit and discharges into a errant part of the circuit, the opamps are at risk of being damaged.

 I don't know if this is what might have happened with your amp, but I recommend discharging the cap completely before putting the board in the tin. To do that, disconnect the battery, then turn on the amp and let the opamps drain the cap for a few seconds. You'll see the LED glow for a brief moment as the charge is being drained. Then, turn off the power, install the board into the tin and check for short circuits before reconnecting the battery.


----------



## civilmonkey

Quote:


  Originally Posted by *amb* 
_One thing to keep in mind, the power switch is after the reservoir capacitor C4. This has the benefit that as you turn off the amp, the power goes away immediately rather than drain down with the capacitor, which removes a possible source of turn-off noise. However, this arrangement means that C4 is charged at all times (when the battery is connected). Even when the battery is removed it will still stay charged for a long time. If, while installing your board into the tin, for some reason the charged capacitor finds a temporary short circuit and discharges into a errant part of the circuit, the opamps are at risk of being damaged._

 

That, makes sense. I think you have probably figured out my problem. I have two new AD8397's coming in from Tangent, which I will install on the board. I was going to try and figure out how to isolate my DC jack, but as I understand from your post, if I'm careful, I shouldn't need to.

 Thanks for the input and help! I'll post the results when it's all working!


----------



## CedMan

Thanks mb3k, the instruction works and I have a working Mini³fy PINT running at Gain 3 and sounds great, that is after toasting a ground AD8397.

 Here's how I toasted mine, but I'm not sure exactly what caused it, maybe someone can help me, I have a working Mini³fy PINT, tested and all that, then I decided to case it. I have put it in the smallest Hammond case and I was stupid using all non isolated jacks (in/out/pw), I plug in my wallward and turned it on so obviosly my Mini³fy PINT have a toasted groud channel right away.

 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?

 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 ... 

 I'll be using plastic case now ... much safer. 
	

	
	
		
		

		
		
	


	




 Thanks!

 -Ced


----------



## NeilR

Does anyone have an image of a Pint in Mint tin with DC charger jack, top view straight down? Or a link to an image? I am trying to figure out where to put a jack.

 I am also thinking about a Serpac H65, but that seems to be a waste of space. I'm like Goldie Locks, trying to find a case that is just right for this board and 2x9V.


----------



## Teerawit

Quote:


  Originally Posted by *NeilR* 
_Does anyone have an image of a Pint in Mint tin with DC charger jack, top view straight down? Or a link to an image? I am trying to figure out where to put a jack._

 

Aside from the pic on tangent's page 
	

	
	
		
		

		
		
	


	




, here is darkisz's:

http://img214.imageshack.us/my.php?image=pint021mn.jpg


----------



## NeilR

Thanks, Teerawit. For some reason I didn't notice it snuggled between the i/o jacks. That is a really tight case!


----------



## Teerawit

Quote:


  Originally Posted by *NeilR* 
_Thanks, Teerawit. For some reason I didn't notice it *snuggled between the i/o jacks*. That is a really tight case!_

 

Yeah, that's about the only way to do it. Good luck


----------



## 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. However the opamps are not hot. The L/R opamp is about 35degrees celcius while the ground opamp is about 38degrees celcius. Not even noticeably warm to my finger.

 I used all the parts as in the mini3-fied list, but omited U2, R1 and D1. And since I don't have a SMD diode handy (one always forget at least one part when buying stuff), I modified an axial 1A 50V diode and used it for D2.

 Anyone have an idea if I got a problem?

 Thanks.


----------



## NeilR

I'd like to find a case exactly the width and length of my 5G ipod. I think that is the ideal case size (for an iPod). That would be about 2 3/8" x 4". That would open up about 3/8" of breathing room.

 The tins are a good size for the Nano, though.


----------



## Teerawit

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. However the opamps are not hot. The L/R opamp is about 35degrees celcius while the ground opamp is about 38degrees celcius. Not even noticeably warm to my finger.

 I used all the parts as in the mini3-fied list, but omited U2, R1 and D1. And since I don't have a SMD diode handy (one always forget at least one part when buying stuff), I modified an axial 1A 50V diode and used it for D2.

 Anyone have an idea if I got a problem?

 Thanks._

 

What are your DC offset readings?


----------



## 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?


----------



## Filburt

Quote:


  Originally Posted by *amb* 
_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?_

 

I used the ones Tangent lists in his part list from Digikey. The one he notes as being 50 ohms.

 I measured the resistance between the two pins and I was seeing what appeared to be less than an ohm of resistance, so essentially nothing. However, do you think it may be causing problems. I noticed the picture from blueworm appears to bridge the two pins with just solder, in addition to bridging to that one end of the ferrite.


----------



## amb

Quote:


  Originally Posted by *Filburt* 
_I used the ones Tangent lists in his part list from Digikey. The one he notes as being 50 ohms.

 I measured the resistance between the two pins and I was seeing what appeared to be less than an ohm of resistance, so essentially nothing._

 

The "50Ω" rating is at ultrasonic frequencies (probably 100MHz, need to verify this on the datasheet). When you measure the resistance with a DMM, it's at DC (0Hz). The ferrite is just a wire with ferrous material wrapped around it to give it some inductance, so at DC it's essentially a stright wire with negligible resistance, but the impedance rises at very high frequencies.


----------



## Filburt

Quote:


  Originally Posted by *amb* 
_The "50Ω" rating is at ultrasonic frequencies (probably 100MHz, need to verify this on the datasheet). When you measure the resistance with a DMM, it's at DC (0Hz). The ferrite is just a wire with ferrous material wrapped around it to give it some inductance, so at DC it's essentially a stright wire with negligible resistance, but the impedance rises at very high frequencies._

 

Okay, fair enough. So any ideas on what to try in terms of modifying. I checked my solder joints and they seem clean. Can you think of anything in particular to watch out for?


----------



## amb

Quote:


  Originally Posted by *Filburt* 
_Okay, fair enough. So any ideas on what to try in terms of modifying. I checked my solder joints and they seem clean. Can you think of anything in particular to watch out for?_

 

Nothing in particular, just go through everything carefully to make sure you didn't make a mistake somewhere, such as using a wrong value part, or installing a part in the wrong location. In addition to visually checking the solder connections, use your DMM to check for continuity where there should be, and open circuit where there shouldn't be connections. Use the schematic diagram as your guide. The circuit is simple enough you should check every "net", and it shouldn't take long to do that.

 Your 85mA current is measured in series with the batteries without any wallwart or audjo source connected, and the volume control is set to minimum, right?

 Anyway, it's past 3am and I'm going to sleep now. Hopefully you'll solve the problem soon.


----------



## Heady

Here are the pics of my mis-behaving PINT:

Front view

Back view

 I was very careful building this as I have read of the problems involved. Please have a look and see if I had made a mistake somewhere.

 Thanks.


----------



## tomb

There's a solder bridge between two of the right pins on the Ground Channel opamp (U3).


----------



## Heady

Quote:


  Originally Posted by *tomb* 
_There's a solder bridge between two of the right pins on the Ground Channel opamp (U3)._

 

Yes, it is according to amb's instructions for mini3-fying the PINT.


----------



## __redruM

To start, where is R4. Is it optional in the minified config?

 Otherwise, how about using a 10-100Ohm resistor for L1, instead of a ferrite? This would seem to be the next step if you weren't minified. Amb, will this have the same taming effect in the minified config?


----------



## Filburt

Quote:


  Originally Posted by *amb* 
_
 Your 85mA current is measured in series with the batteries without any wallwart or audjo source connected, and the volume control is set to minimum, right?_

 

Correct.


----------



## Heady

Quote:


  Originally Posted by *__redruM* 
_To start, where is R4. Is it optional in the minified config?

 Otherwise, how about using a 10-100Ohm resistor for L1, instead of a ferrite? This would seem to be the next step if you weren't minified. Amb, will this have the same taming effect in the minified config?_

 

R4 is under the C3.


----------



## nysulli

i measured my current draw this morning, 62ma without any phones hooked up, seems just a bit high, and the ground opamp feels hotter then the L/R one, do you think its good enough to just let go, or should i track down the slight oscilations i have, I do have access to a scope, but it could be a few days before i can get to it

 that being sad, the setup is the standard ad8735 opamp (or whatever the number is), gain of 3, minified, using the L1's tangent originally suggested at the release of the PINT, to add, my DC offsets are all under 1mv, IG-OG, OG-OL, OG-OR, the amp is being powered by 2 9v's


----------



## __redruM

Quote:


  Originally Posted by *Heady* 
_R4 is under the C3._

 

Interesting, was it just easier to solder that way?

 Also, Using a 10ohm resister at L1 may help your issues...

 Edit: Did you read the following on tangent's site: "Do not use both C3 and L1 at the same time. They have opposite effects. If you need L1, adding C3 will at least partially defeat its purpose."


----------



## Teerawit

Quote:


  Originally Posted by *__redruM* 
_
 Edit: Did you read the following on tangent's site: "Do not use both C3 and L1 at the same time. They have opposite effects. If you need L1, adding C3 will at least partially defeat its purpose."_

 

ya, but C3 and L1 are both necessary in the mini^3fied circuit.


----------



## __redruM

OK, I was confusing Tangent "Low Noise" Pint with the Mini3 converted Pint. Does replacing L1 with a 10 Ohm resister help, if it is outside the feedback look?


----------



## FallenAngel

I can't see it very well in the picture, but you did cut the trace on the PCB from the OpAmp (pin 7 i think), right?


----------



## amb

Heady, have you checked to see if your DMM is actually reading a reasonable current? I don't see anything obvious in the photos, but I assume you checked all nets with your DMM in ohms mode? Does it actually sound ok?

 nysulli, 62mA is still within range. The AD8397 datasheet says that at high supply voltages (24V specified, but two 9V batteries come close), the quiescent current is typically 11mA but can be as high as 15mA per amp. There are two amps per chip, and there are two chips. Considering that Rled is 4.7K you probably have close to 4mA flowing through the LED. The ground opamp will run warmer than the L/R opamp after playing music because it has to source/sink the return current from both channels. I wouldn't worry too much about it.

 __redrum, in a Mini³fied PINT, L1 is no longer within the feedback loop. You can substitute 10Ω resistors for L1 for the L and R channels but not for the ground channel, or you will kill stereo channel separation. For those who still have problems with cable-induced oscillations it might be a worthwhile experiment to *add* an additional 10Ω resistor in series with each of the L and R channel outputs to see if it makes any difference. Since the ferrite has much more impedance than 10Ω at high frequencies I wouldn't advocate removing them in favor of resistors only.

 For those with too much quiescent current even without any cables connected, then the problem won't be solved by adding resistors or changing ferrites (because that's not where the problem is).


----------



## Filburt

Damnit...

 I tried resoldering the cap on C3L...and after taking it off and putting it back on, my power draw shot up to 160mA. I ended up just replacing both the cap and the resistor thereafter, and it's still at 160mA. What happened?


----------



## tomb

Quote:


  Originally Posted by *Heady* 
_Yes, it is according to amb's instructions for mini3-fying the PINT._

 

Doh! my bad!


----------



## amb

Quote:


  Originally Posted by *Filburt* 
_I tried resoldering the cap on C3L...and after taking it off and putting it back on, my power draw shot up to 160mA. I ended up just replacing both the cap and the resistor thereafter, and it's still at 160mA. What happened?_

 

Geez, I wish I could tell you, but I feel your pain...


----------



## Filburt

Quote:


  Originally Posted by *amb* 
_Geez, I wish I could tell you, but I feel your pain... 
	

	
	
		
		

		
		
	


	


_

 

Maybe the board is bad. I had to use some CA to fix a manufacturing flaw on the side where the copper for the ground plate was exposed. It could just be some manufacturing defects are at work here, and my soldering simply aggrivated some other defect. Maybe I should try to get another board from tangent.

 Gosh, I wish I could tell what's wrong with this thing. I don't think I've blown a chip up yet, and it seems like this is due to oscillation of some sort. I just can't figure out how to fix it!


----------



## Heady

Quote:


  Originally Posted by *amb* 
_Heady, have you checked to see if your DMM is actually reading a reasonable current? I don't see anything obvious in the photos, but I assume you checked all nets with your DMM in ohms mode? Does it actually sound ok?_

 

amb - I haven't got the time to check my DMM yet but will soon. On another note, a sharp-eyed forumer in sgheadphone.net commented my C3 caps looked odd. I may have used the wrong values and will be checking soon. Sigh, I need a microscope.

 The strange thing, is the amp sounds good to me now. Of course, I am old so my high frequency sensitivity is probably gone, so I won't hear any oscillations in the form of high pitch whistles or screeching.

 But thanks, you have been a great help to all of us struggling to get this amp working.


----------



## Heady

amb - I have checked my DMM and it is reasonably accurate with the current draw. I used two AA batteries with 3.024V thru a 219.5ohm resistor and got a reading of 13.54mA which seems to be about right.

 I have also checked the capacitors and I have all the correct ones placed. The supposed error was probably due to the color of my pic being off.

 Can you elaborate on "checking the nets" as you have mentioned in one of your earlier post?

 Thanks.


----------



## cire

just finished my PINT last night. mini'fied with a gain of 6. this thing is incredibly quiet, while listening through ksc75 with the volume turned all the way up, there was almost zero noise. i guess i'm lucky in that my pint had no complications.


----------



## amb

Quote:


  Originally Posted by *Heady* 
_Can you elaborate on "checking the nets" as you have mentioned in one of your earlier post?_

 

Looking at the schematic, you'll see a number of components connected to each other. Each node of these connections is a "net". For example, the non-inverting input to the L/R opamp is connected to one leg of R2 and one leg of C1. That is one net, albeit a simple one with only three connections. Some nets have many more. Be sure to use the correct schematic. If you had Mini³fied your PINT, then the alterations should be reflected on the one you're working with.

 With the amp power off (and all capacitors discharged), you check for continuity between each of those components on the same net with your DMM in ohms mode to make sure they are connected (0 ohms), and check that net against other nets to make sure they are _not_ connected. Between nets that have resistors across them, you should measure the value of the resistor. For example, at the inverting input of the L/R opamps, if your R3 value is 1.2KΩ, then you should read 1.2KΩ between that net and the virtual ground net. However the meter should read about 101.2KΩ between the inverting input of the opamp and the non-inverting input (the resistance of R2 + R3) if your C1 is really a capacitor. If you Mini³fied your PINT, then the reading is more like 2.2KΩ at minimum volume position (R2 || R1) + R3, note that the R1 here refers to the 1K resistor installed in place of C1, not the actual R1 in the schematic. At maximum volume position on a Mini³fied PINT, the measurement should be (R2 || (R1 + Rpot)) + R3, which is about 11.1KΩ.

 As you can see, you need to account for all the resistances between nets which can be a series or parallel combination of various resistors.

 This is complicated slightly more by nets that are bridged by large electrolytic capacitors which will cause the reading to briefly show something between nets due to capacitor charging by the voltage from the DMM, so you'll want to let the reading settle (to "inifinite"). The opamps and diodes will also affect readings between certain nets, so measure the continuity with your meter both ways (swap the leads). For the opamp, since it contains circuitry inside, may skew the ohms reading between certain nets.

 Nevertheless, going through this exercise will help you determine if there are problems with parts values used, solder bridges, poor soldering, possible defective parts, and force you to think about all the interconnections of the circuit which may yield a new understanding about any malfunctions.


----------



## Heady

Thanks amb for your very informative post. Unfortunately, the current built I have is beyond help. I will use your info for my next built. I am now thinking of soldering the opamp last, so I can check and measure all the connections prior to soldering them in. Do you think this is feasible?


----------



## amb

Quote:


  Originally Posted by *Heady* 
_I am now thinking of soldering the opamp last, so I can check and measure all the connections prior to soldering them in. Do you think this is feasible?_

 

Yes, you could do that, but it might be a litle harder to do. With all the other parts in the way, you'll have to be careful with the soldering iron tip not to melt anything else.


----------



## Filburt

Alright, tangent sent me a new board. This one is fantastic...better build quality than any board I've seen thus far.

 Anyhow, I did this thing on autopilot as I was up all night writing a paper, and ended up using ferrites instead of resistors. Everything turned out fine, though. Power draw is ~58mA, and DC offset is less than a mV.

 So I now have a working 8397/6172 hybrid, and standard dual 8397. Yay!


----------



## dhp

Quote:


  Originally Posted by *Filburt* 
_Alright, tangent sent me a new board. This one is fantastic...better build quality than any board I've seen thus far.

 Anyhow, I did this thing on autopilot as I was up all night writing a paper, and ended up using ferrites instead of resistors. Everything turned out fine, though. Power draw is ~58mA, and DC offset is less than a mV.

 So I now have a working 8397/6172 hybrid, and standard dual 8397. Yay! 
	

	
	
		
		

		
		
	


	


_

 

what's the difference in the boards? A pad came off on my old one though :|


----------



## Filburt

Quote:


  Originally Posted by *DieInAFire* 
_what's the difference in the boards? A pad came off on my old one though :|_

 

The dimensions are exactly as they should be, ergo no parts of the board are shaved off where they aren't supposed to be (as was the case on the defective board). Overall build quality seemed better in general, including durability of pads.

 Who/What is that in your avatar?


----------



## dhp

Quote:


  Originally Posted by *Filburt* 
_The dimensions are exactly as they should be, ergo no parts of the board are shaved off where they aren't supposed to be (as was the case on the defective board). Overall build quality seemed better in general, including durability of pads.

*Who/What is that in your avatar? *_

 

not me


----------



## cire

despite contrary belief, Daniel is an ugly chick with ginormous breasts


----------



## Filburt

That is just such a strange looking picture. It looks like a photochop or something, but knowing the mighty internet it's probably real in some way.


----------



## tangent

Quote:


  Originally Posted by *DieInAFire* 
_what's the difference in the boards?_

 

It can only be manufacturing variation...there has only been one board run.

  Quote:


 A pad came off on my old one though :| 
 

Sorry to hear that, but that can happen with any board with enough abuse. Repeated soldering and resoldering, putting strain on the joint while it's being heated, using too hot an iron, etc. Technique and using the right tools can prevent some of these problems.

 What were you doing when it happened?


----------



## Heady

Quote:


  Originally Posted by *tangent* 
_Sorry to hear that, but that can happen with any board with enough abuse. Repeated soldering and resoldering, putting strain on the joint while it's being heated, using too hot an iron, etc. Technique and using the right tools can prevent some of these problems.

 What were you doing when it happened?_

 

Well, I now know one thing I must never do when trying to desolder parts - stick the iron tip down the hole of the PCB, nothing's worse for lifting the traces off!


----------



## FallenAngel

This is such a great thread, I decided to post my Mini3fied PINT difficulties here. I am building 2 PINTs, one of them I woun't even mention until later cause I think the Ground OpAmp is fried, so here is the second that's still kicking.

 First off, these are my modifications to the config:

 R3: 1.5k
 R4: 3.0k
 C7: 25V 1.5uF 10% "B" Tantalum Cap (Mouser URL)
 C6: Not used

 I made the pin 6 lead to the Ground OpAmp and soldered Pins 6 & 7 together. As far as I know, all instructions were followed to the dot, but of course as with most DIY, there are funky problems. I have also went over every single solder joint and reflowed them so they're nice and shiny.

 The Ground OpAmp gets pretty hot, not like burning hot right away, but I woun't want to keep my finger on it for more than 5-10 seconds.
 I also get a very precise and constand 4.0V of DC offset on both channels. The really weird part was, I measured and got this DC offset, put the amp to rest, next day I tried it and DC offset was 2mV! Of course I was like WOW! it fixed itself and cased it up. Then I tried playing something and it sounded like crap, tons of distortion, I measured DC offset again, still very low, but like 5 minutes later, it jumped up to 4.0V again. That's when I got totally confused.

 I also noticed one very strange thing, I get 7.0VDC between OG and IG, which I've read means my ground channel is broken, but I have no idea what that means so I'm not sure how to fix that. Can somebody help?

 I will post pics tonight when I get back from work.

 Thanks guys!


----------



## Filburt

Did you make sure that, after cutting the one trace, that continuity was actually broken?


----------



## FallenAngel

Yes, used DMM to check discontinuity between Pin 6 and OG. It was cut ok.


----------



## Filburt

Quote:


  Originally Posted by *FallenAngel* 
_Yes, used DMM to check discontinuity between Pin 6 and OG. It was cut ok._

 

Alright. It sounds like your ground chip is blown.


----------



## FallenAngel

I'm curious as to why/how? I mean the PINT did play, just really badly.


----------



## Filburt

Quote:


  Originally Posted by *FallenAngel* 
_I'm curious as to why/how? I mean the PINT did play, just really badly._

 

There are many things that could have happened. Oscillation could have fried it. Too much heat might have been able to. Momentary reverse supply could have as well. AD8397s fry really easily.


----------



## FallenAngel

Damn, that sucks! Just to confirm though... would the amp really still play music with a fried ground chip and would it really have such precise DC offsets on both channels?


----------



## The Monkey

Hi gang,

 I'm measuring between 29-30 mA current draw with my Pint (stock, from Tangent's parts list (AD8397)) with 1 9V battery. Does that sound right?


----------



## cire

Quote:


  Originally Posted by *The Monkey* 
_Hi gang,

 I'm measuring between 29-30 mA current draw with my Pint (stock, from Tangent's parts list (AD8397)) with 1 9V battery. Does that sound right?_

 

its slightly on the low side i believe, but should be ok.


----------



## Heady

I have finished my second built of the PINT and have done so very carefully. And I still have the same problem of oscillations and thus high current draw of about 170mA.

 Tangent has suggested replacing the L1 inductors with low values resistors. My questions are:
 1. What values are suitable? 
 2. Do I replace the L1 only for the ground or all 3 L1s.

 The built uses the mini3 configuration suggested by amb.

 Thanks.


----------



## tangent

Quote:


  Originally Posted by *Heady* 
_What values are suitable?_

 

As it says in the documentation, 10 to 100 ohms.

  Quote:


 Do I replace the L1 only for the ground or all 3 L1s. 
 

Since the resistors are outside the feedback loop now, you can only do it with the left and right channel resistors. With the resistors inside the loop, I believe you could have done it with the ground channel resistor as well.


----------



## Heady

Quote:


  Originally Posted by *tangent* 
_As it says in the documentation, 10 to 100 ohms._

 

I have to buy the resistors in lots of 50 for each value, granted they are not expensive. But 10 - 100 ohms is a wide range. I am asking what is a good value to start with? And what increments to work on if the first value don't work. I don't want to have a box full (fuller?) of unused parts. 
	

	
	
		
		

		
			






  Quote:


  Originally Posted by *tangent* 
_Since the resistors are outside the feedback loop now, you can only do it with the left and right channel resistors. With the resistors inside the loop, I believe you could have done it with the ground channel resistor as well._

 

If I un-mini3-fy the built, I replace all 3 inductors with the resistors. With the min3-fy built, I replace only the L/R inductors.

 Sorry if I am being so confused. I thought it was only my ground opamp which was oscillating. I am not good with electronic knowledge, my training was in body parts not electronics.


----------



## amb

Quote:


  Originally Posted by *Heady* 
_If I un-mini3-fy the built, I replace all 3 inductors with the resistors. With the min3-fy built, I replace only the L/R inductors.

 Sorry if I am being so confused. I thought it was only my ground opamp which was oscillating. I am not good with electronic knowledge, my training was in body parts not electronics. 
	

	
	
		
		

		
		
	


	


_

 

Yes, this is because with the ground ferrite taken out of the feedback loop, if you change it into a resistor it will increase the output impedance of the ground opamp, and that would adversely affect the stereo separation.

 Changing just the L/R ferrites to resistors (or switching to "stronger" ferrites) may be enough to tame an unstable ground opamp, _if the oscillation is caused by capacitive load_ at the output. This is because the ground opamp still "sees" the L/R opamps' outputs via the load, so they all interact in some fashion. However, if any of your opamps oscillate even without anything plugged into the headphone jack, playing with ferrites or resistors probably won't help at all. I would start looking at other causes of problems, such as inadequate power supply bypassing. You may also want to try lowering the rail splitter resistor values from 47KΩ to 20KΩ.


----------



## tangent

Quote:


  Originally Posted by *Heady* 
_But 10 - 100 ohms is a wide range. I am asking what is a good value to start with?_

 

It's in the documentation: start high and work your way down.


----------



## FallenAngel

Hey guys, some good news and some bad news, I replaced the ground chip with an AD45048 and the offset stablalized quite a bit. It is now around 5mv OG->OL and about 4mv OG->OR at full volume.

 The bad news is the current draw is pretty huge. It starts off at around 80mA and slowly starts climbing from there. I waited a few minutes until it reached 110mA and turned it off. Not sure exactly what that means and would appreciate a little help understanding what could be wrong.

 Thanks


----------



## Filburt

Quote:


  Originally Posted by *FallenAngel* 
_Hey guys, some good news and some bad news, I replaced the ground chip with an AD45048 and the offset stablalized quite a bit. It is now around 5mv OG->OL and about 4mv OG->OR at full volume.

 The bad news is the current draw is pretty huge. It starts off at around 80mA and slowly starts climbing from there. I waited a few minutes until it reached 110mA and turned it off. Not sure exactly what that means and would appreciate a little help understanding what could be wrong.

 Thanks_

 

It means oscillation.


----------



## Filburt

Quote:


  Originally Posted by *FallenAngel* 
_Damn, that sucks! Just to confirm though... would the amp really still play music with a fried ground chip and would it really have such precise DC offsets on both channels?_

 

Yes, it could still play sound through it. I know from experience


----------



## FallenAngel

Uhm... Just to ask the obvious next question... how do I fix oscillation in the PINT? I read tangent's "Working with Cranky Op-Amps" but unfortunatly I don't have an engineering background and some of the solutions seem like they are written in a different language all together.


----------



## Heady

Quote:


  Originally Posted by *tangent* 
_It's in the documentation: start high and work your way down._

 

I was afraid of that. Looks like I will have to built up a collection of 1026 resistors in those values. Sigh!

 On another note, amb has mentioned improving the bypassing to stop oscillations. Can one just solder a polyester cap to the V+ and V- legs of the opamp? And what values if this is possible? Thanks amb.


----------



## n_maher

Quote:


  Originally Posted by *FallenAngel* 
_Uhm... Just to ask the obvious next question... how do I fix oscillation in the PINT? I read tangent's "Working with Cranky Op-Amps" but unfortunatly I don't have an engineering background and some of the solutions seem like they are written in a different language all together._

 

Unfortunately there's really only one answer, and it's the obvious one. You have to track down what is causing the oscillation. Is that easy? Perhaps no, but that's the reality of the situation. There's only so much that people here are going to be able to help even if you post pictures and so on. As I discovered in the past with one of the PPA's that I helped a friend build sometimes solutions are not easily found and require both learning and rebuilding. So, hit the books my friend. Try to figure out what might be causing the oscillation and start trying to eliminate it. 

 Nate


----------



## FallenAngel

Heady: There are already caps on V+ and V-, they are C8.

 Would lowering this value help oscillation?


----------



## Heady

Quote:


  Originally Posted by *FallenAngel* 
_Heady: There are already caps on V+ and V-, they are C8.

 Would lowering this value help oscillation?_

 


 Hi, I have built two PINTs following the list of parts exactly and both do not work correctly. If you read the thread, some post back, amb suggested that if everything is correctly built and the opamps still oscillate, he thinks that bypassing caps may need to be increased in values. I am asking him if polyester caps instead of ceramics can be used and what values to use.

 Basically, I can discern two main lines of opinion here re: PINT and they are documented in this thread. One is the straight PINT and the other is the mini3-fied PINT.

 Tangent provides his opinion on the straight PINT while amb seems to be the authority on the mini3-fied PINT.

 I have a friend who has built 3 of the PINTs and have had no problems. I built two with the same parts and both of mine don't work. So it must be me. 
	

	
	
		
		

		
		
	


	




 I have put in considerable time and money on this project and while I am enjoying the challenge and learning, unfortunately, I have nothing working yet. And I have built several cmoys, Pimetas and others in the past, so I am not a newest newbie. This amp is not consistently reliable as is and Tangent has said so.


----------



## tangent

Quote:


  Originally Posted by *FallenAngel* 
_how do I fix oscillation in the PINT?_

 

I think you're looking for easy solutions. If there were an easy solution, I'd have just designed the amp with it included. You're at the point where easy solutions have failed, and you will have to either get down to engineering, or start throwing wild guesses at the problem, or abandon the project. Them's your choices.

  Quote:


  Originally Posted by *Heady* 
_Looks like I will have to built up a collection of 1026 resistors in those values. Sigh!_

 

No, that's not whta it means. It means that if you want to buy just one value that will fix the problem, use the highest recommended value: 100 ohms. Going lower is to improve performance, at the risk of a less effective fix.

  Quote:


 Can one just solder a polyester cap to the V+ and V- legs of the opamp? 
 

Yes, but if the problem truly is inadequate bypassing -- and it certainly may not be! -- then you should stick with ceramic caps in the standard positions. Also, "improving the bypassing" doesn't necessarily mean making the value larger. In fact, oftentimes, a lower value for the bypass cap will do a better job, because it will have a higher self-resonance frequency. I'd try 0.01uF before I tried something higher than 0.1uF.


----------



## Heady

Quote:


  Originally Posted by *tangent* 
_No, that's not whta it means. It means that if you want to buy just one value that will fix the problem, use the highest recommended value: 100 ohms. Going lower is to improve performance, at the risk of a less effective fix.

 Yes, but if the problem truly is inadequate bypassing -- and it certainly may not be! -- then you should stick with ceramic caps in the standard positions. Also, "improving the bypassing" doesn't necessarily mean making the value larger. In fact, oftentimes, a lower value for the bypass cap will do a better job, because it will have a higher self-resonance frequency. I'd try 0.01uF before I tried something higher than 0.1uF._

 

Thanks Tangent for clarifying these points. Ok, doesn't looks so bad now. I also got some TS922s (the only ones I could find from your list of alternates) to substitute the opamps with if all these don't work. I hope they are not as cranky as the AD8397s.


----------



## FallenAngel

Hey guys, I'm just curious, what Caps are you using for C4?

 I'm using 470 µF / 16V from Tangent's parts list and I'm running off 2 9V rechargables which are actually around 16.5V. Would this be a problem now and how much of an issue would this be when I plug in my 24.0V TREAD to recharge them?

 I never even noticed at first when I ordered the initial parts, so now I have 3 of those and 3 more of the 680 µF 10V and no idea what to do with them.

 Just in case, I just ordered some ELNA Duorex II 25V 1000uF from www.PartsConnexion.com, great canadian store, even though prices in USD, it's cheap and fast shipping to me.


----------



## blueworm

The value of the power cap C4 in the pint needs to higher than the supply voltage because its is the actual voltage the cap see's.

 This is not the case on the pimeta for example, since in normal conditions the power caps only see half the supply voltage even so it is recomended that the caps are rated above the max voltage, just in case the railspliter fails.

 In my first pint I used a panasonic FC 330 uF 25v.
 In my mini3'fied pint I used a elna cerafine 470 uF 25v.
 In both cases pints are supplied by 2x 9v.


----------



## 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-


----------



## SubRosa

Voltage is not being split evenly, V- is approx. 9V while V+ is approx. 6V. (With two 9Vs)

 EDIT: I measured 15V across C6, that's why it smoked; it doesn't seem the resistor divider is working but I've replaced them and it's still not functioning correctly, what's up?


----------



## MisterX

Quote:


  Originally Posted by *SubRosa* 
_EDIT: I measured 15V across C6, that's why it smoked; it doesn't seem the resistor divider is working but I've replaced them and it's still not functioning correctly, what's up?_

 


 Do you have the C7s installed the right way around? 
 Remember the stripe on the tantalum capacitors marks the positive lead not the negative lead.


----------



## SubRosa

Quote:


  Originally Posted by *MisterX* 
_Do you have the C7s installed the right way around? 
 Remember the stripe on the tantalum capacitors marks the positive lead not the negative lead._

 

*Kisses-Your-Feet*

 I had one of them reversed, I now have a completely working PINT.

 *Slaps self for making same mistake twice.*


----------



## Filburt

Quote:


  Originally Posted by *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._

 

Did you make sure you oriented C7 and C6 correctly?

 Edit: I see MisterX asked the same thing before me...hadn't refreshed the page before I posted.


----------



## FallenAngel

Well, I measures 0.8mV across IG-OG, DC offset below 9mV, but chip still oscillates. Current draw now starts from 40mA, then jumps to 80mA and it steadily goes up from that.

 I guess I'll start measuring all the nets to see if I find something off, and if nothing pops up obvious, guess it's LM6172


----------



## mb3k

Tangent, maybe I'm looking at the schematic wrong (it's 3:30am) but shouldn't the R4 on the second page of the schematics be in parallel with C3?


----------



## MisterX

the original schematic is fine.


----------



## tangent

Quote:


  Originally Posted by *mb3k* 
_shouldn't the R4 on the second page of the schematics be in parallel with C3?_

 

Why do you believe that? Seriously; I'm curious.

 Here's the EAGLE version of the schematic, which is tightly coupled with the board layout. The only way to get a board layout that doesn't match the schematic in EAGLE is to commit a design error, and I run frequent automatic design rule checks while laying out a board.


----------



## mb3k

Quote:


  Originally Posted by *tangent* 
_Why do you believe that? Seriously; I'm curious.

 Here's the EAGLE version of the schematic, which is tightly coupled with the board layout. The only way to get a board layout that doesn't match the schematic in EAGLE is to commit a design error, and I run frequent automatic design rule checks while laying out a board._

 

I'm most likely getting mixed up with the mini³fied version where R4 is in parallel with C3.


----------



## MisterX

Quote:


  Originally Posted by *mb3k* 
_I'm most likely getting mixed up with the mini³fied version where R4 is in parallel with C3._

 


 Still not right cause L1 is outside the feedback loop in the mini3fied thing.


----------



## mb3k

Okay, forget what I said completely.

 Today I constructed a Mini³fied PINT with a gain of 4 (R3=1.33kohms, R4=4.02kohms) and a ELNA Cerafine cap for C4 (ELNA Cerafine 470µF/25V) running off of a STEPS supply at 24V.
 I get these test values:
 Current Draw: 0.11A 
 IG to OG: 2.2mV
 OG to OR: 2.0mV
 OG to OL: 3.9mV
 Both opamps gets very hot, but listening to the amp it's perfectly fine - no distortion when I turn the pot either. The ELNA cap gets very slighty warm too.
 Do these values, especially the current draw, sound reasonable?

 EDIT: I do not have C6 installed.


----------



## cire

your current draw looks to be twice as much as it should. something has to be wrong.


----------



## dhp

hm, what problem would occur if you failed to cut pin 7 on the ground opamp?


----------



## kklee

I've been lurking here for quite a while and figured it's about time to give back to the community.

 I built a PINT (default parts, not Mini³fied yet) that seemed to be working fine, but had a high current draw of 170mA. The really strange thing was that it would turn on with a draw of 50mA, but would slowly creep up to about 80mA and then shoot up to 170mA within a few seconds.

 The problem went away as soon as I added C6. I'm guessing that there was an oscillation that took a little time to get started.

 ...Ken


----------



## mb3k

I finally got a steady 50mA current draw somehow, and I didn't even touch the circuit, but now there's no sound from either channels.
 My best guess is the op amps finally fried. Frustrating.
 What's everybody's opinion on C6?


----------



## [AK]Zip

Quote:


  Originally Posted by *mb3k* 
_I finally got a steady 50mA current draw somehow, and I didn't even touch the circuit, but now there's no sound from either channels.
 My best guess is the op amps finally fried. Frustrating.
 What's everybody's opinion on C6?_

 

I have built quite a few of these and on a few of them I left C6 off to try and it worked just fine without it.

 -Alex-


----------



## cire

i've built two minified PINTs so far and zero issues with populating everything.

 after playing with my PINT powered by my digital variable PSU, i've come to a couple conclusions when it comes to considering voltage (keep in mind, i used crappy sony cans):

 -audible distortion starts at about 3v. its pretty slight at that voltage, but as you go lower, it gets more and more crackly, like bad AM reception. the thing pretty much dies at 2.3v

 -current draw is constantly ~50ma from 18v down to 4.5v. lower than 4.5v, the draw shoots the hell up to 180ma, but when voltage drops to 3.2, the current also drops to a low 20ma


----------



## kklee

Quote:


  Originally Posted by *cire* 
_
 -current draw is constantly ~50ma from 18v down to 4.5v. lower than 4.5v, the draw shoots the hell up to 180ma, but when voltage drops to 3.2, the current also drops to a low 20ma_

 

Now that you mention it, I noticed the same thing. I turned on my power supply at 0V and turned it up watching the current draw. At first I thought something was wrong when I saw that it rose to ~180mA at 4.5V, but as I kept turning up the voltage (expecting smoke at any second!), it dropped down to ~50mA and stayed there all the way to 18V.


----------



## NeilR

Just to add a data point here, I built up my first Pint last night, Mini3-fied, and it fired right up, drawing about 51mA. The chips get very hot by my way of thinking and I thought I might have had a problem, but there are no oscillations on the scope and it sounds great. 

 The SMD work was very interesting with all the different SMD bits that went into it.

 Thanks to Tangent and all the contributors to this and other threads. Especially AMB foir the Mini3 mod.

 Now I just have to decide on a case....

 Regards,
 Neil


----------



## Filburt

Quote:


  Originally Posted by *NeilR* 
_Just to add a data point here, I built up my first Pint last night, Mini3-fied, and it fired right up, drawing about 51mA. The chips get very hot by my way of thinking and I thought I might have had a problem, but there are no oscillations on the scope and it sounds great. 

 The SMD work was very interesting with all the different SMD bits that went into it.

 Thanks to Tangent and all the contributors to this and other threads. Especially AMB foir the Mini3 mod.

 Now I just have to decide on a case....

 Regards,
 Neil_

 

Did you include C6?


----------



## NeilR

Quote:


  Originally Posted by *Filburt* 
_Did you include C6?_

 

Yes, I did. Tangent's specified part.

 I made a decision to run this with 1 9V rechargeable. With that battery, I am drawing 44ma, which is a little better than the 51-52ma I drew at around 22V. The chips also run much cooler, of course. That decision had more to do with casing considerations than anything else.


----------



## threepointone

Hey, I was just thinking--If we're using the PINT for low impedance IEMs, current is more important than voltage, correct? So it'd probably be better for me to maybe use two 9Vs in parallel for longer battery run time? Can you charge batteries in parallel with simple modifications to this charging circuit, or are there more problems to be considered in this configuration?


----------



## cetoole

Quote:


  Originally Posted by *threepointone* 
_Hey, I was just thinking--If we're using the PINT for low impedance IEMs, current is more important than voltage, correct? So it'd probably be better for me to maybe use two 9Vs in parallel for longer battery run time? Can you charge batteries in parallel with simple modifications to this charging circuit, or are there more problems to be considered in this configuration?_

 

It is not a good idea to have NiMH batteries in parallel. It would be a better idea to have 8 or so NiMH AAA batteries in series, which would also give you far superior battery life (900-1000mAH for the best NiMH AAA, compared to ~270mAH for the best NiMH 9v PP3 battery), and not take up too much additional room. Doubt it would fit a mint tin, but I havnt actually used one ever, and there are other casing options around.


----------



## cire

the problem with running NiMH batteries in parallel is that they have low impedence, so the higher voltage one essentially ends up feeding current into the lesser voltage one. this problem doesn't arise for alkaline batteries because their impedences are high enough to prevent it.


----------



## Filburt

Quote:


  Originally Posted by *NeilR* 
_Yes, I did. Tangent's specified part.

 I made a decision to run this with 1 9V rechargeable. With that battery, I am drawing 44ma, which is a little better than the 51-52ma I drew at around 22V. The chips also run much cooler, of course. That decision had more to do with casing considerations than anything else._

 

Okay, I was just asking. C6 seems to really help quell oscillations in the mini3 config, then. I don't have C6 installed and the best I could pull off was about 56mA, which from what I've gathered is quite low w/ C6 omitted. I had to do everything practically flawlessly to get it there 

 I may just start installing C6 and making it easier on myself, if I build any more


----------



## amb

Quote:


  Originally Posted by *Filburt* 
_Okay, I was just asking. C6 seems to really help quell oscillations in the mini3 config, then.
 ...
 I may just start installing C6 and making it easier on myself, if I build any more 
	

	
	
		
		

		
		
	


	


_

 

My Mini³fied PINT does not have C6 installed, and it is stable. The reason why C6 was omitted was because in the current "real" Mini³ prototype there is no such capacitor, and my Mini³fied PINT was serving as a test mule where I wanted to test the Mini³ circuit on the PINT pcb layout for comparison purposes, so aside from the battery charging circuit, everything else was made to be identical to the Mini³ to avoid introducing other variables.

 That said, however, I don't see any reason why you shouldn't install C6. It is simply some extra supply rail decoupling with a different capacitor type.


----------



## threepointone

I was just wondering, has anyone with problems tried cleaning the flux off the board to see if that helps at all? The only reference to flux and PINT in these forums is in a FS post by someone who couldn't get theirs to work and didn't have a flux cleaner. And of course, tangent cleans all his boards with isopropyl alcohol. I know it's a unlikely, but maybe this is why some people have misbehaving PINTs while it seems like most of tangent's own PINTs are fine?

 and also, what's the typical current draw of a PINT? (2x AD8397 configuration)


----------



## cire

Quote:


  Originally Posted by *threepointone* 
_and also, what's the typical current draw of a PINT? (2x AD8397 configuration)_

 

depends on the voltage:
 ~4.5 to 24v = ~50ma
 ~3.2 to ~4.4v = ~180ma
 ~2.5 to ~3.1v = ~20ma


----------



## cmirza

Quote:


  Originally Posted by *cire* 
_depends on the voltage:
 ~4.5 to 24v = ~50ma
 ~3.2 to ~4.4v = ~180ma
 ~2.5 to ~3.1v = ~20ma_

 

Im still pretty new to DIY stuff. So if you have a draw of ~50ma and use a battery with ~250mah capacity, you should expect ~5 hours of usage from the device?


----------



## cire

that would be true if only companies didn't exaggerate their specs


----------



## FallenAngel

Wow! I just installed C6 in my Mini^3fied PINT and it stabalized a huge amount more. Now I'm getting around 50mA current drawn, but unfortunatly it still goes up 
	

	
	
		
		

		
			





, but much slower now. After 2 minutes it went up to 52mA, but every 10 seconds or so, it goes up another 0.1mA! Bah!


----------



## Filburt

Quote:


  Originally Posted by *FallenAngel* 
_Wow! I just installed C6 in my Mini^3fied PINT and it stabalized a huge amount more. Now I'm getting around 50mA current drawn, but unfortunatly it still goes up 
	

	
	
		
		

		
		
	


	




, but much slower now. After 2 minutes it went up to 52mA, but every 10 seconds or so, it goes up another 0.1mA! Bah!_

 

If it sounds OK, it's probably fine at this point.


----------



## MisterX

FallenAngel:
 How are you obtaining these results? 
 Is the amp loaded at all or just sitting there with no load on it?


----------



## FallenAngel

MisterX: I plugged in my cheap $40 mp3 player as source, but didn't turn it on. Then I connected my DMM between the positive lead of my battery to the positive lead of the board (B+) and turned on the amp to almost max volume. The DMM is set to DC Amps "< 200mA", and i see the little .1's go up up up.


----------



## jl123

Don't know if you already posted one but a pic could help. Also what are you running on your L1s?


----------



## MisterX

My bad.....I assumed that load on the implies something connected to the output of the amplifier. 
	

	
	
		
		

		
		
	


	



 Like say for instance a dummy load. 
 IIRC Tangent has a tutorial for how to make a dummy load on his site somewhere. 


 What is your DC-offset doing as the current draw increases? 
 Is it also increasing?


----------



## SubRosa

Hello, back again.

 Though Mister X's help seems to have fixed the problems I've had, any time I try to add C6 the capacitor smokes, now, the suggested C6 in Tangent's guide is rated for 10V and I read the full voltage of two 9Vs across its pads, which is what I should be seeing correct? (C6 is before the resistor divider); but when I put in a 25V tant it got incredibly hot and then smoked too. What's the problem here, this is only the power section, before the bulk of the "complicated stuff", simple bypassing. So, ideas? 

 Also, anyone have any idea why I can't measure current draw with my DMM?


----------



## MisterX

Quote:


 Also, anyone have any idea why I can't measure current draw with my DMM? 
 

Is the fuse blown?


----------



## jl123

Are you orienting them correctly? The stripe indicates positive.

 MisterX put up a nice graphic on the first page to show how to measure current draw.


----------



## cetoole

Quote:


  Originally Posted by *SubRosa* 
_Also, anyone have any idea why I can't measure current draw with my DMM?_

 

Are the test probes in the correct jacks on the meter? I havnt seen any DMMs that use the same jacks for current measurement as voltage.


----------



## SubRosa

Yes, C6 is oriented correctly.

 I know the procedure to measure current draw, it just doesn't read anything and the amp doesn't turn on.

 EDIT: It's a cheapy, the probes are hardwired. Could that be the problem?


----------



## jl123

Also remember to change it back. Don't want to go shorting anything out when trying to measure voltage. 
	

	
	
		
		

		
		
	


	




 If the amp won't power on with the meter inline then it's the meter. The biggest issue I think is try and figure out why the amp is smoking the c6.


----------



## NeilR

Quote:


  Originally Posted by *SubRosa* 
_Hello, back again.

 Though Mister X's help seems to have fixed the problems I've had, any time I try to add C6 the capacitor smokes, now, the suggested C6 in Tangent's guide is rated for 10V and I read the full voltage of two 9Vs across its pads, which is what I should be seeing correct? (C6 is before the resistor divider); but when I put in a 25V tant it got incredibly hot and then smoked too. What's the problem here, this is only the power section, before the bulk of the "complicated stuff", simple bypassing. So, ideas? 

 Also, anyone have any idea why I can't measure current draw with my DMM?_

 

The Mouser part specified in the parts list is a 25V part. The Digikey part is a 10V part. Seems to me that the part should be a 25V part for a 2x9V amp and that is probably why it fails.

 If you want to test that that is the problem, bypass one of the battery clips and run the amp at 9V with a fresh C6 10V part.


----------



## SubRosa

Quote:


  Originally Posted by *NeilR* 
_The Digikey part is a 10V part. Seems to me that the part should be a 25V part for a 2x9V amp and that is probably why it fails.

 If you want to test that that is the problem, bypass one of the battery clips and run the amp at 9V with a fresh C6 10V part._

 

Yes, I ordered from Digikey. (Not being rude) In my post I stated I'd tried 25V tants in C6 and they've smoked too.

 EDIT: Sometimes I wonder...

 I cut down to one 9V because the only fresh tant I had left was a 10V and...it didn't smoke, didn't get hot, everything is fine...

 Before it had smoked with either one or two 9Vs, I'm not complaining, just...ugh.


----------



## SubRosa

Quote:


  Originally Posted by *cire* 
_depends on the voltage:
 ~4.5 to 24v = ~50ma
 ~3.2 to ~4.4v = ~180ma
 ~2.5 to ~3.1v = ~20ma_

 

Sorry to double post but is this consistent with what other people are seeing? Could others with PINTs test this for me. As I stated, my DMM won't measure current draw and it looks like I'll be using one 9V now, so that would put me in the 180ma range if this info is universal, unless I buy a 9.6V NiMH.

 Thanks.


----------



## amb

Quote:


  Originally Posted by *SubRosa* 
_Sorry to double post but is this consistent with what other people are seeing? Could others with PINTs test this for me. As I stated, my DMM won't measure current draw and it looks like I'll be using one 9V now, so that would put me in the 180ma range if this info is universal, unless I buy a 9.6V NiMH._

 

No, my own observation is that the dual AD8397 config will draw a total of ~50mA between 15V-24V of supply voltage, dropping to around ~40mA around 9V, and then go up a bit to ~50mA-60mA at around 5V or 6V. All currents are subject to chip-to-chip tolerances and are thus a bit "hand-wavy", but 180mA is definitely not normal at any supply voltage.


----------



## Heady

Quote:


  Originally Posted by *cire* 
_depends on the voltage:
 ~4.5 to 24v = ~50ma
 ~3.2 to ~4.4v = ~180ma
 ~2.5 to ~3.1v = ~20ma_

 

Hi cire, can you please tell us if these figures are what you measured with your PINT with AD8397 opamps. Or did you compile them from the results posted by others.

 Thanks.


----------



## The Monkey

Quote:


  Originally Posted by *amb* 
_No, my own observation is that the dual AD8397 config will draw a total of ~50mA between 15V-24V of supply voltage, dropping to around ~40mA around 9V, and then go up a bit to ~50mA-60mA at around 5V or 6V. All currents are subject to chip-to-chip tolerances and are thus a bit "hand-wavy", but 180mA is definitely not normal at any supply voltage._

 

Based on very limited testing, my results with 9V are very similar to amb's.


----------



## cire

Quote:


  Originally Posted by *Heady* 
_Hi cire, can you please tell us if these figures are what you measured with your PINT with AD8397 opamps. Or did you compile them from the results posted by others._

 

its what i measured using my digital benchtop PSU


----------



## Filburt

Sorry, I didn't see the post where you said you were smoking C6. Did you make sure you oriented them correctly? C7 also?


----------



## Heady

Quote:


  Originally Posted by *cire* 
_its what i measured using my digital benchtop PSU_

 

Thanks cire. I did get 160mA while using 4.5v but the amp was oscillating, could hear some odd sounds.


----------



## SubRosa

Quote:


  Originally Posted by *Filburt* 
_Sorry, I didn't see the post where you said you were smoking C6. Did you make sure you oriented them correctly? C7 also?_

 

Yep, everything was oriented correctly; I don't know how, but it's cleared itself up. Just gotta' case it up now.


----------



## FallenAngel

Great news 
	

	
	
		
		

		
			





, after hooking up a cheap mp3 source and some crappy headphones, I'm measuring 50mA - 55mA of current draw off 2 9V batteries, it kinda jumps around while playing music, but it does sound pretty damn good. DC offset is below 10mV at full blast.

 Listening to it off my TREAD right now with MS-2s and it sounds really good, I really don't know whether I like it more than the Pimeta which cost me more than twice as much.

 I declare this Mini^fied PINT complete. Just finished casing it in a mint which, with some creative positioning (I've got a huge 1000uF ELNA cap in there) actually fits everything including a big DC power jack with 2 9V's. Pictures soon.

 Mini^fied version done, time to clean up the mess on the second, Tangent's Low Noise version, there's a headache in the making, and for those who see the time, yes it is 3AM


----------



## amb

Quote:


  Originally Posted by *FallenAngel* 
_Great news 
	

	
	
		
		

		
		
	


	




, after hooking up a cheap mp3 source and some crappy headphones, I'm measuring 50mA - 55mA of current draw off 2 9V batteries, it kinda jumps around while playing music, but it does sound pretty damn good. DC offset is below 10mV at full blast._

 

Yes, it's normal for the current draw to dynamically vary while playing music with a headphone (or dummy load) connected. The ~50mA figure is for quiescent (i.e., idle, no sound, volume control minimum) condition.

 Congratulations for a successful build.


----------



## Heady

After getting a new analog multimeter, I am happy to announce that my second built, with AD8397 opamps, L/R opamp mini3-fied but ground opamp as per Tangent, now appears to be working normally. Current draw is about 50mA. This is with 9V battery. Could not get it to work with 3 or 4 AA batteries.

 The first built is not resurrectable. RIP.


----------



## mb3k

I just built another.
 Works fine, gain of 4, but aaround 70-80mA. But very very low dc offsets.
 Hopefully it's alright


----------



## cire

just built a PINT with a pair of AD45048s and it works fine as far as i can tell. the only thing worth noting is that the offset is a bit higher than all the other 8397 PINTs i've built at 13mv. the 8397 ones were normally around 6-8mv


----------



## Filburt

Quote:


  Originally Posted by *mb3k* 
_I just built another.
 Works fine, gain of 4, but aaround 70-80mA. But very very low dc offsets.
 Hopefully it's alright_

 

Probably mild oscillation. Try throwing C6 in.


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## mb3k

Quote:


  Originally Posted by *Filburt* 
_Probably mild oscillation. Try throwing C6 in._

 

It's already in.
 It's running off of a STEPS at 24V.


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## tangent

Quote:


  Originally Posted by *mb3k* 
_It's already in. It's running off of a STEPS at 24V._

 

Try lowering the STEPS' output voltage.


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## mb3k

I have a feeling the gain of 4 is not high enough for the AD8397 to be stable enough. Tangent, I've tried running off of a single 9V, and the draw is 60mA, but the op-amps still get burning hot.
 I'll try swapping R3 & R4 for a gain of 6 and see what I get.


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## [AK]Zip

Quote:


  Originally Posted by *mb3k* 
_I have a feeling the gain of 4 is not high enough for the AD8397 to be stable enough. Tangent, I've tried running off of a single 9V, and the draw is 60mA, but the op-amps still get burning hot.
 I'll try swapping R3 & R4 for a gain of 6 and see what I get._

 

I am running a gain of 4 with 1 9v and I am having no problems...

 -Alex-


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## sheya

Perhaps this question will label me as too much of a neophyte to have attempted to build a PINT, but here goes.

 I have a minified PINT built, but I haven' t hooked up the power supply yet. I don't know which pad goes to which wire. Where do W-, B-, M+, M-, W+, B+ hookup? I intend to use 2x9volt batteries, so I have two +, two - for the batteries, and one + and one - for the charger. Which pad is for which? I tried figuring it out based on the schematic, but I found it confusing and am not sure.

 Any help would be appreciated, I'd like to hook up the power supply correctly so I don't fry the amp in learning how to hook it up.

 Thanks-
 Aaron.


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## MisterX

W+ = External DC input Positive
 W- = External DC input negative


 For two batteries wired in series: 
 M+ = Battery 1 Positive
 B- = Battery 1 Negative
 M- = Battery 2 Negative
 B+ = Battery 2 Positive

 For a single battery:
 B+ = Battery Positive
 B- = Battery Negative

 Clear enough?


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## cire

Quote:


  Originally Posted by *sheya* 
_Where do W-, B-, M+, M-, W+, B+ hookup?_

 

wow, uhm...yeah... here we go: the markings are fairly self explainatory. W- and W+ are the pads for the wallwart, B+ and B- are the pads for the battery and M+ and M- are shorted together and are for if you intend on using two batteries in series.

 damn, beaten by the X


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## mb3k

Quote:


  Originally Posted by *sheya* 
_Perhaps this question will label me as too much of a neophyte to have attempted to build a PINT, but here goes.

 I have a minified PINT built, but I haven' t hooked up the power supply yet. I don't know which pad goes to which wire. Where do W-, B-, M+, M-, W+, B+ hookup? I intend to use 2x9volt batteries, so I have two +, two - for the batteries, and one + and one - for the charger. Which pad is for which? I tried figuring it out based on the schematic, but I found it confusing and am not sure.

 Any help would be appreciated, I'd like to hook up the power supply correctly so I don't fry the amp in learning how to hook it up.

 Thanks-
 Aaron._

 

W+/- is for the *w*all
 B+/- is for the *b*atteries
 M+/- are pads that are common points connected together to make it easier/cleaner to connect two batteries.

 EDIT: Dang, beaten by both of you. That was really fast.


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## sheya

Thanks for your responses, I appreciate your help.

 -Aaron.


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## sheya

I'm listening to my minified PINT right now with my Etymotic ER4P w/S adaptor. All seems to be well, I'm using the minified version. I have less than 10ma of offset, and the chips are reasonably cool. Now I just have to case it up, making sure to isolate all the jacks from the case. 

 I obviously haven't been able to do any critical listening or comparison, but at first listen, it sounds very good, using an audioquest ministereo plug to RCA cable, playing CD's through my Parasound CDP1000.

 This was my first surface mount project, and it really wasn't difficult at all. The hardest part was seeing which way the diodes are supposed to go, even with a magnifying glass and a bright light it was hard to see the line.

 I understand the discontinuation of the project, because of problems that people have had with building the amp, but from my experience of building one PINT (I have two more to build), it isn't difficult or troublesome. Granted, I minified it right away because I didn't order the correct part for the output capacitors, and I had the resistors and other parts to make the minified version on hand. 

 Thanks to all who have posted in this thread and others about the PINT, reading them helped me a lot in building the amp. And thanks to Tangent for making such a great product that can be built for such an affordable price.

 -Aaron.


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## Heady

Didn't tangent said he may change his mind and still sell the PINT pcb for at least another lot of pcbs? Maybe tangent will change his mind if enough people ask him nicely?


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## Heady

Ok, sorry for re-surrecting this thread even though PINT is no longer available from Tangent.

 I asked for help before with my PINT builts. To be fair to Tangent, the second built was fine. It just doesn't want to run at 4.5V which is what I used to power it. When I switched to a 9V battery, the PINT ran fine.

 I notice once the 9V battery approaches 6V, I get the strange whistles etc indicating that oscillations are probably present. At 9V, the current draw is about 55mA.

 So there, see, Tangent. It wasn't your fault.


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## splaz

Okay. Still have not got round to starting one as I'm getting some parts.

 Question about the ferrites. Are the DC resistance and current specs important ?

 The difference is 0.1 as compared to 0.01 dcr and 500mA compared to 6000mA.


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## amb

Quote:


  Originally Posted by *splaz* 
_Question about the ferrites. Are the DC resistance and current specs important ?

 The difference is 0.1 as compared to 0.01 dcr and 500mA compared to 6000mA._

 

DC resistance should ideally be low so that it doesn't waste power and negate the low output impedance of the AD8397. The current rating should be high enough to handle the highest output current the amp might deliver without magnetic saturation (which causes distortion). Between your two choices, the "smaller" ferrite with 0.1Ω DCR is more than low enough and 500mA is also more than the opamp's output rating. The "bigger" ferrite would be overkill in this application. Would it even fit the space on the board?


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## splaz

Both are 1206. Different manufacturers. 

 Better spec one is Maruta, 33 ohm @ 100MHz, it's in tangent's part list, from Mouser.

 The lower spec is Fair-rite 30 ohm @100MHz, from RS Components.

 Closest value I can get relatively easily. Good to hear the specifications are fine though.


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## splaz

Okay. Every single part except this one I have sorted.

 C6. I've read through the parts selection guide. Tangent says that it is not needed, sort of a 'just in case' part. I'd rather have it in. Problem is I can't seem to easily find a 4.7 microfarad in 35V in the right package size. I can however fairly easily get a 2.2 microfarad in 35V rating.

 Thing is, does 2.2 still fulfil the purpose of the part ?

 Tangent stated that it provides additional bypassing in the frequency between C4 and C5. I'm assuming the value is important to that function.


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## quicksilver96

On Tangent's parts list, he has "4.7*+* µF/25 V tantalum caps, 3528-21 size" listed. I used Digikey P/N 399-3368-1-ND, 6.8 µF/25 V tantalum caps in the above size. They are $1.35/ea, I have a few extra PM if you want a couple.


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## nysulli

mouser also carries the part, as listed on tangents parts list, i highly suggest ordering it just in case, its removed some mild oscilations in a few cases, mine for example went from 63ma to 54ma draw after adding c6 and the opamps are noicably cooler as a result


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## splaz

Location to the left... 

 Bit of a hassle ordering from the US just for those. Thanks for your help anyway.

 Looks like I'll just go to Farnell for them.

 That or I'll just settle for powering it off less. I was thinking of using 24V but the 25V specs are a tad worrying if you take into account possible problems like tolerances, slight variations or manufacturing flaw/error in the parts themselves, the fact the supply may not be exactly 24V and ripple. Even with drop accross the diode I'd rather not risk it. All the other parts I'm using are rated to 35V or higher anyway.

 Also, just thought I'd cram another question in here. Seriously should be the last. For anyone that's done a PINT with 2x9V batteries. Would an electroylytic cap 20mm high fit ?

 non-ninja edit: Would it fit in a mint tin... you know your standard penguin, altoids thing that I'll have fun trying to find over here ?

 from what I've seen it should. But alot of things should but can't... so thought I'd ask.


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## FallenAngel

I built a PINT with 2x9V batteries in a Mints TIN and the cap I'm using is a 25V 1000uF ELNA Duorex II which is pretty huge, it's 16 x 25mm and it just barely fits.


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## splaz

wow. This ain't that big, a 10x20. Would be nice to trade that height for a bit of width but no such luck in RS's range of case sizes. But I should be able to make that fit if you can do that.

 Okay now I'm sure I'm 100% sorted for parts. Now to break the news to my wallet that more purchases are coming.


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## rjkdivin

Quote:


  Originally Posted by *splaz* 
_Okay. Every single part except this one I have sorted.

 C6. Tangent says that it is not needed, sort of a 'just in case' part. Problem is I can't seem to easily find a 4.7 microfarad in 35V in the right package size. I can however fairly easily get a 2.2 microfarad in 35V rating.

 Thing is, does 2.2 still fulfil the purpose of the part ?
_

 

Try Mouser part no. 80-T491B475K025 from Tangents original parts list. It is 4.7uf in 25v SMD Tantalum. I'm going to start my Mini3ized Pint up without C6 to begin, but I have some on hand in case needed. I got 12 from Mouser about a month ago.

 As to the 2.2uf as a replacement, I don't know for sure, but it seems pretty close in value.....AMB???

 Robert


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## rjkdivin

I fired up my first Pint (Mini3ized) tonight and it sounds great.....very dynamic, and very quiet.

 I got the following measurements: (no load and inputs not shorted)

 Running at 9V:
 Current - 63mA
 IG to OG - .8mV
 OG to OR - .09mV
 OG to OL - .13mV
 Temperature of U3 - 98 deg F
 Temperature of U1 - 105 deg F

 Running at 18V:
 Current - 70.5mA
 IG to OG - 1.8mV
 OG to OR - .05mV
 OG to OL - .09mV
 Temperature of U3 - 106 deg F
 Temperature of U1 - 113 deg F

 Do these look okay?

 Using an input source and HD-600 as load, the current and temperatures remain approximately constant at both voltages. So far I cannot hear any difference in sound quality as I vary my bench supply between 9V and 18V. I'm reluctant to try it up any higher as the Op-Amp at 18V - 113 deg F is feeling pretty warm.

 At this current I'm not sure how long two 9v. 270mAh batteries would last...7hrs?... and I'm wondering if it might be good to swap the ground channel Op-Amp for a lower current model?
 Robert


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## MASantos

You said your PINT is minified but you have instaled R4. In the minified configuration you must stack R4 and C3 together and place them http://www.apuresound.com/pint/files/mmm.pdfin the C3 position. Check here for more information about minified PINT .

 Also, I believe that with one 9v battery you are drawing more current than you should. My pint draws 44mAh with one 9v. 

 QUOTE=rjkdivin]I fired up my first Pint (Mini3ized) tonight and it sounds great.....very dynamic, and very quiet.

 I got the following measurements: (no load and inputs not shorted)

 Running at 9V:
 Current - 63mA
 IG to OG - .8mV
 OG to OR - .09mV
 OG to OL - .13mV
 Temperature of U3 - 98 deg F
 Temperature of U1 - 105 deg F






[/QUOTE]


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## rjkdivin

Quote:


  Originally Posted by *MASantos* 
_You said your PINT is minified but you have instaled R4. In the minified configuration you must stack R4 and C3 together and place them the C3 position. 

 Also, I believe that with one 9v battery you are drawing more current than you should. My pint draws 44mAh with one 9v. _

 

Thanks MASantos....you are correct.....I forgot to remove R4 on the front of the board before I tested it. I do, in fact have R4 and C3 stacked at the C3 position per AMB's instructions.


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## MASantos

double post


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## rjkdivin

I removed the extra R4 on the front of the PCB. It did not change the current, offset, or temperature measurements in any significant way, but it did open up the sound perceptably....it still sounds very good. When I get to it, I will run an A-B comparison with an M3 and my Hornet.

 My R4(s) are sized with R3 for gain 11. Would going to gain 6 reduce the current draw?

 Robert


----------



## amb

Quote:


  Originally Posted by *rjkdivin* 
_As to the 2.2uf as a replacement, I don't know for sure, but it seems pretty close in value.....AMB???_

 

The value is a bit ad hoc, so 2.2µF is probably ok.

 Your current draw is a bit higher than I'm used to seeing, but not far off the mark. Higher voltage gain (R4 and R3 values) should buy you a bit more margin of stability for L/R channels, but it wouldn't make much difference at the ground channel where the gain is 1.


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## rjkdivin

Quote:


  Originally Posted by *amb* 
_Your current draw is a bit higher than I'm used to seeing, but not far off the mark. Higher voltage gain (R4 and R3 values) should buy you a bit more margin of stability for L/R channels, but it wouldn't make much difference at the ground channel where the gain is 1._

 

I now have two Minified Pints up and running....one at a gain of 6, and one at 11. They both seem to be quite stable using my HD-600s and at voltages between 9v and 18v from my bench supply. I've switched both to the LM6172 for the ground channel opamp and kept the AD8397 for left and right. The temperature of the opamps climbs about 3 or 4 deg F. when going from 9v up to 18v., but still reasonable at about 104 deg max.

 Using gain 6 gives the pot a slightly more usable range.

 Changing to the LM6172 on the ground channel dropped the idle current dramatically down to about 30mA, which now seems a bit low....is this normal....or close to it?
 Robert


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## tangent

Quote:


  Originally Posted by *rjkdivin* 
_Changing to the LM6172 on the ground channel dropped the idle current dramatically down to about 30mA, which now seems a bit low....is this normal....or close to it?_

 

Seems reasonable to me. Around 25 mA for the 8397, and around 5 mA for the 6172. Both are temperature and supply voltage dependent, so study the datasheets carefully if you want a more exact answer.


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## rjkdivin

Quote:


  Originally Posted by *tangent* 
_Seems reasonable to me. Around 25 mA for the 8397, and around 5 mA for the 6172. Both are temperature and supply voltage dependent, so study the datasheets carefully if you want a more exact answer._

 

Thanks Tangent!....have you given any more thought to selling these boards again? I'd really like to build one more.
 Robert


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