Hi. I just finished a tiny preamp kit and I need some help figuring out what resistors to use to control the gain. The gain is set by the ratio of a 2.2k and 100r resistor. The equation is gain = 1 + (2200/100) = 23 which is equivalent to 27dB.
I need to lower the gain a bit but I have no idea about the maths.
Here is the preamp kit
Pre-Champ Versatile Preamplifier Kit | Jaycar Electronics
I need to lower the gain a bit but I have no idea about the maths.
Here is the preamp kit
Pre-Champ Versatile Preamplifier Kit | Jaycar Electronics
2200/220 +1 = 11 which is perhaps still too much for a line stage. Does this fit your definition for "a bit"? 🙂
Ehm, you've already done the maths in your post? If you are not sure about the resistors to change, you need to find a schematic and post it here.
BTW, the easiest way to make the change might be to parallel another resistor on the back of the 2k2 one to get a lower value.
BTW, the easiest way to make the change might be to parallel another resistor on the back of the 2k2 one to get a lower value.
Yes, it is the easiest. Some ancient opamps may not be happy driving a very low feedback resistor.
Looks like a 2 transistor discrete. Should be able to drive 1k perhaps but depends on current in second device.
Copied and pasted from the kit instructions. I had no idea which resistor to change or by what value.
So you're saying that if I lower the value of the 2.2k resistor the gain will drop? And yeah if I just parallel another resistor on the back of the other 2.2k one then that would make sense.
There are 3 2.2k resistors and I'm not sure which one to change. Schematic and layout are attached...
Hi,
don't change the 2.2k, because this resistor is part of the DC biasing too. Increase the 100ohm resistor.
Sajti
don't change the 2.2k, because this resistor is part of the DC biasing too. Increase the 100ohm resistor.
Sajti
Ok. Thanks. What I am trying to achieve is matching the signal to a poweramp with a 5.2v input sensitivity. So from my audio interface with a max output of 10dBu and with a 500R resistor in place of the 100R on the preamp would i be getting close to this number of 5.2v max output signal?
You would be lucky to get more than approx. 3V RMS out of this preamp before clipping on a 12V supply .
Your power amp needs 5.2V input for max output , that's very insensitive .
+10dBu (2.45V) , 5.2V (+16.53dBu).
Your power amp needs 5.2V input for max output , that's very insensitive .
+10dBu (2.45V) , 5.2V (+16.53dBu).
Ah ok. I wonder if it's possible to make it more sensitive? It definitely got a whole lot louder when I added the preamp. More than loud enough for my purposes which is why I wanted to lower the gain a bit to hopefully get rid of the noise created after adding the preamp.
It was just an observation . If you have plenty of volume then change the 100R to 500R and see how it goes . Do you even need the preamp with +10dBu output from your audio interface or did you mean -10dBu .
Well it is loud without the preamp but not loud enough for my needs. So just want to find a balance. I'll try changing the 100R to a 500R and maybe add a 10k log pot between the preamp and the power amplifier.
So when the source i.e the line level signal from my audio interface is not enough to get full power from the power amplifier, is there any loss in quality or is it simply just not as loud?
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