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Transformer + jfet!John Larkin wrote:
Eeyore wrote:
John Larkin wrote:
Eeyore wrote:
Phil Hobbs wrote:
Eeyore wrote:
National's LME49710/20/40 amd LM4562 seem to have the best figures at
2.5nV/sqrt Hz but in a practical circuit I found the venerable NE5534
with its 3.5 nV/sqrt Hz was quieter, presumably due to lower input noise
current in that particular configuration.
The LMEs also have insanely low THD
RL = 600ohms 0.00003% (typ)
http://www.national.com/pf/LM/LME49710.html
http://www.national.com/pf/LM/LM4562.html
Does anyone know of anything better without sacrificing unity gain
stability or THD ?
What resistance values are you assuming? Not one month ago, in this
very boutique, I posted a link to a new part with some really cute
specs--the ADA4898-1.
http://www.analog.com/static/imported-files/Data_Sheets/ADA4898-1.pdf
I gather it's probably intended for lower source resistances than yours,
but its combination of low eN and low Cin is amazing.
Yes, my source resistance may dominate. It's a new module for SSL 4000E/G
professional sound mixing desks to convert the 'channel buckets' into a
monitor desk for Digital Audio Workstations. I was shocked at how high their
mix resistor values were (15k). Crikey, even at Studiomaster in the latter
days I was using 4k7 !
It's certainly amazingly quiet though.
I'm not familiar with the THD being quoted in dBc though. Can you assist there ?
15K? Sounds like jfet turf.
That's the feedback resistor value in an inverting summing amp thay may be fed from
up to 32 sources simultaneously, giving an Rin of 400 ohms approx.
Just done the sums. Does anyone want to slap me round the face with a wet fish ?
I make 400 ohms 2.6nV/sqrt Hz ! I wasn't expecting it to be that noisy. I didn't
mess up did I ?
That's about right. So the summing resistors are about 400*32 = 12.8K
each. Each input has a gain to the output of a bit over 1. Noise gain
is close to 40.
I wonder if multi-group summing would be any better.
That would be ideal and is a method implemented in some more modern products. In this
case we're stuck with what we have i.e. a single mix bus.
Graham
Do you know how much good audio transformers cost ! I like Lundahls but you get such aEeyore wrote:
John Larkin wrote:
Eeyore wrote:
John Larkin wrote:
Eeyore wrote:
Phil Hobbs wrote:
Eeyore wrote:
National's LME49710/20/40 amd LM4562 seem to have the best figures at
2.5nV/sqrt Hz but in a practical circuit I found the venerable NE5534
with its 3.5 nV/sqrt Hz was quieter, presumably due to lower input noise
current in that particular configuration.
The LMEs also have insanely low THD
RL = 600ohms 0.00003% (typ)
http://www.national.com/pf/LM/LME49710.html
http://www.national.com/pf/LM/LM4562.html
Does anyone know of anything better without sacrificing unity gain
stability or THD ?
What resistance values are you assuming? Not one month ago, in this
very boutique, I posted a link to a new part with some really cute
specs--the ADA4898-1.
http://www.analog.com/static/imported-files/Data_Sheets/ADA4898-1.pdf
I gather it's probably intended for lower source resistances than yours,
but its combination of low eN and low Cin is amazing.
Yes, my source resistance may dominate. It's a new module for SSL 4000E/G
professional sound mixing desks to convert the 'channel buckets' into a
monitor desk for Digital Audio Workstations. I was shocked at how high their
mix resistor values were (15k). Crikey, even at Studiomaster in the latter
days I was using 4k7 !
It's certainly amazingly quiet though.
I'm not familiar with the THD being quoted in dBc though. Can you assist there ?
15K? Sounds like jfet turf.
That's the feedback resistor value in an inverting summing amp thay may be fed from
up to 32 sources simultaneously, giving an Rin of 400 ohms approx.
Just done the sums. Does anyone want to slap me round the face with a wet fish ?
I make 400 ohms 2.6nV/sqrt Hz ! I wasn't expecting it to be that noisy. I didn't
mess up did I ?
That's about right. So the summing resistors are about 400*32 = 12.8K
each. Each input has a gain to the output of a bit over 1. Noise gain
is close to 40.
I wonder if multi-group summing would be any better.
That would be ideal and is a method implemented in some more modern products. In this
case we're stuck with what we have i.e. a single mix bus.
Transformer + jfet!
The noise current will also flow in the input resistors.Eeyore wrote:
ggher...@gmail.com wrote:
Eeyore wrote:
ggher...@gmail.com wrote:
John Larkin wrote:
Eeyore wrote:
Phil Hobbs wrote:
Eeyore wrote:
National's LME49710/20/40 amd LM4562 seem to have the best figures at
2.5nV/sqrt Hz but in a practical circuit I found the venerable NE5534
with its 3.5 nV/sqrt Hz was quieter, presumably due to lower input noise
current in that particular configuration.
The LMEs also have insanely low THD
RL = 600ohms 0.00003% (typ)
http://www.national.com/pf/LM/LME49710.html
http://www.national.com/pf/LM/LM4562.html
Does anyone know of anything better without sacrificing unity gain
stability or THD ?
What resistance values are you assuming? Not one month ago, in this
very boutique, I posted a link to a new part with some really cute
specs--the ADA4898-1.
http://www.analog.com/static/imported-files/Data_Sheets/ADA4898-1.pdf
I gather it's probably intended for lower source resistances than yours,
but its combination of low eN and low Cin is amazing.
Yes, my source resistance may dominate. It's a new module for SSL 4000E/G
professional sound mixing desks to convert the 'channel buckets' into a
monitor desk for Digital Audio Workstations. I was shocked at how high their
mix resistor values were (15k). Crikey, even at Studiomaster in the latter
days I was using 4k7 !
It's certainly amazingly quiet though.
I'm not familiar with the THD being quoted in dBc though. Can you assist there
?
Graham
15K? Sounds like jfet turf.
John-
15K? Sounds like jfet turf.
Yes, Aren't you going to be dominated by the current noise? Speaking
of jfet opamps, Do you have a low noise favorite? I like the OPA134
from Burr-Brown (TI). But am always looking for something better.
George
That depends how many inputs are assigned. As these are going only to be monitoring
desks, the number of inputs will be 24 or 36 typically.
"That depends how many inputs are assigned. As these are going only
to be monitoring
desks, the number of inputs will be 24 or 36 typically.
So the suming node will see ~ 400-600 ohms. Current noise shouldn't be
a problem
here,"
Ahh I see it's one big summing junction. But what is the feedback
resistor? (I know nothing about high end audio stuff.)
Its value, correcting for the gain structure mess-up of the original design will be 7k5,
i.e a voltage gain of around -18x , but must be stable with nothing routed which equates
to a stable gain of -0.5x. I don't see a problem with the stability issues, I thought it
out on the walk back from the supermarket.
" Its value, correcting for the gain structure mess-up of the original
design will be 7k5"
OK I'm still kinda new to noise calculations, but won't the opamp
current noise of 1.5pA/rtHz give you something like 10nV/rtHz at the
output with the 7.5k ohm feedback resistor. Not that bad really given
the voltage noise of the resistor.
Nevertheless shows how critical resistor values are in high-performance audio. This mixing deskggher...@gmail.com wrote:
Eeyore > wrote:
ggher...@gmail.com wrote:
Eeyore wrote:
ggher...@gmail.com wrote:
John Larkin wrote:
Eeyore wrote:
Phil Hobbs wrote:
Eeyore wrote:
National's LME49710/20/40 amd LM4562 seem to have the best figures at
2.5nV/sqrt Hz but in a practical circuit I found the venerable NE5534
with its 3.5 nV/sqrt Hz was quieter, presumably due to lower input noise
current in that particular configuration.
The LMEs also have insanely low THD
RL = 600ohms 0.00003% (typ)
http://www.national.com/pf/LM/LME49710.html
http://www.national.com/pf/LM/LM4562.html
Does anyone know of anything better without sacrificing unity gain
stability or THD ?
What resistance values are you assuming? Not one month ago, in this
very boutique, I posted a link to a new part with some really cute
specs--the ADA4898-1.
http://www.analog.com/static/imported-files/Data_Sheets/ADA4898-1.pdf
I gather it's probably intended for lower source resistances than yours,
but its combination of low eN and low Cin is amazing.
Yes, my source resistance may dominate. It's a new module for SSL 4000E/G
professional sound mixing desks to convert the 'channel buckets' into a
monitor desk for Digital Audio Workstations. I was shocked at how high their
mix resistor values were (15k). Crikey, even at Studiomaster in the latter
days I was using 4k7 !
It's certainly amazingly quiet though.
I'm not familiar with the THD being quoted in dBc though. Can you assist there
?
Graham
15K? Sounds like jfet turf.
John-
15K? Sounds like jfet turf.
Yes, Aren't you going to be dominated by the current noise? Speaking
of jfet opamps, Do you have a low noise favorite? I like the OPA134
from Burr-Brown (TI). But am always looking for something better.
George
That depends how many inputs are assigned. As these are going only to be monitoring
desks, the number of inputs will be 24 or 36 typically.
"That depends how many inputs are assigned. As these are going only
to be monitoring
desks, the number of inputs will be 24 or 36 typically.
So the suming node will see ~ 400-600 ohms. Current noise shouldn't be
a problem
here,"
Ahh I see it's one big summing junction. But what is the feedback
resistor? (I know nothing about high end audio stuff.)
Its value, correcting for the gain structure mess-up of the original design will be 7k5,
i.e a voltage gain of around -18x , but must be stable with nothing routed which equates
to a stable gain of -0.5x. I don't see a problem with the stability issues, I thought it
out on the walk back from the supermarket.
Graham- Hide quoted text -
- Show quoted text -
" Its value, correcting for the gain structure mess-up of the original
design will be 7k5"
OK I'm still kinda new to noise calculations, but won't the opamp
current noise of 1.5pA/rtHz give you something like 10nV/rtHz at the
output with the 7.5k ohm feedback resistor. Not that bad really given
the voltage noise of the resistor.
"OK I'm still kinda new to noise calculations, but won't the opamp
current noise of 1.5pA/rtHz give you something like 10nV/rtHz at the
output with the 7.5k ohm feedback resistor. "
Opps, please ignore that last post. I see the current noise gets
divided by the source and feedback resistors .. my mistake!
" Its value, correcting for the gain structure mess-up of the originalggher...@gmail.com wrote:
Eeyore wrote:
ggher...@gmail.com wrote:
John Larkin wrote:
Eeyore wrote:
Phil Hobbs wrote:
Eeyore wrote:
National's LME49710/20/40 amd LM4562 seem to have the best figures at
2.5nV/sqrt Hz but in a practical circuit I found the venerable NE5534
with its 3.5 nV/sqrt Hz was quieter, presumably due to lower input noise
current in that particular configuration.
The LMEs also have insanely low THD
RL = 600ohms 0.00003% (typ)
http://www.national.com/pf/LM/LME49710.html
http://www.national.com/pf/LM/LM4562.html
Does anyone know of anything better without sacrificing unity gain
stability or THD ?
What resistance values are you assuming? Not one month ago, in this
very boutique, I posted a link to a new part with some really cute
specs--the ADA4898-1.
http://www.analog.com/static/imported-files/Data_Sheets/ADA4898-1.pdf
I gather it's probably intended for lower source resistances than yours,
but its combination of low eN and low Cin is amazing.
Yes, my source resistance may dominate. It's a new module for SSL 4000E/G
professional sound mixing desks to convert the 'channel buckets' into a
monitor desk for Digital Audio Workstations. I was shocked at how high their
mix resistor values were (15k). Crikey, even at Studiomaster in the latter
days I was using 4k7 !
It's certainly amazingly quiet though.
I'm not familiar with the THD being quoted in dBc though. Can you assist there
?
Graham
15K? Sounds like jfet turf.
John-
15K? Sounds like jfet turf.
Yes, Aren't you going to be dominated by the current noise? Speaking
of jfet opamps, Do you have a low noise favorite? I like the OPA134
from Burr-Brown (TI). But am always looking for something better..
George
That depends how many inputs are assigned. As these are going only to be monitoring
desks, the number of inputs will be 24 or 36 typically.
"That depends how many inputs are assigned. As these are going only
to be monitoring
desks, the number of inputs will be 24 or 36 typically.
So the suming node will see ~ 400-600 ohms. Current noise shouldn't be
a problem
here,"
Ahh I see it's one big summing junction. But what is the feedback
resistor? (I know nothing about high end audio stuff.)
Its value, correcting for the gain structure mess-up of the original design will be 7k5,
i.e a voltage gain of around -18x , but must be stable with nothing routed which equates
to a stable gain of -0.5x. I don't see a problem with the stability issues, I thought it
out on the walk back from the supermarket.
Graham- Hide quoted text -
- Show quoted text -
Thats when you load the Tr with a VE, and have the mix R's on theJohn Larkin wrote:
snip
I wonder if multi-group summing would be any better.
That would be ideal and is a method implemented in some more modern products. In this
case we're stuck with what we have i.e. a single mix bus.
Transformer + jfet!
Do you know how much good audio transformers cost ! I like Lundahls but you get such a
little thing for so much money. Say $80 ea. The client has indicated btw that cost is a
major factor so it might be back to 5532/4s (good enough - the rest of the desk is stuffed
with them) and a discrete front end.
Check out that 2SA1083/4/5 btw. www.profusionplc.com has them in stock (they can be tricky
to get hold of) and a link to the data sheet.
Graham
Have you tried the zero Z transformer method?
"OK I'm still kinda new to noise calculations, but won't the opampOn Sep 22, 9:44 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com
wrote:
ggher...@gmail.com wrote:
Eeyore wrote:
ggher...@gmail.com wrote:
John Larkin wrote:
Eeyore wrote:
Phil Hobbs wrote:
Eeyore wrote:
National's LME49710/20/40 amd LM4562 seem to have the best figures at
2.5nV/sqrt Hz but in a practical circuit I found the venerable NE5534
with its 3.5 nV/sqrt Hz was quieter, presumably due to lower input noise
current in that particular configuration.
The LMEs also have insanely low THD
RL = 600ohms 0.00003% (typ)
http://www.national.com/pf/LM/LME49710.html
http://www.national.com/pf/LM/LM4562.html
Does anyone know of anything better without sacrificing unity gain
stability or THD ?
What resistance values are you assuming? Not one month ago, in this
very boutique, I posted a link to a new part with some really cute
specs--the ADA4898-1.
http://www.analog.com/static/imported-files/Data_Sheets/ADA4898-1.pdf
I gather it's probably intended for lower source resistances than yours,
but its combination of low eN and low Cin is amazing.
Yes, my source resistance may dominate. It's a new module for SSL 4000E/G
professional sound mixing desks to convert the 'channel buckets' into a
monitor desk for Digital Audio Workstations. I was shocked at how high their
mix resistor values were (15k). Crikey, even at Studiomaster in the latter
days I was using 4k7 !
It's certainly amazingly quiet though.
I'm not familiar with the THD being quoted in dBc though. Can you assist there
?
Graham
15K? Sounds like jfet turf.
John-
15K? Sounds like jfet turf.
Yes, Aren't you going to be dominated by the current noise? Speaking
of jfet opamps, Do you have a low noise favorite? I like the OPA134
from Burr-Brown (TI). But am always looking for something better.
George
That depends how many inputs are assigned. As these are going only to be monitoring
desks, the number of inputs will be 24 or 36 typically.
"That depends how many inputs are assigned. As these are going only
to be monitoring
desks, the number of inputs will be 24 or 36 typically.
So the suming node will see ~ 400-600 ohms. Current noise shouldn't be
a problem
here,"
Ahh I see it's one big summing junction. But what is the feedback
resistor? (I know nothing about high end audio stuff.)
Its value, correcting for the gain structure mess-up of the original design will be 7k5,
i.e a voltage gain of around -18x , but must be stable with nothing routed which equates
to a stable gain of -0.5x. I don't see a problem with the stability issues, I thought it
out on the walk back from the supermarket.
Graham- Hide quoted text -
- Show quoted text -
" Its value, correcting for the gain structure mess-up of the original
design will be 7k5"
OK I'm still kinda new to noise calculations, but won't the opamp
current noise of 1.5pA/rtHz give you something like 10nV/rtHz at the
output with the 7.5k ohm feedback resistor. Not that bad really given
the voltage noise of the resistor.
George- Hide quoted text -
- Show quoted text -
Transformers are not even remotely plausible for budget reasons. Why would you want one anywayEeyore wrote:
Do you know how much good audio transformers cost ! I like Lundahls but you get such a
little thing for so much money. Say $80 ea. The client has indicated btw that cost is a
major factor so it might be back to 5532/4s (good enough - the rest of the desk is stuffed
with them) and a discrete front end.
Check out that 2SA1083/4/5 btw. www.profusionplc.com has them in stock (they can be tricky
to get hold of) and a link to the data sheet.
Have you tried the zero Z transformer method?
Thats when you load the Tr with a VE, and have the mix R's on the
input side?
I've got Ted Fletchers VE cct somewhere, but never tried it
no transformer, that was not really apparent in my previous post)Martin Griffith wrote:
Eeyore wrote:
Do you know how much good audio transformers cost ! I like Lundahls but you get such a
little thing for so much money. Say $80 ea. The client has indicated btw that cost is a
major factor so it might be back to 5532/4s (good enough - the rest of the desk is stuffed
with them) and a discrete front end.
Check out that 2SA1083/4/5 btw. www.profusionplc.com has them in stock (they can be tricky
to get hold of) and a link to the data sheet.
Have you tried the zero Z transformer method?
Thats when you load the Tr with a VE, and have the mix R's on the
input side?
I've got Ted Fletchers VE cct somewhere, but never tried it
Transformers are not even remotely plausible for budget reasons. Why would you want one anyway
?
Graham
It was only an idea. Ted's cct uses a single opamp as a balanced mix (
Ah ! No balanced bus available here, although there is a 0V sense line.Eeyore wrote:
Martin Griffith wrote:
Eeyore wrote:
Do you know how much good audio transformers cost ! I like Lundahls but you get such a
little thing for so much money. Say $80 ea. The client has indicated btw that cost is a
major factor so it might be back to 5532/4s (good enough - the rest of the desk is stuffed
with them) and a discrete front end.
Check out that 2SA1083/4/5 btw. www.profusionplc.com has them in stock (they can be
tricky to get hold of) and a link to the data sheet.
Have you tried the zero Z transformer method?
Thats when you load the Tr with a VE, and have the mix R's on the
input side?
I've got Ted Fletchers VE cct somewhere, but never tried it
Transformers are not even remotely plausible for budget reasons. Why would you want one > anyway
?
It was only an idea. Ted's cct uses a single opamp as a balanced mix (
no transformer, that was not really apparent in my previous post)
way, with a diff amp, I'll try and find Ted's circuit if you areMartin Griffith wrote:
Eeyore wrote:
Martin Griffith wrote:
Eeyore wrote:
Do you know how much good audio transformers cost ! I like Lundahls but you get such a
little thing for so much money. Say $80 ea. The client has indicated btw that cost is a
major factor so it might be back to 5532/4s (good enough - the rest of the desk is stuffed
with them) and a discrete front end.
Check out that 2SA1083/4/5 btw. www.profusionplc.com has them in stock (they can be
tricky to get hold of) and a link to the data sheet.
Have you tried the zero Z transformer method?
Thats when you load the Tr with a VE, and have the mix R's on the
input side?
I've got Ted Fletchers VE cct somewhere, but never tried it
Transformers are not even remotely plausible for budget reasons. Why would you want one > anyway
?
It was only an idea. Ted's cct uses a single opamp as a balanced mix (
no transformer, that was not really apparent in my previous post)
Ah ! No balanced bus available here, although there is a 0V sense line.
Graham
Yep, you just loose 6dB signal level, but get exceptional cmrr that
Well it's always interesting to take a peek.Eeyore wrote:
Martin Griffith wrote:
Eeyore wrote:
Martin Griffith wrote:
Eeyore wrote:
Do you know how much good audio transformers cost ! I like Lundahls but you get such >> >>>a
little thing for so much money. Say $80 ea. The client has indicated btw that cost is a
major factor so it might be back to 5532/4s (good enough - the rest of the desk is stuffed
with them) and a discrete front end.
Check out that 2SA1083/4/5 btw. www.profusionplc.com has them in stock (they can >> >> >be
tricky to get hold of) and a link to the data sheet.
Have you tried the zero Z transformer method?
Thats when you load the Tr with a VE, and have the mix R's on the
input side?
I've got Ted Fletchers VE cct somewhere, but never tried it
Transformers are not even remotely plausible for budget reasons. Why would you want one
anyway
?
It was only an idea. Ted's cct uses a single opamp as a balanced mix (
no transformer, that was not really apparent in my previous post)
Ah ! No balanced bus available here, although there is a 0V sense line.
Yep, you just loose 6dB signal level, but get exceptional cmrr that
way, with a diff amp, I'll try and find Ted's circuit if you are
interested.