Last update 10/8/07

HAMPTONE MICPRE TECH SUPPORT BLOG:  This page was created 11/02/06, and contains answers to tech questions I received via email.  Please search this page before sending tech questions.  Thank you.  Scott Hampton

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TOPIC: MICPRE IMPEDANCES, MIC SLPITTING

Q: Can you tell me what the input impedance is?  I ask for a couple of reasons.  For one thing, I have a couple of ribbon mics that have a stated impedance of 600 ohms.  They need a relatively high input impedance to sound their best.  They also need relatively high gain, so it would be good if I could use the HVTP2 with them.

A: Checkout the HVTP2 and HJFP2 micpre "Details" pages, I just added specs.  HVTP2    HJFP2

Q: Secondly, I often use my mic pres in parallel with others.  I do a lot of live recording, and we always split the mics - sometimes to as many as four mic pres.  For example, this weekend I'm recording a show where there will also be an FOH feed, a monitor feed, and a webcast feed in addition to my recording feed.  It's helpful to have a rough idea of the input impedance of these pres to predict how they will behave when used together.

A: The proper way is using mic splitters, one mic driving two pres is less than ideal, though it usually works.

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TOPIC: HOW TO FIND THE TEST POINTS

Q: Hey Scott.  A little confused.  Keeping in my mind that I didn't complete basic electronics 1 or anything near that... So I tested "gain module 1" of channel 2 I think.  I don't know what the difference is between the 2 gain stages.  In your instructions (attached file, I'm sure you've seen it before), it "seems" to me like there is only one testing place.  I don't know where to put the test probe, as I don't really read schematics yet.  I've included an example of how I might know where to test, don't laugh.

I filled in the spreadsheet and read NOTE 3 as that "seems" to be a problem.  I'm reading some electronics books as we speak, but nothing about testing yet...

Hope some of this makes sense. Thanks, Mark

A: Mark No problem, let me try to explain.

Each channel has two identical gain blocks, and each is electrically equivalent.  The page in the instructions titled "HJFP2 Gain module testing"  shows one of the 4 total in the kit, and lists both resistor values, say R10 and R16, where R10 refers to the first gain stage, and R16 is the second (all the top part numbers refer to the first stage, bottom to the second).  Then its really a matter of looking at the schematic, and layout and seeing where these parts physically join.  It really takes no electronics background, just the ability to follow the copper traces on the board and match then to the schematic to find the test points.  You have two layouts, both are a top view (side with components) one shows the traces, one without.   The point say where U2, U3 and C4 join is test point V7, where U1 connects to R10 and U2 is test point V2.  Does that make sense?  You marked in red V7, not V2.  SH

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