Single-ended outputs to differential inputs?

(Part of the on-going saga of installing a MK][ in a Lexus RX300)

In my car's factory setup the CD changer in the glove box sends a differential signal to the amp for each channel, each on a pair of wires. That is to say the voltage that matters is the what appears across the two wires. The empeg's outputs as we all know are relative to ground (both the 1 and 4 volt outputs).

So how to convert the single-ended output from the empeg to the needed differential inputs? Presumable I could use some of the transformer-based signal isolators like this. But what about things like impedance and voltage levels? I can't find anything that says what the typical voltage difference is. Anyone know the specs and/or a design or source?

You could first try just grounding one side and feeding signal into the other; this should work. Try with a low volume first. You will loose the extra noise immunity that differential gives you, but I suspect you won't have many problems - the main reason to use differential on a changer bus is to stop noise pick up without using any shielded cables.

Ford's ACP changer bus uses a similar system, as 600 ohm differential. The car outputs are 100 ohm, so there will be no issue driving the load.

Hugo

I got one of Pioneer's CD-RB10 adapters and took it apart. This connects two RCA input jacks to Pioneer's IP-Bus with its differential audio signals. The adapter contains NOTHING. The RCA jacks are just wired to the audio signal wires in the IP-Bus connector.

The shields on the RCA connectors are isolated from the grounded metal enclosure. The installation guide says that the inputs should be limited to 1 volt. So I guess that answers my original question at least for the stock Pioneer bus.

I believe Altman is correct. There should be no danger in wiring the left - and the right - inputs together to work with the Rio. Just make sure the signal levels are compatible.

Would you be able to post the actual wiring diagram of the unit. I have a Pioneer Head unit and a cable hooked up to it. According to what you are saying (and the fact that my Pioneer headunit can select CD even though there's no changer present) I should be able to wire my empeg audio outs directly to my Pioneer as long as I know which wires to tap into.

I would greatly appreciated it if you could do this for me!!!

Thanks!

René

The attached JPEG shows the pin-out.

THANK YOU THANK YOU THANK YOU!!!! You just made my day/install!!!

Don't forget the 1 volt warning. The empeg dock outputs are 4 volt. I guess a simple 4-to-1 resistive divider would take care of this. Any comments from a real engineer? Impedence? Appropriate resistor values?

4 volt out ---/\/\/\/\---------O--------/\/\/\/\-------- signal ground
...................3R......1 volt out......1R

From what I read on Crutchfield's website it states that 'The auxiliary source must have a output voltage of 1 volt (or less), or a volume control to adjust output level."
http://www.crutchfield.com/cgi-bin/S-75vZkJtRRuv/ProdView.asp?a=&s=0&g=50900&id=essential_info&i=130CDRB10
So I should be safe with the empeg's volume turned down a bit.

You wouldn't happen to have the color codes so I don't have to break out my meter??

Thanks again!!! Now I can get rid of the Cassette adapter (ewww) that I've been using since Sept of 2000!

OK, just promise never to crank the volume up more than 1/4 (or is it logrithmic?).

I took apart a CD-RB10 (connects only to head unit) and a CD-RB20 (goes between head unit and CD changer). The color codes agree. See the attached JPEG

So since you took apart a 20 as well do you think that it would be possible to simply patch into the audio lines and also use a cd-changer with just the original cable? Just wondering because then I could also plug my changer in and use that when I forget to take the empg.

Thanks a million!

The CD-RB20 is a horse of a different color. It is powered, contains at least two surface mount ICs, 20-30 caps and what I guess is an isolation transformer.

So why not just buy a '20?

More curious then anything. I am too cheap to even buy a 10... let alone a 20.

I do appreciate the information a bunch though!

René

"I am too cheap to even buy a 10... let alone a 20"

Uh, what did you pay for your empeg?

Ok then... I knew that was coming.

Actually I saved for a long while fom my Mark II unit and my MkIIa is still sitting on my Credit Card. I buy things where I see value and I really didn't see the value in the CD-RB10... and you kinda pointed out the worthlessness of the 10. The 20 was just a shot in the dark, I never really considered buying that one anyways. Another factor is the fact that I can't seem to find a supplier of these parts located in Canada. I am at least 180 kms from the nearest Radio Shack so I am pretty much left to shop online. I don't like buying from US sites due to the duties that I always get hit with, unlike shopping from Europe which I have gotten everything duty free. (NAFTA???!!!)

Thanks again for the help! I truly appreciate it.

The CDRB20 IMHO is pointless.
When you select aux yeah it cuts out the CD, but from the people Ive spoken too, if the AUX is still playing when the CD is on then you hear both the CD and AUX audio together!

Now that struct me as being a little silly.
Needless to say that I didnt want to find out with my own money
So....
If you guys want to have a look at the schematic of the RB20, I stuck it up a couple of years ago, forgot the hit counter tho. Its a little over 1mb of jpeg, enjoy!

Yeah, that flaw is described in the included docs and on the Crutchfield site. I won't be using it anyway as the Pioneer changer in my Lexus has a custom Toyota (er, Lexus) hook-up. I'll just switch the audio lines in the harness between the changed and the enpeg with some signal relays.

A nice touch is to have the inputs auto switch.
Sense audio on the CD inputs and turn off the audio line coming from the aux device. If you installed the empeg in there, you could use that little circuit to pull the mobile mute line down when playing CD.
In fact it makes you wonder why Pioneer didnt see fit to do that in the first place!