op amp following 12ax7 tube
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Hi,
before i attempt anything i would like to just clarify a couple of things. These appear in burdij post.
When placing clamping diodes on the op amp input do i place two diodes back to back and solder then to ground and to the input?
Second the caps on the power supplies, are these to take out any last ripple
from the power supply? and so go from each input to ground with the caps in parallel.
Hope this makes sense, Thx for all the help.
Andy
before i attempt anything i would like to just clarify a couple of things. These appear in burdij post.
When placing clamping diodes on the op amp input do i place two diodes back to back and solder then to ground and to the input?
Second the caps on the power supplies, are these to take out any last ripple
from the power supply? and so go from each input to ground with the caps in parallel.
Hope this makes sense, Thx for all the help.
Andy
burdij
Well-known member
There are two ways to apply a clamp. To use the method you describe, the diodes would be zeners, two 15 volt units would work. You can also clamp to the plus and minus op amp supplies with regular diodes. This is probably the method I would use as the input voltages are then referenced to the op amp supply voltages. To use this method, a diode with its cathode connected to the +15v supply and anode to the cap end of the input resistor of the opamp and a diode with its anode end connected to the -15v supply and its cathode connected to the cap side of the input resistor. If the input rises above the opamp's plus supply by one diode drop, the diode will conduct. Conversly, if it falls more negative than one diode drop below the negative supply, the other diode will conduct.
The bypass caps for the opamps should be located close to the power input pins on the opamp package. The reason for putting them there is that it effectively creates a local supply of stored energy for the opamp to draw on for fast transient performance.
The bypass caps for the opamps should be located close to the power input pins on the opamp package. The reason for putting them there is that it effectively creates a local supply of stored energy for the opamp to draw on for fast transient performance.
Thx burdij,
when you say cap end or side of the input resistor do you mean the blocking cap from the tube stage, so this would mean the diodes will join at the same place and the resistor lies between this point and the op amp.
Thx Again, Andy
when you say cap end or side of the input resistor do you mean the blocking cap from the tube stage, so this would mean the diodes will join at the same place and the resistor lies between this point and the op amp.
Thx Again, Andy
Hi, im putting together a parts this for this project and need advice on
what type of resistors and caps to buy ( as in low noise/wattage).
The main ones for now are the input and feedback resistors, 1m and 5.6m,
what type and what wattage is suitable. Ill be using a tl071 op amp.
Thx
what type of resistors and caps to buy ( as in low noise/wattage).
The main ones for now are the input and feedback resistors, 1m and 5.6m,
what type and what wattage is suitable. Ill be using a tl071 op amp.
Thx
did you ever get a working circuit for this purpose? I have a similar question over in the drawing board right now.
http://www.groupdiy.com/index.php?topic=27196
Except mine is an instrument preamplifier and a balanced output. Does anyone have anyone suggestions for it?
http://www.groupdiy.com/index.php?topic=27196
Except mine is an instrument preamplifier and a balanced output. Does anyone have anyone suggestions for it?
