How effective are hum eliminators for unbalanced to balanced conversion?

[canidoit]

I have a long run unbalanced cable going to my old school Akai X5000 reel recorder. I was considering buying a Hum Eliminator so that I can convert my unbalanced line in of the X5000 to accept balanced in so that I can use a long XLR balanced cable run instead.

I was considering a cheap one like this unit Alctron HM-2 Hum Eliminator - Transformer Isolator - 1/4" and XLR Inputs which is passive but has a transformer in it.

Is this correct, converting unbalanced to balanced must require a transformer?

Would I need something better for the hum eliminator like the Ebtech HE-2 2-channel Stereo Hum Eliminator or for this purpose, its not really necessary?

Thank you.

 

[Bo Deadly]

Yes, they work and are a good solution. Just use it at the end that is unbalanced so that the long run is balanced of course.

Although transformer quality can vary which will affect primarily low frequency reproduction and distortion. So if you buy a good one you might get better LF and THD. Although the THD can be minimized by controlling the level. Meaning just don't put a really high level signal through it. But a consumer R2R like that is going to accept a fairly low level so that's fine.

Another option would be an active circuit. It would be a trivial circuit that would probably cost $20 USD. But of course there's no profits in that so you might have trouble finding a device like that. I'm sure someone makes them but of course they won't be $20 USD.

 

[user 130681]

A DI box is the better solution.

 

[JohnRoberts]

Transformers are effective at interfacing with unbalanced feeds. Transformers come in many levels of performance and price.

JR

 

[Bo Deadly]

A DI box is the better solution.

Agreed. The drive of the R2R is probably not great so a high Z step down DI w/ transformer is more likely to preserve bandwidth and yield lower THD. But of course the other end will need to amplify and, depending on the DI, provide 48V.

Or, again, just use an active buffer.

 

[canidoit]

A DI box is the better solution.

What do you mean?
The signal travels this way:
DAW balanced out > long balanced cable > hum eliminator > short unbalanced rca cable > X5000 line in

Doesn't a DI have an unbalanced input or did you want me to feed it backwards like below and it will work?
DAW balanced out > long balanced cable > DI XLR out/DI TS in > unbalanced rca cable > X5000 line in

Or do I have to add a preamp:
DAW balanced out > long balanced cable > DI XLR out/DI TS in > mic/line preamp > unbalanced rca cable > X5000 line in

 

[Newmarket]

A DI box is the better solution.

Well that depends on the level/impedance of the source. But start with a 1:1 "10K" transformer and take it from there. It doesn't seem to be a mic pre level input ?

 

[Newmarket]

Agreed. The drive of the R2R is probably not great so a high Z step down DI w/ transformer is more likely to preserve bandwidth and yield lower THD. But of course the other end will need to amplify and, depending on the DI, provide 48V.

Or, again, just use an active buffer.

The OP's signal chain here is into the R2R from a DAW output.

 

[Whoops]

A DI box is the better solution.

No,
Not in this case.

The Op wants Balanced Line level to Unbalanced Line level

A DI box is Hi-Z unbalanced instrument level to Balanced Microphone Level

 

[rogs]

I've found these very useful for this task: DTI – Dual Transformer/Isolator – ART Pro Audio

And I was surprised just how well this cheap unit does, considering the price : Behringer | Product | HD400

Bo Deadly's advice in post #2 on keeping the level down is probably useful to keep in mind with that cheaper second item....

 

[Bo Deadly]

The OP's signal chain here is into the R2R from a DAW output.

Ok! Then I change my mind. Sort of.

If the signal is going from the R2R to audio interface, a DI would be a good solution.

If the signal is going from the audio interface to R2R, then I would use a custom balanced to unbalanced cable with resistor U pad attenuator buried in the RCA jack cover (if it's possible for that type of connector to fit with the R2R connectors). No hum eliminator necessary.

Although using a completely passive DI to step down from the audio interface to R2R might be just right actually. If the nominal audio interface level out is say +4dBu, then stepping down through the DI 20dB would present -16dB to the R2R which might be just about right for recording. But it does sort of lock you into that relatively moderate level.

Or, again, just use an active buffer.

 

[Whoops]

Although using a completely passive DI to step down from the audio interface to R2R might be just right actually. If the nominal audio interface level out is say +4dBu, then stepping down through the DI 20dB would present -16dB to the R2R which might be just about right for recording.

Using a passive DI, it would have to be used backwards.
You would connect the interface Balanced Line Level to the DI’s Mic Level output, and then take the signal to the recorder from the DI’s unbalanced instrument input.
Using a Passive DI backwards is a Step Up and not a Step Down…

 

[Bo Deadly]

Using a passive DI, it would have to be used backwards.
You would connect the interface Balanced Line Level to the DI’S Mic Level output, and then take the signal to the recorder from the DI’s instrument input.
Using a Passive DI backwards is a Step Up and not a Step Down…

That would definitely not work. The impedance of the R2R is probably 10Kish which means the impedance seen by the audio interface out would be like 75 ohms which could stress the audio interface output and equate to distortion. And that's without considering the awkward difference in levels.

 

[Bo Deadly]

It's always good to look at the schem to understand exactly what you're dealing with. This appears to be the input section of the X5000:



So apparently there are three ways to enter:

1) Mic in takes mic level signal probably in the -60dBu range
2) The DIN connector takes a signal roughly 20dB hotter or -40dBu
3) Line in is probably consumer level -10dBu or it looks like maybe -20 or so

Because the DIN and line are just attenuated in front of mic, the mic input is the most direct route.

So the best solution IMO would be a custom balanced to unbalanced cable with builtin U pad attenuator of -60dB with a low characteristic output impedance of say 100 ohms.

However, the DIN connector would work perfectly fine too and you wouldn't have a presumably ugly cable in the mic input on the front. So again, a U pad of -40 dB would work but you would need to find a DIN connector that you can hackup with the 3 resistors.



The DI would work well with either the DIN or mic input (step down of course).

I wouldn't mess with the line in.

 

[Whoops]

The DI would work well with either the DIN or mic input (step down of course).

A DI would not work, it's the opposite of what the Op wants.
Op wants to go from Balanced Line level and unbalance it to feed the recorder. So he needs an interface device that has a Balanced input (I presume +4dBu Balanced Line Level) and convert it to -10dBv unbalanced consumer Line level (in this case)

A DI is the opposite, it's input is unbalanced and converts it to Balanced microphone level.

 

[Whoops]

I have a long run unbalanced cable going to my old school Akai X5000 reel recorder. I was considering buying a Hum Eliminator so that I can convert my unbalanced line in of the X5000 to accept balanced in so that I can use a long XLR balanced cable run instead.
I was considering a cheap one like this unit Alctron HM-2 Hum Eliminator - Transformer Isolator - 1/4" and XLR Inputs which is passive but has a transformer in it.

It would work, but the problem with those cheap boxes is that they use a small and cheap transformer inside.
The problem with a cheap transformer is that probably you will have limited frequency response, and like Bo Deadly said in the second post you will have higher distortion than the incoming signal, specially in the Low end as the transformer will start to saturate.
As you are recording I assume you want to preserve the signal as much as impossible from the output device into the recorder and not have something in the middle that will degrade your signal.

A solution could be to buy 2 good quality transformers and build a box yourself, for example Lundahl transformers, that way the signal would not suffer as much as with a cheap transformer. The problem is that good transformers are very expensive.

Is this correct, converting unbalanced to balanced must require a transformer?

Not really. A transformer is just one way of doing it.
Another good way of doing it is using a quality Opamp like the THAT Corp 1280 which has excellent audio performance, and might be one of the most transparent ways of doing the conversion.




You could DIY a box with 1x THAT 1280 inside and with and external or internal PSU (positive and negative rail of 6 VDC to 36 VDC).
It would be easy to build, cheap, and you would have a transparent interface.
You could have your long run of cable with a Balanced signal and have this box next to the recorder to have the minimum amount of unbalanced cable/signal possible

Another option in case you don't want to DIY an unit, you could buy a box that does the same thing (active devices, no transformers used):


https://www.canford.co.uk/Products/95-654_SONIFEX-RB-BL2-PRO-INTERFACE-Bi-directional-single-stereo
Or a cheaper, but also good alternative:


https://artproaudio.com/product/cleanbox-pro-dual-channel-level-converter/

Would I need something better for the hum eliminator like the Ebtech HE-2 2-channel Stereo Hum Eliminator or for this purpose, its not really necessary?

As you can't control the quality of the transformers used in those boxes I would go through the active route

 

[Whoops]

So the best solution IMO would be a custom balanced to unbalanced cable with builtin U pad attenuator of -60dB with a low characteristic output impedance of say 100 ohms.

I don't see how can that be the best solution as Canidoit said he wants to run a long run of XLR cable, Balanced signal going to the recorder. So that means the most amount of cable needed would be for balanced signal to take advantage of CMRR, and then the short cable possible of unbalanced signal.

Doing a balanced to unbalanced cable is easy and NBD, but then it would lose the advantage of a Balanced signal, that is CMRR at the receivers end.

Maybe I'm missing something, but as I see it with a Balanced to unbalanced cable the Long Run of XLR cable would just be using an Unbalanced signal

 

[canidoit]

Would it make a difference in audio quality if I was to use long unbalanced cables instead of long balanced when in the end I will be using a hum eliminator?
DAW out > long unbalanced cable run > hum eliminator > short unbalance cable > X5000 in
DAW out > long balanced XLR cable run > hum eliminator > short unbalance cable > X5000 in

There looks like a very easy DIY using RCA > transformer > RCA

sourced from DIY Ground Loop Isolator

What would be the cheapest transformer I could use that would get me audiophile results?

Thank you all for the replies!

 

[Bo Deadly]

Would it make a difference in audio quality if I was to use long unbalanced cables instead of long balanced when in the end I will be using a hum eliminator?

No. The hum eliminator is just a transformer in a box. And it doesn't matter if the signal on the lines is actually balanced or single ended. The transformer will work exactly the same.

UPDATE: I just noticed you said long UNbalanced cables. In that case I would say YES, it would make a difference because the ring would be connected to the sleeve. You may not realize this but the hum eliminator 1/4" are TRS not TS. So you would want to use balanced cables for the long run regardless. Then it wouldn't matter which end the HE was at. If you happen to have long TRS instead of long XLR, it shouldn't matter which end the HE is at.

But again, IMO, you don't even need a transformer. If the cable is going up two floors and through a mechanical room over to the other side of the building, then the CMRR offered by a high quality transformer would help. But if the cable is just going from one end of a room to another and it's a high quality fully shielded cable, then you don't need a transformer. You could just use a U pad at the R2R end. Get a DIN connector and put two 40dB U pads inside with short pieces of cable w/ XLR connectors. Now you have a balanced to unbalanced adapter cable. The series resistance of the U pad will provide good ground isolation which is where 90% of the noise is going to come from and if the audio interface outputs are ground sensing, they will also provide CMR. Leave the shields unconnected at the DIN end.

 

[JohnRoberts]

The cables used matters, but less than transformers.

JR