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Boost Pedal Design Pregunta


JGale

Question

A single knob boost Pedal.

- Jack Orman's MOSFET Boost, can run at 18V. It's a MOSFET. Everyone like MOSFETs, yah. It has a transistorized unity gain buffer at the end of it's chain. It's a SMD implementation and very small.

- A JFET, unity gain buffer, can run at 18V, put it in the switch "loop", the "backside" of the 3PDT foot switch. When the boost is engaged, the buffer is not and vice versa. 

- An 18V power pump set to allow either 9V or 18V to each component, buffer and/or boost.

Would you buy something like this? Would you use it?

 

 

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I'm one of those nitwits that keeps everything true bypass. Because I've never tried a buffer to hear the actual difference...

Really should try one  especially with the long cable runs I have between the pedalboard and the amp at the church gig...

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On 6/19/2022 at 8:09 PM, JGravelin said:

Please describe in detail what the benefits and trade-offs would be across the 3 variations. More information for us 'tards would be helpful if you want feedback?

 

JFETs were originally designed for low noise applications and have a very high input impedance compared to MOSFET (read as: improved fidelity with Lo-Z pickups, most mics, etc. as a source signal). Low noise JFETs in the industry (Fairchild 2N5457, et al.) are going the way of the dodo, however, and that could be a point of consideration if producing these.

MOSFETs generally provide higher gain and exhibit higher distortion. They also have high input capacitance (>=10x that of JFET) and lower input impedance, and this manifests as reduced frequency response with Hi-Z source signals like most guitar pickups, keys, etc. - mostly in the high frequency range. That said, plenty of great effects run on 'em.

I like the concept of this pedal w/the JFET buffer in the bypass position and the MOSFET in the "boost/face-melt" mode... but something to consider might be the addition of  a "true bypass" toggle to switch between JFET and true-bypass mode when desired.

 

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18 hours ago, chromium said:

Low noise JFETs in the industry (Fairchild 2N5457, et al.) are going the way of the dodo, however, and that could be a point of consideration if producing these.

 

A couple of the effects PC Boards I have bought have a thru-hole and SMD footprint footprint for the JFET's since the SMD versions are often easier to get these days. They also make small adapter boards where you mount the SMD part to the board and then the board installs like a normal TO92 part.

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Thanks!!

Here's what I'll do then. Build the pedal to accept 9Vdc - 18Vdc CtrNeg and let the user decide which. The JFET buffer will wire up out of the effect loop (foot switch toggles Boost/Buffer) with a switch to bypass the buffer. Jack Orman talks about it here:

"I have never seen this connection in a pedal but it is interesting nonetheless. The buffer is inserted in the true bypass loop and converts the pedal to buffered bypass. The interesting feature is that the bypass is buffered but the pedal input is not. This allows one pedal to have a dual function. The effect circuit (pcb) drives the signal chain when it is active, but the buffer drives the signal path when the effect is bypassed. Since the effect pcb is isolated from the buffer, it performs as it always has, but when the footswitch is toggled, the pedal becomes a standalone buffer"

buff-mod11.jpg

It sounds like it makes sense to isolate the buffer and the effect.

"The mosfet booster module has a low impedance output that can drive longer cables, tone controls or following circuits easily. It also isolates the guitar pickups from the output loading, which will give more clean sound."

mospcb2.jpg

Now for a timely and provocative HFC-themed graphic for MyFrenDan©️ to paint on!

Found a graphic...

images_edited.jpeg

Now I just need that cartoon blonde pushing back her hair in the Far Side comics, kind of angularly drawn with yellow curly hair. Nothing so far...

Edited by JGale
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On 6/22/2022 at 12:47 PM, JGale said:

Thanks!!

Here's what I'll do then. Build the pedal to accept 9Vdc - 18Vdc CtrNeg and let the user decide which. The JFET buffer will wire up out of the effect loop (foot switch toggles Boost/Buffer) with a switch to bypass the buffer. Jack Orman talks about it here:

"I have never seen this connection in a pedal but it is interesting nonetheless. The buffer is inserted in the true bypass loop and converts the pedal to buffered bypass. The interesting feature is that the bypass is buffered but the pedal input is not. This allows one pedal to have a dual function. The effect circuit (pcb) drives the signal chain when it is active, but the buffer drives the signal path when the effect is bypassed. Since the effect pcb is isolated from the buffer, it performs as it always has, but when the footswitch is toggled, the pedal becomes a standalone buffer"

buff-mod11.jpg

 

 

If desired, you could also add a "true bypass" option as well - using an additional toggle or push-pull pot:

r3xeYwl.png

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New Pedal Day, or more commonly known as "I gotta new (sorta) pedal today."

I had to build it. One of the problems I have with Aion is the gage for resistors is less than I am comfortable with bending the leads at. Aion uses these nice Mil-Spec resistors...the end result just looks sloppy.

The circuit is nothing magical, it is a TS gain stack with an EQ in the middle and a recovery stage. At each end is a transistor buffer. The big difference is three fold: the IC is a MOSFET vs. JFET, the clipping in the stack is two diodes in series and the HPF feeding the gain stack is full range. The mushy, gooey almost fuzz that results is the magic. Like most MOSFETs (IMHO) this has big shoulders and lots of presence. I socketed the HPF to up the corner frequency and I am most happy with the results.

The clip switch lets you select from single Red LED to single 1N914 to two 1N914 in series. Three different choices of compression and gain. I'ma think I build a second and socket all the good stuff.😎

fCZBe-dwsd5kt7a37gmrckfkbswslw.jpg

Edited by JGale
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