Print Page - [Q] in/out impedance

Title: [Q] in/out impedance
Post by: 6l6gc on December 29, 2005, 02:11:21 PM

Hi, everyone! :icon_rolleyes:

Please let me know these circuits 'Input/Output Impedance'.
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http://www.generalguitargadgets.com/pdf/ggg_ic_buffer.pdf
http://www.generalguitargadgets.com/diagrams/buffer_jfet_sc.gif
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thanks.
&
Happy new year~ ;)

Title: Re: [Q] in/out impedance
Post by: bioroids on December 29, 2005, 03:06:26 PM

Hi!

On circuit 1)(Opamp) the input impedance is the parallel result of the 3 2M2 resistors, for about 733kohms. The output impedance is very low, just the output impedance of the opamp wich can be less than 100ohms if i'm not mistaken.

On circuit 2) (Jfet) the input impedance is the parallel result of the 2M2 pull down resistor and the 2 1M biasing resistors (the FET impedance itself is much higher and will not change things), for a total of 407 kohms aprox. The output impedance, I'm sure it is low, but I dont know how much. The opamp output Z is lower, that's for sure.

Seems to be a mistake on the Jfet buffer schem, the transistor is drawn as a bipolar.

Hope this helps

Luck!

Miguel

Title: Re: [Q] in/out impedance
Post by: Sir H C on December 29, 2005, 04:20:27 PM

Yeah, if the second one is really an NPN transistor you have to add the emitter resistor to the equation which is beta*( 3.3k || Rload). So that is added in parallel with the other resistors. Output impedance, 3.3k in effect because when the circuit is pulling the output down, that can only happen through the 3.3k resistor. Pulling up the output impedance is lower but requires more details about the transistor to really give a value.

Title: Re: [Q] in/out impedance
Post by: 6l6gc on December 30, 2005, 12:26:07 PM

thanks very much guys ;)

Can I those circuits...substitute for D.I Box? (Guitar equiped with passive pups -> Audio card:10K ohm input)

Title: Re: [Q] in/out impedance
Post by: bioroids on December 30, 2005, 01:29:06 PM

Yeah, I think that can work.

I use AMZ Mosfet Booster for that, that way I can raise the volume besides adapting the impedance.

Miguel

Title: Re: [Q] in/out impedance
Post by: 6l6gc on December 30, 2005, 01:32:31 PM

Oh, that's good idea!
Where can I find "AMZ Mosfet Booster schematic,pcb layout,wiring layout" ?

Title: Re: [Q] in/out impedance
Post by: bioroids on December 30, 2005, 01:37:13 PM

http://www.muzique.com you should look around there for the schem. I dont know if there's a pcb somewhere, maybe on general guitar gadgets, or tonepad.

Luck

Miguel

Title: Re: [Q] in/out impedance
Post by: 6l6gc on December 31, 2005, 01:34:16 AM

thanks, bioroids!

AMZ PROJECT is in GGG & tonpad.

thanks

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DIY Stompboxes => Building your own stompbox => Topic started by: 6l6gc on December 29, 2005, 02:11:21 PM