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

Rick Ruskin[_2_] November 27th 19 03:14 AM

Input transformer for Spectra Sonics 101 preamp
 
I have a trio of racked 101 preamps with 502 eq's. Can anyone
recommend an input transformer with a reasonable step-up to increase
the gain up from the 40db max they deliver now?

RR


Scott Dorsey November 27th 19 02:28 PM

Input transformer for Spectra Sonics 101 preamp
 
Rick Ruskin > wrote:
>I have a trio of racked 101 preamps with 502 eq's. Can anyone
>recommend an input transformer with a reasonable step-up to increase
>the gain up from the 40db max they deliver now?


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.
Not that a 1:1 transformer might not help the miserable CMRR on those things.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Rick Ruskin[_2_] November 27th 19 03:49 PM

Input transformer for Spectra Sonics 101 preamp
 
On 27 Nov 2019 09:28:21 -0500, (Scott Dorsey) wrote:

>Rick Ruskin > wrote:
>>I have a trio of racked 101 preamps with 502 eq's. Can anyone
>>recommend an input transformer with a reasonable step-up to increase
>>the gain up from the 40db max they deliver now?

>
>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.
>Not that a 1:1 transformer might not help the miserable CMRR on those things.
>--scott



The current version of these units state 64db of gain with the same
101 card. Where is the extra gain coming from?

RR

Don Pearce[_3_] November 27th 19 03:59 PM

Input transformer for Spectra Sonics 101 preamp
 
On Wed, 27 Nov 2019 15:49:00 +0000 (UTC), Rick Ruskin
> wrote:

>On 27 Nov 2019 09:28:21 -0500, (Scott Dorsey) wrote:
>
>>Rick Ruskin > wrote:
>>>I have a trio of racked 101 preamps with 502 eq's. Can anyone
>>>recommend an input transformer with a reasonable step-up to increase
>>>the gain up from the 40db max they deliver now?

>>
>>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.
>>Not that a 1:1 transformer might not help the miserable CMRR on those things.
>>--scott

>
>
>The current version of these units state 64db of gain with the same
>101 card. Where is the extra gain coming from?
>
>RR


Probably an extra stage of amplification, or if the design allows, a
change of feedback resistors to get more gain from the existing
circuit.

d

[email protected] November 27th 19 04:17 PM

Input transformer for Spectra Sonics 101 preamp
 

> >The current version of these units state 64db of gain with the same
> >101 card. Where is the extra gain coming from?
> >
> >RR

>
> Probably an extra stage of amplification, or if the design allows, a
> change of feedback resistors to get more gain from the existing
> circuit.
>
> d


some info here
https://groupdiy.com/index.php?topic=11466.0

m


Scott Dorsey November 28th 19 04:07 PM

Input transformer for Spectra Sonics 101 preamp
 
Rick Ruskin > wrote:
>On 27 Nov 2019 09:28:21 -0500, (Scott Dorsey) wrote:
>>Rick Ruskin > wrote:
>>>I have a trio of racked 101 preamps with 502 eq's. Can anyone
>>>recommend an input transformer with a reasonable step-up to increase
>>>the gain up from the 40db max they deliver now?

>>
>>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.
>>Not that a 1:1 transformer might not help the miserable CMRR on those things.

>
>The current version of these units state 64db of gain with the same
>101 card. Where is the extra gain coming from?


Who knows? Folks butcher perfectly good consoles, stick the modules into
boxes and God only knows what they do from that point. There are all kinds
of ways you might modify them to get more gain out of them.

The 101 was a general purpose gain module... you could use it as make up
gain on a mix buss, or make-up after a passive equalizer. Using it as
a mike preamp is a bit of stretch but certainly Spectrasonics did on some
models.

These were intended for 600 ohm inputs and 600 ohm outputs since they
would likely be buried in the middle of a long console signal chain. So
if you want to get a little more voltage gain out and you're not driving
a 600 ohm load, you might get away with a step-up transformer on the
-output-, maybe stepping it up to 5kohms which woould be fine to drive a
lot of modern gear.

You might be able to tweak some resistor values on the board too, and get
a little more gain out of the design at the expense of linearity. 40dB
is an awful lot for this design already, though. And it wouldn't be a
Spectrasonics 101 any longer, it would be something else.

If it were me, I'd put a balanced input stage in front of the thing,
two nice large area transistors with a few dB of gain, maybe stick a
little global feedback around it. But of course then it wouldn't be just
a Spectrasonics 101 anymore either.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Rick Ruskin[_2_] November 28th 19 09:16 PM

Input transformer for Spectra Sonics 101 preamp
 
On 28 Nov 2019 11:07:08 -0500, (Scott Dorsey) wrote:

>Rick Ruskin > wrote:
>>On 27 Nov 2019 09:28:21 -0500,
(Scott Dorsey) wrote:
>>>Rick Ruskin > wrote:
>>>>I have a trio of racked 101 preamps with 502 eq's. Can anyone
>>>>recommend an input transformer with a reasonable step-up to increase
>>>>the gain up from the 40db max they deliver now?
>>>
>>>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.
>>>Not that a 1:1 transformer might not help the miserable CMRR on those things.

>>
>>The current version of these units state 64db of gain with the same
>>101 card. Where is the extra gain coming from?

>
>Who knows? Folks butcher perfectly good consoles, stick the modules into
>boxes and God only knows what they do from that point. There are all kinds
>of ways you might modify them to get more gain out of them.
>
>The 101 was a general purpose gain module... you could use it as make up
>gain on a mix buss, or make-up after a passive equalizer. Using it as
>a mike preamp is a bit of stretch but certainly Spectrasonics did on some
>models.
>
>These were intended for 600 ohm inputs and 600 ohm outputs since they
>would likely be buried in the middle of a long console signal chain. So
>if you want to get a little more voltage gain out and you're not driving
>a 600 ohm load, you might get away with a step-up transformer on the
>-output-, maybe stepping it up to 5kohms which woould be fine to drive a
>lot of modern gear.
>
>You might be able to tweak some resistor values on the board too, and get
>a little more gain out of the design at the expense of linearity. 40dB
>is an awful lot for this design already, though. And it wouldn't be a
>Spectrasonics 101 any longer, it would be something else.
>
>If it were me, I'd put a balanced input stage in front of the thing,
>two nice large area transistors with a few dB of gain, maybe stick a
>little global feedback around it. But of course then it wouldn't be just
>a Spectrasonics 101 anymore either.
>--scott





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?

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

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

RR

Phil Allison[_4_] November 29th 19 12:20 AM

Input transformer for Spectra Sonics 101 preamp
 
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

geoff November 29th 19 12:26 AM

Input transformer for Spectra Sonics 101 preamp
 
On 29/11/2019 1:20 pm, 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
>



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

geoff

Rick Ruskin[_2_] November 29th 19 02:43 AM

Input transformer for Spectra Sonics 101 preamp
 
On Thu, 28 Nov 2019 16:20:10 -0800 (PST), 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.


You know this for a fact or are you making an assumption?
>
> An input tranny that gave 10dB more gain would reduce the impedance to 60 ohms. Way to low for any modern mic.


Ok. That's an answer I can understand.
>
>
>You won't take no for an answer - will you ?


I'm merely asking for info and advice. You can take the snarkiness
and shove it up your ass.

RR


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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