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  1. BobK

    Smart phone charging.

    You should use a switching regulator. A linear regulator from 12V to 5V will waste 60% of the power, whereas a switching regulator can waste as little as 10%. I am not sure what your are asking about discharging the battery. If you mean to purposely discharge it, I don't see why. Bob
  2. BobK

    TDA2030A Headphone Amp Gain too high

    Where do you see that minimum gain in the datasheet. I am looking at this one: http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/CD00000129.pdf Bob
  3. BobK

    How to connect multiple amplifiers

    I looked at the datasheet for the LA4460. A couple of observations: It is a bridged amp, so it can produce 4x the power I computed before. It has a gain of 51db which is a voltage gain of 345. This is way too much if you are giving it line level inputs, which explains why you get so much...
  4. BobK

    Current limiter add on

    Seeing as AAs are typically 2000mAH, I don't see why 10000 for a D cell is a stretch. Bob
  5. BobK

    How to connect multiple amplifiers

    Using darlingtons in the output, you can only get about 2V from the rails, so 4V sounds about right. Your 12W figure cannot be right. Given that the most swing you can get is 6V p-p that is 4.6V RMS and V^2/R is 21.3/4 = 5W. With an 8 Ohm speaker this falls to 2.5 W. With your 4V swing, that...
  6. BobK

    40106 output current capability?

    If you look more closely at that table, there is a column titled "conditions" In this table, it list the output voltage as 4.6V to get -0.5ma of output current. Yes, you can get more current out, but that it the current that can be guaranteed when the output voltage is 4.6V. At higher...
  7. BobK

    How to connect multiple amplifiers

    All of the grounds should be connected together, with no resistor. Bob
  8. BobK

    Current limiter add on

    An NiMH D cell is about 10000mAH at 1.2V or 12WH, so more like 2 of them than 10. Bob
  9. BobK

    Amplifier question

    I thought Steve explained it well, but since you did not seem to understand I will try to elaborate. Any signal source consists of a voltage and an impedance. The impedance can be thought of (in the simple case) as a resistor in series with the output voltage. Say you have a source that...
  10. BobK

    A bit colour blind..

    The colors in the picture are quite readable, I cannot believe they could be a burnt versionn of 270 which would be red violet brown Bob
  11. BobK

    understanding Ferrite Rings

    Switching power supplies do not like a no-load condition. By using PWM after it, you are creating periods where there is no load, and the power supply is needing to adjust quickly to that every PWM period, so it is throttling back and fortch at the PWM frequency. I don't know if this would...
  12. BobK

    what exactly is Voltage

    The correct analogy is not that voltage is analogous to gravity, it is gravitational potential that it is analogous to. And in a uniform gravitational field, that is proportional to height, which is the analogy Steve was using. Bob
  13. BobK

    Tri-amping with active crossovers

    You would not have to design any amps. There are plenty of them out there for less money than you could build one for. Check Ebay. Bob
  14. BobK

    Negative Voltage on Breadboard with no negative voltage input

    Or, if dealing with small signals, you can just use an op amp to split the rails. Just tie the output to the - input and place a 1:1 divider on the + input. The output is then at 1/2 the supply. Use about 10K resistors. Bob
  15. BobK

    A bit colour blind..

    The fourth band is the tolerance, but black does not make sense. It looks gray in the picture, is it maybe silver, which would be 10%? 3.9K is orange white red. It might have a gold band for tolerance, which would be 5% Bob
  16. BobK

    EL Wire Project for 50cc Scooter

    EL wires runs on about 100V AC, not 3V DC. The original power supply uses an inverter to produce the 100V AC from the 3V batteries. Your best bet is to find and EL power supply that runs from 12V. They should exist. Bob
  17. BobK

    Reducing SIGNAL voltage to tiny servo from 5V to ~4V

    The lower resistor is not a 4.7K, it looks like a 0.47 Ohm resistor: yellow, violet, silver. You want yellow, violet, red. Bob
  18. BobK

    A bit colour blind..

    3.9K Bob
  19. BobK

    Power loss and Energy loss

    Watts is a measure of power. Which is energy per second. You do not lose Killowatts every second, you lose KiloJoules every second. If you are losing power at a rate of 1W then you are losing 1 Joule of energy every second. Bob
  20. BobK

    what exactly is Voltage

    I give up. Bob
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