Hi Pongo,

You have to solder the resistor with any power supply. They're used to set voltage of Tridents. One of them is 1.2V and the other two are 3.3V as I recall.

Thanks
Do

Now you make me wonder... You're probably right on that one.

Don't have any information on how it is calculated either.

Shunted current I assume.
What is the values of resistors provided with the 3v3 and 1v2 tridents?
Anybody read or measured?
Sorry, but I haven't got them to play with yet!

Some curiosity driven measurements and guesses:

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While playing 24/92 S/PDIF files I measured the current drawn by Buffalo II on the different supplies using a cheap DMM. I get:
VDD (1.2V): 90-115 mA
DVCC (3.3V): 16 mA
VDD_XO (3.3V): 13 mA
I did not measure AVCC as I assumed it to be very low (I may be wrong as the each side of the dual-shunt supply seems to draw >100 mA @ 5V!).
The current drawn by DVCC and VDD_XO are rather constant (in the time domain of my DMM!) while VDD varies quite a bit with music transients.
As I think to have read that you can draw up to 75 mA on the Volumite header (which is fed by DVCC) I guess that the default 3v3 Tridents must be set to shunt > 16+75 mA. So if my lousy math gets me there R4 = 12-10 ohms to supply 100-120 mA....... as usual I'm very likely to be wrong!

Thanks LeonvB,
Never noticed the "Document Repository".....
BTW in "Appendix: DIP switch settings", for Switch 2, in the comments column it reads: "Has no meaning if switch 1 is OFF". I think it should be: "Has no meaning if switch 1 is ON".
Cheers,
Nic

Since I also have two of the 3.3v tridents I wish to use to their full current capacity, it would be great to know which of the three values R values supplied (10R,15R,20R) or any other for that matter would be preferable.....from both the guide and the previous posts 10R seems to be the right one...right?

Edited by user 14 years ago  | Reason: Not specified

Hi Russ,
Is that 1.2V across R4 for both 3.3V and 1.2V versions? So the 10ohm R4 would set max current at 120mA. Can the current be safely increased by using a lower value for R4 or is that about the max for the trident?

Thanks Russ.
The reason I asked is because I tried a 3.3V trident in another application but it didn't run properly. With the 20ohm R4 it only has max current of 60mA, so I'm guessing more is needed. An R4 of 8ohm would allow 150mA, but I will try first by paralleling the 20ohm with a 15ohm to see if that works. Hopefully I won't kill this gem of a product.

Hi Russ,
The increased current fixed the issue with no magic smoke. Thanks.

No. You will lose a little filtering, but not much. I wouldn't worry over it.

The DVCC trident comes with a 20 ohm resistor for R4 included. Applying the '~1.2 Volts across R4' condition, I get 60ma max current. I am not sure what the DAC chip actually draws from DVCC, but the guide says an additional load of 75ma can be drawn from DVCC from the I2C header. If the chip was to draw say 50ma then we would need a CCS of ~125ma. Does that mean I need to use a different R4 or have I got the calculation wrong somewhere?

The real question I would like answered is whether I can use a volumite and exaU2I (less then 20mA) both drawing current from DVCC and still use a 20 ohm resistor in my trident or should I parallel a 15 ohm as discussed earlier?

A side thought, wouldn't you want ~50mA of current headroom for shunt to work well or is the trident headroom lower?