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Amp Camp Amp Kit V1.6
Amp Camp Amp Kit V1.6
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Old 4th November 2019, 08:26 AM   #591
Mooly is offline Mooly  United Kingdom
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Amp Camp Amp Kit V1.6
You may well have to do as I detailed in post #571 which should allow some voltage measurements to be taken without the PSU objecting.
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Old 4th November 2019, 03:26 PM   #592
myleftear is offline myleftear  Switzerland
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Smile Done!

I'm through!

My ACA is playing music!

It was so insightful fun! Almost sad it's already over.

There are a few questions left though:

I connected my mac through a Herus DAC, play music with iTunes/Music (output controlled by bitperfect), and there's a constant hiss, audible when the music is quiet... could it just be the setup, or something inside? (Haven't measured anything except the bias (11.9 - 12.0 v left, 12.0 - 12.1 v right)

And, I think I'll do just a second ACA, for the fun, the experiment, and the mono block. While building, I often was confused by the PCB's being identical. Building one channel upside-down to have a symmetrical layout in the chassis should work, shouldn't it?

here's some images:
Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.

The sharp-eyed observer will see that I had to solder a extension to the power-cables...
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Old 6th November 2019, 04:31 AM   #593
bobertbk is offline bobertbk
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Ok. I wish I had read that last post before testing since I did detach the left (hot) board from the chassis to solder some of the connections under the board and then turned it on. The Q1 and Q2 did get blazing hot. I'm not sure if I destroyed them.


In any case I left the right board attached to the chassis and took all resistor and Q readings with the board facing me (R1-R4 closest to me). I recorded either the top/bottom or left/right resistor reading, depending on its orientation. You can see the results in the attached image. Many strange readings.


R11, R12, and R14 are particularly strange because the reading isn't stable. I indicated the voltage as 8* because it seemed to bounce between 6.5 and 10 or so.
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File Type: png left board.png (381.8 KB, 149 views)
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Old 6th November 2019, 09:19 AM   #594
Alan4411 is offline Alan4411  Wales
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bobertbk, question - where did you put your Negative meter lead to take the readings?

Yes some of those readings are strange, Q1S for instance is (should be) connected to the GND / 0 volts track, so cannot measure +24 volts, it should be 0 volts...
The resistor R9 is also (should be) connected to the GND track, so also should measure 0 volts where you have 9.9 volts. The 4.5 volt reading is reasonable.
Same again for R14 which also has one end connected to the GND track... you should not measure any voltage on either end.

So you either have a bad connection somewhere, likely to do with the 0 volt lines, or possibly you have a wire strand, solder blob or lead touching or bridging?
The other readings (apart from the R11 and R12 ones, which will be due to what ever is causing the the R9 /14 problem) look within a working range.
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Old 10th November 2019, 09:37 PM   #595
myleftear is offline myleftear  Switzerland
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Default Basic understanding: bias

Hello again.
I begin to slowly develop a very basic understanding of what I built. But many things are still a big ?... like the bias (no, I get what the bias is, but not in its depth. So:
What happens if I lower the bias to, say 10V? Nothing except that the amp starts to clip earlyer? And gets a bit less warm?

Thanks to all of you!
David
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Old 11th November 2019, 08:01 AM   #596
Mooly is offline Mooly  United Kingdom
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The heat dissipation should stay the same if you alter the midpoint voltage (bias is misleading because so many immediately think of quiescent current adjustment here).

With the midpoint set accurately each transistor dissipates the same power. If you alter the midpoint to say 6 volts then one transistor will dissipate much more power than the other due to the different voltage now dropped across each device. The current flow is unaltered.

The one with least voltage across it will be cooler. The total power dissipation of the two devices added together remains the same.
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Old 11th November 2019, 03:22 PM   #597
fcarlson is offline fcarlson
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Default C1 Positive and Negative

Here is a stupid question that I have looked all over for, and the feedback is too general for me to act. Also, the ACA 1.6 build guide is extremely vague.

Which are the positive and negative leads on the C1 Cap? There is a Neg marker on the label but it is offset. Also one of the leads has a stamp that means something.

Unless I am missing something, which is highly possible, this is a really severe oversight in the build guide not to clearly (REALLY CLEARLY) let the person tell which lead is which. The other Caps are no problem - long lead is positive.

Thanks so much.

FRC
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Old 11th November 2019, 07:02 PM   #598
Mooly is offline Mooly  United Kingdom
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The wrapper identifying the negative on a large cap should not be offset enough to cause confusion... maybe a picture of your actual cap might help.
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Old 11th November 2019, 08:00 PM   #599
fcarlson is offline fcarlson
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Default C1 Positive and Negative

Quote:
Originally Posted by Mooly View Post
The wrapper identifying the negative on a large cap should not be offset enough to cause confusion... maybe a picture of your actual cap might help.
Thanks so much. This solved it for me.
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Old 11th November 2019, 08:02 PM   #600
Mooly is offline Mooly  United Kingdom
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that's good.
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