Trying to implement a Hiz guitar preamp. (to line out)

[lagoausente]

an open circuit would be less objectionable if the failure gain defaults to unity rather than WFO.

What´s WFO?
I´m still looking for a good dictionary of electronic/forum abreviations on the web...

 

[JohnRoberts]

Sorry not really a technical term .

Slang term "Wide F___ing Open" means all controls to the max..

JR

 

[lagoausente]

:grin:
Well, there would be nice an online dictionary also for slang terms.

 

[AMZ-FX]

[quote author="JohnRoberts"]In an ideal world your PS will be centered by the 10k resistors but any significant load imbalance like asymmetrical output clamping might be problematic. A stretch I concede but I worry about such things. [/quote]

In this design, I'm not worried about it. A stretch as you suggest and not likely to be a problem.


[quote author="JohnRoberts"]In one design I did to split a single supply for bipolar use, I used a simple pair of NPN and PNP transistors with their emitters tied to v/2 (your GND), both bases tied to the junction of a divider like your 2x 10ks[/quote]

Transistors? We don't need no stinkin' transistors! :grin: You could also use an opamp to buffer the pseudo-ground reference, which would be simple.

best regards, Jack

 

[Guest]

Non-linear pseudo - ground reference? Let it better have higher dynamic resistance, but linear one...

 

[JohnRoberts]

[quote author="AMZ-FX"]

Transistors? We don't need no stinkin' transistors! :grin: You could also use an opamp to buffer the pseudo-ground reference, which would be simple.

best regards, Jack[/quote]

Sure you could use an opamp, or a v/2 IC, but then you'd be wasting some more battery life whether it's working or not.

If' you're not worried, I'm surely not worried...

JR

 

[AMZ-FX]

Just a quick note about the circuit... do not use the balanced and unbalanced outputs at the same time. Use one or the other, to keep everything playing nice :grin:

regards, Jack

 

[clintrubber]

[quote author="audiox"]Why to use a hard-to-get rev log potentiometer instead of making R4 adjustable (normal log potentiometer)?[/quote]
Before I could see the actual circuit (previous machine didn't show the pic) I was expecting a cap in // with R4, so the answer could have been: to keep the upper roll-off frequency constant.
But there's no cap in the schematic above, so this didn't became the answer :wink:

 

[clintrubber]

FWIW, here's more TL072 DI-stuff:

http://www.d-r.nl/dnrsite/pdfmanuals/DI-box-Manual.pdf

 

[lagoausente]

I think a good idea to link aswell the link a pic of the original shem by Samuel Groner.
I have built it. For some reason, an oscillation tone appeared when there was no load at the input. I solved it, using a switching jack, and making a shorting input. When plug the jack, the input gets unshorting.
The oscillation came from a non-optimal layout design, and a posible capacitive coupling between in and out. Samuel gived me some guidelines for avoiding the problem. I will not rebuild mine, but probably could be useful for any of you if you are planning to build it, to avoid posible oscillation problems.

[quote author="Samuel Groner"]The input is a very high impedance node when left open and any capacitive coupling to the output might provoke oscillation. The easiest fix would be to just use a shorting input jack. Otherwise you can play with the layout--distance from input to output helps. In addition to this, you might want to use shielded cable from the jack to the opamp input. [...]

* R1-R3, C1, C2, D1, D2 close to the noninverting opamp input, cable from jack to R1 shielded (shield grounded)
* R4, R5, C3 close to the inverting opamp input
* The wires for R6, C4 routed away from the output and noninverting input, perhaps even shielded (shield grounded)
* R7, R8, C5 close to the other opamp inverting input

The rest should not be critical in placement. If nothing helps, you could try increasing C3 and C5 (say to 220 pF and 100 pF maximum), but this should not actually be necessary. It's really a question of layout I'd say. [/quote]