Is my tube amp picking up radio signals?

ecod123 · « **on:** 28 Oct 2010, 12:48 am »

I recently purchased my first tube amp and loved it. It was blissful until I went close to my left speaker one day to dust it and heard what I thought was radio noise. Turned down the volume and there was a discernible radio station playing. However, the right speaker does not exhibit the same problem.

Both speakers also have the very low level hum. Note: the radio station signal is mostly discernible when I am staying right next to the speaker but it's slightly louder in the evening as I can discern it from 2 to 3 feet away.

Over a week of observations and trying to isolate the problem (changing IC's, power chords, speaker cables, switching components), I have the following observation:

1. The source of the problem is not the IC's or power cords.
2. It is the same radio station all the time. Seems to get louder in the evening.
3. Could be the speaker cables. I switched the speaker cable connector at the amp ends but the radio nosie persisted (DIY cables with banana plugs). The cable run on to left speaker was substantially longer than to the right speaker (my equipment are to the right of the right speaker). Replaced the cables with manufacturer factory sealed speaker cables and the noise lessened but still there.
4. I moved the tube amp into another room with more efficient speakers (98db) and now the radio station signal is clearer and louder. And I can now hear it on my right channel but fainter than the left. The speakers cables are DIY with banana plugs.

At my usual listening volume of -40, the radio noise is drowned out but now that I know it's there, I seems to listen for it when there is a break in music and it's really bugging me.

I am hoping that my tube amp is not the cause but rather perhaps the speaker cables or maybe my power source. I just can't figure this out so I am hoping a fellow AC members with more experience can provide some help. Also a dealer recommended the PS Audio powerplant premier power conditioner but that's quite pricey.

Other potential fact that may or may not be pertinent. I live in a house built in the 40s but have seen renovations by previous owners but not sure if the electric wiring have been upgraded. My house is in a residential area but 50 yards from utility company high voltage power tower and transmission lines.

Sorry for the ramblings but wanted to provide as much info as possible. I would buy the PS Audio PPP if it would solve the problem. Appreciate any feedback or help. Thanks.

JohnR · « **Reply #1 on:** 28 Oct 2010, 01:42 am »

Could be a cold solder joint. They're tough to find... is the amp circuit board or point to point?

bregez · « **Reply #2 on:** 28 Oct 2010, 01:56 am »

Try a different pair of speaker cables. Two pairs with a 5' length would be sufficient (to trouble shoot) . Just use cheap zip cord. Are you picking up AM or FM?
Brad

ecod123 · « **Reply #3 on:** 28 Oct 2010, 02:28 am »

Quote from: JohnR on 28 Oct 2010, 01:42 am

Could be a cold solder joint. They're tough to find... is the amp circuit board or point to point?

Not sure. Probably circuit board - Onix SP3 II.

ecod123 · « **Reply #4 on:** 28 Oct 2010, 02:42 am »

Quote from: bregez on 28 Oct 2010, 01:56 am

Try a different pair of speaker cables. Two pairs with a 5' length would be sufficient (to trouble shoot) . Just use cheap zip cord. Are you picking up AM or FM?
Brad

I'm pretty sure it's an AM station.

JohnR · « **Reply #5 on:** 28 Oct 2010, 02:54 am »

Unfortunately it doesn't look that easy to work on -

http://www.audioholics.com/reviews/amplifiers/onix-melody-sp3-tube-integrated-amplifier-review/Insidefull001.jpg/image_view_fullscreen

However, I'd suggest at least just making sure it's not a socket by cleaning and inserting/reinserting tube each a few times. While I wouldn't actually recommend it, you can sometimes find a loose socket by wiggling the tube from the top while the amp is on (small signal tubes only)...

If you are going to open it up, I'd first try bypassing the attenuator to see if that's causing it - there are a lot of joints in that.

By the way, how do you know it's not the ICs? Are they shielded?

bregez · « **Reply #6 on:** 28 Oct 2010, 03:02 am »

what are you using for a preamp?

Hugh · « **Reply #7 on:** 28 Oct 2010, 03:06 am »

It's an integrated amp. so no preamp is needed.

Hugh · « **Reply #8 on:** 28 Oct 2010, 03:11 am »

Did you buy it used from an individual?

Did you also happen to ask the seller whether or not he/she bought it as B-Stock?

The reason why I asked is because it might be one of those crappy pieces av123 blew out before they closed their door for good.

Also, I am not sure if the high power line would effect this due to the 50yard distance but I'd not be surprised if it is indeed.

A good power conditioner would eliminate this problem.

Quote from: ecod123 on 28 Oct 2010, 12:48 am

I recently... Sorry for the ramblings but wanted to provide as much info as possible. I would buy the PS Audio PPP if it would solve the problem. Appreciate any feedback or help. Thanks.

ecod123 · « **Reply #9 on:** 28 Oct 2010, 03:22 am »

Quote from: JohnR on 28 Oct 2010, 02:54 am

Unfortunately it doesn't look that easy to work on -

http://www.audioholics.com/reviews/amplifiers/onix-melody-sp3-tube-integrated-amplifier-review/Insidefull001.jpg/image_view_fullscreen

If you are going to open it up, I'd first try bypassing the attenuator to see if that's causing it - there are a lot of joints in that.

By the way, how do you know it's not the ICs? Are they shielded?

John R,
Thanks for the link - it's helpful to see the guts of the amp.

I pretty much tried all configurations of all my IC's (monster, cobalt, onix, audioquest, purity labs) but no help.

ecod123 · « **Reply #10 on:** 28 Oct 2010, 03:26 am »

Quote from: Hugh on 28 Oct 2010, 03:11 am

Did you buy it used from an individual?

Did you also happen to ask the seller whether or not he/she bought it as B-Stock?

The reason why I asked is because it might be one of those crappy pieces av123 blew out before they closed their door for good.

Also, I am not sure if the high power line would effect this due to the 50yard distance but I'd not be surprised if it is indeed.

A good power conditioner would eliminate this problem.

Hugh,

Bought it on Audiogon, so not sure if it's a b-stock or what vintage. Can we tell by the serial number?

ecod123 · « **Reply #11 on:** 28 Oct 2010, 03:44 am »

Quote from: Hugh on 28 Oct 2010, 03:11 am

A good power conditioner would eliminate this problem.

Anyone with a suggestion on a good power conditioner that's hurts less on the pocket than the PS Audio PP Premier?

Hugh · « **Reply #12 on:** 28 Oct 2010, 04:10 am »

My initial thought is the high power line has something to do with this but let me investigate further.

Quote from: ecod123 on 28 Oct 2010, 03:26 am

Hugh,

Bought it on Audiogon, so not sure if it's a b-stock or what vintage. Can we tell by the serial number?

woofersus · « **Reply #13 on:** 28 Oct 2010, 03:46 pm »

The high voltage lines probably have something to do with it, but there's not much you can do about that. Is your home's electrical system grounded?

Coming from a pro audio background, I've worked in electrically "noisy" places before, so here's the things I've learned to help lessen such interference:

1. use balanced interconnects where possible and never run an unbalanced IC more than about 15ft. (I realize you can't do balanced here, but if you ever replace the amp it's something to think about)
2. Don't run your power cords parallel to a speaker cable or IC. Keep them as far apart as is practical and if they must cross try to do it at as perpendicular an angle as you can.
3. Keep interconnects and speaker cables as short as possible, and NEVER EVER coil up the extra slack.

If it IS the amp, then the most likely thing to pickup signals like that is the transformer I think. It's possible you didn't notice the issue with previous amps because they all had much smaller ones. It's still a good idea to follow some of the advice above though. Clean everything out and check for bad solder joints and such. It may also be a good idea to check the tubes for excessive microphonics by tapping them gently with a pencil or something to see how much noise it transmits through the system. If it makes much noise at all you may need to replace that tube, as none of the tubes in that amp have strong microphonic tendencies.

Tim Evans
East Street Audio
Onix, Melody, & ACA

ecod123 · « **Reply #14 on:** 28 Oct 2010, 06:31 pm »

Quote from: woofersus on 28 Oct 2010, 03:46 pm

The high voltage lines probably have something to do with it, but there's not much you can do about that. Is your home's electrical system grounded?

Woofersus,
Thanks for the input. Yes, the home's electrical system is grounded.

When time permits this weekend, I will follow thru' on yours and the other suggestions.

iGrant · « **Reply #15 on:** 31 Oct 2010, 02:55 pm »

Roll tubes from one channel to the other and see if the station goes to the other channel, when/if it does you might have found a culprit tube, either replace the tube or use a RF tube shield. Might be the problem and solution.

Cheers,
Ian

Quiet Earth · « **Reply #16 on:** 31 Oct 2010, 03:31 pm »

Sounds to me like you've narrowed it down to the amp, not the AC power.

Search google and the audio forums for zobel network. Plenty to read but try to stay focussed on filters for eliminating RFI.

You might want to try a zobel network across the positive and negative outputs of your amp, and/or across the inputs your speakers. Your network would be built in the interest of notching the AM radio band.

yeldarb · « **Reply #17 on:** 31 Oct 2010, 04:42 pm »

I had a Soundcraftsman pre-amp that picked up radio signal when I was using the phono section. Very faint but annoying. Never could get rid of it, regardless of cables, location, turntable, etc. Finally sold it and buyer hasn't complained. I did tell him, too.

Soundcraftsman used a lot of wire wrap connections. Very durable and reliable but, maybe, they were the right length to act as an antenna.

weitrhino · « **Reply #18 on:** 31 Oct 2010, 08:07 pm »

ecod123,

Pull the negative speaker side from the amp and see if the radio signal goes away. Then reconnect it and pull the negative side from the speaker and check again. It's likely you'll isolate this to the ground plane. In the twisted pair world this can be filtered out, but I'm not personally aware of a product specifically for use with speakers.

Niteshade · « **Reply #19 on:** 31 Oct 2010, 10:57 pm »

Nasty problem! Here's a few questions:

1] Does it pick up the station when interconnects are disconnected form the amp?

2] Does it get worse if you put your hand by any of the tubes?

3] What happens if the inputs are shorted?