The quietest audio op-amp with ultra-low THD

their

I was

input

same

for a

XL's were after my time, so maybe I left earlier. It's all a bit hazy now.

les...

les...

pcb IIRC.

and 18

still

It's so

least as tech

Geoff was the owner, iirc it was Jim Cousins doing most of the design work and some other guy who I cant remember at this time. This was after Chas Brookes had left.

les...

noise

their

there ?

fed from

fish ?

didn't

In this

Transformer + jfet!

John

igures at

le NE5534

input noise

y gain

in this

cute

-1.pdf

han yours,

L 4000E/G

into a

w high their

the latter

u assist there

king

134 .

be monitoring

gn will be 7k5,

d which equates

s, I thought it

" 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

figures at

able NE5534

er input noise

ity gain

o, in this

y cute

98-1.pdf

than yours,

SSL 4000E/G

s' into a

how high their

n the latter

you assist there

eaking

PA134

er.

to be monitoring

y e

sign will be 7k5,

ted which equates

ues, I thought it

"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!

George

at

NE5534

noise

yours,

4000E/G

their

latter

assist there ?

fed from

fish ?

didn't

In this

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.

has them in stock (they can be tricky to get hold of) and a link to the data sheet.

Graham

figures at

NE5534

input noise

gain

this

yours,

4000E/G

into a

high their

latter

assist there

monitoring

will be 7k5,

which equates

I thought it

The noise current will also flow in the input resistors.

Graham

figures at

venerable NE5534

input noise

gain

this

cute

than yours,

4000E/G

into a

high their

the latter

assist there

be monitoring

design will be 7k5,

which equates

issues, I thought it

Nevertheless shows how critical resistor values are in high-performance audio. This mixing desk didn't have the best reputation in that regard and I can see why now. I was using low R values in really low cost equipment not long back. Usually a case of make it as low as possible compatible with what the op-amp will drive happily.

Graham

products. In this

such a

cost is a

is stuffed

can be tricky

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

martin

get such a

cost is a

desk is stuffed

can be tricky

Transformers are not even remotely plausible for budget reasons. Why would you want one anyway ?

Graham

get such a

that cost is a

desk is stuffed

can be tricky

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)

I had just spent the morning simulating modem/phone transformer in virtual earth configs. Quite interesting (sort of), I got quite reasonable results.

martin

you get such a

that cost is a

desk is stuffed

(they can be >>

you want one > anyway

Ah ! No balanced bus available here, although there is a 0V sense line.

Graham

you get such a

that cost is a

the desk is stuffed

(they can be >>

you want one > anyway

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.

martin

you get such >> >>>a

cost is a

the desk is stuffed

(they can >> >> >be

you want one >> >

Well it's always interesting to take a peek.

Graham