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Input transformer for Spectra Sonics 101 preamp



 
 
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  #1  
Old November 27th 19, 04:14 AM posted to rec.audio.pro
Rick Ruskin[_2_]
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Posts: 7
Default 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

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  #2  
Old November 27th 19, 03:28 PM posted to rec.audio.pro
Scott Dorsey
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Posts: 16,655
Default 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."
  #5  
Old November 27th 19, 05:17 PM posted to rec.audio.pro
[email protected]
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Posts: 609
Default 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

  #6  
Old November 28th 19, 05:07 PM posted to rec.audio.pro
Scott Dorsey
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Posts: 16,655
Default 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."
  #7  
Old November 28th 19, 10:16 PM posted to rec.audio.pro
Rick Ruskin[_2_]
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Posts: 7
Default 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
  #8  
Old November 29th 19, 01:20 AM posted to rec.audio.pro
Phil Allison[_4_]
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Posts: 457
Default 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
  #9  
Old November 29th 19, 01:26 AM posted to rec.audio.pro
geoff
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Posts: 1,546
Default 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
  #10  
Old November 29th 19, 03:43 AM posted to rec.audio.pro
Rick Ruskin[_2_]
external usenet poster
 
Posts: 7
Default 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

 




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