Optical Input To Rca Output Converters!

**nate@s-curves** · 12-21-2005, 04:12 PM

On a similar note does anyone know how to 'balance' the unbalanced audio coming out of our mother boards? Balance may not be the right term but it was a term we used when I worked in a post production house, it was used to take audio and bring it to the right voltage, and it made it so it didn't distort. Am I making sense? Does something like this exsist? Thanks.

**BassBinDevil** · 12-21-2005, 05:11 PM

The Creative Labs Extigy is fairly cheap, and will turn S/PDIF (optical) into analog.

As for unbalanced to balanced.... "balanced" means instead of signal and ground, you have 3 wires, where one is signal, the other is -signal (the opposite polarity), and ground. This means there's a bigger signal being transmitted, even though the voltages aren't any higher, which puts the noise down lower. And it also helps reject "common-mode" noise, since if noise is added to +signal and -signal, it cancels out later on. I can't describe it very well here. Balanced is common in pro audio, and there's some high-end car audio that uses it.

So, to convert unbalanced (RCA) to balanced (XLR), there's two main ways:
1) Transformer. This comes with the added bonus of complete isolation from ground loops. The problem here is that for decent frequency response you need a "broadcast quality" transformer, which is costly.
2) Op-amps. Use a pair of opamps, one wired inverting (x-1) and the other non-inverting (x1); put a small resistor (33 ohms?) on the output of each amp for stability in case of long cable runs. Cheap; can be done with an 8 pin dual opamp and a handful of precision resistors. No isolation from ground loops. There may be a dedicated chip that does this from Analog Devices, part of the SSM (solid state music) line of audio chips.

**Nic** · 12-21-2005, 07:13 PM

Originally Posted by nate@s-curves

On a similar note does anyone know how to 'balance' the unbalanced audio coming out of our mother boards? Balance may not be the right term but it was a term we used when I worked in a post production house, it was used to take audio and bring it to the right voltage, and it made it so it didn't distort. Am I making sense? Does something like this exsist? Thanks.

thats what the gain knob on your amp is for

**Nic** · 12-21-2005, 07:14 PM

Originally Posted by BassBinDevil

The Creative Labs Extigy is fairly cheap, and will turn S/PDIF (optical) into analog.

As for unbalanced to balanced.... "balanced" means instead of signal and ground, you have 3 wires, where one is signal, the other is -signal (the opposite polarity), and ground. This means there's a bigger signal being transmitted, even though the voltages aren't any higher, which puts the noise down lower. And it also helps reject "common-mode" noise, since if noise is added to +signal and -signal, it cancels out later on. I can't describe it very well here. Balanced is common in pro audio, and there's some high-end car audio that uses it.

So, to convert unbalanced (RCA) to balanced (XLR), there's two main ways:
1) Transformer. This comes with the added bonus of complete isolation from ground loops. The problem here is that for decent frequency response you need a "broadcast quality" transformer, which is costly.
2) Op-amps. Use a pair of opamps, one wired inverting (x-1) and the other non-inverting (x1); put a small resistor (33 ohms?) on the output of each amp for stability in case of long cable runs. Cheap; can be done with an 8 pin dual opamp and a handful of precision resistors. No isolation from ground loops. There may be a dedicated chip that does this from Analog Devices, part of the SSM (solid state music) line of audio chips.

this post is completly correct but i dont think thats what he ment by balanced

edit: actually i dont get what you mean by a bigger signal being transmitted so the noise is lower. My understanding is that the differance between + and - carries the signal, if noise gets induced it effects both wires and thus the differance between + and - is still the same so the signal is largely uneffected (ethernet networking works on this same principle i believe)

**caduceus** · 12-22-2005, 01:37 AM

http://store.topmicrousa.com/dav-2100.html

I searched high and low for something simple to convert optical to RCA, and found this some time ago. I use it with my PVR box but it could potentially be used in a car application. Been using it for a year, and it works for me.

=caduceus=

**reiner15** · 12-22-2005, 09:07 AM

Originally Posted by caduceus

http://store.topmicrousa.com/dav-2100.html

I searched high and low for something simple to convert optical to RCA, and found this some time ago. I use it with my PVR box but it could potentially be used in a car application. Been using it for a year, and it works for me.

=caduceus=

looks nice! do you happen to have any larger photos? perhaps of your setup?

**caduceus** · 12-23-2005, 03:30 AM

Originally Posted by reiner15

looks nice! do you happen to have any larger photos? perhaps of your setup?

Sorry, I don't have any pix, as it's hidden deep beneath a tangle of cables behind my plasma/entertainment system. It's about as big as a typical paperback book.

It's one of those no-brand, made-in-china-gadgets-that-everybody-wants-but-nobody-can-find things.

The green LED on the front glows when it's powered (and is powered by a wallwart AC adapter). I only use it for the audio (from PVR to DVD recorder), but it has S-video <--> composite converters on it also. I bought one of their TOSLINK splitters from them also to split off audio to my receiver, and that works great and needs no external power source.

P.S. I'm not affiliated with topmicrousa, just a happy customer.

=caduceus= (still in planning stages for carputer)

**nate@s-curves** · 12-23-2005, 08:50 AM

Originally Posted by Nic

thats what the gain knob on your amp is for

No that will amplify the noise in the signal as well.

**Reverant** · 01-06-2006, 04:51 AM

You might want to try Creative's DDTS-100 Decoder.. It will take an optical input and it will output to a wide number of channels, ranging from 2 to 7.1 channels. Having done various things with Creative's products on my car, my guess is that it requires 12V to function properly, so it will be easy to install on any car.