Remote power supplies

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Lurcher300b
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Re: Remote power supplies

Unread post by Lurcher300b »

Yep, just be aware "noise" in this context is not always something you can hear from the speakers. Its why I measure things, but each to their own.

Daniel Quinn
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Re: Remote power supplies

Unread post by Daniel Quinn »

If you can't hear it, why bother?

Lurcher300b
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Re: Remote power supplies

Unread post by Lurcher300b »

Because, just because you can't hear something, doesn't mean that its effect on the sound cant be heard. However it can be much harder to know what is causing the difference in sound.

Simple and old example, the pilot tone from a FM decoder. Not audible, until you record the output on a tape recorder, when the bias frequency on the record head could beat with the pilot tone and create an audible result.

Geoff.R.G
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Re: Remote power supplies

Unread post by Geoff.R.G »

Lurcher300b wrote: Tue Sep 03, 2019 3:00 pm Because, just because you can't hear something, doesn't mean that its effect on the sound cant be heard. However it can be much harder to know what is causing the difference in sound.

Simple and old example, the pilot tone from a FM decoder. Not audible, until you record the output on a tape recorder, when the bias frequency on the record head could beat with the pilot tone and create an audible result.
Quite right. Additionally, noise is an unwanted use of energy so, if you have inaudible noise on the input and pass it through an amplifier you are diverting some of the available power to amplifying the noise. Additionally that power needs to be dissipated in the output transistors. The whole amplifier runs hotter and there is less power to deliver transients cleanly. Amplifying noise is similar to driving a car with a roof rack fitted, the performance is affected, you burn more fuel but you don't have to put in the effort or removing the problem.

Lurcher300b
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Re: Remote power supplies

Unread post by Lurcher300b »

Geoff.R.G wrote: Wed Sep 04, 2019 8:10 am
Lurcher300b wrote: Tue Sep 03, 2019 3:00 pm Because, just because you can't hear something, doesn't mean that its effect on the sound cant be heard. However it can be much harder to know what is causing the difference in sound.

Simple and old example, the pilot tone from a FM decoder. Not audible, until you record the output on a tape recorder, when the bias frequency on the record head could beat with the pilot tone and create an audible result.
Quite right. Additionally, noise is an unwanted use of energy so, if you have inaudible noise on the input and pass it through an amplifier you are diverting some of the available power to amplifying the noise. Additionally that power needs to be dissipated in the output transistors. The whole amplifier runs hotter and there is less power to deliver transients cleanly. Amplifying noise is similar to driving a car with a roof rack fitted, the performance is affected, you burn more fuel but you don't have to put in the effort or removing the problem.
And all that assumes the amplifier is linear.

valvesRus
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Re: Remote power supplies

Unread post by valvesRus »

The more I think I know the more I realise how much I don't know. :)

Geoff.R.G
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Re: Remote power supplies

Unread post by Geoff.R.G »

valvesRus wrote: Wed Sep 04, 2019 11:39 am The more I think I know the more I realise how much I don't know. :)
Don't feel too bad about that, I have spent the last 1/2 hour reviewing non-linear amplification, it is over 30 years since I did any in-depth radio study and much has changed in that time. Class D, and above, amplifiers for example just weren't readily available and certainly weren't on the CAA Cat R license syllabus. A quick look on Amazon suggests that there are some sold for Hi-Fi use, not that I have tried any of them.

Geoff.R.G
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Re: Remote power supplies

Unread post by Geoff.R.G »

Lurcher300b wrote: Tue Sep 03, 2019 2:23 pm Yep, just be aware "noise" in this context is not always something you can hear from the speakers. Its why I measure things, but each to their own.
I have no objections to measurement, or the use of a 'scope if that is what gets the job done. The 19KHz pilot tone can be seen on an instrument even if it can't be heard.

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Re: Remote power supplies

Unread post by _D_S_J_R_ »

My own experience is that hum is a real possible problem with MC stages when the gain is so high on low level signals. DQ posted about the transformer cover he found useful in his Phono 1 with built in transformer and now set for MC. I believe that toroids have a kind of fig 8-shaped magnetic field (Lurcher help please), so separating the supply laterally may actually be slightly better if space allows for an MC phono stage.

Not sure power amps are as critical and again, if toroids are used, fitting transformer cases may well aid if aid is needed. NVA amps of all sizes are hardly hum prone and these with large adjacent transformers.
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karatestu
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Re: Remote power supplies

Unread post by karatestu »

Dave - i found moving transformers further away brought benefits even when there was no hum to start with.
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