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Author Topic: U47: Does Supply Voltage Have An Effect On Sound?  (Read 2337 times)

Kai

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Re: U47: Does B+ voltage have an effect on sound?
« Reply #30 on: December 10, 2020, 05:39:24 pm »

... (for example: transformers in NG don't shorten with time and age, and output voltages creep up with time for entirely different reasons).
The author correctly mentiones that shorted windings in a transformer CANNOT work to boost output voltage, instead makes it unusable.
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klaus

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Re: U47: Does Supply Voltage Have An Effect On Sound?
« Reply #31 on: December 10, 2020, 08:49:06 pm »

Just to be clear: neither the author nor I LINKED the two. I should have put a semi-colon or period between the two statements. 
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Klaus Heyne
German Masterworks®
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Kai

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Re: U47: Does Supply Voltage Have An Effect On Sound?
« Reply #32 on: December 11, 2020, 12:30:03 pm »

A question that arises in this context:
Klaus, have you ever experienced a U47 capsule broken by overvoltage?

I guess 75 or 85 V (at worst) are too low for arcing and creating burned, conductive traces, but ...

But, what happens to the capsule when the tube filament breaks  - does that happen in a way that it becomes open circuit, practically?
You could see maybe 150 V bias without the tube load.

Ever faced something like that?
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klaus

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Re: U47: Does Supply Voltage Have An Effect On Sound?
« Reply #33 on: December 11, 2020, 01:48:35 pm »

I have not.
This brings up the old "let's fix a problem that should (but does not) exist" issue: to what extent should we design systems and their components for problems that in theory should exist but in practice never occur?

I am reminded of the many unnecessary replacements of filter capacitors in Neumann NG power supplies by "techs" not familiar with the model - the kind of tech who assumes electrolyte leaking out of the capacitors' vent holes in NG supplies indicates that they need to be replaced...

Or the "tech" who sees a crack in the plastic of the original blue rectifier of NU67 power supplies and assumes it's shot and must be replaced...

Or the "tech" who replaces all capacitors in mics, insisting a "recap" is in order...

In these instances and in many more, the level of the tech's experience, rather than broad theoretical ideas determine whether repairs are really needed. That's why the term "tech" sometimes warrants quotation marks.

One could even argue that applying a more rigorous scientific approach, rather than acting on "what we generally know to be true" would lead to the same conclusion (to act or not) as that of extensive experience alone*: "recapping" (i.e. replacing capacitors) of studio consoles makes sense. Components deteriorate from stress inflicted by heat cycling, current flowing through them, etc. It makes less or no sense to periodically replace components that are un-stressed and idling, with minimal current flowing through them (microphones).

Then there is the 800-pound gorilla in the room: a tech who sees a "problem" as justification to make money (subject for another thread).

*Hyundai records even the smallest technical or cosmetic flaw detected during final inspections off the assembly line: corrections are implemented immediately that benefit all future cars coming down the line. The practical augments, sometimes even drives, the theoretical.
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Klaus Heyne
German Masterworks®
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Kai

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Re: U47: Does Supply Voltage Have An Effect On Sound?
« Reply #34 on: December 11, 2020, 05:57:57 pm »

Very few of my vintage mics have had a component replaced.
The longevity of those is astonishing.
That's true for a lot of stuff from that era.

Later on, about end of the 70s, components began to shrink in size.
Mainly electrolytic capacitors suffer from not enough knowledge in construction or even installation.
The killer are bent capacitor pins where they leave their case (e.g. to fit circuitboard mounting holes with wrong spacing).
This damages the seal and makes the cap leak for sure.

I guess these are the main reasons why it's necessary to recap lots of 1980s+ large scale consoles.
Only after the turn of the millennium things started to partly become better on the capacitor front.
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