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  1. AnalogKid

    8 channel sinusoidal function generator

    Many opamps have a unity gain crossover of greater than 1 MHz, so for a simple voltage follower there are many choices. However, 150 mA peak at 1 MHz is not a simple app note circuit to copy. Some current feedback opamps designed for the DSL market might handle this. Separate from that, what...
  2. AnalogKid

    First amplifier build

    If by first build you mean your first electronics assembly project, you are umping in way out there toward the deep end of the pool. Starting with a heavy and stiff chassis, you have to punch several different sizes of large holes for the tube sockets. Also, the transformers were almost...
  3. AnalogKid

    Need Help w/ a simple project

    How big a box? 100% exposed metal on all surfaces, or only certain areas? ak
  4. AnalogKid

    Resiter Divider / Resister Watt ratings

    https://en.wikipedia.org/wiki/Buffer_amplifier Scroll down to "Voltage buffer examples". The first one is an opamp voltage follower. Since you don't need an output that is accurate down to 0 V, you can run on a single power supply rail, ass opposed to bipolar supplies like + and - 12 V. How...
  5. AnalogKid

    Resiter Divider / Resister Watt ratings

    I'm saying that if a 2-resistor divider straight into the Arduino doesn't perform the way you want, then a resistive divider followed by a buffer of some kind such as a voltage follower is almost certainly work for you. What is the input voltage range of the Arduino that you want to use? The...
  6. AnalogKid

    Resiter Divider / Resister Watt ratings

    Mostly, the input draw of the Arduino. Using Ohm's Law, you can calculate that a 5:1 divider made up of 4 ohms and 1 ohm produces the same output voltage as one made up of 400K and 100K, but the series current in the latter divider is 100,000 times less. The problem (remember, "mostly") is...
  7. AnalogKid

    Negative Voltage

    In the physics of the situation, a point (thing, node, pin, whatever) can have a measured voltage that is "negative" with respect to ground if it has lotsa electrons, because an electron has a "negative" charge. In this sense, a "positive" voltage is a place where there are fewer electrons than...
  8. AnalogKid

    High pass filter

    The calculator in post #1 is for a simple R-C filter, and is not appropriate for a speaker crossover. ak
  9. AnalogKid

    High pass filter

    It probably is just a capacitor in series with the speaker, with the speaker acting as the shunt element. High value bipolar electrolytics for the speaker market are not as expensive as you might think, but they are specialty parts. ak
  10. AnalogKid

    Please help with Kinetic Audio Amp

    In your first photo, the jack o the upper right is similar to this: The hole is the sleeve contact. Notice to the right that the tip contact has an extra piece of metal touching it. That is the switch pin. The tip and switch are a normally-closed SPST switch. When you insert the plug it...
  11. AnalogKid

    Please help with Kinetic Audio Amp

    You don't say anything about how the two output connectors functioned when they were "stock". It looks like one is connected to the 8 ohm tap through a switch in the other that also connects to the 4 ohm tap. How are the two connectors labeled on the outside of the unit, and is there anything...
  12. AnalogKid

    Decibel Calculation

    I agree. A 43.429% error is a frustrating problem. I understand your frustration, but the problem here is that we actually do know what we're talking about, and we are not refusing to answer your question because we're pedantic jerks. The mathematical definition of a bel has been around for...
  13. AnalogKid

    sneak in video signal on an old dvd player

    The player electronics might be too tightly integrated into the display electronics to find a clean insertion point. Also, usually those kinds of devices have ASICs (application specific ICs, what use to be called custom parts), so it will be very difficult to find data. The chipset might have...
  14. AnalogKid

    sneak in video signal on an old dvd player

    What you want to do is not clear. If this is a DVD player, why do you want to feed a video signal *into* it? DVD players make outputs, not inputs. ak
  15. AnalogKid

    9v Guitar Amp w/out LM386

    In round numbers, you're recreating the guts of an LM386. ak
  16. AnalogKid

    Decibel Calculation

    Why would it? That conversion factor is wrong. If it makes the results correct, then there is a problem somewhere in the calculation engine. Access is a database program, not even remotely related to something to use for calculations. I haven't run the numbers, but Access might be performing...
  17. AnalogKid

    9v Guitar Amp w/out LM386

    No, it's the way it is supposed to work. One problem with schematic B is that Q1 is "dangle-biased", where the base current is kept so low that the circuit's operating point is set by Q1's gain. This value varies with changes in collector current and temperature, making the operating point...
  18. AnalogKid

    9v Guitar Amp w/out LM386

    In schematic B, the Q2 emitter is grounded so that transistor is running wide open no matter what its collector load is. I like using the output capacitor and speaker as part of the bootstrap. I saw that a loooong time ago, then forgot about it. Cute. ak
  19. AnalogKid

    Specific IC s used in solar circuit

    The solar cell output voltage is proportional to the ambient light. Monitoring it's output voltage is the same function as monitoring the resistance of an LDR. ak
  20. AnalogKid

    Two transistors to switch on/off two relays with an arduino from one pin

    0.4 V is a typical output voltage for a logical low output. Nothing about the transistors would pull it that low. Are you sure you are programming the pin correctly? In other words, what is the output pin voltage with the transistors not connected? ak
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