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  1. Audioguru

    help to identify

    The capacitors are very old metalized plastic film type. The line indicates the outer wrap that should be grounded or connected to a low impedance source so the capacitor does not pickup interference from the air. Some fairly modern Oriental capacitors look like yours but European and American...
  2. Audioguru

    PREAMPLIFIER QUESTION BPA-100S Logitek PREAMP

    You spelled Logitech wrongly so maybe you also spelled the part number wrongly? Their website does not list any preamplifier. Maybe it is old and not shown anymore?
  3. Audioguru

    I'm Back- sort of

    The opamp circuit in post #165 has no distortion diodes so its massive gain of 221 times will cause 7V peak-to-peak squarewaves at the 1uF capacitor output. if the opamp is in a pedal at the guitar and connects to an audio cable then it needs a 100 ohms resistor on series between the 1uF output...
  4. Audioguru

    I'm Back- sort of

    The sequence of connecting the points 1 to 5 does not matter since they all connect to the same place in the circuit.
  5. Audioguru

    I'm Back- sort of

    Points 1, 2, 3, 4 and 5 should all be connected very close together. If they are miles apart then their wires would be antennas that pickup mains hum and all kinds of other interference. The 10k tone control feeds C29 that is 22nF. Then when it is used at maximum resistance, 706Hz is reduced...
  6. Audioguru

    I'm Back- sort of

    You have lots and lots of distortion now.
  7. Audioguru

    I'm Back- sort of

    Distortion produces many high frequency harmonics. If the amplifier and speakers (missing tweeters) cannot produce high frequencies then the severe distortion produced by the diodes when the gain pot is at maximum resistance might not be noticeable. Here are frequency response graphs of typical...
  8. Audioguru

    I'm Back- sort of

    If you look at the knob and see the slider going around the resistive track clockwise and counter-clockwise you can see the resistance changing. Clockwise and the gain and distortion from the diodes are high. Counter-clockwise and the gain is 1 and no distortion because the diodes are shorted.
  9. Audioguru

    what is AC dual 24V?

    If the amplifier is class-AB type then each stereo channel produces about 12W into 8 ohms (20W into 4 ohms) and the sub-woofer channel produces 38W into 8 ohms (63W into 4 ohms) when the supply is 33VDC. With a 24VDC supply, each channel will produce about 6.3W into 8 ohms (10.5W into 4 ohms)...
  10. Audioguru

    I'm Back- sort of

    To make high frequencies appear to be boosted, resistors and capacitors can reduce the level of all low frequencies. Most guitar speakers are missing the high frequencies above 2kHz or 3khz produced by a tweeter. High frequencies are boosted up to normal (by the inductance of the pickup...
  11. Audioguru

    I'm Back- sort of

    The guitar recording seems to have the high frequencies cut but sounds clear and clean. I played a trombone in my high school band and travelled all over British Columbia winning band contests. Live, no amplifier or speakers.
  12. Audioguru

    I'm Back- sort of

    The very high output level of the opamp without diodes will have loud and harsh distortion, but only if you reduce the input level feeding your power amplifier to prevent the power amplifier from clipping. The much lower level with diodes will have softer distortion. The 1N4148 and 1N914 diodes...
  13. Audioguru

    I'm Back- sort of

    The output of an opamp is about 7V peak-to-peak when the battery is 9V and there are no diodes in the negative feedback. With the diodes the output of the opamp is about 1.2V peak-to-peak that produces much less loudness. Since the diodes bypass the gain pot and reduce the gain in addition to...
  14. Audioguru

    what is AC dual 24V?

    Why does this audio amplifier have no audio specs? Is it because it is no-name-brand and is sold on ebay by people who know nothing about audio amplifiers? The ad says 100W x 2. Is that peak Whats at horrible clipping distortion so its real output is only 20 Watts x 2 with low distortion...
  15. Audioguru

    I'm Back- sort of

    Yes, the ground wire (or 0V wire) of a modern electrolytic capacitor is marked with an arrow or thick line. A long time ago the + wire was marked with a "+" instead which is why the + is marked in modern schematics.
  16. Audioguru

    I'm Back- sort of

    An electronic tremolo on-off can be done with a 555 oscillator driving a 2N7000 Mosfet. Each time the Mosfet is turned on it shorts the signal to ground. You probably need a pot to set the speed of the pulses and maybe another pot to set how much the signal level is cut for each pulse.
  17. Audioguru

    I'm Back- sort of

    A kill momentary pushbutton would be wired with a shielded audio cable parallel with the guitar pickup. A pushbutton with gold plated contacts (very low current rating) works reliably for audio and costs the same as a pushbutton with silver plated contacts (high current rating) that get corroded...
  18. Audioguru

    I'm Back- sort of

    Your opamp had no DC input bias voltage. Your 220nF capacitor value reduced the levels of all low frequencies at 727Hz and below. 3.3uF passes all guitar frequencies because it is 15 times more. Make the preamp like this:
  19. Audioguru

    I'm Back- sort of

    The sound is very low in volume compared to the Youtube clip. At a proper volume, it should pump out the same punch as in the video. By the way, I used the TL081 (which has the same pin settings as the 4558D). No. The pin numbers on a TL081 opamp are completely different to a 4558 dual opamp...
  20. Audioguru

    I'm Back- sort of

    The opamp output pin1 does not connect to a 1k resistor. I think the capacitor to ground is missing again:
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