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#59873 - 16/01/2002 18:22 Single-ended outputs to differential inputs?
Sipho
member

Registered: 08/01/2002
Posts: 103
Loc: Utah & Silicon Valley
(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?

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#59874 - 16/01/2002 23:06 Re: Single-ended outputs to differential inputs? [Re: Sipho]
altman
carpal tunnel

Registered: 19/05/1999
Posts: 3457
Loc: Palo Alto, CA
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

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#59875 - 23/01/2002 10:38 Re: Single-ended outputs to differential inputs? [Re: altman]
Sipho
member

Registered: 08/01/2002
Posts: 103
Loc: Utah & Silicon Valley
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.

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#59876 - 23/01/2002 12:48 Re: Single-ended outputs to differential inputs? [Re: Sipho]
Neutrino
addict

Registered: 23/01/2002
Posts: 506
Loc: The Great Pacific NorthWest
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.
_________________________
No matter where you might be, there you are.

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#59877 - 25/01/2002 06:34 Re: Single-ended outputs to differential inputs? [Re: Sipho]
ShadowMan
addict

Registered: 09/06/1999
Posts: 559
Loc: Newfoundland, Canada
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
_________________________
12 gig empeg Mark II, SN: 080000101
30 gig RioCar SN: 30103114
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#59878 - 25/01/2002 17:15 Re: Single-ended outputs to differential inputs? [Re: ShadowMan]
Sipho
member

Registered: 08/01/2002
Posts: 103
Loc: Utah & Silicon Valley
The attached JPEG shows the pin-out.


Attachments
61406-CD-RB10 pin-out.jpg (305 downloads)


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#59879 - 26/01/2002 05:56 Re: Single-ended outputs to differential inputs? [Re: Sipho]
ShadowMan
addict

Registered: 09/06/1999
Posts: 559
Loc: Newfoundland, Canada
THANK YOU THANK YOU THANK YOU!!!! You just made my day/install!!!

_________________________
12 gig empeg Mark II, SN: 080000101
30 gig RioCar SN: 30103114
My blog

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#59880 - 27/01/2002 14:39 Re: Single-ended outputs to differential inputs? [Re: ShadowMan]
Sipho
member

Registered: 08/01/2002
Posts: 103
Loc: Utah & Silicon Valley
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

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#59881 - 27/01/2002 18:53 Re: Single-ended outputs to differential inputs? [Re: Sipho]
ShadowMan
addict

Registered: 09/06/1999
Posts: 559
Loc: Newfoundland, Canada
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!
_________________________
12 gig empeg Mark II, SN: 080000101
30 gig RioCar SN: 30103114
My blog

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#59882 - 27/01/2002 23:11 Re: Single-ended outputs to differential inputs? [Re: ShadowMan]
Sipho
member

Registered: 08/01/2002
Posts: 103
Loc: Utah & Silicon Valley
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


Attachments
62073-CD-RB10 pin-out, rev 2.jpg (164 downloads)


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#59883 - 28/01/2002 09:08 Re: Single-ended outputs to differential inputs? [Re: Sipho]
ShadowMan
addict

Registered: 09/06/1999
Posts: 559
Loc: Newfoundland, Canada
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!
_________________________
12 gig empeg Mark II, SN: 080000101
30 gig RioCar SN: 30103114
My blog

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#59884 - 28/01/2002 15:57 Re: Single-ended outputs to differential inputs? [Re: ShadowMan]
Sipho
member

Registered: 08/01/2002
Posts: 103
Loc: Utah & Silicon Valley
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?

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#59885 - 29/01/2002 10:57 Re: Single-ended outputs to differential inputs? [Re: Sipho]
ShadowMan
addict

Registered: 09/06/1999
Posts: 559
Loc: Newfoundland, Canada
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
_________________________
12 gig empeg Mark II, SN: 080000101
30 gig RioCar SN: 30103114
My blog

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#59886 - 29/01/2002 20:07 Re: Single-ended outputs to differential inputs? [Re: ShadowMan]
Sipho
member

Registered: 08/01/2002
Posts: 103
Loc: Utah & Silicon Valley
"I am too cheap to even buy a 10... let alone a 20"

Uh, what did you pay for your empeg?

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#59887 - 29/01/2002 20:55 Re: Single-ended outputs to differential inputs? [Re: Sipho]
ShadowMan
addict

Registered: 09/06/1999
Posts: 559
Loc: Newfoundland, Canada
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.
_________________________
12 gig empeg Mark II, SN: 080000101
30 gig RioCar SN: 30103114
My blog

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#59888 - 30/01/2002 07:02 Re: Single-ended outputs to differential inputs? [Re: ShadowMan]
thenominous
member

Registered: 22/12/2001
Posts: 189
Loc: UK
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!

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#59889 - 30/01/2002 18:26 Re: Single-ended outputs to differential inputs? [Re: thenominous]
Sipho
member

Registered: 08/01/2002
Posts: 103
Loc: Utah & Silicon Valley
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.

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#59890 - 31/01/2002 03:04 Re: Single-ended outputs to differential inputs? [Re: Sipho]
thenominous
member

Registered: 22/12/2001
Posts: 189
Loc: UK
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!

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