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Boost Pedal Design Pregunta


JGale
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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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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?

 

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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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