Questions about Dano/jack ormans buffer, solutions anyone?

[knealebrown]

so i built this

http://www.beavisaudio.com/techpages/Buffers/BuildOneBuffer.gif

here it is in all its retro styled glory



Anyway im from the U.K so i couldnt get the PCB Dano suggests (the radioshack one) so i transferred it too stripboard/veroboard and wired it up as shown replacing the battery snap with a boss style dc jack and using a socket for the Opamp.

I have two problems:

1. A popping when i flick the on switch.
2. The circuit is not unity gain

Apart from this there are no other problems. the signal passes through fine and is cut when the switch is in the off position

I have checked over and over again that my vero/stripboard design matches Danos, any ideas anyone?

[snoof]

We need to know...

-How is the switch wired?  Are you cutting power or is it a bypass, or something else?
-When you say it's not unity gain, does that mean that it outputs less than unity?
-Voltages on all the op-amp pins.

[knealebrown]

cool, sorry about lack of info:

-one pole on the switch is wired too the +ve of the dc power jack the other other pole is wired too the +ve on the stripboard.
-when i plug straight into my amp the signal is as strong as it ever will be, but when i put the buffer in line its at a lower level (volume-wise)

how do i measure the voltage across the op amp pins (using my DMM obviously) but do i use one probe on each pin and the other too ground?

thanks for the help

[Mark Hammer]

1)  The circuit, as shown, IS unity gain.  However, buffers have the effect of increasing "presence", making the signal seem louder, sort of like a 1.5x amp.

2) If you built from the schematic shown, note that it is not really a self-contained circuit.  Missing is the sort of power smoothing that would de-thump the switch for turning the power on, and that it needs terminating resistors at the input andoutput to avoid switch-popping when using a true-bypass switch..  Consider running a 100 ohm resistor from 9v to pin 7 of the chip, and a 47uf-100uf cap from pin 7 to ground.  Also, consider running a 2M2 resistor (or thereabouts) from the input to ground, and a 10k resistor from the output to ground.

[snoof]

how do i measure the voltage across the op amp pins (using my DMM obviously) but do i use one probe on each pin and the other too ground?

blk probe to grnd, red probe to each pin and notate voltage.  If you are switching power on and off while the thing is plugged in, it's bound to make some noise.  Consider a bypass switch instead.

[knealebrown]

Thanks mark, its not unity gain , theres a drop in volume when i put the buffer in line.

heres the voltages across the opamp pins

Pin 1          0.16v
pin 2          4.62v
pin 3          4.4v
pin 4          0v
pin 5          0.16v
pin 6          4.62v
pin 7          9.28v
pin 8          0.05

Makes me wonder why dano would post a seemingly complete build on his site if it needs more components?

The popping is not so much a problem as i intend to have the buffer on always but it would be best to get rid of it, no?

any suggestions guys? im still a noob at this so thanks for the lesson.

[puretube]

"A circuit works only as good as it`s power supply",
a wise man once said...

"+9V" is not a power supply   -   it is just a labeling  of the DC-voltage
the powersupply is supposed to spit out...

(in the most optimal case, the PS would offer a zero impedance (=shortcircuit) for all AC-voltages)

[knealebrown]

1)  The circuit, as shown, IS unity gain.  However, buffers have the effect of increasing "presence", making the signal seem louder, sort of like a 1.5x amp.

2) If you built from the schematic shown, note that it is not really a self-contained circuit.  Missing is the sort of power smoothing that would de-thump the switch for turning the power on, and that it needs terminating resistors at the input andoutput to avoid switch-popping when using a true-bypass switch..  Consider running a 100 ohm resistor from 9v to pin 7 of the chip, and a 47uf-100uf cap from pin 7 to ground.  Also, consider running a 2M2 resistor (or thereabouts) from the input to ground, and a 10k resistor from the output to ground.

can i just run the two resistors from the inputs and outputs too ground across the tip and sleeve on the input and output jacks? also can that 47uF-100uF cap be an electrolytic?

chears

[knealebrown]

just did what you said mark, still not unity gain. Also im only getting a pop when i turn it on now but not when i turn it off.

Hmmm frustration the cruelest of natures feelings

[tiges_ tendres]

I think you are getting a pop when you turn it on because you are not bypassing the circuit with the switch but rather turning the power on and off.  I think applying the power in this way is what is making it pop. 

[snoof]

If you are switching power on and off while the thing is plugged in, it's bound to make some noise.  Consider a bypass switch instead.

can i just run the two resistors from the inputs and outputs too ground across the tip and sleeve on the input and output jacks? also can that 47uF-100uF cap be an electrolytic?

yes, yes


It's such a simple crkt, either you have a bad part (not likely) or your wiring is wrong (bridged traces?).  Post some pics.

Makes me wonder why dano would post a seemingly complete build on his site if it needs more components?

it's not a complete crkt as Mark says, it's really a crkt snippet.  Although it wouldn't hurt for him to add a note to that page about the recommended additional parts.

[anchovie]

The best way to avoid popping with power-switched effects is to turn your amp on last and off first!