DAT-Heads Digest #404DAT-Heads Digest #404
  Re: DAT-Heads Digest #402 (Bill Vermillion)
  re: Market posting (Hans C Larsson)
  Sony DAT tape error rates (Fred Armentrout)
  Market posting (Seth Breidbart)

From: Bill Vermillion <bilver!bill@peora.sdc.ccur.com>
Subject: Re: DAT-Heads Digest #402
Date: Tue, 26 Jan 93 8:53:16 EST

>DAT-Heads Digest #402, Volume #1 Mon, 25 Jan 93 20:30:03 EST
> Fixing the R/S PZM mike (Norm Strong)
Norm Strong writes:

>From: Norm Strong <strong@tc.fluke.COM>
>Subject: Fixing the R/S PZM mike
>Date: Mon, 25 Jan 93 09:13:54 PST
>Has anyone come up with a good fix for the R/S PZM that will eliminate
>the battery, and the xfmr? I'd like to feed my PZM's into a capacitor
>coupled balanced input preamp that has phantom power.

>I like boundary layer mikes; I just don't like the fidelity of this
>particular one. But the price is right.

>Norm Strong (strong@tc.fluke.com)
>2528 31st S. Seattle WA 98144 USA

Well Norm, (and all) here is something I snagged of the net many moons

>From bilver!tarpit!peora!masscomp!think.com!sdd.hp.com!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!att!att!cbnewsc!cptvideo Thu Mar 21 23:49:07 EST 1991
Article: 20055 of rec.audio
Path: bilver!tarpit!peora!masscomp!think.com!sdd.hp.com!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!att!att!cbnewsc!cptvideo

From: cptvideo@cbnewsc.att.com (david.vlack)
Newsgroups: rec.audio
Subject: Re: PZM
Summary: The PZM mod
Keywords: RS
Message-ID: <1991Mar20.223852.24967@cbnewsc.att.com>
Date: 20 Mar 91 22:38:52 GMT
References: <8239@mentor.cc.purdue.edu> <1991Mar20.145149.12364@bilver.uucp>
Distribution: usa
Organization: AT&T Bell Laboratories
Lines: 376

For all you PZM folks, here is what I have on the subject. The copywrite
notice seems to allow republication on usenet. Here goes...

> Recently I've heard of a modification to the Radio Shack PZM
> mic to improve performance (hopefully bass performance).
> I own two of these toys and use them regularly, what's the modification.
> Thanks,
> Joe Klinger
> att!iexist!jgk

Joe (et. al.),

This mod is affectionately referred to the ``Rastocny'' mod and
it's been quite a while since I posted it, so I'll post it again.
I'm still using this modified mic in a lot of situations, but I have a
few others that I use when conditions are right.  The problem is finding
the right place and a big enough surface to use them properly.


About recording pianos, Crown recommends that you tape two of them
inside of the lid.  I place the mikes in various positions depending upon
the room.  When recording in a large hall, I place them on the floor about
five feet apart and 12' from the bend in the sound board (it's an
unconventional approach; I've never seen anyone else use it).  When recording
in a small room, I tape them to the lid in various positions, depending
upon the type of piano.

Crown has several published tips on using the PZMs.  If you can find a
dealer near you, they may have these articles in stock.

PZMs are wishful-sinful mics: they sound pretty good but they need to be
placed against a large surface to work properly.  Sometimes this is just
not possible and you have to try other mics or go to extremes to find a
surface.  And unfortunately, PZMs have a rising top octave response :-(
But they are seldom seen by the audience!

===============================cut here==============================

    Copyright 1988, 1989 Philip M. R. Rastocny All Rights Reserved.

    This article or any form thereof may not be used for profit or
    republished in any way without written permission from the author.
    Distribution is granted to subscribers of this electronic network
    news service for personal use only.

> <
> <
> All appropriate warnings about voiding warranties and possible self <
> destruction of equipment, and safety hazards to your person apply <
> here. If you're careful, you'll get a nice piece of gear; if you're <
> not, you'll have a smouldering piece of junk, or you may obtain <
> electrical burns, or you may even die. I assume no responsibility <
> for any results, good or bad. These mods assume that you have <
> good technical ability in that you know what you're doing when <
> modifying a circuit. Always be careful and work safe. These <
> modifications are not recommended for novices. If you doubt your <
> abilities, don't attempt these modifications. <
> <
> <
> The author assumes no responsibility for erors <
> that may apppear in dis articl. <
> <


The RS PZM microphone is an omnidirectional electret microphone patterned
after a principal invented by Crown International called the pressure zone
microphone (hence, PZM).  The output impedance of the stock microphone
is about 600 ohms (unbalanced) and it requires a phantom supply voltage
from -1.5V to -12V DC for operation.  The stock microphone has a supply
module and built-in line-matching transformer to convert 600 ohms unbalanced
to about 10K ohms unbalanced.  The problem with this stock PZM is twofold:

1) you cannot use long cable runs on the mic since the line is unbalanced
2) the matching transformer used in the module is terrible

So the mods outlined below address these two problems by describing a
method of using a standard balanced microphone cable in conjunction with
an unbalanced (single-ended) microphone input configuration common to
most consumer tape recorders.  There are compromises made when using this
approach, but the benefits in the case of this PZM far outway the


The stock assembly consists of a mic, a coax cable, a supply module, a
twinax (2-wire shielded) cable and a 1/4" phono plug as shown next.

=====                  ==============
|mic|---coax cable-----|power supply|----twinax cable---1/4" phono plug
=====                  ==============

1.  Cut off the 2-wire shielded cable between the 1/4" plug and the power
    supply.  Toss the phono plug.
2.  Take the mic apart (screws on the bottom).  Unsolder the coax cable
    from the mic element and replace with the 2-wire cable from step #1
    above.  This is a somewhat static sensative device so work with a
    grounded soldering station and appropriate clothing.  Connect the
    low side to the dark color wire and high side to the light color
3.  Connect the other end of the 2-wire cable to an in-line male XLR
    connector.  You should now have something that looks like this:

                                                         male XLR

mic         n/c  --------------------------------------- shield (pin 1)
electret    high -------light wire---------------------- pin 2
element     low  -------dark wire----------------------- pin 3

4.  Make some long mic cables from some twinax or 2-wire microphone cable.
    I made three 75' and three 25' cables for my setup.  Shields are
    connected on each end to pin 1 and the case on one side (I think it's
    the female side) as shown next.

  female XLR                                             male XLR

case------shield --------------------------------------- shield (pin 1)
            high --------------------------------------- pin 2
            low  --------------------------------------- pin 3

The next step is to build an in-line supply that also adapts the XLR
connectors to the 1/4" phono mic input of most consumer tape recorders
as shown next.  There should be one of these supply boxes built for each
mic used.

female XLR-------|supply/adapter module|-------------1/4" phono plug

5.  Cut a 24" piece of 2-wire mic cable and connect an in-line female XLR to
    it as you did in step 3 above.
6.  Cut a 24" piece of coax and connect an in-line 1/4" male phono plug to
7.  Cut holes large enough in a small steel project box to run the cables
    through.  Add chaffing and strain relief to these two cables.
8.  Connect the shields from the two cables AND the low side of the 2-wire
    mic cable to the same point (single point) on the project box.
    (If you prefer to use chassis mounted XLR and phono connectors, instulate
    these connectors from chassis ground and wire the cases internally to this
    same single-point ground.)
9.  Connect the "+" side of a 9V transistor radio battery jack to this
    single point ground.
10. Connect the "-" side of this battery jack to a 2.2K ohm 1/4 watt resistor.
11. Connect the other end of the resistor above to the high side of the
    2-wire cable.
12. Connect a 10 uF mylar or metalized polypropylene capacitor from the
    high side of the 2-wire mic cable to the center conductor of the coax

    You should now have something that looks like this:

XLR                                                        1/4" phono plug

 1 ---shield-----+---+---- single-point ground ---------------shield-----
 3 ---low--------|   |                                  ------hot--------
 2 ---high-----      ----- "+"  "-" --- 2.2K ohm -----  |
              |             9 volt                   |  |
              |             battery                  |  |
              +---------------------------------------  |
              |                                         |
                           10 uF

When the mics are not connected, there is no drain on the battery so there
is no need for a switch.

Close up the project box and plug in the microphones and the tape recorder.
I think you'll be surprised by the improvement in these otherwise inexpensive
and ho-hum mics.


If you are *ABSOLUTELY POSITIVE* that the input stage of your tape recorder
or mixer has an input capacitor (of adequate voltage) and then a load
resistor, you can replace the 10 uF cap with a piece of wire.  (See below.)


       input                                       input
mic   stage cap                       mic         stage cap
jack----||--------input stage         jack----------||--------input stage
              |                                |
            load                             load
            resistor                         resistor
              |                                |
            ground                           ground

If you decide not to or cannot replace the input stage cap with wire,
you should replace the input stage caps of the tape deck or mixer with
an equivalent value of equal or higher voltage mylar or metalized
polypropylene capacitor to obtain the best performance.


You can eliminate any or all of the XLR connectors if you wish to make
a custom length, dedicated mic setup.  The reason that I suggest the
XLRs is that as soon as you get serious about recording, you instantly
find out that you need about 10' more of cable than what the custom
lengths are to do what you want.  With the XLRs, you can add or remove
cable for each situation.

For permanent installations in a mixer or tape deck, you could build
a phantom supply similar to what is shown next.

==========  ===========     ==========
|12V c.t.|  |full wave|     |-12 volt|     2.2K     2.2K     2.2K
|xformer |--| Bridge |-----| reg. IC|-----\/\/-----\/\/-----\/\/-----> -12V out
==========  ===========  |  ==========  |        |        |
                        ---      |     ---      ---      ---
                        --- 220uF|     --- 220uF--- 220uF--- 220uF
                         |       |      |        |        | 
---------------------------------------------> gnd

You can gang the passive RC components together to run several channels from
the same bridge.  You could also put all of this inside of a "Bud" box.
I recommend using all similar value components since parts are cheaper by
the dozen.

This concept provides more than adequate ripple rejection and if you want a bit
improved high frequency clarity, shunt all 220uF caps with 0.1uF polypro.

I've also done this for budget portable systems.  I use one per channel:

            2.2K          2.2K
9V battery--\/\/----------\/\/-----> -9V out
    |            |     |
    |           ---   ---
    |     0.1 uF---   --- 220uF
    |            |     |
-------------------------------> gnd

I drag a pair of these supplies with hard-wired 20' cables, a Sony
Walkman Pro, and a light weight pair of earphones out with me backpacking
and get some wonderful wildlife and wilderness recordings on batteries!

You can also replace the massive square metal plate with a piece of
plexiglass with tapered edges.  The edges do influence the response of
the microphone, but in some situations, what you place the mics on or
near will equally degrade the response, so what the heck.  My portable
rig uses the plexiglass plates; I usually pack in about 45 pounds worth
of stuff and shaving off every ounce that you can helps.


One person asked ``Why such a big capacitor?''  Well, it has to do
with the uncertainty of the input impedance of your tape recorder or
mixer.  If you have a low input impedance (say 1,000 ohms or less)
you need this big of a capacitor to get the low frequency response
available with this microphone.  If you have a high input impedance
(say 10,000 ohms or more), you can get away with a smaller capacitor.
If you use a lot of different tape recorders and mixers or if you
don't know what the input impedance will be, it's better to use the
big cap (and that's why I recommend it).

Some folks have asked why I don't shunt the mylar with a small exotic
cap.  The answer is simple: the PZM has a rising top octave response.
The mylar tames a little of the peak; a shunt cap would only exagerate it.


Some sources for 10uF esoteric capacitors are:

Manufacturer    Type    Part Number     L x W (mm)      DCV

ChateauRoux     m-pprop ?               64 x 22 ?       250
El. Concepts    m-pprop 5MP12D106K      38 x 20         100
El. Concepts    m-pprop 5MP12F106K      57 x 23         200
El. Concepts    m-pprop 5MP12J106K      57 x 39         400
IAR "Wonder"    m-pprop X series 10uF   57 x 29         310
Illinois        m-pest  106MWR063K      32 x 14          63
Illinois        m-pest  106MWR100K      32 x 19         100
Illinois        m-pest  106MWR250K      44 x 20         250
Illinois        m-pprop 106MPW160K      ?               160
Illinois        m-pprop 106MPW250K      ?               250
Illinois        m-pprop 106MPW630K      ?               630
?(Meniscus)     mylar   ?               ?               100
Panasonic       m-pest  E1106           31 x 16         100
Paxton          mylar   8uF             38 x 19 ?       100
Seacor          m-pprop PMWAF100KG      ?               100
Seacor          m-pprop PMWFF100KG      ?               100
Sidereal        m-pprop ?               49 x 19         100
Sidereal        m-pprop ?               57 x 27         200
Sprague         m-pprop 735P106X9100USL 38 x 23         100
Sprague         m-pprop 735P106X9200WVL 57 x 26         200
Sprague         m-pprop 735P106X9400ZVL 57 x 42         400

I haven't had time to research all of the sources.  I'd appreciate it
if you could contact me if you have other sources to contribute or
corrections/updates to this list.  Addresses and telephone numbers
for the above capacitors are:

* Digi-Key, 701 Brooks Ave S, PO Box 677, Thief River Falls, MN 56701
  (800) 344-4539

* Electronic Concepts, PO Box 627, Eatontown, NJ 07724
  (201) 542-7880

* Gateway Electronics, 5115 N. Federal Blvd., Denver, CO 80221
  (303) 458-5444

* Illinois Capacitor, 3757 W Touhy Ave., Lincolnwood, IL 60645
  (312) 675-1760

* Meniscus Systems, 3275 Gladiola SW, Wyoming, MI 49509-3224
  Mylar; best prices on ChateauxRoux
  (606) 534-9121

* Seacor Inc., 123 Woodland Ave, PO Box 541, Westwood, NJ 07675
  (201) 666-5600

* Sidereal Akustic, 1969 Outrigger Way, Oceanside, CA 92054
  SiderealKap, ChateauxRoux
  (619) 722-7707

* Sprague Electric Co.  There's probably a sales office in or near your
  town.  Ask for Engineering Bulletins #2092 and #2752, and catalogs
  #ASP-420K and #C-567A.

* TRT, Box 4271, Berkeley, CA 94704
  IAR "Wonder Caps"
  no telephone number published


                Yours for higher fidelity,

                 _ __         _
                ' )  ) /     //
                 /--' /_  o //
/ / /_<_</_

                Phil Rastocny
AT&T Bell Laboratories
                Room 31D39
                11900 N. Pecos St.
                Denver, CO 80234
                (303) 538-4199

Disclaimer - My employer had nothing to do with the creation of this
                article.  This article was thrown together in a hurry.

>You can send mail to the entire list via one of these addresses:
> UUCP: ...!uunet!virginia!dat-heads

Bill Vermillion - bill@bilver.oau.org  bill@bilver.uucp
                - ..!{peora|tous|tarpit}!bilver!bill