Quick question, 4:1 & phase

[Boba7]

Hey guys

Im thinking of building another 4:1 that I'd use in my acoustic rig. But because Im splitting the signal in various ways, I'd be happier if the 4:1 output was in phase with the input signal.

My 2 questions:

- the output of the 4:1 is out of phase right?

- if I put an inverter buffer (last one here: http://www.muzique.com/lab/buffers.htm) to get my signal back in phase, it'd be better to place it at the output of the 4:1 right? Im thinking it'd be good to keep the 4:1 high impedance.
So just a simple inverter opamp buffer should make it? Anything I have forgotten or Im missing?

Thanks a lot guys!

[madbean]

Yes, the 4:1 output is out of phase with its input. Something I try to avoid with most projects but this one obviously not.

I would not do it exactly as shown on the Muzique schematic. There's no need for a high input impedance into the added "buffer" stage since you already have a nice low impedance output from the previous stage. Using 10k resistors instead of 1M gets the job done and with less potential noise. Only "bad" thing about the schem below is both pin7 and pin2 of the added IC will be sitting at 4.5v, so a bi-polar 1uF for C3 would be a better choice. However, you could change it to 220n or even jumper through it.

One last possible mod if you are feeling crazy - make R19 a 100kA volume control instead. That would give you a master volume for the signal/compression mix. It's something I would have liked to put in the 4:1 but there was no room on the PCB.

[blearyeyes]

Makes me want to build one!

[Boba7]

That's great, thanks a lot!

Master volume control sounds cool but Im not sure it'd be practical, since there are already 2 volume pots, dry & wet. Could be a but confusing. But yeah, could be cool too... hmmmm

I didnt exactly understand the pin2&7 sitting at 4.5v but using a film 1uf would be no problem.

Thanks a lot!

[Boba7]

Im pretty sure I read somewhere else about BJT inverting buffer (or was it jfet?), I'll have to look for it cause it could be more practical (takes less space).

I love the 4:1, and with this phase thing corrected (not that it's a problem if I just play electric cause then it's just perfect as is)  its gonna be perfect.

[Boba7]

So I designed a pcb that's basically a 4:1 that goes into an inverting buffer, as discussed here. I also put in there a compression indicator led, and a trimpot for the sensitivity mod that Jon Patton came up with.
Not the best looking pcb haha but oh well

No intention to sell anything, so I hope it's alright. It was really a project for myself (though I do have some pcbs left of course)


http://www.madbeanpedals.com/forum/index.php?topic=27758.0