MKH415T servicing?

[Icantthinkofaname]

Can the MKH415T be converted to run on P48? I saw a deal on one that was too good to pass up (assuming it works properly), so I ordered it, along with a P48 to T12 barrel adapter and a 3 pin Tuchel to XLR cable. Ideally I'll have an XLR jack installed and have it run on phantom power (I didn't see any 415TU or 416TUs around here).

Aside from that sort of mod, is there anything else that can be done to bring it closer to a 416, like reducing the self noise a bit?

 

[soliloqueen]

nevermind i can't read

 

[mad.ax]

I added the 415T schematic in the tech docs section.
https://groupdiy.com/attachments/mkh415t-circuit-png.94638/
There you can also find the MKH416P48 which is what you'd want to achieve
https://groupdiy.com/attachments/mkh-416-48v-pdf.62543/
Compare them... 3 transistors vs 7! Not the easiest job...
Even if you manage to build a 416P48 board and squeeze it in that little space, the 415 have likely a different capsule, therefore the end result will not be identical...

My advice would be to keep the 415T as it is, including its DIN connector cause that's a good reminder to not plug it in a P48 lead...

 

[Icantthinkofaname]

I added the 415T schematic in the tech docs section.
https://groupdiy.com/attachments/mkh415t-circuit-png.94638/
There you can also find the MKH416P48 which is what you'd want to achieve
https://groupdiy.com/attachments/mkh-416-48v-pdf.62543/
Compare them... 3 transistors vs 7! Not the easiest job...
Even if you manage to build a 416P48 board and squeeze it in that little space, the 415 have likely a different capsule, therefore the end result will not be identical...

My advice would be to keep the 415T as it is, including its DIN connector cause that's a good reminder to not plug it in a P48 lead...

I do believe it's a different capsule. I'm not sure how different, but enough that the 415 is considered to be warmer sounding than the 416, but the documentation still shows a high shelf boost of like 2.5dB.

 

[Icantthinkofaname]

Does anyone know who can service an MKH415T if it needs it? Sennheiser tells me MKH415Ts are "unrepairable", I think the capsule is discontinued like the ones in the 435 and 406 (though I wouldn't mind a 416 capsule going in there if possible). Updated with my new question.

Still waiting for the 3 pin small Tuchel to XLR cable. I already have the mic and the barrel adapter, but that's XLR to XLR so I can't use it yet.

 

[RuudNL]

If you change the capsule for a different type, you also have to change the fixed frequency correction network for the capsule used. (See the schematics.)

 

[Ivan K.]

I used MKH405, 415, 805, 815 and later 816 microphones in my cine sound career. None ever failed. The whole idea behind a frequency modulation scheme was that it would be far more reliable than a high voltage, polarized (or Electret) capsule, especially in humid and rough location conditions.

Yo u can buy a 3-pin female DIN-pattern connector from www.binder-usa.com and make your own cable using Canare star-quad or equivalent Mogami cable if you can solder. Otherwise, pre-made cables are available on eBay and Reverb.

Good luck,
Ivan

 

[Icantthinkofaname]

I used MKH405, 415, 805, 815 and later 816 microphones in my cine sound career. None ever failed. The whole idea behind a frequency modulation scheme was that it would be far more reliable than a high voltage, polarized (or Electret) capsule, especially in humid and rough location conditions.

Yo u can buy a 3-pin female DIN-pattern connector from www.binder-usa.com and make your own cable using Canare star-quad or equivalent Mogami cable if you can solder. Otherwise, pre-made cables are available on eBay and Reverb.

Good luck,
Ivan

Mine looks like it was owned by a TV station, cause it has TVO (a TV station in Canada) engraved into it with the serial, so I'm thinking it at least got serviced every now and then when Sennheiser still serviced them.

 

[Icantthinkofaname]

Got it open, capsule looks fine but the electronics have seen better days.
Does this look like it just needs a good cleaning, or would it need actual repairs?

 

[gyraf]

if it works, don't touch it.
RF microphones are very complicated beasts

/Jakob E.

 

[Icantthinkofaname]

if it works, don't touch it.
RF microphones are very complicated beasts

/Jakob E.

Can't currently test it. Waiting on a Tuchel to XLR cable.

 

[Gerard]

The transistors used in some of the older Sennheiser MKH-series mics are very low-voltage rated germanium types. I have some MKH 110 low frequency mics (one is an MKH 110/1, which claims to go down to 0.1 Hz at -3 dB!), which require an 8 V supply on pin 3 (AC126 transistors, Veb 10 V). Someone plugged one of them into a T12 supply and cooked it; transistors dead. I must get around to replacing the transistors.

Also, be aware that the RF circuit is tuned to the specific capsule; if you change the capsu, you would have to know how to re-tune the RF circuit.

I also have a couple of MKH 415T mics; they work very nicely with a P48-to-T12 converter in the line. I keep everything DIN on the T12 or 8 V side of things, XLR only on the P48 side; it helps remind me not to plug a T12 mic directly into a P48 supply.

 

[Icantthinkofaname]

It's working, I don't know if the noise is typical for the mic, or if it's added by the T power adapter, or if something needs to be fixed.

Sample comparing to NTG3:
https://gearspace.com/board/so-much-gear-so-little-time/1382809-will-mkh-415t-need-service.html

if it works, don't touch it.
RF microphones are very complicated beasts

/Jakob E.

Looks like it works. I'm not sure whether it's noisy for a 415 or not. Should I clean the back of the PCB, or is it not high impedance enough to matter?

The transistors used in some of the older Sennheiser MKH-series mics are very low-voltage rated germanium types. I have some MKH 110 low frequency mics (one is an MKH 110/1, which claims to go down to 0.1 Hz at -3 dB!), which require an 8 V supply on pin 3 (AC126 transistors, Veb 10 V). Someone plugged one of them into a T12 supply and cooked it; transistors dead. I must get around to replacing the transistors.

Also, be aware that the RF circuit is tuned to the specific capsule; if you change the capsu, you would have to know how to re-tune the RF circuit.

I also have a couple of MKH 415T mics; they work very nicely with a P48-to-T12 converter in the line. I keep everything DIN on the T12 or 8 V side of things, XLR only on the P48 side; it helps remind me not to plug a T12 mic directly into a P48 supply.

Can you listen to my samples on Gearspace and comment on how my MKH 415 sounds compared to yours?

 

[Icantthinkofaname]

Bumping cause I'm not sure what the issue is. I cleaned the PCB which didn't help (definitely looks less nasty), but I wasn't sure if that would in the first place. I'm using a PSC P48 to 12T converter, I'm not sure if it's that, or something wrong with one of the components. I saw a review mentioning it introduced a lot of noise to someone else's mic, but because I don't have a recorder or mixer that has 12v T power I can't test the mic itself.

 

[moamps]

I have repaired Senn 416 mics three times. Once the capsule was in short, and in the other two cases the oscillator did not work at all; the quartz crystal was defective (it is sometimes mechanically very sensitive). If you can, check with an oscilloscope whether the oscillator is working.

 

[the groke]

I recapped a non-working MKH 104 and 404 and that brought them back to life. It was very tricky finding decent caps that fit. It's tight in there. One was very noisy afterwards. You can sort of adjust one trim by ear to reduce hiss, thought it's not at all the right way to do it. Still, doing that made mine good enough for some uses. There is an ex-Sennheiser tech in Denmark who can do the proper procedure. PM me. best - DT

 

[Ivan K.]

It has been many years since I adjusted a 415 or other in the family, but pretend you are adjusting the discriminator of an FM receiver. With a scope, a 1 kHz oscillator driving an active speaker (or amp + passive speaker), adjust L1 for max amplitude, and L2 for lowest distortion. Speaker output needs to be high enough to get a decent waveform, but don't clip. If I recall, the coils are interactive, so go back and forth for best results.

To check noise, If you have a good, very quiet (<1uV), external power supply, try it and vary the voltage between 8 to 12V and see if the noise is lower at a particular voltage I suspect 12V will be fine and that the problem is with your supply. Get a copy of the Sennheiser power supply schematic to make sure you are feeding the mic correctly.

If I recall, their noise spec was 1uV! I was never impressed with PSC equipment. I built some battery supplies for these mics, and at that time, used LM723 chips as the quietest, and had to select between brands for who had the quietest. LM 317 or LM7812 are too noisy. Today, I'd use an LT3045 (0.8uV), powered by 2 x 9V batteries in series. If you just want to buy a supply, these are the kind I made, still available on eBay: coherent communication microphone ps3 power supply - Tested | eBay. I have not made these in years and have no connection to the seller.

Good luck!

Ivan

 

[Gerard]

I have repaired Senn 416 mics three times. Once the capsule was in short, and in the other two cases the oscillator did not work at all; the quartz crystal was defective (it is sometimes mechanically very sensitive). If you can, check with an oscilloscope whether the oscillator is working.

I'm goanna bump this thread again as I never yet got around to repairing the damaged MKH 110 (see message 12 above). NSince then, I have 'acquired' two more MKH 110s; they work but are noisier than I expected - noisier than another MKH 110 and an MKH 110/1 I have that seem to work perfectly. I have also managed to find some AC126 transistors. A rather blurry schematic for the MKH 110/1 suggests it uses an AT125 for the oscillator and an AC125 for the output. However, I have not been able to find much in the way of tech details of the AC125 vs the AC126; I have an ancient copy of Towers International Transistor Selector, which suggests they have the same voltage ratings and similar Hfe.

Could I use an AC126 in place of an AC125?

What type of transistor is an AT125? Beyond the obvious that it is a germanium-type PNP. Google search yields nothing. Is there a reasonably-priced alternative, in case I fave to replace an oscillator transistor?

Would the coils need to be retuned after replacing a transistor or two, assuming all passive components are unchanged?

Any other points to watch out for when repairing early MKH-series mics?

 

[Lampie519]

I can check if i have some AC125 transistors in the junk box....
Germanium transistors don't like to be heated so be careful with soldering.

 

[Lampie519]

This is what i found :