Author Topic: Slurpee - getting filter but no auto-wah  (Read 489 times)

taeagan

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Slurpee - getting filter but no auto-wah
« on: November 10, 2016, 10:28:27 AM »
So full disclosure - I built the slurpee schematic but on a Veroboard layout. So I used the schematic from madbean and subbed part values and/or swapped in pots where appropriate on the tagboard layout.


http://tagboardeffects.blogspot.com/2013/06/ehx-bassballs.html

With this schematic:

http://www.madbeanpedals.com/EP/schematics/Slurpee.gif


Basically I get a filtered effect - the bass and treble pots work and the distortion switched in and out both work as well.  However, I get no auto-wah type effect.  The response control doesn't seem to do anything.  Here are voltages:

IC1 (1458):
1 - 4.3v
2 - 4.3v
3 - 4.2v
4 - 0v
5 - 0v
6 - 1.9v
7 - 2.1v
8 - 8.6v

IC2 (4558):
1 - 4.4v
2 - 4.3v
3 - 4.3v
4 - 0v
5 - 4.3v
6 - 4.3v
7 - 4.4v
8 - 8.6v

The two transistors in the tone circuit (the bottom two in the layout) measure:

C - 0v
B - 0.65v
E - 0v

The transistor following IC1 and the attack and decay controls (the one off to the right of the board in the layout) measures:

C - 8.6v
B - 8.6v
E - 8v

Any ideas?  I checked over and over again for solder bridges, cap and diode polarity, layout, etc.... I don't know the circuit well enough to understand why I would get the filter effect but no auto-wah.

taeagan

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Re: Slurpee - getting filter but no auto-wah
« Reply #1 on: March 21, 2017, 07:43:21 PM »
So I decided to revisit this one tonight.  I had placed a Mouser order, so I ordered some different varieties of 1458 chips and none of them seemed to make a difference in the performance of the pedal. 

Has anyone built this?  I get some change in tone when I mess with the bass and treble pots and the distortion switches in and out (doesn't sound that great).  But the auto-wah part of the circuit seems to do nothing.  No changes when I adjust the sensitivity, attack, or decay pots.  No auto-wah effect at all.  Any thoughts? 

taeagan

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Re: Slurpee - getting filter but no auto-wah
« Reply #2 on: March 24, 2017, 01:46:38 PM »
Is the polarity of the tantalum cap reversed in the spec in the slurpee doc? That seemed to get me a somewhat functional auto wah. Still doesn't blow me away or sound like some of the bassballs clips I hear online.