switching between two amplifiers; issues of power

Leaving them on without a load (speakers) will not cause any harm! Leave an IC connected between preamp and each amp through a y - connector if your preamp lacks two sets of outputs.

As a side bar, I’d suggest looking at speakers that aren’t so difficult to drive. It will make your amplifier choices easier and sound quality will improve too, all things considered.

Oz

I'm under the impression that when making a switch as you described above one should always power off first.

As indicated on pages 15 and 24 of the ICEpower300AS1 datasheet its + and - output terminals both have 27.25 volts of DC on them. (A number of other older ICEpower modules are like that). So **if** the physical arrangement of the connectors on the amp makes it possible for either conductor of the speaker cable, when being connected or disconnected while the amp is turned on, to briefly but simultaneously come in contact with the output terminal and either the ground sleeve of a nearby RCA connector, or the metal release tab of an XLR connector, or the chassis of the amp, or the shell of the plug on a connected interconnect cable, damage would be very possible.

Regards,
-- Al

Very helpful. Many ways to cause damage with wires floating between amps in the power "on" position, although technically no harm arises in having the amps on without interconnects. 

Always power off when making connections like this. Then it will be okay to leave on with nothing connected.

The amp btw was fine. For every watt of power you get about a watt of heat. Touch a 300 watt light bulb for reference. That's how much heat the amp has to dissipate, one way or another. If you run one 300 watt amp so hard it gets hot then guess what? Next one will too. Maybe not where you put your hand, but that same heat does have to go somewhere. 

@millercarbon 

So, the first amp is the lovely STA200, outputting 80wpc, and I've got it pushing a 4ohm nominal, down to 3.1 load. The amp does fine at modest volumes. I've been posting about this, from a variety of angles, for the past several weeks. It's a struggle because the amp's sonics are about as good as I would expect to do, for under maybe $3000.00 I could be mistaken and I'm eager to hear some suggestions, but I can't go the direction of tubes in this very hot climate, so we are talking ss or class D suggestions.

Back to the Nuforce: it is not recommended to run this amp on 4ohm speakers, but when I bought my Tekton's I was told the speakers run so easily it shouldn't be a problem. 

I am understanding that class D 300 wpc will run quite a bit differently, owing to crazy high efficiency, compared to SS in the Nuforce. 

1 watt into an 80% efficient amp would seem to yield 1/5 watt in heat?

Hey.  I still own some IcePower 250 modules.

1 - Do not change anything on the input while the amp is on. This includes powering up/down the preamp.

2 - Yes, you may disconnect speaker cables and reconnect them while the amp is on, but suggest muting the audio since you could feel a tingle, or accidentally short the connections.

3 - IcePowers take a very long time to warm up, like 48-72 hours, but they don't cool down in a minute.  You can leave them on except for the short period of time you are disconnecting any inputs OR turning a preamp back on.

1 watt into an 80% efficient amp would seem to yield 1/5 watt in heat?

@listening99

Yes, but they have a fixed idle power you are not accounting for, on the order of 5-10 watts. So take the efficiency and add the idle power, more or less. :)

In your example, it’s’ probably something like th 5W idle + 1/5 W = 5.2 W.

The excellent and more powerful Job amp should be on your list IF your new amp does not meet expectations. We have one in the studio, it is rarely powered down.

@tomic601 That's interesting... Mrdecibel convinced me to stay away from the Job, suggesting it would have similar difficulty, owing to the low impedance of my speakers, dropping down to 3.1 ohms, according to claims by one owner of Tekton Moabs. I also understand they not longer make the Job 225, and I understand this might be related to design flaws and reliability. I've heard a variety of reliability comments on the Job, and your comments come out on the positive side...

It seems the Job would have an easier time supporting LARGE LOUD bass notes, like the kind that open the live version of Styx's "Snowblind" (song 5, on the first disc), on their Caught in the Act, album. I'm actually more 'asking' if the Job amp would do better, specifically in terms of handling LOUD BASS and in managing heat at louder play. The Nuforce STA200 is wonderful, vivid, clear, particularly skilled in rendering the music and imparting a feeling of the space, but things shift a bit when  I'm asking for average delivery levels of 90+ db, with peaks in high 90's or above. Give it an hour in that territory and the heat sinks are VERY hot, maybe not burning, but very hot, and the entire chassis is also hot. I've always brought the volume level down at that point and things seem to cool well.

I want to clarify that aside from the heat, the other issue is that I want to be able to play the very biggest bass notes without difficulty. The NuForce does not play Royals by Lorde particularly well. I do not pursue this kind of music but rarely, but if I'm going to buy another amp, I think I want it to be able to handle the big stuff. That's the primary motivation, although I'm intrigued by class d. As mentioned, things are too hot in my home for tubes, during the summer. This is why I've got what some are reporting is an excellent low-cost decently powered class D amp heading this way...

A couple of caveats. I had (still have) a similar situation. I have a pair of tubed mono block amps that I use for serious listening and a SS amp which I keep as a backup or use when I just want some background music on but don't want to put hours on my tube amps. Both are connected through a Beresford switch box to my single pair of speakers. When I want to swap amps or do an A-B comparison, its simply a matter of throwing the switches on the Beresford. DO NOT CONFUSE THIS WITH A SPEAKER SELECTION SWITCH BOX. The Beresford is specifically designed for the exact purpose of swapping amps to a single speaker load. Also I believe i read somewhere that tube amps should never be left on without a load connected. This is consistent with the Beresford design the circuitry of which  includes dummy load resistors to prevent a powered on tube amp from seeing an open load. 

J.Chip

Well, mr decibel is one who’s input I trust for sure. We don’t run an hour in the high nineties for many reasons... this isn’t a lecture but watch your ears !!!! Royals is a high power density track ( give me a bit and I will post the RTA of that track on my virtual system page - I was recently using that to help a fellow audiogon member size his amplifier ( with less efficient speakers than yours )
your hour requirement drives duty cycle. In an A/B amp, you need a beefy power supply, lots of output devices and a way to get the heat out. Look under the hood on the 225 and it will indeed be lacking, so I retract my recommendation. I would point you to Van Alstine IF the class D disappoints. I will let you know when I put up the RTA photo - it is a great track for taxing a system.

Yes, my use of high nineties was for projection out of windows into my backyard. With alleged 98db speakers, I didn't think this would be a problem (for the Nuforce), but it did heat up (considerably) over the hour... 

Within the 12x14.5 room of primary listenership, Peaks are more in the high eighties, or lower, for most of my listening. I should try Royals in that context, but truth-be-told, I'm fairly tired of the song. It's more a sonic biceps flex than anything else.

Just received Trio Jeepy CD from the culture of Amazon, and the hints of the original space of recording come through. Love the distance-impression of the sax, out on the left, the chunky and springy percussion off the right, the sweet double-bass in the midst. The Nuforce is perfect for this. 

I'd be interested to learn more about how the RTA of Royals interacts with an amp. 

@tomic601 You mention, "Van Alstine IF the class D disappoints." I did a search, nothing came up that matched... 

Try Audio by Van Alstine

OK I posted the screenshot of RTA with Royals. A fun track for sure to flex the bass a bit. You can find it on my virtual system Poverty Bay Sound. Have fun, i hope your search is going well.
Jim

Hello Listening99.  Power is a funny thing. The numbers don't fit into our brains very well.  If you've watched Vu meters while music is playing, you know a 10 db jump is not all that impressive. The loudness difference between 1/10 of a watt and 1 watt is the same difference as between 80 watts and 800 watts! So 300 watts is not nearly four times louder than 80 watts. It's just under 6 db louder. 320 watts would be 6 db louder than 80 watts. So it's NOT a matter of perceivable loudness, it's a matter of the apparent ease of an hi wattage amp not running out of power and clipping at say, 200 watts when an 80 watter would have run our of power and clipped the wave, which sounds bad. A current hungry speaker (low impedance) is going to tax any amp, so it's good to have one that can deliver the goods when needed. Good luck with the new amps they will play cleaner at volumes where the 80 watter was struggling. Place them where they can have plenty of ventilation. Keep Smiling!

@boomerbillone - your post is appreciated... maybe I should have opted for the 800wpc d-sonic, given your spirited claims. I will have the new 300wpc amp for a 30-day trial, so we will see how it goes. Should be here Thursday and I will definitely set it in motion that evening.

Thanks for sharing,