There is a Crown DC-300 for sale at Maxwell's house of music in Jeffersonville IN. At least it was in a Louisville.Craigslist.org ad 12/13/19 with multiple devices shown, usually his ad although he doesn't list his name. Warning, these contain an obsolete op amp that if damaged is irreplacable.
Used for controlling DC actuators on diesel motor throttles and like applications. In '74-'77 I worked for a company that did exploration for oil with bladders driven by 3000 hp of hydraulic pumps. Two V-12 Catepillar diesels in parallel. The bladder swept 1/2 to 20 hz to produce an acoustic signature from the earth under the sea. The hydraulic flow was controlled by a vickers solenoid valve driven by a sweep generator. Daft procedure no longer used I believe. You might have enjoyed being present. What I heard was not infrasound but the rattling of the tin sheds on the deck.
Used for controlling DC actuators on diesel motor throttles and like applications. In '74-'77 I worked for a company that did exploration for oil with bladders driven by 3000 hp of hydraulic pumps. Two V-12 Catepillar diesels in parallel. The bladder swept 1/2 to 20 hz to produce an acoustic signature from the earth under the sea. The hydraulic flow was controlled by a vickers solenoid valve driven by a sweep generator. Daft procedure no longer used I believe. You might have enjoyed being present. What I heard was not infrasound but the rattling of the tin sheds on the deck.
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Please clear my doubts, I´m straight answering your original question but need more details.
As I see it, unlike any type of "piston" speaker, your modulated fan CAN go down to DC.
In fact, all fans produce Acoustic DC, just unmodulated.
In yours, blades rotate at constant speed and output is produced by varying blade pitch ... please confirm/deny.
Yes that is correct ... like a helicopter controls blade pitch
IF so, a DC supply drives the electric motor, and Audio power drives the blade actuators. Yes/No
Yes ... the motor is a 220 volts 3 phase design that is controled buy a VFD (Variable Frequency Drive) and runs at 800 RPM
IF so, please provide the actuator schematic, with coil data: drive voltage needed, and resistance/impedance.
Speaker motor came from a 15" subwoofer with a 2" voice coil and a spider diameter of 7". Impedance is 8 ohms and can support 150 watts RMS
If none of this applies and you actually want to drive a bidirectional rotary motor with Audio, then I´m out of this, sorry.
Good luck with your project
As I see it, unlike any type of "piston" speaker, your modulated fan CAN go down to DC.
In fact, all fans produce Acoustic DC, just unmodulated.
In yours, blades rotate at constant speed and output is produced by varying blade pitch ... please confirm/deny.
Yes that is correct ... like a helicopter controls blade pitch
IF so, a DC supply drives the electric motor, and Audio power drives the blade actuators. Yes/No
Yes ... the motor is a 220 volts 3 phase design that is controled buy a VFD (Variable Frequency Drive) and runs at 800 RPM
IF so, please provide the actuator schematic, with coil data: drive voltage needed, and resistance/impedance.
Speaker motor came from a 15" subwoofer with a 2" voice coil and a spider diameter of 7". Impedance is 8 ohms and can support 150 watts RMS
If none of this applies and you actually want to drive a bidirectional rotary motor with Audio, then I´m out of this, sorry.
Good luck with your project
I like the op-amp input buffer and a FET diff-amp with ~zero bias current avoids the issue with different bias resistors but matching FETs may be an issue. In any case, an offset trim pot seems the obvious solution. An offset trim can be added to any amplifier.
I don't know if anybody said this. Ideally any ultra low frequency device needs time alignment. Not impossible to do. When a pipe organ the organist is this device. When correct the sound is deeper and sweeter. I doubt this application has this requirement.
It's said people who live near wind farms feel unsettled. Even though not vary audible they feel something. My dad for years thought something like a big truck was running nearby. He walked for miles at night trying to find it. I heard it but couldn't get excited. I later found that we lived near a high pressure gas pipeline. These are known for this problem. From what I know what we might hear is a harmonic. Funny thing with dad was in the end he forgot about it.
It's said people who live near wind farms feel unsettled. Even though not vary audible they feel something. My dad for years thought something like a big truck was running nearby. He walked for miles at night trying to find it. I heard it but couldn't get excited. I later found that we lived near a high pressure gas pipeline. These are known for this problem. From what I know what we might hear is a harmonic. Funny thing with dad was in the end he forgot about it.