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RA4PA Tech Notes

Running a Medusa PreAmp off an external battery


Product: RA4PA, RA16PA, RA16SD
Version: All
Date Added: 2007-07-12


Customers looking for extra battery life for their Medusa PreAmp can purchase the PZ-BAT external battery pack from TDT.

Alternatively, off the shelf 6V batteries, such as a motorcycle battery or a battery for use with emergency lighting, can be adapted for this purpose. Two options for batteries are:



An example of a charger is

These batteries have a capacity of about 6 Amp-hr, which should power an RA16PA for over 60 hours between charges. If longer run times are desired, you can select a similar battery with a higher Ah capacity.

This type of battery can be connected to the voltage inputs of the PreAmp using a Digi-Key connector (part number SC1051-ND). The connector will have to be wired to the battery.


The SC1051-ND connector is center negative. Inverting the connection will damage the PreAmp.

Using RZ processors, BioAmp input appears clipped or larger than expected


Product: RZ2, RZ5, RA16PA, RA4PA
Version: All
Date Added: 2006-09-19


When using the RZ2 or RZ5 processor BioAmp input from the Legacy Medusa PreAmps will appear too large or clipped unless a scale factor is applied.


The Legacy Amp, RA16PA/RA4PA inputs must be scaled by a factor of .000833 The RZ Input Macro applies the appropriate scale factors automatically. However, if the macro is not used in the circuit, the user must use Scale Add or MCScale to ensure the scale factor is applied.


Use the RZ2_Input_MC macro for RZ2 or RZ5_AmpIn and RZ5_AmpIn_MC macros for the RZ5.

Some RA16PA and RA4PA generate a 3 kHz noise that masks neural activity


Product: RA16PA, RA4PA
Version: Serial numbers < 3000
Date Added: 2002-12-17


Some RA16PA and RA4PA with serial numbers < 3000, generate a 3 kHz noise that masks neural activity.


The voltage regulation on the preamplifiers has been modified to provide better control of voltage variation. The preamplifier has also been modified so that low battery voltage is indicated earlier. This 3 kHz noise artifact is not generated on all headstages with all electrodes. We recommend updating to the new preamplifiers only if your system generates this noise.