Matador

FEELER: Chinese U87 Mike Body Prototype PCB's
« on: March 14, 2012, 12:52:28 AM »
This is a feeler for an experimental/prototype PCB meant to be installed as a replacement for the many popular Chinese U87 clone bodies (from companies like Aurycle, MXL, Nady, Carvin, etc).  Most of these bodies can hold two of these boards.



The board features a prototype grid much like what would be found on commercially available Veroboard systems.  The boards feature an interconnected grid of 0.1" spaced plated through holes, which are grouped into nets of 3 or 4 holes.  Net's can be bridged through components like resistors or capacitors, or can be wired from net to net under the board vertically with small 22-26 gauge wire to make net groups the same.

Basic features:

1) 4 teflon standoff's along the top for Hi-Z connections to capsule backplates or diaphragms (most mikes typically use at most 3, however if one wanted to experiment with providing different bias points for individual backplates this would be possible)
2) One JFET component footprint for the main input amplifier, with the gate pin pointed at the rightmost Hi-Z connection point
3) 44 net groups of three or four holes
4) 36 ground nets
5) 4 VDD groups, each with 8 to 10 connections, connected through copper pours on the top copper.  This provides for up to 4 cascaded pi-filters for VDD with at minimum fanout of 7 to other traces
6) Full copper pour of ground node on the bottom
7) 7 net groups along the bottom for connecting to transformers and XLR sockets.

I can also add to the top silk layer with all of the top layer interconnections in case the traces are difficult to read through the solder mask.

I am thinking standard FR4 boards, 0.063" thickness with 1 oz copper.

For price, and depending on the interest, I'm looking at a cost of $20 per board set, which would include:

1) 4 Keystone Teflon standoffs
2) Two of the above boards
3) Shipping anywhere in the US via USPS in a flat rate padded envelope

Please post a reply here if you are interested, along with the quantity.

I may also add a keepout of the ground pour on the bottom under the Hi-Z connections.  With my design rules, the soldermask should completely cover the ground pour and the annular rings should be well isolated, but when dealing with 1G impedances better safe than sorry. ;)

Also, since I haven't contacted my fab house, any reasonable changes/suggestions are welcome.


Blue Jinn

Re: FEELER: Chinese U87 Mike Body Prototype PCB's
« Reply #1 on: March 19, 2012, 07:06:53 PM »
W/o looking I'm assuming this is roughly the same dimension as poctop's U87 clone.

You might want to put more mounting holes on the sides, as some of the other mics (e.g. MXL 2006 -- which has the smae circuit as the MCA SP1 so I'd assume the boards are either the same or similar) have boards that fit slightly differently. I'm intrigued, but don't want to be stuck with only the MXL 2001'sh type body.

not my thing. I am here just to unbalance the equation --pucho812

 http://www.bluejinn.org

Matador

Re: FEELER: Chinese U87 Mike Body Prototype PCB's
« Reply #2 on: March 20, 2012, 01:18:40 AM »
W/o looking I'm assuming this is roughly the same dimension as poctop's U87 clone.

You might want to put more mounting holes on the sides, as some of the other mics (e.g. MXL 2006 -- which has the smae circuit as the MCA SP1 so I'd assume the boards are either the same or similar) have boards that fit slightly differently. I'm intrigued, but don't want to be stuck with only the MXL 2001'sh type body.

Yes, the boards are identical in size to the U87 clone.

If anyone has detailed measurements of the other boards I can see about making a common size with more mounting holes:  unfortunately I don't own the mikes in question above.

Blue Jinn

Re: FEELER: Chinese U87 Mike Body Prototype PCB's
« Reply #3 on: March 20, 2012, 01:27:03 PM »
I have a MXL2006 (which uses the same circuit as the SP1 and a bunch of other mics so I'd guess the circuit board as well) Please give me a few days and I can measure it and post back here.

not my thing. I am here just to unbalance the equation --pucho812

 http://www.bluejinn.org

Blue Jinn

Re: FEELER: Chinese U87 Mike Body Prototype PCB's
« Reply #4 on: March 23, 2012, 03:18:38 PM »
I took a quick look at the 2006 board. I didn't have time to completely measure it. however, it is *about* the same outer dimension as the 2001 board, or the poctop U87 board. Maybe 1 -1.5mm smaller. However, the holes if you measure from the top are about 5/8" down, as opposed to the U87 board which are about 7/8" down, if that makes sense.

I found this photograph:

not my thing. I am here just to unbalance the equation --pucho812

 http://www.bluejinn.org

Matador

Re: FEELER: Chinese U87 Mike Body Prototype PCB's
« Reply #5 on: March 23, 2012, 04:25:35 PM »
I took a quick look at the 2006 board. I didn't have time to completely measure it. however, it is *about* the same outer dimension as the 2001 board, or the poctop U87 board. Maybe 1 -1.5mm smaller. However, the holes if you measure from the top are about 5/8" down, as opposed to the U87 board which are about 7/8" down, if that makes sense.

If you take out the two screws from one of the boards, what is the distance from the center of each hole in the board?  Or if you want to ballpark it, what is the distance between the center of the head of each screw?

I'll upload a 1:1 sized PDF of the board, and you can print it out, and lay it over the top and see how much it's off exactly.

Blue Jinn

Re: FEELER: Chinese U87 Mike Body Prototype PCB's
« Reply #6 on: March 25, 2012, 04:43:42 PM »
I took a quick measure of the screw heads, and the distance appears to be 1 and 5/16th inch. I have a mm tape measure somewhere.
not my thing. I am here just to unbalance the equation --pucho812

 http://www.bluejinn.org


 

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