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

[Triode]

For example

I'm mostly well versed in digital electronics, I get into analog stuff for filtering, but recently to build up my analog skills I've been considering building an audio amp.

Many of the designs out there mention adding mass to make it sound better. I realize that a good analog amp is often heavy because of big heat sinks and the transformer, but I don't know how adding mass that is just mass would really improve anything. I know with mechanical vibrations a large amount of damped mass helps you (that's why those big old heavy milling machines from the 50's are so nice) but in a device where the vibration is electrical what does it do?

I can imagine a few scenarios. Is it the shielding? A thick metal shell as in the design above will certainly block out EM noise, but that doesn't explain the heavy wooden block. Is it to spread heat? Again that doesn't explain the wood, and then you would use a proper heat sink. Maybe it's more of a thing where it just feels right, heavy = good quality? I only suspect this because many amplifier designers don't mention mass and if it were important it seems like they would at least give it a nod.

As a side note, if anyone has any good DIY amplifier designs, or pages talking about design considerations I would like to see them. I'm thinking I want to build an AB amp, simply because D sounds like it is high speed PWM, which is something I am already familiar with from controlling motors and actuators. Plus, though it is hotly debated, many audio snobs seem to think class D sucks, though others say digital to the end is best, anyway, I don't want to get into their war on that issue, so I figured I'd just build an AB amp.

 

[JimB]

Aluminium pan and big wooden board - very interesting and a good talking point when you are having a laugh with your mates.

But to think that it improves the "sound" is just plain Audiophoolery.

JimB

 

[Overclocked]

Comon now, dont you know that expensive gold oxygen free wires improves your sound over 9000 times?

On topic: Ive built the gainclones smaller cousin, the LM1875 from the datasheet (25W Mono), and it sounds great! I paired it with $50 speakers from Amazon for my computer. The only issue I have is grounding near my pot for volume control, otherwise its a pretty solid amp. No noise from my powersupply.

 

[cowboybob]

For a tube type amp I can see it. Additional mass, beyond that provided by the power and audio transformers, would help dampen mechanical, sympathetic grid/plate vibrations from poor chassis segregation from support structures.

And a little more iffy, but perhaps wood within or around the amp cabinet to further dampen air vibration effects.

But, obviously, of lesser (but not absolutely zero) concern for solid state amps although, to an audiophile (which I am not), it might matter.

 

[Nigel Goodwin]

I can imagine a few scenarios. Is it the shielding? A thick metal shell as in the design above will certainly block out EM noise, but that doesn't explain the heavy wooden block. Is it to spread heat? Again that doesn't explain the wood, and then you would use a proper heat sink. Maybe it's more of a thing where it just feels right, heavy = good quality? I only suspect this because many amplifier designers don't mention mass and if it were important it seems like they would at least give it a nod.

Sorry, but it's just total crap, and utterly meaningless.

Where I would 'slightly' agree is that a heavy, well built amplifier, with a large mains transformer, large PSU capacitors and large heatsinks is likely to sound better and be more reliable. But that's nothing to do with 'mass', it's simply using components better able to handle heavy loads.

Makes no difference if it's valve or transistor, meaningless terms like 'mass' are completely irrelevant, and used just to try and con readers (such as the above mentioned 'oxygen free cables' ).

 

[moty22]

I support this claim.
If the amp is heavy it makes your house heavy and vibrates less from outside noises, the music sounds better then.

 

[Tony Stewart]

Rack mount hardware if design well is designed to survive a fall onto a concrete floor with SS handles.

But the biggest fault with large units is they must apply PU adhesive to large parts to prevent vibration from causing metallurgic fatigue in the solder joints. I've witnessed this in Stovetop control boards with Relays failing due to a micro-crack annular ring in the solder, perhaps from slamming the oven door every use within a few years. Apple $2500 CRT's failing just after the warranty. etc etc.

Most PC PSU makers follow this and apply to all large caps, coils and other parts.

However I remember a very expensive Transmitter for GOES 1 being tested by an Test Engineer at Bristol Aerospace where he had the unfortunate luck of duct tape used for the I/O cables in a Tenney Environmental desktop chamber. that stuck the Transmitter to the door and crashed on the desktop (6") Since the drop height of stop height ( compression) gives the resulting G force, Engineers at NASA calculated it might degrade the transistor crystalline structure and demanded a rebuild.

Yet I have designed ultrastable OCXO's to survive a 100g drop test from 30 ft with a 1" shaft into a block of lead, 50g acceleration on spintable at 3600 RPM, and 15g swept frequency vibration operating to maintain 1e-10 stability specs. So I know how challenging it can be but can be done.

It's not mass. but rigidity with anti-resonant shock absorption dampers like PU. After I did some research I discover experts use fragility curves of max g vs t vs velocity to get a damage boundary curve.

This is how I expect the most rugged instruments are designed with these curves as part of the specs.
Heavy parts fail with low g high velocity from inertial .
Very light parts fail from high g very short time duration due to impact zone being near zero causing structural resonance.
I calibrated all the accelerometers with -1.00 = gravity and then read + peak shock when testing 5.25" disk drives with and without packing material.
never learnt this in school but discovered this law of physics

g = drop height/ stop height , ( stop height can be near zero if nothing compresses, but in reality something moves.)

Thus 10g = 1 m drop into a 10cm linear cushion just as 10g is a 1cm drop onto a thick matt with 1mm compression, but the inertia from velocity is different, hence damage depends on flexibility of mounts yet rigidity of mounting locally. The time duration gives velocity and with mass more inertia requiring proper shock isolation at board level but more restraint inside for components.

 

[Nigel Goodwin]

I support this claim.
If the amp is heavy it makes your house heavy and vibrates less from outside noises, the music sounds better then.

Can you support this claim in double blind tests?

 

[moty22]

Can you support this claim in double blind tests?

Of course I can, with the conditions that the amp is very heavy and the music is by Frank Zappa.

 

[Veraxis]

I think that the question may be more basic than people think here. I think the idea of adding mass is so that, in the case of a very heavy, high-power speaker-- such as a subwoofer-- the actually movement of the speaker driver can vibrate the speaker tower at low frequencies, and you don't want the speaker casing to be so light or loose that any of the casing audibly rattles or vibrates on the floor when the speaker is playing. or maybe people believe that it does something more than this?

 

[Tony Stewart]

When we did shock & Vibe tests at work, in the 70's it was a 10kW vacuum Tube Amp that powered a neoprene rimmed woofer 0.5m in diameter and could be rotated in x or y axis and support 500 lbs
and the shaker was a massive electromagnet.

The bass and midrange response was pretty loud up to 3 kHz and shook the entire building especially object under test with midrange resonances.

heavy....

My towers are on Titantium spikes on the floor for rigidity, the 8 cones are mounted neoprene. 1.5" walls 5ft high.

I can carry it, but it can bring the Grateful Dead back alive.


as a sidenote to yours.... scrap the AB AMP and go vacuum tube all the way and shoot for 90 dB SNR 0.01% THD... Awesome when I hear my 70's friend also in EE design & build this. pre-amp and separate power amp with Philips, non crossover 12" speakers in a large tuned solid cabinet. Punchy and clear.

 

[Nigel Goodwin]

Of course I can, with the conditions that the amp is very heavy and the music is by Frank Zappa.

Sorry, but I think you're talking complete rubbish

 

[Nigel Goodwin]

I think that the question may be more basic than people think here. I think the idea of adding mass is so that, in the case of a very heavy, high-power speaker-- such as a subwoofer-- the actually movement of the speaker driver can vibrate the speaker tower at low frequencies, and you don't want the speaker casing to be so light or loose that any of the casing audibly rattles or vibrates on the floor when the speaker is playing. or maybe people believe that it does something more than this?

I think you've missed the point, we're talking about AMPLIFIERS here, not speakers, where I don't think anyone would disagree that speakers with solid cabinets are going to sound better than flimsy ones.

 

[moty22]

Sorry, but I think you're talking complete rubbish

Sorry, I'm doing my best to fit in.

 

[cowboybob]

Sorry, I'm doing my best to fit in.

moty22, I got it, even if some other(s) did not. Hang in there. Absolutely no need to apologize.

Snarky (or just plain rude and from the ill bred) comments, unfortunately, are still voiced even in the best of families...

 

[moty22]

moty22, I got it, even if some other(s) did not. Hang in there. Absolutely no need to apologize.

Snarky (or just plain rude and from the ill bred) comments, unfortunately, are still voiced even in the best of families...

Thank you cowboybob for the kind words and the support. I detected 'angry Nigel' right from the start and luckily it didn't take long to get used to him.

 

[Ian Rogers]

He needs to decaff!!!

 

[Diver300]

Like a lot of Audiophoolery, this might be based on some shortcoming of some designs.

Poor design can result in vibrations being picked up by the electronics, which could cause distortions. Mistakes could include poor contacts, including potentiometer wipers, or proximity of coils to metal structures. You could even get issues from stray capacitance varying, but that is less likely at audio frequencies.

Also you could get audible noise being generated by the electronics. The magnetic effects would be the obvious ones, so that inductors producing forces on nearby metal, or wires not tied down properly moving in response to magnetic fields, like this.

Any of those problems would be lessened if the amplifier were heavier.

It only needs to happen once to become an Audiophoolery legend. It is also highly unlikely that adding weight to an amplifier would make it worse.

 

[audioguru]

Piezo items like ceramic capacitors can pick up vibrations. That is why a ceramic capacitor should never be used to couple audio or video signals. I use small film capacitors instead but use the ceramic capacitors as power supply high frequency bypass caps.

Your ears affect your balance so you might feel better if you are heavier instead of the amplifier being heavier. I was thinking about how I feel when my dog sits in my lap then I thought completely differently about my wife sitting in my lap.

 

[picbits]

I've also read up on ceramic capacitors both acting as microphones and in other cases small "speakers" - I've come across whistling ceramic capacitors in the past.

Fortunately as I get older, my hearing has got less sensitive and it bothers me far less