# Optical 2 S/pdif converter?

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#### Ryssen

I have optical out on my sattelite reciver and am going to use it on a s/pdif mixer,is there a converter?DIY maybe.
I am not going to open the reciver,I want it outside...

#### Ryssen

Simple as that?Hmm,maybe if I open the case and take the signal before the transceiver it becomes even simpler?

#### Iain McNeill

ooooh oooh oooh
ground loops with a satellite receiver???

I think this is the perfect application for optical!!

#### Ryssen

Ok,I will try the outside circuit...

#### Jambo

I think it's as simple as powering an optical receiver and connecting it to your SPDIF input.

Pretty much, except that the output from the optical receiver will be TTL (probably 3.3V) and a coaxial SPDIF input won't be wanting an input as high as that. It would probably be fine, but to be on the safe side use a potential divider to drop it down to ~1V.

#### Ryssen

Ok,then I have to take the impedans (75 ohm) in the equation?

#### Jambo

Ideally, yes.

I worked out the following, I'm pretty sure it's right for a source impedance of 75Ohms, but please someone correct me if I'm wrong...

An externally hosted image should be here but it was not working when we last tested it.

Obviously you'll need to choose the nearest standard values to those, and also make sure that your optical receiver is happy with the relatively low impedance.

Hmm, actually the more I look at this the more I think that the transmission line will only 'see' R2 and as such R2 should be 75ohms, rather than the combination of R1 and R2 being 75 ohms, anyone? If that's the case then you need R1 to be around 170ohms.

#### zigzagflux

No, the output impedance of your circuit is R1 in parallel with R2. You had it right the first time.

#### Jambo

I thought so... thanks

#### Ryssen

Thanks!I´ve ordered some parts..

#### Ryssen

Well its working now.

An externally hosted image should be here but it was not working when we last tested it.

I think the sound is a little more distinkt.But! There is a slight delay in the sound and the picture,how can that be?
Why I did this is beacause my Roland M-1000 digital mixer has the optical in on the front,and the back has 4 coax digital inputs.
But why the delay?

#### Iain McNeill

very nice construction!

It would appear that the satellite DAC has less latency than the sum of the satellite transmitter, the roland receiver and the roland DAC. You'd think the DACs would be comparable so why so much latency on the optical system? Are we talking 10's or 100's of milliseconds here?

#### Ryssen

It´s hard to tell how many ms,but you can see that their mouths are moving slightly before the sound.
I guess theres no easy way of fixing this?

#### Iain McNeill

That's pretty significant lag.

All I can say is check all the hidden menus on your monitor/receiver/source to see if there's any latency adjustments. You'd think it'd be the other way around with all the video format conversions going on today.

Maybe selecting 720p or some different format will incur a little delay in the video that helps mitigate the problem. Don't know. I'd be interested in your discovery though.

Can you post your component model#'s and maybe the community can help?

#### Ryssen

The sattelite receiver is PACE460 and TV is Samsung 42" plasma.
And M-1000 digimixer at the moment I use a DEQ2496 as DAC.
Somme times the sound seems in synk but an hour later slightly not..

#### Archwn

Ryssen said:
Simple as that?Hmm,maybe if I open the case and take the signal before the transceiver it becomes even simpler?

For the record, I did this to old DENON cd player. It works on some DACs and some won't play. I think it is what Jambo concerns.

#### Fin

Coax to optical

I've got a Pioneer DVD/HDD recorder with a coax digital output...and an amp with only optical inputs. Which would be better/easier: install an optical output in the recorder or a coaxial input in the amp...and how is it done.

Thanks

#### Iain McNeill

I would say its 10x easier to add an optical output. Basically take the digital out signal and wire it into the appropriate TOTX transmitter. (You need to pick the right voltage - 3.3V or 5V)

However, adding an coax input to the amp would be much harder and expensive but could produce lower jitter. Search for the S/PDIF input circuits here and on the web. There's a HUGE discussion on how to do it right.

#### Fin

Thanks Iain

In that case I'll add an optical output to the recorder (I'm not chasing the ultimate in sound quality with this setup as I have another system for that).

Is it as simple as tapping into the signal that enters the rear of the coaxial output's RCA....and wiring it to the input of an optical transmitter like this one (along with the an appropriate 3.3V supply for the transmitter)?

Optical transmitter - Jaycar

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