Modding cheap chinese t.bone sc100II mics

  • Thread starter Thread starter Lale
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Lale

New member
Hi!

First of all, I've been checking this forum out for a while and I've got excellent information about mics and other stuff. Thank you all.
I have experience of different types of microphones already and this forum has widen my knowledge quite a bit.

This is my first topic here, so try to be gentle, thank you ;)

I got a pair of second hand cheapo chinese t.bone sc100II small diaphgram condenser microphones for 50 EUR a pair (including the wooden box, stereo boom and adapters (yes, this is called as a good deal)). I tested the mics and they sound surprisingly good already. The capsule is decent enough to put out recordings very well, I assume, and knowing that components of the circuit are definitely quite bad, I'm planning to do some modifications inside the mics.

I opened up the mics and this is how they look:

TBa.jpg


and the back side of PCB (switches are: -10dB and bass-roll-off):

TBb.jpg


So, this seems to be very common circuit and I know that I should change at least couple of capacitors to improve the sound.

First of all, C13, right after the capsule. Value is 1000pF.
1000pF polystyrene should fit there quite easily and that's not a problem in any way. So, thats going to jump in.

My problem is that circuit has a bass-roll-off and I'm not sure which capacitors I should change to make the signal path better; C3 and C4 or C14 and C15? Values for these caps are: C3, C4: 10nF and C14 and C15: 220nF.

So, i want to keep the bass-roll-off and change the capacitors without affecting the roll-off. Could someone give me advice what I should do?

I'm also heading into a problem to find decent capacitors to fit inside the microphone. Panasonic V series metallized capacitors should be ok but I'm not ableto find them anywhere (in EU) else than ordering from US. That means around 30EURs (apprx $40) for postage and handling... Any suggestions where to find them in EU? Or any suggestions for other good sounding common capacitors to fit inside the mic?

And if there's some other suggestions to improve the sound, you're welcome to tell.

I will do recordings before and after the modding and will post a link right here.

Thanks a lot in advance!

Lale, Finland
 
Sorry Lale, this is my first time to see 'In-erds' of a mic...Soooo thats what causes all that noise to travel on to bigger things :D I'm sure someone will be to your rescue very soon...Hope ya get your answers..cause I haven't a clue... :) eurt
 
Yes, this is the inner organs of one microphone. To be more specific: one microphone among great deal of other microphone designs. :)

Anyway, I figured out the bass-roll-off... Switching between the C3/C4 and C14/C15 does the bass-roll-off. Bigger value means bigger bass response. So in another words, if I want to keep the bass-roll-off and improve the quality equally, I should change all four capacitors. This does mean that I will head into problem with space. Maybe I just bypass the switch and use the mic preamp's low-cut (if needed)...makes any sense?
Or if someone knows really good tiny capacitors to fit the space provided...hints are needed.
Further, how does it affect if I put a bigger value capacitor instead of C14's and C15's 220nF? Turns the microphone more bass responsive? Where's the reasonible limit?

Also, I would like to know how much influence (sound-wise) does the input amplifier stage FET have? Is there any kind of reason to change it?
What about output stage transistors? They don't have the role worth of upgrading, right?

Lale
 
Yes, polystirene C13 will indeed make a difference. The two caps close to XLR are part of RF filters and if you don't have problems with interference you could remove them.

The "shy" bass is due to low value of C14 and C15. Find some nice film 1 Mf or higher, which would fit. Depending on their value you will need to recalculate C3 and C4 for the same roll off. Of course, they should be quality film, as well.

Where in Finland you are? I will be in Helsinki for a couple weeks mid-May, so if you ship the caps to me in US, I could bring them along.
 
Thanks Marik!

Welcome to Finland!
Really nice offer from you to bring caps with you!
I live in Tampere, two hrs away from Helsinki.
Anyway, i'm visiting Helsinki every now and then and getting them via you sounds possible.
Really really nice..

I will inform more about that later. I willl do further research to find them locally whatsoever.

What about the FET? What's the deal with it?

Lale
 
Heading to another problem with roll-off...

I found a formula to calculate the bass-roll-off frequency
( C = capacitor value, f = roll-off-frequency, Z = impedance )

f = 1 / ( 2 * pi * C * Z ) -> a bit of math and...

C = 1 / ( 2 * pi * f * Z )

Now, what is the value for Z?
Microphone impedance? ... i don't think so.
Input impedance of recording device? ... That's variable depending on a pre so...i don't think so.

Of course I could calculate the value for the impedance used if i just had the specs sheet and knew the present roll-off-frequency... but, of course, i do not have the specs. :)

I think I need some serious help here. :D

Lale
 
Well..
Here again, me answering for my own questions :rolleyes:

Bass-roll-off works with parallel capacitors! of course!
According to original values and with some maths, i'm able to get the same roll-off with 1uF parallel with 0,047uF (nearest component value available).
Simplified electronic thinking...damn.

I also checked out the sizes of panasonic "V" caps and noticed that they are not going to fit...darn
But, I did find the alternative caps which will fit: Epcos B32529. They are metallized polyester film capacitors, but I don't have any kind of idea if they are good for audio use. At least they are small enough and I'm able to order them easily.

Here's the link for PDF specs of the cap:
http://www.farnell.com/datasheets/60143.pdf

If there's someone who can say something about these caps and could give me some kind of idea why they are good or why they are not, i would be very grateful indeed.

Thanks again,

Lale
 
> What about the FET? What's the deal with it?

It should be fine--don't bother.

>Bass-roll-off works with parallel capacitors! of course!

Glad you figured it out. Just calculate the original value in paralleled operation, and then recalculate C3 C4 with a new value of C14 C15.

I am not familiar with Epcos, but usually polyesters are not in favor for audio. Try it--in any case it cannot be worse than stock ceramics.

Also, make a search here and on www.groupdiy.com forum for MXL603 mods. It seems both of them with some modifications share the same schematics, originally developed by Schoeps. You should find some discussions and also parts list (at least for USA).
 
Lale, I think you don't have to recalculate C3 and C4, just keep with the original values but try fit in polystyrene ones like this:

3358951 10 nf polystyrene 7.5 x 7.5 x 13 mm (too big?)
http://www.farnell.com/datasheets/43510.pdf

The C3 and C4 caps are on signal path all the time, C14 and C15 only when the roll-off is not used. As these caps are paralled with C3/4 when the bass roll-off is off, the total capacitance is ~1.01 uF. It may be that below the roll-off point the bass level drops a bit (at least if the 10 nF is polystyrene and the 1 uF is polyester). Parallelling caps reduces the ESR (right?) which is a good thing I think.

I'm also getting the same mics from t-mann. 135 EUR / pair. Aren't these built by Feilo (or other Shanghai co)?

-Mikko
(Tampereelta, nääs.)

Edit: the 10NF from Farnell seems to be polypropylene type after all. It should still be OK.

For the 1UF also this one would (maybe) suite:

PF tilauskoodi: 3891161

Valmistaja: EVOX RIFA

Valmistajan osanumero: SMR15 105K100B06L4 BULK

Kuvaus: CAPACITOR, 1.0UF 100V; Capacitance:1.0µF; Voltage rating, DC:100V; Capacitor dielectric type:Polyphenylene Sulphide; Tolerance, +:10%; Tolerance, -:-10%; Case style:Radial; Length / Height, external:14.5mm; Width, external:18mm; Depth, external:7.5mm;
 
Last edited:
mhelin said:
This SC100-II is propably the same microphone as Alctron HST-02A. YOu can get them cheap here:

http://www.microphonics.de/

Also the HSMC001 model seems to be the same LDC as TSM MT87 (not 100% sure though).
Click to expand...


I think with the two shockmounts and stereo bar that the SC100 II are a better deal. Thomann have an excellent returns policy too.
 
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