DIY Balun

[george a]

Hi All

Does any bosy know where to look for info on making your own 110 ohhm to 75 ohm balun ?

Can't seem to find any reaonably priced commercial unit here in OZ..
Can you somehow use a cheap 300/75 ohm TV balun in a modified form?

I am looking input digital signal from CD player into my DCX2496 xover..
many thanks in advance.
Cheers

[Jocko Homo]

Well, you won't.......

A balun is a form of broadband transformer, that uses transmission line techniques. You are only going to have integer ratios with a balun.

In your case, the best thing to do would be to get rid of the rotten XLR connector, since it is useless at SPDIF frequencies, repalce it with a BNC connector, and lower the Z to 75 ohms. Easier to do, and will sound better.

Yes, they do make 110:75 ohm transformers. None are worth a darn.

Jocko

[george a]

Hi Jocko


Are you saying all I have to do is remove the XLR from the back of my DCX and replace with a BNC receptacle????? no changes to wiring??
Does changing the receptacle alone change the impedence to 75ohm?? (no too bright in the electrocns dept I is..)

Sounds too simple ..

No one else seems to have taken this approach, all seem to bother with transformers and such - am I missing something???

[wa2ise]

Are you looking to drive a length of CAT 5 cable? Balanced 110 ohm impedance if I recall correctly. A one to one ratio would be fairly close, but the mismatch can cause reflections that, depending on the cable length, can mess up the reception of the bits at the far end.

[george a]

I'll run probably 75 ohm coax abot 6-7 metres at most

Cheers

[Jocko Homo]

6-7 meters is a very good length.

If it has AES/EBU inputs, it should be differential already. An outside chance it is single-ended. In either case, yes! Just use a good 1:1 transformer, and load it for 75R. The RX chip is high-Z. It does not care what the liine Z is.

Jocko

[george a]

Hi Jocko

When you say "just load it for 75R"doe that mean just place a 75 R across the input or outputside and in parallel or series.
pardon my ignorance.
Many thanks in advance

[Extreme_Boky]

6-7 meters is a very good length.

Hi Jocko,

I played with different coax cables and their length. Found that very low capacitance cables work really good - like CRO probes coax cable (4pF!). RE length: found that at least 2-3 meters cables work better than very short ones.

Reflection? Bouncing?

Thanks,

Extreme_Boky