lathehand
Cast Iron
- Joined
- Jan 31, 2005
- Location
- San Francisco Bay Area
A few years ago, I built a small dynamic balancing machine and amplifier. The input to the amplifier is a switching network which provides plane separation and calibration of the meter to directly read the amount of unbalance. This network must remain double-ended – ungrounded – until the signal exits the network and is grounded in one leg to input to a 741 op amp amplifier.
The problem is that the switching network includes two potentiometers and the net effect is that the input resistance of the network changes during the process of separating the planes and calibrating the correction weights. The amplifier is my design but the network was reverse engineered from a professional amplifier. The original design used 10K potentiometers and I copied that. However, the internal DC resistance of the pickups is 6K and the potentiometers are loading the pickups. I determined that a good input resistance would be between 500K and 1M, and closer to 1M.
I thought the easy way would be to install a buffer stage between the pickups and the switching network so the pickups would always see the same impedance. The problem is that I am inputing a double-ended signal from the pickups and I need a double-ended output signal to the network. That has turned out to be more difficult than I had expected.
To summarize, I need a buffer with high impedance input which can be either single or double ended and a low impedance double ended output at about 30 HZ. I've thought of signal isolation transformers and I poked around the web and found audio driver chips such as TI DRV 134. http://www.ti.com/lit/ds/symlink/drv134.pdf I am not familiar with these chips so am looking for help and other circuits that might be suitable.
TIA
Carl
The problem is that the switching network includes two potentiometers and the net effect is that the input resistance of the network changes during the process of separating the planes and calibrating the correction weights. The amplifier is my design but the network was reverse engineered from a professional amplifier. The original design used 10K potentiometers and I copied that. However, the internal DC resistance of the pickups is 6K and the potentiometers are loading the pickups. I determined that a good input resistance would be between 500K and 1M, and closer to 1M.
I thought the easy way would be to install a buffer stage between the pickups and the switching network so the pickups would always see the same impedance. The problem is that I am inputing a double-ended signal from the pickups and I need a double-ended output signal to the network. That has turned out to be more difficult than I had expected.
To summarize, I need a buffer with high impedance input which can be either single or double ended and a low impedance double ended output at about 30 HZ. I've thought of signal isolation transformers and I poked around the web and found audio driver chips such as TI DRV 134. http://www.ti.com/lit/ds/symlink/drv134.pdf I am not familiar with these chips so am looking for help and other circuits that might be suitable.
TIA
Carl