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how to protect the amp from bad voltage?

#61
agedhorse said:
For the most part, yes.
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It's worth mentioning that most of what people probably imagine a power conditioner doing is actually baked into the design of a modern SMPS.

I read an APC white paper several years ago which described all the things the so-called power conditioning in a basic (standby) UPS didn't cover. It was mostly an explanation of the conditions a SMPS is supposed to be able to handle on its own. I don't remember the numbers, but I do recall thinking it covers any conditions where I would feel safe plugging in gear of any kind.
 
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#62
Jim C said:
My question is what was the max voltage for design criteria then and now?
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When the nominal voltage was 117 VAC, an acceptable range of 105-125 VAC was typical for the power supply designs used. The question is, what is the optimal line voltage for the best sound and what the optimal voltage is for component service life. It depends on the amp’s design. Just because they say 125VAC is acceptable, it doesn’t mean that the amp will sound and perform the same as at 105VAC.

Component maximum ratings such as power supply capacitor voltages and max tube plate voltage factor in.
 
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#63
It depends.

Maybe 10% true, 90% myth.

IME, one of the best ways to sell accessories is to generate a perception of need and if you can cultivate a bit of fear… all the better. It the guitar world, the arguments get taken to an absurd level ime.

That said, there are some amps that are sensitive to high line voltage. As a generality, most domestic amps were designed around 115-117V nominal line voltage but there are real exceptions.
 
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#64
Granted the thread is 12 years old, but different amp types react to line voltage differently. So far as I know, most if not all of the newer Class-D heads have built-in regulated power supplies, so the actual power amp circuit sees roughly the same voltage no matter what. Of course it still means that the power supply has to survive what it's being fed.

Some earlier amps were unreasonably tolerant of line voltage. Class-AB amps with unregulated power supplies had to handle a range of voltages because the rail voltages varied even during normal operation of the amp.

I remember a gig where the vocal PA decided to quit, right as we were starting to play. "The show must go on," so we quickly patched the vocal mic through my bass amp, and I played my upright unplugged. We got through it just fine. Right when we finished, the PA head turned back on. Hmmm...

Turns out the entire band was plugged into the same circuit as the lights, which were on a dimmer. The venue dimmed the lights just before we started to play, and turned them back up afterwards. I estimate that my bass amp might have been running on as little as 50 or 60 Volts. We weren't playing loud. It was a GK MB150 combo. On the other hand, the PA head had an under-voltage protect circuit.
 
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#65
fdeck said:
I estimate that my bass amp might have been running on as little as 50 or 60 Volts. We weren't playing loud. It was a GK MB150 combo.
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Something else this points out is a standard dimmer creates a horrendous distorted waveform. In your case, the amps power supply didn't carry this through to the audio.

Power conditioners are always claiming the clean up the power. Nothing affordable actually does. And it's not needed as most amps are designed to non-ideal mains waveform. There's plenty of lab equipment that is designed to provide distorted a main waveform that the design engineers use to test their amp designs.
 
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#66
seamonkey said:
Something else this points out is a standard dimmer creates a horrendous distorted waveform. In your case, the amps power supply didn't carry this through to the audio.

Power conditioners are always claiming the clean up the power. Nothing affordable actually does. And it's not needed as most amps are designed to non-ideal mains waveform. There's plenty of lab equipment that is designed to provide distorted a main waveform that the design engineers use to test their amp designs.
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Indeed, and the voltage / current waveform of a line frequency power transformer is already distorted by the behavior of the rectifiers and filter caps, even when being fed with a pure sine function.
 
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#67
fdeck said:
Indeed, and the voltage / current waveform of a line frequency power transformer is already distorted by the behavior of the rectifiers and filter caps, even when being fed with a pure sine function.
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Even a lot of EEs are unaware of this. Often when I tell someone that the current flow from the mains is not sinusoidal like the voltage is, they reply, "but it's a linear supply." "No, it's not actually linear. It conducts current only at the peaks of the voltage waveform, when the voltage is high enough to forward-bias the rectifiers feeding the reservoir caps. That's what makes the power factor <<1."

Many engineers learn about power factor in terms of phase angle between E and I but not in terms of conduction angle.
 
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#68
Forget all this widdle-waddle engineering talk and get you one of these!
yz27e184gd9txoscjto8.jpg

Only $9999.99 and your power will be good forever! Pro AudioPower chord included (sug. retail price, $788)
 
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#70
fdeck said:
Indeed, and the voltage / current waveform of a line frequency power transformer is already distorted by the behavior of the rectifiers and filter caps, even when being fed with a pure sine function.
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Bob Lee (QSC) said:
Even a lot of EEs are unaware of this. Often when I tell someone that the current flow from the mains is not sinusoidal like the voltage is, they reply, "but it's a linear supply." "No, it's not actually linear. It conducts current only at the peaks of the voltage waveform, when the voltage is high enough to forward-bias the rectifiers feeding the reservoir caps. That's what makes the power factor <<1."

Many engineers learn about power factor in terms of phase angle between E and I but not in terms of conduction angle.
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In case people are curious - this is what current spikes looks like from a line frequency power supplies. Old class-ab amps. (the diagram doesn't
A-closer-look-at-power-factor-correction-2.png


That spiky current is never brought by "Power Conditioning" marketing.

Good news is SMPS - generally include Power Factor Currection (PFC) into the design. Governments in some parts of the world now require it be dealt with at high power levels.
 
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#73
seamonkey said:
In case people are curious - this is what current spikes looks like from a line frequency power supplies. Old class-ab amps. (the diagram doesn't
View attachment 4648664

That spiky current is never brought by "Power Conditioning" marketing.

Good news is SMPS - generally include Power Factor Currection (PFC) into the design. Governments in some parts of the world now require it be dealt with at high power levels.
Click to expand...

It wasn't just class AB amps; the Crown K series amps of the 1990s used basically a class D output section but with line-frequency power supplies.
 
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#76
Bob Lee (QSC) said:
It wasn't just class AB amps; the Crown K series amps of the 1990s used basically a class D output section but with line-frequency power supplies.
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There were some Euphonic Audio iAmps and Aguilars that used that format too.
 
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#77
Passinwind said:
There were some Euphonic Audio iAmps and Aguilars that used that format too.
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Yes, my Euphonic Audio iAmp800 has a Class D power amp and a linear power supply with a ten-pound toroidal transformer, more than half the weight of the entire amp. That being said, it definitely had more punch, warmth, and girth than the iAmp Pro that followed it with a switching power supply.
 
#78
Frank Miller said:
Yes, my Euphonic Audio iAmp800 has a Class D power amp and a linear power supply with a ten-pound toroidal transformer, more than half the weight of the entire amp. That being said, it definitely had more punch, warmth, and girth than the iAmp Pro that followed it with a switching power supply.
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Quite likely that the power supply difference was not the cause of the perception. I suspect that the iAmp Pro has significant additional differences throughout the amp.
 
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#79
agedhorse said:
Quite likely that the power supply difference was not the cause of the perception. I suspect that the iAmp Pro has significant additional differences throughout the amp.
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Yes, the iAmp Pro used an ICEpower 1000ASP with a built-in power supply while the iAmp800 used a proprietary Class D amp with a linear power supply. So, even though I was discussing the use of a Class D power amp with a linear power supply, the power amps did, in fact, have completely different circuit topologies.
 
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