14-04-2015, 04:44 PM
My Velleman Mono Preamp kit 'K1803' has just arrived, and its a really dinky little thing (PCB is 30mm x 40mm) and excellent value for money from ESR Electronics at just £3.90.
Really not worth going to the trouble to make a PCB and source the bits separately.
The stated supply voltage range is from 10 - 30V DC, with 12V printed on the PCB. Though it might well work off a new PP3 battery, I don't think it would be happy when the Voltage tails off to 8V or below. I therefore thought I might connect two PP3s in series, making 18V and using say a 78L12 12V regulator. As the preamp only draws 10mA a TO92 plastic cased one would suffice. I think that all that's needed is a cap on the input and output, as I've drawn in the sketch below. If I use two PP3s, the Voltage could fall to 15.2V for the regulator to still function, so would give decent battery life. However, I'm just wondering if the 78L12 will be happy sinking 6 Volts, albeit as I say, the current drawn will be modest, at 10mA.
You might wonder whether it's worth bothering with a regulator - if it will stand from 10 - 30V why not just poke two PP3s in and be done with it? There's a pre-set on the PCB to set the gain level, and if I set it with 18V, the gain will obviously diminish as the battery Voltage tails off, but maybe that won't matter, because the volume control of the radio into which the I-pod will be playing via the gram socket could simply be turned up.
So, the questions I'm asking are:
1) Should I just run it straight off two PP3s in series without a regulator to fix the voltage at 12V?
2) If I do used a 12V regulator, will it be happy with 18V input?
3) Do the values of the two caps in the circuit below look OK if I do use a regulator?
I think the presumption with the kit is that it will be run from a fixed voltage of between 10 - 30V - not a reducing voltage from a couple of PP3s, hence, my thoughts that a 12V regulator would be desirable.
Any views anyone please?
Really not worth going to the trouble to make a PCB and source the bits separately.
The stated supply voltage range is from 10 - 30V DC, with 12V printed on the PCB. Though it might well work off a new PP3 battery, I don't think it would be happy when the Voltage tails off to 8V or below. I therefore thought I might connect two PP3s in series, making 18V and using say a 78L12 12V regulator. As the preamp only draws 10mA a TO92 plastic cased one would suffice. I think that all that's needed is a cap on the input and output, as I've drawn in the sketch below. If I use two PP3s, the Voltage could fall to 15.2V for the regulator to still function, so would give decent battery life. However, I'm just wondering if the 78L12 will be happy sinking 6 Volts, albeit as I say, the current drawn will be modest, at 10mA.
You might wonder whether it's worth bothering with a regulator - if it will stand from 10 - 30V why not just poke two PP3s in and be done with it? There's a pre-set on the PCB to set the gain level, and if I set it with 18V, the gain will obviously diminish as the battery Voltage tails off, but maybe that won't matter, because the volume control of the radio into which the I-pod will be playing via the gram socket could simply be turned up.
So, the questions I'm asking are:
1) Should I just run it straight off two PP3s in series without a regulator to fix the voltage at 12V?
2) If I do used a 12V regulator, will it be happy with 18V input?
3) Do the values of the two caps in the circuit below look OK if I do use a regulator?
I think the presumption with the kit is that it will be run from a fixed voltage of between 10 - 30V - not a reducing voltage from a couple of PP3s, hence, my thoughts that a 12V regulator would be desirable.
Any views anyone please?
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
