Orion MKII Receiver Frequency Response
Posted: Mon Jan 30, 2023 6:31 pm
Attached are frequency response plots from my ANAN 7000 with ASIO VAC engaged and measured with SpectraPlus-SC software. SpectraPlus-SC has a built-in ASIO driver. Both measurements were taken with a 4096 filter size in LSB mode, 5 kHz receive bandwidth, no weighting, and peak-hold sweep mode (red-colored sweeps), 10 dB/vert. div.
The first plot shows a band noise sweep, the second shows a sweep from an RF signal generator. The frequency response flatness is exceptional, all the way down to 20 Hz.
I've not measured the response from the headphone jack as my current ChannelMaster file bypasses all audio panel connections. It would be an interesting test as a function of headphone loading impedance. The Orion MKII uses 10 uF audio coupling capacitors at the headphone jack, driven from a Lo-Z active source impedance.
According to Sony, the average impedance of Sony MDR-7506 studio headphones over a 20 Hz - 20 kHz response is 63 Ω, but the true impedance is a function of frequency. Assuming 63 Ω, the -3dB turnover point is approximately 250 Hz. However, at least one measurement source shows an average of 80 Ω, with a maximum impedance of 113 Ω at 64 Hz and minima of about 76 Ω at 1 kHz and 7 kHz. This would account for much better real low-end response than Sony's specification sheet suggests.
Long ago, I bridged the existing 10 uF coupling caps at C16 and C17 with 100 uF, bringing the total coupling capacitance to 110 uF. Using the same 63-ohm headphone impedance, we can simply move the decimal point to the left, and we get a -3dB response down to approximately 25 Hz. Probably the only time this matters is for: (i) ESSB and some AM reception; and (ii) use with low impedance headphones (e.g., 8Ω types) that predate the use of neodymium magnets.
By using an ASIO sound interface, the headphone circuit's frequency response is limited by the device's own output circuit topology -- which generally conforms to the highest studio standards.
Paul, W9AC
The first plot shows a band noise sweep, the second shows a sweep from an RF signal generator. The frequency response flatness is exceptional, all the way down to 20 Hz.
I've not measured the response from the headphone jack as my current ChannelMaster file bypasses all audio panel connections. It would be an interesting test as a function of headphone loading impedance. The Orion MKII uses 10 uF audio coupling capacitors at the headphone jack, driven from a Lo-Z active source impedance.
According to Sony, the average impedance of Sony MDR-7506 studio headphones over a 20 Hz - 20 kHz response is 63 Ω, but the true impedance is a function of frequency. Assuming 63 Ω, the -3dB turnover point is approximately 250 Hz. However, at least one measurement source shows an average of 80 Ω, with a maximum impedance of 113 Ω at 64 Hz and minima of about 76 Ω at 1 kHz and 7 kHz. This would account for much better real low-end response than Sony's specification sheet suggests.
Long ago, I bridged the existing 10 uF coupling caps at C16 and C17 with 100 uF, bringing the total coupling capacitance to 110 uF. Using the same 63-ohm headphone impedance, we can simply move the decimal point to the left, and we get a -3dB response down to approximately 25 Hz. Probably the only time this matters is for: (i) ESSB and some AM reception; and (ii) use with low impedance headphones (e.g., 8Ω types) that predate the use of neodymium magnets.
By using an ASIO sound interface, the headphone circuit's frequency response is limited by the device's own output circuit topology -- which generally conforms to the highest studio standards.
Paul, W9AC