civilmonkey
100+ Head-Fier
- Joined
- Feb 17, 2006
- Posts
- 126
- Likes
- 10
Hello,
First off, great forum folks. Everybody here makes it a joy to DIY audio because of this resource here. Sorry in advance for this long post!
After creating a few CMOYs, and A47s, I moved up to a PIMETA, and it sounds great! My configuration is stock as per Tangents site, here are questions people might have:
-R4 = 4.75K for a gain of around 5.6
-AD8620 (L/R channel), AD8610 (Ground) on Brown Dog adaptors
-Powered by 22 VDC from stock TREAD (supplied by 26V 400mA AD-DC wallwart)
-Biased into Class A using JFET cascodes (saturated current for Q2 around 3mA, and 2ma for Q1)
-2 buffers on all channels (including ground). R11 resistor of 100 ohms (again, all chanels).
-ALPS097, with ground strap to IG pad (to fix slight hum when touching POT)
-6.8 WIMA caps
-ELNA Cerafine 470µF x 4
1. I created all my buffer stacks before realizing that most people don't stack buffers on the ground. I'm assuming that it won't negatively affect my sound quality, but please let me know.
2. Here was my first problem and solution: measuring from the IG pad to the left, right, ground output pins (26 mV, 16 mV, 4 V). I removed the ground buffer stack, and fixed a cold solder joint connecting the buffers. New DC offset is 10mV,11mV,26mV. Measuring from IG to OG, I can less than 1 mV. DC offsets are still higher then I'd like, but I've spent the weekend on this now! (BTW, my source puts out less then 1 mV offset.)
3. I understand about DC offset on L & R channels damaging headphones. Does DC offset on the ground channel have implications?
4. Finally: My PIMETA draws 58.8 mA (steady). This seems high to me:
Amps: 3 x 4 mA = 12 mA
Class A Bias: 2 x 3 mA = 6 mA
Buffer stacks = 3 x 10 = 30 mA
LED: 2mA (measured)
TLE2426: < 1mA
Total is around 50 mA, unless I'm missing something.
As far as touble shooting goes:
-flux is off the board
-I can't see any cold solder joints, v- and v+ on pins is consistent from chip to chip and within 0.1V.
-resistance from input voltage (positve and negative) to power pins on all chips is 0 ohms
-amps stay cool, the buffer stacks are luke warm (finger need to press hard to feel the heat, but it's there).
I can live with the current draw if I can't explain it, but I like to know what's going on!
Thanks in advance.
First off, great forum folks. Everybody here makes it a joy to DIY audio because of this resource here. Sorry in advance for this long post!
After creating a few CMOYs, and A47s, I moved up to a PIMETA, and it sounds great! My configuration is stock as per Tangents site, here are questions people might have:
-R4 = 4.75K for a gain of around 5.6
-AD8620 (L/R channel), AD8610 (Ground) on Brown Dog adaptors
-Powered by 22 VDC from stock TREAD (supplied by 26V 400mA AD-DC wallwart)
-Biased into Class A using JFET cascodes (saturated current for Q2 around 3mA, and 2ma for Q1)
-2 buffers on all channels (including ground). R11 resistor of 100 ohms (again, all chanels).
-ALPS097, with ground strap to IG pad (to fix slight hum when touching POT)
-6.8 WIMA caps
-ELNA Cerafine 470µF x 4
1. I created all my buffer stacks before realizing that most people don't stack buffers on the ground. I'm assuming that it won't negatively affect my sound quality, but please let me know.
2. Here was my first problem and solution: measuring from the IG pad to the left, right, ground output pins (26 mV, 16 mV, 4 V). I removed the ground buffer stack, and fixed a cold solder joint connecting the buffers. New DC offset is 10mV,11mV,26mV. Measuring from IG to OG, I can less than 1 mV. DC offsets are still higher then I'd like, but I've spent the weekend on this now! (BTW, my source puts out less then 1 mV offset.)
3. I understand about DC offset on L & R channels damaging headphones. Does DC offset on the ground channel have implications?
4. Finally: My PIMETA draws 58.8 mA (steady). This seems high to me:
Amps: 3 x 4 mA = 12 mA
Class A Bias: 2 x 3 mA = 6 mA
Buffer stacks = 3 x 10 = 30 mA
LED: 2mA (measured)
TLE2426: < 1mA
Total is around 50 mA, unless I'm missing something.
As far as touble shooting goes:
-flux is off the board
-I can't see any cold solder joints, v- and v+ on pins is consistent from chip to chip and within 0.1V.
-resistance from input voltage (positve and negative) to power pins on all chips is 0 ohms
-amps stay cool, the buffer stacks are luke warm (finger need to press hard to feel the heat, but it's there).
I can live with the current draw if I can't explain it, but I like to know what's going on!
Thanks in advance.