Shure 52A - Rebirth (mod)

Transmutant

Transmutant

New member
Hello!

I was annoyed how you can only use this mic for so few things. I could not find pictures of one fully opened so I thought what the hell. You can always buy new if it's destroyed? Right. ;)

The inner circuit was fairly simple. A chain on components was connected parallel to the capsule signal. 15mH choke, 22ohm resistor and two 22uf condensers. This circuit creates a (around) 390Hz dip. Something you would do to the sound in the mix. The thing is, it's not always the frequency that needs to be cut. It all depends on the size of the kick drum and the thickness of the shell. Besides you could use this high SPL mic for other things too. The preset EQ just makes it harder to use.

Disconnect any component from the chain and the preset EQ is bypassed. I drilled/carved/filed a hole in the back and installed a switch between the choke and R1 so you I can do A/B comparison. The resistor was the easiest to work with because the legs can be lifted up.

The leads from the capsule were really thin and long. I decided to shorten those too while I was at it.

I created an album with pics. Go check it out.
 
In your circuit, you show the two capacitors connected together back to back? You'd normally connect them like batteries + to -, then + to - again, rather than as a block? Are you certain this is how they are wired on that PCB - maybe on the board they are wired in parallel, and you couldn't see the track? This would shift the centre frequency down an octave or so?
 
I added 2 more pics to my album so you can see for yourself. Those condensers are connected together to create an unpolarized capacitor. Otherwise there could be nothing going trough and having just one condensers would do nothing. It would probably break. I asked someone who knows better and he said it's common to make unpolarized out of polarized. Has nothing to do with frequency shifting.
 
It's fair to say using reversed electrolytics is not rare - they pop up in crossovers and in opamp tone control circuits, just the fairly high value made me wonder if there was a chance they're not wired quite as per the diagram? It was the centre frequency that made me wonder - it seems quite high for a designed frequency - sort of where perhaps you'd be sticking in a bit of boost for the click, leaving the thud much lower down. It has everything to do with frequency - and being polarised or not doesn't change that. Stick volts through an electrolytic and they go pop nicely, in a mic circuit they won't break.

The actual circuit, with the resistor and back to back, reverse connected electrolytics does mean the resonance calculation is a bit more complex than the simple calculator can do, so the frequencies will be different but still in the same area.

I'm not sure why Shure chose to use this configuration to produce a non-polarised electrolytic chain - there seems little point. I guess the question is what does the filter switching in and out sound like?

It's been a long time (1980) since I had resonance calculations in my exams, but drawing out the entire circuit, with the mic element connected adds too many unknown factors to produce an accurate result for the precise cut frequency, as your friend will confirm.

All I wondered was if the small PCB definitely connected them in series as shown? In my head the near 400Hz cut just seems a bit strange?
 
I work in an electronics factory and talked this through with our leading designer. I showed him the schematics and he told me all you just said and more. The two condensers connected together back to back is only half of their value (in this case 11uF). I also added a calculation of this to the image so if anyone had anything to ask there would be more in the picture than just the basic connection. I don't know so much of all this stuff so I ask around and experiment.

The around 400Hz makes sense to me. Anything else would not be usable in our hearing range. Or you might want to debate this too. They thought it's usable when they made it at Shure. Us debating is utter pointless. The math is there.

I used this to calculate the it. Type in the values and there you go.

CALCULATOR
 
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rob aylestone said:
IIt's been a long time (1980) since I had resonance calculations in my exams, but drawing out the entire circuit, with the mic element connected adds too many unknown factors to produce an accurate result for the precise cut frequency, as your friend will confirm.
Click to expand...

Don't want to sound like a dick, but maybe you should do some calculation. I am not so good at it I could do it without aid (calculator) and in this case it would not make much sense. The whole point of my post was NOT to redesign this. Just to say that there is a preset passive filter that can be removed. That's all. If you want to take this further then buy one, open it, math the hell out of it and make it better.
 
rob aylestone said:
It was the centre frequency that made me wonder - it seems quite high for a designed frequency - sort of where perhaps you'd be sticking in a bit of boost for the click, leaving the thud much lower down. It has everything to do with frequency - and being polarised or not doesn't change that. Stick volts through an electrolytic and they go pop nicely, in a mic circuit they won't break.
Click to expand...

I was thinking have you maybe mixed 400Hz and 4000Hz in your head? I mean 4K is where you'd want to boost for 'click' and secondly think about the condenser as a battery. In a way that's what it it. It is charged and then it releases the energy when it's fully changed. Right?! Now if you would charged a battery the wrong way it would break. The electrolytic condenser can take 1/3 of its typical input the wrong way without breaking. So it might break in this connection if it was alone in series with the resistor and choke. Again, we are working with AC (mic output), not DC so the condenser will be charged both ways as the polarity of the signal changes.

And I want to add... If you think something might be something or then it might not, or at least you think it might not is not a good starting point for a debate. Try it out. do your own math and prove me (and my friend) wrong. I'm a bit pissed because I thought this might be useful MOD and the first reply I get is 'I got it wrong and did not see all the connections'. Like I didn't double check. I think the only thing I got wrong was the headline and that's sorted. ;))))

Enjoy the mod. Not the math!
 
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That is NOT what I said, there's no need to be pissed - it's not worth getting upset about. It did just seem a little strange to do the design like that. It's not rare, but maybe just for production reasons if they already wanted to use that particular inductor?

I'm pretty impressed you made the filter switchable - my real interest is in the effect, what it sound like with and without. 400Hz is pretty high and wired in the other mode the notch would be lower - that was all. I wasn't criticising your ability, knowledge, friends skills - just asking a simple question. The damage notion is a bit OTT, though - microphone level simply cannot do any damage to a capacitor. DC with some current can, quite spectacularly sometimes.

So if you are for a debate - (not really sure now) do you think Shure got it right, putting in the filter - or do you prefer the sound without. 4KHz is pretty high, and I like the clicky sound in the 4-5 hundred area myself.

The calculator you linked to is ok for simple stuff, but lacks the ability to deal with the damping factor the resistor introduces - doesn't alter the centre frequency though, so difficult to predict the impact of the filter.

Could you record us a bit of with and without - that would be pretty interesting.

As I said - I really didn't mean to wind you up, and it didn't even dawn on me you'd think I was having a pop - because I really did wonder about the frequency, and parallel wiring would have dropped the notch to something I'd have probably done with eq?
 
Like I said. I like to have 400Hz in the mix. Not notch it. I want a natural THUD out of a bassdrum and preset filters is not the way to go. So I prefer the filter bypass position better. Again, it's a matter of taste. Rob, you like to boost 400Hz, I like to have it flat but as far I know most people like to cut 400Hz from everything. Because it somehow takes away room from other instruments. It's like people throw that in without looking what's already there... So I don't think Shure got it right. They are working around the frequency area that appeals to most, but to me that's part of the sound.

I always (try to) get the sound I want before mixing. Later on I EQ (and compress) the drums in buss so everything is tilted towards where the whole instrument (whole drumtrack) needs to go. Again this is just my way.

I just don't know what you were talking about having two modes. There is filter ON and filter OFF. Or maybe I just didn't understand what you meant. I don't know and can't speculate why they made it so at Shure, maybe they saw people EQing the 400Hz and thought "let's make is so it's like that before EQ". Who knows. They made it and I drew it... If you want to see just how common it is to EQ 400Hz just google "drums 400Hz".

Here's one of those links. The One Drum EQ Trick That [Almost] Always Works
 
It would be interesting - mainly because there was some talk that these mics were using a mic element that was quite like a 57, so without the filter we could hear exactly what it sounds like. I wonder if the filter could be replicated by eq, or if the addition of it does more than just notch? No panic - just something that intrigues me - because I didn't even know the mic had an internal filter!
 
400hz is a very common frequency to take out of a kick drum. I tend to get rid of some 800-900hz as well, because I like a wet kick.

The 'click' on a kick drum is around 1k, if you like the sound of the 1970's. 3k if you like 80's -90's. I generally get the attack of my kicks with a high shelf at around 8k, depending on the drum and the music...

BTW, you tend to get the best sound out of a 52 when you place it just inside the hole. When you put it all the way in the drum, you end up with that basketball sound, even if you have some absorbsion in the kick.
 
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That's the thing. I hate the baskeball sound. I usually get the best 'modern' kick sound when I add a subkick mic to the mix. But when it comes to rock songs I do prefer the 70's sound. Then it's large condenser infront of the resonant head. Listen to the Wings albums or even Zeppelin or Springsteen.
 
Transmutant said:
That's the thing. I hate the baskeball sound. I usually get the best 'modern' kick sound when I add a subkick mic to the mix. But when it comes to rock songs I do prefer the 70's sound. Then it's large condenser infront of the resonant head. Listen to the Wings albums or even Zeppelin or Springsteen.
Click to expand...

You get the basketball sound from putting the 52 inside the kick. If you put it just at the hole, it wont happen.

The basketball sound comes from all the reflections in the kick. if you put some foam or a blanket (not necessarily touching the heads) in there to absorb the reflections, it wont happen either.
 
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