ruffrecords
Well-known member
I decided to start a new thread following on from the old 6dB EQ thread in the Drawing Board. This is mainly because the thinking has moved on a lot and I am now well into designing PCBs for it.
As it stands, the design will feature:
1. Up to 10dB boost/cut in 2dB steps
2. Up to 6 bands
3. Up to 10 frequencies per band
4. Mid bands will be RLC bell shaped response
5. Highest and lowest band can be shelving instead of bell shaped
6. Optional variable sharpness
7. 600 ohm operating impedance
The EQ will be mono. If you want stereo you can build a pair. Because all parameters are switched they should track quite well.
I plan to use Don Audio RM8 inductors and may have some specials designed for this project.
I have chosen a 600 ohm operating impedance because it allows the use of lower values of inductance which should avoid any out of band self resonance effects they may be a problem for people using higher sampling rates.
As I mentioned in the last Drawing Board post, there will be three types of PCB
1. A common switch board. This holds two Grayhill 1 pole 12 way switches. One is the boost/cut level control and the other is the frequency select switch. Both are connected to 12 way Molex connectors.
2. EQ board which holds the LCR required for a particular band. Not sure how many variations of this there will be. We may need one dedicated to bass because it will need a larger inductor than the other (but standardising on Don Audio RM8 cores might avoid this) . A second would use a smaller inductor for low mid and a third might use axial leaded inductors for high mid or high. Any of the boards could be used for shelving high just by shorting out the inductor position. Similarly, the larger inductor types could be used as a shelving low just by shorting out the capacitor positions. This board will connected to the 12 way connector from the frequency select switch. I am toying with the idea of this board piggy backing onto the switch board if only to keep frequency selective connections as short as possible.
3. Interconnect board. This has the EQ in and out connectors, the single resistor ladder used by all bands and a bunch of 12 way Molex connectors that connect to each band.
An initial layout of the two switches board is attached. The three blue circles are 3mm clearance hole for piggy backing the EQ board. RQ and the connector Q are options for varying the Q. I don't really think these should be necessary as the Q should be determined principally by the characteristic resistance of the circuit and the inductor values. The Q control simply alters Q by adding series resistance but it also reduces the amount of boost/cut
Cheers
Ian
As it stands, the design will feature:
1. Up to 10dB boost/cut in 2dB steps
2. Up to 6 bands
3. Up to 10 frequencies per band
4. Mid bands will be RLC bell shaped response
5. Highest and lowest band can be shelving instead of bell shaped
6. Optional variable sharpness
7. 600 ohm operating impedance
The EQ will be mono. If you want stereo you can build a pair. Because all parameters are switched they should track quite well.
I plan to use Don Audio RM8 inductors and may have some specials designed for this project.
I have chosen a 600 ohm operating impedance because it allows the use of lower values of inductance which should avoid any out of band self resonance effects they may be a problem for people using higher sampling rates.
As I mentioned in the last Drawing Board post, there will be three types of PCB
1. A common switch board. This holds two Grayhill 1 pole 12 way switches. One is the boost/cut level control and the other is the frequency select switch. Both are connected to 12 way Molex connectors.
2. EQ board which holds the LCR required for a particular band. Not sure how many variations of this there will be. We may need one dedicated to bass because it will need a larger inductor than the other (but standardising on Don Audio RM8 cores might avoid this) . A second would use a smaller inductor for low mid and a third might use axial leaded inductors for high mid or high. Any of the boards could be used for shelving high just by shorting out the inductor position. Similarly, the larger inductor types could be used as a shelving low just by shorting out the capacitor positions. This board will connected to the 12 way connector from the frequency select switch. I am toying with the idea of this board piggy backing onto the switch board if only to keep frequency selective connections as short as possible.
3. Interconnect board. This has the EQ in and out connectors, the single resistor ladder used by all bands and a bunch of 12 way Molex connectors that connect to each band.
An initial layout of the two switches board is attached. The three blue circles are 3mm clearance hole for piggy backing the EQ board. RQ and the connector Q are options for varying the Q. I don't really think these should be necessary as the Q should be determined principally by the characteristic resistance of the circuit and the inductor values. The Q control simply alters Q by adding series resistance but it also reduces the amount of boost/cut
Cheers
Ian