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-   -   Input transformer for Spectra Sonics 101 preamp (http://www.audiobanter.com/showthread.php?t=141841)

Rick Ruskin[_2_] November 29th 19 02:45 AM

Input transformer for Spectra Sonics 101 preamp
 
On Fri, 29 Nov 2019 13:26:05 +1300, geoff >
wrote:

>With all this effort into turd-polishing I can't help but wonder "why ?".
>
>geoff


I like the way they sound but find them too gain shy for certain mics.

RR


Scott Dorsey November 29th 19 03:46 AM

Input transformer for Spectra Sonics 101 preamp
 
Rick Ruskin > wrote:
>
>Are you saying that a step-up transformer on the input simply will not
>work or just that it will alter the performance of the card?


The step-up transformer doesn't give you free gain.... power is conserved
so there is no way to get power out of nowhere.

What the step-up transformer can do is to match a low-impedance load to
a high impedance load, so you lose less power in the process. This works
well if the load is severely mismatched (say, a microphone that wants to
see 600 ohms going into a 1M tube stage) but if the load is already matched it
doesn't help any.

>Would adding a resistor to the feedback loop along with the 502 eq
>that is already there do anything to increase gain?


Dunno, I'd have to sit down and do the math.

>As far as I know, the 101 was used as the front end on all
>Spectra sonics consoles until the 110 came along.


It was. It was also used as make-up gain for all kinds of other things.
It was a handy general-purpose gain module.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Phil Allison[_4_] November 29th 19 05:35 AM

Input transformer for Spectra Sonics 101 preamp
 
Scott Dorsey wrote:

---------------------


> >As far as I know, the 101 was used as the front end on all
> >Spectra sonics consoles until the 110 came along.

>
> It was. It was also used as make-up gain for all kinds of other things.
> It was a handy general-purpose gain module.
>



** We talking about the same manufacturer who sold thousand of cheap and nasty, 19inch rack mount, stereo power amplifiers back in the 1970s ?

Those things were plain horrible, almost total rubbish.

Made Phase Linear, SAE, Dynaco 400 kits and even local maker's products look classy by comparison.



..... Phil





Rick Ruskin[_2_] November 29th 19 06:45 AM

Input transformer for Spectra Sonics 101 preamp
 
On Thu, 28 Nov 2019 21:35:18 -0800 (PST), Phil Allison
> wrote:

>Scott Dorsey wrote:
>
>---------------------
>
>
>> >As far as I know, the 101 was used as the front end on all
>> >Spectra sonics consoles until the 110 came along.

>>
>> It was. It was also used as make-up gain for all kinds of other things.
>> It was a handy general-purpose gain module.
>>

>
>
>** We talking about the same manufacturer who sold thousand of cheap and nasty, 19inch rack mount, stereo power amplifiers back in the 1970s ?
>
>Those things were plain horrible, almost total rubbish.
>
>Made Phase Linear, SAE, Dynaco 400 kits and even local maker's products look classy by comparison.
>
>
>
>.... Phil


I'm talking about the company founded by Bill Dilley that built parts
(preamps, eq's, line amps, power supplies; etc.) that Flickenger,
Auditronics, and others used to build consoles. They also built
theirr own consoles and the 610 complimiter, among other audio
devices. If they made any of the cheap gear you're thinking of, they
didn't do it under the Spectra Sonics brand.

RR

Phil Allison[_4_] November 29th 19 09:36 AM

Input transformer for Spectra Sonics 101 preamp
 
Rick Ruskin wrote:

-----------------
>
> Phil Allison


> >
> > ** We talking about the same manufacturer who sold thousand of
> > cheap and nasty, 19inch rack mount, stereo power amplifiers
> > back in the 1970s ?
> >
> > Those things were plain horrible, almost total rubbish.
> >
> > Made Phase Linear, SAE, Dynaco 400 kits and even local maker's
> > products look classy by comparison.
> >
> >
> >
> >.... Phil

>
>
> I'm talking about the company founded by Bill Dilley that built parts
> (preamps, eq's, line amps, power supplies; etc.) that Flickenger,
> Auditronics, and others used to build consoles. They also built
> theirr own consoles and the 610 complimiter, among other audio
> devices. If they made any of the cheap gear you're thinking of, they
> didn't do it under the Spectra Sonics brand.
>


** You are 100% correct !

I was thunk'n bout "Spectro Acoustics".

Who made POS like you see in this U-tube:


https://www.youtube.com/watch?v=e438136yRss


Gives me the heebie jeebies just lookn'.



..... rgds, Phil





[email protected] November 29th 19 07:32 PM

Input transformer for Spectra Sonics 101 preamp
 
On Thursday, November 28, 2019 at 7:20:13 PM UTC-5, Phil Allison wrote:
> Rick Ruskin wrote:
>
> -------------------
> >
> > >
> > >No, because the input impedance on those is already 600 ohms. It is
> > >dominated by the emitter resistor on Q1. If you put a step-up transformer
> > >on there, you get an even lower input impedance which is probably not
> > >what you want.
> > >
> > >There's no free gain to be had here.

> >
> >
> >
> > The current version of these units state 64db of gain with the same
> > 101 card.

>
>
> ** Bull****, it ain't the same card.
>
> An input tranny that gave 10dB more gain would reduce the impedance to 60 ohms. Way to low for any modern mic.
>
>
> You won't take no for an answer - will you ?
>
>
> ..... Phil


10dB effective gain would require a 3.33:1 turns ratio which would reduce the Z from 600 to about 180 Ohms.
m



Phil Allison[_4_] November 29th 19 11:09 PM

Input transformer for Spectra Sonics 101 preamp
 
wrote:

-------------------------
>
> >
> > ** Bull****, it ain't the same card.
> >
> > An input tranny that gave 10dB more gain would reduce the impedance
> > to 60 ohms. Way to low for any modern mic.
> >
> >
> > You won't take no for an answer - will you ?
> >
> >

**------------------------------------
>
>
> 10dB effective gain would require a 3.33:1 turns ratio



** 10dB = 10^0.5 = 3.16


> which would reduce the Z from 600 to about 180 Ohms.



** Absurd since impedance varies with the SQUARE of the turns ratio.

Plus defies "conservation of energy" as +10dB is a 10 times power
increase so the same voltage must be fed into a load resistance 10 times lower.

From 600 to 60 ohm.


..... Phil


[email protected] December 2nd 19 03:14 AM

Input transformer for Spectra Sonics 101 preamp
 
Phil, you are correct.
My error.
Mark


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