John Curl's Blowtorch preamplifier

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#17,324
VivaVee said:


Safety has been improved by changing the standard Australian/NZ/European mains scheme which has a single phase 230V referred to ground to a system that has two phases with 115V referred to ground.

Lesser volts means fewer bodies, everything else being equal.

This two phase system for getting 230V will be familiar to US engineers (well, electricians anyway) as standard indistrial practice.
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My proposal really was just for a 1:1 isolation transformer at the mains input of the amplifier. For saftey, the secondary circuit must always be earthed to prevent the amplifier circuitry from becoming live in the event of a primary-secondary breakdown of the transformer.
By adding an isolation transformer, its secondary circuit can be earthed instead of the power supply for the amplifier, avoiding the mains earth ground loop.
The isolation transformer from Farnell just happens to have twin 115V secondaries and the centre connection is just a convenient point to return to earth.

Cheers,
Glen
 
#17,328
hitsware
please do not make this type of comment.

One line of a secondary has to be earthed per code. Whether it's the earth or neutral. With balanced power there is no neutral, hence, the reason to earth the center tap of the secondary of the 1:1.

And a toaster is a double insulated device that has passed lots of UL/CSA/VDE testing. DIY products do not get this type of testing and many diyers do not understand what agency approval/recognition means to say nothing of building gear to the UL standards like; creepage and clearances, hi pot testing, leakage, etc etc.

There are also safety reasons why items like a toaster do no have an earth.

I do compliance engineering for the day job...
Mike
 
#17,329
hitsware said:
>For saftey, the secondary circuit must always
>be earthed to prevent the amplifier circuitry
>from becoming live in the event of a
>primary-secondary breakdown of the transformer.

How likely is that ?
If that possibility worries you then
DO NOT use your toaster !
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A very intelligent comment. Thank you.
 
#17,330
john curl said:
Well, here you go again, Scott. Criticizing the efforts of others. Maybe YOU couldn't hear any other differences, so what?
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Well who did I criticize? I even admitted that I sort of convinced myself that a couple of the changes improved a stock unit. You already told me that my choice of equipment doesn't empower me to comment on the audibility of anything subtle. I contribute what little I can here based on 35yr. of designing amplifiers for some tough customers with about $350M in product shipped.

You know we just had a company wide technical "jam session" and one grumpy 60yr old designer got up in public and told some 20 something guy that he wished he had thought of his trick and said he took it right back to his lab to use it. Not much of that attitude here.

BTW it was a nifty new fully complimentary current mirror that might even pass a prior art search. I know people appriciate that I can't share the best stuff because it does not belong to me.
 
#17,331
Figure I better explain a little more.

A step down xfmr like we use will probably be a class 2 unit. This means that it's thermally protected if the secondary shorts; i.e. either it will current limit below a certain VA rating or the secondary will open or in some units there is a thermal breaker inserted into the secondary. Opening of the secondary is a safety failure mode.

For a 1:1 xfmr current limiting can be done but usually isn't due to cost. Yes, it will limit, but at a level that can be dangerous.

So, if the secondary is shorted to earth there isn't anything to limit current, at least not within a time frame that would be considered safe.

Before I get flamed; there are exceptions to this, if you know what the exceptions are then you understand, if not, then please follow agency safety rules.
 
#17,332
Mike Gergen said:
Figure I better explain a little more.

A step down xfmr like we use will probably be a class 2 unit. This means that it's thermally protected if the secondary shorts; i.e. either it will current limit below a certain VA rating or the secondary will open or in some units there is a thermal breaker inserted into the secondary. Opening of the secondary is a safety failure mode.

For a 1:1 xfmr current limiting can be done but usually isn't due to cost. Yes, it will limit, but at a level that can be dangerous.

So, if the secondary is shorted to earth there isn't anything to limit current, at least not within a time frame that would be considered safe.

Before I get flamed; there are exceptions to this, if you know what the exceptions are then you understand, if not, then please follow agency safety rules.
Click to expand...


Surely a primary fuse (which is mandatory anyway) on the 1:1 is sufficient?
 
#17,337
Wall of Sound

John, let me switch gear

Let me ask you, what is the wall of sound?

Is it the Wall of Sound - music production technique for pop and rock music recordings developed by record producer Phil Spector at Gold Star Studios during the 1960s.

http://en.wikipedia.org/wiki/Wall_of_Sound

or

The Wall of Sound was an enormous public address system designed specifically for the Grateful Dead's live performances by legendary audio engineer and LSD chemist Owsley "Bear" Stanley. The Wall of Sound fulfilled the band's desire for a distortion-free sound system that could also serve as its own monitoring system.

http://en.wikipedia.org/wiki/Wall_of_Sound_(Grateful_Dead)

Is it our lovely Bear, who has magic silver wire?
 
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