Roland UA-1G SPDIF Hack

[adriangin]

The google Document is here...
https://docs.google.com/document/d/158VtQc6O_QZ9YzMwBb9U-JITLrv5NGZRZh_BfZ14-r4/edit?hl=en

Overview
Take a look at this for some reference.
http://www.diyaudio.com/forums/showthread.php?t=162712

This is a great little USB 1.1 Audio Interface. But it can be improved as you will see...
First of all, it's got:
1x Stereo Line Out (via 2 RCA Jacks)
1x Stereo Line In (via 2 RCA Jacks)
6.5mm Guitar Input Jack, 3.5mm Mic Jack (both are Mono inputs only which is sad)
Headphone Output (with variable volume)
3.5mm SPDIF Optical Out shared via the Headphone Output Jack
3.5mm SPDIF Optical In shared via the 3.5mm Mic Jack.
So if you need a cheap SPDIF audio interface then this could be an option.
Geek Information:
AKM AK4556 Codec
AKM AK4114 DIT
Texas Instruments 8051 TUSB3200 Microcontroller
GP1FD210RP and GP1FD310TP Optical Receiver and Transmitter Modules

Limitations:
Cannot do full duplex 96kHz. It can only EITHER RECORD or PLAY at 96kHz. Oh well.
While recording digital audio via SPDIF, it CANNOT do anything else except playback the decoded digital audio back out through the LINE OUT and Headphone jacks / Optical SPDIF out.
The 3.5mm Mic jack is not a LINE IN, it is MONO input only.
Lack of RCA SPDIF jacks. Many professional audio devices such as samplers, mixers and the like have SPDIF In/Out in RCA format. These cannot be interfaced with the UA-1G as it only outputs and receives in optical format.
This topic will resolve the last point and add RCA SPDIF IN/OUT whilst maintaining the original optical In/Out functionality. Disclaimer: I don't take any responsibility to any damage done by you taking these steps. Do it all at your own risk. It worked for me.
There is also a nice website here: www.epanorama.net/documents/audio/spdif.html

The video is here: http://www.youtube.com/watch?v=BRuGZHJuukI


#1 Open up the Unit
There are two clips at the front of the unit and two screws underneath the sticker which has the in/out and peak lights. Remove the sticker. Undo the two screw. Remove the cover.


#2 SPDIF Out Toggle
SPDIF Out is only enabled if the unit detects the TOSLINK mini cable in the Digital Out jack. We need a method to 'trick' the unit into outputting SPDIF. Since most users will operate in the 'Advanced Mode' we can hi-jack this switch for our use.

Simply solder a connection from the Digital Out Jack PIN4 to the '4th' Pin of the Advanced Mode Switch. When you want to output SPDIF set the swtich to "Advanced Mode = OFF". As the unit only determines the operating mode at startup, start the unit up in "Advanced Mode = ON" and toggle the switch as neccessary.

Note that Analogue audio via the Line Out will still be enabled. Plugging in headphones will also force the unit to output Analogue Audio signal to the Headphones and disable the SPDIF out.


#3 SPDIF Out Connections
Connect to 'Pin7' of the Output Audio Jack to a TTL -> SPDIF converter. The unit outputs a nominal 3.3V as it's TTL output, so we need to voltage divide it using a few resistors and also buffer the signal. See the schematic. To drive the transistor buffer, take the 3V3 from the LED driver Vcc Pin (Pin 8). See the Datasheet @ http://media.digikey.com/pdf/Data%20Sheets/Sharp%20PDFs/GP1FD210TP,310TP.pdf




#4 SPDIF IN
The GP1FD210RP Optical Receiver provides the optical SPDIF signal (if there is one) to the TUSB3200 uP. The TUSB3200 uP will only process it if the DIP Switch #5 is set to DIGITAL REC Source. You need to set this switch if you want to use SPDIF IN.
We need to share the signal path to the TUSB3200 with both the Optical and Wired SPDIF signals.
Disconnect the Optical Receiver output by desoldering the capacitor on the top side (See photo). Wire the optical receiver output to a capacitor as shown in the schematic. Also add in the SPDIF Jack. This will allow the Optical Signal or the RCA SPDIF signal (but not both) to share the one line.
If there is an Optical Signal and an RCA Signal, the Optical Signal will 'win' and override the RCA signal, but this cannot be relied upon. For now just use one input at a time please

Desolder this capacitor and note the Via that is also circled too.



Connect this 100nF capacitor as shown. One side should connect to the Optical Receiver Output Pin (Pin 9) and the other should connect to the Via which was connected to the desoldered capacitor above.

See the receiver datasheet @
http://media.digikey.com/pdf/Data%20Sheets/Sharp%20PDFs/GP1FD210RP.pdf




#5 Grounding the Signals
You also need to ground the signal. You can steal this from the USB ground wire. It does take some time to heat up the pad.


#6 Drill Some Holes
Cut out some spaces for where you want to put your SPDIF RCA jacks into. Mount. Put it back together and enjoy, like me






Cheers,

Adrian