50 Foot Interconnect

[cpd]

I need to run 50 feet of RCA interconnect from my phono pre amp to my receiver (through the walls, attic, and crawl space). I'm not really a big believer in high priced cables, but have never used anything at that length. Does anyone see a problem using a monoprice or tartan cable at that length? I'd prefer not to drop $150 on a BJC.

 

[markw]

At that length, the cable itself won't be your problem. The length itself, which may cause the loss of some highs, and shielding (or lack thereof) will be. Try a "low priced" one and see if it works for you. If not, then try one of the more expensive ones but I wouldn't expect much of an improvement,

If possible, see if you can return them. It might be worth paying for that option.

 

[Irvrobinson]

50 feet is at the fringe of acceptability for any single-ended cable. A balanced cable with XLR connectors would be preferable to guard against added noise or other distortions, but I understand that a balanced cable is probably not an option with your equipment. You may also have too much insertion loss (a voltage drop) with 50 feet of cable, that causes you to use more gain (turning up the volume control to obtain the same level), which could also increase your perception of noise or interference.

You won't know until you test it, and Monoprice sells a 50' cable pair for $12, so even if you're unhappy with the results it's not a big financial loss. I think there's an excellent chance the Monoprice cable will work just fine. If it doesn't, a more expensive cable is very unlikely to help. I wouldn't waste any money that way. If you have noise or volume problems you'll need some different equipment or you'll need to get the two components closer together, IMO.

 

[highfigh]

High impedance is the problem on long runs. The resistance causes voltage drop and if you want to send the signal that far, use a line driver or at the very least, some kind of balun. I have used baluns for sending audio from one system to another, in different parts of the house. Because the balun isolates one end from the other, ground loops are prevented. Some baluns add 1dB, to counter any voltage drop. They're passive, so noise won't be added by the baluns.

However, the quality of the baluns or line driver can have a serious effect on sound quality, so be aware that it may not be as good as if the turntable was close to the system preamp.

 

[Irvrobinson]

High impedance is the problem on long runs. The resistance causes voltage drop and if you want to send the signal that far, use a line driver or at the very least, some kind of balun. I have used baluns for sending audio from one system to another, in different parts of the house. Because the balun isolates one end from the other, ground loops are prevented. Some baluns add 1dB, to counter any voltage drop. They're passive, so noise won't be added by the baluns. However, the quality of the baluns or line driver can have a serious effect on sound quality, so be aware that it may not be as good as if the turntable was close to the system preamp.

What are you suggesting he do? Use a balun to convert to balanced and then reconvert to single-ended at the opposite end? If they're passive they can't add 1db. Also, I'm unfamiliar with baluns such as you describe. A couple of Google searches revealed mostly what I'm familiar with, antenna-related stuff, and active audio baluns that convert to coax or CAT.

Personally, I still think that if the output impedance of the phono pre-amp is low enough it will tolerate the insertion loss of the 50' cable. If not, there are several alternatives for small RIAA pre-amps that might do better. I've noticed Music Hall makes one for about $90 that has an output impedance of 1K ohms that might do the trick, if his current equipment can't do it.

 

[highfigh]

What are you suggesting he do? Use a balun to convert to balanced and then reconvert to single-ended at the opposite end? If they're passive they can't add 1db. Also, I'm unfamiliar with baluns such as you describe. A couple of Google searches revealed mostly what I'm familiar with, antenna-related stuff, and active audio baluns that convert to coax or CAT.

Personally, I still think that if the output impedance of the phono pre-amp is low enough it will tolerate the insertion loss of the 50' cable. If not, there are several alternatives for small RIAA pre-amps that might do better. I've noticed Music Hall makes one for about $90 that has an output impedance of 1K ohms that might do the trick, if his current equipment can't do it.

So, a small transformer can't convert the incoming AC signal to higher output? Really? How does a 120VAC primary produce 400+VAC, to be rectified and used for tube plates?

These are used extensively in custom integration and may/may not include video.

Google search results (might have been more specific than yours)-
https://www.google.com/search?q=Audio+balunl&ie=utf-8&oe=utf-8#q=stereo+audio+balun+transformer

Another way is by using a distribution amp, like CE Labs, Audio Control, Radial, etc. Some of those have level controls so losses don't occur, but many provide unity gain.

I would be concerned with noise over a 50' cable in a house- lots of opportunities for noise pickup. OTOH, I had the electrician who wired for my detached garage add a conduit for my use. Unfortunately, he didn't install what I asked, but I did get two Cat5e out there and I used that for quite a while for the analog audio from my server to the receiver in the garage. It had a ground loop, but I was able to cure that with an AV balun using RJ45 terminations. They can be cheap and they work.

 

[Irvrobinson]

So, a small transformer can't convert the incoming AC signal to higher output? Really? How does a 120VAC primary produce 400+VAC, to be rectified and used for tube plates?

Transformers can raise or lower voltage, but can't increase power. Conservation of energy.

 

[cpd]

I expected I might be pushing it. 50 feet is the ideal route - I could get away with 35 feet running along the floor of a closet as opposed to over it. Do you think that would be more apt to work?

 

[Irvrobinson]

I expected I might be pushing it. 50 feet is the ideal route - I could get away with 35 feet running along the floor of a closet as opposed to over it. Do you think that would be more apt to work?

You can't know without experimentation. When I lived in San Diego I had all sorts of problems with RFI and could easily tell the difference between single-ended and balanced cables, and I even needed a power isolation transformer for the pre-amp and the digital electronics. In the other cities I've lived, no audible difference for reasonable cable runs, and the isolation transformer is just a fancy-looking extension cord.

I have a 35 foot run between my pre-amp and amp in my main system, but I use an XLR-XLR cable. I never tried a single-ended one. My suggestion is still that you spend $12 and give the 50 foot RCA run a shot. It just may work.

 

[WaynePflughaupt]

Seven replies and no one has mentioned that most local building and fire codes require CL-2 or -3 rated low voltage wiring in walls and attics?


Regards,
Wayne A. Pflughaupt

 

[highfigh]

Transformers can raise or lower voltage, but can't increase power. Conservation of energy.

Like a 25V or 70V system- raise the voltage with a transformer, transmit the signal, use another transformer to reduce the signal to a usable level. Right?

 

[highfigh]

Seven replies and no one has mentioned that most local building and fire codes require CL-2 or -3 rated low voltage wiring in walls and attics?


Regards,
Wayne A. Pflughaupt

I guess some assumptions were made.

 

[highfigh]

I expected I might be pushing it. 50 feet is the ideal route - I could get away with 35 feet running along the floor of a closet as opposed to over it. Do you think that would be more apt to work?

Is it easy to run the cable? Try something like these-
http://www.bhphotovideo.com/c/product/588697-REG/Intelix_AVO_A2_WP110_Stereo_Audio_Wallplate_Balun.html

This particular one is rated for up to 2500' with Cat5e.

 

[highfigh]

Is it easy to run the cable? Try something like these-
http://www.bhphotovideo.com/c/product/588697-REG/Intelix_AVO_A2_WP110_Stereo_Audio_Wallplate_Balun.html

This particular one is rated for up to 2500' with Cat5e.

BTW- Cat5e is like the Swiss Army Cable- the uses vary wildly. Make sure to use CL2 rated cable. If it doesn't have that rating, look for CM- no need to use CMP because it's for plenum.

This is a rating chart- total overkill, but it covers all bases-
https://www.cablewholesale.com/support/technical_articles/cable_ratings_and_materials_and_counterfeiters.php

 

[Irvrobinson]

Like a 25V or 70V system- raise the voltage with a transformer, transmit the signal, use another transformer to reduce the signal to a usable level. Right?

Yes. So-called 70v systems use high impedance, low current signaling to reduce transmission losses and allow large numbers of speakers to be wired in parallel. Of course, the downside is that you need a transformer at every speaker for the voltage / impedance step-down, and the small el-cheapo transformers that most systems use can only handle low power (before saturation) and they usually limit frequency response, especially in the bass. That's why the 70v strategy is normally restricted to speech PA systems and background music. Free lunches are non-existent in physics.

 

[PENG]

Like a 25V or 70V system- raise the voltage with a transformer, transmit the signal, use another transformer to reduce the signal to a usable level. Right?

You can step up the voltage but if the long run resulted in high frequency loss already the transformer won't compensate that for you. IRV is talking about insertion loss but that really don't apply that much to audio interconnects that carry relative low frequencies and you can't match impedance in such application anyway. In telecommunication, impedance matching is very important to minimize insertion loss. I think if the OP gets a good quality cable that has the lowest possible impedance he should be fine.

 

[cpd]

Well -- that escalated beyond my comprehension quickly. I appreciate everyone's input. I ordered two in-wall rated 50 foot runs of monoprice RCA (subwoofer) cable. I'll let you know how it all turns out.

Thanks!

 

[Irvrobinson]

You can step up the voltage but if the long run resulted in high frequency loss already the transformer won't compensate that for you. IRV is talking about insertion loss but that really don't apply that much to audio interconnects that carry relative low frequencies and you can't match impedance in such application anyway. In telecommunication, impedance matching is very important to minimize insertion loss. I think if the OP gets a good quality cable that has the lowest possible impedance he should be fine.

I disagree, PENG, about insertion loss not being a factor in line-level audio cables. In fact, I just experienced it when setting up my wife's band a couple of weeks ago. We were running an Apple Macbook into the mixer and a long cable generated insufficient volume while a much shorter cable didn't, so we moved the Macbook. I've also seen this problem with some cheap DVD players. I'll reiterate that I think a 50' single-ended cable will probably work, and for $12 from Monoprice the OP should just try it, barring attention to Wayne's issue.

 

[PENG]

I disagree, PENG, about insertion loss not being a factor in line-level audio cables. In fact, I just experienced it when setting up my wife's band a couple of weeks ago. We were running an Apple Macbook into the mixer and a long cable generated insufficient volume while a much shorter cable didn't, so we moved the Macbook. I've also seen this problem with some cheap DVD players. I'll reiterate that I think a 50' single-ended cable will probably work, and for $12 from Monoprice the OP should just try it, barring attention to Wayne's issue.

You may have disagreed a little too quickly if you missed the point I made about audio interconnects that carry relatively low frequencies like analog signals. Yes, I would be more careful with video cables and interconnects for digital audio. We both are saying 50' ones are probably fine right? I only mentioned telecom because for those transmission lines we have to worry about characteristic impedance matching as well since you were talking about insertion loss. For analog audio interconnects we don't have to worry about insertion loss due to impedance mismatching but of course still have to be concerned with noise and excessive impedance for longer lengths.

 

[highfigh]

Yes. So-called 70v systems use high impedance, low current signaling to reduce transmission losses and allow large numbers of speakers to be wired in parallel. Of course, the downside is that you need a transformer at every speaker for the voltage / impedance step-down, and the small el-cheapo transformers that most systems use can only handle low power (before saturation) and they usually limit frequency response, especially in the bass. That's why the 70v strategy is normally restricted to speech PA systems and background music. Free lunches are non-existent in physics.

No free lunch unless you're moving at almost the speed of light, where it appears that other people are moving slower and you can take their food.

WRT 25V/70V, you're right- the cheap transformers definitely limit the low end and I doubt they're doing much good for the high end but they work great for speech and background audio. That said, the speakers for these uses are much better than they were in the past- I remember buying in-ceiling speakers for 70V in the late-'70s for not much more than five bucks (Calrad, Vanco, etc).

Losses can't be eliminated because, as you posted, there's no free lunch in physics but many methods of sending low level signal over (relatively) long distances have been developed and used in consumer systems for quite a while. Some can be a bit surprising when the low cost and simplicity are seen. I went to a supplier a few months ago and saw that they have baluns for digital audio. Two wires from Cat5e going in, RCA plug going out and rated for 180 meters. I thought it was worth a shot, so I tried them in a house I'm working on- they not only worked to send the digital audio from the kitchen to the rack in the basement, I was able to connect a second one at the receiving end for the home theater on the 2nd floor almost 100' away. Plugged into the S/PDIF input of the Krell home theater processor and it works great.

I'm probably going to start a separate thread about this, but I was told by someone in the A/V business that changing to a better optical 'cable' improved the sound and that someone else noticed the difference, too. How, unless the original had problems?