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Author Topic: small ic preamp  (Read 4701 times)

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Offline weroflu

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small ic preamp
« on: April 01, 2015, 12:13:20 PM »
Built this recently

https://oshpark.com/shared_projects/wLhDZUDM

Stereo fixed gain unbalanced in/out on 1/8" mini connectors. Still need to tweak the layout a little bit since connectors don't sit right, but it works and sounds really good. No mic power on board, works with a 9v pp3, designed for use with battery-powered microphones (cmbi's for me). The ic was socketed and I tried it with both Max412 and LME49720, both sound good, the 49720 maybe a little better. I could have actually gotten this a lot smaller but since it was a first attempt I didn't know how small I could handle with the iron. Next time I'll use solder paste and not be afraid of soic packages.

Something similar could easily be adapted for use with dynamic microphones with an inamp, but I have none currently.

Thinking about doing a 4 channel version in maybe 1/3rd more space which would make it very compact, but only for specialized applications.

I don't want to get into a situation where people are asking for pip or this or that, but I would like to make it available for people to do what they want with it. A 4 channel could easily sit in an altoids tin, maybe even 6 channel.

Also have on my mind doing a transformer input version. Lundahl has small input transformers, trannies and stereo preamp both will fit in an altoids tin. Yet another idea was a ghetto altoids modular 6 channel 1) pre 2) mixer.  This is probably too much brainpower but who knows. If I can find a small usb battery, maybe altoids size or slightly larger that can power everything including phantom then I might devote some time to the modular idea.

It was sort of an experiment to see if it would sound better than the Sony M10 preamps, and that it did by a large margin.


(Schematic credit to Ricardo of Micbuilders)

pics added. If you look close there's no ic on the board, because this is a different design (aka fail), but they are about the same size.

wrapped in saran, packing tape, then copper foil.
« Last Edit: April 01, 2015, 12:47:42 PM by weroflu »

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Re: small ic preamp
« Reply #1 on: April 01, 2015, 12:42:23 PM »
Very cool.
volition > vibrations > voltages > numeric values | numeric values > voltages > vibrations> virtual teleportation time-machine experience
made easy- >>Improved PAS table<< | made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline weroflu

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Re: small ic preamp
« Reply #2 on: June 14, 2015, 04:03:48 PM »
v2, first one drowned in potting compound.


Offline weroflu

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Re: small ic preamp
« Reply #3 on: June 14, 2015, 04:29:56 PM »
If you go back a post I got as far as shielding it in copper foil and then I still needed an enclosure - hence the potting compound. I made a cardboard mold and then poured in the compound. The compound got inside the (wrong type of unsealed) jacks and that was that. So second choice was a mint tin, though it's bigger than I wanted it to be, it's all done and it works. This time around I used sealed jacks, and could have tried again with the potting goo but who needs the hassle.






Offline maux

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Re: small ic preamp
« Reply #4 on: June 15, 2015, 03:21:29 PM »
The Schematic ?
« Last Edit: June 15, 2015, 03:26:10 PM by maux »

Offline Hypnocracy

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Re: small ic preamp
« Reply #5 on: June 15, 2015, 09:18:48 PM »
_____________
hypno on teh Archive

This must be heaven -- 'cause here's where the rainbow ends
If this ain't the real thing, then it's close enough to pretend

Offline weroflu

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Re: small ic preamp
« Reply #6 on: June 16, 2015, 04:55:48 AM »
eagle schematic and brd files attached as zip

*this is a fixed gain preamp set with two resistors, next one maybe i'll add in variable gain

boards here

https://oshpark.com/shared_projects/aCwc3puF
« Last Edit: June 16, 2015, 04:57:56 AM by weroflu »

Offline maux

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Re: small ic preamp
« Reply #7 on: June 16, 2015, 09:25:52 AM »
Thank you !
very simple schematic....perhaps too!


Offline weroflu

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Re: small ic preamp
« Reply #8 on: July 12, 2015, 02:04:19 PM »
Finished 4 way switch with variable gain, layout done.

This concludes just about everything  I wanted, but as long as I have not yet sent it out for fab, I'm wondering if there is something I didn't know I wanted. Phase, not really needed, variable gain would be nice but pots aren't accurate. I was looking into digital pots, and this might be a possibility with arduino and maybe even an android bluetooth control to avoid having to use a screen, but off in the future.

Then I was thinking of adding in two wire pip mic functionality( purely as a samaritan), but not sure about how to handle very low impedance mics as this is designed for a 500ohm mic, and I definitely do not want to be accountable for people frying their dpa 406x's.


Offline weroflu

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Re: small ic preamp
« Reply #9 on: August 21, 2015, 12:57:21 PM »
Tested the gain switching, boards are back and everything works and sounds really good.

I'm just about finished with a PIP, 3-wire, 4 way gain switch pre for the Sennheiser KE4 capsules aka MKE2 microphones. I assume these would work with a lot of 3-wires with a change in source resistor value - maybe there can be variable source resistor.

Along the same lines a 2-wire PIP pre will work, not sure if there will need to be different boards.

I think I'd like to make a low cost diy preamp available here, non-profit, if any of the solder monkeys want to think about assembling.
The sound quality is very high, on par with the offerings here.
These fit perfectly into an altoids tin so all you need for casework is two holes, and it cuts the case cost down a lot.
I like the flip tops because you can get inside to access switches without the need for more hole drilling.
Parts cost could be under $15-$20 not including labor.

If there is interest there could be something like a collective effort where people handle parts, some assemblers are involved (paid), and then it's self-sustaining.

Also thinking about doing a super low profile preamp roughly 1x1.5 x .25 inches, watch cell powered, could be pip also, fixed gain but battery life would be low.







Offline weroflu

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Re: small ic preamp
« Reply #10 on: September 28, 2015, 10:16:15 AM »
first board layout finished for Sennheiser ke4 mics:

9v pp3 battery
18k source resistor
PIP
two 3.5mm input jacks
one 3.5mm stereo out
4 way gain switch: 20, 30, 40, 50db
mini on/off switch
fits in altoids tin

Untested but it should work.

If there is interest I will upload to oshpark or attach schematic and board files

I am not sure what else needs to be done to have these work with different 3 wire mics aside from changing the source resistor value.

Next stop is similar boards for 2 wire mics.

Offline weroflu

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Re: small ic preamp
« Reply #11 on: September 28, 2015, 10:26:28 AM »
The smallest I was able to get a fixed gain non-pip board was .6" x 1.6", that was using  switchcraft sealed  jacks. I think I can get it smaller using just regular 3.5mm connectors but I have to figure out how to securely attach them to the board. With  2-wire mics and a23 battery that should be about the smallest preamp to date. Watch batteries are not possible.

Offline weroflu

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Re: small ic preamp
« Reply #12 on: September 28, 2015, 10:38:19 AM »
This is unrelated but very interesting:

https://by-rutgers.nl/ME6211-PRO37R.html

The recordings are phenomenal considering the capsules  he used.

It's way above my technical level but this part of it caught my eye:

...with some cautious I could conclude that the noise floor of the mike (ME62) corresponds with a sound level of 34 dBSPL (fast) respectively 23 dBSPL (slow)! Not bad, but these simply assembled figures stretch the truth. The noise figures are much, much better!! (see below). If we forget about the 50 Hz hum, the noise corresponds with a few dBSPL, which verges on the incredible.



Offline weroflu

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Re: small ic preamp
« Reply #13 on: October 17, 2015, 08:09:54 AM »
eagle .brd file for ke4 mics aka mm hlso

untested

« Last Edit: October 18, 2015, 03:37:43 AM by weroflu »

Offline weroflu

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Re: small ic preamp
« Reply #14 on: October 17, 2015, 12:01:43 PM »
eagle .brd file for dpa 406x mics

9v through 10k resistors for power

untested

4-6 channel version should be easy if this works


« Last Edit: October 18, 2015, 05:47:40 AM by weroflu »

 

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