t.Bone SC 450 (MXL2001) Mod

[Nen'O]

Hello,
Is there anyone here who already modded t.Bone SC 450 microphone?
I got a used pair cheap, where should I start mod from?
I find mic sound thin, narrow and lifless.
Beside recapping it would it be good move to replace transformer with Lundhal 1968 transformer?


This mic is very similar to MXL 2001 and many other same rebranded mics. I went through few posts here and got few ideas but it would be nice to get direct advice from someone who already did mod.

Thanks

 

[LevinGuitar]

Do you saw this thread? I found interesting ideas in Matador's schematic, still haven't tried yet.

https://groupdiy.com/threads/mxl-microphone-circuit-simulation-how-to-simulate-the-capsule.58727/

 

[mhelin]

SC 450 is pretty good mic as it is, the first stage is copied from U87. However, you could replace the FET with 2N3819 (same as U87), increase the 220pf feedback capacitor to 470 - 680 pF and maybe remove the 1nF cap and 1G resistor by connecting the capsule directly to the FET gate. Also replace the 4u7 output cap with a better one. Then you might try finding a better capsule like TSC-2 or similar. You could also add a DC/DC converter to get a little higher output (use polarization voltage of 60-70V). You could also remove the PNP stage and use U87 type transformer (T13, 9.5:1 or so). Anyway, the sound of U87 type microphones is like that you describe if you compare it to tube mics, but it will make things to glue better in mix. If you are after tube mic sound modding that mic doesn't help you.

 

[kingkorg]

If you are after tube mic sound modding that mic doesn't help you.

One 'trick' i do sometimes is to increase THD by biasing the FET slightly off, to get some more harmonics and emulate some tube harmonics. Not all tube magic is in THD but i get nice results. No need to "upgrade" the stock transformer in that mic.

 

[RuudNL]

Often I get the impression that people 'upgrade' their microphone only for the sake of upgrading...
To find that after a lot of trouble and spending money, the 'modded' microphone sounds exactly the same as before. (Exceptions are possible, of course.) Personally I don't believe in 'better' capacitors for example, I never heard any difference.

 

[Nen'O]

Hi All,
Thanks for your replies.



I don't have that much experience with mic modding but the mod I did on Apex 460 turned that mic into much much better microphone and it wasn't that expensive mod considering how good and useful mic is now.

SC450 is my second mod, I did little voice comparison of stock mic with some other transformer based mics. Se Electronics 2200 E, Sontronics STC - 2, Neumann U87. SC450 really sounds like it needs some help, nothing like other transformer based mics or even my all time fav tranformeless AT4040.

This is advices I got from old cat Dave.

R7 in the MXL2001 can remain the same but R6 can also be optimized with a 5K pot. Somewhere around 2.2K to 2.7K will optimize the gain structure.

I usually change C8 to a 22ufd/35v tantalum.

This way any resonance between the inductance of the output transformer and C8 falls into the sub-sonics below the audio range.

Plus
C2 470p Styroflex
C3 820p Styroflex


I'll start from here and leave rest as it is. If mic needs new capsule i'll go with Mhelin advice, TSC-2 sounds like a good choice..


@mhelin do you know how can add omni option to this mic?

@kingkorg I'll try your trick with biasing the FET.....you saved me some $$. I'll stay with stock transformer

@RuudNL got your point, I'll keep number$ as low as posible...lets hope for the best
as for better capacitors case, former AKG engineer once told me..people read numbers and not hearing.

Cheers
N

 

[Icantthinkofaname]

Often I get the impression that people 'upgrade' their microphone only for the sake of upgrading...
To find that after a lot of trouble and spending money, the 'modded' microphone sounds exactly the same as before. (Exceptions are possible, of course.) Personally I don't believe in 'better' capacitors for example, I never heard any difference.

But the internet gurus say ceramic capacitors are microphonic so you have to use film capacitors or Google and the CIA will spy on you! /s

 

[mhelin]

@mhelin do you know how can add omni option to this mic?

Use a switch to connect the back and front diaphragms. It may be difficult to install one though, you could reuse the low cut switch though. At least on my SC450 there is a place for extra HPF @ 100 Hz push button switch on the PCB (but you have to open the mic to switch it on/off). Don't know how to wire it though.

 

[Nen'O]

Hi thanks,
Think it's the same mic, mine has 100Hz - 6DB marked on PCB but I really don't care that much about low cut.
Turning low cut into omni/cardiod switch sounds like brilliant idea.
Do you know how to do it?
Guess I need to connect the rear diaphragm wire through low cut switch to ground to get OMNI and when the switch lifts the rear diaphragm off ground to get Cardiod?

 

[kingkorg]

Be extremely careful how you do it. It needs to be clean job. Any residue, bad contacts, long dangling wires might introduce noise, microphonics.... Try to do befofe/after takes under exact same conditions to compare the noise level. The addition of omni might cause more harm than benefit. Omni response with most LDC is usually mediocre, maybe check how it sounds before making the permanen mod by just connecting back and front diaphragms. I tend to use these extra switches to change level of de-emphasis curves/levels/shapes.

 

[mhelin]

I haven't added omni switches either or built multipattern mics (and actually removed such features from mics modded for friends). Once I considered using a reed relay with an external magnet, that could be wired quite cleanly, but it has to be fixed somehow to the body (using B8000 glue or something).

 

[xeawr]

I have modded a number of these, as they were dirt cheap (at least a couple of years back) and the first one turned out alright, nothing special though. The one I did after that turned out to be a wonderful sounding mic. Seems like the capsule was already decent and the small mods I did really took it to another level. It was one of the few experiences where I noticed how much different components shape the sound of a mic.

I replaced all caps in the signal path. For convenience (aka "simplification") I removed the low cut and pad switches. Cleaned everything really well and then - I'm almost too afraid to admit - in subsequent blind tests, I picked it instead of my U87 a number of times.

Use PP or Styroflex caps wherever you can. However I chose cap types according to the place in the circuit (Styroflex are being recommended as coupling caps for example - although I used a 820p MKP cap in this one). I also tweaked the values to bring the sound closer to a U87Ai (680pF if I remember correctly for C3 - HF roll off...).

I'm really allergic to the look of these mics though... the head basket shape gives me headaches by just thinking about it.

Good luck!

 

[xeawr]

also what kingkorg says. Record before and after modding. Also don't forget to record silence to compare before and after modding noise levels.

I just noticed you wrote you had two. If they are similar (enough) in sound, you can use an unmodded one for reference. Do before and after recordings ANYWAY .

All the best!

 

[Icantthinkofaname]

I'd take a look at the internals of the t.bone SC460 if you can find pictures of one, or a schematic, because it actually does have a cardioid/omni switch. But you'll also need a dual diaphragm capsule since omni on an LDC is cardioid+cardoid. Omni also isn't great on an LDC. It's usable but it's not completely non-directional if that's what you think you'll be getting. I wouldn't do something like mic a group with an multipattern LDC in omni because I find the sides suffer a bit. I haven't done any sort of scientific testing, just speaking into my multipattern mics on omni from different angles, and it happens on my AT4050, CAD M179s, iSK BM-600, Behringer B2 Pro, and my C414 B-ULS. Maybe it's better at a distance but close miking I don't really care for dual diaphragm omni or hypercardioid.

 

[Nen'O]

Hi all,

Recapping went smooth and without problems. I decided to keep all tantalum caps and only replace ceramic caps with styroflex and film.
Swapping R6 resistor with 5k potentiometer As a Variable Resistor didn't work out.
Can someone educate me how to do it? How to fit pot. in place of resistor?

Thanks

 

[xeawr]

is that 5k pot for re-biasing? Skip that for now. Solder the original resistor back in and compare to the before sound. Also, some caps need time, before they sound right. Be sure to use the mic for a while, or at least leave it turned (I didn't believe this until I almost sent a new mic back as "faulty" because of this phenomenon. It sounded pretty normal after an hour or two IIRC).

Go slow. Change one cap at a time and record again, listen to what changed. This doesn't only train your modding, but also your hearing skills!

Cheers!

 

[analogguru]

Also, some caps need time, before they sound right.

What ? Please elaborate....

 

[Nen'O]

is that 5k pot for re-biasing? Skip that for now. Solder the original resistor back in and compare to the before sound. Also, some caps need time, before they sound right. Be sure to use the mic for a while, or at least leave it turned (I didn't believe this until I almost sent a new mic back as "faulty" because of this phenomenon. It sounded pretty normal after an hour or two IIRC).

Go slow. Change one cap at a time and record again, listen to what changed. This doesn't only train your modding, but also your hearing skills!

Cheers!

Hi,
Thanks for the advices.

Actually I did put mic back and test against un-modded mic after changing each cap.
C 8 did the most heavy lifting, I kept there tantalum as it was in stock mic and changed it from 4.7mf to 22mf 35v.
It did help with tightening up the low end. It's possible that it filtered out low rumble capsule was picking from mic's shell resonance. Before changing C8 just tapping on mic shell caused sustained doooinnng sound, with new cap tapping on mic shell sounds lot more acceptable short thump sound.
Here is the list of new caps
C2 - 440p 100V Styroflex
C3 - 680p 400v Styrpflex
C5 - .47mf 100v MKS
C8 - 22mf Tantalum

Rest caps are tantalum or film stock.

Still, I'd really appreciate if someone jump in and explain me how to solder 5k pot in the place of resistor. I tried with vertical trimm pot but legs just won't fit in those holes and trying to somehow extend it with the wire and solder it didn't worked out, too.

I'll take your advice and leave mics connected to burn in, it's something I usually do with tube gear.

Cheers

 

[Tubetec]

Try connecting the pot as a rheostat , connect wiper and the grounded end together and the other terminal to where the upper end of the resistor was , if theres DC at that point it may be noisey when you move the control , best just use the pot to find the sweet spot then replace with the nearest standard value .

 

[xeawr]

What ? Please elaborate....

Here's the story. I once received a mic, went to the control room and hooked it up in a free minute. The highs were muffled, the bass was boomy. In fact I checked if I talked into it off-axis (cardioid only mic). Nope, everything was correct, except it sounded horrible. So I immediately contacted the seller and said that maybe I received a faulty mic (I couldn't believe it was supposed to sound like this). I agreed to test it again and I left it hooked up in the control room in a corner somewhere, while working on other projects. I checked after a couple of mins and didn't notice that bass heavy sound. The next time I checked (might have been 3-4hours later), it sounded totally different - when compared to the first test, it sounded like a entirely different microphone. I was like "what?".

I kinda mentally put it aside for the moment until I stumbled across a thread where someone noticed, that it is quite normal that caps can change their sound in the first couple of minutes/hours, if they're new. Another guy commented and said that in his build the "bass was overwhelming at first" (I'm paraphrasing) which correlates precisely with my experience.

By now I own a number of mics of this kind and they all sound very very similar (think 'Neumann tolerances'). So this is clearly not due to a faulty mic (that miraculously 'healed').

I think we all now and agree that a tube sounds different after it has been used for a long time. So, generally speaking, there is such a phenomenon. However I think it's utter BS when (hifi) people claim that their cables, or other technical devices need to break in, etc. etc.
Fet equipment to me is pretty much, "turn on", "let it warm up for a couple of minutes", use it. I never noticed sound changing after hours of use.

There has always been a thin line between ingenuity and illusion.