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xlr to phono, buzzing sound from amp
john11
post Dec 1 2012, 09:07
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Hi and thanks for reading this post.

I just purchased a hrt music streamer pro usb dac to connect my pc to my amp.

The hrt has output via 3pin xlr and my quad 405-3 amp has input via phono so i used a mini xlr to phono adaptor..

Immediately upon plugging in the hrt i heard a loud buzzing sound which fades after the first 10 seconds, this has never happened before but it now happens every time even when the amp is totally disconnected and i am trying to find out why it keeps doing this.

I contacted David from net audio who makes the 405-3's who said it sounds like the bridge rectifier is damaged and it is charging the power supply smoothing capacitors at different rates.

I don't know if this is possible as the capacitors and bridge rectifier are brand new and i choose really high quality vishay units so find it hard to believe they have failed so early.

The mini xlr phono adaptor connects pin 1 and 3 of the xlr to the outer screened cable to the phono and pin 2 is hot.

Do you think it is okay to use these adaptors or are there any compatibility issues as some people do not connect the drain wire.

Any advise on what to do or which way to go would be appreciated.

Many thanks in advance. John.
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Glenn Gundlach
post Dec 1 2012, 19:38
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QUOTE (john11 @ Dec 1 2012, 00:07) *
Hi and thanks for reading this post.

I just purchased a hrt music streamer pro usb dac to connect my pc to my amp.

The hrt has output via 3pin xlr and my quad 405-3 amp has input via phono so i used a mini xlr to phono adaptor..

Immediately upon plugging in the hrt i heard a loud buzzing sound which fades after the first 10 seconds, this has never happened before but it now happens every time even when the amp is totally disconnected and i am trying to find out why it keeps doing this.

I contacted David from net audio who makes the 405-3's who said it sounds like the bridge rectifier is damaged and it is charging the power supply smoothing capacitors at different rates.

I don't know if this is possible as the capacitors and bridge rectifier are brand new and i choose really high quality vishay units so find it hard to believe they have failed so early.

The mini xlr phono adaptor connects pin 1 and 3 of the xlr to the outer screened cable to the phono and pin 2 is hot.

Do you think it is okay to use these adaptors or are there any compatibility issues as some people do not connect the drain wire.

Any advise on what to do or which way to go would be appreciated.

Many thanks in advance. John.

First question is why buy a balanced output device to use in a unbalanced system? It's extremely likely the HRT is active balanced output - no transformers. Your adapter has a short between pins 1 and 3 meaning the only limit on the output current of that opamp is the build out resistor inside the HRT. This will cause increased power consumption of the HRT. If it DOES have an output transformer you must have that 'short' to complete the circuit. When I worked at a Hollywood dub house we came up with a 'universal' passive adapter by replacing the shorting wire with a 1000 om resistor. The circuit was still completed for a transformer but only lightly loaded on the unused (shorted) phase. I made hundreds of them over the years.

Try this. Cut the short and add nothing else. If it works (very likely) you're done and ignore the other pin. If you want to do it 'right', get something like the Henry Matchbox (we use LOTS of these in Hollywood) which does an active balanced-unbalanced interface in both directions (record and play). If you want to do it REALLY right, return the Pro and get a unit with unbalanced outputs and avoid all the hassle.

http://audio-video-supply.markertek.com/br...enry%20Matchbox

Just an FYI, my Gigabyte motherboards with the common Realtek codecs claim analog 108 dB S/N. As you may have guessed, I do broadcast level video and audio for a living. I did _not_ measure the S/N of my PC but I'm absolutely certain it exceeds 80 and realistically gets into the mid 90s but I don't claim that. Point is, why an external DAC? The Realtek data sheet looks to be on a par with other consumer DACs and contrary to common belief, you'll find these same ADCs and DACs in hundred thousand dollar VTRs and mixing consoles.

As for a 'partially failing' bridge rectifier. in 40 years of repairing first consumer and then broadcast gear, I have yet to find a 'partially failing' bridge. When they fail they completely short the power transformer and take out the fuse which will look to have an 'explosion' inside the glass in contrast with a simple opening of the circuit. If you do something really DUMB like put a larger value fuse you risk potential fires and worse. IMO you have a better chance of winning the lottery than to be the owner of a 'partially failing' bridge rectifier. I'm not saying it's impossible but......

G
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john11
post Dec 2 2012, 09:32
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Hi. Thank you for the response.

The amp is making the buzzing sound all the time now even when it is standalone and totally disconnected from everything.

I do think you are right and the best thing to do is sell the hrt and hope i can at least get some of my money back.

What do you think the amp problem may be, obviously it has something to do with the hrt as it only happened

when that was utilized.

Thank you. John.
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Glenn Gundlach
post Dec 2 2012, 11:53
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QUOTE (john11 @ Dec 2 2012, 00:32) *
Hi. Thank you for the response.

The amp is making the buzzing sound all the time now even when it is standalone and totally disconnected from everything.

I do think you are right and the best thing to do is sell the hrt and hope i can at least get some of my money back.

What do you think the amp problem may be, obviously it has something to do with the hrt as it only happened

when that was utilized.

Thank you. John.


Is there a way to capture some of the buzz and post it? The signal shape can be very revealing if you know what you're looking for.

As for selling the HRT, what are they going for on eBay? 'Completed listings' of actual sales is a good indicator.

G
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john11
post Dec 8 2012, 09:08
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Hi. Thanks for the response.

Sorry for the lateness of my reply the weekend is here so i will have some free time to try your suggestion concerning the hrt and will post back asap.

Many thanks. John.
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Speedskater
post Dec 8 2012, 15:28
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If the amplifier buzzes with no interconnect signal cables attached, then it's either the amp's power supply or a broken internal signal wire that is the problem.


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Kevin
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smz
post Dec 8 2012, 15:57
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I totally agree with Speedskater that it is probably a problem with the amp itself.
Anyway I think you can find interesting this page at Rane about interconnecting balanced to unbalanced equipment.

Sergio


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Sergio
Revox B150 + (JBL 4301B | Sennheiser HD430)
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