Mic Pre Front-End PCB
- Thread starter Rochey
- Start date
Help Support GroupDIY Audio Forum:
thats a low blow dude 
I have a day off tommorrow from work, I'll be working on my backlog of products for the online shop.
More details soon.
I have a day off tommorrow from work, I'll be working on my backlog of products for the online shop.
More details soon.
Ptownkid
Well-known member
Hey roch, i'm good with what you left on my messenger.
cheers
cheers
[quote author="flaheu"]
These stuff are exactly what I need.
I would like to make them myself, would you mind sharing the eagle files ?
[/quote]
Flaheu,
Graphics of the schematics and the layout are open source for private use only. They can be found at: http://www.tendolla.com/designgallery/main.php/v/frontend/schematic.png.html
They are double sided PCB's, which doesn't make them terribly simple to DIY at home with copper boards.
Completed PCB's will be available soon. Bare PCB's should be available from the www.expataudio.com website, and kits with all the components and the pcb should become available through another forum member :grin:
Thanks again for taking interest.
/R
These stuff are exactly what I need.
I would like to make them myself, would you mind sharing the eagle files ?
[/quote]
Flaheu,
Graphics of the schematics and the layout are open source for private use only. They can be found at: http://www.tendolla.com/designgallery/main.php/v/frontend/schematic.png.html
They are double sided PCB's, which doesn't make them terribly simple to DIY at home with copper boards.
Completed PCB's will be available soon. Bare PCB's should be available from the www.expataudio.com website, and kits with all the components and the pcb should become available through another forum member :grin:
Thanks again for taking interest.
/R
codered
Well-known member
Rochey,
I was wondering if you've looked at the Digi pres.I believe we can control gain etc from PT and the implementation is through MIDI.It'll be a really great thing if we could have this feature.
I was wondering if you've looked at the Digi pres.I believe we can control gain etc from PT and the implementation is through MIDI.It'll be a really great thing if we could have this feature.
Hello Codered -- you make a good point.
I believe you could control these mic pre's from a midi-source, but you'd need to implement it through the midibox.org system. (I wouldn't know where to start I'm afraid)
Essentially, these boards will take a small logic voltage (3.3V or 5V) and use it to switch the relays.
The Mic Pre itself will come after this board.
/R
I believe you could control these mic pre's from a midi-source, but you'd need to implement it through the midibox.org system. (I wouldn't know where to start I'm afraid)
Essentially, these boards will take a small logic voltage (3.3V or 5V) and use it to switch the relays.
The Mic Pre itself will come after this board.
/R
Just an update for you folks,
Prototypes of these boards have now been ordered, and will be released under the expat audio brand soon.
The last revision was made and uploaded in png form to:
http://www.tendolla.com/designgallery/main.php/v/frontend/
a few snippets of changes have been made here and there, and discussed between Keith and I.
Stay tuned for more details
Prototypes of these boards have now been ordered, and will be released under the expat audio brand soon.
The last revision was made and uploaded in png form to:
http://www.tendolla.com/designgallery/main.php/v/frontend/
a few snippets of changes have been made here and there, and discussed between Keith and I.
Stay tuned for more details
Proto's are back.
They look sweet, and I've started populating the boards.
I also made my own DIY lightbox this weekend, and took a picture with my cheapie canon "point'n'click" camera.
They look sweet, and I've started populating the boards.
I also made my own DIY lightbox this weekend, and took a picture with my cheapie canon "point'n'click" camera.
I'm sorry to say this design has more flaws than merits. I hope you have fixed the phantom switch that actually shorts the 48 v rail to ground.
But the main problem is that almost everytime, actuating a switch will create a loud click and may even destroy the input stage. This is because none of the switches is galvanically connected to a reference point. If you have phantom on the input, one of the set of input caps will be polarized and reach a state of equilibrium, but the set of caps that is not used will be left floatin with any stray voltage is left in them. When you switch them, you will send 48 volt common mode on the input stage -guaranteed to move your speaker cones right through the room.
But the main problem is that almost everytime, actuating a switch will create a loud click and may even destroy the input stage. This is because none of the switches is galvanically connected to a reference point. If you have phantom on the input, one of the set of input caps will be polarized and reach a state of equilibrium, but the set of caps that is not used will be left floatin with any stray voltage is left in them. When you switch them, you will send 48 volt common mode on the input stage -guaranteed to move your speaker cones right through the room.
[quote author="abbey road d enfer"]I hope you have fixed the phantom switch that actually shorts the 48 v rail to ground.[/quote]
[quote author="abbey road d enfer"]
If you have phantom on the input, one of the set of input caps will be polarized and reach a state of equilibrium, but the set of caps that is not used will be left floatin with any stray voltage is left in them. When you switch them, you will send 48 volt common mode on the input stage -guaranteed to move your speaker cones right through the room.[/quote]
Thats a really *really* good point. Keith and I discussed that this morning, and plan to put in a "bleed" resistor to discharge those caps over time (a few seconds or so). It's value will most likely be in the 100K or so region, so it shouldn't affect the audio too much, but just give a discharge path for the capacitor.
Stay tuned, and THANK YOU for the feedback.
/R
[quote author="abbey road d enfer"]
If you have phantom on the input, one of the set of input caps will be polarized and reach a state of equilibrium, but the set of caps that is not used will be left floatin with any stray voltage is left in them. When you switch them, you will send 48 volt common mode on the input stage -guaranteed to move your speaker cones right through the room.[/quote]
Thats a really *really* good point. Keith and I discussed that this morning, and plan to put in a "bleed" resistor to discharge those caps over time (a few seconds or so). It's value will most likely be in the 100K or so region, so it shouldn't affect the audio too much, but just give a discharge path for the capacitor.
Stay tuned, and THANK YOU for the feedback.
/R
Ptownkid
Well-known member
and this is why i love this place...especially when people are receptive to constructive criticism.
Rock on.
Rock on.
hello folks,
a quick change later - the high-pass filter has been removed. Both Keith and I came to the conclusion that using the caps to high pass and essentially DC clock phantom power would be a pretty poor idea.
Most users we've talked to actually use high pass at the microphone, or even further in the system, do it in software later on.
As such, the circuit has been simplified significantly.
More details on the tendolla.com design gallery.
/Rochey
a quick change later - the high-pass filter has been removed. Both Keith and I came to the conclusion that using the caps to high pass and essentially DC clock phantom power would be a pretty poor idea.
Most users we've talked to actually use high pass at the microphone, or even further in the system, do it in software later on.
As such, the circuit has been simplified significantly.
More details on the tendolla.com design gallery.
/Rochey
Hey, just my $0.20...
Some years ago I designed this pcb, it using relay to switch
beetween Kennedy's schem. Hi-Z input/mic and
common toggle switches for phantom/pad/phase....
http://i251.photobucket.com/albums/gg291/diy33609/pre_in1.jpg
http://i251.photobucket.com/albums/gg291/diy33609/pre_in2.jpg
I don't see any need in relays on phantom/pad/phase/etc.
unless you going to build fully digitally controlled preamp.
My $0.2, again
Some years ago I designed this pcb, it using relay to switch
beetween Kennedy's schem. Hi-Z input/mic and
common toggle switches for phantom/pad/phase....
http://i251.photobucket.com/albums/gg291/diy33609/pre_in1.jpg
http://i251.photobucket.com/albums/gg291/diy33609/pre_in2.jpg
I don't see any need in relays on phantom/pad/phase/etc.
unless you going to build fully digitally controlled preamp.
My $0.2, again
you mean like the front end to: http://focus.ti.com/docs/prod/folders/print/pga2500.html :wink:
For other applications - it allows control from simpler switches, or, switching multiple channels from the same switch.
A simple D-Type-Flip flip can act as switch from a simple push to make momentary switch.
Thank you for your feedback though - I've no doubt that people have made these types of circuits for quite a while now
For other applications - it allows control from simpler switches, or, switching multiple channels from the same switch.
A simple D-Type-Flip flip can act as switch from a simple push to make momentary switch.
Thank you for your feedback though - I've no doubt that people have made these types of circuits for quite a while now
keefaz
Well-known member
[quote author="Rochey"]
A simple D-Type-Flip flip can act as switch from a simple push to make momentary switch.[/quote]
And this way you can use cool cheap illuminated push buttons like the square MEC ones instead of the expensive EAO :wink:
A simple D-Type-Flip flip can act as switch from a simple push to make momentary switch.[/quote]
And this way you can use cool cheap illuminated push buttons like the square MEC ones instead of the expensive EAO :wink:
I'm keeping a blog on http://tendolla-audio.blogspot.com/ of my work with the MSP430 to do control of the the relay boards. Early days yet... So far I have only managed to do debounce on one switch. But in the next few days I hope to scale the I/O up to 3 switches, and show it connected to the new mic front end.
Cheers
/R
Cheers
/R
A brief video update
http://www.youtube.com/watch?v=F60YHgBPH3Q
http://www.youtube.com/watch?v=F60YHgBPH3Q
Ptownkid
Well-known member
Cool, you got it working, sweet!
