John Curl's Blowtorch preamplifier part II

[Steve Eddy]

Originally Posted by john curl

Perhaps, Steve. And perhaps not. Everyone else, just tap your audio and video equipment with your fingernail and hear what happens.

Oh it'll ring like a bell alright.

Just because it's thicker and therefore stiffer, it doesn't mean it's less resonant. It'll be quite resonant. You telling me you've never struck a thick piece of aluminum before?

se

[john curl]

Just my preamp, Steve.

[john curl]

The CTC Blowtorch was built to try to make the very best simple preamp that we could make. Did we go too far? I don't think so, but we could 'cut a few corners' and still have an acceptable preamp. For example, the last 7 preamps that I personally had to put together, used quality copper wire, rather than silver wire. The sound was good, but slightly softer than the pure silver wire. I did an A-B test, myself.

[jan.didden]

Originally Posted by Steve Eddy

Oh it'll ring like a bell alright.

Just because it's thicker and therefore stiffer, it doesn't mean it's less resonant. It'll be quite resonant. You telling me you've never struck a thick piece of aluminum before?

se

You can make an enclosure thicker, heavier, put braces in, and the only thing you change is the frequency at which it rings. Speaker manufacturers discovered that a century or so ago

jan didden

[Groove-T]

Originally Posted by scott wurcer

If you're DIY why not use fusable links of silver wire?

I make service for broken hi-fi gear, otherwise this would maybe not be a bad idea basically.

But my earlier boss saved some money due repairing broken fuses in some Conrad Johnsons with a piece of copper wire, calculated with magic cubes . They used BUSS fuses, very expensive, but safe and tehy said, the sound is better,
After the cheap fuse fix we often had blown circuits and output tubes....

I have seen some products with circuit breakers( Rowland) , because they found this the better sounding solution.

I have seen krells with regulated power supply, using dc sensors and similar protections instead of output fuses, the claimed ist sounds better.
Unfortunately they used fuses in the regulator power supply, which did NOT blow off when a capacitor there had a shortcut. This resulted in a burned stand by transformer ( this thingie sucked more than 90 Watts in standby and had no thermal protection) and the capacitor burned a hole into the board. Finally the main circuit breaker stopped the smoke and prevented a fire.

I have seen big Thresholds, when they failed, the output fuses protected themself while the output devices shortcutted themself and then the main circuit breaker did their job.

In the end, for the sound i feel its the best to avoid fuses whenever possible, without supressing safety of course.

[Rod Coleman]

Originally Posted by janneman

You can make an enclosure thicker, heavier, put braces in, and the only thing you change is the frequency at which it rings. Speaker manufacturers discovered that a century or so ago

jan didden

OK, but what about the effects in the real application?

Consider two preamps, mounted on similar shelves. One has a Heavy, stiff chassis, one has a consumer-grade 0.7mm thick chassis, maybe with enough stiffening to prevent it from twisting when you pick it up.

Fire identical acoustic waves from a loudspeaker at each, from say 2m.

Which chassis transmits more of the incident acoustic energy to a circuit board inside the chassis, mounted on identical pillars?

[jan.didden]

Originally Posted by Rod Coleman

OK, but what about the effects in the real application?

Consider two preamps, mounted on similar shelves. One has a Heavy, stiff chassis, one has a consumer-grade 0.7mm thick chassis, maybe with enough stiffening to prevent it from twisting when you pick it up.

Fire identical acoustic waves from a loudspeaker at each, from say 2m.

Which chassis transmits more of the incident acoustic energy to a circuit board inside the chassis, mounted on identical pillars?

Don't know, and I would venture that none here have really looked at this in some systematical way.

Then again, what would the effect be of the vibrations on the PCB? How about all that presumably high-end stuff with mains transformers mounted on a PCB? Or, (gasp) mains transformers mounted on the chassis, using the chassis as a sound board?
Point is, there so much speculation here it would put a stock exchange veteran to shame

jan didden

[EUVL]

> Which chassis transmits more of the incident acoustic energy to a circuit board inside the chassis, mounted on identical pillars?

I wonder if you would be interested in energy or vibration amplitude (displacement)..

In any case, energy is force x displacement.
Force is pressure x area, so same in both cases, I assume.
Vibration amplitude is less for higher masses and higher stiffness for the same force.

As a first approximation, you can assume that the PCB will follow the case, vibrationally.

Guess you can draw your own nconclusions.

Patrick

[ThorstenL]

Hi,

Originally Posted by janneman

Don't know, and I would venture that none here have really looked at this in some systematical way.

You may venture.

Originally Posted by janneman

Then again, what would the effect be of the vibrations on the PCB? How about all that presumably high-end stuff with mains transformers mounted on a PCB?

Measurable additional noise at the mains frequency and multiples. It is often mistaken for being due to electrical/magnetic pickup and one can spend amusing lucubrations trying to reduce them...

Originally Posted by janneman

Or, (gasp) mains transformers mounted on the chassis, using the chassis as a sound board?

Well, there one often gets a lot of noise being radiated by these sound boards.

I once walked into a shop, being really annoyed by the loud buzzing noise. I eventually traced it to BOTH of the very big and very expensive M..... [brand deleted to protect the innocents] monoblocks...

Originally Posted by janneman

Point is, there so much speculation here it would put a stock exchange veteran to shame

Indeed, the problem is there are too many here intend on scoring points in the defencing (I use the archaic form of the word on purpose) of indefensible positions (like that all that High End stuff is BS, that cheap components are as good as expensive ones, that thin sheet metal chassis are as good as more solid ones and that everything sounds the same anyway).

If they actually occasionally stopped to think about things and asked themselves some questions they might find that the world is by far more complex and as a result interesting place than they imagined...

But most prefer false certainties to true uncertainties...

Ciao T

[Rod Coleman]

Originally Posted by EUVL

> Which chassis transmits more of the incident acoustic energy to a circuit board inside the chassis, mounted on identical pillars?

I wonder if you would be interested in energy or vibration amplitude (displacement)..

In any case, energy is force x displacement.
Force is pressure x area, so same in both cases, I assume.
Vibration amplitude is less for higher masses and higher stiffness for the same force.

As a first approximation, you can assume that the PCB will follow the case, vibrationally.

Guess you can draw your own nconclusions.

Patrick

I think you can, too.

The stiffer, higher mass chassis face will reflect greater proportion of the incident energy. The flimsy chassis will be displaced, and transmit energy to the internals mounted to them, and reflect less.

Whether one believes this matters is up to the designer of the product.

John clearly believes it is important, and so would-be designers of high performance audio may do well to investigate it further, and decide for themselves whether it is worth pursuing. To be clear, I do not suggest that one should copy what John does, but to investigate, weigh and consider.

The effect upon various capacitors, and other components of acoustic energy has been noted here and widely elsewhere, and would be part of the evaluation.

So, Jan, there may be some speculation involved to begin with, but product design often begins with speculation. It's what you do next that counts - evaluation, comparison, redesign, and testing the finished article for fitness for its intended purpose. John's doing something right.