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Old 28th July 2011, 09:22 PM   #1171
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Short and sweet, thanks Salas!
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Old 29th July 2011, 01:39 PM   #1172
cersepn is offline cersepn  United States
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Finally wired up everything and took extra careful safety measures when hooking up the power. Seems to have powered up fine

Thank you, Salas and TeaBag for all the hard work you guys have put into the project! Not forgetting the thousands of DIYA members who contributed to this thread!

This is my first project so please forgive me for all my stupid questions.
I tested the V+/V- and the values hover between +9.48 to +9.50 and -9.43 to -9.44. Are the values supposed to hover? I tested them after leaving it on for about 5 minutes. Did i do something wrong and is this perfectly normal?

I'm not sure how to test for dc offset. Is what i'm doing in the picture correct?
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Old 29th July 2011, 01:44 PM   #1173
Tea-Bag is offline Tea-Bag  United States
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Yes, normal voltages in my book. You might be able to get 10v or so with mixing around with LEDs, but the +/- difference is normal. Besides, you bought matched set from Ed, why bother.

-
DC offset meaurements look correct. output to ground voltage. Should be <10mv offset.
If it's way high, then don't hook it up to amp yet.
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Last edited by Tea-Bag; 29th July 2011 at 01:47 PM.
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Old 29th July 2011, 01:45 PM   #1174
akira is offline akira  France
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I think you should ground the input (put the input at ground potential) to measure DC offset on the output. Please wait for some more expert comment.
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Old 29th July 2011, 01:51 PM   #1175
Salas is offline Salas  Greece
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Quote:
Originally Posted by cersepn View Post
I tested the V+/V- and the values hover between +9.48 to +9.50 and -9.43 to -9.44. Are the values supposed to hover? I tested them after leaving it on for about 5 minutes. Did i do something wrong and is this perfectly normal?

I'm not sure how to test for dc offset. Is what i'm doing in the picture correct?
Its looks like its the DVM's A/D converter to display translation not deciding the 3rd digit if the reading is somewhere in between. Not really a hover.
You put the probes OK for DC offset. How much?
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Old 29th July 2011, 02:01 PM   #1176
Salas is offline Salas  Greece
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Quote:
Originally Posted by akira View Post
I think you should ground the input (put the input at ground potential) to measure DC offset on the output. Please wait for some more expert comment.
There is no gain and a differential amp so it won't change much, but in general its correct to ground the input. Here we just do rough initial checks that the circuit isn't wrong though, and if there is some DC in a faulty case we better avoid since there is no capacitor. Not to stress a JFET.
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Old 29th July 2011, 02:33 PM   #1177
cersepn is offline cersepn  United States
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Thank you, Tea Bag and Salas! You guys are really awesome.

I set the DMM to 200 mV. Measures 01.6 on L and 00.3 on R. So is it read as 1.6 mV and 0.3 mV? Any other tests i should be doing before hooking it up to the amp? Thanks again!

Last edited by cersepn; 29th July 2011 at 02:36 PM.
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Old 29th July 2011, 03:14 PM   #1178
Salas is offline Salas  Greece
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Yep, its mV and really low. See the voltage drops on the black resistors so we know what current the regs run.
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Old 29th July 2011, 03:43 PM   #1179
cersepn is offline cersepn  United States
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I get 1.61v and 1.71v. While probing the leads of the resistors, my fingers slipped and some sparks flew. I should have been more careful, I think the resistor leads got burnt. Will it cause any problems?

I re-measured the V out and offset values and they seem fine, no change from before.
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Old 29th July 2011, 04:01 PM   #1180
Salas is offline Salas  Greece
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Its just a small battle scar for luck. No consequences. Your currents are near enough, ready to listen.
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