What is responsible for soundstage in a preamp design?

[user 133392]

Les Tyler and I wrote a brief history of active mic preamps and the Demrow/Cohen topology in "The Handbook for Sound Engineers Ed 4." It begins on pdf page 40: https://www.ka-electronics.com/images/pdf/Ballou_Chapter_12_0601308.pdf#page=40

Cohen's 1984 AES paper: https://proaudiodesignforum.com/images/pdf/Cohen_Double_Balanced_Microphone_Amplifier_AES_1984.pdf

I've seen some really good THAT1510/INA217/SSM2019 designs and I've seen some really bad ones. The ICs are sometimes much better than the layout, component choices, design decisions etc. allow.

 

[k brown]

..."active mic preamps'... ?

 

[user 133392]

..."active mic preamps'... ?

Yes. Added Cohen's 1984 paper.

 

[k brown]

Are there transformers with sufficient gain to make a 'passive' mic preamp?

 

[Ricardus]

I'm starting to think we are being trolled.

I've been thinking it for some time.

As I mentioned to one of the other mods in a PM recently, remember the guy from last month that swore at everyone, and sounded like a home-hifi nut? Well any number of new members are beginning to follow in his footsteps.

And the number of new signups seems unusually high to me in the last few months.

 

[Tubetec]

Why do people here feel the need to continually quote phrases in isolation ,then go on the attack ,
It only invites trolls into the discussion , it serves no other purpose than a divisory circumstance , if you have a point then make it clearly
theres no need to re-hash someone elses garbage in the process ,
I get tired reading re-tweets of the same thing over and over ,
let your argument be self supporting .

Expletives deleted , pardon my undiplomatic tone ,

 

[JohnRoberts]

Are there transformers with sufficient gain to make a 'passive' mic preamp?

Transformers don't have gain, they have turns ratios...

JR

 

[Tubetec]

Free gain over a limited bandwidth , your quite entitled to you opinion too though .

 

[k brown]

I just found it very odd, that paper's author's multiple use of the phrase "active preamp". All mic preamps are active - very strange use of terminology; a transformer input pre does it's unbalancing passively, but that doesn't mean only transformerless pres are 'active'. I think it's just sloppy word craft; 'active preamp' is redundant and unnecessary - and can be misleading to beginners.

I know 'transformerless-input' is more tiring to type, but it's much more accurate.

 

[user 37518]

Why in f**k do people here feel the need to continually quote phrases in isolation ,then go on the attack ,
It only invites trolls into the discussion , it serves no other purpose than a divisory circumstance , if you have a point then make it clearly
theres no need to re-hash someone elses garbage in the process ,
I'm sick to fuck reading re-tweets of the same bullshit over and over ,
let your argument be self supporting or fuck off .

Relax, Tubetec. I know we've had our differences in the past, but no reason to loose control. Don't let people on the Internet (me included) to throw you off balance, I have felt like you do, but take a few steps back and relax.

 

[user 37518]

I just found it very odd, that paper's author's multiple use of the phrase "active preamp". All mic preamps are active - very strange use of terminology; a transformer input pre does it's unbalancing passively, but that doesn't mean only transformerless pres are 'active'. I think it's just sloppy word craft; 'active preamp' is redundant and unnecessary - and can be misleading to beginners.

Magnetic amplifier - Wikipedia You might find it interesting.

 

[user 37518]

Are there transformers with sufficient gain to make a 'passive' mic preamp?

Magnetic amplifier - Wikipedia In a sense, yes. Not by only using a trafo, but in combination with DC supplies

 

[k brown]

Magnetic amplifier - Wikipedia You might find it interesting.

I wasn't speaking theoretically, but about real-world microphone preamps. Has there ever been a 'non-active' mic preamp on the market?

 

[user 37518]

I just found it very odd, that paper's author's multiple use of the phrase "active preamp". All mic preamps are active - very strange use of terminology; a transformer input pre does it's unbalancing passively, but that doesn't mean only transformerless pres are 'active'. I think it's just sloppy word craft; 'active preamp' is redundant and unnecessary - and can be misleading to beginners.

I know 'transformerless-input' is more tiring to type, but it's much more accurate.

See post #131, you might find it interesting

 

[user 37518]

I wasn't speaking theoretically, but about real-world microphone preamps. Has there ever been a 'non-active' mic preamp on the market?

Nothing theoretical about it, they were not that uncommon in the 50s.

 

[k brown]

Nothing theoretical about it, they were not that uncommon in the 50s

How much gain could they provide?

 

[user 37518]

How much gain could they provide?

From Wiki:

A magnetic amplifier was used as voice modulator for a 2 kilowatt Alexanderson alternator,

So I would say that quite a while was possible.

Also, not trying to refute you, I just thought you might find that interesting, that is all.

 

[abbey road d enfer]

let your argument be self supporting or fuck off .

Language, sir!

 

[k brown]

From Wiki:


So I would say that quite a while was possible.

Also, not trying to refute you, I just thought you might find that interesting, that is all.

Indeed.

 

[abbey road d enfer]

Are there transformers with sufficient gain to make a 'passive' mic preamp?

Define "sufficient gain".
I suppose you mean voltage gain.
It depends very much on the level issued by the microphone and the destination of signal.
One could imagine a microphone with an output of about -20dBu. A 1:10 xfmr would elevate the signal to 0dBu, which may qualify as line level, but then it would certainly need at least one active stage to present it to the subsequent circuits, e.g. a magnetic head or the input of a A/D converter.
In order to produce -20dBu, the mic would almost certainly need an active stage, or use a very large transducer which wouldmake it impractical and of dubious use.
At least one active stage is needed in the signal chain.

 

[abbey road d enfer]

I just found it very odd, that paper's author's multiple use of the phrase "active preamp". All mic preamps are active - very strange use of terminology; a transformer input pre does it's unbalancing passively, but that doesn't mean only transformerless pres are 'active'. I think it's just sloppy word craft; 'active preamp' is redundant and unnecessary - and can be misleading to beginners.

"Passive " preamp is a common occurence in HiFi litt.
Googling "passive preamp" returns 11 600 000hits !
Are we wrong?

 

[k brown]

"Passive " preamp is a common occurence in HiFi litt.
Googling "passive preamp" returns 11 600 000hits !
Are we wrong?

Yes, another very sloppy word usage; they're passive enough, but 'preamp'? I suppose in the sense that it comes before an amplifier. ; - )