DIY HPF Stompbox?

[fdeck]

What does the difference of impedence between the piezo and my amp do?

The answer might be: Nothing. And the reason is that the impedance problem with piezo pickups depends on both the pickup and the amp. If the piezo has high capacitance, and / or the amp already has high input impedance, then the impedance buffering function of a preamp might be unnecessary in your case.

If there is an impedance problem, it would be marked by a change in tone, such as a loss of low end.

 

[boomertech]

Since the electronics wizards seem to be here, I have an FDeck series 2. It is wonderful as a High Pass Filter. I also use the phase switch which definitely helps with my upright. What I just don't understand is the impedence deal. The HPF, when both knobs are turned up all the way(full volume, minimum HPF) the tone and volume seem to stay the same, with or without the FDeck. What does the difference of impedence between the piezo and my amp do?

Thanks for any thing you can tell me

If your piezo pickup sounds the same with and without a 10M buffer, then your amp has a high enough impedance for that pickup so that you have negligible loading effects.

-Frank

 

[fdeck]

i drew up a veroboard layout and built one and it works perfect:

Very cool!

Incidentally, if anybody wants a couple of the "proper" PN4416 JFETs, don't hesitate to ask. I have a lifetime supply. What happened is that a few years ago, I went to order more PN4416's, and usually the Mouser website shows a few alternative parts. All of the alternatives were flagged as "obsolete." I checked stock at a few other sites, and it looked like there might be a looming shortage of PN4416's, so I bought a big pile of them.

If you don't mind using surface-mount, then the MMBF4416 is a good substitute. There's an article at my commercial web page about JFET substitution. But what I got away with in my circuit -- JFET stages with no bias adjustments -- was kind of a stroke of luck, and depends on the JFETs having fairly tight tolerances. I tested a large number of these parts before committing to the design, to make sure it could handle the spread of parameters. Since I now own every JFET that I will ever use, I don't have to worry about it any more.

 

[leonard]

I had a look at a generic datasheet for 2N4416. The casing was explained there. So I guess I can use this component then.

 

[BadExample]

Excellent! Start the press!

I see two paths to making sure the part will work. You can either build it and see if it does what it should, then if it doesn't work, you can ask Sir Francis The Kind if he can send you a couple from his stock. The other way would be to do a bit of a test, JFET Study - hpftechllc Very simple circuit you can make without a board. This is how he tested alternate FETs to determine suitability.

D to +9v battery, G to - on battery, S to one end of a 3.3K ohm resistor, other end of resistor to -, plug in battery and measure - to S, or measure across the resistor. You would have to remove the ESD wire, if that is what it is. You can solder just the tips of the FET leads, then snip them off after test leaving plenty left to form and fit the board, use a spare, or use a plug in type breadboard to test.

Best of luck, and please keep us posted!

 

[BadExample]

Oh yes, this is the only type of socket I use: [Invalid or Expired Link Removed]

The so called machined pin socket. They are very reliable and you can plug in and unplug all day and they remain reliable, the cheap square pin sockets so often used, not so much. A big plus is you can get a large socket like the one I linked and snip the plastic around three pins and use them for your JFETS. I just buy 40 pin sockets and toss the remainder of the socket in with my parts. I think it would be good to socket the FETs in your project, just in case you do need to go to another part. You can even socket the 10M ohm this way if there is any question about what it's value should be.

 

[Stewie]

Originally, I hung the FDeck behind my tailpiece with rubber bands. Handy to have the knobs accessible while away from my amp. For Christmas, my family gave me a brand new Line 6 G10 wireless. If I plugged the transmitter into the HPF, I got a high pitched warble out of the amp.

I now run the HPF on top of my amp. With a stock Fender BXR300 head and 2 15s, I can keep up with 50 watt guitar amps and a heavy handed drummer.

 

[leonard]

I don't know when I will have the time to actually build it but with all this information it's actually gonna happen.

If there's no footswitch is it a stombox at all?

Is the volume control necessary? I have a volume pedal on my board and I like simplicity.

Maybe I'll hang it behind my tail with rubber bands. And have the knob accessible.

 

[BadExample]

Still can stomp on it if you like. Especially if it misbehaves. Could call it a pedal and not stomp it

 

[karter2000]

Very cool!

Incidentally, if anybody wants a couple of the "proper" PN4416 JFETs, don't hesitate to ask. I have a lifetime supply. What happened is that a few years ago, I went to order more PN4416's, and usually the Mouser website shows a few alternative parts. All of the alternatives were flagged as "obsolete." I checked stock at a few other sites, and it looked like there might be a looming shortage of PN4416's, so I bought a big pile of them.

I'd love to get a couple of those from you, if possible!

 

[Feral Feline]

+1 (or a few ...)

Will paypal you some Dosh, @fdeck, for your warez, postage feeze & troubulz.

I got my HPF-Pre III through a sale in the GASsifieds, 'cause at the time you weren't shipping overseas, and if that is still the case I can have a friend State-side forward me the bits — totally happy with my III, but was bit hard by the "DIY" bug...

 

[leonard]

Anybody remember this project of mine? I'm finally on the testing stages!

I was too slow to buy the local 2N4416 Jfets. They were sold out. So I bought ten pieces of 2N5485:s and measured them according to @fdeck's instructions here:
JFET Study - hpftechllc
The highest readings I got were 2,15 and 2,11 volts and I used those two jfets.

I just did my first test run with the circuit. It seems to be somewhat working. It cuts the frequencies the way it should but the gain is extremely low. The phase switch seems to cut the gain even more.

There might be some mistakes on the circuit. I need to go through it tomorrow. I hope the jfets are not too far off. There's no way I could tell just yet.

My R13 is 2.2k instead of 2k. @johnk_10's veroboard layout was tight but great. One thing that caused some confusion was that I had to bend the jfet legs weirdly to fit the layout.

 

[delta7fred]

I built one using BC327 and 2N3819 (because I had them in stock) and it works perfectly (thanks @fdeck).

 

[leonard]

I built one using BC327 and 2N3819 (because I had them in stock) and it works perfectly (thanks @fdeck).

Did you use Johnk's layout? Did you bend the jfet legs?

 

[delta7fred]

Did you use Johnk's layout? Did you bend the jfet legs?

No I did my own perf board layout so was able to make it fit the transistor pinouts.

When you cross the transistor legs slip a bit of plastic sleeving over them to stop then shorting out (strip a few mm of covering off some connecting wire).

 

[leonard]

Ok, so the morning revealed two resistors totally missing from my circuit. It works fine now! Taking breaks is always a good idea it seems. Now it's time to drill the case.

@BadExample are you still out there?

 

[Feral Feline]

...Speed in reply is over rated. In fact I hear it can lead to bug eye syndrome!

GADZKS!

Bug-Eye Syndrome!

Is this reply slow enough?


__________________

No I did my own perf board layout so was able to make it fit the transistor pinouts.

When you cross the transistor legs slip a bit of plastic sleeving over them to stop then shorting out (strip a few mm of covering off some connecting wire).

Would you be able and willing to post your perf layout here?


__________________



@leonard : Thanks for the follow up!

Reminds me I still need to get those JFETs from Monsieur Deck, but I still won't be making one of these for a long(er) while.


What size enclosure are you sticking it in?

 

[leonard]

@Feral Feline :

What size enclosure are you sticking it in?

Here's the enclosure on the left. Hammond 1590B. I got some jazz bass style knobs. The footswitch and the led are for the phase switch. It's gonna be an always on pedal. It will be difficult to drill neatly with hand tools at home.

 

[delta7fred]

Would you be able and willing to post your perf layout here?

I will if I can find it, it is scribbled on a bit of paper so may take a bit of interpreting.

I've tried a few times to get to grips with DIY Layout Creator (or whatever it is called) but come from an era when designs were done with a pencil and paper and having to learn another software tool to get ideas down seems very alien to me.

 

[Feral Feline]

A photo of the paper is enough, much obliged.

I've messed with DIY LC and understand. Pencil and paper is a great way to go.


Kind of like the ol' radio in the '63 Beetle my dad had when I was a kid. Turn the volume knob and the radio came on, immediately.
Pullout one of the 5 preset buttons, tune in a station and push the button in and voila a preset station!
It worked, very well.

My current car's "radio" can't get music going 'til after I've driven about a block already 'cause it's still booting up. The preset programming is a nightmare and never seems to work properly and the station seek can't lock on to even the strongest of terrestrial radio signals. Too many bells and whistles.
It works, very poorly.


I'm all for adding in all the bells and whistles, but only if everything actually works.

I digress.



@leonard : Looking good!

Check out some "home drill tips" on youtube before you start drilling. I learned the hard way that prep (paint, drilling ... organising a kids camp for 200 campers) is always the most time-consuming and difficult part of the process.

Since I'm not great at it, here's my procedure:
Measure thrice
Punch imprint
Guide hole
Small bit
Medium bit
Large bit
The larger the whole, the more steps/bits.

Sometimes I get it right.