Topic: DIY Built in -20db attenuator in BBOX?

[lordbelial]

Hi have a DIY request from a friend, he wants a specific Bbox designed for DPA4061 but he wants to run into mic-in on his PCM-M1 Dat.

After discussing that point, I think he needs some attenuators at the mic-in input, and I thought I could build some attenuator in this DIY DPA bbox:



I've reading this article: http://www.uneeda-audio.com/pads/ but I cannot figure out which could be the perfect solution in order to build the attenuator in the BBox.

Maybe adding a solution like this (paging: http://www.epanorama.net/circuits/line_to_mic.html)

20 dB PAD for line to electret microphone input

This circuit is designed to interface consumer (-10 dBu) signals to microphone input that is designed for two-were electret microphone capsules. This circuit provides around 20 dB of signal attenuation (typically enough to make thigns work, if more attenuation is needed use higher R1 value) and blocks the DC bias used in the electret microphone input to get to the line signal side (C1 does this). This circuit look like around 1 kohm signal source to at the mic side, whic matches pretty well to electret capsule characteristics (similar impedance and provides DC path for bias to go to ground).

                 C1
+Line level in --||----R1-----.-- +Mic level output
                       +              |
                                       |
                         .----R2---.
                         |
Ground (input)----+--------------- Ground (output)


R2 = 1 kohm
R1 = 10 kohm
C1 = 10 uF

Any help will be appreciated.

Thanks!

[rowjimmytour]

here ya go:
http://www.uneeda-audio.com/pads/
http://ca.geocities.com/dkleined@rogers.com/audio/PassiveAttenuatorBox.htm

[Sunday Driver]

here ya go:
http://www.uneeda-audio.com/pads/
http://ca.geocities.com/dkleined@rogers.com/audio/PassiveAttenuatorBox.htm

Great links, thanks!

[lordbelial]

here ya go:
http://www.uneeda-audio.com/pads/
http://ca.geocities.com/dkleined@rogers.com/audio/PassiveAttenuatorBox.htm

Thanks for the info.

Tomorrow I'll work in some design/draft and I'll post it so all the DIY'ers can tell me if the design is good or not.

[illconditioned]

Hi have a DIY request from a friend, he wants a specific Bbox designed for DPA4061 but he wants to run into mic-in on his PCM-M1 Dat.

After discussing that point, I think he needs some attenuators at the mic-in input, and I thought I could build some attenuator in this DIY DPA bbox:



I've reading this article: http://www.uneeda-audio.com/pads/ but I cannot figure out which could be the perfect solution in order to build the attenuator in the BBox.

Maybe adding a solution like this (paging: http://www.epanorama.net/circuits/line_to_mic.html)

20 dB PAD for line to electret microphone input

This circuit is designed to interface consumer (-10 dBu) signals to microphone input that is designed for two-were electret microphone capsules. This circuit provides around 20 dB of signal attenuation (typically enough to make thigns work, if more attenuation is needed use higher R1 value) and blocks the DC bias used in the electret microphone input to get to the line signal side (C1 does this). This circuit look like around 1 kohm signal source to at the mic side, whic matches pretty well to electret capsule characteristics (similar impedance and provides DC path for bias to go to ground).

                 C1
+Line level in --||----R1-----.-- +Mic level output
                       +              |
                                       |
                         .----R2---.
                         |
Ground (input)----+--------------- Ground (output)


R2 = 1 kohm
R1 = 10 kohm
C1 = 10 uF

Any help will be appreciated.

Thanks!

Yes, that is correct.  Replace the 100k resistor above by the 10k + 1k.  That will give you (approx.) -20dB attenuation.

  Richard

[lordbelial]

Hi have a DIY request from a friend, he wants a specific Bbox designed for DPA4061 but he wants to run into mic-in on his PCM-M1 Dat.

After discussing that point, I think he needs some attenuators at the mic-in input, and I thought I could build some attenuator in this DIY DPA bbox:



I've reading this article: http://www.uneeda-audio.com/pads/ but I cannot figure out which could be the perfect solution in order to build the attenuator in the BBox.

Maybe adding a solution like this (paging: http://www.epanorama.net/circuits/line_to_mic.html)

20 dB PAD for line to electret microphone input

This circuit is designed to interface consumer (-10 dBu) signals to microphone input that is designed for two-were electret microphone capsules. This circuit provides around 20 dB of signal attenuation (typically enough to make thigns work, if more attenuation is needed use higher R1 value) and blocks the DC bias used in the electret microphone input to get to the line signal side (C1 does this). This circuit look like around 1 kohm signal source to at the mic side, whic matches pretty well to electret capsule characteristics (similar impedance and provides DC path for bias to go to ground).

                 C1
+Line level in --||----R1-----.-- +Mic level output
                       +              |
                                       |
                         .----R2---.
                         |
Ground (input)----+--------------- Ground (output)


R2 = 1 kohm
R1 = 10 kohm
C1 = 10 uF

Any help will be appreciated.

Thanks!

Yes, that is correct.  Replace the 100k resistor above by the 10k + 1k.  That will give you (approx.) -20dB attenuation.

  Richard

Thanks Richard,

Your help is always appreciatted. I'll take advantatge for asking you some other question. Since this BB+Attenuator box is going to be designed especifically for the mic input of a PCM-M1, I guess i should re-calculate the capacitor value for the mic-in impedance (4,7K)? Or this value should be OK?

[illconditioned]

Yes, you can recompute the capacitor value, but 10uF should be fine for many inputs.  You could probably get away with a much smaller cap (2.2uF or even 1.0uF) in some applications.

  Richard

[lordbelial]

Just worked on the schematic.

You can find it attached in this reply, just let me know if there's something that looks weird...

Thanks.

The schematic was removed for editing. Find it below.

[illconditioned]

Just worked on the schematic.

You can find it attached in this reply, just let me know if there's something that looks weird...

Thanks.

I think the polarity of the capacitor is wrong.  Flip it over.

I'm also thinking you probably don't need all of -20dB attenuation.  Try something like -10dB or so.  See whatever you need to run your recorder at a very low mic gain, but don't overload.  Try increasing the 1k resistor to 2.2k, or even 4.7k and see if that is enough attenuation.  No point attenuating so much that you need to introduce preamp noise from the mic input on your recorder.

  Richard

[lordbelial]

Just worked on the schematic.

You can find it attached in this reply, just let me know if there's something that looks weird...

Thanks.

I think the polarity of the capacitor is wrong.  Flip it over.

I'm also thinking you probably don't need all of -20dB attenuation.  Try something like -10dB or so.  See whatever you need to run your recorder at a very low mic gain, but don't overload.  Try increasing the 1k resistor to 2.2k, or even 4.7k and see if that is enough attenuation.  No point attenuating so much that you need to introduce preamp noise from the mic input on your recorder.

  Richard

thanks Richard,

I think That I'll try something like -10db attenuation (4,7K resistor). That makers 20 log10 (14,7/4,7) = 9,90 db of attenuation more or less...

I've posted the "definitive" design on this post.

[aegert]

+t For effort... Nice...

Any Idea how long the battery will power 2 4060's?

As for the pad on those 4061's way up font you could need the 15db fer sure.. Using a dip switch or jumper with 3 precision resistors will give you select ability...

Thanks Again!
A

[lordbelial]

+t For effort... Nice...

Any Idea how long the battery will power 2 4060's?

As for the pad on those 4061's way up font you could need the 15db fer sure.. Using a dip switch or jumper with 3 precision resistors will give you select ability...

Thanks Again!
A

Thanks! Well, All I did was mixing two concepts. the original DPA schematic was found here in the TS forum, but I cannot remember which thread or section. The gif was lying around in my computer.

The selector switch is a feature I was thinking about. It could be nice to have external selection of the attenuation (0db, -10db, -20db). Hopefully I could work on the design and assembly along this week... Pictures on the way.

regarding the battery life time... I assume it will give MANY hours.