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Monday, 30 April 2012

Balanced to Line Microphone Preamp VeroBoard Stripboard

this is a nice high quality microphone preamp without all the added audiowank you usually see on these things - it uses quite expensive parts mainly because I got them as free samples from Texas Instruments.

I recorded a few songs with it - acoustic ones in order to show what it's like on acoustic guitars because that's where it excels 

you can of course add phantom power to this however you need to add it pre- the diodes (they are there to protect the instrument amplifier IC) and you also need to make the 2 input caps (C1 C2) non polarized ones 






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41 comments:

  1. Anonymous27 December 2012 at 12:04

    Hi Paul. My name is Fredrik. I'm from Sweden and i'm interested in building this one for my studio. I'm a noob when it comes to electronics, but I've built a few guitar pedals on vero. Which kind of pot should I use (log/lin ect)? Thanks!

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  2. DrStevenson27 December 2012 at 12:13

    just a linear one.
    make sure you post a picture of it when you're finished!

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  3. Anonymous4 January 2013 at 13:18

    Hey Paul, great site :) do you think you could do a veroboard layout for a phantom powered version? Or maybe just some instructions? Also, is it possible/necessary to have a balanced output on this?

    Thanks!

    Nick

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    1. DrStevenson4 January 2013 at 13:36

      it's possible to make it balanced out however it really isn't necessary with the preamp.
      the only reason to use balanced cables is for the reduction of noise.

      I'll have to have a look into the phantom power thing, I did add it to mine but it was more of a hack after I'd done all of this post



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    2. Anonymous4 January 2013 at 14:10

      Thanks for the reply :)

      Yes, Phantom power and balanced outs would be an interesting update to this layout. I've had a look for the IC's and they seem to have extra letters (e.g INA217AIDWT? Do these make any difference?

      Finally (!) its nice to know what kind of standard mic pre you're building so do you have anything you might compare it to that is produced commercially?

      I think its great that these sites are out there, I don't have a background in electronics but thanks to guys like you we can gain access to a whole world of info :)

      Nick

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  4. DrStevenson4 January 2013 at 14:32

    well it's my own design but the standard is comparable to API type preamps - it is objectively very good, it's a pre-cursor to a more feature packed version I'm working on which will one day make an appearance on here.

    to make this balanced out you would typically either add support circuitry or if you wish to add a little flavour - a audio transformer
    see image http://2.bp.blogspot.com/-kT8sXBwdQOQ/UObng3c-nVI/AAAAAAAAATI/zkndip5tTtI/s1600/Audio+Transfomer.gif

    if you give me a link to the ICs you've found I'll check them for you but it sounds like they are the right ones

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    1. Robo3 March 2013 at 18:33

      Can you add OP275 for doing the filter and phase reverse for the balanced output?

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  5. Anonymous4 January 2013 at 17:16

    That sounds amazing, can't wait to see that! Think I'll hold off this build and wait for the big brother :)

    Won't trouble you with IC's at the moment but will send links when I attempt the build

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  6. Justin4 February 2013 at 04:05

    Am planning on giving this a go soon... some newb questions, built a few vero guitar fx pedals but also dabble in home recording..

    Can you use this with a standard 12v dc power supply (amp rating?)

    If I choose to do the balanced output will any 1:1 audio transformers work? Had a look and there are many options regarding primary and secondary impedance, dc resistance, operating frequency etc. Maybe you would be kind enough to post a link to one you might use?

    If I were to use it with a seperate phantom power supply I assume the voltage is only sent down the mic cable to the the microphone and not through to the Preamp, meaning i would not need to change the cap values? Is that right.

    Many thanks for the layout...

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    1. DrStevenson4 February 2013 at 12:57


      I can't remember exactly how many mA it draws but it is well under 500mA so if you just use something like a 500mA 12v DC adapter it should be good.

      I've attached a picture showing how phantom power is connected - everything on the board stays the same.

      with audio transformers I tend to just use ones salvaged from old computer network cards and modems however you can buy something like this http://uk.farnell.com/jsp/displayProduct.jsp?sku=1172419&CMP=e-2072-00001000&gross_price=true

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  7. Unknown16 March 2013 at 11:56

    This is looking great, and Im building 2 of theese guys. Since Im a beginner I have some questions: It looks like the circuit have 4 polarized caps (electrolytic I guess?) and the rest should be polyester or similar caps. Which way should I put the polarized caps?

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    1. DrStevenson16 March 2013 at 15:02

      if you look closely at the caps you'll see one side is shaded - that's the negative side.
      this post explains better http://www.paulinthelab.com/2012/08/using-stripboard-key-to-my-diagrams.html


      don't forget to send me pictures when you've built it

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  8. Unknown3 April 2013 at 15:14

    This comment has been removed by the author.

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    1. Unknown3 April 2013 at 15:16

      Oh, and if I want two channels, do I just make two of these?

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    2. DrStevenson7 April 2013 at 20:33

      don't use a switchmode supply it will be noisy.
      yes - make 2 if you want 2 channels

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  9. Anonymous28 May 2013 at 17:25

    Planning on making 4 of these and put them in a rack case salvaged from something or whatever, for the phantom power, do you have any ideas for stepping up 15v to 48v?

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  10. Unknown10 January 2014 at 18:25

    Hey Paul- In regards to the transformer vero you posted, is there a rail on that vero that goes to the +15vdc?

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  11. Unknown14 January 2014 at 02:26

    This one:

    http://2.bp.blogspot.com/-kT8sXBwdQOQ/UObng3c-nVI/AAAAAAAAATI/zkndip5tTtI/s1600/Audio+Transfomer.gif

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  12. Unknown27 March 2014 at 20:55

    hello, this looks great, planning on building a few inside a single box to get a multi channel mic preamp however what components would I remove to just use a single 15v power supply to cut down on costs?

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    1. DrStevenson27 March 2014 at 21:13

      you'll have to show me once you're done.
      you can't remove any of the components - the LT1054 converts a single supply into a dual supply which you need for the amplifier ICs

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    2. Unknown28 March 2014 at 14:45

      I see, cheers for the reply and layout i've already built something from there, I made a channel switcher guitar pedal using your signal splitter layout to switch between 2 separate fx chains, not true bypass of course but sounds good

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  13. chadster5 September 2014 at 23:02

    Cool layout , thanks . I will be building this soon , can the opa606 be replaced by any other opamps such as lm833 or 5532 I have a few in my parts bin

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    1. DrStevenson5 September 2014 at 23:38

      well, not those ones = the OPA606 is a single op-amp. I'm not sure how other op-amps would perform but technically they should at least work

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    2. chadster6 September 2014 at 00:36

      Thanks for the fast response , I should've read the data sheet :-) I'll check my parts and start building.

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  14. chadster20 September 2014 at 09:42

    I've been looking at the lt1054 and the supplier has two types one says dc-dc convertor and the other says inverting step up -5v , which one would be right ?
    Here are links to them
    http://au.rs-online.com/web/p/dc-dc-converters/5456004/
    http://au.rs-online.com/web/p/charge-pumps/6624750/
    Thanks for your help .

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    1. DrStevenson20 September 2014 at 09:56

      they're both the same - charge pumps are DC-DC converters. it's just another case where shops don't standardise what things are
      which ends up confusing people.

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    2. chadster20 September 2014 at 10:24

      You're a champion thanks for getting back so quick, I'll order them soon.

      Delete
  15. tom k23 September 2014 at 10:56

    Hey Paul, thanks for the layout! I put this together about a year ago and it worked but it has an annoying high pitched oscillation. I sorta put it on the back burner until recently wanting to use this type of circuit again. I read that with super low input resistance less than 10ohm you'll get oscillation. I was using a sm58. Could it be the charge pump making the noise?
    -tom

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    1. DrStevenson24 September 2014 at 23:21

      try just putting a 100u capacitor from 15vin to ground.

      the charge pump runs at about 25kHz so if you can hear that I would have to assume you were a dog :)

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  16. tom k27 September 2014 at 21:37

    Thanks Paul! Took care of my oscillation problem but now I'm picking up radio Disney. Any suggestions on eliminating rf interference?

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  17. chadster3 October 2014 at 07:36

    hi building this one now and I'm wondering if the xlr ground is connected to circuit ground or left unconnected? I've built plenty of guitar pedals but it's the first xlr style for me.

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  18. Anonymous31 December 2014 at 01:59

    Cheers for the layout man, however looks like TI wont send samples of the INA217 anymore. Would the pin compatible LT1167 work?

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    1. DrStevenson31 December 2014 at 07:46

      it would probably work yes however as you change the gain the bandwidth decreases with that IC
      when you hit a gain of 1000 it's actually cutting into the audio spectrum (at 12Khz) - it's worth trying if you're getting samples though
      you may not need higher than 12Khz and you may not have it turned up to 10!

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  19. mambonassau25 February 2016 at 05:33

    Was there ever a phantom power update on this? I really want to build it, but I'm swimming in condensers and want to make sure it will be usable in my setup. (Even a short breakdown of your hack would work - I'm not against extra wires and veros floating around!)

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    1. tom k25 February 2016 at 06:10

      This comment has been removed by the author.

      Delete
    2. tom k25 February 2016 at 06:13

      threw this together. notice the added cuts under the two 6.8k resistors, moved cuts on the top two rows and the link. since the protection diodes are already in the layout all you need was the two 6.8k resistors.
      http://img.photobucket.com/albums/v355/tomkogut/balancedtolinewithphantom_zpstwyezkbu.jpg~original

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    3. mambonassau27 February 2016 at 01:37

      Awesome! I assume you've verified?

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    4. moreryan24 September 2017 at 07:07

      Hey Tom K, now that photobucket has spoiled all our fun, would you be able to upload that file somewhere else, or again, I'd love a vero for a preamp w phantom!

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