[fandersen]

I'm getting ready to build a Chime USB DAC and I would like to add a Toslink interface to allow me to use the Chime with an Apple Airport Express. I was thinking of getting the Twisted Pear Audio Toslink input kit (http://www.twistedpearaudio.com/digital/torx.aspx) and connecting its output to one of the S/PDIF inputs on the Chime. The power for the Toslink module could come from the Chime's H+.

Does this mod look reasonable?

[poty]

I don't see any problem. Maybe you should made some "disconnection" filtering to divide digital and analog grounds. See the Chime schematic for an example of this.

[fandersen]

Maybe you should made some "disconnection" filtering to divide digital and analog grounds. See the Chime schematic for an example of this.

Not sure I understand. Do you mean there should be filtering between the ground of the Toslink output and the chassis ground?

[dnewman]

I'm getting ready to build a Chime USB DAC and I would like to add a Toslink interface to allow me to use the Chime with an Apple Airport Express. I was thinking of getting the Twisted Pear Audio Toslink input kit (http://www.twistedpearaudio.com/digital/torx.aspx) and connecting its output to one of the S/PDIF inputs on the Chime. The power for the Toslink module could come from the Chime's H+.

Does this mod look reasonable?

I did much the same thing with one of my Chime's, albeit I built the toslink circuit all myself.  Don't use the H+ for power: instead steal from the power supply for the HagDac.  I didn't worry about ground separation -- just shared ground with the HagDac circuitry (on the input side for the HagDac).  The HagDac gets +8 VDC off of R411: you can take your +DC off of one side of R411 and ground off of the other side of R411.  (See the second page of schematics in the Chime manual.)

Dan

[fandersen]

I did much the same thing with one of my Chime's, albeit I built the toslink circuit all myself.  Don't use the H+ for power: instead steal from the power supply for the HagDac.  I didn't worry about ground separation -- just shared ground with the HagDac circuitry (on the input side for the HagDac).  The HagDac gets +8 VDC off of R411: you can take your +DC off of one side of R411 and ground off of the other side of R411.  (See the second page of schematics in the Chime manual.)

Dan

Thanks Dan. Tapping into R411 looks like a better idea.

Flemming

[poty]

Not sure I understand. Do you mean there should be filtering between the ground of the Toslink output and the chassis ground?

Something like L17, C50-55 circuit in the hagdac schematic on page 12.

... Don't use the H+ for power: instead steal from the power supply for the HagDac.  I didn't worry about ground separation -- just shared ground with the HagDac circuitry (on the input side for the HagDac).  The HagDac gets +8 VDC off of R411: you can take your +DC off of one side of R411 and ground off of the other side of R411.  (See the second page of schematics in the Chime manual.)

Yes, it's better (as soon as the hagdac has already had the decoupling circuit), but only if the power supply (especially the transformer) has additional power for the device.

[dnewman]

There should be plenty of power to spare in the HagDac's power supply.  My TORX177 based circuit worked out to a max consumption of around 50 mA.  (The average consumption was around 35 mA, if I recall correctly.)  But that was mine: I've not done a similar analysis for the Twisted Pear circuit.

Dan