TRS Phantom Power box to power onboard buffer?

[Big Fat Walrus]

Hello all

My attempts at searching are coming up empty, but I seem to recall reading a thread awhile back in which RG had detailed such a thing - Maybe I am imagining it or am just confused.

Anyway, the story is this: I would like to place an onboard buffer into my bass. But there is just no way I can fit a 9v battery into the tiny control cavity (additional routing is off the table). And I have considered building a coin cell stack-type holder device, but don't really like the idea of having to unscrew the cavity cover repeatedly to change batteries anyway (even if it is only every 6 months).

So - in a perfect world I would like to use a TRS cable to power the buffer from an external Hammond style enclosure. I use a Boss pedal board, so have (relatively clean) 9v on hand already. I was thinking it would be nice to bump this up to 12v or even 18v, and then send it through the cable to power the buffer circuit inside the instrument's control cavity. Instrument cable goes into box R, output cable goes to rest of board from box L. Simple and clean (though not necessarily easy).

I am all ears for any suggestions here - cable type, caveats, warnings; anything. I am relatively decided on taking this path forward, but am still open to valid persuasions against it.

As to the insides of the potential Hammond box, I would like to either assemble/populate an existing RTS PCB, or find a design that works well on a perma/proto type board; I would rather not 'dead bug' something inside the enclosure. I am solid with an iron and with following instructions, but am a little (a lot) lacking in the ability to read and decipher true schematics.


Thank you all in advance! Your time is appreciated

[idy]

Welcome to the forum. I think the thing you are looking for is this

http://www.till.com/articles/PreampCable/

What problems are you experiencing that the buffer will help with?
Have you tried a normal buffer, in a box on the floor...wait you have a boss pedal board? You mean Boss pedals that have buffers already?

Phantom power does not require a third conductor, just blocking cap.

Since you are buffering (no gain) a passive signal, 12-18v headroom seems unimportant. And charge pumps can be noisy.

[Big Fat Walrus]

Yes, I have seen that article. Thank you. But no, I was thinking of sticking an actual buffer circuit inside the instrument itself, not inside the cable housing. But I guess the power box would be the same. But as I said above, going from schematic to solderable protoboard is beyond me (don't laugh!)

And by a Boss pedal board I mean a BCB-60 board; a molded gun-case looking job with an integrated wall wart supply powering 7 power plugs / pedals. To that end, the first pedal inside the case is true bypass (as they all are, until the last pedal. A Boss Giga Delay; so output buffering is already covered).

Fair point on the headroom- so maybe 9v from the box would do just fine. And I could do without any additional noise.

The buffer would be nice to preserve some high end on a rather dark bass, but also to heighten a bit of 'punch' in certain situations. I would be installing a bypass switch to keep the original tone an option when desired. Additionally, my new home has a fair bit of EMI interference that I can't seem to shake in its entirety. Shielding will happen soon (over the weekend likely), but I was under the impression (perhaps mistakenly) that a buffer before any cable run would help to shed a little bit more of that noise (and yes, the instrument is grounded properly, yes the amp is as well, yes it has two HB pickups, yes the dimmer switches are being replaced, so on and so forth).

And I also like the sound of active basses I hear on recordings when played solo - I just have no desire for any gain. So a switchable buffer seems like the best of both worlds, no?

Maybe I'm wrong though...

[idy]

How small do you need it? There are Vero layouts that are pretty small....
https://tagboardeffects.blogspot.com/2014/08/buffers.html

The 8x7 is about 1/2"x 3/4."

A smaller ready made one is from amz
http://www.muzique.com/schem/buffmod1.htm

plenty of ways to go at it.

I would build or buy one and try it to see if it makes a difference before getting fancy. Like on of those old Dan Armstrong things that plug right into the guitar...or EHX LPB-1...or a clip on the strap, not pretty, but to experiment.

There won't be any circuitry in the box on the floor will there? just a power jack, mono out jack and TRS to the instrument. But bypass, that would be a switch on the bass?

[crane]

I have the above mentioned "preamp cable" preamp built into my guitar. but I power it with an onboard 9V battery. Draws very little current - I think I have never changed the battery.
Using a mic cable and TRS jack has it's drawbacks - if your cable breaks - you can't just grab any spare one - you need a TRS one which are not that common. Just a point to think about.

[Big Fat Walrus]

Thanks, IDY.

But I have the buffer part squared away. The PCB or layout I am looking for would be for the phantom box 'guts' only.

[antonis]

Hi & Welcome..

So, you  need a simple buffer PCB or layout for +48V power, or what..??

[Big Fat Walrus]

Hey Antonis-

Yeah pretty much. I think 9v will be plenty though, no need for true 48v phantom.

Basically I am looking for advice on how to safely and quietly take a standard 9v pedal wart and plug it into an enclosure that would send the 9v up into the instrument Jack.

Maybe some supply filtering on the 9v jack, and maybe an on / off toggle on the top for when plugging in or removing it the cable. But that is all- just a feeder box.

Oh and yes to IDY- the buffer on / off switch would be on the instrument. If there was one on the box it would only be used to cut power to avoid shorting something as the cable was inserted.

Thank you all for your replies

[Big Fat Walrus]

So perhaps using the term 'Phantom' is making this request confusing. I am only looking for a box to deliver 9v remotely to an instrument from the floor. I have drawn up a little sketch of what I mean below (and included a blank version if anyone feels inclined to draw on it).

The area marked PCB is where I would like to filter the supply. That is what I really need the most help with. Any beyond that, if someone can just look at the layout and say if this is a safe way to do this.

Thanks!

[antonis]

R value depends on buffer current and affortable voltage drop..
C value comes out of formulae: C = 0.16 / (f x R), where f << 100/120 Hz (rectified mains frequency)..
CLR value comes out of: (9 - V_LED) / I_LED

Practical values are: R = 10R - 47R, C = 100μF - 470μF and CLR = 2k7 - 10k

[Big Fat Walrus]

Hey Antonis-

Awesome! Many many thanks for this. I can't be the only one interested in making one of these, so hopefully other novices who fear frying their pickups (or burning down their house!) will see this and benefit from the knowledge posted. I actually have one of these trinkets (https://shop.pedalparts.co.uk/product/humstop) laying around from a fuzz project, and see that the basic format of what you posted is about the same. I didn't realize that power filtering could be as simple as it appears to be. I thought it would involve many more components.

QUESTIONS:

A) I would like to include an input polarity protection diode to my box as well - I can just lay that across the +/- wires leaving the DC jack before they hit the rest of the PCB, right?
B) Don't I need some sort of diode (or a fuse even?) on the hot wire leaving the switch before it gets to the 'TO INSTRUMENT' jack? Maybe I am just overthinking this.
C) I was thinking of using a 3 pin XLR jack on the power box, and using an XLR to 1/4" cable to the instrument. Is this a bad idea for any reason I am not thinking of (other than a weird cable)?

Anyway, thanks again, man. I really appreciate your insight

[antonis]

A) Yes, as far as diode Cathode (strip band) faces to (+)..
(shunt reverse polarity protection)

B) IMHO, No..

C) A stereo jack (and stereo plug) should also be fine..

[Big Fat Walrus]

Hey Antonis-

That is great. Thanks for your time.

A PCB with all the in / outputs / ground plane accounted for hanging from the switch would be perfect for this, but designing all of that is way over my head. I will work up a design for a permaproto board (I really like these in various sizes for development: https://www.adafruit.com/product/589) and check back once again before I solder it all up to make sure I haven't overlooked something...


Thank you again for your help

[antonis]

designing all of that is way over my head.

Just 4 items on 8 X 5 hole board..






P.S.
If there isn't 270μF cap handy, go to 220μF or 330μF(preferable)..

[Big Fat Walrus]

Hey Antonis-

Wow; thanks! I just sat down to plot all of this out. But I am glad I checked here first.

By the way, those graphics are great. Did you make all those images yourself and move them into place? Very nice.

Since you have been so helpful, let me pick your brain just a bit more if you will indulge me...

QUESTIONS:

A) The capacitor should be electrolytic, correct? (legs aligned appropriately)
B) Your layout has only one capacitor, and a 10R - 47R range for the resistor (not the CLR). Why does the fuzzdog 'drop in' PCB have two capacitors (C1 = 100u and C2 = 47n) and a 100k resistor? Is this overkill, poor design, or what? (I have attached a picture below). Just trying to wrap my head around the theory here and learn more about the underlying concepts at work.

Again, thank you very much for looking all of this over. This forum is great!

[FiveseveN]

Why does the fuzzdog 'drop in' PCB have two capacitors

Due to their construction, electrolytic capacitors have high parasitic inductance, meaning they stop being capacitors at higher frequencies. A smaller cap (with lower ESL) is often used to compensate for this. https://circuitdigest.com/tutorial/understanding-esr-and-esl-in-capacitors
Probably not important for the task at hand.

and a 100k resistor?

No no no! The document says "100R minimum 1/2W rated". 100R is 100 Ohms, 100K is 100000 Ohms. It forms an RC low-pass filter with the capacitor(s).

[antonis]

By the way, those graphics are great. Did you make all those images yourself and move them into place?

https://bancika.github.io/diy-layout-creator/

P.S.
Adding C2 (10nF - 100nF) should do no harm..
My only objection concerning Humstop C2 is the type of capacitor.. - IMHO, it should be a ceramic one( for the purpose it's placed there..)

[Big Fat Walrus]

Ha-

Yes, I know K means 1000 - that was simply a typo. I was only wondering why the values differed.

But I guess I never thought about the RC filter part (duh). I never thought about filtering like it was adding a 'tone knob' to the DC jack shunting electrical junk to ground. Very helpful.


Thanks!

[antonis]

But I guess I never thought about the RC filter part (duh). I never thought about filtering like it was adding a 'tone knob' to the DC jack shunting electrical junk to ground.

There isn't any "tone" knob simply because "tone" pertains to frequency, hence concerns AC only..
(Frequency of DC is, or should be, 0 Hz - a parallel to X axis flat line..)

What you want to filter here is DC "ripple", which is a result of  - possibly - inadequate smoothing right after AC rectification..
https://www.electronics-tutorials.ws/diode/diode_6.html

P.S.
Hum stopper/eliminator is a bit more complicated case and has to do with ground loops also..

[Big Fat Walrus]

Yeah, the 'tone knob' analogy isn't an entirely accurate one - but something clicked when fiveseven mentioned the filter and it started to help me get my head around the concept.

Thanks for the links, I will definitely check those out. Half the fun of a hobby like this is (to me) the making, but the learning is the other half.

Thanks for helping me get further down the path...