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  1. audioguru2

    Sequential Timers with PWM Motor Speed Control

    Hi Guys, Boo-Hoo! :'( :'( My electric model airplane crashed and got broken many times. Luckily I'm retired and have lots of epoxy glue so I have the time and resources to fix it each time. The fuselage broke in half. I joined it with epoxy glue and painted the scars and you can't see them. Even...
  2. audioguru2

    BJT power supply

    Hi Ante, Are you feeding your 555 from the little fused wire for the fuel pump? In my son's car, the fuel pump was getting only 9V and couldn't pump enough fuel for his boosted turbo until much heavier wire was installed for it. Install your own wire for the 555 from the battery and you won't...
  3. audioguru2

    ElCheapo PSU

    Hi Autir, You have three 1/2A supplies so the transformer's current rating should be 2.1A. The 12V regulator needs a minimum of 15V input and the ripple on the main filter cap might be 1V. The rectifier bridge needs up to 2.5V (the rectifier current might be 20A pulses) so the total minimum DC...
  4. audioguru2

    Capacitors in amplifiers: polarity or not?

    Input C3 (I changed it to C2) has the opposite polarity of C1 to make a non-polarized pair. Input C3 (C2) isn't needed since the electret mic end is very positive and the base of the transistor is much less positive. The polarity of C3 for a dynamic mic is shown correctly since the mic is a DC...
  5. audioguru2

    Convert Voltage

    Hi Alun, For about 50ns of each output transition, both Mosfets will conduct 10A to hundreds of amps from the power supply to ground. That's why I suggested using a SMPS IC with its dead-time controlled to avoid both Mosfets in series conducting at the same time. :( The little 555 is bad by...
  6. audioguru2

    PC speakers amp with TEA2025

    You have a very good point. ;D Since R5 and R6 are 330 ohms and are in series with 50 ohm resistors inside the IC, they reduce the gain from 201 down to only 27. At first I thought it was good, because it also reduces the noise and distortion and extends the high frequency response. But after...
  7. audioguru2

    PC speakers amp with TEA2025

    C1 and C2 in your circuit are 100uF, the bootstrap capacitors. I confused C1 and C2 in your circuit. The datasheet's input caps C1 and C2 are a low value. Your circuit has them (C7 and C8) much larger probably to charge slowly and reduce pop. It is best to use 150nF as recommended by ST Micro...
  8. audioguru2

    Convert Voltage

    It would be simple with a TL494 variable-frequency oscillator with its opposing outputs driving an H-bridge made from two pairs of complimentary Mosfets. I gave the details in your other posted topic. You'll need some inverters to drive the H-bridge with some dead-time for the seriesed Mosfets. ;D
  9. audioguru2

    ElCheapo PSU

    Hi Staigen, Often we say exactly the same thing at the same time. ;D
  10. audioguru2

    PC speakers amp with TEA2025

    Hi Autir, ST's circuit is very similar to yours. You don't have pin 16 connected to VCC and your C12's negative wire should go to ground. Your circuit has R5 and R6 added to reduce the gain, and R1 and R2 added to reduce the pop when supply voltage is applied with the volume control low. The...
  11. audioguru2

    Capacitors in amplifiers: polarity or not?

    No. Polarity is extremely important with polarized capacitors, that is why it is marked. If they are installed backwards they blowup like a bomb if the charging current is high enough! Carefully try it. With a low charging current a backwards polarized capacitor leaks a lot of DC current and its...
  12. audioguru2

    veroboard pen: minor cuts and failure :'(

    Veroboard is a name-brand and its good quality is well known. Stripboard copies could be bad like the one made in Taiwan that smells like it is made of dung. RadioShack had a type of stripboard made of cheap phenolic and with very thin copper. Its holes were too big for most parts leaving the...
  13. audioguru2

    ElCheapo PSU

    Hi Autir, The 78xx series of voltage regulators have an opamp inside with its high frequency response rolled-off for compensation. Therefore for a quickly changing input voltage or load current the output voltage will have a transient change. An output capacitor filters the transient. To obtain...
  14. audioguru2

    ElCheapo PSU

    Hi Autir, I have seen capacitors across rectifiers in old RF and audio circuits but I have never used them and new circuits don't have them. It was to stop the buzz caused by the rectifiers switching very quickly and spraying high frequency transients around. If you look closely at the...
  15. audioguru2

    veroboard pen: minor cuts and failure :'(

    Hi Autir, I have used a lot of Veroboard for many years and have never seen the "brushing tool" you have. I purchased from Vero a handtool which was a drill bit in a wooden or plastic handle, called a "spot face-cutter". Most of the time I use my drillpress to cut the copper tracks. If the drill...
  16. audioguru2

    Capacitors in amplifiers: polarity or not?

    Non-polarized film capacitors have lower distortion than polarized electolytics. Film capacitors above about 1uF are very expensive so frequently electrolytics are used. You can buy non-polarized electrolytics which are two polarized ones in series and connected with opposing polarities, like C1...
  17. audioguru2

    Camping Music Box - PROJECT

    Hi Hamoodyjamal, You have a good idea to use computer self-powered speakers. My new computer came with pretty good-sounding speakers that are powered by a 12VDC/1A wall-wart. I took one apart now and it has a 3" (77mm) 4 ohm speaker that is very heavy and has the biggest magnet I've seen on such...
  18. audioguru2

    BJT power supply

    With the engine driving the alternator, high voltage spikes are caused when a battery terminal makes poor contact with the battery. Many cars have cruddy battery posts and people replace the "failing battery" instead of cleaning and tightening the connections. ;D
  19. audioguru2

    Convert Voltage

    Hi Ante, I was thinking about using one of TI's class-D audio amps for double the output current, but they all have a bridged output. ;D
  20. audioguru2

    BJT power supply

    Kevin, The voltage doubler is the standard 555 driving a boost capacitor, 2 diodes and a filter capacitor for a low current voltage that is higher than the supply voltage. The gate voltage of the source-follower Mosfet needs to be up to 6V higher than its source voltage (the supply voltage) for...
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