EP Booster: Bright and Fat switches doing nothing?

[Plexi]

Hi there!
Built yesterday this preamp, using layout from effectslayout blog.
Used 2n5457 and BC549.

Is the bright and fat switches a big improvment in sound, or just a very subtle effect?
I can't ear any noticeable change, at all.
As I can read, I'm not the only one out there.

Anyone?

Thanks!

[Elijah-Baley]

Hi!
Indeed, I can read here: http://effectslayouts.blogspot.it/2015/06/xotic-ep-booster.html
"Fat switch absoultamente not appreciate any change"

And also I'm reading the comments here: http://tagboardeffects.blogspot.it/2012/02/xotic-ep-booster.html
"Fat switch doesn't seem to give a very noticable change", and there are some other comment like this.

Maybe you can try alternative critical components around the siwtches, or remove the switches, I guess the boost work fine even without all these modes.

[Plexi]

You're right Elijah-Baley
I checked all the board, components, and tried the preamp in the fx loop of the amp; played a note, and changed the switches.
Nothing at all... 

I was thinking: maybe the fet isn't working properly?
I should try another fet, but I changed many components to know if something fails that copper is starting to lift up from the board in some places.

I use the schematic and read this blog too:
http://revolutiondeux.blogspot.com.ar/2012/01/xotic-ep-booster.html

[Elijah-Baley]

This is a pedal I never built, but maybe some mods in that web page you linked could be useful
You could use switch for other parts, input and/or output cap, for example, or increase the fat switch caps, though them are pretty big already.
Did you try it even with distortion and overdrive pedal?

I use always the same components of the layout, at least when it is possible, else some other verified equivalent component.
If the board is ruined I suggest to you, if you really want this pedal, to build it again, using socket pin for critical parts. Every time for transistors and ICs. Useful for diodes, too.
http://www.taydaelectronics.com/30-pin-dip-sip-ic-sockets-adaptor-solder-type.html
http://www.taydaelectronics.com/8-pin-dip-ic-socket-adaptor-solder-type.html
So you can swap the transistor any time you want.

[PRR]

I hate plans without schematics.

The fat switch does nothing. It adds 100uFd across a 10uFd. But the 10u is already as "fat" (deep bass) as you could ever want. Take out the 100uFd. Take out the 10uFd next to it and put it where the 100uFd was. Now put a 0.68uFd or 0.47uFd where you took-out that 10uFd. The "norm" connection will be shaved-bass. The "fat" connection is full bass.

I'm really lost at that Brite network. Ah, I see? Change the 15K to 10K or 5K, it will be more obvious. Strictly this is "dull or not-dull", but if it is distorting it is naturally bright and a dull option is useful.

[Elijah-Baley]

I hate plans without schematics.

The page with the schematic was linked, but you're right, here the schematic:



100uF and 10uF seem even to me pretty big. Your solution about the fat switch could give to the pedal a right and balanced versatility. Honestly, the Brite network is too complicated for me.

Give us some news about your progress, Plexi.

[Plexi]

Thanks Elijah and PRR!

This is a pedal I never built, but maybe some mods in that web page you linked could be useful
You could use switch for other parts, input and/or output cap, for example, or increase the fat switch caps, though them are pretty big already.
Did you try it even with distortion and overdrive pedal?

I use always the same components of the layout, at least when it is possible, else some other verified equivalent component.
If the board is ruined I suggest to you, if you really want this pedal, to build it again, using socket pin for critical parts. Every time for transistors and ICs. Useful for diodes, too.
http://www.taydaelectronics.com/30-pin-dip-sip-ic-sockets-adaptor-solder-type.html
http://www.taydaelectronics.com/8-pin-dip-ic-socket-adaptor-solder-type.html
So you can swap the transistor any time you want.

I tried it with everything: simple coil, humbuckers, clean amplifier, crunch amplifier, high gain, input, fx loop, my toaster ... everything! 

The board is fine, a bit manipulated and some traces almost lift up; I used some IC sockets I had on hand, and cut them to fit the 3 pins of the fet.

I hate plans without schematics.

The fat switch does nothing. It adds 100uFd across a 10uFd. But the 10u is already as "fat" (deep bass) as you could ever want. Take out the 100uFd. Take out the 10uFd next to it and put it where the 100uFd was. Now put a 0.68uFd or 0.47uFd where you took-out that 10uFd. The "norm" connection will be shaved-bass. The "fat" connection is full bass.

I'm really lost at that Brite network. Ah, I see? Change the 15K to 10K or 5K, it will be more obvious. Strictly this is "dull or not-dull", but if it is distorting it is naturally bright and a dull option is useful.

Great idea!
I'll try that now.
I was thinking all the opposite about the brite mod: in put there some bigger resistors.
I'll try with 5k.

What is doing that 2n5088 at the end? Am I wrong, or its an output buffer?

Maybe I'll build the classic echoplex preamp... straight from the old schematic...maybe  get better results (not too much hype I guess)

[Mark Hammer]

I think it is also worth considering that sometimes guitars, speakers, or both, lack the bandwidth for things like those switches to actually result in any audible change.

That was one of the things that pretty much killed enhancer/exciter pedals.  As outboard units, they add considerable zing to acoustic instruments in a mix, listened to through speakers with 20khz bandwidth.  But plug a Les Paul or SG into one, and feed it to an amp with a 4x12 cab, and you will find the user asking "Is this thing on?  I see the LED but I can't hear any difference."

The thing you feed the pedal, and the thing you listen to it with, have to have the required bandwidth for any additions at the top or bottom to be audible.  That is not instead of the explanations and good points offered up so far, but in addition to them.

[Plexi]

Now I get it, and that's what I though when PRR says that 10uf is already full bass, and adds a 100uF cap.
Maybe it's full bass for the freqs we (guitar and amp) use, and not for acoustic or mix, as you say Mark.

Ok, I have some update:
- Placed 10uf where the 100uf was, and put a 270nf cap where the 10uf was: great treble sound without the 10uf cap, bit lo-fi preamp. Nice warm bassy sound with both caps.
- Remove the 15k and try with 5k: not change at all. So, y put there a 27k resistor: and there appeared the highs on.

I think both switches are redundant: both adds highs/cut bass.
If you ask, I prefer to add the 10uf cap. Why not a on-off-on switch there, with 2 caps in the outer lugs to have 3 eq? 

[Mark Hammer]

Here's something I like to do.

Instead of a switch between C2 and C3, and a 10k pot, you get yourself a 20k W-taper pot (log in one direction from midpoint, and anti-log in the other direction - often used for EQ boost cut controls), and keep your 270nf / 10uf pair.

The AC gain of Q1 is determined by the combined parallel resistance of R1 and whatever the value of the pot is.  below the specific impedance of the cap, that resistance will be dictated ONLY by R1.  But above some minimum frequency, dictated by the cap value, the AC gain will be dictated by the cap and pot resistance.

Tie the wiper of the pot to the source of Q1.  When the wiper is at midpoint, you will have 10k on one side and 10k on the other, in parallel with 4k7 (R1).  Together, that gives a DC resistance of 2K42, so let's make R1 a little bigger...say, 6K8.  As the pot wiper is rotated in the direction of the 270nf cap and the combined parallel resistance of that pot half and R1 gets smaller, you apply boost; but only to that portion of the spectrum above the range dictated by the cap value.  As you rotate in that direction, the resistance in the other half of the pot won't result in any appreciable change to the total parallel resistance.

Rotate the pot the other way, and now the same thing will happen, but gain will be applied above a lower frequency range dictated by the cap value.  So, in one direction from midpoint you get mids and highs boosted, while in the other direction you get full-range boost.  One pot, no toggle, and NO SWITCH-POP!

The hi-cut switch, as shown in the drawing from Elijah, selects between a rolloff at 48khz, and a rolloff just above 3khz.  Given that this is for guitar, and anything that tames hiss is good, I will suggest the following:

- get a 3-position on-off-on toggle
- make R6 zero ohms and R7 18k
- the common of the toggle goes to one end of R7
- from one outside toggle lug, solder a 22k resistor
- from the other outside toggle lug, solder a 10k resistor
- solder the two free ends of those resistors together, and connect them to the other side of R7

In the middle switch position, your "default" R7 resistance will be 18k, yielding a treble cut around 2.7khz.  With the switch connecting the 22k in parallel with 18k, your rolloff will be around 4.8khz.  With the switch connecting the 10k parallel resistor, your rolloff will now begin around 7.5khz.  That's probably as much bandwidth as one would need for electric guitar.  If the intent is to use it with acoustic sources, then I guess make the 10k a 6k8 instead, to push the rolloff up even higher.

There you go; variable bass and mid boost, plus three different treble rolloffs with a single pot and toggle.

[Plexi]

Yesterday a friend of mine asked me for one of these.
After insist in the old, beloved and simple Echoplex preamp, without all the redundance this design have for nothing...the hype wins.

So, I'll made it to my way:
- Instead the useless "boost" c10K pot, place there an small 39R resistor
- Instead the15k res that is bypassed (bright sw), I've put there a 30K resistor. Now the switch have a reason to live in this preamp
- Placed 1uf instead the 10uf cap, as same as the bright switch: now it have any sense
- 47k res to ground at the output, removed
- Placed A10k as master volume

Again: extremely redundant, and that rare output buffer sucks all the Jfet mojo