Tandy / Radio Shack / Realistic PZM microphone modifications and tests!

[@scotsam7590]

I too have tried this phantom power to PZM mod. There's a couple of mistakes that I made that are worth noting for anyone else who should try this. Symptom: upon testing the mic after making all the changes, the output is just a whole lot of hum and crackle if you touch the capsule and no audio signal. Cause: The fine trace wire between the black capsule connection and the capsule casing remained present after attempting to cut it. It was so small, apparently buried under black paint or plastic and I couldn't see it to cut it. A session with the sharp of a pin scraping back and forth achieved it. In the original muzines instructions (referred to in the comments) it suggests at a way-stage to test that the new trace to red connection is present AND that the trace to black has been cut. Test with a multi tester. Apparently I got no "buzz" but the black connection was still viable. Symptom: the mic is now on phantom power and giving an audio signal but there is NO bass and the gain has dropped. It's like a narrow band pass filter has been applied. I have a test recording before the mod and it's definitely a thinner sound after the mod. Cause: I don't know. Anyone? Is this a problem with me misunderstanding the wire reversal at the capsule (which contains an op amp and a capacitor?) or perhaps I have damaged the existing 10microfFarad capacitor when reversing it. Any suggestions appreciated.

[@gwEmbassy]

Thanks for this super long and detailed post Scot and Sam. I’ll pin it so that people can refer to it!

[@rogerbranton7596]

Thanks for the words of encouragement. I was happy with how it all went back together. I trimmed away a tiny bit of the battery compartment to make way for the two resistors. But alas, upon testing, all I got was a nasty hum. So I'll open it all up again and track down the problem!

[@gwEmbassy]

This mirrors my experience too. Lots of this type of faff.

[@MattNolanCustom]

Thanks for this video. I've been meaning to do this mod to two old PZMs I've had for years. Finally did but I was getting very strange results. The solution was - swap the red and black wires on the capsules. This is not in the instructions as far as I can see. So you helped answer a mystery. I'm not sure why, but it was making the capsule draw a lot of current and basically collapsing the phantom power. I believe the reason the original mic has a positive ground is because while the electronics are in a little metal screening box the battery is not. If you used a negative ground, the whole outer case of the battery itself might act like an antenna to pick up interference.

[@gwEmbassy]

I think you are right Matt

[@johnroesch689]

one of the best sounding mics i have. i did the xlr mod years ago. didnt know of the phantom

[@gwEmbassy]

It’s great :)

[@wul01]

20 odd years ago I modded the mic to take a 9 volt battery, which improved it too, that mod only required modding the battery compartment.

[@gwEmbassy]

I expect that worked pretty well!

[@wul01]

gwEm’s gwEmbassy yea it did similar results to you. Still have it so where.

[@jamesarter5498]

@@wul01 I'd be interested in knowing how you did this? I'd love to do the phantom power mod but I dont' think I really have the patience (and sklllset!) to really nail it. I wonder if the 9v battery option is worth a shot

[@wul01]

@@jamesarter5498 can’t remember exactly , but I’m guessing I just soldered a battery clip to the ecpxisting battery terminals, and fastened the battery to the case.

[@Friedegg.Jellyfish]

Absolutely useful! Thanks a ton:D

[@gwEmbassy]

👍 you’re welcome :)

[@spiro6363]

Hi GwEm, many thanks for posting this vid, I was just about to try this out on one of my old PZM that’s been knocked around, I was planning to convert one to use as a LISTEN mic in our studio live room. Good demonstration .

[@gwEmbassy]

Thanks! I will be doing another PZM mod this week, so watch out for that video in a month or so :)

[@JRP3music]

My band used them for acoustic guitar and kick mic in old demos long ago.

[@gwEmbassy]

Cool!!

[@JRP3music]

My brother found it, I am going to mod it. Thought we had 2. It will neat to revisit it.

[@gwEmbassy]

It’s a lovely old piece. I would do the XLR mod, but not the phantom power.

[@JRP3music]

I think the 9volt mod, would be easier. I plan to do it soon.

[@proto2149]

Impressive how a low budget mic can sound really good!

[@gwEmbassy]

Yes! I think it still holds up very well :)

[@pdw1955]

Could you publish the things you changed with the capsule? I understand that originally the black wire is connected tot the capsule and the case. The red one not. You seperated the blackwire from the case. But not clear is what you did any further. You just connected the red wire to the case as well?

[@gwEmbassy]

Which of the mods are you trying?

[@pdw1955]

@@gwEmbassy xlr and phantom power

[@gwEmbassy]

For these mods, I used the instructions here: www.muzines.co.uk/articles/realistic-pzm-modification/1342 and here: www.muzines.co.uk/articles/phantom-powering-the-realistic-pzm/4087 The XLR is a good modification, but I think the phantom power is not worth all the extra effort.

[@pdw1955]

@@gwEmbassyThank you very much. It is clear to me now. Regards

[@traceysheneman8652]

Nice video. From my limited understanding, changing the wiring at the capsule converts the operation of the built-in field-effect transistor from a relatively high impedance drain terminal output to a lower impedance source terminal output. An additional benefit is more linear output due to local (degenerative) feedback in the source circuit. With 6-12 volts applied, a higher maximum linear output should be achieved with this modification.

[@gwEmbassy]

I’ll take your word for that Tracey, I’m not a big mic expert. I find it interesting tech

[@rogerbranton1752]

I'm smack in the middle of doing this same mod, from the same set of instructions. I don't mind this kind of work but dealing with the small confines makes it a tad tricky. Any suggestions for fitting it all back in the case? Those 22K resistors aren't big but there's just no extra space allotted for them in the original design!

[@gwEmbassy]

No suggestions, it is a total pain in the rear though, I feel your pain!

[@rogerbranton1752]

@@gwEmbassy Fair enough, LOL!

[@gwEmbassy]

Keep going, you’ll get there eventually. The mod took me several hours and lots of swearing. It was tedious that’s for sure.

[@BeesWaxMinder]

I’ve had a quite a few of these over the years and the only mod I ever did was to put the 9v battery clip in instead of the 1.5v battery and I really thought it was great I recently bought one off eBay where the seller claimed to have the XLR mod but it arrived today to find there was no box for ANY battery at all between the XLR and the microphone itself!😳 Can this thing still work…? I’m fearful of plugging it into phantom power! In the comment section you seem to indicate (pardon me if I’m completely wrong about this!) That phantom power is not a good mmod to do… Can you explain why, please? Thanks!

[@gwEmbassy]

It may still work without the battery box. It depends completely on how they did the mod. I don’t like the phantom power mod as it is a lot of work for little gain. In my opinion of course!

[@BeesWaxMinder]

@@gwEmbassy .Thanks for your swift reply! I don’t really want to open up the item because of I’m trying to get it sent back to eBay and the seller is resisting strongly(!) But as far as I can see they have just wired the electret element on the black plate right up to an XLR with no battery box/preamp/transformer and they say it works fine into a mixer…🤷‍♂️

[@gwEmbassy]

Ah right! In that case yes : get your money back!

[@BeesWaxMinder]

@@gwEmbassy 🤞👍

[@STEVEFINNERTY]

I just got a 2and hand pzm offa Ebay, not used one of these for 29 years, I remember the battery mod, though forgotten just what that was,, my pzm came with xlr,, after watching this vid I've realized I would definatly fuck the above mod up !,, does it make much difference from xlr to xlr with phantom ?.,

[@gwEmbassy]

The phantom mod is a massive pain in the arse. I would just do the XLR mod.

[@helmanfrow]

Can't really see anything on the circuit board the way it was filmed.

[@gwEmbassy]

Yeah, sorry about that. It was difficult to even capture this.

[@helmanfrow]

@@gwEmbassy It's all good. I had similar issues so I bought a magic arm, a super clamp and a 1/4"-20 phone holder. I can clamp it to the side of my desk or to the shelves above, or even to a mic stand and position my phone camera as needed. Works wonders!

[@ansarbouatila9097]

Just soldering an xlr connector to a 2 lead (signal and ground) cable doesn't make the assembly balanced. Cutting the trace on the capsule is only done when you're aiming for a Linkwitz modification and with one resistor (around 80k) and an electrolytic cap soldered right into the xlr you can discard the battery box completely: it brings phantom power down to about 8V.

[@gwEmbassy]

I think you might have misunderstood the mod. The point where the XLR is inserted a two signal wires plus a separate screen. Several ways to get phantom power to this thing. I have another video coming up on that.

[@thomaseddie9450]

@@gwEmbassy I purchased two of these way back in 1986 and basically just stored them away as I was disappointed at that time with the response from them. I also purchased four tie pin electret mics at the same time. I am very interested in the other ' Several Ways to get phantom power' video, do you have some info? I appreciated the time and effort that you have already put in your video. Thank You, Tom.

[@gwEmbassy]

kzbin.info/www/bejne/amixqH17oJ6rm6s

[@traceysheneman8652]

The Realistic PZM has a built-in unbalanced input (two wire) to balanced output (three wire) microphone transformer, permitting a fully balanced XLR connection. Radio Shack undoubtedly decided to skip this option, and chose an unbalanced TS (tip-sleeve) plug as the mic is aimed at a nonprofessional consumer market.

[@STEVEFINNERTY]

These mics by the way where the sound of manchester for quite a while..

[@gwEmbassy]

They were often talked about when I was a kid

[@yenaurapourtoulmonde]

Did appreciate that you didn't use lousy autofocus...

[@gwEmbassy]

Thanks ;) lousy manual focus instead ;)