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PPA v2 construction discussion
Feb 12, 2011 at 10:15 PM Post #976 of 1,084
Quote:
nixnada said:
It has worked wonderfully the last 6 years. But last year the solderpoints on the input wires started to fail
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Input wiring can't explain hot buffer chips. Something else is wrong.
 
For what it's worth, though, if you've destroyed the rear input pads, you can just run longer wires to the front set. I'd braid them together to try and get some shielding benefit from the ground wire.
 
 
Quote:
I found that it draws a lot of current about 500 mA from a 9 V battery. Also there is a large voltage drop about 3 volts, so something is drawing a lot of power.
 
The buffer chips (those are the intersil ha3-5033-5) are getting hot all 3 of them. After about 10 seconds too hot to touch.
Click to expand...

 
It sounds like the buffers are destroyed. I see that you've left out D1, which could mean you connected power backwards once, which will kill chips very quickly. If that happened, the op-amps might be dead, too, though perhaps the isolation JFETs saved them.
 
 
Quote:
nixnada said:
I suspect oscillation because the IN (leg 4) on the buffer transistor is building up voltage as it gets hotter and hotter.
Click to expand...

 
You also left out all the bypass caps, which could explain oscillation and heat. But, the fact that it worked for 6 years argues against that.
 
Try removing the buffers and replacing them with jumpers. If they're the only part that died, you've just created a glorified CMoy. If it sounds okay, it confirms the death of only the buffers.
 
Feb 13, 2011 at 2:13 PM Post #977 of 1,084
 
 
Quote:
It sounds like the buffers are destroyed. I see that you've left out D1, which could mean you connected power backwards once, which will kill chips very quickly. If that happened, the op-amps might be dead, too, though perhaps the isolation JFETs saved them
Click to expand...

You're right! And what a stupid mistake that was. I just realized that i had the D1 in my inventory, but somehow have missed putting it to good use. Come to think of it i'm pretty sure that i have reverse voltaged the d... thing fiddling with the powersupply.
 
Quote:
You also left out all the bypass caps, which could explain oscillation and heat. But, the fact that it worked for 6 years argues against that.
Click to expand...

I will try installing the bypass caps and see if it helps
 
Quote:
Try removing the buffers and replacing them with jumpers. If they're the only part that died, you've just created a glorified CMoy. If it sounds okay, it confirms the death of only the buffers.
Click to expand...

I tried jumpering the buffers and although i did hear the testtone, it was horribly distorted. So my guess is that pretty much all the chips are fried
eek.gif

 
 
Seems i must place some orders for new IC's.
 
I'm unsure of how many transistor buffers i need for each channel, and if they need to go in the order of the numbering on the board? ie. could i place a transistor in 1 and 4 position?
 
I'm using it with HD600. Thank You very much for input.
 
Feb 13, 2011 at 6:02 PM Post #978 of 1,084

Quote:
nixnada said:
I'm unsure of how many transistor buffers i need for each channel
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It's covered in the docs, here.
 
 
Quote:
[Do] they need to go in the order of the numbering on the board?
Click to expand...

 
All four spots are equivalent in each channel. You could put one buffer in position #1 in the left channel, one in #2 in the ground channel, and one in #3 in the right channel, if that made you happy.
 
Feb 18, 2011 at 3:46 AM Post #979 of 1,084
Update on my problem:
 
I have now installed bypass caps (1uF), fresh transistors, new wiring, reverse voltage protection and new opamps (opa627).
 
Although it did solve the problem with hot chips and an insane amount of curent draw it still don't sound right.
 
A fresh round of measurements reveals that the quiescent current draw is now abt. 70 mA compared to over 500 mA before, i recon this is acceptable. However when i measure the oR, oG and oL against iG i get a voltage of 500 mV
basshead.gif

 
The curious thing is that it is constantly 500mV even with no signal input.
 
So could it be that something else is broken because of the reverse voltage stunt?
 
Once again thank you very much for input.  
 

 

 
Feb 18, 2011 at 5:11 PM Post #980 of 1,084
You say "fresh transistors", but from your previous posts, I think you mean "fresh buffers."  All transistors on the PPA board are named with a Q prefix. You didn't replace any of them, right?  I don't immediately see why you should have, just trying to add some clarity.
 
Also left untouched, which could also affect this, are the TLE2426es.  In fact, these are just as likely as the op-amps to have been damaged, because they contain op-amps.
 
Feb 26, 2011 at 2:51 AM Post #981 of 1,084
Update:
I am happy to report the PPA is working now :)
I changed the rail splitters and buffer transistors.

However i now have issues with the powersupply. There is noise with no input connected which gets worse when touching the volume knob and turning up the volume . I am sure it has to do with my new power supply. With batteries there is no noise.
I might have made a poor choice here http://docs-europe.electrocomponents.com/webdocs/0d52/0900766b80d523c7.pdf
Bought the 24V version.
Is it because it is switched?
Can this be remedied?


Anyways thanks for help.
 
Feb 26, 2011 at 4:17 AM Post #982 of 1,084
That sounds like the pot ground strap isn't installed, or has caused a conflict with another connection, like V-, through the case.
 
Feb 26, 2011 at 11:40 AM Post #983 of 1,084
Last update:
ok now everything works :D
Amazing how much effect a toothbrush and some alcohol can have. Absolutely no noise now whatsoever not even when volume turned to max. So i was wrong thinking it was the powersource. I think the alcohol had some isolating stuff in it.
Yes im a happy camper now :wink:
Next project bass boost and maybe a y1. But for now i will enjoy a fully working PPA

Thanks Tangent. Your detailed files got me through this once again:D
 
May 11, 2011 at 4:10 PM Post #984 of 1,084
Hi! I have three boards which I am building. I have first bent most of the resistors to the circuit. Next I solder them.

 
I need to build these pretty fast. Any suggestions for quick completion techniques?
 
May 11, 2011 at 4:37 PM Post #987 of 1,084
I would install the higher gain value resistor for R4 and then calculate a resistor
in parallel to create the lower gain value you need. Switch in the parallel resistor
when you want the lower gain. That way there is no chance for an
accidental open loop.
 
May 11, 2011 at 5:08 PM Post #988 of 1,084


Quote:
avro_arrow said:
I would install the higher gain value resistor for R4 and then calculate a resistor
in parallel to create the lower gain value you need. Switch in the parallel resistor
when you want the lower gain. That way there is no chance for an
accidental open loop.
Click to expand...


I have hard time figuring out the correct way to use the switch. Could you draw a schematic for it? It would help a lot. I know, if there is open loop, DC offset gets very high and headphones can burn.
 
 
May 11, 2011 at 5:33 PM Post #989 of 1,084
Lets say the two values of resistor you want are 6k04 for the higher gain and
4k02 for the lower gain. 12k1 in parallel with 6k04 is about 4k...close enough.
Solder in the 6k04 resistor for R4 as normal. Now, make a wire to go from one
side of R4 to your switch with the 12k1 resistor in it. The return wire from the
switch goes to the other side of the R4. Repeat for the other channel.
The switch needs to be a double pole, on/off (single throw).
 
I can draw you a schematic if you need but I am short on time at the moment...
 
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