Thoughts on this little oddity, anyone ...?

It looks like others answered what I sort of suspected where they wanted to try to balance out the + and - rails when the audio peaks. I've never actually seen this before though.

That reminds me- does anybody unnderstood what Carver's "power steering" was supposed to be or mean in their amps?

"Cydrome Leader"

** Bob Carver was an expert at coming up with high falutin' names for various clever dodges he used to save weight and cost.

His " Magnetic Field " amps were nothing of the kind. They simply employed a triac based voltage regulator in the AC supply to improve the regulation factor of a ridiculously small iron transformer.

In his M400 and PM-2 designs, these puny transformers would emit cracking noises and *smoke* if you ever bench tested them at rated power for more than 60 seconds. No thermal shut down was fitted to save the trannies either.

From the blurbs on "Power Steering" it applies to 5.1 channel amps and allows one audio channel to dominate the load on PSU at any given time. Likely a simple boost inhibit circuit that allows the use of a puny AC transformer again.

... Phil

Probably refers to "rail-switching" where higher voltage power supply rails are switched in on demand. (during musical peaks).

Has several advantages including being able to get away with a smaller power transformer and smaller heat sinks. Reduces power dissipation at idle and at low power.

It's said that such amps can sound nasty - not sure I've ever noticed that.

Mark Z.

Hmm, was anybody in the 70s not obsessed with triac pre-regulation in all sorts of power supplies?

nice.

I own an older 5 channel carver amp. I recall upon opening it that the power supply seemed way small for the alleged rated power across all channels. The manual said something about this power steering crap, but the block schematic didn't show anything indicating it was anything other than "you can overload a channel a little bit before it burns out or the fuse blows." It seems ok as far as amps in the early surround sound era were. My DVD+sound setup is straight from 1998 and is this complex mess of stuff running into a technics decoder and from there there are 5 RCA cables running to each channel on the carver amp. There's some goofy fiber link between the DVD player and the technics thing. Prior to this, I had a stack of multiple stereos running everything. For a crappy action movie where everything explodes, balance doesn't really matter.

I'm not even sure how you'd do this these days if you didn't get one of this does everything consumer amps.

The Carver PM1.5 had both the triac and inadequate transformer, and rail switching. High rail was + and - 125v IIRC.

Gareth.

Er, actually I seem to recall now being corrected on that figure once before by Mr Allison, and it is slightly less? 117?

Gareth.

According to the manual:

"CONSTANT POWER SWITCH Set the rear panel slide switch to match the impedan= ce of the speakers used. Use the combined impedance value if you are connec= ting speakers in series or parallel. Choose the nearest match if the value = is not exactly 4 or 8 ohms. Note that no damage will be done if the switch = is left in the wrong position. However, you may not benefit from the full c= apability of the amplifier. =F4=8F=B0=80 Constant power explained The typical amplifier is optimised to= produce full power into 4 ohms and therefore considerably less into 8 ohms= . The PA Series features a unique facility that ensures you get full power = output into either 4 or 8 ohm speakers. It does this by reconfiguring the p= ower supply for optimum current (4 ohms), or voltage (8 ohms)."

Perhaps this is why. They also have the ability through switches to delega= te signal to the individual amps for mains and monitors.

"Cydrome Leader"

** What drugs are you on ?

Carver amps were the virtually the only ones to use the idea and the first ( M400) came out in the early 1980s.

( Yamaha made a version and sold about 5. )

... Phil

"Gareth Magennis"

** No rail switching as such, just diode steering.

The regulated DC rails were +/- 23, +/- 55 +/- 80 and +/- 125.

... Phil

Huh? I would suggest Mr. Carver was doing what he was best known for; taking an unneeded or ordinary function, obfuscating or renaming it, and making it a "feature".

More likely, although I have not checked the schematic, that the "impedance switch" is like those of modern surround receivers: changing the transformer output voltage downward for "4-ohm" operation, and higher for "8-ohm" operation.

Like the rail-switching, this reduces quiescent power dissipation and heat losses, but also limits full power capability.

Example:

I ran into an older McIntosh MA-6100 the other day. I didn't remember it had a "4-ohm - 8-ohm" switch. So I tested it.

In the "4-ohm" position, it was a 50-watt per channel amp.

In the "8-ohm" position, it got about 90 watts at clipping.

Mark Z.

"Mark Zacharias"

** The paragraph is from Allan and Heath.

.... Phil

I'll have to look at that on my scope, but off the top of my head, I thought that the trigger point was still adjustable on external and could be set anywhere on the trigger signal and if so, I'm not sure that I see how it helps to trigger the scope externally from the same sine wave as it would use internally on auto trigger. I can see how it would be helpful to have a fixed trigger point, virtually at the beginning of a cycle, by squaring up the generator's output, and then feeding that to the external trigger input.

Arfa

"Arfa Daily"

** But it is NOT the same sine wave !!!!!!!!!!!!

Various audio devices invert, phase shift, phase modulate and even time shift sine waves !!!

** Best set the trigger level to a zero crossing of the generator feed so the same wave on the scope starts at a zero.

I have mine so the first half cycle is positive when there is no phase shift.

With external synch, the scope is always triggered and the level on the screen does not matter.

FFS - TRY IT !!!!!!!!!!!

... Phil

Want some?

As I said, all sorts of old power supplies were made with SCRs and preregulators before the transformer.

The smaller HP/Agilent bench power supplies are still made this way. I guess you get a smaller heatsink and a little more efficiency.

"Cydrome Leader"

** But not in audio amplifiers !!!

You PITA f****it troll.

... Phil

Oh goody, you're so smart, you just figured out that "all sorts of power supplies" is not a subset of audio amplifiers. When did this occur to you?

Yeah, ok. I tried it today, and I see what you're saying now. Once you've set the trigger point on the sine sample from the generator that you're driving the external trigger input from, then that's it fixed for all subsequent measurements and you should be able to see any phase shifts or inversions. When I said about squaring up the sample, I was thinking that by doing this, not only do you phase lock the scope to the original wave, you also have an always-known point that the triggering is locked to. If you did the squaring with a decent comparator, that trigger point could be fixed within a few degrees of the zero crossing for all cases, eliminating the need to twiddle the trigger level, and pick some arbitrary point anywhere on the rising or falling slopes of the sine.

Arfa

The most likely reason is that it reduces the peak current drawn from each side of the power supply.

Whatever Bob meant it to mean. Bob was notorious for coming up with desciptions that bore little or no relationship to how the circuit actually worked.