Sennheiser MD431 electronics repair?

[raketenmann]

Dear GroupDIY
I bought a pair of 80's Sennheiser MD431 microphones. Both sound dull, having not the highend extension I believe they should have. Unfortunatelly I don't have a working MD431 to compare, but compared to similar mics as Sennheiser, Heil or Shure Vocal mics with sort of the same Frequency response, there is a drastic fall in the range from 5-15kHz.
As I said: I bought a pair of these mics, they sound pretty similar, seems that they've been a pair for the last 30 to 40 years and are of the same era. Checking the diaphragm shows me, that there is everything OK: no damage, no dirt on it, no dirt in the magnet gap. A 80Hz sine wave works without any distortion on it. So I am 100% shure that it has nothing to do with the capsule. As both mics do have the same condition and also lack of of high end I suppose there is a part of the electronics that has gone bad over the years.

If this is so - I suppose there should be others with the same experience - and hopefully with a solution for the problem.
I'll attach a picture of the electronics found in the mic. I don't understand much about electronics, so hopefully someone can make guesses or even has a service manual for that mic that shows all of the elements.

Thanks already for any comment on this!

 

[panman]

Only saw this post now for some reason. I have a few of those mics, but they do not have that problem. I believe I also have at least one fully working electronics for you to try out and exclude/confirm a capsule/electronics failure. But I am off the country now and expect to return only this coming weekend.

 

[raketenmann]

Only saw this post now for some reason. I have a few of those mics, but they do not have that problem. I believe I also have at least one fully working electronics for you to try out and exclude/confirm a capsule/electronics failure. But I am off the country now and expect to return only this coming weekend.

Dear panman
Thank you for your reply. Well, in the end I will probably just send the mics to you anyway but let's finish first the open projects. safe travels!

 

[abbey road d enfer]

Wow! Never seen so many inductors in a dynamic mic. No wonder it's so expensive.

 

[abbey road d enfer]

I bought a pair of 80's Sennheiser MD431 microphones.

Out of curiosity, can you measure the DC resistance of the capsule and verify the value of the resistor across the XLR. I read 10k for the latter but I'm not sure.

 

[Tubetec]

Im quite interested in doing more about passive dynamic mic equalisation , its seem like a usefull technique .
HPF to kill proximity effect and another filter to pull back some of the mid forwardness associated with dynamics .
Member Rossi made an LC filter for Shure type mics , it just notches out a little of the midrange 'honk' .
Shure Sm-7b incorporates the humbucking coil in an LC filter ,
the same principle might be applied to almost any dynamic capsule .

 

[abbey road d enfer]

Im quite interested in doing more about passive dynamic mic equalisation , its seem like a usefull technique .

I would say it's useful to the manufacturer, for whom it allows publishing satisfying graphs.
In terms of practical benefit to the user, it can be debated.
For a no-EQ set-up, it makes some sense, however it will never be as good as a decent condenser mic.
For live use, one can live with some "mid forwardness", it's what most users of SM57/58 do.
For most applications EQ is a given, and EQ done electronically is way better than passive since it encompasses both EQ needed for compensation of equipment deficiencies and that needed for artistic reasons.
The main reasons for passive EQ are:

• presenting a flat-ish frequency response, which however is not a guarantee of a good sounding mic
• making the mic "sounding good", but one's good sound is another's cacophony
• correctly a blatant defect, which should be adressed by redesigning the mic

The Sennheiser MD431 looks to me like something that could only come from teutonic engineers, destined to sell to people who buy from specs - there's a lot of them in Germany, operating in theaters and broadcast.
IMO, the supposed advantages do not justify the added cost. The fact that it is nearly absent of riders and rental mic lockers seems significant to me.
It would be interesting to evaluate this mic without the EQ; I don't think the MD431' capsule is used in any other Sennheiser mic.
Let me be clear: I don't want to diss Sennheiser here, I'm just questioning the well-funded of their choice, and more generally of this practice.

Shure Sm-7b incorporates the humbucking coil in an LC filter ,

As do most of the mics that have some passive EQ in them, switchable or not, since in most cases, the humbucking coil is part of the capsule.
The SM7 is definitely in the first two categories, since many broadcast mixers don't have EQ, and a condenser mic would not be suited to "mic-licking".
That being said, the SM7B is my second go-to vocal mic, particularly when the singer performs in the same room as the musicians, where using it in touching proximity helps with spillage.

 

[rock soderstrom]

The Sennheiser MD431 looks to me like something that could only come from teutonic engineers, destined to sell to people who buy from specs - there's a lot of them in Germany, operating in theaters and broadcast.
IMO, the supposed advantages do not justify the added cost. The fact that it is nearly absent of riders and rental mic lockers seems significant to me.

Your critical comments have an existing real background. In fact, the design of the MD431 is an example of what makes German engineers tick. Whether it has to be done that way is another matter.

On the other hand, the result speaks for itself (which, despite all the over-engineering and complexity, is always the primary goal of Teutonic engineering).

I don't know what it's like today, I've been out of the live business for a long time. In the past, the MD431 was omnipresent for vocal tasks. I can absolutely not confirm a "nearly absent of riders and rental mic lockers", rather the opposite.

The MD431 was the ultimate workhorse on German stages and TV studios for decades.

My personal opinion for those who are interested. It is probably the best dynamic live microphone for vocal tasks.
I still appreciate it very much and like to use it myself with my own voice. A fantastic microphone, everyone should try it. The relationship to the MD441 is audible, the MD431 is slimmer in the bass, which makes sense for a handheld stage microphone. Otherwise, the same classy sound, a dynamic microphone of the best kind.

Just my 0.02$

 

[abbey road d enfer]

The MD431 (in the wired or related wireless versions) was the ultimate workhorse on German stages and TV studios for decades.

I won't dispute that; actually, it concurs well with "destined to sell to people who buy from specs - there's a lot of them in Germany, operating in theaters and broadcast."
Different countries, different manners.
I checked with Dushow, the largest PA hire company in France, out of about 4000 mics, they have only 7 MD431's. The switch on it seems to be a significant deterrent.

My personal opinion for those who are interested. It is probably the best dynamic live microphone for vocal tasks.

Is it because it requires less EQ?

I still appreciate it very much and like to use it myself with my own voice.

I surmise you use it live. The relationsip between a singer and their mic is complex and very personal.
My favourite dynamic mic is a Samson S12 (not in production). Nothing in the specs explains that, it's just that I feel more comfortable with it.
Now I have given up on dynamic mics, I use the ZOOM SGV6.

 

[abbey road d enfer]

@raketenmann
Sorry for hijacking your thread.

 

[raketenmann]

Hey there

Thanks a lot for all the input.

As you can see my post ist old (from May) and since then I lost a little bit the interest on working on these mics.

I bought two of these together for 100 Euros and did some minor testing. I found the High End to be dull - but it is hard to tell because I have no clue how a 100% working MD431 is supposed to sound. So @panman probably you could just send me one of yours to try out.

Since then, I did open both mics to see, if there is something missing or wrong. Stupid as I am however I broke one mic (probably a broken coil wire) because there is no resistance on the capsule anymore. My idea was to put the capsule directly to an XLR to see how this sounds. But since one mic is broken, I can't do an A/B comparison anymore, so that's the reason I stopped working on them...

When I started repairing mics as a hobby, I was so naive to think as if a diaphragm is clean and can move freely, the mic is working fine. Unfortunatelly I found out that this is not the case and often some high end is missing for reasons I still can't explain... :-(

 

[abbey road d enfer]

But since one mic is broken, I can't do an A/B comparison anymore, so that's the reason I stopped working on them...

But you still have them, yes?
Check my post #5.

 

[Tubetec]

Thanks for the explanation Abbey ,

Im not against using EQ ,
I can typically get away with 3 band with swept mid in a live scenario ,
four band is preferable sometimes
but passive eqing to get something like a SM58 to sound more like you want it just seem sensible ,
pulling out the low end bump that occurs with close micing especially , thats needlessy eating into the headroom of the mic pre's on transients .

Of course I understand this approach is mic specific and in the end a single filter probably wont make a 58 a stand alone plug and play mic without extra active eq treatment .
There always a variation from source to source that needs to be acounted for , and absorbtion varies depending on the number of bodies you have in the room also .

Im currently involved in setting up a small live venue with recording ,
Its destined for spoken word and small musical ensembles , mainly acoustic ,
The equipment was specced before my involvment with the project and Im not happy with the typical modern live digital gear they got .
Its way to complicated to expect people with out much technical knowledge to be able to opperate , which is a key factor , acessibility and no screen gawping or menus is another requirement ,
I find I cant hear properly when Im looking down at a screen ,all Im getting is the reflected sound off the console top panel , for me tieing in the visual sences with a screen also reduces my brains ability to concentrate on the sound .
Essentially I want something a blindman can opperate ,only touch and ears required .

The SSL Six with a couple of SSL2 pres submixed in looks like a viable option ,
Eq is very limited , just two band on the two main mic inputs ,

As Ive mentioned before I'd like to make an XLR adapter incorportaing a passive switched HPF specifically for use with a Shure 57/58 capsule and preamp with an input Z of 1200ohms and a flat frequency responce .
A three position dual pole slide switch like used in Shure mics is easy to find ,
in conjunction with internal jumpers to select few different curves it becomes a tuneable mud filter at the input to the system , right where you want it .

Heres how the SM58 frequency responce varies with distance , its seems to be a broad hump centered around 200hz , worst case (@3mm)we need around -15db gain at 200hz relative to a distance of two feet .

 

[GeorgeToledo]

The fact that it is nearly absent of riders and rental mic lockers seems significant to me.

 

[abbey road d enfer]

Essentially I want something a blindman can opperate ,only touch and ears required .

I understand that; it pertains to the "no-EQ" scenario.

As Ive mentioned before I'd like to make an XLR adapter incorportaing a passive switched HPF specifically for use with a Shure 57/58 capsule and preamp with an input Z of 1200ohms and a flat frequency responce .

There is no doubt that the most important audio process is HPF.

in conjunction with internal jumpers to select few different curves it becomes a tuneable mud filter at the input to the system , right where you want it .

Making it in a separate box is a good decision; it puts it under the care of the designated "operator".
Having it on the mic tends to put it under the dubious responsibility of talents; it often results in switches being in the wrong setting.

 

[abbey road d enfer]

View attachment 112851

One exception doesn't make a rule.
He was also known to wield a unique guitar. And he had a unique voice.

 

[rock soderstrom]

Is it because it requires less EQ?

I know how to use an EQ and I'm not afraid of turning it if necessary. But yes, I appreciate microphones that already sound very good by themselves...that is, of course, as always a matter of taste.

Besides the top sound, the MD431 has a very good handling on stage, its off-axis behavior is great and the feedback susceptibility is lower compared to high end handheld condenser microphones.

I still have the older version, very robustly built and also versatile on other sources, even in the recording studio a top microphone.

One exception doesn't make a rule.

LOL, I would not call this an exception
I could list many, very prominent names that have been seen on tour with this microphone (and its direct relatives) in the past

The microphone was not only popular with the old heroes of the last 30 years, a quick web search revealed it is currently still in use on big stages.

Dave Grohl & Foo Fighter, Kings of Leon, PJ Harvey, Bon Iver...

 

[rock soderstrom]

BTW, I found this, I am not sure if its 100% correct.

 

[Khron]

It definitely can't be 100% correct - DR5's both sides are shorted out (and is thus made redundant). Or actually, i doubt connecting XLR pins 2 and 3 together would be very constructive either (with the vertical connection on the left side of DR5)

 

[rock soderstrom]

It definitely can't be 100% correct - DR5's both sides are shorted out (and is thus made redundant). Or actually, i doubt connecting XLR pins 2 and 3 together would be very constructive either (with the vertical connection on the left side of DR5)

Yes true, this needs to be corrected. Where is the switch/ reed relay?