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'Optimus' PZM/boundary any good ?

Sorry for this budget-question, but how useful is the boundary ('PZM') mic that Radio Shack has for US$39.99 ?
It's the Optimus #33-3022.

Since someone here will be visiting the US soon I was thinking about asking hI'm to get me a pair.

http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=&product%5Fid=33%2D3022

Applications will mostly be for loud sources, like room for drums or guitars.
(Will add the 'usual' PZM-mods)

Any good ? At least usable ? Or just a cheap mic with a bad capsule ?


Thanks,

Peter

Comments

Member Wed, 03/17/2004 - 08:14
PZM/AMT M-40 Piano mic

Have you checked out Applied Mic Technology and their instrument mics? The M-40 is their Piano mic and according their reviews plenty of big name musicians use it on piano as well as many other instruments with a lot of success. I am going to record a 9' grand piano soon and am considering one myself, just want to hear one somewhere first.

BB

jonyoung Mon, 02/09/2004 - 05:52
Peter, I own one (haven't used it in quite a while to be honest). I think I remember some one telling me the capsule is made by Crown, but it's nowhere near their PZM. This one is unbalanced and has a battery compartment in the mic cable attached for two size AA batteries. If it could be modded to use with regular phantom power it would be more useable. I used to use it with a Portastudio for doing guitar/vocal rough sketches, fine for that. Actually, I'm doing some guitar tracks today and will plug it into my board for research and let you know what happens.

sapplegate Mon, 02/09/2004 - 09:39
Sounds like you're already aware of this, but just in case...

Jensen transformers has this app note for connecting phantom to the PZM in conjunction with one of their transformers.

http://www.jensentransformers.com/as/as070.pdf

Never tried it so I can't comment on its effectiveness, but coming from Jensen, it should be cool. Of course you'll probably spend more on the transformer than you do on the mic, but that's another story...

Member Mon, 02/09/2004 - 11:47
Thanks all for the responses, I'll sure ask the person to get me two of these mics.

Last question: they're reasonably sturdy, right ? Saw the total weight (including cable) is 10.93 oz. (310 g) so I assume the mic body itself is from metal, not plastic.

from riversedge:
Actually, I'm doing some guitar tracks today and will plug it into my board for research and let you know what happens.
Thanks ! Will that be electric ? Other PZM's I tried turned out to be somewhat noisy; if your recording happens to be of an acoustic instead of elec. I guess an eventual noisy side would show up.

from RecorderMan:
it's a good deal
Trusted source ! ;) Thanks.

from Old House Scott:
Jensen transformers has this app note for connecting phantom to the PZM in conjunction with one of their transformers.

http://www.jensentransformers.com/as/as070.pdf

Never tried it so I can't comment on its effectiveness, but coming from Jensen, it should be cool.
Thanks. I'll definitely mod them to balanced and preferrably phantom as well. 1/8 Inch (3.5 mm) plugs :td: and XLR-3 :tu:

Of course you'll probably spend more on the transformer than you do on the mic, but that's another story...
I'll probably go for an active circuit, so that'll keep cost comparable to the mics themselves.

Bye & thanks again,

Peter

jonyoung Mon, 02/09/2004 - 13:55
Peter, Just finished the session, electric through a vintage Fender Deluxe amp. I close mic'd with an ATM29HE ($200 vocal dynamic, much like SM57 tonally) and the PZM on wall about 2 ft away. The PZM won hands down. I connected it with a passive DI box, had the mic pre at about 75%. It sounded exactly like his rig. I may buy another! I doubt it would have eough gain for acoustic unless I cascaded through two channels on an outboard pre, and then noise would probably be an issue. The body is metal. Happy shopping.

Kent L T Mon, 02/09/2004 - 14:51
The secret to the pressure zone microphones is how they are mounted. The sound bounces off of the surface around the mic into the mic(the capsule recieves no direct sound). You can get different sounds by changing how and on what it is mounted to. Mount one on a 4x4 plexiglass sheet and suspend it from the ceiling for room miking. I have heard of it being used for drums. Mount it to the inside of the lid of a Piano. If the area it is mounted too is too small the low end response drops off. You probably already knew most of this but thought I would mention it anyay because it is such a different type of mic and fun to experiment with.

Member Mon, 02/09/2004 - 15:17
Thanks all again, this really exceeds the expectations I had - expecting something like "no the present-day Optimus model is no longer the real deal".

Good to hear it's made of metal, would not live long otherwise I'm afraid. :( Our guitar player has a pair of another brand, for recording band rehearsals we usually put coloured paper between the wooden floor and his PZMs to avoid stepping on them.

Riversedge, your Optimus-mic is still unmodified ?

Kent, about mounting them on large surfaces, yes I knew but good to hear they can be used up in the air as well. The 4x4 plexiglass you suggested, that's four by four foot ? (the Netherlands here)


About experimenting, sounds like it'll be usable both for closer micing (say on the floor a few feet from a drumkit or guitar-amp) - or for more room-sound as well when moved further away.

I've those various Crown-pdf-articles around; now that actually a few of such (related) mics are upcoming I'll get those files out again.

Bye & thanks again for the good info I got on these mics,

Peter

jonyoung Mon, 02/09/2004 - 15:39
Peter, Mic is unmodified. I'm sure I got some noise rejection from going through the direct box to a balanced line. The gain required was a little more than a decent dynamic, but not much. Try close mic on guitar amp from the wall, I think you'll get better balance of tones than from the floor. They're often used on a large table to record business conferences as well.

Member Tue, 02/10/2004 - 13:31
from Riversedge:
Peter, Mic is unmodified. I'm sure I got some noise rejection from going through the direct box to a balanced line. The gain required was a little more than a decent dynamic, but not much.
That's good news, already good results from the unmodified unit.

Try close mic on guitar amp from the wall, I think you'll get better balance of tones than from the floor. They're often used on a large table to record business conferences as well.
So that's the amp facing the wall ? Hmm, would
quite suit the setup I sometimes use at rehearsals for making guitar a bit less spikey in the room: Twin Reverb tilted back on its legs upward - facing a wall.


from Kent:
Sorry I didn't notice where you were. Yes 4 feet x 4 feet you can play with the size but that size will give you a good sound field. Try different surfaces for sound shaping.
No problem ! I'll try wood first, but have seen PZMs used as drumoverheads (actually more 'sideheads') mounted on plexiglass.
I'll experiment.

Thanks,

Peter

Member Wed, 02/11/2004 - 15:33
Thanks Riversedge, I thought the Jensen schematic used something like 110k resistors (so 55k 'effective'), so the full 48 V won't reach the capsule - but you've got a point there - depending on the currentdraw of the capsule a proper resistor value should be chosen. Or another circuit topology wuth for instance a zener etc.

Those capsules can have more than 1.5 V but I don't know what the actual limit would be. It's indeed good to be careful here.

Bye,

Peter

teleharmonic Wed, 02/11/2004 - 17:30
Peter,

Seems that you have this worked out but FYI there is also a step by step set of instructions for modding the PZM on this page.

http://www.itrstudio.com/pzm.txt

The Radio Shack PZM is actually just an omni electret capsule mounted close to the metal plate on the inside. I am pretty sure that you can build your own using those cheap panasonic omni capsules. Not that the RS mics are going to break the bank! But it may be worth playing around with down the road... those panasonic capsules are only a few bucks and i doubt the capsules in the RS mic are any better... it is something i've been meaning to try... as soon as all my other responsibilities magically fall away and i have oodles of free time.

cheers,
greg

Member Thu, 02/12/2004 - 09:01
hallo peter,

i got two older 'tandy/radio shack' pzm's (always nice to record in stereo). i use 9 Volt batteries (taped to the side) with good results. it gives you more bass (and less noise, i think), wich you'll need!
i use 'm to record rehearsels and gigs and they are amazing for it.
it took me some time to get used to the fact that they are not directional. ideal for 'room'-recording.
i even saw them taped inside a piano in a theater in Naaldwijk (nl!).
i love 'm.

grote groeten,
will

Member Wed, 02/18/2004 - 15:02
Thanks again all,

from Greg:
Seems that you have this worked out but FYI there is also a step by step set of instructions for modding the PZM on this page.
...
The Radio Shack PZM is actually just an omni electret capsule mounted close to the metal plate on the inside. I am pretty sure that you can build your own using those cheap panasonic omni capsules. Not that the RS mics are going to break the bank! But it may be worth playing around with down the road... those panasonic capsules are only a few bucks and i doubt the capsules in the RS mic are any better...
Thanks for the additional info. Yes, stumbling on those PZM-mods was what drew my attention and now a few years later the opportunity comes along to mod a pair (if all goes well, depending on 'my US-contact' :-)

I've seen alike suggestions that omni-mics can be placed near a wall (a few mm) for the 'PZM-effect' but ready-made is indeed nice for convenience and that one doesn't have to take care that the small distance is not disturbed by mic-stand movement etc

it is something i've been meaning to try... as soon as all my other responsibilities magically fall away and i have oodles of free time.
Sounds like we're living in the same imperfect world ;)


from Will somewhere else in the Netherlands:
i got two older 'tandy/radio shack' pzm's (always nice to record in stereo). i use 9 Volt batteries (taped to the side) with good results. it gives you more bass (and less noise, i think), wich you'll need!
Having tried someone else's PZM-like mics (forgot which brand) this sounds familiar - got the impression they can be somewhat noisy for some applications.

Thanks again all & bye,
(bedankt & grote groeten as well !)

Peter

Member Wed, 02/18/2004 - 17:59
Radio Shack no longer carries PZM mics. Crown pulled the license from them. Crown NEVER made the Radioshack PZMs, they were outsourced by Radioshack. They were garbage, and still are, thats why Crown yanked the licensing.
The boundary mics "by Radioshack" are now cheap electrets mounted close toa boundary, not even close to the PZM concept.

Do yourself a favor, amd locate a real Crown PZM, or better yet find one made by Ken Wahrenbrock, prior to selling his license to Crown.

Member Thu, 02/19/2004 - 02:40
Radio Shack no longer carries PZM mics. Crown pulled the license from them. Crown NEVER made the Radioshack PZMs, they were outsourced by Radioshack. They were garbage, and still are, thats why Crown yanked the licensing.

Do yourself a favor, amd locate a real Crown PZM, or better yet find one made by Ken Wahrenbrock, prior to selling his license to Crown.
Thanks for the info - hmm, quite something else. Since the pair I asked someone to buy will have been bought by now, I'll just fiddle around with them and see what they can do for me.
Indded is there quite a difference in price between 'serious manufacturers' of PZM-like types and the RShack-models but I guess this is partly a name thing - and of course also partly better materials, design and quality control.


The boundary mics "by Radioshack" are now cheap electrets mounted close toa boundary, not even close to the PZM concept.
This _is_ the PZM-concept, not ?


Thanks,

Peter

jonyoung Thu, 02/19/2004 - 06:45
The Crown is a fabulous mic, but after Peter's inquiry (my RShack PZM is about 15 yrs old) I decided it was worth plugging in, now that I have decent gear. I'll be using the track in the mix with no EQ, not bad for $40. I'm willing to get a new one just to see what the diference is. You never can tell what result you're going to get until you try. A friend came over with his upright bass a few months ago, and the best sounding mic to capture the "growl" was a $50 Audio Technica semi-pro vocal dynamic. Go figure.

teleharmonic Thu, 02/19/2004 - 12:01
The boundary mics "by Radioshack" are now cheap electrets mounted close to a boundary, not even close to the PZM concept.
This _is_ the PZM-concept, not ?
Yes, that IS the PZM concept as i understand it...

I understood that the difference between the Radio Shack mics and the Crown mics was not the actual acoustic principle but the quality of componentry,design and manufacture...

greg

fromwithin Thu, 02/19/2004 - 13:02
I have an older realistic radio shack pzm a friend let me borrow but dismissed it as a 'cheapie' mic. lately i've been hearing a lot of really good things about them though (glance through the tape op book and you'll see them mentioned quite a bit). in the rob schnapf and tom rothrock interview they mention using it on beck's lead vocal for 'loser'. can't be half bad, im gonna try using mine on my next drum recording session as an overhead and see what i get.

Member Thu, 02/19/2004 - 15:03
from Riversedge:
The Crown is a fabulous mic, but after Peter's inquiry (my RShack PZM is about 15 yrs old) I decided it was worth plugging in, now that I have decent gear. I'll be using the track in the mix with no EQ, not bad for $40. I'm willing to get a new one just to see what the diference is. You never can tell what result you're going to get until you try.
I see now - at first thought you had this present day model (the Optimus #33-3022 at US$39.99). If you happen to get this model as well
it'd be more than interesting to hear how you think it compares to your older RShack-model.
Nice to hear that simple cheaper gear can still have decent uses !

from Teleharmonic:
I understood that the difference between the Radio Shack mics and the Crown mics was not the actual acoustic principle but the quality of componentry,design and manufacture...
OK, could try swapping elements if the results sound like they could use some help.

Thanks everybody,

Peter

Member Mon, 02/23/2004 - 19:31
the jensen mod seems a bit out of line... I don't know what particular one they recommend, but the cheapest jensen transformers made are about 50 bucks, most of them with specs for mic output are more like 80 to 100.

I did the mods listed at this web site. In the course of 2 or 3 years I did all of them.
http://www.itrstudio.com/pzm.txt

started with the cable modifications, some improvement, and I still have one with that setup. it can work great with really loud source material, but it's a bit noisy.



later on I did the christopher hicks mod #1, that was seriously better, then I did hicks mod #2 on a third mic. that one rocks and I changed number 2 to the same mic. I'ts loud as s*** now, and it's super quiet as well. I use em all the time. If you can solder a bit it's well worth the time and energy. cost about 15 dollars per mic and that includes a new case for the electronics, a slightly bigger metal plate and an xlr jack for the mics.

One caveat though, if you do the FET circuit (mod#2) you should install a transistor socket for each of the transistors and buy about 2 dollars worth (10 to 20 of them)
substitute until you find the quiet ones. This is pretty much standard procudure for working with transistors. If you look in the tech talk forum you can find out more about this.

Later
Sleeper

Member Tue, 02/24/2004 - 15:47
Tried them this evening and so far a few things poped up: they sound OK but I need to find better positioning (just put them on the floor and hadn't much time to check the sound there). Highs seemed a bit dull, but I'm suspecting the positioning first. The Crown & other info will be studied for better positions and I'll probably have to make me some plexiglass construction.
(I'm actually wondering how exactly people tape them to walls, the lid of a Steinway etc :eek: )

One other thing that I was wondering is about what is the limiting factor in these mics w.r.t. overload (as in their unmodded form, so prior to any Linkwith-mods etc).
Is it the very capsule itself, the FET or just the low battery voltage of 1.5 V ?


I did the mods listed at this web site. In the course of 2 or 3 years I did all of them.
This is great - I just started thinking about of
all those mods & possibilities which mods should I do and there's Sleepers post with info on which mods make a difference. Thanks !

One caveat though, if you do the FET circuit (mod#2) you should install a transistor socket for each of the transistors and buy about 2 dollars worth (10 to 20 of them)
It's a bipolar (PNP) I understood, right ? But OK, will make a selection. Couldn't find much on the BC479 but guess a BC560 will do fine.


Bye / thanks,

Peter

Member Tue, 02/24/2004 - 20:28
Peter,
now that I think about it, I think i used a 2n3904 or 2n3906, I remember it being the most common sub for whats on the schematic... but in keeping with the radio shack theme I got them there. at any rate, I still went through at least a half a dozen before I found one that wasn't noisy, (this one was also much louder). I'm a bit obsessed with jfet selection as I built a the hamptone JFET preamp and i'm about to make a couple of 1176 clones

I just changed servers and haven't figured out how to post images yet, but I have a PCB for this.
PM me if you want it and I'll send you the pdfs
Kelly

Member Sat, 04/24/2004 - 16:17
PZM Mics

I have used a pair of Realistic PZM mics for drum overheads for about 12 years now - typically not to pick up the entire set, but to grab just the cymbals. I cut most of the lower frequencies.

The tracks by themselves sound terrible and thin, but once they're added to the full mic'ed drumset, they add GREAT clear high-end! Not harsh or distorted, they are the clarifying finishing touch that completes the character of the drum set.

Both my PZM's have had the simplest, quickest, easiest modification: 2 9-volt batteries wired in series for power (18 volts instead of the single AA 1.5 volts). Much more signal, much less noise!

Any time that I can get one for cheap, I pick it up. I expect to be using them for many more years. When I got word that they were being discontinued, I ran around to all of the Radio Shack's in my area, and picked up whatever was left - usually floor models - the clerks thought I was nuts: "You sure you want this? It's been out on the shelf, there's no box or paperwork...most people don't like these funny-looking microphones."

In fact, I even had a client who didn't want me to use the PZM. I asked him why not, and he told me "Because it doesn't LOOK like a microphone.". NO KIDDING.

Frankly, you can't go wrong with these cheapie mics - they have their own applications, they sound pretty darn good, and they're super cheap. Find an aquaintance who doesn't realize what he has, and buy it from him. YOU WIN!

Member Tue, 03/02/2004 - 18:13
This _is_ the PZM-concept, not ?
No not really. The patent for a "PZM" has the diaphragm parallel (pointing down)to the boundary causing the pressure zone to have uniform pressure versus frequency characteristic in the desired frequency range.
"Boundary" mics have the diaphragm perpendicular to the boundary in order to eliminate comb filtering.
No one can make a PZM exept Crown, the rest are stuck using the boundary method, though it works, its not as effective as a PZM.
Even Crown's PCC (which use the boundary method)mics arent as good as PZMs.

teleharmonic Wed, 03/03/2004 - 05:43
Originally posted by SME:
The patent for a "PZM" has the diaphragm parallel (pointing down)to the boundary causing the pressure zone to have uniform pressure versus frequency characteristic in the desired frequency range.
"Boundary" mics have the diaphragm perpendicular to the boundary in order to eliminate comb filtering.
No one can make a PZM exept Crown, the rest are stuck using the boundary method, though it works, its not as effective as a PZM.
The original Radio Shack mics were proper PZM mics. As I understand it, they licenced the PZM concept from Crown but then Crown pulled the licence and RS started using the boundry design that you are referring to.

I have one of the old RS mics which i have been meaning to mod so it is opened up... the capsule is mounted parrallel in the manner you are describing.

I wonder if the 'boundry ' mic design that you are describing has the capsule mounted 45 degrees to eliminate comb filtering or to eliminate patent infringement!? I don't know, just thinking aloud.

greg

teleharmonic Wed, 03/03/2004 - 05:49
Originally posted by Peter Vermeeren:
Yep, sorry, this was probably quite stupid - but still, not something I would dare to stick on an expensive surface like a piano (or a drummers chest...
I don't think it is a stupid question... People talk about using PZMs on piano a lot. Seriously... anything else that people use to adhere these things that won't leave a layer of goo on a nice piano?

greg

jonyoung Wed, 03/03/2004 - 08:00
Why not a small screw? That's what the keyhole in the top of the plate is for. I don't think a 1/2" #6 screw is going to permenantly ruin the tone or resale value. You can always fill in the hole and burn in new lacquer if you intend to sell it. Any solvent you might use to remove glue residue might do more harm to the finish anyway.

Member Thu, 03/04/2004 - 02:38
Hi,

Interesting points w.r.t. PZM vs boundary etc.


I don't think it is a stupid question... People talk about using PZMs on piano a lot. Seriously... anything else that people use to adhere these things that won't leave a layer of goo on a nice piano?
Why not a small screw? That's what the keyhole in the top of the plate is for. I don't think a 1/2" #6 screw is going to permenantly ruin the tone or resale value. You can always fill in the hole and burn in new lacquer if you intend to sell it. Any solvent you might use to remove glue residue might do more harm to the finish anyway.
That's about the mic-side of things, but I guess
Teleharmonic was more worried about the instrument ?

But keyhole ? Hadn't noticed that - will look tonight, would be convenient.

Bye,

Peter

jonyoung Thu, 03/04/2004 - 06:23
Peter, I was referring to drilling a small hole in the piano lid. I also do cabinet and furniture building, so repairing wood is second nature. I think having residue on the piano from the glue on the tape is harder to fix! MY RS PZM has a keyhole at the top of the plate, maybe the new ones don't. Even so, why not drill a hole there too? :c:

Member Thu, 03/04/2004 - 11:33
Peter, I was referring to drilling a small hole in the piano lid. I also do cabinet and furniture building, so repairing wood is second nature. I think having residue on the piano from the glue on the tape is harder to fix! MY RS PZM has a keyhole at the top of the plate, maybe the new ones don't. Even so, why not drill a hole there too?
Hi Riversedge, sorry for my misunderstanding - I should have realized that at 'resale value' etc (although here in Europe some people tend to ask 'special' prices for the older RadioShack/Tandy PZM's - but that's another story).

I checked my RS-mics (#33-3022) and didn't see any mounting hole - but that will likely change. ;)

Thanks,

Peter
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