VSi60 Tube Amp Startup Power Needs


Hi,
I have an ARC VSi60 integrated amp that is rated to use 350-500 watts of power to generate 50 watts RMS to the speakers. I'd like to purchase an online/double conversion UPS battery backup to isolate it from the rest of the house (puts out pure sine wave AC) because I noticed that when I was checking its bias voltage and the dryer kicked on, the bias voltage dropped by 5 VRMS. The dryer is on a different circuit entirely from the amp, but it's clear to me that when the AC, dryer, dishwasher, and garbage disposal run at the same time, with an oven thrown into the mix, there will be a much larger draw and this will not be good for the amp. I've also had trouble with the bias voltage drifting lately, and this was immediately after we had some power dips in our area (lights dimmed). Anyway, the UPS backup I'm planning to get is an Eaton EX1000, 900 watts. I talked with ARC tech support to find out peak power at startup for the VSi60 amp, and they don't know. The tech rep said it could very well exceed 900 watts when the caps are filling, but he doesn't know for sure. Does anyone have any experience using UPS's with their tube amps, and if so how much startup power do they need compared to their rated power? I would have thought that a 900 watts UPS would be sufficient for an amp rated at 350-500 watts (of input power). I also called Eaton's tech support and they said that their EX series UPS's can handle any startup power need without a problem, as long as it's within the rated 900 watts of the UPS. Alternatively, is there a way to measure startup power for the amp? Thanks. -Stuart
stu007
Hi Stuart, this issue has come up before. A while ago, I also spoke with Kal, ARC's customer service rep, about the wisdom of using power regenerators and conditioners for my gear. My amp is the ARC Ref 150, which is rated at 150 wpc (8 ohms). My amp idles at 375 to 400 watts and will draw 800+ watts when "working." Incidentally, I checked the specs on the VSi 60, your amp is spec'd to draw 300 watts at rated output, 500 watts maximum, and 200 watts at "idle" which does not impress me as being that excessive.

I would not be too concerned about your amp's power draw at start up unless you're blowing fuses. As the ARC rep told you, the power caps are charging at start up and you really should wait at least 15 to 20 mins before using the amp until the rest of the circuits settle down.

In addition, it's normal that bias voltage will drift a bit. You mentioned 5 VRMS. I assume you mean 5 mV DC?? Per ARC information, your tubes bias at 60 mV DC. I assume bias is within spec if it measures +/- 5 mV (check your manual or call Kal). If so, 5 mV fluctuations do not impress me as being hyper-critical.

All of that being said, here's what does concern me. Kal previously suggested to me that I do NOT use a power conditioner or AC regenerator because my amp may draw more current on dynamic transients than the conditioner or regenerator can deliver.

The result will be a diminution of the amp's ability to delivery "clean" power to the speakers when needed. Further, if the amp's power supply is starved juice, distortion may increase if the amp is called upon to deliver more power than it can deliver.

Your case is even more critical than mine because the power supply of the VSi 60 is spec'd at 166 joules. By contrast, the Ref 150 is 1040 joules. What this means is that your amp's ability to call upon its power reserve is limited. So, providing your amp with ample power access is very important.

In short, I think you should plug your amp directly into the wall. I encourage you to call Kal and hear it directly from him. And if you do hear it differently, please post it here or send me a PM to correct my misconception.

Next point about the power draw when using all of your appliances. If you check the A'gon Forum, you'll see that folks have discussed this issue many times already. I believe the consensus is that if possible try and run dedicated lines from the fuse panel for your rig. Seems like your integrated amp might take its own line. I assume you have other components, like a CDP/DAC and maybe a turntable and phono pre. Separate line(s) for those components (especially the digital gear) might make sense.

Hope this helps.

Cheers.
Bifwynne really gives an excellent answer. Very good advice. The only thing I can think to add is, do you notice a difference in sound quality when the other appliances in your house turn on? That's what would motivate me to make changes (at least in your case).
You might want to upgrade your service entrance if your household power needs are that significant. Running amps through power conditioners will close in and degrade your sound so best if you can avoid. I know someone who even installed a separate dedicated entrance just for the audio equipment.