Speaker Sim




This is a speaker sim I designed to be more versatile than my Celestion G12H sim. This was designed to have a range of tones but the two speakers I focused on emulating were the Jensen P12Q and the Celestion G12M "Greenback". It is made up of a JFET buffer, two resonant lowpass filters to give the high-frequency rolloff and the resonant peaks at 2-5kHz, an adjustable resonant highpass filter to adjust the bass rolloff and resonance, and an adjustable band-reject filter to take out some mids if necessary. The bass control increases the highpass filter's resonance and increases its cutoff frequency as it is turned up.  The mid control decreases the depth of the band reject filter as it is turned up. The bass and mid controls are voiced to give a wide range of speaker tones. This circuit has around a 13dB gain at most, so if that causes clipping, a resistor can be put in series with the input as a voltage divider.

v1.2 I've added a treble control, which helps to emulate different micing positions.

Click on the schematic to open the image.

All below information is only accurate for v1.1, which didn't have the treble control.

Here are the ranges of the bass and mid controls. The green lines show the controls at maximum, the blue lines at minimum and the red lines at half. The top graph shows the mid control and the bottom one shows the bass control. Click on the images for clearer lines.
Mid Settings

Bass settings


Unverified layout (actually for circuit version 1.2):

Some of the wires and cut tracks are difficult to see, so here's a layout with lighter parts.


I'd suggest putting in the wires last, except for those that go under R11.

Suggested Control Settings:
US (Jensen P12Q): Mid 0%, Bass 25%
UK (Celestion Greenback): Mid 100% Bass 0%
Bulldog Cab Sim: Mid 25% Bass 50%

If you have any questions or comments, email me or post them at www.diystompboxes.com/smfforum