DIY Audio Projects Forum

I purchased a class D board that uses Balanced inputs.
What do I have to do to change the inputs to RCAs?

Hey Moose,

what kind of input? XLR or Terminals?

You should use shielded instrument cable for this task.

From RCA (i.e.: CD out) to Balanced (your inputs):
RCA positiv (signal) to balanced positive,
RCA negative (ground) to balanced negative,
the shielding of the instrument cable hooks up to balanced ground - only at this side. The RCA side is not connected to the balanced ground via the shielding.

_________________
Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.

Hi Tom:

Sorry for the delay in replying. I'm a newbie to this form as wll as electronics. I mistakenly thought that
I would get an email when a reply to my query was posted. I would prefer to replace the XLRs? on the
back panel of my enclosure with RCAs.
I hope this attchment helps.

Thank you &Regards,
Moose

Hey Moose,

you can set your user profile preferences to receive eMails upon board / thread replies:

User Control Panel > Board preferences > Edit posting defaults > Notify me upon replies by default = Yes.
The UCP is on the right corner at the top of the Pages.

OK - it is no problem to use RCAs on your enclosure. I just didn't know how the amplifier board connections look like.
Like mentioned before, you can connect the source output to the board as followed:

For the Left channel use:
Source RCA positive to amplifier board positive input (pin 9)
Source RCA negative (ground) to board negative input (pin 10)
Shield to amp board ground (pin 7).

Right channel -
Positive = pin 11, negative = pin 12, ground / shield = pin 7 or pin 8
It is important to know that unbalanced to balanced inputs may cause some little problems.
Balanced connections usually are used to eliminate potential differences between enclosures / devices and to eliminate the influences of magnetic fields.
It is not easy to explain it in a minute. Please read through the linked article for further information. You'll find a lot of informations about unbalanced to balance connections in here:
http://www.benchmarkmedia.com/caig - DL the PDF document and read through it.

If possible, go for shielded instrument cable (shielded balanced cable with 2 wires and shield) to connect the source to your amp board, or use shielded RCA cables like this one:
http://diyaudioprojects.com/Power/DIY-Shielded-RCA-Interconnect-Cables/

_________________
Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.

Much Thanks Tom

Regards,
Moose

Hi Tom:
Re read the Diy cable project several times & the benchmark media article also. I can't wrap my head around how one gets 3 wires out of the SC Tricone MK II wire. Shudn't there be 2 insulated wires enclosed by a shield? According to benchmark the shield shud be grounded to the signal sending component would that be the preamps Disc Ground?
Regards,
Bert

Hi Bert,

the Tricone Interconnect (Instrument Cable RCA Project) only was meant as an example which shielding to use.
The cable itself surely must have 2 inner cores / conductors. That's one for the positive signal and one for the negative signal.

This Link guides to a page with more examples on how the cable could look like: http://www.sommercable.com/3__default/index.html
A Tricone is not that far away from this topology. Microphone cable has 2 conductors for example.

The shield should be connected to the Source and the Amplifier. When you want to use RCA plugs on both sides, you want to connect the shield at the source and the amp ground.
If you hook up the shield to the source only, the shield conductor will act like an antenna and high frequency or stray fields may be injected to the source signal reference path (ground) -
as the source ground becomes the signal reference for both devices by attaching the source ground to the balanced negative input which is in the same path now AND also ground referenced. Not so good!
Then better leave both shield ends open (not connected) and only hook up the signal conductors. Possible potential differences between the chassis now will be ignored as common signal.

It is possibly the absolute best way to use shielded microphone cable (2 conductor # 22 to # 24 AWG) and leave the shielding open at both ends (unconnected).
It is the easiest way and doesn't cause any confusions and the chance to catch up stray fields or HF is very low... If you plan to use an plastic or wood enclosure for the ClassD toy,
balanced shielding is nonsense anyway. It only plays a little role when you build it into a metal enclosure and connect the balanced ground to the enclosure.

BTW - i switched the connections for pin 11 and 12 in the last post. I overlooked that the pin tracks are crossed at the bottom of the drawing.
So - Right channel: Positive = pin 12, negative = pin 11.

_________________
Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.

Thanks again Tom,

Stuff that is simple & obvious to you needs to get
pounded into thius newbie brain.

Cheers, Bert