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Old 25th January 2013, 07:14 PM   #2391
tofurky is offline tofurky  United States
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Originally Posted by tofurky View Post
i read through dozens of pages of the thread and did some searches, but i did not see a clear reason why a 15v/9v r-core is suggested. 9v to a 9v regulator with a 1.3v dropout voltage? is this because with a small load, the transformer will actually output something significantly higher, like 12v or so?
duh, so rectifying 9vac gives ~12.7 (9v * sqrt(2)), minus the 2x 1.1v drop of the diodes in the bridge. so ~10.5v full load, and more than that otherwise. gives at least a 1.5v dropout, which is more than the 1.3v the MC7809CTG specifies. makes sense, sorry to ask an apparently silly question

and, some rough measurements by cutting and pasting in a photo editor show me that the terminal spacing is 5mm.
thanks,
-matt
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Old 27th January 2013, 03:32 AM   #2392
tofurky is offline tofurky  United States
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using the method outlined at How to Calculate Capacitors for a Bridge Rectifier | eHow.com
peak current: .2a (guess)
.2a * 5 = 1a (?)
peak voltage: 9vac * sqrt(2) = 12.7vac
bridge drop: 12.7v-1.1v = 11.6v
times freq: 11.6v * 60hz = 696vhz
1a/696vhz = 0.001437f = 1437uf (vs 2200uF)
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Old 27th January 2013, 07:02 PM   #2393
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i read that even though PR9372 2.2kohm is on the BOM, 2.4kohm is actually the correct value?
The corrrect value is 2.4K, PRP were indicated as 2.2K because they were not available as 2.4K.
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Old 30th January 2013, 06:32 AM   #2394
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Default Just getting started

Having read this forum 'til my eyes bled and brain hurt, it's finally time to embark on assembly of my first mini 2496 DAC (AK4396 from Zoe Tsang). A few questions if I may?

1. For those who installed inductors at L1, L2 what value inductance did you choose? For those who avoided inductors altogether, did you feel justified in the end?
2. Did many here install larger value caps at C38, C39? (My board states 220uf, but others are marked 330uf. Anyone use 470uf or larger?)
3. Also caps at other points in the circuit? (e.g., C30, C35?)
4. Anyone use stealth/schottky diodes in diy-bridges and notice a difference?

Thanks.

nightcap
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Old 1st February 2013, 08:43 AM   #2395
atupi is online now atupi  Romania
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1. i used 47uH
2.78xx reg do not like big caps on output (use <470uf)
3.BOM is enough
4. no

I made a small add-on shunt stabilizer for the LPF opamp and obtained a huge improvement on voice presence, soundstage and details. (Regulator Design v1.3 post #7)
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Old 1st February 2013, 10:24 AM   #2396
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Thanks mate. What size caps did you install that are less than 470uf?

Interesting shunt reg. Might try that later, following successful basic kit assembly, as a hot-rod tweak.
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Old 1st February 2013, 04:22 PM   #2397
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atupi,
why did you use 47uH when I saw 1.5uH reccomended.

Could you pleaase post some photos of this shunt stabalizer - it would be appreciated.

Stuart
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Old 1st February 2013, 05:24 PM   #2398
atupi is online now atupi  Romania
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@nightcap-used 220uf but remove it after installed a separate reg for LPF opamp.
47uh i had on hand.
See a picture of my reg (both rails).
In the second picture i marked how i detached de positive rail from the remaining MC7812.
If anyone interested i can share de pcb layout, no big deal. Tried to obtain a pcb as small as possible.
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File Type: jpg dac pcb back.jpg (110.8 KB, 439 views)
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Last edited by atupi; 1st February 2013 at 05:33 PM.
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Old 2nd February 2013, 09:41 AM   #2399
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Hi Atupi,
thanks for the photos - photos = understanding without language problems.

It's time we who live in the EU demand that Esperanto be taught in all EU schools along with our national languages result - no communication problems on forums or when travelling or working in each others countries but bad news for lawyers/interpreters and scam artists.

Atupi - it would be good to see a PCB layout but for those who don't want to go this route would a discrete op-amp be another simpler answer?

Re. these inductors - it would be good to see Dario's and Erin's and others opinions on this issue. Ie. how important are they to performance of the DAC.
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Old 2nd February 2013, 01:08 PM   #2400
hotiron is offline hotiron  Scotland
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Default Bypassed CS8416 with TE7022

Running at 24bit 96Khz sounds way better.
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