Probleme mit Tonebender MKII

  • Hallo Leute,

    Ich kann Deutsch lesen, ich schreibe es aber leider nicht mehr so gut wie fruher. Deswegen werde ich mein Problem in Englisch beschreiben, ihr könnt mir aber einfach in Deutsch antworten!

    Alright, so the Tonebender MKII is the second kit I'm building from Das Musikding, so I'm kind of a newbie to the world of DIY pedals. The first one I did was the Plexi-Drive, which worked at the second attempt, after I figured out I did the classic thing of soldering the in and output the wrong way around.

    With the MKII I get sound in bypass, but when I engage the pedal the sound is gone but the LED is working. I've used an audio probe to find the issue while using a frequency generator. When I test at the output the frequency is still there but very quiet. After going through the signal path, I noticed the drop in volume when it gets to Q2, the second transistor, the capacitor before that (C4) is still loud. When I check with a multimeter (measuring from the bottom side at the solder joints), all three points of the transistor show up to 9v and the same goes for R8. However, on R6 I only get a reading on the multimeter on the side closest to the second resistor, the other side stays at 0 both from the solder point as well as the lead of the resistor on the other side.

    Is R6 the problem (resistor not working) or might it be somethig with the transistor itself? From here on the sound is very weakend but still there up to the output, at least as tested with the audio probe. With a guitar I head nothing though. Who can help me figure out what to do next?

    Kind regards,

    John Nada

  • Hi John,

    welcome to the board. Can you take some pictures of the board backside and frontside and post it here?
    Also post a link to the schematic please.
    By the Way: 9 Volt on every pin of a transistor is a very bad thing. :D

    Gruß Markus


    ---- in der Beschränkung zeigt sich erst der wahre Meister -----

    Einmal editiert, zuletzt von coolfool (19. Januar 2019 um 19:14) aus folgendem Grund: bad english ;-)

  • EDIT!


    I redid my measurements. The first time I did them, I grounded to the ground tip of the DC-jack. Someone on a different forum pointed out that this is not to be the correct way of doing this. Sorry guys, I'm a rookie. I did all of it again with the ground to the enclosure. Here are the new results:


    R1 (top): 0
    R1 (bottom): 0
    R2 (top): -0.08
    R2 (bottom): 0
    R3 (left): -8.99
    R3 (right): -1.82
    R4 (top): -8.99
    R4 (bottom): -8.30
    R6 (top): -8.99
    R6 (bottom): -0.15
    R8 (left): -0.07
    R8 (right): -0.07
    R9 (left): -8.99
    R9 (right): -8.96
    R10 (left): -8.45
    R10 (right): -8.96


    C1 (top): 0
    C1 (bottom): 0
    C2 (plus): 0
    C2 (minus): -0.08
    C3 (plus): 0
    C3 (minus): -8.99
    C4 (top): -8.11
    C4 (bottom): -0.07
    C5 (plus): 0
    C5 (minus): -0.03
    C6 (top): 0
    C6 (bottom): -8.96


    Q1C: -8.46
    Q1B: -0.07
    Q1E: 0
    Q2C: -0.16
    Q2B: -0.08
    Q2E: 0
    Q3C: -8.17
    Q3B: -0.16
    Q3E: -0.08


    D1 (ring side): 0
    D1 (plain side): -8.99


    And once again as a reminder, I get a full sound until I get into Q2, there the sound starts to get a lot weaker.

    3 Mal editiert, zuletzt von John Nada (20. Januar 2019 um 00:51)

  • Hi John!
    Nice picture - looking as well!
    Perhaps you first check the pinout of the transistors? Most simply you're just looking online for the pinout of your types of transistors and compare this with the printing on the board. Also focus, whether the pictures are top or bottom view.
    Good luck + Greetings,
    Lötbert

    Einmal editiert, zuletzt von Loetbert (19. Januar 2019 um 21:45)

  • Hi John!
    Nice picture - looking as well!
    Perhaps you first check the pinout of the transistors? Most simply you're just looking online for the pinout of your types of transistors and compare this with the printing on the board. Also focus, whether the pictures are top or bottom view.
    Good luck + Greetings,
    Lötbert

    Hey Lötbert, thanks! Do you mean if I connected CBE of the transistors the right way around? If so, the three pins on the transistors (which should be the E-side of the transistor) are torwards the edge of the PCB, which sould correspond with the PCB-layout. I already checked this out, since it was the first time I used these kind of transistors ofcourse. As far as I can figure out, they should be mounted the correct way.

  • Hi again,
    yes, as far I can see from the pictures the AC12x are mounted correctly.
    Two things are questionable to me in the moment:
    1. There is a DC-voltage on R1 where no one should not be. So what has been connected to the input when you meassured the above values? I don't see clearly from the pictures, perhaps something like a solderblubb in the switch?
    2. There is a relatively high DC-voltage on Q1. But you wrote first, that by audioprobe the signal passes it. On the other hand the Base of Q2 is - german - quasi ein virtueller Nullpunkt (virtual zeropoint? sorry my English!) - means it's little difficult measuring an AC-voltage there. What I want to say is, interchanging Q1 and Q2 might be worth a try.
    Better luck today,
    Lötbert

    2 Mal editiert, zuletzt von Loetbert (20. Januar 2019 um 00:04)

  • Thanks for helping me along Lötbert,

    1. Someone on a different forum pointed out that my way of measuring (with the ground to the ground tip of the dc-jack) was wrong. Rookie mistake I guess. I measured the transistors again for him with the ground to the enclosure and this is what came out:


    Q1C: -8.46
    Q1B: -0.07
    Q1E: -0

    Q2C: -0.16
    Q2B: -0.08
    Q2E: -0

    Q3C: -8.17
    Q3B: -0.16
    Q3E: -0.08

    I don't really see a solder bulb on the switch, but since the audio probe points out the drop in volume after C4 I figured it would rule out the 3PDT, since the issue occurs in the signal path of the PCB itself.

    2. The high voltage on Q1 might be explained by my way of measuring, as mentioned above, and I hope the new I measurements I provided help. I just switched them around and the outcome is unfortunately the same. I've been testing with a different amp since audio probing today, because that one has a headphone jack, so I was able to turn up the volume and find out that the low sound still leaking to the output is also there with a guitar plugged in, it's only a bit easier to here when you're sending a high beep when audio probing. But there is some sound leaking, but there is a dramatic loss of volume somewhere along the signal path.

    Und wenn Englisch nicht so einfach geht, ist es fur mich echt kein Problem in Deutsch zu antworten. Ich habe eine Deutsche Mutter und bin Zweisprachich aufgewachsen, nur schreibe ich leider die letzte Jahre so wenig Deutsch das es mir ein wenig schwer geht das zu machen. Dabei ist es mit dem "Fach Lingo" auf Englisch hier auch ein wenig einfacher, ich muss das meiste halt lernen von Google was DIY-kits angeht, und dan lernt man das meiste halt auf Englisch.

    Einmal editiert, zuletzt von John Nada (20. Januar 2019 um 01:10)

  • By the way, I just did the measurements with the multimeter again, since someone on a different forum pointed out that the way I grounded it (on the ground tip of the DC-jack) is not the correct way and gave strange results. I edited the original post, so for all the new measurements my multimeter gave me, they are now up there in the list.

  • No, the guy on the other forum is, what we name in german a "Korinthenkacker" if he isn't able or willing to substract 9.
    Did you plug only a passive Guitar when you took the measurements? Hope you didn't plug anything to the in- or output which took the same powersupply? Always dangerous with positive ground effects like this.
    Possibly the DC-Voltage on R1 is loaded on the electrolytic C2 by plugging the input, which ist the powerswitch too - that's a dangerous concept in my opinion, especially together with such big input-C and pulldown-R. Possibly this "antibias" is transportet to and between the coupling-Cs of the previous and following stage. That's why I asked for.

  • No, the guy on the other forum is, what we name in german a "Korinthenkacker" if he isn't able or willing to substract 9.
    Did you plug only a passive Guitar when you took the measurements? Hope you didn't plug anything to the in- or output which took the same powersupply? Always dangerous with positive ground effects like this.
    Possibly the DC-Voltage on R1 is loaded on the electrolytic C2 by plugging the input, which ist the powerswitch too - that's a dangerous concept in my opinion, especially together with such big input-C and pulldown-R. Possibly this "antibias" is transportet to and between the coupling-Cs of the previous and following stage. That's why I asked for.

    To be honest, I'm not skilled enough yet to understand everything you're saying. While testing with the multimeter I only had a loose patch cable plugged in, I figured that since I'm only measuring the electric flow, I wouldn't need any actual audio signal but ofcourse I might be wrong here. I have the pedal powered to a seperate power supply while testing and I have no active guitars, the frequency I send to the pedal for audio probe is coming out of an audio interface. Ofcourse, in the end I would like to use the pedal on my power supply with my other pedals, not a daisy chain but a little brick ;)

  • ... and perhaps you try soldering C4 again once more...

    Well, I was wondering (and please correct me if I'm wrong here):

    At C4 the level is still loud on both ends during the audio probe. So you could be right ofcourse, the issue could be C4, but I wonder if the outgoing signal wouldn't have had dropped then already?

    What I did notice though, is that Q1 gets powered by R4, which has more than -8v on both ends, Q3 gets powered by R10 which has more than -8v on both ends, but Q2 (where the issue starts) has -8v on one end and just -0.15v on the other. Isn't that just the issue, the reason why the volume drops after C2? Either the resistor losing its incoming power, or that one end which isn't soldered properly and doesn't put out enough power, dropping the signals volume going into Q2?

    Not sure if that makes sense, but as far as my newcomer-brain can comprehend and melding the results of my multimeter and audio probe testing, this makes sense somehow. Hoping you can tell me if this actually does.

  • Hi!
    Nevertheless we actualy did't solve the problem I'm rejoyced you liked it!
    The voltage you meassured on R1 now seems explicable - and I know the inner resistance of your multimeter (it's 5M!). When you meassured to -9V this makes a voltage divider together with the R1. If you meassure it to ground there will be zero volts.
    The voltages on Q2 and Q3 are o.k. Usually the voltage on the emitter of Q3 rises immediately when plucking the strings.
    Voltage on Q1 is very much in my opinion. This part of the circuit is difficult, as one usually has to select the Q1 by leakage current for a drop there at about half of the supply voltage. But as your audio probe there was o.k. it will not matter in the moment.
    What you did by audio probe is forcing the pins of C4 to it's pad or just meassuring the pin. So you really should try to resolder it. Please remove the transistors therefor, as these germanium transistors don't like any heat. Anyway you could heat the iron little more than you did. For circuits like this 15 to 30 Watts would be o.k. with a tenperature of 330°C for Pb lead and 360°C for Pb-free lead. Short and hot is much better than longer and less. Most of your solders look o.k. but the one on C4 looks some cold/forgotten as far I can see from your picture.

  • Hi!
    Nevertheless we actualy did't solve the problem I'm rejoyced you liked it!
    The voltage you meassured on R1 now seems explicable - and I know the inner resistance of your multimeter (it's 5M!). When you meassured to -9V this makes a voltage divider together with the R1. If you meassure it to ground there will be zero volts.
    The voltages on Q2 and Q3 are o.k. Usually the voltage on the emitter of Q3 rises immediately when plucking the strings.
    Voltage on Q1 is very much in my opinion. This part of the circuit is difficult, as one usually has to select the Q1 by leakage current for a drop there at about half of the supply voltage. But as your audio probe there was o.k. it will not matter in the moment.
    What you did by audio probe is forcing the pins of C4 to it's pad or just meassuring the pin. So you really should try to resolder it. Please remove the transistors therefor, as these germanium transistors don't like any heat. Anyway you could heat the iron little more than you did. For circuits like this 15 to 30 Watts would be o.k. with a tenperature of 330°C for Pb lead and 360°C for Pb-free lead. Short and hot is much better than longer and less. Most of your solders look o.k. but the one on C4 looks some cold/forgotten as far I can see from your picture.

    Thanks, that was it! I resoldered C4 again and now it's working and damn, that thing sounds good! I can't thank you enough, you saved me from a lot of headache :)

  • If you want to, there are still little things to improve:
    1. Exchange the 4,7uF electrolytic C2 by a good foil capacitor (for example "MKT") of about 220nF up to 1uF. This won't fit by pin distance but you could make it fit or solder it on the bottom.
    2. Selecting your 3 transistors by meassuring them in position of Q1. The one with the highest voltage difference to ground get's Q3, the mid one get's Q2 and the lowest remains in Q1.
    3. Fixing the body of the transistors in position and insulated with some (not too much!) 2-K-epoxi-glue to each other and their neighbours.
    On the other side: never change a running system.
    As you get addicted by this straight and dynamic sound, you could also consider these points in your next electronical projekts...

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