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  #1  
Old June 6th, 2004, 9:11 AM
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Angry VTF-3R New Hum

I unplugged the RCA connector on my VTF-3R, plugged it back in, and immediately got hum at set volume. I turned the volume control down, and the hum goes down with it. If I wiggle the RCA connector, sometimes the hum goes away but immediately comes back.

Any suggestions before I try something else?
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  #2  
Old June 6th, 2004, 1:07 PM
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Sasha_G Sasha_G is offline
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Try pressing the sides of the connector inwards a little so that they press a little snugger against the RCA Jack. I have gotten this hum before will loose connectors. Let us know if it works!
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  #3  
Old June 6th, 2004, 2:07 PM
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Thumbs down No, that doesn't help.

Quote:
Originally Posted by Sasha_G
Try pressing the sides of the connector inwards a little so that they press a little snugger against the RCA Jack. I have gotten this hum before will loose connectors. Let us know if it works!
Here is further information. The first RCA connector was of the type that has four segments to the sides, all gold plated. They were already so tight that it was hard to force on and off. I used pliers to squeeze them tighter -- no beneficial result. So I abandoned the regular hookup, pulled in a separate DVD player, didn't plug it into power, used a store-bought coax cable (RCA-to-RCA), and connected the player to the sub. No hum. Plugged in the power cable for the DVD player. Hum. Reversed the cheater plug on the sub's power cable. Hum. So all I have is the DVD player and the sub, connected by the RCA-coax-RCA cable. One blade on the DVD player's power cable is larger than the other, so it can only be plugged in one way. Reversing the sub's power cable has no effect on the hum.

Final piece of information. The hum begins as soon as the RCA center electrode makes contact. The hum doesn't change as the RCA shield-ring seats.. However, if I push hard on the RCA connector in the direction of the bottom-left corner of the sub, as viewed from the back of the sub, the hum abruptly quits, but comes back as soon as I take the pressure off the connector. If I plug the cable into the upper of the two RCA jacks, I get the same hum, but pushing on the connector doesn't make it quit.

It sounds to me like the shield connection inside the amp has lost ground integrity.
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  #4  
Old June 6th, 2004, 2:58 PM
tgrisham tgrisham is offline
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The same thing happened to my VTF-3R. The technical folks at Hsu suspected a faulty ground on the RCA input (private communication). I switched to a new 350W Mark II amp and will use it instead, but the previous problem didn't go away. It was suggested that I try re-soldering the ground on the RCA input, but I haven't done that yet.
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  #5  
Old June 6th, 2004, 3:59 PM
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Question How would one "resolder the ground on the RCA input?"

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Originally Posted by tgrisham
The same thing happened to my VTF-3R. The technical folks at Hsu suspected a faulty ground on the RCA input (private communication). I switched to a new 350W Mark II amp and will use it instead, but the previous problem didn't go away. It was suggested that I try re-soldering the ground on the RCA input, but I haven't done that yet.
I removed the screws holding the amp in the box and gently peeped in. The wires to the speaker are spade-lugged onto the speaker and stapled onto a strength member inside the box. I suppose I could remove the staple, pull the spade lugs, and have the entire amplifier case out of the box. However, from the little view I could get, the amplifier case looks fairly well sealed up. If I could get at the inside of the amplifier case, and if the backside of the RCA jack assembly were accessible then, I have no doubt I could do the soldering. However, it's not a really happy solution, puts the burden of making it work on me (the customer), and I would worry about the warranty.

I've commented before that I think those RCA jacks are a cheesy input to an otherwise really well crafted unit. Hsu seems to think coax is the best kind of cable to connect the sub to the amp, so the input should at least be a BNC. Further, given the troubles with ground loops, for these high-end units, Hsu should put an audio isolation transformer at the input.
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Old June 6th, 2004, 7:30 PM
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Quote:
Originally Posted by tgrisham
The same thing happened to my VTF-3R. The technical folks at Hsu suspected a faulty ground on the RCA input (private communication). I switched to a new 350W Mark II amp and will use it instead, but the previous problem didn't go away. It was suggested that I try re-soldering the ground on the RCA input, but I haven't done that yet.
Tech Support has asked me if I can solder and is suggesting the same thing to me. I can solder, even made a living at soldering years ago, but as I said in a previous response, it doesn't look like a trivia effort.
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Old June 7th, 2004, 7:12 AM
DNelms DNelms is offline
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Cool You are not alone......

I was having a similar problem. My 7 year old HRSW10V (yes 7 years old. HSU subs can stand the test of time) began to buzz. I thought that this was possibly a ground problem or the sub's 150 watt amp going out. I began to gather as much info on ground loops and grounding as possible, and saving for a new sub. After attempting to diagnose the problem, I discovered that the problem was not the ground, not the subs amp, but my preamp, specifically the subwoofer output channel. The pre/pro was dead quiet in the other 5 channles, but the sub channel would hum when active.

So now I am back to where is was 5 years ago, 3 separate pre/pros (for those of you that are wondering why 3, well here you go - one form Dolby pro logic, one for Dolby Digital, and the final one for DTS). Well after setting everything back up and firing up the system, the hum/buzz is gone. And guess what, my system sounds better and the sub is rocking! I am almost tempted to not get a new sub (I said almost.)

Why all this rambling, sometimes the sub buzz is only a symptom, the sub may not be the cause of the problem.

(I still am trying to save up for a VTF-3.)
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  #8  
Old June 7th, 2004, 7:48 AM
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Supposed to be simple.

Quote:
Originally Posted by tgrisham
The same thing happened to my VTF-3R. The technical folks at Hsu suspected a faulty ground on the RCA input (private communication). I switched to a new 350W Mark II amp and will use it instead, but the previous problem didn't go away. It was suggested that I try re-soldering the ground on the RCA input, but I haven't done that yet.
Tech Support says the hardest part is pulling the spade connectors off the speaker. I don't see that as a problem. They say the amp case is held on by four little screws, and once the case is removed the RCA is directly accessible. I'll try it today and report.
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  #9  
Old June 7th, 2004, 6:36 PM
Ddavidson Ddavidson is offline
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Tech support is right, its not a hard job even for someone like me with no thumbs and two left feet. There was an almost step by step discussion on removing the VTF-3 amp here somewhere I will try to find it.

http://www.hsuresearch.com/forum/sho...7&postcount=17

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  #10  
Old June 7th, 2004, 7:55 PM
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"The rest of the story," . . .

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Originally Posted by Ddavidson
Tech support is right, its not a hard job even for someone like me with no thumbs and two left feet. There was an almost step by step discussion on removing the VTF-3 amp here somewhere I will try to find it.

http://www.hsuresearch.com/forum/sho...7&postcount=17

Ddavidson
as Paul Harvey says.

Once the entire box is out, then you have to take out the small screws that hold the plastic back-box onto the face-late and pry the back-box loose from the face-late (I had to use a thin-bladed knife to get between them). Once the back-box is off, then the fun begins. What to solder? The two RCAs are attached to a small printed circuit grand-daughter-card, and the grand-daughter-card is soldered to a daughter-card, which is connected to the mother-board. It appears that there are two leads for the center conductors of the two RCAs, and the shields come out to one additional lead -- snugged up to the face-plate between cards, of course. Since my problem appears to be a break in the shield circuit, I resoldered the shield lead. It took a pencil soldering iron and an eight-inch piece of solder to reach in. Also a head-band-mounted light to be able to see.

Skipping over the part about re-stapling the speaker wire and reassembling the whole thing, it still hums.

So I'm sending the whole amp back to be fixed.

This is not something I would suggest be tackled lightly.
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  #11  
Old June 8th, 2004, 9:14 AM
Ddavidson Ddavidson is offline
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Quote:
This is not something I would suggest be tackled lightly.
I do tend to take some things for granted. I forget that many people are not as used to pulling apart electronics as I am. Although I still have the common sense to know when I am out of my depth.

Anyone not feeling totally relaxed in doing this sort of thing should obviously not be doing it.

Ddavidson
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  #12  
Old June 8th, 2004, 9:48 AM
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For calibration . . .

Quote:
Originally Posted by Ddavidson
I do tend to take some things for granted. I forget that many people are not as used to pulling apart electronics as I am. Although I still have the common sense to know when I am out of my depth.

Anyone not feeling totally relaxed in doing this sort of thing should obviously not be doing it.

Ddavidson
I have a Ph.D. in electrical engineering, am a Registered Communications Distrubution Designer, and have been in the business just about 50 years. I supported myself halfway through engineering school building Heathkits for the EE Department.

The problems with this particular exercise are: (1) Tech Support said to resolder the tips. The tips work, since the hum starts as soon as the center conductor makes contact. It's the shield circuit that has the fault; (2) the shield circuit is not visible except as the end of a pigtail sticking through on the lead-side of the printed circuit board. It didn't look like a cold joint, but I resoldered it anyway; (3) without using a solder-sucker and pulling the grand-daughter-board off the daughter-board, there are no electronics to pull apart; (4) it's awfully easy to put too much heat on a printed circuit board and end up with the leads lifting off the board -- then you've got trouble! and (5) what about the warranty?

It's baffling that Tech Support would casually recommend that customers undertake this exercise without any more than a question whether the customer knows how to solder.

War story. Many years ago (in the days when circuits were made using resistors, capacitors, and transistors) I worked in a research laboratory that frequently brought in young engineers. We had one engineer who complained that he couldn't make a fairly simple circuit work and asked for advice. We looked at his circuit and immediately recognized that all of his solder joints were "cold." We asked him to show us how he did his construction. He'd hold his soldering iron about six inches above the objects to be soldered, feed solder onto the iron, and let the solder fall on the objects. He was amazingly accurate, but that's not the generally recommended technique for getting a low-resistance joint.
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Old June 8th, 2004, 6:51 PM
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Returned for Repair

I shipped the entire amp back today for repair. I paid shipping back to Hsu, and Hsu will pay shipping back to me.

I'll report results of the process as it goes along.

Meanwhile, my home theater is down to just the Ventriloquist. I already had the receiver crossover disabled, so the Ventriloquist is at least better than the speakers that come with a TV.
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