Author Topic: Quick question, 4:1 & phase  (Read 435 times)

Boba7

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Quick question, 4:1 & phase
« on: February 20, 2018, 01:16:40 PM »
Hey guys

Im thinking of building another 4:1 that Iíd use in my acoustic rig. But because Im splitting the signal in various ways, Iíd 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, itíd be better to place it at the output of the 4:1 right? Im thinking itíd 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

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Re: Quick question, 4:1 & phase
« Reply #1 on: February 20, 2018, 02:25:13 PM »
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.
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blearyeyes

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Re: Quick question, 4:1 & phase
« Reply #2 on: February 20, 2018, 02:37:36 PM »
Makes me want to build one!
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Boba7

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Re: Quick question, 4:1 & phase
« Reply #3 on: February 20, 2018, 03:29:11 PM »
Thatís great, thanks a lot!

Master volume control sounds cool but Im not sure itíd 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

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Re: Quick question, 4:1 & phase
« Reply #4 on: February 20, 2018, 04:22:57 PM »
Im pretty sure I read somewhere else about BJT inverting buffer (or was it jfet?), Iíll 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 itís a problem if I just play electric cause then itís just perfect as is)  its gonna be perfect.
« Last Edit: February 20, 2018, 04:52:31 PM by Boba7 »

Boba7

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Re: Quick question, 4:1 & phase
« Reply #5 on: April 07, 2018, 04:54:39 AM »
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

« Last Edit: April 07, 2018, 10:22:29 AM by Boba7 »