Condor Cab=20
Sim
professional-quality frequency response in a DIY-friendly=20
circuit
by runoffgroove.com
| This project is rated 2 out of 3 for the level = of=20 complexity. |
Typical DIY speaker cabinet simulator designs are simple builds, but = often=20 fall short of a convincing frequency response due to the oversimplified = designs.=20 Our goal was to design a speaker cabinet simulator suitable for direct = recording=20 and headphone playing, capable of outperforming existing designs, but = still within the reach of do-it-yourself builders.
The starting point was the published response of a single 10 inch = Jensen P10R=20 speaker. We chose to emulate a 4x10 cabinet, so low frequency response = was=20 shifted down slightly from the published curves to account for the = larger=20 cabinet and the combined cone area of four speakers.
The circuit is composed of the following functional blocks:
A frequency response graph of the Condor is shown below. For = comparison, the=20 Bulldog Cab Sim response curve is shown with a dotted red line. Note = how the=20 steeper roll-off of the Condor removes more high frequency content. = When those=20 are present, the resulting sound can seem harsh and unrealistic - = especially=20 when using a distortion pedal.
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Marshall reponse curve mod The Condor can be modified to reproduce the frequency response = of the=20 Marshall speaker simulator that is included on their amps with an = XLR=20 output (as traced by Ed Rembold, available at Aron's=20 Selected Schematics). Substitute the following components: Bridged-T notch filter: replace the 1n and 15n caps with 2n2 = and 6n8,=20 respectively. High-pass filter: replace the 18k and 100k resistors with 12k = and=20 120k. Low-pass filters: replace the 3n9 caps with 4n7, and replace = the four=20 22k resistors with 15k or 18k (16k is the nominal value, if you = can get=20 it; otherwise use 15k for slight extra treble, or 18k for some = less=20 fizz). The below graph compares the original Condor =
frequency=20
response with the Marshall mods. Notch Depth Switch mod While the above modifications will accurately reproduce the = Marshall=20 speaker simulator's response curve, so many components differ from = the=20 stock Condor that using a switch to toggle between the two is not=20 feasible. However, a compromise is available if we focus our = efforts on=20 the Marshall notch depth. By adding and removing capacitors in = parallel=20 with the notch caps, we can produce a notch depth that = approximates the=20 notch produced by the Marshall speaker simulator. Best of all, a = DPDT=20 switch can be used to toggle between the two modes - or a 3PDT can = be used=20 to allow LED indicators for each response. As shown in the partial schematic below, the 1n "bridge" cap is = unchanged while the stock 15n cap is changed to a 6n8. A 1n2 and = 8n2,=20 both with a single-pole switch in series, are placed in parallel = with=20 those caps, respectively. By using a DPDT switch for the two = single-pole=20 switches, we can open a switch while closing the other. When the = 1n2=20 "bridge" cap switch is open and the 8n2 switch is closed. The 6n8 = and 8n2=20 caps are in parallel, which creates a total capacitance of 15n. = Those=20 values produce a notch as found in the stock Condor. As the DPDT switch is activated, the 1n2 cap is added in = parallel with=20 the 1n, forming a 2n2 cap. Simultaneously, the 8n2 cap is = switched out,=20 leaving just the 6n8 cap to ground. The notch depth is now = roughly half=20 of the stock circuit, which is close to the Marshall response. In addition to the added midrange content produced by the = decreased=20 notch depth, more treble frequencies are present and the overall = output is=20 increased. Remember, this modification does not reproduce the = Marshall=20 response, but is a good "halfway point" that adds to the = usefulness of the=20 stock Condor. Refer to the below schematic for the necessary=20 modifications. A 3PDT switch wiring diagram is also shown, but = you can=20 ignore the middle column and use a DPDT if you don't want LED=20 indicators. The Notch Depth Switch mod was implemented in the official=20 runoffgroove.com Condor build, shown below. The blue LED = indicates that=20 the stock notch is active, while an amber LED is used to indicate = the=20 Marshall notch. |