Topic: 3wire batt bocx for AT943

[j.mart]

Ok, i need something to do this upcoming weekend.

Could someone help me to find the schematics to a 3-wire batt. box for a pair of AT943?

Is it the same as the AT853?

[graemecogger]

Those are the capsules in the SP-CMC-8, I believe?  If so, this should do the trick:



The ideal value for R1 depends on the caps - on my stereo pair, the ideal values vary by over 20%.  Something around 30k should be fine, though.
The values for C1 and R2 are not critical - as chosen, the capacitor will give no significant bass rolloff into any reasonable load.  R2 simply prevents the output from having a DC voltage on it prior to plugging in.

Obviously this needs to be duplicated for the 2 channels.

HTH

[poorlyconditioned]

Those are the capsules in the SP-CMC-8, I believe?  If so, this should do the trick:



The ideal value for R1 depends on the caps - on my stereo pair, the ideal values vary by over 20%.  Something around 30k should be fine, though.
The values for C1 and R2 are not critical - as chosen, the capacitor will give no significant bass rolloff into any reasonable load.  R2 simply prevents the output from having a DC voltage on it prior to plugging in.

Obviously this needs to be duplicated for the 2 channels.

HTH

+T Graeme.

That is pretty similar to what I've got at: www.cs.uwaterloo.ca/~mannr/AT853

Comments:
- I generally put a nonpolarized 2.2uF/100V for C1.  In case I plug into phantom power accidently.  (I don't know what happens if I reverse polarize an electrolytic cap C1 with 48V.  Do you know if it will survive?)
- I use a 22K resistor for R1, sometimes down to 10K if I want it to work with other caps (like AKG CK91/2/3).
- Adding and output resistor (R2) is a good idea.  I didn't think of that in my design

Keep posting circuits and gear guts folks!

  Richard

[j.mart]

f'ing sweet! It's a bit more organized and clear than the sketch i've found (by poorlyconditioned, thanks anyway!).

Tomorrow's gonna be a long day

thanks again

[j.mart]

Ah, i've heard this box could cut down up to 10db to the mic signal. Is this true? Anyone satisfied with the overall performance of these thingy's?

Greame, you don't happen to have a nice schematic for a DIY pre-amp would you?

[graemecogger]

+T Graeme.

That is pretty similar to what I've got at: www.cs.uwaterloo.ca/~mannr/AT853

Comments:
- I generally put a nonpolarized 2.2uF/100V for C1.  In case I plug into phantom power accidently.  (I don't know what happens if I reverse polarize an electrolytic cap C1 with 48V.  Do you know if it will survive?)
- I use a 22K resistor for R1, sometimes down to 10K if I want it to work with other caps (like AKG CK91/2/3).
- Adding and output resistor (R2) is a good idea.  I didn't think of that in my design

Keep posting circuits and gear guts folks!

  Richard

If you reverse polarise an electrolytic by 48V then what happens will depend on how much current the power supply can provide and how big the capacitor is.

I was once testing a large DC converter in which someone had fitted a 470uF/63V cap backwards.  Unfortunately, the supply feeding this thing could provide 50V at 60A (yes Amps, not milliAmps).  The result on switching on the converter was a loud bang, a jet of flame shooting out through the fan and a pool of acid on the workbench

On a smaller scale, I've had lower value electrolytics explode with much less than 50V in the reverse direction.  It's not too bad, but the smoke is unpleasant and it makes a bit of a mess inside the case.

For a phantom power supply, it probably can't provide much current so the results would probably be less drastic.  It's still a very bad idea, however, and the cap would be unlikely to survive for more than a few seconds!  I'd definately go for some sort of non-polarised capacitor if there's any risk of significant reverse voltage.

By the way (in case anyone is interested) varying the value of C1 is generally how the 'bass cut' battery box versions work.  The values to use depend entirely on the input impedance of the pre-amp you are driving.

[graemecogger]

Ah, i've heard this box could cut down up to 10db to the mic signal. Is this true? Anyone satisfied with the overall performance of these thingy's?

Greame, you don't happen to have a nice schematic for a DIY pre-amp would you?

The 3-wire connection should give lower distortion in general, better overload levels and a lower output impedance (better for driving long-ish cables).  It can, however, reduce the gain.  How much it reduces depends on the value of the resistor in the 'normal' battery box and the input impedance of the pre-amp.

My iRiver iHP-120, for example, provides a 2K2 pull-up resistor to allow the mics to be used without a battery box.  This value is so low that a 3-wire 9V battery box might actually give a slightly greater output!

I can post a pre-amp circuit some time soon, with a number of provisos:
- it is designed for my uses and the inevitable compromises may not be the same ones you want to make
- it will be almost the same as Richard's, with my suggested mods, from this thread:
-- http://taperssection.com/index.php?topic=57173.0
- it won't have been tested for sound quality at this stage.  Companies producing these for a living have the luxury of building prototypes and tweaking the circuit and components until they sound at their best.

[j.mart]

Ah, i've heard this box could cut down up to 10db to the mic signal. Is this true? Anyone satisfied with the overall performance of these thingy's?

Greame, you don't happen to have a nice schematic for a DIY pre-amp would you?

The 3-wire connection should give lower distortion in general, better overload levels and a lower output impedance (better for driving long-ish cables).  It can, however, reduce the gain.  How much it reduces depends on the value of the resistor in the 'normal' battery box and the input impedance of the pre-amp.

My iRiver iHP-120, for example, provides a 2K2 pull-up resistor to allow the mics to be used without a battery box.  This value is so low that a 3-wire 9V battery box might actually give a slightly greater output!

I can post a pre-amp circuit some time soon, with a number of provisos:
- it is designed for my uses and the inevitable compromises may not be the same ones you want to make
- it will be almost the same as Richard's, with my suggested mods, from this thread:
-- http://taperssection.com/index.php?topic=57173.0
- it won't have been tested for sound quality at this stage.  Companies producing these for a living have the luxury of building prototypes and tweaking the circuit and components until they sound at their best.

Hey, i'm really not demanding any work by you! I tought you found a schem for that batt and posted it here. You've been helpful enough for today

[j.mart]

Checked that http://taperssection.com/index.php?topic=57173.0 ... Seems hard to do as hell, and it's not a job for me... Guess i'll have to give away some $ for a pre-amp

Thanks

[poorlyconditioned]

Checked that http://taperssection.com/index.php?topic=57173.0 ... Seems hard to do as hell, and it's not a job for me... Guess i'll have to give away some $ for a pre-amp

Thanks

Believe it or not, the hardest part of all this DIY is mechanical.  Fitting all those parts in a very small area, soldering to tiny surface mount packages, getting secure connectors and battery holders, etc.  Most of the time I just kludge stuff, using existing cases, a dremmel tool, hot melt glue and shrink wrap.

At some point I should team up with a mechanical person and it could probably turn out a lot nicer.

  Richard

[j.mart]

Checked that http://taperssection.com/index.php?topic=57173.0 ... Seems hard to do as hell, and it's not a job for me... Guess i'll have to give away some $ for a pre-amp

Thanks

Believe it or not, the hardest part of all this DIY is mechanical.  Fitting all those parts in a very small area, soldering to tiny surface mount packages, getting secure connectors and battery holders, etc.  Most of the time I just kludge stuff, using existing cases, a dremmel tool, hot melt glue and shrink wrap.

At some point I should team up with a mechanical person and it could probably turn out a lot nicer.

  Richard

I still have to browse the boxes-o-junk that i have in my garage, and i know that i don't have many stuff to complete the pre-amp... But the pics of your pre-amp are REALLY intimidating.

One thing's for sure... I'm gonna need help

[lordbelial]

ARGH!

So many projects to build up...

I guess in a couple of weeks I'll be able of building all the stuff i want to build, and then, I'll post the results...

Nice jobs and +T for all.

[cybermansrev]

I can post a pre-amp circuit some time soon, with a number of provisos:
- it is designed for my uses and the inevitable compromises may not be the same ones you want to make
- it will be almost the same as Richard's, with my suggested mods, from this thread:
-- http://taperssection.com/index.php?topic=57173.0
- it won't have been tested for sound quality at this stage.  Companies producing these for a living have the luxury of building prototypes and tweaking the circuit and components until they sound at their best.

If you have time please do post your schematic for a preamp, it's always nice to see potential projects.

[Zaphod]

So what exactly is the benefit of running a three wire battery box, instead of a standard Soundpro type battery box?

[j.mart]

So what exactly is the benefit of running a three wire battery box, instead of a standard Soundpro type battery box?

Higher SPL handling