Hi, I'm currently putting together an balanced parametric EQ and would like to implement a +/-6dB input gain control using a 21 step rotary switch with step 11 as 0dB - center tapped.
Unfortunately my skill set is limited to assembly and I'm not really sure how to do this so i'm wondering if anyone can advise?
Here is the schematic of the project.
Any help appreciated!
Unfortunately my skill set is limited to assembly and I'm not really sure how to do this so i'm wondering if anyone can advise?
Here is the schematic of the project.
Any help appreciated!
I would use the stepped attenuator (stereo I assume) on the inputs and program the first gain stage to be +6dB. Let's say the maximum resistance of the stepped attenuator is "X" ohms. You will need X to form a voltage divider that can create 0 to 12dB of attenuation so that, combined with the +6dB gain in the first active stage, you get an overall +6 to -6dB gain. -12dB is a voltage gain of 0.2512, so you need Y/(X+Y) to equal 0.2512, where X is the end-to-end resistance of the potentiometer or stepped attenuator, and Y is an additional resistor between the stepped attenuator and ground. We can reorganize the formula into a more useful form:
Y = (0.2512*X) / (1-0.2512)
For example, if X=10kohm, this works out to Y= 3355 ohms. Checking:
3355/(10000+3355) = 0.251216777
You connect the input signal to one end of the potentiometer or stepped attenuator. The wiper leads on to the +6dB gain stage. The other end of the potentiometer or stepped attenuator is connected to the additional resistor with Y ohms resistance. The other end of the Y resistor is connected to ground.
Thanks for the reply, very helpful.
I'm wondering through, if I use a 10K LIN attenuator (21 step, 499R chain of resistors - I already have this built), how can I ensure that step 11 (5.4k ohms) will be at unity gain/0db?
And BTW, value Y you mention above, would that be in place of R6 and R7 in the schematic? What would I need in R21? I'm assuming R20 is where the 10K 'stepped variable resistor/rheostat' would be inserted?
I'm wondering through, if I use a 10K LIN attenuator (21 step, 499R chain of resistors - I already have this built), how can I ensure that step 11 (5.4k ohms) will be at unity gain/0db?
And BTW, value Y you mention above, would that be in place of R6 and R7 in the schematic? What would I need in R21? I'm assuming R20 is where the 10K 'stepped variable resistor/rheostat' would be inserted?
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