Bootstrapping is a form of positive feedback. As you suggested, positive feedback comes with a number of side-effects, most of which are undesirable most of the time. The side-effects are the opposite of what you get with negative feedback.
So: positive feedback increases distortion. It narrows bandwidth. It reduces phase margin and stability. In principle, it increases both noise and voltage gain by the same amount, so that signal-to-noise ratio remains unchanged.
Agreed! Actually, a JFET is probably the best available input device for a guitar amplifier. A good JFET has much less noise than a vacuum tube, at the source impedance of a typical guitar. And JFETs also have the high input impedance that guitars need.
Sadly, discrete JFETs are now an endangered species. They won't be available much longer. Many of the old standby JFET part numbers are already gone for good.
-Gnobuddy
Just wanted to say thanks Gnobuddy. Ive learnt much from what you've posted and I appreciate your positive and insightful posts.
About 10 years ago, I got myself a 100 pack of 2n5457 jfets. I still have more than half of them so they should see me for buffers for a good few years yet!
About 10 years ago, I got myself a 100 pack of 2n5457 jfets. I still have more than half of them so they should see me for buffers for a good few years yet!
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It looks as though the Darlington BJT booster concept has legs (see attached image). Input resistance is around 1.7 meg ohms, and no bootstrapping needed.
The input coupling capacitor probably should be bigger; that will lower the source impedance at low frequencies, which should reduce flicker noise.
I won't bother to build it, since it won't get me any closer to having Gilmour's guitar-playing abilities! 🙂
-Gnobuddy
The input coupling capacitor probably should be bigger; that will lower the source impedance at low frequencies, which should reduce flicker noise.
I won't bother to build it, since it won't get me any closer to having Gilmour's guitar-playing abilities! 🙂
-Gnobuddy
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You're very welcome! 🙂
Now, that was a very good idea. Unfortunately for me, there were a lot of good ideas I did not have ten years ago!
I did buy a few 2N5457s recently. They are $3.57 (CAD) each at Digikey now.
-Gnobuddy
ive tried a few jfets in guitar circuits, and i reckon 2n5457's are just right in 9v circuits, either source-follower buffers or common source boost and drive circuits. They can crunch nice and softly when pushed depending how much current runs through them.
I really appreciate your answers.
At first I wanted to build this buffer from General Guitar Gadgets that uses a TL071:
Buffer – IC | General Guitar Gadgets
But then I checked this video using headphones:
Buffer Pedal Shootout Pete Cornish LD-1, JHS Little Black Buffer, Lehle Sunday Driver, Boss TU2 - YouTube
I think Cornish LD-1 (BC549) and Lehle Sunday Driver (ICL7660S/OPA2132PA) performs a lot better than JHS (TL072).
I opened this thread and now I'm not sure what pedal to make.
The schematic posted from JohnDH that uses a J2N5457 should be a better choice?
The Cornish vero board will have a negative impact on low frequencies?
At first I wanted to build this buffer from General Guitar Gadgets that uses a TL071:
Buffer – IC | General Guitar Gadgets
But then I checked this video using headphones:
Buffer Pedal Shootout Pete Cornish LD-1, JHS Little Black Buffer, Lehle Sunday Driver, Boss TU2 - YouTube
I think Cornish LD-1 (BC549) and Lehle Sunday Driver (ICL7660S/OPA2132PA) performs a lot better than JHS (TL072).
I opened this thread and now I'm not sure what pedal to make.
The schematic posted from JohnDH that uses a J2N5457 should be a better choice?
The Cornish vero board will have a negative impact on low frequencies?
Lets hear about exactly what you want to use the buffer for, ie what will it be driving into: just a guitar amp? a pedal chain? do you want to be able to drive direct into a mixer line in? Also, will you power it from batteries or from a wall wart (ie is low current consumption of any interest).
My advice would be, lets hear what Gnobuddy thinks and do that.
If you go with a jfet type, then We could discuss a few tweaks to the jfet buffer to optimise it for your use.(as drawn above, it was optimised based on low parts count and low current to build inside a guitar).
If its a bipolar transistor design, I think either Gnobuddies two transistor or amended 1 transistor Cornish look very interesting.
My advice would be, lets hear what Gnobuddy thinks and do that.
If you go with a jfet type, then We could discuss a few tweaks to the jfet buffer to optimise it for your use.(as drawn above, it was optimised based on low parts count and low current to build inside a guitar).
If its a bipolar transistor design, I think either Gnobuddies two transistor or amended 1 transistor Cornish look very interesting.
Why not use one of those genius-designed, super optimized Burr Brown opamps with ultra low noise JFET inputs?? OPA134 is available in both DIP-8 packages and surface mount; its noise is extremely low (8 nV/rt.Hz), and it's got JFET inputs with ultra low Ib spec so it can operate just fine with 1 megohm input impedance. What's not to like? And oh by the way, it's max supply voltage is 36V so you can run it off two 9V batteries in series, and guarantee yourself it'll never run out of headroom, even when the batteries are 95% discharged.
You can set the lowpass corner frequency wherever you please; in the attached schematic I've positioned it mighty doggone low.
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You can set the lowpass corner frequency wherever you please; in the attached schematic I've positioned it mighty doggone low.
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This is my unfinished pedalboard:
I don't know if I f***** it up the impedance, but this is the way I made the pedalboard inputs/outputs
I don't know if I messed the send/return signals, because I put one shared aluminum case. I hope this doesn't make ground loop issues.
This are my pedals:
There are two DIY stompboxes: a germanium fuzz face and a Tubescreamer. I want to add in the near future a digital Delay, a digital Reverb and a DIY Chorus.
My amp is a Marshall MA50C. It's a tube amp made in Vietnam. Overdrive channel is crap, but clean channel is decent (a little muddy compared to a JCM800, but the Joyo EQ fix this). Valves are made in China and the speaker is a 12" AX-75 from Eminence.
Anyway, I want the pedalboard to live longer than the rest of my gear, so I don't want to choose what Buffer to build thinking on my amp nor my Edwards Les Paul with Seymour Duncan hambuckers.
I suppose I can place a Buffer in this place of the chain:
Guitar > Pedalboard > Wah > Ge Fuzz Face > **Buffer** > Compressor > Tubescreamer > Box of rock > Boss SD-1 (buffered) > Amp
Maybe I should go for a buffer that has no problems with germanium fuzz faces, this way I can put it right after the Wah.
The Tremolo and the EQ will be connected in the FX loop chain.
I don't have a clue what buffer should I build, only that it should sound better than integrated buffers from Boss.
I don't know if I f***** it up the impedance, but this is the way I made the pedalboard inputs/outputs
I don't know if I messed the send/return signals, because I put one shared aluminum case. I hope this doesn't make ground loop issues.
This are my pedals:
There are two DIY stompboxes: a germanium fuzz face and a Tubescreamer. I want to add in the near future a digital Delay, a digital Reverb and a DIY Chorus.
My amp is a Marshall MA50C. It's a tube amp made in Vietnam. Overdrive channel is crap, but clean channel is decent (a little muddy compared to a JCM800, but the Joyo EQ fix this). Valves are made in China and the speaker is a 12" AX-75 from Eminence.
Anyway, I want the pedalboard to live longer than the rest of my gear, so I don't want to choose what Buffer to build thinking on my amp nor my Edwards Les Paul with Seymour Duncan hambuckers.
I suppose I can place a Buffer in this place of the chain:
Guitar > Pedalboard > Wah > Ge Fuzz Face > **Buffer** > Compressor > Tubescreamer > Box of rock > Boss SD-1 (buffered) > Amp
Maybe I should go for a buffer that has no problems with germanium fuzz faces, this way I can put it right after the Wah.
The Tremolo and the EQ will be connected in the FX loop chain.
I don't have a clue what buffer should I build, only that it should sound better than integrated buffers from Boss.
Power from wall wart. Using a cheap power supply with daisy chain, but it produces ground loop noise, so I'm looking for better options.
*I tried to correct my bad english writing, but I don't know how to edit my previous post.
> I don't know how to edit my previous post.
You get only a few minutes to go back and edit. Enough to fix fumble-fingers. Not enough to change the past. Apparently back-editing has been a problem here, the current policy is considered appropriate for this mob.
Within the time-out, you will see a
icon below your post.
You get only a few minutes to go back and edit. Enough to fix fumble-fingers. Not enough to change the past. Apparently back-editing has been a problem here, the current policy is considered appropriate for this mob.
Within the time-out, you will see a
[emoji54]> I don't know how to edit my previous post.
You get only a few minutes to go back and edit. Enough to fix fumble-fingers. Not enough to change the past. Apparently back-editing has been a problem here, the current policy is considered appropriate for this mob.
Within the time-out, you will see aicon below your post.
THANKS
For those who prefer discrete components instead of ICs, here's a voltage follower with very wide output swing, Figure 1 below.
Don't be frightened by my squirrely use of scientific notation; R1 is simply 22 megohms and R4=1.2 megohms.
Input impedance is plotted in Figure 2; it remains above 1 megohm out to 20 kHz.
Frequency response is plotted in Figure 3. The green curve is the circuit's response when the optional components are omitted (Roptional = 0 ; Coptional = 0). The blue curve is the circuit's response when the optional components are included; the -3dB rolloff is about 30 kHz. You can finagle this by jacking around with the values of the optional components.
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Don't be frightened by my squirrely use of scientific notation; R1 is simply 22 megohms and R4=1.2 megohms.
Input impedance is plotted in Figure 2; it remains above 1 megohm out to 20 kHz.
Frequency response is plotted in Figure 3. The green curve is the circuit's response when the optional components are omitted (Roptional = 0 ; Coptional = 0). The blue curve is the circuit's response when the optional components are included; the -3dB rolloff is about 30 kHz. You can finagle this by jacking around with the values of the optional components.
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Honestly, it really doesn't matter. Your musical talent, your ability to play the guitar, and your ability to connect with your audience, all are far more important than any buffer you use (or don't use).
Adding some sort of buffer can make a (slight) change in your sound; changing between two or three good buffer designs will make hardly any difference at all. I bet your audience will neither know nor care what buffer you're using.
My own experience is that it is very easy to get so many different opinions and choices on the Internet that I become paralyzed, and end up building nothing at all. That is the worst possible outcome - so please don't let it happen to you!
If you like the Cornish booster, by all means, build it! These are simple circuits, using only a few dollars worth of components, and they only take a little of your time to build. So if you build the Cornish design and then don't like it, just set the board aside, and build another circuit to see if you like that one better!
If you do build the Cornish booster, I would recommend that you use a 0.047 uF (same thing as 47 nF) capacitor instead of the 4.7 uF capacitor shown on the veroboard layout. This will fix the problem of the subsonic "hump" in the frequency response, and it won't change the sound of the booster at all.
You can also leave out the 50k resistor (top right corner of the veroboard). It does nothing whatsoever.
Incidentally, I find that the most expensive parts when you build a pedal are usually the metal case, and the switches, pots, input and output jacks, and power supply jack. You can do your initial tests without a metal case. That way, if you don't like the pedal, you can re-use the switches, jacks, and case in your next attempt, with a different circuit of your choice. The case won't have holes in it in all the wrong places from your previous pedal experiments!
As an aside, if you think you might want to experiment with more than one circuit, another possibility is to make yourself a little test and experiment fixture. Mount a solderless breadboard on a piece of wood plank. Add a piece of L-shaped aluminum extrusion to carry a power supply jack and two 1/4" jacks on it. Drill a couple more holes in the aluminum to mount pots and switches.
Now you can experiment very easily with different circuits, and when you find one you like, you can build that one properly on Veroboard or whatever. You can see an example here: DIY Breadboard
(Personally, I would solder solid-core wires to the pots rather than use clip-leads, but that is a trivial detail.)
It has a poor low-frequency response, sure. But lots have been built and sold, so chances are the problem hasn't really been a show-stopper for anyone.
Best of all, you can fix the problem very easily - just replace that 4.7 uF capacitor with 47nF (same as 0.047 uF). Problem solved!
-Gnobuddy
My first attemp was a painful failure, I wasted some nice Wima caps for a buffer that didn't work. This is the last time I make a stripboard with a knife.
The second time I build it using cheap generic caps. I made the PCB following this layout:
Perf and PCB Effects Layouts: Cornish Buffer
It works great, I'm very pleased with the result.
Next time I will make a buffer with a switch for toggling between this cornish buffer and the IC buffer from general guitar gadgets. I could yet use another switch for toggling between 4.7uf and 47nf caps.
The second time I build it using cheap generic caps. I made the PCB following this layout:
Perf and PCB Effects Layouts: Cornish Buffer
It works great, I'm very pleased with the result.
Next time I will make a buffer with a switch for toggling between this cornish buffer and the IC buffer from general guitar gadgets. I could yet use another switch for toggling between 4.7uf and 47nf caps.
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