How to check if an opamp buffer is woking properly.

[arma61]

Hi m8s

I've built the AMZ Dual Buffer seen here

http://www.muzique.com/tech/op-amp.htm (toward the end of the page)

Looks like it's working, I mean I can get the signals out of OUT1 and OUT2 the same as the input signal (talking about level and quality).

But how do I check if it's working properly as a buffer to drive long cable? surfing the net I've found, among others, this site

http://screaminfx.com/tech/why-and-when-to-use-a-guitar-buffer-pedal.htm

The video is quite clear on how a buffer works and what's supposed to do.
I've tried to simulate the same with all the cables I have, joined through "unpowered" true bypass pedals, I think I had something like 20 meters (metres :-) ), something like 55 feet, but still I cannot simulate that signal loss so clear in the video.

I don't need a buffer for myself, or may be I need it but I don't care too much I like how my setup works in my bedroom  , but I was asked to build one so I need to know in advance if it's working or not.

Or is the fact that I have the same signal  IN, OUT1, OUT2 symptom that the buffer is working good ?

Thanks for help to everybody,
Ciao

Armando

[PRR]

> 20 meters (metres :-) ), something like 55 feet

Nearer 66 feet.

If you are going to drive THAT much cable (more than I think Jack intended), you should perhaps add 220 ohms in series with C5 and C6, so the opamp is not directly driving so much capacitance.

A TL072 +220r should drive a mere 66 feet flawlessly for audio purposes. 222 ohms into 2,000pFd is a 300KHz low-pass. 20mA max into 2,000pFd is 10V/uS. These are "flawless" specs for 6KHz 0.1V/uS signals.

I used to drive much longer cable with full-bandwidth audio with a buffer of similar performance. -1db at 50KHz at 500 feet.

OTOH 66 feet 2,000pFd of cable directly on a passive pickup will shift your pickup's top-ring/cut down about an octave. Takes all the zing off.

If you use an active pickup or have any electronics between guitar and long-cable, that's different.

> I need to know in advance if it's working or not.  ...in my bedroom

1) get 100-foot spool of cheap TV coax, put ends on. (I found almost that much abandoned cable in my new house, I'm still pulling the stuff out.)

2) tack 2,000pFd (2nF) across a cable as a fair approximation of long-cable loading. (I used 10,000pFd for bench-testing 500-foot performance in an 8-foot room, but followed with actual-cable testing to verify.)

[arma61]

Thx Paul for your reply, still digesting it 

In the test I did I use a cheap strato copy with standard SC pickup, no electronic in between the guitar and the amp, it's a Tiny Giant Amp with and a cabinet from an old HIFI set. Could this be the culprit?

Still don't understand why I cannot hear any difference in the test I did, I've tried again with guitar connected wither with a patch cable, 20cm!, and with 2 8m cables, no differece at all. Is my set so good!!! can't believe it!

Probably I need to get my Peavey Revolution back from the basement and do another test with higher volume, poor my neighbours!! 

Unfortunately I don't have that much lenght of TV cable!! I should dismantle the entire wiring of the building     


Still I ask, bing the 2 outs the same as the input signal is this a signal that the crk is working properly?

Thanks again
Armando

[DavenPaget]

Follow the classic way of buffer testing by wiring 1nf across the cable per se PRR

[arma61]

ok m8s

looks like the hifi cabinet isn't good enough for this kind of test

fired up my Peavy Rev, set the volume to almost half way    ,  2x1nF across the cable and got the "dulled" signal, connected it to the buffer and, I'm quite sure, I can hear a difference now when I switch the buffer on and off.

Time now for the PCB and housing, then hand it to the "customer" and wait for comment/complain, at least I know now it doing its job properly, enough or not is up to the customer's needs/set up, isn't it ??

Thx a mil for your help m8s
Ciao
Armando

[arma61]

ok, looks like cannot access anymore to the link at the top.

Probably I did,unconsciously, something wrong posting it ?!?

in case I apologize with AMZ and Aron... I love you both, that's sure!!

Looks like I need now to study how an opamp works    if I want to have a buffered and a boosted out! I'm quite sure I saw it in that page.

Cheers m8 and again sorry if I did something wrong, that was not mean 


Armando

[amz-fx]

Hi Armando,

I changed the link to the opamp pcb.  It is only for people who purchase the pc board. I ask that the links to the pcb support be kept private.

There is nothing super secret or groundbreaking there, but I like to have some bonus info that is just for those who support my site.

It's not a big deal, and if you send me an email, I will send you the new link.

Email page: http://www.muzique.com/email.htm

Best regards, Jack

[arma61]

Hi Jack

thx, very kind, and thx for your reply.
I don't understand how this happened, I get there while I was seaching for "buffer" on yahoo.com ->images and that page come out, saw it.. like it... as almost the stuff from AMZ (Overdrive Pro on top!!)

Anyway, apologize again if I created any trouble to you.


Ciao
Armando