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#463
swalter said:
checked with the guys in the general O2 thread, agdr was so kind to answer promptly. The values in the BOM (1.0uF) are the correct ones for C6 and C7.

Stefan
Click to expand...

Oh well, as they are only there to filter the regulator from the AC supply it might only be an issue if you run it the amp off AC while using it. Any HQ cap should do,you mentioned getting some tants, they should be okay.

I am not going to change mine as I have no intention to use the AC input, but I will test the noise when I get a chance, doubt there would be enough hear though.

Tony
 
#465
Roulston said:
I just rechecked the latest documentation pack on NWAVGUY's blog and he changed the BOM 0n 30 Nov to have the 6 caps all 0.22uf including C6 & C7 but as I said, I doubt it will matter much.
Click to expand...

The O2 spreadsheet BOM link under that documentation package link on RocketScientist's "O2 details" page is more recent, Dec 2011

https://docs.google.com/leaf?id=0B5...ZDBmYi00YjA4LTk1NzgtZTMwNTAzMWQ3Y2Iy&hl=en_US (download button in upper right corner)

but the capacitor thing isn't very important. That was a mod I cooked up due to the U6 datasheet, that RocketScientist adopted. Might only help in a few odd cases if U6 is overheating due to oscillation. The 0.22uF should be just fine for probably 99% of the builds. If someone is buying the caps for the first time go with 1uF if you want, since the price is about the same, but if you already have the 0.22uF no need to change unless you are having odd U6 heating issues.
 
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#466
Thanks AGDR, I had assumed the doc set in the blog was the most current.

You describe the change to prevent U6 going into oscillation, not U5? of do they both have the potential to oscillate and what the threshold condition that might make them do so?
Anyway, might be a problem if and only if you use the AC supply.

Glad for your clarification though, version control is a beach.
 
#469
Roulston said:
You describe the change to prevent U6 going into oscillation, not U5? of do they both have the potential to oscillate and what the threshold condition that might make them do so?
Click to expand...

The issue is actually just with the negative regulator, U6. Turns out the positive regulator MC7812 and the negative MC7912 are asymmetric in that respect. Check out the value of "Co" in the application circuit in the lower right corner of the first page of the datasheets for the two:

http://www.onsemi.com/pub/Collateral/MC7800-D.PDF

http://www.onsemi.com/pub/Collateral/MC7900-D.PDF

Note on that first and second pages the two chips have very different circuit layouts, probably to avoid having to use a PNP pass transistor in the negative regulator, and hence the different values of "Co" to stabilize the chip. So since the negative regulator recommends the 1.0uF RocketScientist just upped both of them. If a regulator did start oscillating the net result would likely be abnormally large amounts of heating of just that regulator.
 
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#470
I had a look at the datasheet for the -ve version, and noted the advice, but they gave no narrative. Must The cap be that value? Just curious that they don't describe the condition and why that value, or for that matter why not add the cap to the internal of the reg as every example they gave required it. It might have one of those, " oh bugger" moments post production.

Tony
 
#474
The wall wart was never part of the GB as there are too many local variations and it is cheaper to buy locally, likewise batteries IMHO.

The cases are over due except for black apparently. Jokener advised he had plenty of PCBs and kits as I recall.
 
#478
After checking the O2 blog with regard to the cap and resistor values (difference between BOM and shipped values) I ended up building it using the parts supplied.
Testing with DMM showed all values within spec, so I fired her up with a ratty old set of headphones and a very cheap source. A least if things blew up I would not regret it.

No problems. It works fine.

I have not yet had time for a good listen. A quick listen using an Ipod Classic (line out) source and Beyer Dynamic DT770 80 Ohm headphones revealed that, although it sounds good, the Decware (OPA2132 based) Zen Head sounds better. My wife, who uses the Zen Head daily, also preferred the Zen Head to the O2.

PS Thanks Jokener for putting the GB together. It has been fun building this little amp. Now I hope to enjoy it!
 
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#480
@Everybody that is interested in ordering: Yes, I continue to offer kits.
But as of right now, I have no stock.
(Except for those that have already ordered their kits, those are set aside and will be shipped ASAP.)

I should also have a few more cases available, but I will post an update on this as soon as I have cought up with all the orders.
During the last week I only shipped 5 packages, because I was out of town over the weekend and unexpected work appeared on a very tight deadline.
But I kept putting together shipments and I will dedicate a few more hours to this tomorrow.
That way I should be able to ship about half of the remaining orders on Monday morning.

Also, 25 transformers should arrive shortly and then I will have them in stock again.

Best regards,
Jokener

P.S.: The PDF has not been updated during the last week, but you can expect to see an update to it tomorrow during the late evening (German time, as always).

P.P.S.: @pby: I shipped your order the same day as Roulston's shipment. Since it has still not arrived, I will check your address again and get in contact via PM tomorrow.
 
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