Thanks but what about zero feedback designs?

I got to know a few military folks when our company produced an updated air-data computer for the Air Force. One of the sergeants that I worked with, used to tell a story of his supervisor who would hold the circuit breaker in when trying to find a short circuit somewhere in the airplane's long cable harnesses. His method was to hold it until visible smoke emerged, then he would go to lunch and let his techs replace the burned wiring.

@@marianneoelund2940 Thanks for sharing. One more item. The servo that was created, a collaboration of GE & MIT, was indeed used on the Army tank project but stabilized the 5in gun on Navy ships.

Power supply voltage variation is covered by the amplifier's feedback loop. In other words, it easily compensates for those variations - especially when the input and middle stages are supplied with regulated power and only the output stage is exposed to supply ripple, as Paul described for PS Audio's products.

Yes between Springfield and Boston

I was thinking the same thing, but with todays modern resonant soft-switching topologies you could easily make an electrically quiet SMPS that would do the same thing, and make the amplifier have similar efficiency to a class-D amp. But given that companies like Benchmark make class-D amplifiers that are cleaner than a lot of DACs, it doesn't really make as much sense now for the home-audio world. Still it could be of a simpler design and still have the same benefits. That said, I use my own SMPS design in my compact linear amplifiers because the amp can have less distortion and noise than a conventional mains transformer, not to mention no massive magnetic field to deal with. From a distortion perspective, the big issue is the low (120 Hz) rectified AC that recharges the caps. Unless LOTS of capacitance is used, the distortion rises with frequency due to the nasty sawtooth ripple on the power rails. The amp is good at rejecting it at low audio frequencies, but the falling gain margin with frequency makes it less effective higher up. It can even be seen in distortion plots as actual ripple on the harmonics at high frequencies.

@@mysock351C The Benchmark AHB2 isn't a class-D design, actually. It has a monstrous switching power supply. The amp as such is a feed-forward THX design.

@@hermannschmidt9788 My mistake I was thinking that since it has a switching supply in it. But yes, it's a feed-forward design which is why it measures so well. Still the hypex modules have about an order of magnitude less distortion than Paul's linear amplifiers, and his other ones, which is why the Class-H type designs are pretty much defunct at this point. I also suspect the same fate awaits linear supplies. My last amplifier I designed an SMPS for it since it actually has _less_ distortion than a linear due to the better regulation. And probably also why the ABH2 stuck in my head, since it's a linear amplifier stage with a switching supply and from their comments they did it for the same reasons, namely, to get away from the large transformer and its powerful magnetic fields.

@@mysock351C Yes, Benchmark seems to have left linear supplies for good. The advantages of switchers are compelling. However, I am not yet convinced in every application. I've modified the DAC2 with a linear supp. and super regulators (Walt Jung type) and the positive effect was substantial. Almost nobody deploys highly sophisticated regulators. Those make all the difference. A standard three-pole regulator design is not superior to a well-designed and filtered SMPS. A combination of SMPS + SuperReg would be interesting, but for that I would have to swap the SMPS to get the voltage headroom.

@@hermannschmidt9788 Regarding the regulators, yes they will make a difference since the amplifier itself will not be obliged to have to reject the ripple itself. But one has to ask if the juice is worth the squeeze? Much like you can wrap an op-amp around a conventional amplifier IC to get really low distortion numbers. Obviously, I don't think there is anything wrong with posting stellar specs, but its kind of a moot point to have an amplifier with 0.0005% THD only to hook it up to speakers that will have around 0.1-0.3% THD in the midrange and treble regions for most listening.

Thats because batteries have a rather high output impedance. I modified a boom box and the type of batteries I used affected the bass quality.

@@andershammer9307 They were NiMH types which had a fairly high current capacity. If memory serves, 4/5 AA. The output stage was a SRPP using 6SN7 - so I tended to leave it on - and that ran the batteries down (dohh .... !) - which is why I changed them out. But the PCM-63 had a burried zener reference and I think the data sheet said that there was no advantage in running the analogue separately to the digital supply (they came out of the ic on seperate pins) so I was a bit surprised on how much a difference there was. But then, as we all know, audio can be like that ! I wouldn't have thought a crystal controlled power supply to a turntable motor would change the sound but change it it did - likewise two different CD transports were very different - and I still haven't figured that one out at all !!

@@mrb.5610 That is why we have to rely on our ears not test equipment.

@Douglas Blake First, thanks for your quick reply Can you explain please, sorry for not understanding Can you send me an email where I can send pictures? Thanks

@Douglas Blake Thanks a Lot

Current is limited by protection circuits, and the threshold is usually time-dependent (sometimes also voltage-dependent), rather than a fixed number that they could quote on their spec sheets.

My guess - most amps don't need to worry about a high current output. A little bit of ohms law? Most speakers are nominal 8ohm impedance, dropping to 3-4ohms somewhere in the frequency range At 8ohms a 30W output is roughly 15V @ 2A, this drops to 11V @ 2.7A across a 4ohm load. You would normally only be using a couple of watts output so current draw is negligible. A 30A peak current output implies the amp is designed for lower impedance speakers.

@Douglas Blake To be perfectly rude, the only flaw I see is that you didn't give the OP that answer the first time.

@Douglas Blake Yes, I saw that you hadn't answered the OP. Ironic that you would spend longer "correcting" me. Why did you reply to me anyway? My original reply was in response to the OP, did youtube send you a notification?

@Douglas Blake I originally replied to the OP, not you. I'd suspected youtube had been screwing with the reply notifications for a while. Thanks for the confirmation. My guess is that the OP hasn't been notified and likely won't see any of this.

I prefer "worst this year" sauce....

Here in the UK most find it odd how Americans pronounce our counties and cities! Worcestershire for instance is generally pronounced ‘wuster sh’ and not ‘warsestershire’. Even in the UK southerners exaggerate the shire part except they say ‘sheer’ for counties and yet say ‘shire’ for horses. The english language really takes a battering.

@@AnalogueGround might be taking a battering, but it took out many other languages on the way! Anyway it's a mixed up language, and those unusual English place names are often Saxon based (Germanic, dutch or danish in origin).

What do you mean?

How many channels do those amplifiers have? What speaker impedance is the power rating for, and what is the minimum rated speaker impedance?

Not pulling your leg im guessing ... Check the exact spec. Big transformer and low power output means it's probably biased high and dissipates a lot more heat. Also some designs will use way more overhead then needed (although transformers should always be rated higher than the max power of the amp into a given load.

The video is about power supplies. Why do you believe power supplies for tube amplifiers have any advantage?

@@marianneoelund2940 In a word - 'choke'. Because toobes are low current, high voltage devices, you can use a choke to reduce the ripple on the supply voltage rails - historically, this was done because high value capacitors weren't available. This pulses the mains transformer a lot less - these pulses can and do carry over into the surrounding circuitry and do absolutely no favours to the sound quality. Put some numbers into a simple psu simulator like Duncan Amps PSUD2 and you might be surprised on how nasty the current waveform in the supply transformer is in a transistor amplifier with huge reservoir capacitors !

@@mrb.5610 Additionally tube amps usually use this (I don't know the English word for it) cube type transformers and not these circular ones, they do magic to the sound since they work like a transformer with a build in capacitor. (I know it is also true for all other transformers but with this classic transformer design they do it a lot better)

@@snakeoilaudio Toroidal ! Toroidals are nice and compact but don't take kindly to saturation - which happens when they're pulsed with large currents feeding large reservoir capacitors .... funny that ! It's easy to rate a transformer feeding a nice resistive load - you can design one to be on the limit of saturation. But into a capacitative load and things start to get messy very quickly.

@@mrb.5610 Ah yes, I remember those now. A full "pi" CLC filter can produce very smooth DC. I have actually looked at the power input current waveform for solid state amps, as I have a current probe for my Tek scope. The first surprise was that it wasn't quite as "peaky" as I expected; the second surprise was how much the voltage peaks on the AC line are flattened, and I don't mean because of the amplifier. It looks that way, even on an unloaded circuit, with 3-5% harmonic distortion. Another interesting finding: We have 7.2kV 3-phase power distribution lines running along our street, and I can actually sample the current in those lines by running a large wire loop around our living room, and connecting it to the scope. The current waveform is quite far from sinusoidal, with very significant surges at the peaks. I suspect it's largely due to transformer designs that skimp a bit on core material.

That's in England..

ive heard _Werster_

@@googoo-gjoob ya, I'll give you that one.

Nah fam it's Wista