In these audio amp designs, what does adding "mass" and "rigidity" accomplish?

[KeepItSimpleStupid]

Triode:

Audio will ALWAYS generate noise in forums. In the the era, the better amps weighed more. Thus weight tending to symbolize quality.

If you want an amp to build, I'd suggest The Leech Amp. https://users.ece.gatech.edu/mleach/lowtim/ Ampzilla from Great American Sound was a nice amp in it day as well. There was a construction article in Radio Electronics. The GAS100 (rebranded) IC was a common one at the time

I chose to build a variation on the Leach Amp. Mistakes will really annoy you. It's dubbed as a Low TIM amplifier. Rise time and frequency response are off the charts.
To make it better, you will have to understand it.

The power supply suggested is lacking. Mine lacks a power switch. It runs cool. I would like to see clipping indicators over temp indicators and a power light.
I put effort into slow turn on-ramp up of audio and a 2RU form factor and easily serviced. My turn-on circuit could be better.

 

[audioguru]

Long ago when vacuum tubes (valves) were used in audio power amplifiers, output transformers were needed to match the tubes high impedance to speakers low impedance. For good low frequency response and power the transformers needed to be big and heavy. Their power transformer was big and heavy too because the tubes had heater filaments.
Modern amplifiers do not use output transformers so they are not heavy (but the power transformer might be big and heavy).

 

[MrAl]

Hi,

Direct mechanical vibrations can in fact cause audio noise in amplifiers because some of the internal components are somewhat sensitive to mechanical vibration. There are various components that will be more sensitive than others such as inductors and capacitors where resistors wouldnt be as affected.
But how much can this really influence the sound even with the most critical listener?
Well, if there is a component that is mildly sensitive to a given level of vibration at a given frequency, then an increase in vibration will result in an increase in audio noise, it's as simple as that. So we know for sure that there is some effect. How much effect depends on the level of vibration and the construction of the component in question. For example, if an inductor was not varnished it could easily lead to audio noise generation with mechanical vibration. Just how much however is probably too hard to determine theoretically, but a measurement would reveal a more clear picture. For most power levels i would almost be that there is usually negligible effect, but for high power levels where the speakers happen to be closer to the amplifier it's really a matter of measurement as the speaker audio pressure could cause more than acceptable movement of the amplifier enclosure. More mass would certainly help in that situation, but int he low level scenario it probably doesnt matter.

Of course a secondary factor is longevity. Vibration is often a cause of premature failure, so reduction could help a lot. If we could reduce the vibration of incandescent bulbs we could probably get more life out of them because vibration is the final straw that breaks the filament, due to a few possible vibration causes.

Class D is an interesting type of amp, because it doesnt wast nearly as much energy as any linear class. Just like a linear vs switching regulator, the Class D transistors states are all either completely on or completely off, meaning much less power wasted, while the linear class transistors are always in their linear mode. This not only lowers wasted energy, but also relaxes the capacitor size needed for good base response.
It's true that there could be lower frequency components that might be a source of noise, but they should be minimal in a good design.

 

[Nigel Goodwin]

This not only lowers wasted energy, but also relaxes the capacitor size needed for good base response.

I'm dubious about that claim (and it's 'BASS' - not 'BASE' - Meghan Trainor would know ).

Assuming the class-D amplifier has a switch-mode PSU, then of course the capacitors are greatly reduced in size, but it would be just the same for a class AB amp using a switch-mode supply (of there have been various examples over the decades). But if you have a class-D amplifier with a linear PSU, then you still need large reservoir capacitors due to the low supply frequency.

Personally I think class-D is the way audio is heading, and I'm VERY happy with my class-D, switch-mode, PA mixer/amp

But even greater advantages come with small amps (radios etc.) where it greatly increases battery life - unless it's a DAB radio, which decreases it considerably.

 

[MrAl]

Hi,

Ha ha, yes my sleepy spelling of "bass" is kinda funny, i think i'll leave it like that just for kicks.
Good caps are best for the bass response anyway, so i wont argue that point. But i will say that if they use a linear power supply ahead of the switching section, they dont know how to design power products.
I agree that class D is the future. I dont mind that much i guess, but if i had to design a small amp right now i might use a regular analog design anyway, say under 5 watts. Over that we start to loose too much power as im sure you know. I did a calculation on this a while back on this very forum i think, and had shown that there was a lot of power wasted with analog when the power level is higher. Percentage wise though there's always a lot wasted. Too bad, as analog is so much simpler.
My first class D amp was back in the early 80's when i used a 555 timer as the PWM mechanism, just to see what would happen, mostly because even back then people were fascinated with them. Dont remember now how well it worked but it did work to some extent.

 

[Nigel Goodwin]

My first class D amp was back in the early 80's when i used a 555 timer as the PWM mechanism, just to see what would happen, mostly because even back then people were fascinated with them. Dont remember now how well it worked but it did work to some extent.

I would have thought fairly poorly

The way to go, even back then, was a triangle generator and a comparator.

Commercially though I disagree with 'small amps', if you're running off batteries using class-D can greatly improve battery life.

As for making your own HiFi amp, I would suggest analogue is still the way to go, and there's something very satisfying about a nice beefy analogue amp

 

[MrAl]

Hello again,

The 555 thing was more just to play around with than anything else.

We actually did do that similar to the triangle and comparator approach, but miniaturized everything into one ASIC chip, for AC converters which is basically the same except with fixed frequency. Back then the ferroresonant converters were a little more common too.

Yes, battery operated devices are more common now. I was taking more about head phone amplifiers and small speaker amps for TV's and PC's.

Yes there is something elegant about analog...simple and quiet.

 

[tvtech]

Does a little NAD 3020A count

2 Ohms no problem for it as a speaker load. Even tried blowing it up when it was new in 1984 and under Warranty still. Drove it into a dead short (piece of wire). Gave me the middle finger and showed me who is Boss.

Still working today. Tough little amp.
The fact that it's claim to fame was amazing/warm/pleasant sound also helps.

Still the same today 30 Years later. Gold.

Except...the front cheap plastic panel where the controls are...had a little "accident" a while back where I managed to put my elbow through it. Lost my balance again. Frigging ears and stuff.

As I sit and look at it and compare it to my Rotel RA 820 with a nice Aluminum face...I have to make it better. Please excuse the grubby look of the Rotel. It was in storage for the best part of 10 Years.

It needs a clean up. Was my parents one that I convinced them to buy along with Ditton's.
Remember Celestion....and all the great speakers they made in the Eighties??

Regards,
tv