Search results

Search Forums New Posts
  1. duke37

    Audio level with potentiometer

    The volume control is normally connected to earth at one end and to the signal at the other end. A slider picks up the voltage for output. If the slider is near earth, the voltage is minimal. If the slider is at the 'top' then the signal will be maxixmum. Volume controls usually have a...
  2. duke37

    +DC_out_rtn, what does this mean..

    Often the sense terminals are connected to the respective output terminals via high value resistors so that the sense circuit works and the output terminals is controlled.. If the sense terminals are connected to the load, then that is where the voltage is controlled so any voltage drop in the...
  3. duke37

    1980 Soviet Radio Cassette amplifier problem.

    The quiescent current consumption will be about 10 or 20mA. The current will rise dramatically when the amplifier is driving the speaker. The power must come from somewhere. The distortion on number 6 (AM) sounds just like the signal from radio Luxemburg which used to be received in the UK. i...
  4. duke37

    FM fading

    The aerial is close to the window which, I think has a metal spacer separating the glass. The aerial is fed at a corner so the sensitivity will be maximum at 45 degrees to the horizontal. Try with the feed at the bottom or side. What polarisation does the transmitter use? A reflector could be...
  5. duke37

    Current flow in or out?

    Stranded wire will be little better than solid if the strands are not insulated from each other. Getting more surface area is usually achieved by using large diameter tube. Litz wire has many very thin strands insulated from each other and is the devil to solder. It is often used in radio...
  6. duke37

    Current measurement circuit , Shunt resistor value Selection

    The shunt resistor will affect the current it is measuring, depending on the circuit. If you want more output, it may be better to put some gain in the op-amp.
  7. duke37

    Simple FM Radio receiver

    It looks as if this is a superregenerative circuit. These are fiendishly complicated for such a low component count.The two transistors are connected as a fast oscillator, collector to base, collector to base. The audio comes from T1 collector which also drives T2 base. The timing of the...
  8. duke37

    1980 Soviet Radio Cassette amplifier problem.

    Why complicate things? You have a good FM radio and a good amplifier which work well together. What does it sound like? You have an AM radio which is distorted. The distortion could be due to variation of the power supply or a faulty VT5 (unlikely). I have not worked out the AM AGC. Look at the...
  9. duke37

    1980 Soviet Radio Cassette amplifier problem.

    A few mm of unshieded wire will not pick up significant signal if properly terminated. The FM signal can be seen at VT11 collector and the AM signal at the collector of VT12. If these signals are clean , then the AM and FM radios are OK. Oscillation at any frequency is probably due to bad...
  10. duke37

    1980 Soviet Radio Cassette amplifier problem.

    The first graph in #76 is a clipped square wave which has all harmonics to infinity. The higher harmonics are removed giving the shape shown. Some of your waveforms have a mush on top of the sine wave. Where does this come from? You need a clean sine wave to find problems. Also a clean zero...
  11. duke37

    Ferrite rod antenna explanation

    The wooden rod is used so that you do not have to wind the coils on the delicate ferrite rod. L1 should be separated from L2 and L3 because of capacitive effects. You seem to have done a very neat job.
  12. duke37

    1980 Soviet Radio Cassette amplifier problem.

    It almost looks to me that the signal has a high frequency component when the volume is turned up. High frequency oscillation is not uncommon when by-pass capacitors are not in good order.
  13. duke37

    Ferrite rod antenna explanation

    I have never seen a ferrite rod 90mm diameter, they are more likely to be 9mm diameter and 100 to 150mm long. The schematic looks to be a medium wave receiver. Do you have strong signals in yout area. Make a wooden rod the same diameter as the ferrite rod. Wind some paper around it and glue...
  14. duke37

    1980 Soviet Radio Cassette amplifier problem.

    I had another look at the schematic and the only part between the radio and amp is block A7. This is far too complicated for me to understand. There are no active components but there are two potentiometers which could be faulty. R10 has a tapped track and it will be difficult to find a replacement.
  15. duke37

    1980 Soviet Radio Cassette amplifier problem.

    I suggested looking at the signal source for distortion. This implies using the scope to look for clipping or other funny waveforms. Use another radio to listen to the same station. It is unlikely that the FM and AM radio sections are both wrong but you should work your way from the radio to...
  16. duke37

    1980 Soviet Radio Cassette amplifier problem.

    I have two single channel scopes, both using valves. One works, the other, a Heathkit OS1, is waiting for me to rewind the mains transformer. Look at the signal source for distortion. FM. Test point Kt, junction of C56 and C57 AM. Voltage on C58.
  17. duke37

    1980 Soviet Radio Cassette amplifier problem.

    You have a scope, much, much better than mine:). You have a volume control so overdriving can be limited. Look at a voltage source and work through towards the output until some distortion appears. Please do not describe the supply voltage as - 8.7V, it is almost certainly positive.
  18. duke37

    1980 Soviet Radio Cassette amplifier problem.

    Depends where you measure the input.. The gain is R31/R32 or 15k/56 = 280 1300/5 = 260 which is very close. The amp seems to be running boooootifully. Do not go fiddling with R18 and R38. I told you how to set these up ages ago. R18 sets the amplifier output voltage to half the power supply...
  19. duke37

    Mackie RC4 speaker no sound

    Do not replace components on a whim, this is a way of introducing more faults. Remove the boiled capacitor. Clean up the board with meths. Check the tracks under the brown area for continuity. Check the speaker for resistance (between 4Ω and 15Ω) What active devices are used. Try to draw a...
  20. duke37

    Mackie RC4 speaker no sound

    Electrolytic capacitors go leaky after a considerable time particularly if they are abused. I think the bad one is the capacitor feeding the speaker so will not do anything if no speaker is connected. If you are VERY lucky, this is the only component to be changed. The grott needs to be removed...
Top