Hi, I need to amplify the subwoofer/LFE signal coming out of my receiver to my subwoofer amplifer. I am using a 'professional' type amplifer that requires a stronger line-level signal. I am looking for a simple solution as the sound quality doesn't have to be the best (<200Hz). Maybe there is a simple one-chip solution? Thanks.
--Ferdi
--Ferdi
Any schematics you could point me to? I have some OPA627 and AD8610 chips lying around that I could use. Thanks.
--Ferdi
--Ferdi
nice chips to have 'laying around'... they're amongst the best opamps available so you need not to be concerned about sound quality.
basic (non inverting) opamp circuit:
R1 sets the input impedance, use a 100k resistor for this.
Gain is set with R2 and R3: gain is 1+(R2/R3).
Gain = 2 --> R2=1kOhm and R3=1kOhm.
Gain = 3 --> R2=2kOhm R3=1kOhm
etc...
input capacitor C3 (4,7uF bipolar min. 16V) removes any dc offset from your signal
C1 & C2 are small capacitors (a couple of uF's, rated at least your PSU voltage). bypass these with small (0,02uF) caps if you want.
edit: add a 50ohm resistor to the output of the opamp, this to avoid oscillations of the opamp.
basic (non inverting) opamp circuit:
An externally hosted image should be here but it was not working when we last tested it.
R1 sets the input impedance, use a 100k resistor for this.
Gain is set with R2 and R3: gain is 1+(R2/R3).
Gain = 2 --> R2=1kOhm and R3=1kOhm.
Gain = 3 --> R2=2kOhm R3=1kOhm
etc...
input capacitor C3 (4,7uF bipolar min. 16V) removes any dc offset from your signal
C1 & C2 are small capacitors (a couple of uF's, rated at least your PSU voltage). bypass these with small (0,02uF) caps if you want.
edit: add a 50ohm resistor to the output of the opamp, this to avoid oscillations of the opamp.
Thanks, you meant to put that 50ohm resistor in series with the output, correct? And, I am guessing that it should go after the loop going to R2? So pretty much just before X2?
Also, I've been talking to a friend of mine and he thinks that the output from the opamp should be buffered? Any comments, or is that only necessary when driving capacitive loads like cables?
--Ferdi
Also, I've been talking to a friend of mine and he thinks that the output from the opamp should be buffered? Any comments, or is that only necessary when driving capacitive loads like cables?
--Ferdi
yep before x2.
including a buffer will make it more complicated and this will work on almost any cable.
including a buffer will make it more complicated and this will work on almost any cable.
Thanks for clearing that up. Now on to the power supply. I see that I need +-12volts. What would be a simple solution? I am thinking about using a small transformer (I have a 28V center-tapped) along with an LM317 voltage regulator to make a 24 volt supply, and then using a rail splitter (TLE2426) to make a virtual ground at 12v. That should give me a cheap and simple +-12v supply. Do you see anything wrong with this? Am I over-complicating the PSU? Thanks.
--Ferdi
--Ferdi
As you have a center-tapped transformer you shouldn´t use a rail splitter.
Have a look at this power supply which would be all you need.
http://www.jcscript.de/projects/eaton.html
The capacitance after the regulator can be much lower that 2200uF but there should be some.
Have a look at this power supply which would be all you need.
http://www.jcscript.de/projects/eaton.html
The capacitance after the regulator can be much lower that 2200uF but there should be some.
you can get cheap pcb-mounted transformwers with dual secondaries at almost any electronic supplies stores. they shouldn;t set you back more than a few (~5) euros; something with dual 9V supplies should work fine. After rectifiyng this will give you ~ 12V.
For testing purposes connect 2 9v battieries is series; this will give you 18V. You can use something like this:
cap + leads are connected to +9v (for the top caps) and gnd (for bottom caps). cap - leads are connected gnd (for top caps) and -9v (for bottom caps)
For testing purposes connect 2 9v battieries is series; this will give you 18V. You can use something like this:
An externally hosted image should be here but it was not working when we last tested it.
cap + leads are connected to +9v (for the top caps) and gnd (for bottom caps). cap - leads are connected gnd (for top caps) and -9v (for bottom caps)
matjans, would 47uF caps work for C2/C3 on your schematic? What is the 'ideal' value for them? Thanks.
--Ferdi
--Ferdi
Changing the gain of the power amplifier is the easiest
option if you are capable of identifying the gain setting
feedback resistors in the power amplifer.
🙂 sreten.
option if you are capable of identifying the gain setting
feedback resistors in the power amplifer.
🙂 sreten.
those caps are meant to suppress any psu ripple left after rectification and capacitor banks included with the psu.
You don;t need such big caps, use smaller ones. a 2,2uF bypassed with 0,22uF (or even smaller) should work perfectly for one single opamp (and even that might be overkill).
Using caps that are too big won't help because of the low current drawn by the opamp.
You don;t need such big caps, use smaller ones. a 2,2uF bypassed with 0,22uF (or even smaller) should work perfectly for one single opamp (and even that might be overkill).
Using caps that are too big won't help because of the low current drawn by the opamp.
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