Home |
Search |
Today's Posts |
|
#1
Posted to rec.audio.pro
|
|||
|
|||
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 |
#2
Posted to rec.audio.pro
|
|||
|
|||
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." |
#3
Posted to rec.audio.pro
|
|||
|
|||
Input transformer for Spectra Sonics 101 preamp
|
#5
Posted to rec.audio.pro
|
|||
|
|||
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
Posted to rec.audio.pro
|
|||
|
|||
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
Posted to rec.audio.pro
|
|||
|
|||
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
Posted to rec.audio.pro
|
|||
|
|||
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." |
#9
Posted to rec.audio.pro
|
|||
|
|||
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 |
#10
Posted to rec.audio.pro
|
|||
|
|||
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 |
#11
Posted to rec.audio.pro
|
|||
|
|||
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 |
#12
Posted to rec.audio.pro
|
|||
|
|||
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 |
#13
Posted to rec.audio.pro
|
|||
|
|||
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 |
#14
Posted to rec.audio.pro
|
|||
|
|||
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 |
Reply |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Spectra Sonics 610 Complimiter? | Pro Audio | |||
Spectra Sonics console | Tech | |||
Spectra Sonics console | Pro Audio | |||
FS: Spectra Sonics 610 Complimiter | Tech | |||
FS: Spectra Sonics 610 complimiter | Pro Audio |