I Got a PCB, with no parts (line buffer) based on NE5534 &NE5532. Looking at the schematic of the first stage (Follower) I am very surprised by how the offset adjustment and the unitary gain are treated.
1- Is it usaal to inject voltage in the Vin+ to adjust the offset ?
2-Normaly compensation is done with a capacity not a resitor (points 1 & 8)
any comment ?
Thanks a lot
Georges
1- Is it usaal to inject voltage in the Vin+ to adjust the offset ?
2-Normaly compensation is done with a capacity not a resitor (points 1 & 8)
any comment ?
Thanks a lot
Georges
As Jan says, it all to blurry...
I see no AC coupling at the inputs and so offset is now a variable depending on source impedance.
The follower does not conform to the recommended topology for using the 5534. Maybe the resistor is an attempt to increase noise gain and achieve stability that way. Not good imo.
Offset control can be done by current injection but again, it does not follow the recommended topology which would be to inject into the inverting terminal for a non inverting configuration.
The DC offset of the first stage is passed to the volume control and as it all seems to be DC coupled the control could be noisy.
The resistor at the output which goes to ground serves no purpose other than attenuating the wanted signal.
I see no AC coupling at the inputs and so offset is now a variable depending on source impedance.
The follower does not conform to the recommended topology for using the 5534. Maybe the resistor is an attempt to increase noise gain and achieve stability that way. Not good imo.
Offset control can be done by current injection but again, it does not follow the recommended topology which would be to inject into the inverting terminal for a non inverting configuration.
The DC offset of the first stage is passed to the volume control and as it all seems to be DC coupled the control could be noisy.
The resistor at the output which goes to ground serves no purpose other than attenuating the wanted signal.
It must be late because it seems kind-of fine to me. Electrolytics tend to be leaky, so the current leakage would create its own unreliable DC offset, so I can understand someone wanting to avoid that.
A possible cost could be the input gain is reduced slightly. I don't know if voltage noise would have much effect if the voltage source is sinking into a low input resistance. PSU noise would be a different issue and unless the supply voltages are already extremely stable, it would probably be better to add a buffer and capacitor.
A possible cost could be the input gain is reduced slightly. I don't know if voltage noise would have much effect if the voltage source is sinking into a low input resistance. PSU noise would be a different issue and unless the supply voltages are already extremely stable, it would probably be better to add a buffer and capacitor.
You need to ac-couple the potentiometer wipers. Don't let bipolar opamp bias current flow through a pot wiper, it will get very noisy after even the slightest wear as interrupting the bias current slams the device into saturation - you circuit has at least another DC path for the current, but its still likely to see very loud transients once the pot wears a bit.
[ BTW this thread really belongs to Analog Line Level part of forum ]
[ BTW this thread really belongs to Analog Line Level part of forum ]
So, under your controle what should I do with a minimum of changes if I would like to use the PCB ? put caps to isolate the potentiometer, change ho the offset and frequence componsation done ?