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  1. KrisBlueNZ

    Dodgy Power Amp Design

    No significant effect. The closed-loop gain is not high, and the signal levels are very high compared to the input offset voltage or any offset caused by input current. Me too. I wasn't suggesting returning the feedback network to that point. The feedback network consists of R6 from the...
  2. KrisBlueNZ

    Another treadmill problem

    OK. I've just discovered that I've missed something important - the big white relay marked JQX-105F-1. This relay is controlled by Q2 and possibly another transistor next to it (it's covered with white goop so I can't tell), and these transistor(s) are controlled by the daughter board. So don't...
  3. KrisBlueNZ

    Dodgy Power Amp Design

    R7 should be a much higher value, especially if you want a reasonably flat low-frequency response. I would use 100k for R7. You can simplify the circuit slightly by doing what I suggested in post #11. That is, (1) delete R7; (2) disconnect the junction of R1 and R2 from C2; (3) connect the...
  4. KrisBlueNZ

    HP 1741A Oscilloscope

    OK, for the 156V rail, can you do the following. 1. Add a 1N4007 diode permanently to the LVPS board, with its anode to the +120V rail (on one end of CR3) and its cathode to the emitter of Q11 (the +156V rail). This will give some protection to Q11. 2. With power on, measure the voltage across...
  5. KrisBlueNZ

    HP 1741A Oscilloscope

    The +120V rail used to be correct, didn't it? If you've disconnected all the outputs from other parts of the scope, that might be why the +120V rail has increased. You really need to measure them under load. The +156V rail is generated by piggy-backing on top of the +120V rail. So if the +120V...
  6. KrisBlueNZ

    LED color organ

    If the input amplifier is oscillating, it's most probably because of an error in the connection of the components that results in the overall feedback around the amplifier being positive, with an overall gain of more than 1, instead of negative, at a particular frequency. A common emitter...
  7. KrisBlueNZ

    HP 1741A Oscilloscope

    If you're going to replace A15U1 (CA3094A) it would be worth checking the voltages around it, and the operation of the HVPS without it, before you install the new IC. This is just a precaution because the CA3094A is a scarce commodity. I also suggest that you fix the +48V regulator before...
  8. KrisBlueNZ

    Dodgy Power Amp Design

    If you hadn't connected the transistors properly the first time you powered it up, you may have damaged one or several of them. For each of the four transistors, disconnect the collector from the circuit and measure resistance from collector to emitter in both directions. They should all read...
  9. KrisBlueNZ

    Another treadmill problem

    OK. The 5L0380R is a switching power supply controller, driving the transformer. There are two separately isolated outputs from the transformer. One powers the control circuitry on the daughter board, and the other powers the components in the corner, which connect to the three white connectors...
  10. KrisBlueNZ

    LED color organ

    That circuit is designed for a 12V power supply. If you use a 9V power supply, the biasing conditions for the transistors won't be quite right. That doesn't explain why the LEDs are constantly ON, though. The fact that the LED brightness responds to the sensitivity pot implies that the input...
  11. KrisBlueNZ

    Dodgy Power Amp Design

    R1 and R2 need to connect to the right side of C1, to provide the DC bias at the non-inverting input of the op-amp. The left end of R6 needs to connect to the inverting input of the op-amp, i.e. the top end of R3, not the bottom end. C4 would normally be connected in the positive output line...
  12. KrisBlueNZ

    Custom Clap On Light Circut Help

    Hi Jack and welcome to Electronics Point :-) That clap detector looks reasonable. You can find more information on the Velleman web site: http://www.velleman.eu/support/downloads/?code=MK139 There are several issues you will have to overcome. First, the board is probably too big to fit inside...
  13. KrisBlueNZ

    Automated Sliding Door

    D'oh! Good idea.
  14. KrisBlueNZ

    HP 1741A Oscilloscope

    You've got Q8 and Q6 swapped over. Other than that it looks OK.
  15. KrisBlueNZ

    Automated Sliding Door

    Right.
  16. KrisBlueNZ

    Automated Sliding Door

    OK, let's stick with the Wildgame timer. You'll need two of them. If the linear actuator consists of, or works like, a motor with a worm or similar gearing system, then yes you should be able to use it. It will save you from having to build the gearing yourself. In other words, if you can...
  17. KrisBlueNZ

    Another treadmill problem

    Stick with digital multimeters. Analogue ones have their place but for measuring resistance they are a mixed bag and can cause confusion. So the 0.021 ohm resistor is probably OK. In that case the MOSFET and diode are probably OK too, but you should check them. OK, assuming the MOSFET and...
  18. KrisBlueNZ

    Automated Sliding Door

    There is no need for a second motor. Any control scheme can be connected to a single motor - all you need is an external relay, or relays, to provide the changeover contacts. If you use two timers, they could both run off the same battery. This could be the same battery that powers the motor...
  19. KrisBlueNZ

    Dodgy Power Amp Design

    C5 isn't necessary but it will reduce distortion. I would keep it. The output series resistor (22 ohm) might help a tiny bit perhaps, if the load is highly capacitive or inductive, but it doesn't need to be so high. A few ohms would be plenty. But with the Zobel network you shouldn't need any...
  20. KrisBlueNZ

    What Is The Ohm Of This Resistor

    I wondered about that, but it's only a small resistor. A resistor in that position would be dissipating quite a bit of power, I think. I guess so... but why would it be run through a hole in the core, instead of around the core as a single turn? Seems pretty strange to me! Edit: to the OP...
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