1% or even 5% resistor are usually accurate enough for most audio circuits.
Balanced transmitter and balanced receiver are a different ball game. To maintain the noise attenuation that balanced can offer the resistors should be better 0.1% and preferably <0.01% for best CMRR.
Your attenuator acts as a receiver for the signal coming from the source.
The same attenuator acts as the transmitter when sending the signal on the the next stage.
If the next stage is unbalanced then your are wasting time and effort and money chasing a solution that cannot improve the sound quality.
You could convert the input of the next stage to balanced to gain the CMRR improvements, but you will throw it all away by using 1% resistors.
Have a look at Rane and Jensen and Self and Pass and read.
Many thanks for the input, mine lineamp is two unbalanced Borbely's preamp & mine power amps are Borbely's 75W RMS Class A so I can get all benefits for balanced operation.
About phono preamp I read some people that don't agree balanced telling that noise level increased due to more electronic components, it's true?
About phono preamp I read some people that don't agree balanced telling that noise level increased due to more electronic components, it's true?
There is a way to get by with less precision values and still get the CMRR. In order to do this the input of the circuit after the control will have to be differential. The schematic I saw earlier was merely balanced, although it used differential inputs on the op amps.
If you simply drop the ground at of the control, it will float. If the input of the line section is truly differential, the control will now exist in the differential domain and slight differences caused by mismatches in parts will no longer be a problem. But to do this, the line stage depicted will have to be modified so that the inputs of both opamps are used for inverted and non-inverted phases.
If one side of the control input is tied to ground, it will still work, but not quite the same way as it does in the schematic. Try it, you'll see.
Thanks for answers,
The schematics posted is only one channel, aren't opamps all is discrete jfets.
As I understood don't need any modification to use mine attenuator, if yes could you explain me how to do?
As you said for non balanced inputs I tied to ground & works perfectly.
If you refer to my earlier post, the schematic of your line stage is balanced but not differential. You can make it differential easily enough, by connecting the inputs of both op amps to both outputs of the controls.
I don't understand you, both + input op amps are connected to both outputs of the controls....could you draw a schematic or explaint me better to understand you?
The minus inputs should be connected to the outputs of the controls too. If you do this right, at the output of one control will the the + input to one opamp and the - input to the other. At the other control output will be the - input to the 1st opamp and the + input to the 2nd opamp.
Ok now I understood that one opamp must be connected inverted for - input, but about the resistors: remain the same or I have to change something?
To run opamps you have to run feedback. But the input this getting the feedback (-) also will have an input resistor. The gain of the opamp will be the ratio between this input resistance and the feedback. I would install a similar input resistor on the + inputs as well, so that the signal is seeing the same input impedances on either the inverted or non-inverted polarities.
Its not a difficult change.
Its not a difficult change.
Both opamps +- in balanced configuration are connected -signal to -signal, in differential configuration will be linked the inputs without entering signal + one opam to - other opam?
- Status
- Not open for further replies.