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Post by lpedrum on Sept 1, 2020 12:03:21 GMT -6
Hi...I have a few old EV PL76 and PL77 and really love these mics, especially on acoustic guitar. However the do tend to get noisy and eventually fail, which is the case with one of mine. There's precious little online about these early electret condenser mics, but I did find a post from 15 years ago on another site. It reads: I've got four PL77AA's, the successor to the PL76A. They're actually very good sounding mics. Generally, the only thing that goes wrong with these mics is the electrolytic capacitor drys out and the mic gets really noisey then quits working completely. I've upgraded all of mine with new high quality 6mF 50v caps, and they work perfectly. I still use them at gigs.
My gear building experience is with kits only, so when it comes to trouble shooting I'm a novice. I've taken the mic apart to try and locate the capacitor mentioned above. I've attached a pic. Question 1. Which component is it? The black one or the white one? Question 2. I can't locate that capacitor anywhere online. Could he have listed it wrong? Does anyone have a suggestion for a replacement? If anyone out there can point me in the right direction here it'd be very much appreciated!  And HERE is a link to the mic schematic. |
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Post by svart on Sept 1, 2020 12:57:23 GMT -6
Hi...I have a few old EV PL76 and PL77 and really love these mics, especially on acoustic guitar. However the do tend to get noisy and eventually fail, which is the case with one of mine. There's precious little online about these early electret condenser mics, but I did find a post from 15 years ago on another site. It reads: I've got four PL77AA's, the successor to the PL76A. They're actually very good sounding mics. Generally, the only thing that goes wrong with these mics is the electrolytic capacitor drys out and the mic gets really noisey then quits working completely. I've upgraded all of mine with new high quality 6mF 50v caps, and they work perfectly. I still use them at gigs.
My gear building experience is with kits only, so when it comes to trouble shooting I'm a novice. I've taken the mic apart to try and locate the capacitor mentioned above. I've attached a pic. Question 1. Which component is it? The black one or the white one? Question 2. I can't locate that capacitor anywhere online. Could he have listed it wrong? Does anyone have a suggestion for a replacement? If anyone out there can point me in the right direction here it'd be very much appreciated! And HERE is a link to the mic schematic. Neither. Both the white and the black part are transistors. i don't see a cap in the pic unless it's on the other side or underneath. 6mF is written in the old way to write microfarad. Instead of mF it's now uF. 6uF is also an odd value, the modern equivalent is 6.8uF. We need a picture of the cap to get an idea of how the leads are mounted. Some come out the ends (axial leaded) and some come out the same side (radial leaded). Spacing can be very different too. |
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Post by johneppstein on Sept 1, 2020 13:26:41 GMT -6
Hi...I have a few old EV PL76 and PL77 and really love these mics, especially on acoustic guitar. However the do tend to get noisy and eventually fail, which is the case with one of mine. There's precious little online about these early electret condenser mics, but I did find a post from 15 years ago on another site. It reads: I've got four PL77AA's, the successor to the PL76A. They're actually very good sounding mics. Generally, the only thing that goes wrong with these mics is the electrolytic capacitor drys out and the mic gets really noisey then quits working completely. I've upgraded all of mine with new high quality 6mF 50v caps, and they work perfectly. I still use them at gigs.
My gear building experience is with kits only, so when it comes to trouble shooting I'm a novice. I've taken the mic apart to try and locate the capacitor mentioned above. I've attached a pic. Question 1. Which component is it? The black one or the white one? Question 2. I can't locate that capacitor anywhere online. Could he have listed it wrong? Does anyone have a suggestion for a replacement? If anyone out there can point me in the right direction here it'd be very much appreciated! And HERE is a link to the mic schematic. I see two various transistors and a resistor in the pic, so the answer would be "non of the above".
Since the schematic shows it connected to the switch, I'd look inside the body of the mic. Look for a cylindrical dingus, probably with a lead out each end, but they could be out the same one, in which case polarity would be indicated by a stripe. Otherwise polarity is indicated by an indentation around the + end.
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Post by lpedrum on Sept 1, 2020 14:02:45 GMT -6
Thanks a lot for the help guys! Here's a pic of the back side of the top components. If that isn't it I'll take apart the switch and see what's there.  |
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Post by svart on Sept 1, 2020 16:16:36 GMT -6
Thanks a lot for the help guys! Here's a pic of the back side of the top components. If that isn't it I'll take apart the switch and see what's there. View AttachmentI'm thinking it has to be under the black plastic mount. The schematic shows 3.3uf just after the 5087 transistor. I'm guessing people increase that for more low end. |
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Post by johneppstein on Sept 1, 2020 18:50:14 GMT -6
Thanks a lot for the help guys! Here's a pic of the back side of the top components. If that isn't it I'll take apart the switch and see what's there. Nope, not there. Just another resistor and what looks to be a side view of a trimpot. Most likely the cap you're looking for is attached to one of the lugs on the switch.
EDIT: I am not seeing any cap marked as 6 uf on that schematic. I am seeing one toward the middle marked at 3.3 uf, but the one on the top only has a voltage rating (4.5 V) and a rating of 3.5 mA (milliamps). I'm using a magnifying glass, BTW.
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Post by svart on Sept 1, 2020 19:36:40 GMT -6
Thanks a lot for the help guys! Here's a pic of the back side of the top components. If that isn't it I'll take apart the switch and see what's there. Nope, not there. Just another resistor and what looks to be a side view of a trimpot. Most likely the cap you're looking for is attached to one of the lugs on the switch.
EDIT: I am not seeing any cap marked as 6 uf on that schematic. I am seeing one toward the middle marked at 3.3 uf, but the one on the top only has a voltage rating (4.5 V) and a rating of 3.5 mA (milliamps). I'm using a magnifying glass, BTW.
The "4.5v/3.5mA" thing is a battery. |
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Post by lpedrum on Sept 1, 2020 22:10:12 GMT -6
Yes, this mic runs on a battery. I'll do my best to get pics of the switch tomorrow along with a few others. Another question while I've got your attention. Most of the mic pieces are held together by some sort of sticky adhesive, not glue. If I can get this working, do you have any suggestions for adhesive? Thanks guys!
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Post by svart on Sept 2, 2020 7:53:38 GMT -6
Yes, this mic runs on a battery. I'll do my best to get pics of the switch tomorrow along with a few others. Another question while I've got your attention. Most of the mic pieces are held together by some sort of sticky adhesive, not glue. If I can get this working, do you have any suggestions for adhesive? Thanks guys! Probably just plain double-sided tape would be fine. Gorilla makes one that's pretty damn sticky but it's a little thick. I've used some regular 3M stuff from HD/Lowes that claims it's permanent but it's also as thin as regular tape. Guess it depends on where you need to put it. You could also glue it. Hot glue is OK but it doesn't stick well to some things. Urethane based glues (Gorilla glue, structural adhesives) are pretty much permanent but are hard to work with. Super glue is fast but it cracks easily and won't handle being jostled around over the years. Silicone adhesives can work but some are runny and some are too jelly like to adhere well. |
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Post by lpedrum on Sept 2, 2020 13:09:05 GMT -6
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Post by lpedrum on Sept 2, 2020 13:16:48 GMT -6
Yes, this mic runs on a battery. I'll do my best to get pics of the switch tomorrow along with a few others. Another question while I've got your attention. Most of the mic pieces are held together by some sort of sticky adhesive, not glue. If I can get this working, do you have any suggestions for adhesive? Thanks guys! Probably just plain double-sided tape would be fine. Gorilla makes one that's pretty damn sticky but it's a little thick. I've used some regular 3M stuff from HD/Lowes that claims it's permanent but it's also as thin as regular tape. Guess it depends on where you need to put it. You could also glue it. Hot glue is OK but it doesn't stick well to some things. Urethane based glues (Gorilla glue, structural adhesives) are pretty much permanent but are hard to work with. Super glue is fast but it cracks easily and won't handle being jostled around over the years. Silicone adhesives can work but some are runny and some are too jelly like to adhere well. thanks much Svart....If you look at the pics I just posted, the brown stuff around the rim above the threads was some sort of adhesive. I gently pried it open with a small screwdriver because there was no obvious way to detach the black plastic housing. It wasn't a dried glue but some sort of sticky adhesive that did the job very well. Being a novice I thought that might be a common thing among electronic builders, but from your response maybe not! |
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Post by svart on Sept 2, 2020 15:39:43 GMT -6
Here are some more pics. As you can see, there are no additional components underneath the circuit board. On the switch there seems to be two. One looks like a resistor? The other small black component may be the capacitor, but I have no idea. View AttachmentView AttachmentView AttachmentView AttachmentThe black thing with "3.3k" is the capacitor. Hard to tell if it has polarity markings but it's either ceramic or tantalum. Ceramic it's non-polar but tantalum and electrolytic have a polarity. Ceramic and tantalum don't go bad like electrolytic do, so it might not need replacing. If you do, ceramic is fine. |
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Post by Michael O. on Sept 2, 2020 15:58:59 GMT -6
Here are some more pics. As you can see, there are no additional components underneath the circuit board. On the switch there seems to be two. One looks like a resistor? The other small black component may be the capacitor, but I have no idea. The black thing with "3.3k" is the capacitor. Hard to tell if it has polarity markings but it's either ceramic or tantalum. Ceramic it's non-polar but tantalum and electrolytic have a polarity. Ceramic and tantalum don't go bad like electrolytic do, so it might not need replacing. If you do, ceramic is fine. That seems to be the case, judging by the looks and the schematic it’s likely to be a tantalum cap, and therefore unlikely to have gone bad (as opposed to failing outright). If it’s not a bad cap, and given that the capsules in these mics are electret-based, it’s entirely possible that the charge of the electret material has faded over time causing lack of sensitivity and a higher noise floor. Which would be a bummer, because these mics are otherwise pretty solid. |
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Post by johneppstein on Sept 2, 2020 16:07:09 GMT -6
Yes, this mic runs on a battery. I'll do my best to get pics of the switch tomorrow along with a few others. Another question while I've got your attention. Most of the mic pieces are held together by some sort of sticky adhesive, not glue. If I can get this working, do you have any suggestions for adhesive? Thanks guys! Probably just plain double-sided tape would be fine. Gorilla makes one that's pretty damn sticky but it's a little thick. I've used some regular 3M stuff from HD/Lowes that claims it's permanent but it's also as thin as regular tape. Guess it depends on where you need to put it. You could also glue it. Hot glue is OK but it doesn't stick well to some things. Urethane based glues (Gorilla glue, structural adhesives) are pretty much permanent but are hard to work with. Super glue is fast but it cracks easily and won't handle being jostled around over the years. Silicone adhesives can work but some are runny and some are too jelly like to adhere well. Most silicone adhesives contain and outgas acetic acid, which is not good for circuitry. |
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Post by johneppstein on Sept 2, 2020 16:19:11 GMT -6
The black thing with "3.3k" is the capacitor. Hard to tell if it has polarity markings but it's either ceramic or tantalum. Ceramic it's non-polar but tantalum and electrolytic have a polarity. Ceramic and tantalum don't go bad like electrolytic do, so it might not need replacing. If you do, ceramic is fine. That seems to be the case, judging by the looks and the schematic it’s likely to be a tantalum cap, and therefore unlikely to have gone bad (as opposed to failing outright). If it’s not a bad cap, and given that the capsules in these mics are electret-based, it’s entirely possible that the charge of the electret material has faded over time causing lack of sensitivity and a higher noise floor. Which would be a bummer, because these mics are otherwise pretty solid. As the owner (and recapper) of a Studer A800, I can tell you that, contrary to what was believed a couple decades age, tantalum caps most definitely DO go bad. They are also VERY sensitive to reverse voltage. When I got my Studer I was told to go ahead and replace all the tantalums with electrolytics. Modern electros last a lot longer than most tantalums. The one problem with replacing a tant with an electro here could be size - tantalums are still smaller.
EDIT: I just saw the new pics and the small black thing on the switch is definitly a tantalum capacitor. If you replace it with another tant, make ABSOLUTELY CERTAIN that you get the polarity right or you will blow it as soon as power is applied. They're intolerant little buggers. I would see if I could find an mini electrolytic that would fit, but it's tight.....
EDIT 2: For gluing the thing back together I would use an industrial contact cement. My first choice would probably be Pliobond (shake before using, even if you get it in a tube) or (second) DAP Weldwood contact cement. One of these is likely what was used originally.
Pliobond sticks to metal very well - JBL uses an OEM version in their recone kits.
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Post by svart on Sept 2, 2020 17:00:38 GMT -6
Took another look on a bigger screen and the cap does have a red dot on top for polarity, so it's most likely tantalum after all. Just because a schematic has a polarity mark doesn't mean the part is polar.
And no, tantalum doesn't go bad with age like an electrolytic cap does. They can be damaged by misuse, but that's not the same thing at all.
However, I do see a crack in the enamel, which might expose the tantalum slug to air, which will make it go bad as it oxidizes, so it's best to replace it now.
I'd go with a ceramic or good electrolytic here unless you just want the tantalum sound.
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Post by lpedrum on Sept 3, 2020 15:22:45 GMT -6
I've been looking at Mouser. Would something like THIS work? I'm not sure what voltage I should be getting. Since the mic is apart there's no harm in swapping this component out and seeing what happens. I have two others. But as somebody else mentioned, the noise floor thing thing could simply be the aging of the capsule. Usually I'm not a big fan of hand held condenser mics, especially live. But for whatever reason this mic is a real winner on acoustic (when the noise floor isn't an issue.) |
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Post by svart on Sept 3, 2020 16:08:15 GMT -6
I've been looking at Mouser. Would something like THIS work? I'm not sure what voltage I should be getting. Since the mic is apart there's no harm in swapping this component out and seeing what happens. I have two others. But as somebody else mentioned, the noise floor thing thing could simply be the aging of the capsule. Usually I'm not a big fan of hand held condenser mics, especially live. But for whatever reason this mic is a real winner on acoustic (when the noise floor isn't an issue.) Should work fine. Yeah, the electret capsules are bad about losing their potency, but they also naturally have a higher noise floor anyway. |
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Post by johneppstein on Sept 3, 2020 17:26:56 GMT -6
I've been looking at Mouser. Would something like THIS work? I'm not sure what voltage I should be getting. Since the mic is apart there's no harm in swapping this component out and seeing what happens. I have two others. But as somebody else mentioned, the noise floor thing thing could simply be the aging of the capsule. Usually I'm not a big fan of hand held condenser mics, especially live. But for whatever reason this mic is a real winner on acoustic (when the noise floor isn't an issue.) Should work fine. Yeah, the electret capsules are bad about losing their potency, but they also naturally have a higher noise floor anyway. Actually those EVs are pretty good about retaining their charge, unlike the really early Sony electrets, which were pretty terrible. By the time EV brought those out the technology was already at least 10 years old (IIRC) and had undergone considerable improvement. |
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Post by johneppstein on Sept 5, 2020 0:38:30 GMT -6
Took another look on a bigger screen and the cap does have a red dot on top for polarity, so it's most likely tantalum after all. Just because a schematic has a polarity mark doesn't mean the part is polar. And no, tantalum doesn't go bad with age like an electrolytic cap does. They can be damaged by misuse, but that's not the same thing at all. However, I do see a crack in the enamel, which might expose the tantalum slug to air, which will make it go bad as it oxidizes, so it's best to replace it now. I'd go with a ceramic or good electrolytic here unless you just want the tantalum sound. Tantalums are somewhat sensitive to thermal cycling, or used to be. |
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Post by svart on Sept 5, 2020 7:38:55 GMT -6
Took another look on a bigger screen and the cap does have a red dot on top for polarity, so it's most likely tantalum after all. Just because a schematic has a polarity mark doesn't mean the part is polar. And no, tantalum doesn't go bad with age like an electrolytic cap does. They can be damaged by misuse, but that's not the same thing at all. However, I do see a crack in the enamel, which might expose the tantalum slug to air, which will make it go bad as it oxidizes, so it's best to replace it now. I'd go with a ceramic or good electrolytic here unless you just want the tantalum sound. Tantalums are somewhat sensitive to thermal cycling, or used to be. Not for a while. I use a lot of tantalums at work these days and I've had to be very careful about how we use them in commercial designs but thermal issues aren't really one of the things you have to watch out for anymore. |
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Post by lpedrum on Sept 5, 2020 13:05:50 GMT -6
I purchased a couple of capacitors and will give it a try. It's a bit of a long shot, but this mic is worth the effort. Thanks guys and I'll keep you posted!
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Post by Guitar on Sept 14, 2020 9:15:04 GMT -6
Cool, good luck with the repairs. Fixing old mics is one of tech's more satisfying pleasures.
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Post by lpedrum on Oct 1, 2020 22:31:01 GMT -6
I want to thank you all for the much needed help with the EV76 mic. I bought a couple of capacitors, swapped one out, and lo and behold the mic works again! I thought this experiment might have a 50% chance at best, so this is a pleasant surprise! I need to find some adhesive at the hardware store to hold the mic parts together and them I'm all set. I'm happy to move this mic out of my box of broken gear (we all have one!) and back into rotation. The new capacitor doesn't seem to have improved the noise floor level, but the mic is still a gem to my ears. Thanks all!
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