Telefunken U47 noise issue

[ZHOUJUN]

As far as I know Telefunkenn USA power supplies are not very reliable, if it's an M940 check out a few capacitors in the red box.

 

[Jessie Pinkman]

Yes

As far as I know Telefunkenn USA power supplies are not very reliable, if it's an M940 check out a few capacitors in the red box.View attachment 134964

Yes, what I have is M940 model. I will check them out for sure. Thank you so much for letting me know

Are there some cases that those capacitors have problems?

 

[Cqwet Dbdfte]

Yes

Yes, what I have is M940 model. I will check them out for sure. Thank you so much for letting me know

Are there some cases that those capacitors have problems?

looks like old school zener /BJT based regulated, RC filtered thing. There is plenty of room for RF chokes an/or ferrite beads on signal- and power lines.
I'd make a copy of the PSU in a new box, and design it for RFI, with power line filters, RF chokes, and a better regulated HF design.
Adjust R20/R19 to desired output voltage. The SIM has bad input supply (20V p-p) to measure the the regulation effectiveness.


The vanilla Mike Maida 1980's circuit has less regulation:

 

[Jessie Pinkman]

looks like old school zener /BJT based regulated, RC filtered thing. There is plenty of room for RF chokes an/or ferrite beads on signal- and power lines.
I'd make a copy of the PSU in a new box, and design it for RFI, with power line filters, RF chokes, and a better regulated HF design.
Adjust R20/R19 to desired output voltage. The SIM has bad input supply (20V p-p) to measure the the regulation effectiveness.

View attachment 134969
The vanilla Mike Maida 1980's circuit has less regulation:

View attachment 134973

Thanks for your information, but I really don’t know about the technical things. Even though you explain with the map detailedly, I can’t understand deeply. Sorry for that. I’m not gonna repair it by myself, but just wanna know somethin’

Can I ask which ones are the capacitors that function as filters? Can you make circles on the pucture I attached?

The big and brown ones?

 

[Mr. Moscode]

Could be heater - cathode leakage in the tube, or a sometime oscillation in the LV PS.

 

[Jessie Pinkman]

Could be heater - cathode leakage in the tube, or a sometime oscillation in the LV PS.

Do you mean it can be occured due to heat?
the tube that you mentioned is brown one, right? What is the function of those tube? Regulation of low and high noise?

 

[MagnetoSound]

Since the problem is intermittent, it may simply be that one of the filter caps has a dry solder joint on one of it’s pins.

The most common of any fault, and fits the symptoms perfectly. I’d start by looking at the solder pads on the bottom of the board.

 

[Jessie Pinkman]

Since the problem is intermittent, it may simply be that one of the filter caps has a dry solder joint on one of it’s pins.

The most common of any fault, and fits the symptoms perfectly. I’d start by looking at the solder pads on the bottom of the board.

I will check it out too! thank you

 

[Jessie Pinkman]

I visited a popular electronics forum to ask about it, and one staff member left this message.
Hope this thing can help you if you suffer from the same issue.

-----------------------------------------------------------------
Probably the capacitors although there could be other reasons. They are the three brown cylinders on the left of the board. They all eventually fail but I'm surprised they died so soon on a relatively new unit. Normally you would expect 5+ years before hum becomes noticeable. They are not expensive to buy and easy to replace.

I'm not sure where you are but my guess is you have 60Hz mains power at your wall sockets. That is the clue, the bridge rectifiers (the four gray things with silver bands at one end near where the yellow and green wires reach) convert the 60Hz AC into pulsed DC at a rate of 120Hz. The capacitors act as reservoirs to hold the pulses at a steadier level before feeding the voltage regulator circuit. If the capacitors become inefficient the reservoir holds less and the pulses start to show across them and then conduct to the rest of the circuit.

 

[Khron]

I would really wonder what DOES turn out to be the exact cause. Those big capacitors are Nichicon, which is one of the very few brands i trust unquestioningly (coincidence or not, they're all Japanese), so those failing "already" is VERY unlikely, especially in such a low-stress environment (100-120Hz, and a handful of mA of ripple-current; at that size, those will be rated for a good few amps, ***at the rated operating temperature***).

The transformer is rated at 12VA, so with the two secondaries in parallel, that works out to a worst-case 100mA.

Maybe one or more of those 1A(?) diodes in the bridge rectifier gave up the ghost? I'd think even that is more likely than those name-brand fat capacitors (manufactured in week 34 of 2020, looks like) kicking the bucket...

 

[Cqwet Dbdfte]

I will check it out too! thank you

90% of problems in new electronics can be found by visual inspection, if you know what you are looking for.
Solder joints should have concave fillets and be shiny (except for lead free alloys that always look suspect).
This could be the PCB or the connectors.
Intermittent noise can be from cellphone transmitting. Test your setup with active call sending voice or data, noise would be in pulses. Keep close to mike, cables, power supply, mixers etc.
The weaker the cell tower the stronger the phone uplink signal.

 

[Jessie Pinkman]

90% of problems in new electronics can be found by visual inspection, if you know what you are looking for.
Solder joints should have concave fillets and be shiny (except for lead free alloys that always look suspect).
This could be the PCB or the connectors.
Intermittent noise can be from cellphone transmitting. Test your setup with active call sending voice or data, noise would be in pulses. Keep close to mike, cables, power supply, mixers etc.
The weaker the cell tower the stronger the phone uplink signal.

I disassembled the PSU again and took a picture of the back side of the board.

I think it looks terrible. Even tho I have literally no knowledge about it, I can feel it.. lol Plz look into it.



Is it bad??

How could the PSU of 10000 dollars microphone be soldered like this?

 

[Mr. Moscode]

Do you mean it can be occured due to heat?
the tube that you mentioned is brown one, right? What is the function of those tube? Regulation of low and high noise?

The tube in the mic. The tube is an amplifier for the capsule voltage and gives it enough power to drive the output so you can plug it into your console.

Not mentioned so far, possible but unlikely are switching transients in the rectifiers but since it comes and goes, it could also be your power line voltage may not be 100% stable. Low line voltage could cause some 120 hz hum to get past any regulation.

It may be a PITA but try to get it fixed under warranty or get an exchange. Since you make a living with it, and the fault is intermittent and could take some time to actually pin down at their shop or may not even occur in Tele's possession, you would have a good case for a warranty exchange for another new one.

Good luck!

 

[Cqwet Dbdfte]

Looks OK. The absence of HF filters on the connectors bothers me.
A bad mike cable could also be at fault. Improper "grounding" etc.
Try the cellphone test.

 

[Mr. Moscode]

I disassembled the PSU again and took a picture of the back side of the board.

I think it looks terrible. Even tho I have literally no knowledge about it, I can feel it.. lol Plz look into it.

View attachment 134986

Is it bad??

How could the PSU of 10000 dollars microphone be soldered like this?

No, it's not bad if the solder joints are good. It's hand soldered for sure. And the board was not intended for wave soldering. Odds are that this was done this way because it is "Vintage gear" so no one would bitch about it being modernized, despite being brand new. And it is unlikely the cause of the problem.

If you are looking for warranty work by Tele then leave it alone, be patient and wait for their response. If they drag their butts keep on them until your get proper warranty service.

From your posts it doesn't sound like you have the experience to do this yourself, no offense intended. I know it's frustrating but without proper gear : a test bench, oscilloscope and an electrically low noise environment, you run the risk of accidentally make things worse with a slip of a test probe. Don't ask me how I know! And if you attempt to service this yourself you'll most likely void the warranty.

Hang in there.

 

[Khron]

How could the PSU of 10000 dollars microphone be soldered like this?

Easy - cheap(?) labor, or expensive labor performed by people who couldn't give two f**ks about it. That being said, i've seen worse, but I'm confused about the two-layer board being "required" for such a dead-simple design... But I guess they had to make it look "worth the money"..?

 

[Mr. Moscode]

A 2 layer board gets rid of jumpers and is cheaper than a single layer board.
Not to defend that board. It has un-plated copper without plated through holes so copper can oxidize, no conformal coating to limit moisture absorption, without through hole plating connections made by component leads from the top to bottom side are suspect, especially if the topside of the through lead is hidden under the component. And the board in the photo seems to never have been cleaned post soldering.

That said - wait until the warranty issue is settled.

 

[Cqwet Dbdfte]

One layer boards are an oddity now, mainly in extremely low end power supplies using paper-phenolic or some archaic junk.
Base PCB material is 2-sided, can be made into one layer by etching off one side, you already paid for.
Who would want that?
Alternatively aluminum one sided boards are now low cost, and can be made into heatsinks, front panels etc.

 

[Biula]

Yes, you are right. Following the method you told me, it’s gone after turning off the power supply while the mic is still working for 2-3 seconds.

As I posted before, someone said the problem is electrolytic capacitor on the similar case(124hz hum noise)

https://repforums.prosoundweb.com/index.php?topic=23670.0

I’m still waiting for a reply from Telefunken, and I’m gonna visit an audio repair shop next week, but If I show you the inside of the power supply, can you recognize what the filter capacitors are?

Actually I bought a brand new mic, and I’ve been using with great care. I totally don’t why this kinda thing happen.

I also wanna know why it works perfectly fine now, but sometimes that hum noise occurs again.

Well, is very easy to identify the filters electrolytics, but I can not advice you to repair it yourself: is a new mike, Telefunken must take care of the problem! The fact the issue is randomly appearing is probably due to a temperature related faulty condenser, also the new ones can develop this kind of problems... to be honest, I trust more a 30 years old Siemens cap than a brand new Chinese one (and yes, Telefunken is NOT the original German brand anymore, they use very common off-the-shelf components... sorry!).

 

[Khron]

to be honest, I trust more a 30 years old Siemens cap than a brand new Chinese one

I can relate, but those new ones in this power supply are Japanese, not Chinese...