On-stage buffer for acoustic guitars

[Samuel Groner]

Samuel, I used TI calculator. 220 pF for 5M1 is what the doctor prescribed.

Sure. I'm just saying that such a high impedance level seems to ask for trouble (e.g. hum pickup)--if it were 220 nF/5k1 no problem...

How much capacitance have 4007?

Use 1N914B or equivalent--with the suggested 1k series resistor they won't die.

Samuel

 

[tv]

Such Hi-Z inputs are best done DC-coupled (with jfet) with 68k-ish serial resistor similar to fender input stages ... imho at least.

 

[Guest]

Ok gentlemen, now I am satisfied.

Added input protection and better mute implemented, also I'll need a LED to show that the channel is on.

 

[Guest]

[quote author="tv"]Such Hi-Z inputs are best done DC-coupled (with jfet) with 68k-ish serial resistor similar to fender input stages ... imho at least.[/quote]

I'll increase the input cup in case of high LF noise, thanks. FAQ that 3'rd order HPF...

 

[tv]

In such case you'll be having 4,5V across the input cap in series with a couple megs resistor trying to impress the pickup with some voltage. You will need to pulldown the input to avoid thumps etc when plugging/unplugging the instrument(s) - i.e. when the input isn't shorted with the jack as drawn on the schem.

Not saying that this "will" happen, just that there is some*** probability to happen.

DC-coupled discrete fet inputs otoh are relatively free from such phenomenons, but they can have other issues.

 

[Guest]

[quote author="tv"]In such case you'll be having 4,5V across the input cap in series with a couple megs resistor trying to impress the pickup with some voltage. You will need to pulldown the input to avoid thumps etc when plugging/unplugging the instrument(s) - i.e. when the input isn't shorted with the jack as drawn on the schem.

Not saying that this "will" happen, just that there is some*** probability to happen.

DC-coupled discrete fet inputs otoh are relatively free from such phenomenons, but they can have other issues.[/quote]

It is what I intended to do implementing discrete input in the 1'st version with 1 megOhm input resistor. People said it should be higher, so now it is 5.1 megaOhm and an opamp for simplicity. However, I can use couple of batteries for better coupling (and dpdt foot switches I don't have), but I definitely need a HPF because the last time digital delay processor clipped causing thumps when some people hardly hit their strings.

Speaking of thumps and other noises I'll instruct all of them to plug in/out guitars only when LEDs don't shine and tell how to use foot switches (there will be big concert with multiple bards: 70'th anniversary of Vladimir Vysotsky).

Anyway, I'll use faders for backup if I see somebody wants to plug in/out.

 

[Guest]

[quote author="Samuel Groner"]
Use 1N914B or equivalent--with the suggested 1k series resistor they won't die.
[/quote]

I've found some small Shottkies in a drawer...

 

[Andy Peters]

[quote author="Wavebourn"]Please criticize, I need something urgently tonight where people will plug in pickups of acoustic guitars. High impedance in, 80 Hz HPF, foot switch with mute. Have no pickup to try...[/quote]

I realize you're into building things, but if I were in your shoes, I'd buy an LR Baggs or a Fishman preamp w/balanced outs to plug direct into the console. Problem solved.

-a

 

[Guest]

Thanks, I made mine, works fine, going on concert now, in rush...

I made the last version, but without opamps (all repeaters like on 1'st schemo). 2 channels in one box for 2 guitars.

BTW, I had to lift gates up: there was only 1.5V on sources.



Thanks all who helped! :guinness: :guinness: :guinness: :guinness: :guinness: :sam: :sam: :sam: :sam: :sam:

 

[Guest]

It worked fine, no hiss (discrete followers), good sound, full band! No need for balanced out: battery powered, high output level, low output resistance.

I'm going to order few PCBs now.

 

[tv]

That's somewhat OT regarding the theme, but as I was searching something for my use I have seen this @ D.Self. This could be used if buzz is onstage and full balanced DI too much? (After the discrete input):

 

[Guest]

In case of on stage buzz I would go with balanced out.