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HPF added to looper with clean blend?

C

CopperheadLXXIX

Aug 9, 2003
1,152
12
Jax, FL
#1
I have a simple looper that has a clean blend knob. In the loop I use an EQ pedal to cut the lows in the loop, so I can put effects in it that are full range but don't want affecting my low end. My question is, I'm trying to consolidate some space on my board, and want to get rid of the EQ pedal, so is there a way to say solder some kind of cap to the loop part to say roll off everything below 200hz? Please don't suggest buying an Xotic Looper with EQ, etc., I'm aware of those options, but looking for a cheap solution if possible. :)
 
#3
CopperheadLXXIX said:
I have a simple looper that has a clean blend knob. In the loop I use an EQ pedal to cut the lows in the loop, so I can put effects in it that are full range but don't want affecting my low end. My question is, I'm trying to consolidate some space on my board, and want to get rid of the EQ pedal, so is there a way to say solder some kind of cap to the loop part to say roll off everything below 200hz? Please don't suggest buying an Xotic Looper with EQ, etc., I'm aware of those options, but looking for a cheap solution if possible. :)
Click to expand...

Yes. It is possible to solder a cap in there. But what cap you need, or how to do it, I wouldn't know much about.

If no one that does chimes in you could try asking the guys in the DIY Effect Makers (club?) thread for some pointers.
 
#5
WARNING- I am not an electrical engineer!

I'm pretty certain it will require more than just a capacitor (if you want any sort of steep roll off below the cutoff frequency), and figuring out exactly what you need will be dependant on the impedance of the signal. Is your looper passive or buffered? I think a buffer of some sort would be ideal to retain a consistent roll-off independant of what's plugged in. That's about all I got- hopefully someone with more knowledge can chime in, but I'd imagine you'd be best off saving up for a well-made existing design like the SFX crossover looper thingie: [Invalid or Expired Link Removed]
 
#6
Max makes great stuff (he built a 2 channel pre for my stereo 12 string that I use often) but I really just simply don't have the cash to blow or even really save for right now. Plus, the low end of the crossover would be wasted as I wouldn't make use of it. I assume the looper I have is buffered; definitely not passive, needs a power source to work. Can't you "stack" caps to make the rolloff a little steeper? It doesn't necessarily need to drop like a rock @ 200hz.
 
#7
Here are the guts:

2uptw1k.gif
 
#8
Even though I can't see what's on that board, I suspect it's not a buffer and therefore is a passive looper.

Running a capacitor in series with the signal will result in a reasonably sharp HPF. Determining the amount... that's a little harder. My guess is that it's pretty small, probably less than .001uF. My suggestion is to buy a bunch of small, cheap caps and run them in series with the lead that goes to each of the loops.
 
#9
Is there a good website for buying caps? Anyway to determine the approximate rolloff for different ones, or would it largely be a guessing/testing game? Sorry for all the questions, I can solder, but am worthless when it comes to the actual knowledge of what goes where and why, etc. in electronics. :help:
 
#10
FunkMetalBass said:
Even though I can't see what's on that board, I suspect it's not a buffer and therefore is a passive looper.

Running a capacitor in series with the signal will result in a reasonably sharp HPF. Determining the amount... that's a little harder. My guess is that it's pretty small, probably less than .001uF. My suggestion is to buy a bunch of small, cheap caps and run them in series with the lead that goes to each of the loops.
Click to expand...

Wouldn't the frequency of cutoff change depending on what was plugged in though? That is how I understand the function of a passive filter, which is why I mentioned the buffer. I sometimes use one of TBer Fdeck's HPF preamps with my rig and it works great no matter what comes before or after (designed for upright bass, but seems to handle the signal from my electrics well enough without noticeable clipping): Invalid Link Removed
My G&L bass has a built-in passive high-pass (the "bass" control) that works noticeably different depending on the signal chain after it (length of cable, presence of a buffered pedal, input impedance of first pedal in line, etc). I also have another bass with an inline passive HPF capacitor (I think I used a .0047uf cap) similar to that found on the bridge pickups of old Rickenbackers, and sometimes its effect is barely noticeable (other times much moreso, much like the G&L).
 
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#13
Putting caps in series just has the effect of creating a smaller cap. For example, three 1μ caps would do the same thing as a single .333μ cap.

The cutoff in such a filter is dependent on the impedance of whatever follows it. Better would be to make an RC highpass filter, which is a series cap followed by a resistor to ground. Lots of online calculators exist to make it easy to find the corner frequency of an RC filter.

However, you'll be disappointed in the slope of the roll-off if you're used to an active EQ. You can put several RC filters in series for a steeper roll-off, but the result is severe volume loss.

Sadly, there's no way to make a simple passive filter that acts like an active one. It would be possible to squeeze an active highpass into your box there, but as far as I know nobody has a simple PCB for that, so you'd need to spend a little time learning to read schematics if you were interested in doing it on your own.

RG Keen has a reasonably easy-to-follow article on this topic, with lots of good info:

Simple, Easy Parametric and Graphic EQ's, Plus Peaks and Notches

You can get a pretty tight Q with this kind of filter, and the parts count is relatively small.
 

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