Is my LT44 transformer suitable for audio (de)coupling?

Heh heh. But I'll guarantee which one sounds better...

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    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

"Don Pearce" Poopie Bear

** More totally asinine crapology from the Pommy RF Fool.

Audio band white noise is totally dominated by high frequency noise !!

Hence - there is no audible "rumble noise" from mic pres based on op-amps or transistors.

** With a FET ?

With a 200 ohms source ??

What drugs is this FUCKING JERK taking ???

Or not taking ??

** Some condenser mics have very low output Zs - less than 20 ohms.

Not wrong to quite the noise for that case.

.......... Phil

Last time I played with this idea I found it very sensitive to RF interference.

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*Always borrow money from pessimists - they don\'t expect it back *

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

I wouldn't put money on that if I were you. I've measured the performance of the Behringer, and I can find no fault with it. It has problems, of course, but they are limitations imposed by cheap implementation - certainly not in the sound department.

d

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Pearce Consulting
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"Dave Plowman (No-News)"

** Matching the source and load impedances RF style does that !!

You Bloody IDIOT !!

......... Phil

Well, there should have been nothing inherently RF sensitive about it. Like any other sensitive system, it needs all the usual RF-proofing tweaks to keep it sane.

d

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Pearce Consulting
http://www.pearce.uk.com

Even if that were correct it is immaterial in most situations where the gain is not set to maximum (and that is the ONLY place a mic amp achieves an equivalent input figure this good). As gain is reduced, output noise begins to dominate and the old Neve mixers still beat most 'modern' designs in that respect.

Put simply, equivalent input noise is only part of the story.

ian

Not that is really matters. An improvement in noise figure of 2.5dB will only improve the signal to noise at very high gains by the same amount. Unless you are using dynamics on very quiet sources, the self noise of your condensor mic is the limiting factor not the noise figure of the mic pre.

Ian

Its a lot easier to reduce the noise figure at a narrow bandwidth at microwave frequencies.

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Member of DAV #85.

Michael A. Terrell
Central Florida

Narrow bandwidth? I don't call a bandwidth of nearly 2GHz narrow. And asitappens, I can achieve these sorts of figure at audio as well.

d

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Pearce Consulting
http://www.pearce.uk.com

2 GHz at 12 GHz is 16.67% which is narrow. Don't tell me that there is no filtering at all. A circulator or isolator has a usable bandwidth which keeps out of band noise out of the amp. One of my KU band receivers is aboard the ISS.

Audio is true broadband, from DC to whatever the upper limit is set at by the design and limitations of the components if it is DC coupled, and from less than 100 Hz if its AC coupled.

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prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Don't these things tend to be measured in octaves, as it were?

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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW To e-mail, change noise into sound.

Not only that, but at low to DC freqs., the noise increases dramatically of most devices. When looking at op-amps I have to often look at DC drifts, which is the largest noise.

greg

Of course there is filtering. The waveguide coupler as a bandwidth, as does the mixer. The image filter then has a bandwidth, and finally the IF amplifier. Despite all this filtering - none of which is lossless - the noise figure still happens. It really isn't easy even compared to audio. Well done for having a receiver aboard ISS, but ground transmitters tend not to be particularly power-limited, so the noise figure probably isn't quite the issue it is with a terrestrial receiver. In fact there would be no point because it is pointing at the earth, which is hot.

But achieving low noise at audio - however you want to describe its bandwidth - is actually pretty trivial. The fact is that manufacturers choose not to implement it because they can make something that is "reasonable" for a lot less money. The business of achieving low noise at audio doesn't rely on being able to juggle S parameters, physical layout, board materials and mechanical design like microwave.

d

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Pearce Consulting
http://www.pearce.uk.com

Yes, but remember we are talking about scraping away at the last vestiges of the state of the art here. Optimum noise match varies over that range, and designing matching structures that keep the complex impedance of the waveguide transition at the exact conjugate of the input transistor noise match over such a bandwidth really is far from simple. By comparison audio is a breeze - I promise.

d

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Pearce Consulting
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"GregS"

** All way outside the audio band and not even slightly relevant since noise is proportional to the square root of the bandwidth.

The band from 0 to 20 Hz has a mere 20 Hz bandwidth !

The audio band is 20,000 Hz wide !!!!!!

So, some 31 times more noise energy audible as high frequency hiss.

** Drivel.

DC drift is due to temp variations.

It is separate from noise.

...... Phil

NO No NO. Look at it on a scope. Look at the charts.

greg

"Dave Plowman (News)"

** Bandwidth in *electronics* is normally quoted in Hz, kHz, MHz, GHz etc.

Octaves are a musical notion, so not used much outside of audio and acoustics.

....... Phil

"GregS"

** Noise is noise - not drift.

You ignored all my other points so I guess you have no clue what the f*ck you are on about.

....... Phil