[Solved] The Screamer Kit problems

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    • [Solved] The Screamer Kit problems

      Hi,
      I bought and built The Screamer kit but it doesnt work.

      Using an audio probe, I noticed that the problem is related to the RC4558: thesound arrives correctly to the pin 3, but no sound comes out from the pin 1 or pin 2. Ialso noticed that the VBias without the RC4558 is 4.5 V, but only 2.3 V withthe chip installed.

      I tried also with tl072cn (with this, Vb is correct but sound very distort with no mode to regulate gain and pot not working), tl072cp and tl471 but the problempersists. And no, I don't have an replacement for rc4558.
      I desoldered every single resistance, diode (received 1n4007 and changed with 1n4001) and every cap to check it. I built it two times desoldering and soldering the pieces, but nothing.

      Here attached the images.


      What could be the problem?
      Images
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    • Hi!
      Sure the 4558 has not been upside down? Did you insulate the pots toward the PCB? Is the R5 still doing it's job?
      Sounds strange, but the 072 should work quite as well (or as badly) as the 4558 does. The 4558 is just mojo, in my opinion I'd prefer the 072 or an 5532 anyway. You switch one diode, that might be usefull (if right installed), but switching the R15/R16 makes no sense in my eyes.
      Helpfull would be a measurement of the voltages (just DC) at all pins of the 4558.
    • Hi!

      there are no problems on R15-R16 (TS9-TS808), I desoldered the cables and put in the resistors without changing the result. Also, removing the IC and jumpering pin3-pin7 in the socket, the sound goes flawlessy from in to out.

      Loetbert wrote:

      Sure the 4558 has not been upside down?
      Yep, it's installed correctly.

      Loetbert wrote:

      Did you insulate the pots toward the PCB?
      Yes, I put the black bumpers arrived with the kit and no one part it's touching the pot.

      Loetbert wrote:

      Is the R5 still doing it's job?
      I measured it and seems working; with the audio probe i checked in the pin 3 of the IC and it works. What's the job of R5?

      Loetbert wrote:

      Helpfull would be a measurement of the voltages (just DC) at all pins of the 4558
      I measured it, I expected 4.5V on 1-2-3-5-6-7 pins but the measures on 1-2-5-6 are in the order of 40mV, OV on GND and 9.06V in Vcc. In pin 3 I have 2.4V.

      This evening I'll go to a shop to buy a new RC4558, just to see if the problem is chip-related.

      Thank you!
    • Hi!

      syntesys wrote:

      there are no problems on R15-R16
      Right, but I bet switching makes no difference in sound.

      syntesys wrote:

      I measured it and seems working; with the audio probe i checked in the pin 3 of the IC and it works. What's the job of R5?
      R5 gives the Bias to the first OP stage. Most of your board is looking very well, but your R5 not quite healthy. If it's broken, the voltage on the output will be going very very down, pulling the Bias via R8 and R9. The result would be the same as yours. You can check the R5 easyly by removing the IC and the battery/power supply and then meassuring the resistance ("ohms") between pin 1 and pin 3 of the open socket. This should be about 20k. If it's much higher you found the troublemaker.

      Good luck so far...
    • Hi Loetbert and thank you.
      Ok, I thought that for R5, good.
      Then, I measured without the chip and the resistance is 20 ohm (also in the pins of the second amp) so the problem is not R5. Installing a new rc4558, I found that all the pins and the VBias is more or less 4.5, so now the bias is correct... But the pedal does not sound.
    • Yesterday I was a lot tired, sorry:
      • On pins 1-3-5-7 I have 4.5V;
      • On pins 2-6 I have 4.0V;
      • With the phrase "the pedal doesn't sound", I meant that even if the voltages are pretty good, the sound arrives to the pin 3 of the RC4558 and then gets lost, there is no sound in the output pin 1;
      • Another thing I noticed is that when I touch the volume pot I can hear a hum going to the amp.
      Launch of a scream or launch of the scream? This is the problem :D

      The post was edited 1 time, last by syntesys ().

    • Hi,
      If pins 2 and 3 both show about 4,5V and if there is Signal at 3 but not at 1, I would assume a shortcut between 2 and 3.
      Good luck Christof
      =O Achtung: Bei Röhrenamps liegen LEBENSGEFÄHRLICHE Spannungen an. =O
      Bevor an einem Gerät gearbeitet wird muss es spannungsfrei gemacht werden und das muss auch überprüft werden. Jeder ist für seine Sicherheit selbst verantwortlich!
    • Hi and thank you all,

      The problem was chip+board fault. In the feedback circuit of the gain amplifier there was an open circuit between gain pot and 51k resistor; making a little bridge and changing the chip, I resolved all the problems. I found the problem checking the resistor between pin 1 and 2: in my case I found that there was an open circuit; then, tested continuity point to point from pin 1 to pin 2.

      Problem resolved, thank you all!
    • syntesys wrote:

      With the phrase "the pedal doesn't sound", I meant that even if the voltages are pretty good, the sound arrives to the pin 3 of the RC4558 and then gets lost, there is no sound in the output pin 1;
      I thought you meant it works and don't like the sound of it.

      syntesys wrote:

      On pins 1-3-5-7 I have 4.5V;

      On pins 2-6 I have 4.0V;
      this made me nervous, because if pin 3 is 4,5V and pin 2 is 4,0V the output pin 1 should rise up to about 8V.

      cebersp wrote:

      a shortcut between 2 and 3.
      I thought of this, too, but this would be a unity gain amp and the audio probe should give the clean signal at the output.

      syntesys wrote:

      The problem was chip+board fault. In the feedback circuit of the gain amplifier there was an open circuit between gain pot and 51k resistor
      Together with the knowlege of PNP input transistors in the 4558 this explains the results, there was no tone because the OP was feedbacked just by a diode. But I wouldn't have thought of it, so...

      syntesys wrote:

      making a little bridge and changing the chip, I resolved all the problems
      is very nice, congratulation to you and thanks for your knobel task!