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Old 13th April 2008, 01:31 PM   #321
OneyedK is offline OneyedK  Belgium
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Quote:
Originally posted by johnm
So does this mean that Peter's values of 2 x 75 ohms is maybe not a good idea then in practice?
Those values are dead wrong, but even with wrong values, you can get good sound. (depends on used cable and DAC configuration)

I like to have stuff that complies to the known standards, in this case S/Pdif, so 291 and 100 Ohm are the correct choices.
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Old 13th April 2008, 01:34 PM   #322
johnm is offline johnm  United Kingdom
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I'm getting great sound now and that's without any resistors at all, however - like you - I prefer to have things done 'by the book' so I'll probably go with those new values to.

Something else I was curious about, is alot of the capacitor values in many of these mods are alot less in value than the originals. Is it OK to arbitrarily change them like this? Surely they were chosen for a reason?
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Old 13th April 2008, 02:48 PM   #323
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Quote:
Originally posted by OneyedK




Toslink? In high end? Tsss... ;-)))
Gee , it is soooooo crappy


Quote:
Originally posted by OneyedK





I like to have stuff that complies to the known standards, in this case S/Pdif, so 291 and 100 Ohm are the correct choices.
I like them
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Old 13th April 2008, 03:48 PM   #324
johnm is offline johnm  United Kingdom
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http://www.airlinktransformers.com/t...with-leads.asp

Shopping around for a cheap transformer here in the UK to use with Peter's PSU board for this project. Does the one above look like a good choice, or is it overkill? (VA rating).

Also does it have to be dual secondaries or could I go for a 0v - 24v instead?

Many thanks,

- John
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Old 13th April 2008, 04:08 PM   #325
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O-24 with Peter Board - unless you modify it - will not work . You need the 2 secondaries or the center tap . As for the transormer listed there I would buy it with my eyes closed
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Old 13th April 2008, 04:14 PM   #326
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Quote:
Originally posted by johnm
http://www.airlinktransformers.com/t...with-leads.asp

Shopping around for a cheap transformer here in the UK to use with Peter's PSU board for this project. Does the one above look like a good choice, or is it overkill? (VA rating).

Also does it have to be dual secondaries or could I go for a 0v - 24v instead?

Many thanks,

- John
It looks fine, and very reasonably priced.

I wouldn't suggest 0-24 secondary since it'll produce an
unregulated dc voltage too close to the max limit of the
LM7808 regulator. Even if the regulator doesn't break,
it'll be running much hotter than needed.

Cheers,
Dennis
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Old 13th April 2008, 04:18 PM   #327
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Even with 12V secondary the regulator runs pretty hot. 24V is out of question.

So, you either choose dual secondary (CT) 2 x 12V or single 12V secondary.

You will be fine with 2 x 10V as well.
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Old 13th April 2008, 04:20 PM   #328
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Quote:
Originally posted by johnm
Something else I was curious about, is alot of the capacitor values in many of these mods are alot less in value than the originals. Is it OK to arbitrarily change them like this? Surely they were chosen for a reason?
The smaller capacitor choices were made for a reason: a better sound. This is mostly with respect to BG N type, they just don't sound good in larger values... and wouldn't fit on the board.
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Old 13th April 2008, 04:23 PM   #329
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Quote:
Originally posted by OneyedK
Those values are dead wrong, but even with wrong values, you can get good sound. (depends on used cable and DAC configuration)
As I like to break rules, I feel perfectly comfortable with completely dead wrong values I tried in listening tests a series resistor of 240R and 62R and the latter sounded better to me, in my system.

I encourage everybody to experiment here and choose values that work best.
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Old 13th April 2008, 04:28 PM   #330
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by OneyedK


Sorry to quote this old post, but I calculated the resistors again.
Theoretically it should be 375 and 93.75 Ohm.
(you still woulld have to subtract the chips output impedance from the 375 Ohm)
That would give a perfect 75 Ohm output impedance, 1Vpp unloaded and 0.5Vpp loaded with 75 Ohm.
Any other value will render the coax into an antenna or ignore s/pdif specs. (and thus the receiver input)

--> calculation based on 5Vpp processor spdif ouput.
--> If it's 3.3Vpp, it should be 247.48 and 107.6 Ohm (If this is the case, Kevin's values are the best option!)

Did someone measure the actual chip output?
(would do it myself but the BB has not yet arrived)
On mine it is 5.0Vpp! (RCEZ32) So my original calculated values were wrong too. Generally the output of a cmos port is considered to be very low impedance - a couple of ohms or less and can usually be neglected in the calculation, particularly at higher voltages where the error it contributes is small.
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