Slow Lorus Emergency!

[Rich_S]

I spent some time playing my new SLow Lorus (see link below) through my 18 Watter clone today.  Overall, it's what I wanted; an outrageous, harmonically-comples distortion pedal.  I can see why Adrian Belew thought of Rhinocerous noises when he played his Rat.

I'm trying to compare it to my old '80s small box Rat, which is tough because I sold the Rat years ago.  The SL seems kind of muffled - plenty of dirt, but not much fizz if I turn the cut control down (in the "bright" direction).  Only about the first 20% of the cut pot is useful - the rest has too much blanket over it.

I want to mount it on my pedalboard tonight (a semi-major undertaking... don't ask), but first I'd like to make the range of the cut control a bit more useful - a bit brighter at the bottom, and more usabale sweep.

Any suggestions for a quick fix?

http://www.madbeanpedals.com/forum/index.php?topic=2040.0

[bigmufffuzzwizz]

Not sure if this will fix your problem but there's a few people who prefer using a different chip for the op-amp in the rat. I believe the op-amp is responsible for most of the clipping so I would think the chip would play a big part in the overall sound. The originals do use a LM308, but builders have chosen LM301 or OP07 over the original choice when comparing them. Both of those chips can be gotten much cheaper then the LM301 at tayda and futurlec.
Maybe you want the ruetz mod?
check out: http://www.diyguitaramp.com/rat.html
http://www.beavisaudio.com/projects/FKR/

[cjkbug]

I'd like to make the range of the cut control a bit more useful - a bit brighter at the bottom, and more usabale sweep.

Any suggestions for a quick fix?

http://www.madbeanpedals.com/forum/index.php?topic=2040.0

did you use the right taper for the pot? the docs call for an audio taper. using a linear taper will bunch up the usable part of the sweep to one end of the control. if you used the proper one maybe sub in a reverse audio. I'll have to check my build to see how my cut control responds. I report back what I find....


ok...played mine for a few minutes and noticed that my cut control acts like what you describe. I guess it didn't bother me enough to change it. You might want to experiment with pot tapers/values. If you want a more usable sweep. I'd try a reverse taper first.

[plesur]

Just finished my Loris, it has exactly the same problem, the tone control is only usable at the far end of it's travel.

Checking out the schematic for the original Rat, the filter control used to work in reverse, the more clockwise it went the more treble it cut. The schematic on the Loris documentation is very similar to the original Rat.

Quick fix: Wire the tone control pot in reverse, i.e. swap 1 and 3 - you get a more usable sweep but the control works 'backwards', more treble cut as you rotate it clockwise

Slow fix: Swap the tone control for a 100K reverse log (C) pot, so the tone control cuts less treble as you rotate it clockwise

[Rich_S]

Having owned a few original Rats over the years, I know how the cut control works, and mine is wired in true Rat style: counterclockwise is brighter.

The problem I'm having is that full CCW is not bright enough, and the upper half sweep in the CW direction is unusably muffled.

[plesur]

Mine is bright enough (for me) at full CCW with the pot reversed. There should be no audible effect from the filter at that point as the frequency for the cutoff is too high for guitar amps to reproduce (and most humans to hear!). Check the values of the filter components in your build, R7 (1k5) and C8 (3n3).

Using a corner frequency calculator http://www.muzique.com/schem/filter.htm, the frequency cutoff point is 32kHz with those values. At full CW rotation, the frequency changes to 470Hz which is pretty muddy.

For more fine tuning, Mark Hammer recommends changing R7 (1k5) to 4k7 and the filter pot to 50k
http://www.diystompboxes.com/smfforum/index.php?topic=82676.msg687886#msg687886 this gives a sweep from 10kHz to 880Hz, quite a usable range for a guitar.

[Mike @ Rawkworks]

Tried these mods to the cut pot as well as changing R4 to a 1kb pot (like . They make a difference! The R4 is very useful when the drive is pulled back. My favorite clipping configuration is the LEDs and the drive/R4 pot dialed back.

I used an OP07 IC. Time to start drilling a box! Another 6.0!

[cjkbug]

Mine is bright enough (for me) at full CCW with the pot reversed. There should be no audible effect from the filter at that point as the frequency for the cutoff is too high for guitar amps to reproduce (and most humans to hear!). Check the values of the filter components in your build, R7 (1k5) and C8 (3n3).

Using a corner frequency calculator http://www.muzique.com/schem/filter.htm, the frequency cutoff point is 32kHz with those values. At full CW rotation, the frequency changes to 470Hz which is pretty muddy.

For more fine tuning, Mark Hammer recommends changing R7 (1k5) to 4k7 and the filter pot to 50k
http://www.diystompboxes.com/smfforum/index.php?topic=82676.msg687886#msg687886 this gives a sweep from 10kHz to 880Hz, quite a usable range for a guitar.

I performed these mods on my slow loris build tonight and report a vast improvement in performance of the cut control. I used a linear taper pot and the sweep and range is 100% useable. there isn't a hint of mud at the lowest end of the cut control. that ones a keeper.

[plesur]

I performed these mods on my slow loris build tonight and report a vast improvement in performance of the cut control. I used a linear taper pot and the sweep and range is 100% useable. there isn't a hint of mud at the lowest end of the cut control. that ones a keeper.

That's good news  

I'm going to do the same to mine.

[bigmufffuzzwizz]

That's good news   

I'm going to do the same to mine.

I'm considering doing this to the guitarpcb rat I built. Do you think it would make a difference on that one too?

[Rich_S]

Looks like I need to place a Small Bear order for (1) 50K pot. (Goes to have head examined.)