[jmhenrie]

I have a full Classe, system wired with balanced interconnects the 5 channel amp keeps blowing the main power supply and I can smell something burning I now have it back from its 4th trip to the factory I have changed out speakers and wire previously and had the bright idea to do a continuity test on the balanced cables I find two legs that pass without shorting out but the 3rd leg shorts out to the metal connector is this how the cables are designed to work?
Tired of constantly repairing a 110 pound amp
Thanks for ant help
Mike

 

[zgeneral]

Why are you using balanced cables in the first place? They're almost always marketing fluff.

 

[jmhenrie]

Why are you using balanced cables in the first place? They're almost always marketing fluff.

they are left overs from my original system about 10years ago, I just got a note from better cables that they used to wire the cables the way I described and found some systems could not tolerate this method, so they no longer terminate their cables that way. They offered to rebuild them for me. In the meantime I will dig around and try find some regular interconnects
Cheers mike

 

[jaddie]

Pin 1 is ground, often but not always connected to the connector shell. That's one flavor of "normal". Pin 2 (+) and pin 3 (-) carry audio, and should never be connected to each other, or pin 1, or the connector shell.

There very little chance that a balanced audio connector would cause a power amp to blow up. I'd look for something nasty coming out of the prepro, like an ultrasonic oscillation. Try idling the amp with just the speakers connected, see if it gets hot or smells. If not, have the prepro checked.

 

[jmhenrie]

Thanks Jaddie wondered how they were wired
I have suspicion its the ssp800 but Classe is denying that posibility so change out the interconnects if happens again the preamp is fhe only thing left
Thaks
Mike

 

[Glimmie]

Why are you using balanced cables in the first place? They're almost always marketing fluff.

For small home systems they are not needed. But balanced interconnects are superior for noise rejection. The professional audio industry uses balanced interconnects exclusively.

USB is a balanced system. so is HDMI, CAT5 Ethernet, and even your old analog telephone was/is a balanced system.

 

[Glimmie]

Thanks Jaddie wondered how they were wired
I have suspciian its the ssp800 but Classe is denying the posibility so change the interconnects if happens again the preamp is fhe only thing left
ThAnks
Mike

I don;t think the input cables could damage the amp either. Unless as suggested above they are some how causing ultrasonic oscillation.

 

[highfigh]

I have a full Classe, system wired with balanced interconnects the 5 channel amp keeps blowing the main power supply and I can smell something burning I now have it back from its 4th trip to the factory I have changed out speakers and wire previously and had the bright idea to do a continuity test on the balanced cables I find two legs that pass without shorting out but the 3rd leg shorts out to the metal connector is this how the cables are designed to work?
Tired of constantly repairing a 110 pound amp
Thanks for ant help
Mike

Make sure the outlets are wired properly and that everything in your system gets its power from the same circuit.

Pin 3 can short to the shell, but it doesn't need to be connected. Also, since Pin 1 is connected to the chassis in many amplifiers AND since it's often necessary to connect Pins 1 and 3 (using unbalanced cables often requires this, to reduce the noise level), it's really not likely that the burning circuit(s) are caused by this.

Even if the preamp and power amp are on different circuits, you shouldn't pop any breakers or burn up the amp unless something is wired wrong.

 

[noway1]

For small home systems they are not needed. But balanced interconnects are superior for noise rejection. The professional audio industry uses balanced interconnects exclusively.

USB is a balanced system. so is HDMI, CAT5 Ethernet, and even your old analog telephone was/is a balanced system.

Why are you using balanced cables in the first place? They're almost always marketing fluff.

They make a difference with noise in my home system and there is no connector worse designed than the RCA which connects hot before ground. So YMMV.

http://www.eetimes.com/author.asp?section_id=1&doc_id=1283456

 

[jaddie]

They make a difference with noise in my home system and there is no connector worse designed than the RCA which connects hot before ground. So YMMV.

http://www.eetimes.com/author.asp?section_id=1&doc_id=1283456

Don't confuse the noise susceptibility of unbalanced audio circuits with the design of the RCA connector. Yeah, it's not great, but the connector design is not the cause of noise pickup. The article is strangely written, especially in an engineering magazine. Basically deriding the RCA design, but for really only one performance reason: the hot contact before ground. Otherwise the reasons given apply to any unbalanced connector, including an XLR wired for unbalanced use. With modern quality RCA connectors, once plugged in, they present to reliability issues, which is about all we're really concerned with for an audio connector.

Circuit topology is a separate issue. However, if devices are properly designed with audio grounds at the same potential, technically the balanced interface can actually be noisier because to pull it off more than twice the number of active devices are required. That raises the noise floor and the opportunities for distortion. If noise immunity is required, then it's an advantage of course. But proper grounding often eliminates the need for that noise immunity.

Anecdotal evidence is fine and interesting, but not the full picture.

Finally, the OP is already using his balanced interconnects. His issue is not with the interconnects, or noise immunity, it's most likely either a DC bias problem caused by a shorted output capacitor in the preamp, or a high frequency oscillation problem in the preamp.

The test question to answer is, does the power amp run just fine with no preamp connected?

 

[highfigh]

They make a difference with noise in my home system and there is no connector worse designed than the RCA which connects hot before ground. So YMMV.

http://www.eetimes.com/author.asp?section_id=1&doc_id=1283456

Who ever recommended making/breaking connections when the equipment is powered up?

RCA plugs and coaxial cable work great for Component video- I don't know why people have a problem with using it for audio.

 

[jaddie]

Who ever recommended making/breaking connections when the equipment is powered up?

BZZZT!

RCA plugs and coaxial cable work great for Component video- I don't know why people have a problem with using it for audio.

The RCA connector was designed as a semi-permanent connection that's not meant to be removed and re-inserted a lot, like hardly ever, and not with power on. But we've come a long way since the original design with advances in jack and connector, plating materials, sleeve, etc. There's really nothing wrong with them if they are good quality to begin with, but since they are the cheapest and simplest of low-level audio connectors (even though there are some very expensive versions). So being that, they'll never be "appreciated" by the high-end-ers.

I know I've found more expensive than these, seems to me TIFF made some with jade shells for a couple hundred a few years back, but well, I ain't a gonna google that one.

Not that it matters, but IIR there have been real 75 ohm RCA connectors made that were pretty good well up to the MHz applications, with Tefon insulation, etc. Otherwise the derned things are technically an impedance discontinuity in a 75 ohm transmission line.

 

[Glimmie]

BZZZT!
Not that it matters, but IIR there have been real 75 ohm RCA connectors made that were pretty good well up to the MHz applications, with Tefon insulation, etc. Otherwise the derned things are technically an impedance discontinuity in a 75 ohm transmission line.

Yes Canare makes 75ohm RCA connectors but IMO, it's just a marketing scam. While a commodity RCA connector is hardly precision 75ohms, NTSC video and SPDIF are at a wavelength where that mismatch for an inch of connector is irrelevant.

We historically used 50ohm BNC connectors and patch panels for NTSC video up into the early 1990s. Only when SDI video came along at 270mbs or 145mhz, did we go to true 75ohm connectors and patch panels. With HDTV at 1.5gbs and higher it is compulsory to use 75ohm connectors. But for consumer video and audio, even SPDIF there is no benefit for true 75ohm RCA connectors.

And if you do have an application where a 75ohm connector is critical, you have no business using an RCA connector to start with.

 

[zgeneral]

They make a difference with noise in my home system and there is no connector worse designed than the RCA which connects hot before ground. So YMMV.

http://www.eetimes.com/author.asp?section_id=1&doc_id=1283456

You're very much in the vast minority. Unless you have a really long run between the pre and amp (not applicable at home) or you have a lot of electrical interference (live next to a power plant) then they're not at all useful. It's typically marketing fluff to get people who don't know better to spend more money.

 

[highfigh]

Yes Canare makes 75ohm RCA connectors but IMO, it's just a marketing scam. While a commodity RCA connector is hardly precision 75ohms, NTSC video and SPDIF are at a wavelength where that mismatch for an inch of connector is irrelevant.

We historically used 50ohm BNC connectors and patch panels for NTSC video up into the early 1990s. Only when SDI video came along at 270mbs or 145mhz, did we go to true 75ohm connectors and patch panels. With HDTV at 1.5gbs and higher it is compulsory to use 75ohm connectors. But for consumer video and audio, even SPDIF there is no benefit for true 75ohm RCA connectors.

And if you do have an application where a 75ohm connector is critical, you have no business using an RCA connector to start with.

Security cameras and DVRs still have BNC, but I wish they didn't. So many of the available plugs and adapters are loose and the connection is far worse than I have seen with cheap RCA plugs. I know how they're supposed to fit, but I rarely see it.

HDMI was intended to be plugged in and left alone. I'd like to meet that freaking gang of idjits.

 

[highfigh]

You're very much in the vast minority. Unless you have a really long run between the pre and amp (not applicable at home) or you have a lot of electrical interference (live next to a power plant) then they're not at all useful. It's typically marketing fluff to get people who don't know better to spend more money.

I'm working on a house and it's out of town, so there's no source of RF, other than what's normal for an isolated house on a bit of a hill. I made cables with XLR (for about the 1000th time) and apparently, they didn't know the words, so I replaced them with Planet Waves cable/RCA ends. No hum. I inserted the jumpers to connect Pins 1 & 3- even more quiet. It's a Krell pre-pro/power amp and it came with two jumpers, but I don't know where the others went. The amp is plugged into one outlet and the rest is in another- I have photos of the electrical pre-wire and the feed came from overhead to a high-mounted box for the projection screen, drops down to the box where the amp is plugged in and then goes horizontal, to the other box. They gave me that whole circuit and nothing else is using it.

I made up the cables in the basement and it was pretty cold down there, so I'm going to use that as the reason they were noisy. I re-soldered one pair after O returned from the trip and am using them in my system- I had started with a pair of Planet Wave from my preamp to power amp, but the XLR are more quiet.

It can be a crap shoot.

 

[Glimmie]

Just a general note:

Using RCA to XLR cables and/or adaptors destroys any benefit of a balanced connection.

Unless both the sending and receiving device are true balanced circuits, you reap none of the benefits of a balanced cable. For all practical purposes, it's still an unbalanced connection just using an XLR connector on one end.

Now that said, there is some minor engineering benefit if a balanced to unbalanced connection is wired a certain way, that is to wire pins 2 to the RCA center and pin 3 to the shield and let the cable shielded only connect to the XLR pin 1. But the benefits are miniscule IMO. And this trick doesn't always work either.

Also there are times when you combine pins 1&3 and other times when you don't depending on if the device is transformer or active output.

Bottom line is unless you understand the application and products you have, it's not an easy task to PROPERLY mix balanced and unbalanced gear.

 

[jaddie]

HDMI was intended to be plugged in and left alone. I'd like to meet that freaking gang of idjits.

Here you go. And your description is quite correct, except to add "self-serving" and "short-sighted" to the list.

 

[jaddie]

Security cameras and DVRs still have BNC, but I wish they didn't. So many of the available plugs and adapters are loose and the connection is far worse than I have seen with cheap RCA plugs. I know how they're supposed to fit, but I rarely see it.

You have to get the good ones. I use BNCs all the time, never had one present a bad connection.

 

[highfigh]

You have to get the good ones. I use BNCs all the time, never had one present a bad connection.

What brand of cable and connectors do you use?