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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 






41 comments:

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

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  3. 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. 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. 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. 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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    Replies
    1. Can you add OP275 for doing the filter and phase reverse for the balanced output?

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  5. 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. 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. 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. 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. 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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    Replies
    1. Oh, and if I want two channels, do I just make two of these?

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

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  9. 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. 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. This one:

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

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

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  15. 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. 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. 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. 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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    1. it's connected to circuit ground aye

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    2. thanks again for your help .

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  18. 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. 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. 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. This comment has been removed by the author.

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    2. 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. Awesome! I assume you've verified?

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    4. 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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