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DIY Mic Preamp Kits

Discussion in 'Preamps / Channel Strips' started by Guitarfreak, Jan 20, 2011.

  1. Guitarfreak

    Guitarfreak Well-Known Member

    I'm currently using a PreSonus FireBox for an interface and I'd like to try my hand in building some basic outboard preamps for my dynamic mics. Opamps work fine, no need for tubes. I would like (but not necessary) one design that is relatively transparent and one that is more of a 'vintage' or coloring preamp. I'll probably tweak the circuits, add things, change things anyway, so I'm looking for a nice base for that.

    I'm undecided as to whether or not I want phantom power, but I would only use it when taking DI recordings of guitar because I use phantom power to power my DI box. Thoughts? I've found a few simple designs, but like I said I'd like a recommendation because I don't know what designs are worth the time and money put in or not.

    Really just considering if it's worth it at this point.
  2. dvdhawk

    dvdhawk Well-Known Member

    When I'm done throwing money in the hole next to the house, I'm going to have a shot at a few of these guys from Seventh Circle:

    DIY Mic Preamp Kits - Seventh Circle Audio

    They seem to have a nice variety of faithful vintage recreations. Everything I've read and heard by users has been positive.
    Op-amps, transformers, everything you need in a kit, circuit boards - solder 'em up. It seems like a good place to start to me.
  3. Guitarfreak

    Guitarfreak Well-Known Member

    Do you think that the T15 model is a step above what I am using now?

    As far as routing goes, is there something that I can use for the preamp output into my converter so that I don't have to buy the entire housing/ribbon cable package?
  4. Davedog

    Davedog Distinguished Member

    This is what I have heard of the Seventh Circle stuff too. And clear instructs as well as quality parts. Also, check out Hamptone. I think he still makes the kits available.
  5. fiddler59

    fiddler59 Active Member

    Hamptone Home Page

    Hamptone still sells micpre kits. I have built both the HVTP2 and the HJFP2 (tube and JFET) and both kits are very complete with everything you need. The design, quality and sound are superb for both preamps !!

    David Blackmon
  6. Link555

    Link555 Well-Known Member

    You want my schematics for lucid? I am not selling kits but you can make it yourself.
  7. JohnTodd

    JohnTodd Well-Known Member

    Yeah...I'd like those plans. Id like to build a one-channel "basic but great" pre-amp just for my vox. What you think?
  8. Link555

    Link555 Well-Known Member

    Sure email me at info'at'steller-studios.com

    just so we are clear this is not a kit, there is no parts and no PCB, just a schematic.

    However I do I have a few unpopulated PCB's left if you want to buy one.
    I have no assembly instructions for this pre.

    and I have plans on making this into a kit.

    This is not for a weekend soldering binge....:)

    That said with a decent amount of time spent studying the schematic, this is very do-able. Hell I did it 3 times now ;)

    I know have 9 Lucid pres in my racks, and I am very happy with them. Great on Drums, acoustic Guitar, cello, bass, and vocals.
  9. 4mc2

    4mc2 Active Member

    Hi Guitarfreak

    The Monteith-Flowers circuit for mic preamp console is very transparency ! ....

    It's a discret pure Class A ..... just 3 transistors with 200 volt PS ( 40 db )
  10. JohnTodd

    JohnTodd Well-Known Member

    Can't find a schematic of the Monteith-Flowers. Can you loan a fella' a link?
  11. For experimenting with different components, an API 312ish preamp provides lots of options for opamps and transformers. Check out those from Bicycle Audio, ClassicAPI, and Eisen Audio.
  12. 4mc2

    4mc2 Active Member

    Monteith & Flowers

    original in J.A.E.S. Vol 25 ( march 1977 )


    the original transistor are hard to find , but with BC550C and BD232 is near as good as the original
  13. 4mc2

    4mc2 Active Member

    in the schema , he have a mistake . The second and third transistor is MPSU10 not MPSA10
  14. JohnTodd

    JohnTodd Well-Known Member

    Thanks! I saw that before and thought it had a tube in it. Serves me right for not looking close enough.

    Anybody build this yet?
  15. RemyRAD

    RemyRAD Guest

    One of the easiest ways to create a DIY preamp, is to just take a lesson from some of those vintage consoles that cut lots of hits. For instance, inside the original Auditronics 501, you'd find a microphone transformer. That was followed by a LM 709, later a Signetics 5534 IC chip op amp. Their original input transformer was their own house brand later replaced by the Dean Jensen 110 series microphone transformer with a 10:1 windings ratio. Then there was a couple of output transistors that was used to buffer the output of the IC chip so as to be able to provide greater current drive. The SSL 4000 was virtually identical. The later Neve consoles utilized the same 5534 chip with output buffer transistors, utilizing their St. Ives windings input transformers and their famous Marinair output transformers. The API 312 also utilized the same microphone input transformer by Dean Jensen which was previously something else just like the Auditronics had, something else. So there is that vintage sound and it's largely dependent upon Transformers as opposed to transistors or chips employed.

    If you don't want the classic vintage sound, don't go for a DIY microphone preamp with any kind of transformer. And you'll get some other kind of generic sound. If you like generic sound, purchase a Behringer or Mackie and don't waste your time building your own microphone preamp.

    My preamps are as classic as I am, old-school.
    Mx. Remy Ann David

    So what have we realized here about
  16. 4mc2

    4mc2 Active Member


    Here , it's for the most fidelity that he can !

    My ear is only judge !

    For me, for the more transparency sound , the circuit design must have the less transistor or tube ....

    With Monteith & Flowers design , if you like to have vintage sound ( most the time tubelike sound ) you can put a transformer for coupling ( not capacitor ) .... it's that I make

    Build this circuit and listen to ! ...... and you will never love the opamp !

    I am a french canadian .... sorry for my not perfect english.
  17. fiddler59

    fiddler59 Active Member


    One of the cleanest pres I have ever been around has trannies in and out The John Hardy Jensen Twin Servo 990. A lot of engineers who record classical music dig this preamp design.

    David Blackmon
  18. Davedog

    Davedog Distinguished Member

    I certainly do
  19. RemyRAD

    RemyRAD Guest

    I utilized the Dean Jensen 990 as the output amplifier, in my custom API on-air console I built for NBC radio. Originally I had put in the 325 cards I had a couple of those 990s lying around the shop. It's definitely a sweet sounding preamp, especially when you use the 6:1 ratio winding microphone transformer, can't remember that part either? One thing you should know John Hardy made a Jensen 990 module in the same form factor as an API 2520. Only problem is, it is not plug-and-play compatible on any API card without adding a few external extra components you must add to the circuit board. So there is really no effective way to be able to just switch your op amp's back-and-forth. For instance, if you were to find an API 312 card or 2, you couldn't just swap out the 2520 with John Hardy's pin compatible 990/2520. Or, whatever his model number is, I can't remember?

    So maybe just for fun and giggles, you might consider the number of microphone input transformers available, obtain a few & put them into the same operational amplifier. You'll hear a distinct character difference from each. With some, a clarity & depth, will be realized, that you'll never get with anything transformer less, transformer lite, transformer free, 0 calorie transformer. You may get sterility, neutrality, metallized, homogenized & perfectly lifeless like sound, if that's what you're looking for? Remember, what's old is new again. A perfect example would be ribbon microphone technology. They all but disappeared a few years ago. I've always been a big proponent because I was taught by a master. Now they are the hottest thing. So you are here asking and we are advising in response to what you are requesting. You obviously already know what you don't want and we have provided you with an alignment, free of charge I might add. So? Whadaya' think?

    Thinking is overrated. Listening is precious.
    Mx. Remy Ann David
  20. JWHardy

    JWHardy Active Member

    Yes and no. API circuits are well designed in terms of basic stability, so installing a 990C in place of a 2520 will at least be stable.

    People have installed 990 op-amps in summing circuits of API consoles and have achieved significantly lower noise and better sound quality. No other changes required. Just a swap of op-amps.

    The 990 can be used in an API mic preamp, and it should do very well, but it might not be as quiet because the API preamps use input transformers with a 1:8 or 1:10 turns ratio, compared to the 1:2 ratio of the Jensen JT-16-B that is the optimum transformer to use with the 990. The 990 is optimized for low source impedances.

    There are always things that can be done to tweak a circuit when using the 990 in place of a 2520 (or other op-amp). There are things that can be done to tweak the original API circuits even with no change of op-amp. It is always a good idea to study circuits to see how stable they are in terms of fundamental design.

    There was a custom variation of the API 550 EQ that Sunset Sound used in a custom console that they built in the mid 1980s or so. This EQ had a few "input bias current compensation" components added to compensate for the higher input bias current of the 990 compared to the 2520. This apparently reduced noises when one or more of the switches were adjusted. There were at least a couple hundred 990 op-amps in that console.

    Thank you.

    John Hardy
    The John Hardy Co.
    The John Hardy Co. Home

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