Noisey MXR Microamp??

[petemoore]

There's like an intuition that can Identify different type noises...SOmetTImes.
 Basically you can find it, but it might take a while. Low noise floor will be there. High end parts probably do help [sometimes] , never really tried many.
 I like dueling circuits sometimes these days, see if I can outperform the one I already like, especially with those dern FF's...
 If everythings 'right' excessive [depends on what you call Excessive] noise shouldn't be a real issue.
  SOMETIMES
 you can hear a certain type of cord noise
 you can wave your hand over unboxed CCT and hear noise changes.
 You can definitely hear leaky caps in an amp intermittent sckrakitching
 You can find the plug that got pulled out of the jack
 you can turn your guitar volume down in time or hit THAT BUTTON
 the atmospheric conditions are perfect
 dank dampness screws with your Shhh
  Cognicance of what matters is the trick to noise intuitions.
 I got lucky twice recently when recording
 I found an inadequate RCA cable..computer frequency was the theory that solved the problem [almost never happens this way]
 The Wireless internet connection was putting ticks in...I unplugged the lighter sized widget at the end of the USB cord [what are the odds?] I remeberd it wasn't doing that before getting that puter connected [the recording computer which I still can't sign in here on...gotta call cable guy  :lol: ...

[mugan]

So... the original one uses metal film resistors? Are u sure? I'm gonna build the tonepad one and i'd like it to be just like the original, so how carbon resistors will influence the sound? I can't find metal film resistors here!

Thank you.

[Fret Wire]

You misunderstood my post. The original Script Logo Micro Amp used carbon comp resistors. When the Duke asked me how the Tonepad project would sound different or better, I said that one of the ways is that you can use quality components, like metal film resistors. The Dunlop reissues use mostly metal film, not the orignals.

I wouldn't use carbon comp resistors unless I had no choice. They will add some noise. Preserve the original values, but use better components. You can improve this pedal by using good parts and a quiet op amp. The original character of this pedal was clean, quiet, no tone coloration, but a slight sparkle or presence added to your sound. When you upgrade the components, it really sounds great. If you can't get metal film, just use carbon film. Anything but carbon comp.

[mugan]

OK thank you for the explaination !

[Hairston]

A couple of things:

a) Duke my good man, did you try using it with a fresh 9v battery and not an adapter? This might be where your hum is coming from.

b) The original vintage Microamps used TL061s, most likely for it's low voltage drain characteristics on a battery (there is no DC adapter jack on them). A very sweet low noise option is definitely is a TL071. If you have a later revision stamped for a dual op-amp, go with the TL072. A NE5532 is also a very nice replacement too, but TL07x are easier to find locally.

c) You can get Metal Film resistors at Radio Shack, but for currenting limiting on LEDs, there is no need for Metal Film. Carbon comp/film will work just fine.

d) If the guts are out of the shielded chassis, yes, it will pick up hum, this is normal. The hum will be more apparent in front of a high-gain preamp such as yours.

e) Duke, since this is your first attempt at a pedal build, I assume you are going to use perfboard and point-to-point it instead of etching it. I would go for a simpler booster project to start, such as the AMZ Mosfet Boost or the LPB1 on Tonepad. Great first projects and they both are excellent transparent boosters similar to the Microamp but using FETs instead of an op-amp.

Good luck

-HB

[Fret Wire]

Hairston, thanks for the info. I've never seen a script logo with the 61's in it, just the 741's. Which version used a dual? The Script logo didn't, and neither did the reissues. Was it during the block logo phase? I believe the block logo's I've examined had single OA's. MXR did some subbing due to availability, but that would mean a new board. I'm curious, I try to keep up on all the MXR versions and their changes.

You're right about the LED resistor, no audio path there. I use metal film resistors, it's just my preference. Although in some ckt's I'd say it's almost mandatory to keep noise down. For a booster, I like metal film. When you consider all the work you put in soldering, wiring, and box prep, I don't mind spending a little more for some extra noise reduction. But I wouldn't recommend carbon comp. Carbon film is just too plentiful and cheap to bother with the carbon comp's.

It was nice having MXR right near us. There's still plenty of former employees around too. :wink:

[Ben N]

Fret Wire:

Are you sure there are no pinout issues between a 741 and a 5534?  IIRC, Paia always had to provide an adapter for the EPFM project boards (originally for 741/7436) because of this.

Ben

[Fret Wire]

Hi Ben, it depends what the ckt has going to the IC. The difference between the 741 & the 5534 are pins 1,5, & 8. On the 741 they are off/null1, off/null2, & NC. On the 5534, it's Bal, Com, & Comp/Bal, extra features if your ckt uses them. The Micro and D+ use 2,3,4,6, & 7. There is spec differences too.

I originally tried them in those ckts and they worked. Later when I saw the data sheet, I saw the differences in operating voltage and pins 1,5,8, and I got nervous.  But stompbox ckts, being simple, it boils down to does it work in the ckt or not.

The TLO71 is a direct pin for pin replacement for the 741. Funny thing is the Burr Brown OPA 134A & OPA177 are also direct pin replacements for the 741, not the 5534. My guess is that they did that because the differences between the 741 and OPA's is greater than the OPA's and 5534. Maybe Paia used pins 1 or 5 differently?

[Duke of Metal]

OMG!!!.. its Hairston  .. hows it going bud??

Thanks for the info. to be honest, I dont like using batteries. Adapters are the way to go for me.  I am gonna try to replace the LED somtime soon and get a repalcement OA too. If the pedal is quiet after I put the pedal back in its box and on the floor, then i might not bother with replacing the OA. if its still noisey, then I'll replace the OA and see what the results are.


Thanks guys.


Duke

[Duke of Metal]

hey guys,
well.. i got a replacement LED and Opamp.. I repalced the LED with a Blue one and it worked fine.

Now.. after I got the Opamp.. i realized that we did nothing. I got the TLO71 like you guys said and thats what the pedal has originally  :?..

but anyways. i replaced it and the problem was the same..  I even put the Circut board inside the MXR case and tried it and same problem.  I notice a little bit of hiss and a bit of hum added to the sound even when the control on the Microamp is all the way down.

I am thinking of ordering a tonepad Microamp PCB and transfer the parts from the MXR Microamp to the tonepad.. question is, can I do that?? do i need extra parts or I can use the exact parts from the MXR to the tonepad??

will the tonepad Microamp PCB fit in an MXR pedal case??

also, where the does DPDT switch get soldered to the tonepad PCB?? and can the Tonepad version be powered with an adapter? or just battery?



Any info would help.


Thanks again guys,
Duke

[petemoore]

but anyways. i replaced it and the problem was the same.. I even put the Circut board inside the MXR case and tried it and same problem. I notice a little bit of hiss and a bit of hum added to the sound even when the control on the Microamp is all the way down.

I am thinking of ordering a tonepad Microamp PCB and transfer the parts from the MXR Microamp to the tonepad.. question is, can I do that?? do i need extra parts or I can use the exact parts from the MXR to the tonepad??

will the tonepad Microamp PCB fit in an MXR pedal case??

also, where the does DPDT switch get soldered to the tonepad PCB?? and can the Tonepad version be powered with an adapter? or just battery?
  ...Something in the circuit is causing the noise, this may be hard to find, did you use a new electrolytic?
 You can probably use the same parts, but I'd compare schematics.
 The DPDT info for true bypass wiring is at GEO.
 I don't know if the PCB'll fit in the MXR case.

[Duke of Metal]

Thanks for the reply Pete..

what kind of switch does the tonepad version use anyways?? cause it doesnt say on the pdf file i downloaded from there.. and where can I get the schematic for the MXR version of the Microamp??


Thanks,
Duke

[petemoore]

what kind of switch does the tonepad version use anyways?? cause it doesnt say on the pdf file i downloaded from there.. and where can I get the schematic for the MXR version of the Microamp??
 Well the only switch I know of for a standard MA is the bypass switch.
 GEO has the bypass article...much better source than my typing.
 circuit input                         circuit output
  input jack                           output jack
              bypass           jumper
 these rep the six lugs of a DPDT, use the DMM to find where the switch show continuity to either side...input jack to BP [in one sw posistion] input jack to circuit side [other sw position].
 If you're not getting that, turn the switch 1/4 turn and test again.
 Edit...my switch representation got kind of skewed when entered...it makes no sense...check the GEO Bypass article.

[Duke of Metal]

hey Pete,
Thanks for the info.. would you be able to give me a link to the page that that has the True Bypass or dpdt wiring link on the geo site?? i looked on there and couldnt find it.

EDIT - I found this page, is it the one?
http://www.geofex.com/Article_Folders/bypass/bypass.htm


thanks,
Duke

[petemoore]

refering to pic in article showing double pole double throw...
 Assign p1 and p2 to in out jacks
 in this case were making P1 for input
 P1 to input jack
 P2 to output jack
 T1A to circuit input
 T2A to circuit output
 T1B and T2B connect with wire for bypass
 These labeled circle dots represent the 6 lugs on the switch...the dotted line means both 'sides' of the switch [each side being an SPDT] are thrown at the same time...hit the switch and both sides switch
 The dotted line shows where the solid lines connect inside the switch.
 The way I figured it out was with a pen/paper, draw six lugs for DPDT, then use the DMM beep mode to map where the connections I can't see inside the switch are made...
 Look for schematics that show dpdt wiring, Bobtavia EZ Build shows the switch body in the schematic...
 Basically you want bypass to connect the signal straight through from input to output jacks...
 Then on the other 'side' you want it fed through the circuit, injack to input, output to outjack.
 Test one side of the switch [spdt]. find where two lugs have continuity. one will be a middle of the SPST [DPDT is two simultaneous SPDT"S] the outside lug will switch 'off' but 'on' to the other outside lug of the SPDT.
 The other side is a mirror...one side for input one side for output.

[petemoore]

All the typing got me to put a 5534 in the MA. I'm not getting any noise, I used Vellman Resistors from a 480pc. pack, they're 5% Cfilm resistors.
 Put it in a box with T.bypass, amazing sounding..

[Duke of Metal]

anybody with an idea of what might be causing the noise??

I tried it with a battery too and its the same thing noise wise. Ofcourse i put the circut back in its case and its still noisey.


Thanks,
Duke