will this 48 V pink noise source work?

[MisterCMRR]

This circuit (largely due to the op-amps) draws 8 to 10 mA, making V+ between 14 V and 17 V, which is plenty for a low level circuit. I have not checked the optimization of the response-shaping feedback network. It interleaves pole and zero frequencies to approximate the -3 dB per octave rolloff of pink noise (if you'd like that optimized for accuracy, my services are available for a fee ). The output is BALANCED in the only way that matters (equal impedances with respect to ground) although only one pin has signal. I'll not beat that horse again!

 

[ruffrecords]

No need to add unnecessary components to keep your CAD software from having a brain fart (this is the tail wagging the dog). In this case there are only two places I can see labeled V-. Just change them both to be the same as all the others labeled with the earth symbol.

Cheers

Ian

 

[gyraf]

..isn't it kinda weird to use a transistor (BC550) specifically made for low-noise in this type of quest..?

 

[Chrisfromthepast]

..isn't it kinda weird to use a transistor (BC550) specifically made for low-noise in this type of quest..?

Yeah I agree, this is the least optimized part of this design. I was worried about not being able to test the noise source at all, if the rest of the circuit is hopelessly wrong.
Now is a good time to evaluate different noise sources.
Is there a reverse biased junction that is commonly used as a noise source?

 

[Chrisfromthepast]

Enclosure defines PCB dimensions, board outline is a prerequisite of the layout. So, ok
I like this form factor for design this simple:

But its from amazon and is slightly the wrong size

Anyone know the right search terms for an enclosure like this?


Other ideas are welcome, this is just what I’ve seen alot of.
Simply searching for extruded aluminum d-series, or the dimensions has yielded junk for me.

 

[Chrisfromthepast]

@MidnightArrakis
The V+ V- nodes are part of the op amp schematic symbol, and place the power nodes (pins 4 and 8) of a dual package op amp in a separate location (usually near the PSU area of the schematic) so that psu decoupling capacitors don’t make your schematic hard to read.
Like the phantom power convention, it is a pattern Im used to. It is meant to ease confusion about which components are part of the signal path, and to eliminate those pesky crossing traces.
Im fine with the convention, but I understand that schematics are drawn dozens of ways.

 

[Chrisfromthepast]

C5 should be no larger than 1 u right?
I originally had the dead simple 100n. But I did not realize this is a source of confusion. Phantom power rails are stiff, and there aren’t transients, so I don’t quite see the need for so much capacitance.

Or replace the values of C5 with C7 to make sure the loop area for the 100n capacitor is tight with pins 4 and 8, and put the 100u capacitor at the junction with the 2k2 resistors is what to do, rather than fix it in layout.

 

[abbey road d enfer]

Phantom power rails are stiff,

Are they? They're 6.8kohm to start with.

and there aren’t transients, so I don’t quite see the need for so much capacitance.

The decoupling cap shuld be commensurate with the load. You have chosen 220uF for the output cap, the decoupling cap should be similar. But maybe you don't need as much as 220uF.
With 220uF, the -3dB point is at about 1.5Hz (-0.5dB@4Hz). Maybe you don't need that.

 

[Chrisfromthepast]

Are they? They're 6.8kohm to start with.

Thanks, yes, stiff is an ignorant description.

You have chosen 220uF for the output cap, the decoupling cap should be similar. But maybe you don't need as much as 220uF.

1.5hz is probably overkill.

 

[nsalis]

Enclosure defines PCB dimensions, board outline is a prerequisite of the layout. So, ok
I like this form factor for design this simple:

But its from amazon and is slightly the wrong size

Anyone know the right search terms for an enclosure like this?
View attachment 117049

Other ideas are welcome, this is just what I’ve seen alot of.
Simply searching for extruded aluminum d-series, or the dimensions has yielded junk for me.

Neutrik calls it “In-Line Housing”. BoXo calls it “Universal connector box for self assembly of D-Type connectors”. these boxes also appear to be larger than the Amazon clone you found. In any case, you could use the Neutrik NM3MD-B connector. This allows you to plug your device directly into an XLR microphone input jack.

https://www.happareute.de/index_pro4_eng.html

ns

 

[nsalis]

Neutrik calls it “In-Line Housing”. BoXo calls it “Universal connector box for self assembly of D-Type connectors”. these boxes also appear to be larger than the Amazon clone you found. In any case, you could use the Neutrik NM3MD-B connector. This allows you to plug your device directly into an XLR microphone input jack.

https://www.happareute.de/index_pro4_eng.html

ns

https://www.mouser.ch/ProductDetail/Neutrik/NM3MD-B?qs=R5cXQUTKuHUvSXnQ38IjvA==https://www.canford.co.uk/NEUTRIK-IN-LINE-HOUSING

 

[Chrisfromthepast]

Thats the one!
Sweet

 

[Chrisfromthepast]

@MidnightArrakis I will not be near the right laptop to fix this design today, and you likely are. So, we’re going with 100uf 63V for all the electrolytic caps. And the pinout will be a transistor that matches the BC548 pinout.
On a PCB this small, component numbers is all that can fit on the silkscreen anyway.
Have at it.
If you can share your PCB dimensions Id love to layout one myself for kicks.

 

[Chrisfromthepast]

designed for this circuit, basically because the enclosure I am planning on using is significantly smaller than the NEUTRIK "NA Housing" enclosure that you are planning on using

Huh? Why would that be? The NA housing is what I desire. The PCB you posted a rendering of is the pcb Im asking dimensions for; nice fit inside of NA housing.

 

[abbey road d enfer]

As an example, you show your R13 and R14 as being 2K2's, but in my schematic I have R14 and R15 as 1K's
per someone's suggestion. However and more recently, since it was disclosed that your circuit is being powered "like a condenser microphone", someone else has stated that my R14 and R15 should be 6K8's, just like a normal "phantom-power" circuit would be.

I don't see that in the whole thread. Anyway that would not make sense at all.

I am planning on using is significantly smaller than the NEUTRIK "NA Housing" enclosure that you are planning on using and my PCB design idea is my personal priority.

Weird. You propose your help for a member but you condition it on your choice of housing. What would that housing be? Is it commonly available? Remember we're DIYers here, we don't have the capacity of ordering hundreds of pieces of custom made metalwork.

 

[abbey road d enfer]

[I don't see that in the whole thread] -- It is mentioned in Post #30 by the OP when he stated, "its phantom powered like a condenser mjc". (NOTE: "condenser mjc" was in the original Post #30).

The resistors in the sending device are 6.8k, defined by the P48 standard. It does not imply at all thet the resistors in the receiving device are 6.8k. Actually, they are almost never 6.8k. You've drawn wrong conclusions.

[Anyway that would not make sense at all] -- Exactly how this circuit is supposed to be powered has been a point of confusion and contention sprinkled throughout this thread. I'm just going by how one of the last responses had made a comment because it is almost the only way for this circuit to be powered..... based upon my limited operational electronics circuit knowledge.

Mr CMRR in post #42 has perfectly summarized the method for achieving the values he recommends.

[You propose your help for a member but you condition it on your choice of housing] -- It appears as though the wording of my comment was not very clear. YES!!!.....I know that the OP wishes to enclose their circuit within a NEUTRIK "NA Housing" enclosure and that's perfectly fine. And, YES!!!.....I could design

You could but wouldn't. I could be king but I have my life to live...

[What would that housing be?] -- I'm not revealing that yet because I am still attempting to obtain some certain CAD-design data from the manufacturer. However, all that I will say is that the connector housing I am planning on using for this circuit is significantly smaller than the "NA Housing" enclosure.

How much smaller can it be when the dimensions of the XLR connectors are fixed and unmovable? What would be the motivation for "significantly smaller"? Small enough to be easy to steal?
I sold a few thousand DI boxes. I made a smaller version. Customers complained they were too eay to steal, and for that reason preferred the old one.

[Is it commonly available?] -- YEP!!! And, it's from one of the "other" leading audio connector manufacturers here in the U.S.!!! It's a standard off-the-shelf catalog item.

Why don't you name it? Why make it a secret?

I feel as though you are somehow blaming and chastising me for -- SOMETHING I HAVEN'T EVEN DONE!!!

No. I'm just mentioning that you offer incomplete service, which results in lengthy discussions that lead nowhere. Actually, have you completed anything for any member here?

-- All that I have done is provide the OP with the NEUTRIK "NA Housing" information

Which the OP already had.

and have made a very simple statement that I am planning on using a -- significantly smaller -- enclosure for this circuit FOR MYSELF!!!

Not only. You said you were submitting your offer of help to whatever dependancy on a putative housing.

I have absolutely -- NO IDEA -- where you are coming from to accuse me of having "hundreds of pieces of custom-made metalwork" fabricated for someone else's circuit!!!

Read again. I have not accused you of that. You presented your choice of housing as something that did not exist yet and was subject to confirmation, which in turn let me believe it was a custom product.

If I didn't know any better, I would say that you are trying to force/push me off of this forum by baselessly accusing me of doing something that I haven't even thought of!!! Is that it???

No. I just can't help noticing that your written expression is ambiguous and results in confusion. As a moderator I'm concerned about it.

If you want to ban me from this forum, Abbey Road.....just say so, OK???

That is not what I "want". I want you to be clearer in your communication.

SHEESH!!!

That was not necessary...

 

[Chrisfromthepast]

[The NA housing is what I desire] -- SO BE IT!!!.....

[The PCB you posted a rendering of is the pcb Im asking dimensions for] -- FIRST: Pick out a male XLR connector that you want to use on the "NA Housing". SECOND: Determine whether or not you would want to mount some other connector or other components on "the other side", -- OR -- do you want to just use a "Blank Cover Plate" on the opposite side as I have shown within my CAD-images? THIRD: THEN.....I will provide you with a set of PCB-dimensions. The "type" of connector that you will use will determine what the PCB "length" dimension will be, so I need that information.

The PCB you see in my CAD-images is a relative "GENERIC" PCB that I came up with just so I could have "something" to work with (for a completely different project awhile ago). But, the -- actual -- PCB-dimensions will be determined upon the XLR connector and other factors surrounding the basic "NA Housing" enclosure.

YOU do your part and then I will provide you with MY part!!! DEAL??? Sound like a plan???

I'm too worn out now from having to defend myself against Abbey Road's accusations against me for how I want to design your circuit for myself, so now that it is 3:00 AM in the morning here right now.....I'm going to bed!!! That just wore me out and it hurt, too!!!

/

Yo, please relax.
I wanted to make this lil thing for fun. You can buy one on ali express. There are a bunch of other topologies that would work. I do not require a layout guy. I just want to learn a tiny bit by solving problems as they come up.
I deal with human problems all them time, so Im learning something here too, but we are not advancing the project one bit by getting emotional.
Please tone it down, or just let this one go.

 

[Chrisfromthepast]

I appreciate your patience. Im SO thankful for this community. The amount of skill and patience is overwhelming.
I've added the KICad bit to a GitHub repository, here to play along with. The parts are roughed out, but no copper yet.
My pedestrian attempt to layout this board is heavily constrained by:
-hubris
-trying to make it easy to build and at home, using through hole and single layer. But, as I try to find these capacitors for the filter network in particular, it may be that the THT varieties are too hard to get in stock. ( I have not been able to lay this out single layer in this size)
-size
I think most parts are going to have to go surface mount and some end up on the bottom of the board in order to get this to fit inside of the NA housing.
Is the tiny size important to anyone? I feel like I should just ask. because Im likely to build it on a protoboard once or twice from the schematic, and never use the printed PCB. but thats just me.
I will just choose a different housing most likely for the first round.

Is this size suitable? What does going smaller get us?

 

[abbey road d enfer]

What does going smaller get us?

Easier to steal.
I believe I already mentioned that.
I've sold buckets of DI boxes. At one time I made a smaller version. My customers didn't like it because they got too easily stolen.

 

[abbey road d enfer]

Looks to me like there's plenty of space, so both the IC and the trimmer could be TH as the rest.