Thanks for responses so far, guys.
I've already tried both in one ac outlet, as well as in different outlets. I have already connected a grounding wire between the amps(per manufacturer's suggestion). The speakers are not powered.
FWIW, I demoed the amps at a local dealer, and there was no problem in their system. That's part of why I think it's a ground loop, and not a repair issue with the amps. They are preowned ;-) , so sending them back is not a real option anyway.
If I can borrow another preamp, I'll try that. The long extension cords are a great idea, I'll try that too.
Does anyone thing this is an airborn RFI issue rather than an AC/ground loop problem? Thanks,
Spencer |
Okay here is what I've tried:
Plugging the amps in next room via extension cords, didn't change anything.
I did try ground lifters on both amps, as well as on only one; no difference
When I have just one amp(either one) connected to the pre, it still hums. Strangely, with the right amp on, removing left interconnect from left amp increases the hum heard in the right speaker slightly. Conversely, with the left amp on, removing right interconnect from right amp decreases the hum heard in the left speaker. With no interconnects or shorting plugs, there is no problem.
Isomax is a possibility. Would the cheapo similar products(e.g. $12 ground loop eliminators on ebay) give me an idea if Isomax would be effective?
As far as trying amps & pre at a friends' house away from radio tower, that might be worthwhile. Borrowing a different preamp and trying that here will be worth trying too. Thanks to all! Cheers,
Spencer |
"I think that what you are experiencing is common to SET amp where the input ground is directly connected to the chassis as soon as it enters the amp. If your preamp is not configured the same, there is always a loop everytime you connect the cable."
Abe, according to the preamp designer, "All of the rca's on the preamp are isolated from the chassis and connected vis the 8 ga. buss. The chassis is grounded thru the charger jack only."
Sorry, if I don't understand, but does that make sense relating to your comment above? Does this further point to need for ISOMAX? Thanks,
Spencer |
Abe,
The battery charger for the preamp is 3prong, and normally is left connected. It engages when you power off the unit. I've tried it both connected and disconnected, & still get hum.
Remember that this preamp worked fine with two other pairs of amps, (Consonace push/pull EL34-based , Atma-Sphere OTL)and no hum. I am going to have a friend bring over another preamp to try here in the next few days. Thanks again.
Spencer |
Ralph,
Recently, I didn't notice the hum or radio signal with other amps. So your comments make sense. However there is no trouble until the interconnects from the pre are connected to the amps. The amps with shorting plugs at their inputs are dead quiet, especially compared to other SETs that I've heard elsewhere.
Prior to changing to my solid state Vendetta Research phono stage, RF was a constant problem using a variety of excellent tube phono stages.
At this point, I'm just going to live with it, as I'm likely to be moving next year anyway. Those who've suggested moving away from the radio tower have nailed it ;-) |
Hi Ralph,
Thanks for your interest.
I did move the preamp over near the amps, and tried multiple different 1m cables, including the highly shielded cheapo ones from a vcr(ie with the red/white/yellow all bundled together), and the hum persists, even when the preamp's power is off.
My DVM doesn't read continuity, but I'll try to borrow one that does.
So do you think that if it's RFI, that the Jensen Isomax transformer would help or not? |
Jim,
Until my new tri-wire speaker cables arrive in a week or so, I can't try anything(the old speakers were sold this week), but I will try running a grounding wire from preamp to power amp chassis.
I did already run a grounding wire from one amp chassis to the other amp chassis, per suggestion from the amp designer.
I'll post again after trying that(as well another preamp), and we'll see what progress is made. Thanks,
Spencer |
Here's an update:
After having a number of other audionuts over to listen, they all tell me that they have more noise in their rigs than I do, and that "Your hum is nothing". Well, I guess we all have different levels of tolerance. Perhaps I should just live with it.
FWIW, I ran a grounding wire from preamp to amp, and it didn't change a thing. I have heard intermittent radio signal from one speaker, when placing my ear next to the tweeter, but it disappears most of the time, and can't be heard from even a couple of feet away. Other than transforming my house into a giant copper encrusted Faraday cage, I don't have any ideas worth pursuing. Thanks to all,
Spencer |
|
