CECAA850 Posted April 10, 2014 Share Posted April 10, 2014 I'm truly sorry you're having problems, BUT this is a great thread. I'm learning a lot at your expense. Quote Link to comment Share on other sites More sharing options...
LarryC Posted April 10, 2014 Share Posted April 10, 2014 If I move cords around (either RCA or power cords to the preamp, CD player etc., it has an effect on the volume of the noise. Those RFI-like symptoms sound like a circuit or connection fault internal in the amp, so sending it to VAC sounds right to me too. Quote Link to comment Share on other sites More sharing options...
babadono Posted April 10, 2014 Share Posted April 10, 2014 eth2, You made two shorting plugs, right? You plugged one into each of the amps and one of the amps is noisy? I agree then with mdeneen there is something wrong with that amp. Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 10, 2014 Author Share Posted April 10, 2014 VAC makes truly stunning gear in all respects, so it probably some small thing or minor issue. Maybe it happened in shipping. (I have had my share of those!) Shipping from Texas (where I bought this) to New York was about $300. So it is at least a $600 problem plus labor/parts. I should have bought a boombox. Thank you all for your help, you have been great. And CECAA...glad to be of service. Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 10, 2014 Author Share Posted April 10, 2014 eth2, You made two shorting plugs, right? You plugged one into each of the amps and one of the amps is noisy? I agree then with mdeneen there is something wrong with that amp. Yes. I made two. Quote Link to comment Share on other sites More sharing options...
joessportster Posted April 10, 2014 Share Posted April 10, 2014 Hey Earl as you are in NY you might ask VAC if they have an authorized service provider in your area, I have found some manufacturers will use good techs in other areas which could save you alot on shipping Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 10, 2014 Author Share Posted April 10, 2014 Thanks, Joe. I just got off the phone with VAC (Brent). He believes, as many of you have told me, that this is an RF noise problem, which could be carried in ion the AC line. The PA90 has a "high bandwidth" (whatever that means). However, he also told me that if shorting the amp out causes the problem to go away, and it does, it is not a problem with the amp. Again, as many of you have told me, noise is a difficult thing to locate. He gave me two recommendations. 1. Buy decent quality interconnects. He said Monster may be an economical choice, but look for good shielding. 2. Buy a APC power filter. .First try it on the equipment leading to the amps. If that does not work, connect it to the amps I currently have a line filter, but will try an APC as suggested Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 10, 2014 Author Share Posted April 10, 2014 I read the manual for your amp and found this comment: "Amps with XLR inputs will only work correctly with fully balanced input signals." So, you have both XLR and RCA input jacks, right? Have you tried the setup using a preamp that has fully balanced XLR outputs? Are these RCA jacks factory installed or customer installed? Since your problem reacts to shorting the RCA input, this could be a critical thing. Maybe you must have a balanced input. Yes, the units come with RCA jacks. VAC said that RCA inputs should be fine, but to get ones with better shielding. I have ordered some. As I do not have a preamp with balance inputs, I can't try this immediately. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted April 10, 2014 Share Posted April 10, 2014 Buy a APC power filter. I'd look at FURMAN as well. Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 10, 2014 Author Share Posted April 10, 2014 Buy a APC power filter. I'd look at FURMAN as well. Any particular model? Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 10, 2014 Author Share Posted April 10, 2014 The two locations are: 1. One level down, same side of house but opposite corner. 2. Opposite side of house and one level down. There are no "clean" areas, but the other two location are pretty quiet; just a very slight hum in one channel. I do have another VAC and the hum is barely audible (but still present). Based on Carl's post, I bought a Furman PL-8C 15 Amp, Advanced Level Power Conditioning, unit. If it does not work, I can return it. Amazon is pretty good about that. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted April 10, 2014 Share Posted April 10, 2014 I don't have that model but I love the Furman that I have. Worst case scenario, you find out it doesn't work and return it. Certainly cheaper than shipping amps if it actually comes to that. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted April 10, 2014 Share Posted April 10, 2014 I'd be very careful about spending too much on AC line conditioners and filters in THIS case But to receive any more factory advise I would think he would have to do his due diligence regarding their suggestions. Quote Link to comment Share on other sites More sharing options...
babadono Posted April 10, 2014 Share Posted April 10, 2014 eth2, Sorry but as mdeneen has stated its hard to help troubleshoot from 2000 miles away. I am a little confused so please humor me and clarify this. When both shorting plugs are installed both amps are quiet? Or one is still making noise? Quote Link to comment Share on other sites More sharing options...
babadono Posted April 10, 2014 Share Posted April 10, 2014 Where did mdeneen get the manual for your amp? I look on VAC website and your model is not listed. Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 10, 2014 Author Share Posted April 10, 2014 Where did mdeneen get the manual for your amp? I look on VAC website and your model is not listed. http://www.vac-amps.com/manuals/Manual_PA90.pdf And when I short out both amps they are both quiet. When I short out only one, only the one I short out is quiet. Quote Link to comment Share on other sites More sharing options...
babadono Posted April 10, 2014 Share Posted April 10, 2014 Ok, cool, thanks. Now you really need the "dummy plugs" so you can work your way backwards towards the preamp. Quote Link to comment Share on other sites More sharing options...
LarryC Posted April 10, 2014 Share Posted April 10, 2014 I'd be very careful about spending too much on AC line conditioners and filters in THIS case***. Because the shorting eliminates the noise, this means something very specific: it means the noise is airborne RFI. It is entering the circuit through the input grid of the first tube which is connected to the RCA jack. The wire which runs from the RCA jack to the input grid is acting as an antenna picking up this RFI and bringing it right into the first tube. When you "short" the jack, you are bringing this wire to GROUND and all noise on the wire is grounded. Did you say it cost $300 to ship this or these to the factory? Why so much, IIRC?Yes, I'm asking because, on balance, I think that's the best solution. I haven't had experience with a typical power conditioner, not even sure what one does; instead, I use a PS Audio power regenerator for pure sine-wave AC power, which does great things for AC motors (TT, CD transport) but is probably not suitable for power amps. I'll be interested to see what you think after you get it. Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 10, 2014 Author Share Posted April 10, 2014 Four units and about 150 pounds plus insurance Quote Link to comment Share on other sites More sharing options...
babadono Posted April 10, 2014 Share Posted April 10, 2014 Where did mdeneen get the manual for your amp? I look on VAC website and your model is not listed. Google. Yeah duh. i was hung up on trying to find info on the PA80/80 in eth2 's signature.Thanks. Quote Link to comment Share on other sites More sharing options...
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