Wednesday, 2 May 2012

MXR Micro Amp with tone control

Request. 


67 comments:

  1. Built it. Not currently working. I used 3.9n caps instead of 3.3n, and had to make a resistor that is 3.02K instead of 3K. Would these cause it to not work?

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    1. The 3n9 and 3.02K wouldn't make a difference, the cap is in the tone stack so even if it slightly changed the response, it wouldn't stop it working. And the difference between a 3K and 3.02K is so irrelevant that normal tolerances of the same resistor would normally show more of a difference.

      I've been over it a couple of times and am fairly confident it matches the schematic. What IC have you used, and are you sure the schematic is verified?

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  2. I am not the one who provided the schematic, so I have no idea if it is verified or not.

    Tried it with both a TL062 and a JRC 4559 with no luck.
    Weird.

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    1. Sorry Will, I thought it was you who requested it because you built it straight away. So many requests so I can't remember who asked for what! :o) I'll check it over again later and try to check if the schematic is verified.

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    2. Mark you are doing awesome work. Hopefully you aren't feeling too swamped!

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  3. Put the TL062 back in and measured it:
    1: 8.97 8: 9.61
    2: 8.42 7: 8.98
    3: 0 6: 8.15
    4: 0 5: 8.12
    Not sure what the significance of these values are, but if you see something wacky let me know.

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    1. Ooh those voltages look nasty. The only pins that looks to be at a sensible voltage are 4 and 8! Can you post a front and back pic of the board

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    2. Found a tiny solder bridge between IC pins 5 and 6 when I went to take a pic, works perfectly now.
      Thanks for all your trouble Mark. Consider this one verified!

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    3. Good stuff, thanks for that Will.

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  4. it was me that i requested this.....thanks a lot to Mark for the quick response!
    hey will how it sounds?is it closed to the original mxr micro amp?

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  5. I built it into a box with a SHO, so I can't hear what it sounds like by itself, but it does seem to have the same character as my normal Micro Amp. The tone stack is surprisingly effective in my opinion. This is a cool design.

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    1. Thats nice!!!i will built it tommorow and i'll tell you my impressions....

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    2. Yes there's a few things I like about it. The tone stack is basically a big muff, but I really like that gain control which is different from the original Micro Amp. It adds gain in the clockwise position, and is a unity gain buffer/voltage follower in the counter clockwise position.

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  6. i have problems with that project.....with the gain control and tone in the middle when i turn on the guitar volume behave like wah and like seagull effect and other white noise...

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    1. You're going to have to go over it with a fine tooth comb and look for burr or solder bridges etc. It certainly seems that Will verified the layout, which means there's a problem with the build or a component. If you're still struggling then post a front and back pic of the board.

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  7. good news!!!problem solved....same to me as WILL a tiny solder between strips......

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    1. Excellent, glad you got it sorted

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  8. has anyone tried this with a bass? just curious... maybe with a cap change it could be cool...

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  9. heres my go on this one, took a chance and boxed it before i even tried the board and worked right off! went with JRC4558. graphics inspired by the movie Lawless and it's soundtrack, a really good soundtrack btw!
    https://dl.dropbox.com/u/2828668/reaperpedals/fire%26brimstone/graphics.jpg
    https://dl.dropbox.com/u/2828668/reaperpedals/fire%26brimstone/board_1.jpg
    https://dl.dropbox.com/u/2828668/reaperpedals/fire%26brimstone/board_2.jpg
    https://dl.dropbox.com/u/2828668/reaperpedals/fire%26brimstone/offboard_wiring.jpg

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    1. oh, forgot to say that i integrated a 9 > 18V doubler so it runs on 18V and thats why it looks a bit wierd :)

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  10. Hi Mark
    Im sure ive built this several times without problem, but ive just built one for a friend and its giving a loud pop when engaging the effect, couldnt find a reason for this, even added a 1m from output to gnd without it fixing the pop....decided to remake altogether...still the same problem...really frustrating !!...any suggestions welcome

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    1. I changed the 1m on input to 10m...fixed...was that a fluke lol ??

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    2. yep a fluke....still popping away

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    3. Try something smaller for the output. Usually 220K works the best for output pulldown.
      +m

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    4. Try a low value resistor like 1K in series with the input wire.

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    5. Hello, this is related to the microamp without the tone control but I thought I would post this here since the pop issue is getting some attention. I have pop too in my build. I have tried 1k resistor in series with the input. 240K from board out to ground, 3pdt bypass (as ivlark's method) and millenium 2 (daughterboard from this site). In all possible combinations. It still pops. I also tried different bs170's when using millenium 2. One thing I have noticed is that, at least when using the millenium bypass, if I disconnect the led (both terminals) I get a very soft pop when turning on the pedal, an no pop when turning off. This is with both the 1k and the 240k resistors. This thing is driving me mad. Someone got a definite method for this pedal? thanks

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  11. Thanks guys will give it a go and report back, I think i got my theory wrong as a larger resistor would have made the pop worse ?

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    1. Nice one Miro...worked a treat thanks. Tried the 1k first but i think i misunderstood.."1K in series with the input wire" as i put it as a pull down and although it certainly got rid of the pop..it also eliminated most of the volume, so if you find the time mark, maybe you would explain what you was meaning

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    2. By series I mean take the disconnected input wire to one end of the resistor, and take the other end to where the input wire is supposed to connect to the board. That is Jack Deville's anti-pop method by using a current limiting resistor directly in the signal path at the input. Using that low value resistor as a pulldown will always kill the signal because the resistance is so low that much of the signal is being immediately dumped to ground.

      In answer to your question before, 10M shouldn't really make it worse but it definitely won't make it better. The pulldown resistor creates a path to ground for any leakage from the input capacitor, and so increasing the value puts more of an obstacle in the way, which might not be detrimental, but will definitely not be better. Personally I wouldn't use more than a 1M for a pulldown.

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    3. Yup. Slowing the input with a "small" value resistor in series is one way to try taming the input pop. It seems that most (schaller trem, duncan pickup booster, etc.) the problem isn't with the input - but with the output popping on the switch. This seems quite common with designs that don't have output coming from the volume pot but from the output cap itself. So 220K from ground to output. That should fix any of those without hurting the output level.
      +m

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    4. You guys make a great team, thank you for answering my questions. I kinda thought that was what you meant Mark, I tip my hat to both you guys

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    5. I have the same issue with the AC Booster. Huge bassy pop on activating and deactivating. I've tried all the above and nothing is shifting it. Shame as it renders it unusable for me.

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    6. This is what I do with popping pedals...

      http://www.muzique.com/lab/led.htm

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  12. Built it today with TL062 and sounds great. Tone control is really miraculous, from thick strong sound to ringing bright tone..

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  13. Could use some help on this one... It works but not right. Volume is significantly lower than when bypassed and only gets to about unity at the top of the sweep. Tone doesn't do mush at all until the last 10% where it introduces a muddy distortion. I've reflowed the joints, scraped for solder bridges, replaced a couple suspect parts, swapped out the IC.

    Here are the voltages:
    1) 4.79. 8) 9.55
    2) 4.79. 7) 9.45
    3) 4.33. 6) 0.23
    4) 0.0. 5) 7.91

    Some pics:

    https://drive.google.com/file/d/0B_Sh_vDhJkMqUzNaNXJPeU5weV9tTkVfSnFqTFdJMU9vMmln/edit?usp=sharing
    https://drive.google.com/file/d/0B_Sh_vDhJkMqV1BNdnlLMFFSYU9kN01SYW1QcW56THBOVjcw/edit?usp=sharing

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    1. photos were just made public... sorry.

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    2. You've got the link under the IC going one row too high

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  14. jerry!!! found your problem mate!!under your ic the top link is at the wrong hole!!!

    wish i could find that quick my mistakes too...

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  15. Yup there it is... I feel a little stupid, but then again the stupid mistakes are easier to find right?

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    1. Thanks everyone! Fixed and working great... I also found a solder bridge down by the connection for tone 2 that has messing with that part of the circuit. I had scraped it before but it was a stubborn enough blob that I had to gouge at it for a while to clear completely. Anyone else find the Tayda veto boards to be a bit fussier to work with? My first board was from Mammoth and it flowed a lot more cleanly. The solder seemed to want to bond easier... Fwiw.

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  16. Once again, a great layout Mark! I´ll use a 100KA volume pot though.....

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    1. Sometimes I look at some of my older layouts and there's something about some of them that I really hate, so I've been updating them when I come across them. With this one it's the stupid huge span radial electrolytic. So I've updated it and made it a column smaller if you want to build the latest one. All connections remain the same so it will also be good to go.

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  17. Replies
    1. Nope. That's a single opamp and this layout needs a dual. Single opamps have a different pinout.
      +m

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  18. This comment has been removed by the author.

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  19. please help, i get my 100uF cap EXPLODE like a bomb,(changed 3 times) all seems good...help

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  20. Most likely the cap is backwards, your power wires are backwards, or you have a solder bridge or misplaced joint on the board

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    1. Thanks for fast reply, I multiple checked it, cap is right, no solder bridge... I use a 9v ac-ac adaptor

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    2. And, the 3n3 caps, i use a little ceramic caps (its really tiny, too much for me, around 4mm, is the number 332 correct?)

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    3. And, the 3n3 caps, i use a little ceramic caps (its really tiny, too much for me, around 4mm, is the number 332 correct?)

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    4. All (well most) of these layouts call for a AC to DC supply only! If you gave this circuit AC that explains the blown cap...and way well have harmed the IC too.

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    5. Wonderful..i use this adapt with all my other (non-diy) pedal and was good..i tried then with a 9v battery, i get no sound, only when i play "harder" i hear a far distortion..is the ic harmed previously on ac courrent? Thanks!

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  22. How comes that this one uses a 100k lin pot for the gain and the normal one uses a 500k inverse log pot?

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  23. I have made the circuit perfectly as far as I can tell and all it produces when switched on is a mild drop in volume! The only difference between the layout guide and mine is that mine has a TL061 OP amp, and log potentiometers. Nothing happens when they are turned at all :( HELP

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    1. TL061 is a single opamp with completely different pinout. This layout is for Dual opamp (with two channels). So it wont' work at all with TL061.

      You'll need TL062, TO072, TL082, JRC4558, NE5322 or similar.
      +m

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    2. Thankyou! I have a TL062 now, but still nothing works! I Have been getting some pretty stranger results though, I get a strange bleeping noise (Very high pitched) when I connect the circuit to an amplifier, why might this be??

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    3. That could be caused by a short circuit - which could be result of an unwanted solder bridge between board strips. Next, you should run a sharp knife between the strips and triple check all the cuts. Use a magnifying glass, that'll com in handy here.

      If that doesn't yield results, then measure voltages from the IC pins. (Set the meter to DC voltage - black lead to board grounds or IC pin 4 - then the red lead to other pins. Do note that the pinout is like this:
      1-u-8
      2---7
      3---6
      4---5
      You should have around 4,5V (+/- 10-20%) at pins 1, 2, 3, 5, 6 and 7. Pin 8 should be at supply voltage. If one of those is completely off, then there is something wrong with components connected to that pin.

      I can promise, you'll feel like a king once you solve it. And you eventually will.
      +m

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    4. Also, if you placed the circuit inside an enclosure already, there is a chance the short could be at the switch.

      And by the way - the high pitch squeeling is called oscillation. Which usually happens when signal is fed back to the input of the circuit too loud. Some pedals oscillate as a feature - but obviously not this one.
      +m

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    5. Thankyou very much! I did indeed have a solder bridge, as well as a misplaced resistor :) After solving these I put the circuit through my usual "test harness" (Input jack, Output jack and power) and noticed that even with the two potentiometers at 0, some sound was still reaching the amplifier. Is this normal? Also, does the direction the op amp is wired into the circuit matter? (Im using a socket)Unfortunately, I dont have a multimeter to test these things, so I am stuck with tapping parts of the circuit with a screwdriver to see whether there's a signal (I think)
      Thankyou very much for your time by the way, I really appreciate your help :)

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    6. The gain completely at CCW (counter clockwise), there will be asignal passing through. If you want it to be silent, you could add a 100K linear pot as master volume (take the output to lug 3, lug 1 to ground and lug 2 is your new output.

      IC orinetation matters a lot. Note the little "u" -like detent on the top. Left of that is the pin number 1.

      I strongly recommend aqcuiring a DMM (digital multimeter). Since you are a electric instrument player, you'll be needing one along the way anyway. You'll want an automatic basic meter with decent/good value. Maybe something like this: http://www.ebay.com/itm/311177607324 - Sure enough, that's not a blue Fluke, but it'll last you a long time while still being quite cheap. I use the previous model and it's been my bench meter for.. dear god.. At least four years now.
      +m

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