Ultrasonic anti-fouling power requirement
Your article states that the power drain for the Ultrasonic Anti-fouling Unit is 220mA at 12V. Instead of using a 12V battery at all times can I use a suitable battery charger as the boat will be in my marina and can be connected to mains? (N. H., via email).
• The circuit draws a peak current of up to 3A at 12V even though the average is only a modest 220mA. Some of this peak is provided by the low-ESR capacitors across the supply rails but you still need a supply that can deliver at least 2.5A (peak) for reliable operation.
Lead-acid battery chargers should only be used in conjunction with a lead-acid battery. If you want to avoid the use of a battery and you have shore power, the unit can be powered from a 12V DC plugpack that can deliver the peak current. The Jaycar 12V 2.5A plugpack (Cat. MP-3490) would be suitable.
Nixie clock is galloping
With regards to the Nixie Clock published in the July & Aug 2007 issues, I have found that my clock is intermittently running much faster. On one occasion, I measured the frequency at the test terminals at 191-192kHz; it should be 32.768kHz. Should I replace the crystal, the 4060 IC or the other parts surrounding the 4060? (M. M., via email).
• Try changing the 2.2kΩ resistor from the crystal to pin 10 of IC7 (4060) to 330kΩ. This will limit the voltage drive to the crystal and, in conjunction with the capacitance to ground, prevent overtone oscillation.
Using the Ultra-LD amplifier for PA work
I’m enquiring about the Ultra-LD Mk.2 Amplifier (SILICON CHIP August. 2008) which was available on a special deal recently. Would this amplifier be suitable to drive a Sound Reinforced FOH (front of house) PA System? Also, would the designated power supply for the Mk.2 be adequate to run two amplifier modules (the power supply for the Mk.3 version was stated as being able to run two modules)? (D. W., via email).
• The Ultra-LD module is quite suitable for PA work provided you do not intend using it to drive a transformer with 100V line outputs. That’s because the DC offset at the output of the amplifier could cause a high current to flow in the primary of the transformer (which can have very low resistance).
We strongly recommend that you incorporate the tiny upgrade PCB that we published in the September 2011 issue, as it greatly improves the stability of the quiescent current setting. The PCB is available from SILICON CHIP for $5. You will need one for each module, so if you order two, the total cost will be $20 including postage and packing.
The power supply will be more than adequate to handle two channels in a PA application.