t. bone SC1100 aka Feilo Z3300 modding, anyone?

[Emmathom]

Yes, I agree, the S sounds are a bit more accentuated but not bad in general. The differences are smaller (in this example) than I expected. I'm looking forward to the acoustic guitar sample...

Which capsule does thomann use in the SC1100? Photo?

Yes I agree that the differences are less than expected...
The original capsule is far from being ridiculous. We'll ear more with the acoustic guitar recording.
Thank you Rock for your participation !

Edit : I am positively surprised too by the quality of the SC400 installed in the 6AK5

 

[soliloqueen]

this is vain but god the flat k47 is a good-sounding capsule. i always forget how good my capsules are in between people posting audio examples.

 

[Emmathom]

Acoustic guitar recorded in addition to previously recorded voices.
Same configuration : original circuits in both mics / one with original caps. / one with Arienne K47flat caps.

I used this time a XR18 audio card in where you can set & visualize the input gain in dB (more precise than a potentiometer position!). The gain has been set to +27dB for original caps. and +33dB for Ari47, so a 6dB difference of sensivity .

Files recorded and available in 24-48
SC1100 guitar Arienne K47F caps
SC1100 guitar original caps

Here, with acoustic guitar, the sound difference is more prononced than with voice and to the advantage of Arienne K47. The sound is softer, rounder, more suitable to strings highs. The mediums are very nice. The winner is no doubt the Arienne capsule

 

[kingkorg]

Late to the party. Has anyone actually measured the transformer ratio? Most of these mics have reported 2:1 range ratio, but whenever i got one of these ST51, MXL2001... type mics in my hands, the actual transformer ratio was 5:1 or 6:1.

 

[Emmathom]

Late to the party. Has anyone actually measured the transformer ratio? Most of these mics have reported 2:1 range ratio, but whenever i got one of these ST51, MXL2001... type mics in my hands, the actual transformer ratio was 5:1 or 6:1.

In my SC1100 pair one transformer was out-of-order so I decided to replace both to keep the same "color".
The original was wired in 1,75:1 ratio
I installed Monacor LTR-110 which are wired in 2:1 ratio
I don't know for ST51, MXL...

 

[rock soderstrom]

Here, with acoustic guitar, the sound difference is more prononced than with voice and to the advantage of Arienne K47. The sound is softer, rounder, more suitable to strings highs. The mediums are very nice. The winner is no doubt the Arienne capsule

+1

 

[Emmathom]

Guys,

I followed @thor.zmt instructions, and with some little adjustements on the way, I'm very pleased with the result !
- no low frequencies "rumble" (but with the heartbit test - a piece of clothe pulled in front of the mic - the mic catches down to 10Hz)
- circuit is stable (not oscillating)
- more than enough gain !
- clean sound on a large frequency response
- pad with 33pF in // with 10pF maybe a bit too much... (will try with 22pF one of these days)

A great success !
Let's mod the second one...

 

[thor.zmt]

Guys,

I followed @thor.zmt instructions, and with some little adjustements on the way, I'm very pleased with the result !
- no low frequencies "rumble" (but with the heartbit test - a piece of clothe pulled in front of the mic - the mic catches down to 10Hz)
- circuit is stable (not oscillating)
- more than enough gain !
- clean sound on a large frequency response
- pad with 33pF in // with 10pF maybe a bit too much... (will try with 22pF one of these days)

A great success !
Let's mod the second one...

Please show the key changes that made the circuit stable (the original one will show VLF oscillation).

On paper at least the gain stage does ~60dB open loop gain with a closed loop gain of ~16dB (10dB with 2:1 stepdown transformer), so some 44dB negative feedback are used, switch in the pad and the feedback is up to 56dB.

The pad is meant for close miking very loud sources.

Thor

 

[Emmathom]

Here the t.bone SC1100 circuits modified by @thor.zmt :
- first version was oscillating and there was a low-sub frequencies rumble (10Hz ~ 50Hz)
- validated version

Corrections :
- the 470uF "-" which was originally connected to 4,7uF output coupling cap input is now connected to its output
- the 22uF K170 source bypass cap is reduced to 1uF (MKP)

 

[Voyager10]

Taking the negative feedback (10pF/33pF caps) from the far side of the 4.7uF output capacitor will give an extra phase shift at low frequencies. Could this be the source of the instability?

 

[Emmathom]

Hi @Voyager10 in practice they are only ~1cm apart (the board is very small you know) and connected by cooper-silver 26AWG PTFE
After testing under the aegis @thor.zmt we found that it was the K170 source byp. capa which is the problem. We reduced from 22uF to 1uf but on one board I took it off and no more rumble

 

[Emmathom]

Last input about SC1100 mods :
The K170 source bypass cap brings rumble. whatever 22uF or even 1uF. So I took it off.
@thor.zmt says it lowers the open loop gain a bit and may bring noise : the gain is ok without this cap and the noise seems ok too (at a decent input gain level / about 40% of the pot course or 10:30am if 0% is 7am and 100% 7pm)
Speaking normally at 30cm from the mic I get -7,5dB in my DAW with gain pot set to 10:30am (I hope it's clear )
Hard to listen to noise without a dedicated damped room (I did quick tests in my house...)

So the last schem attached

 

[Voyager10]

Hi @Voyager10 in practice they are only ~1cm apart (the board is very small you know) and connected by cooper-silver 26AWG PTFE

This isn't a problem with the layout, the (possible) issue I was raising is that the 4.7uF capacitor and the transformer primary create a high-pass filter, which is being included in the negative feedback loop. The filter means phase shift (at lower frequencies) and this might lead to instability.

Anyway, lowering the open-loop gain (by removing the bypass capacitor) will also help fix instability, so if it's working OK now, there's no need to meddle further.

 

[Emmathom]

Ok @Voyager10 , thanks for your explanations... Do you see another way to get rid of this rumble without removing the bypass cap ?

 

[Voyager10]

You could try connecting the feedback and bootstrap capacitors (the 10pF, 33pF and 470uF) to the other side of the 4u7 output cap (i.e. to the BC559's emitter).

 

[Emmathom]

You could try connecting the feedback and bootstrap capacitors (the 10pF, 33pF and 470uF) to the other side of the 4u7 output cap (i.e. to the BC559's emitter).

If I remember well that was the first schematic and it oscillated (voltages were moving without stabilize...)

Edit : only 470uF was connected to BC559's emitter...

 

[Emmathom]

You could try connecting the feedback and bootstrap capacitors (the 10pF, 33pF and 470uF) to the other side of the 4u7 output cap (i.e. to the BC559's emitter).

I tried with morning 1nF FKP2 between capsule and K170 gate : less less breath and a level lost about 7,5dB (but the mic has still more than enough output level)
Now I will try with a silver mica...
Stay tuned

Edit: I just replaced the FKP2 with silver mica > it's night and day!!!
I'm back with the gain of the microphone without the 1nF / a brighter, sexier sound / no particular breath
it's amazing...

The last schem.

Next step : exchanging original capsules with Arienne K47 flat...

 

[damien]

I have a SC1100 from the early batch. Around 2004 If I recall. And they are really good I use it on acoustic guitar, for certain type of vocals and in front of the kick drum to have the full sound from a LDC.
Mine is a bit beaten and has some patina, it's vintage (20y.o) after all but I wouldn't take the chance to modify it since it's good from the get go.

Do you know if they changed the components and capsule in the SC-1100 over time?

 

[Emmathom]

Do you know if they changed the components and capsule in the SC-1100 over time?

Good question... I don't think so but the "t.bone specialist" @micolas could certainly answer !
There are two versions : the first one with golden logo and the recent one with white logo.

Why don't you post pictures of your boards and capsule ?
Here are mine

 

[rock soderstrom]

Why don't you post pictures of your boards and capsule ?
Here are mine

+1
Photos of the capsules are best placed in the photo collection thread, then they are all in one place and can be easily found again *(If the capsules vary over time)