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Old 10th January 2013, 04:35 PM   #3031
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Quote:
Originally Posted by MGeeOne View Post
Thanks for the blog headsup...will digest over the next few days. Then straight to HnH!

Will look out for a suitable PSU too...in fact that might be another good DIY maybe?
The o2 has a very good on-board psu. It just needs ac voltage. I recommend something like the antek an-0109 toroid with it's dual secondaries wired in series for 18vac. Costs $10 and they have 76 of them in stock. Other than that, you could use a filtered ac inlet.

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Old 10th January 2013, 05:13 PM   #3032
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Originally Posted by qusp View Post
because by moving the gain switch to the panel you are taking the feedback loop out to the panel with it and thus increasing the length of the loop and decreasing stability, increasing noise pickup etc.

OK, thanks. Could you elaborate a little more? As long as the wires I use are shielded, how does that decrease stability? If properly shielded, how does the length affect it?

I'm new to this so I'd like to understand a little more about it.
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Old 10th January 2013, 05:24 PM   #3033
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Default A few parts substitution questions- LED, NJM2068DD, C1, C6, C7

Hey guys-

For those who have mounted the power-on LED on a remote panel, what did you use? I see the cautions about it requiring an HE led, etc. Mouser part number?

Mouser is out of NJM2068DD for the next three months. I can order the "noisier" NE5532AP for now and substitute later, but wondered if any other options have emerged.

Also, for C1, C6, and C7 the 1uF 25V cap which is stated as a "non-critical part", any problem using a tantalum? I know tantalums sometimes get a bad rap, but AFAIK they are OK as long as they are voltage rated properly. I happen to have a bunch of tantalum 1uf 35V.

Thanks,
Keith
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Old 10th January 2013, 05:26 PM   #3034
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Quote:
Originally Posted by keithostertag View Post
OK, thanks. Could you elaborate a little more? As long as the wires I use are shielded, how does that decrease stability? If properly shielded, how does the length affect it?

I'm new to this so I'd like to understand a little more about it.
Shielding adds capacitance that could make it worse.

There are electromagnetic waves all around us that can induce signals into the feedback loop and cause distortion or even cause the chip to oscillate. Longer wires are bigger antennas, and the gain switch is a particularly sensitive area.

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Old 11th January 2013, 01:20 PM   #3035
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OK, thanks Eric.

I found the info I needed to test for appropriate LED's on a few pages from October, thanks ADJR and others for such detailed explanations!

I still haven't found a good resolution schematic... the one on Googledocs is practically unreadable.

Keith
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Old 11th January 2013, 02:38 PM   #3036
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Have you tried zooming in on the pdf? It works fine for me on my browser
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Old 11th January 2013, 02:45 PM   #3037
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Yea, tried that. Resolution is so bad I can't read the schematic clearly. NwAvGuy's page says there is a high definition copy somewhere, but all I see are links to the GoogleDocs version.

Thanks,
Keith
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Old 11th January 2013, 02:51 PM   #3038
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Quote:
Originally Posted by keithostertag View Post
Yea, tried that. Resolution is so bad I can't read the schematic clearly. NwAvGuy's page says there is a high definition copy somewhere, but all I see are links to the GoogleDocs version.

Thanks,
Keith

See the attached PDF. It is high res enough if you use Adobe Reader.
Attached Files
File Type: pdf Nwavguy O2 V11 Docs 30 Nov 2011.pdf (137.0 KB, 41 views)
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Old 11th January 2013, 03:22 PM   #3039
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Great! Much better! Thank you so much!
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Old 11th January 2013, 06:01 PM   #3040
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Guys - I need help.

I'm doing an amp and I have a problem I can't fix.

so here is the problem - at low volumes, and at full volume on the potentionmeter, both left and right cups sound the same, anywhere in between, the right channel is very quiet, off balance.

I have tried - Replacing all mosfets, replacing the 2068dd opamp, potentiometer, replacing gain switch, checked all resistors, all diodes are in correct position, re soldered the whole board... I can't figure out what's going on.
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