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Old 13th January 2013, 07:07 AM   #121
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Ok, here's a quick update...

SECOND CHANNEL:
I got the second channel put together but without the new rectifiers (haven't arrived yet.) However, I did add some heat transfer compound between the rectifiers and the sinks. That was... tricky since I didn't want to desolder and resolder the sinks and rectifiers. But I was able to access the trapped screws through the holes of the sinks in front of them. In any case I got it done, buttoned it back up, and voila! It works. They still get really hot AND they aren't smoking. Also, I measured ripple and it's a solid 17mV. No caps on the rectifiers. I figure they're rated for 15A so we'll use them unless I have good reason not to in the future.

We're still clearly in break in mode but it plays music quite nicely.

On DC offset, relative DC offset (+ to -) is still zero and absolute offset is about 7.7V. That's with the pot maxed out.

FIRST CHANNEL:
Speaking of absolute offset, for channel one, I adjusted VR2 to the max and get output to ground at 10V when warmed up. Can't get any lower than that. Relative DC offset from output + to - is essentially zero. Ripple is still solid at 18mV or less. Furthermore, I hear absolutely nothing from the speakers with no signal so I'm not worried about the ripple at all. The only sound I hear is a tiny bit of transformer hum.

Here's a pic of my temporary setup. Right now, path is macbook --> Emotiva XDA-1 --> hotrodded DCB1 --> Alephs.

Click the image to open in full size.

Sounds quite good actually already. Effortless is the best work I can think of at the moment. Lots of caveats of course... clearly biased, don't have golden ears, room setup is terrible, etc.

Thanks to everyone for their help. Special shout out to gl for the differential pairs!

Once I get my function generator, I'll play around with testing.
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Old 13th January 2013, 12:12 PM   #122
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so one half will have 10V x Iq less dissipation , while other will have for same amount more dissipation

having both offsets zeroed ( after temp equilibrium) is a must
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Old 13th January 2013, 03:27 PM   #123
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Hmm. Ok. I'll try to find a trimmer pot with more range to get to zero then. Thx!
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Old 13th January 2013, 03:51 PM   #124
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gimme exact schm you're using and I'll tell what to change

also put here exact value of offset between outputs and gnd , is it positive or negative
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Old 13th January 2013, 05:45 PM   #125
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I get negative 8 and 10V for the two channels.

Here's the schematic.
Click the image to open in full size.

And the BOM:
Click the image to open in full size.
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Old 13th January 2013, 05:53 PM   #126
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exact values for D5, R47,R29,Rp1 and R30

I presume that you set Rp to max (verify , please , with amp off) , and you can't out-gnd offset zero

how's that - you wrote somewhere in previous posts that both offsets are near zero , and now out-gnd offset is suddenly not ?
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Old 13th January 2013, 05:58 PM   #127
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Sorry for not being clear. The dc offset from + to - was always zero. The dc to ground has always been near 10V.

I will confirm rp1 when I get home. But 99% sure it was fully counter clockwise.
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Old 13th January 2013, 06:10 PM   #128
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Quote:
Originally Posted by oneplustwo View Post
....... The dc to ground has always been near 10V.
.......
that was exactly what I asked in first reply , after your post about dissipation difference

Quote:
Originally Posted by oneplustwo View Post
S......

I will confirm rp1 when I get home. But 99% sure it was fully counter clockwise.
that means nothing - it depends how you mount it - can be full value , or full zero ; that's why I asked for confirmation with ohm-meter
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Old 14th January 2013, 07:17 AM   #129
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ZM - sorry, I should have made my post #120 more clear. In any case, at the risk of overstating... output to ground is -8 and -10 for each amp.

Also, I'm confirming the value of RP1 is at full value while counter-clockwise. I'm reading 150R while in place measuring at the points where R29 and R30 connect to it. When turned to full clockwise, it's zero.

The 150R reading confirms its roughly a 200R pot if I calculate the parallel resistances from R29, R30, and R47.

Are you also looking for the voltages across each of the items you mention above? Or just their part values?

If so... here they are:
D5: 8.92V
R47: 3.83V
R29: 4.84V
R30: 3.0V

Thanks in advance for your help!
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Old 14th January 2013, 08:01 AM   #130
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Also, in case you couldn't read the PDF:

200R:Rp1
475R:R29
330R:R30
475R:R47
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