Unbalanced RCA > Balanced XLR Pre-Amp

Hi guys, I figure this topic has probably been flogged to death but I'm looking at this from a slightly different perspective.

Long story short, I've been asked to put a sound system into a large warehouse on a fairly limited budget. My background is car audio and comms, so I have skill in the general area but not particularly pro audio equipment.

The requirements are it needs to grab the output from a TV (in this case, playing from an Apple TV) and output to a Crown XLS402 amplifier which is located around 10m away. I figured the easiest way is to use the TV RCA outputs convert from unbalanced RCA>balanced XLR. I've had my eyes out for a relatively cheap mixer with balanced outputs, but so far no such luck.

Obviously there are off the shelf solutions out there such as the CleanboxPro/related, but that would eat into the budget and mean I have to use much cheaper speakers. I have seen a few active solutions (avoiding transformers), however I have no idea what in particular I should look for.

First up - this. Concerns - not a lot of information there, and no idea if this would be sufficient. Obviously I'd wire it up with the relevant jacks and PSU.

Next - this. Seems much more complicated and I don't think I could get it looking 'decent' due to fixed terminals on both side of the board.

Finally - this. Seems to be a lot more going on.

There was also another board I saw with an integrated power supply but which was only mono. It had 3-4 types of IC's and promised 'tube sound' so I have no idea what to expect.

Does anybody have experience with these, or suggestions?
 
Why converting the low quality TV RCA sound output to a balanced one.
Why not simply using a converter plug going from RCA to XLR.
Or solder the wires of a cable with an RCA plug on one side to an XLR plug on the other side, like shield to pin 1+2 and hot to pin 3.

Hans

Because the signal leads need to run approximately 10m (33') from the TV to the amplifier.

Given that it's in a warehouse, I'm pretty sure there's going to be some interference happening with unbalanced cables.
 

turk 182

Member
2012-10-26 3:03 pm
all of the modules you selected would do what you want but the additional chore of putting them in a case and providing a supply is somewhat of a PITA.(and by the time you put it all together in a case you'll be at the same pricepoint as the Clean Box)
on the cheap you could use a passive DI or matching transformer for your purpose.
if you go with Hans suggestion i'd wire pin 1 and pin 3 common and the hot on pin 2 the input on the Crown xls will like that better(as pin 2 is positive)
i'd try to avoid sending an unbalanced line 10 meters.
 
all of the modules you selected would do what you want but the additional chore of putting them in a case and providing a supply is somewhat of a PITA.(and by the time you put it all together in a case you'll be at the same pricepoint as the Clean Box)
on the cheap you could use a passive DI or matching transformer for your purpose.
if you go with Hans suggestion i'd wire pin 1 and pin 3 common and the hot on pin 2 the input on the Crown xls will like that better(as pin 2 is positive)
i'd try to avoid sending an unbalanced line 10 meters.

I've got basically an unlimited, free supply of cases, PSU's and input/output connectors so that aspect isn't an issue - I really just don't know which (if any) of those is 'ideal'. That being said, the Cleanbox in Australia is $200, so I think knocking up something would be idea.

I've heard that the majority of transformer/passive designs will kill the bottom end, unless you buy the expensive Jensen transfomers? Definitely not my area of expertise so open to suggestions.

The other one I was looking at was this - like I mentioned earlier a bit more complicated and to be honest I don't exactly know what's going on (using FET's to drive the balanced signal instead of an op-amp?) Benefit of this is only requiring an AC transformer (of which I have dozens), downside is I'd need to grab two.
 

Hans Polak

Member
Paid Member
2005-03-17 4:25 pm
Blaricum
Since you have to bridge 10meter, why don't you use the optical output from the Apple TV, and place a low cost D/A with optical input close to your amplifier.
It will give you the best possible noise suppression and you do not have to depend on the bad quality of the analog TV output.
The Fiio Alpen-A17 from Amazon cost $139,- as an example, but on Ebay you can most likely find even more attractive offers.
You can still use an RCA to XLR converter or make the interlink cable yourself, either pin2 or pin3 for the signal, it does not make any difference.

Hans
 
Dread
that last one you linked to is based on an NE5532 the fet's are an added gain stage.
two of them would make for a forty dollar solution.

Brilliant. Any issue running them off a single 12VAC CT transformer? I'm all over good wiring protocols for single ended amps (having build a few SS guitar amps), however not sure about this balanced stuff.

I've got a couple of toroids and Neutrik XLR panel mount connectors so it makes for a cheap solution.

My THAT Driver circuit does exactly what you need. Single-ended/RCA in. Differential/XLR out. You need to add a ±20 V power supply, chassis, and connectors. You get transformer-like performance for a fraction of the cost.

Tom

As perfect as that is.... by the time I get everything here + components (especially the bigger stuff) it doesn't end up much cheaper than a Clearbox or related.
 

turk 182

Member
2012-10-26 3:03 pm
being that it's an Epay supplier i looked for any link to more detailed spec's for the module with no luck i can't find any sort of supply voltage so as to whether a center tap transformer will work is virtually impossible without more details.
from the pic's it does appear to have a complete power supply with bridge rectifier and associated filters so just add x-former and go.
 
1. Make / buy two ~10 m unbalanced RCA to 1/4" TS cables with decent 75 ohm coax (typically RG-59). If you need a stereo 1/8" at the source end instead, I might look at an adapter cable - one-piece adapters tend to be cheap junk. If you're flexible with the adapter cable, you could use ready-made instrument cables. Or just get a 1/8" stereo to 2x 1/4" mono cable, like I have under the desk here.
2. Buy one Behringer HD400.
3. Make/buy two balanced 1/4" TRS to male XLR cables, 60 cm to 1.5 m max.
Problem solved without breaking the bank. Plenty of users with nearfield monitor on their PC can probably attest.

Obviously you won't be running at pro levels there, but pro power amps tend to have an input sensitivity of ~0 dBu (0.775 Vrms), so it should work out.
 
Idiots....lol.

Instant economical solution - ART DualZDirect 2 Channel Passive DI Box
The polarity switching is handy.
This one is passive and there are powered versions available.
Standard equipment in the PA industry.

Art DI.png

Art DI 2.png

View attachment Art - om_dualzdirect.pdf

Dan.
 

infinia

Member
2005-05-15 9:51 am
SoCal
lately most all TV provide ONLY optical audio out. I'd tend to believe the DACs inside an older TV for the analog outputs aren't too good to begin a long OR short journey.
single ended "clean" audio outputs in a TV E.g. consumer digital environment is a dicey proposition esp if controlled by the remote.


id use an optical to SPdif converter/adapter > one 10M coax cable >SPdif DAC with short RCAs
and keep it digital over the long run ( both converters can be had very inexpensively, ~10-20 USD each if you look hard enough*)
*look at 'Monoprice' for the converters then shop them out at the usual HK / china dealers.

otherwise the consumer trend is staying with HDMI with repeaters for longer runs.
 
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lately most all TV provide ONLY optical audio out. I'd tend to believe the DACs inside an older TV for the analog outputs aren't too good to begin a long OR short journey.
single ended "clean" audio outputs in a TV E.g. consumer digital environment is a dicey proposition esp if controlled by the remote.

Television headphone out or line out into DI will work and sound perfectly fine.
Just need DI box, two XLR extension cables, 3.5 stereo plug to dual 6.5 mono plugs, or dual rca to dual 6.5 cable.
RCA female to male mono 6.5 adaptors are available easily and would allow use of standard 3.5 stereo to Dual RCA, or 2RCA to 2RCA cables.

This approach is dependent on using DI box galvanic isolation which is a good thing in this case to keep TV generated/radiated hash out of the audio.
The DI box I mention has 30kHz LPF on the outputs which may be useful in addition to the usual ground lift switching and attenuation, polarity switching is a good bonus.
According to specs there should be essentially no deterioration in sound quality, and indeed may sound nicer than an active solution.

Drew, this is a quick and easy and economical passive solution that would work perfectly fine, and for less than $100 total and 5 minutes to install/configure, this would be my first choice.
This setup would also allow easy connection to other sources like iPods etc.
You say 'warehouse'....you could beneficially halve costs and run the system in mono, you just need an XLR patch lead to bridge both channel inputs, or add a link internally.

Dan.
 
http://www.diyaudio.com/forums/solid-state/181851-help-crown-xls-402-input-board.html

Has the schematic of the input. Well it's differential, but not balanced :)

Goddamnit, really? It says in multiple locations in the manual I have it's balanced :(

Instant economical solution - ART DualZDirect 2 Channel Passive DI Box
The polarity switching is handy.
This one is passive and there are powered versions available.
Standard equipment in the PA industry.

View attachment 537447

View attachment 537448

View attachment 537449

Dan.

I ended up buying 2 of the eBay boards. I've already got jacks/transformer/enclosure/etc, so the entire thing shouldn't cost much more than $50 (assuming everything works).

That's the route I was initially looking at.


Drew, this is a quick and easy and economical passive solution that would work perfectly fine, and for less than $100 total and 5 minutes to install/configure, this would be my first choice.
This setup would also allow easy connection to other sources like iPods etc.
You say 'warehouse'....you could beneficially halve costs and run the system in mono, you just need an XLR patch lead to bridge both channel inputs, or add a link internally.

Dan.

I thought about running mono, but the goal is to have something 'modular' that can be adapted when the business expands to a bigger location/splits and has two smaller locations. Just trying to future-proof on the smallest budget imaginable haha.

Thanks for the suggestion though