MXR Microamp vero layout mistake fixed?

[fallingfurther]

Hello everyone, I am building an MXR microamp on a veroboard.  Here is the layout I found:



It appears the 47pF and the 56K are in series when they should be in parallel.  I think I fixed it here:



Can anyone confirm that I fixed this correctly?  I am new to veroboard layouts.  Here is a link to the schematic: http://www.generalguitargadgets.com/diagrams/microamp_sc.gif

Thanks in advance

[anti-idiot]

i think it's ok.

[fallingfurther]

Update: I built the microamp using the fixed vero layout above, and it works perfect.  The microamp is a great, transparent no BS booster.  Its a nice counterpoint to my rangemaster clone, when I just want a completely neutral boost.  And thanks for the reply anti-idiot.

[rousejeremy]

I recently built this with a 741 and it's great.
What would have to be changed to use a 4558 instead? Would it require a whole new layout or some minor tweaks?

[frequencycentral]

I recently built this with a 741 and it's great.
What would have to be changed to use a 4558 instead? Would it require a whole new layout or some minor tweaks?

741 is a single opamp in an 8 oin package, whereas 4558 is a dual opamp in an 8 pin package, so it would be a different layout with one half of the 4558 being unused.

[rousejeremy]

I'm having a problem with the pot for this. It's a 500k linear and when I get up near ten, sometimes it makes a loud scratchy sound then cuts out. When it does work, it's very distorted when cranked and it sputters then gates as it decays. Why does this happen?

Any advice would be greatly appreciated.

[Renegadrian]

I recently built this with a 741 and it's great.
What would have to be changed to use a 4558 instead? Would it require a whole new layout or some minor tweaks?

I just made a layout from the TONEPAD schematic, with the 4558. Here it is!!!



There are some pedals strangely using duals, while they use only one part of it, like this one or the DOD 250/308.
Basically you just can use a single...
If you understand a little spanish there is an interesting article/build report at pisotones.com.

[mharris80]

I recently built this with a 741 and it's great.
What would have to be changed to use a 4558 instead? Would it require a whole new layout or some minor tweaks?

741 is a single opamp in an 8 oin package, whereas 4558 is a dual opamp in an 8 pin package, so it would be a different layout with one half of the 4558 being unused.

For added fun, the other half can be utilized by mirroring the circuit, like so:
http://www.tonepad.com/project.asp?id=28

[rousejeremy]

I recently built this with a 741 and it's great.
What would have to be changed to use a 4558 instead? Would it require a whole new layout or some minor tweaks?

I just made a layout from the TONEPAD schematic, with the 4558. Here it is!!!



There are some pedals strangely using duals, while they use only one part of it, like this one or the DOD 250/308.
Basically you just can use a single...
If you understand a little spanish there is an interesting article/build report at pisotones.com.

Nice layout! A lot smaller than the previous.

BTW I switched to a TLO61 (from a 741) and the sound is much cleaner.

[Renegadrian]

mmm right I finished it today - the millenium bypass works, and signal gets thru the circuit, but no noticeable fx...
It seems the same sound both bypassed or engaged...Used a 100k pot
add scratch head icon here...

[Renegadrian]

More scratchin' here...The circuit is working, the signal goes thru it and the pot is active, so I just dunno why it doesn't add any gain...I surely have some changes, but nothing so dramatic and also those changes have been tried before by other builders. I have a 1n4148 as diode, a 100n cap to sub the 10n and I tried a 100kB and 250kB pot.
Any ideas?! Why that thing doesn't boost the signal?!

[Renegadrian]

Tried again...Still can't understand what can be wrong...mmm...

[trixdropd]

Read the debugging: what to do thread and do what it says, and this will get figured out...

[Renegadrian]

mmm the schem calls for a 22M at the input, it should be like a pulldown, why 22M? I had a smaller one (10M if my memory is still strong) and put it in, guess it shouldn't make a difference...Same for the diode, it just gives a slight change in the voltage, so I guess a 1N4001 or a 1N4148 should act not so different (also someone reported the use of the 1N4148 with good results)

Also I put 2 el. caps in parallel to get that 15µF value - caps in parallel add their value, right?! So I have one 10µF and one 4.7µF, to get 14.7µF. And that should work too...

Pot is not the REV it needs, but a Linear pot is reported to work well...

So wtf...

[Renegadrian]

Some voltages...
battery reads 9.39V
V at the board is 9.39, and 8.73 after the diode (1N4148)
(The voltage drop of a 1N4001 should be 0.70V so it's the same I believe...)

IC voltages (4558)
1.  1.32
2.  0.11
3.  4.20
4.  0
5.  1.36
6.  1.23
7.  1.39
8.  8.72

[MikeH]

mmm the schem calls for a 22M at the input, it should be like a pulldown, why 22M? I had a smaller one (10M if my memory is still strong) and put it in, guess it shouldn't make a difference

Yeah that 22m is overkill; any standard pulldown size will be fine

Same for the diode, it just gives a slight change in the voltage, so I guess a 1N4001 or a 1N4148 should act not so different (also someone reported the use of the 1N4148 with good results

Yeah, true.  It should also work fine without the diode, so you could jumper it to be sure.

Also I put 2 el. caps in parallel to get that 15µF value - caps in parallel add their value, right?! So I have one 10µF and one 4.7µF, to get 14.7µF. And that should work too...

Also true- but 10uf alone should work fine.  In fact, you'd be hard pressed to hear a difference.

Did you audio probe it yet?

[Renegadrian]

Mike, thx for your answer...Well, the audio signal reaches the end of the circuit, the problem is you just cannot say wheter the fx is on or off...Sound passes but no amplification-gain factor added...

[Renegadrian]

A lot of time has passed but had to try again sooner or later!!!
I found a strange thing in the 4558 layouts, starting from Tonepad one...they had this 10M resistor going to pin 3 (the + in of the unused half) and that was quite strange and useless too, the single opamp version has that resistor fron the voltage divider to the input of the opamp. so it had to go pin 5 of the 4558 and nothing else...made another layout even smaller and it works so good right now...actually I didn't put the jumpers in, so pins 1-2-3 are connected to nothing...
got a 100k B pot hooked up. the thing works quite good!!!

[Renegadrian]

Crazy idea came tonight...a double pedal using half 4558 for the microamp and the other half for a 250/308...what do you think!? I guess that is doable!

[Fender3D]

Looking at your layout, pins 1-2 jumper should be placed, pin 3 should go to Vref not GND, or better, you might use this half for a steadier Vref... (pins 1-2 to Vref, pin 3 to 1/2V splitter)
You can build a bi-pedal   of course, provided you take care no crosstalk will affect each other...
Just a side note... I'd remain at MXR's house with a Dist+ rather than a DOD250....