32 ch. mic pre in a compact design

Hi

I'm not sure if this topic is in the right place, so feel free to move it

I have a compact live recording setup with 24 mic inputs. It's a Focusrite liquid pro 56, a M-audio profire 2626 and a Focusrite octopre mrk1 all run into a macbook pro and Pro Tools.

Recently I upgraded my home setup to a HD Native and the Avid Omni interface, and I am amazed on the big difference in clearity, stereo spread and detail richness compared to the focusrite liquid. I'm therefore thinking on upgrading my portable setup to Pro Tools HD and the old blue 192 interfaces which can be bought at a fair price. But with the 192 interfaces I will need some decent preamps.

Does anybody have or is able to help me with a design on 32 mic pre's in decent but cheap opamp quality and placed on a single pcb? I'm thinking that a gain control, phantom power switch and a pad is all the controls I need...

Thanks in advance

Best regards
Jakob

http://www.ti.com/lit/ds/symlink/ina217.pdf

you'd be surprised how many commercial products have these little buggers at their heart. Look on page 7 for a schematic. The sound is going to be super clean!!

I find this rather impossible to do because there's not enough space to host all the components.

Best I have done so far for INA217 and SSM2019 IC based mic pre is 14 channels on a double layer, with on-board mounted 1/4" TRS connectors for input output, mini push switches, and 9 mm pots for the gain control. Fits into a custom 1U enclosure case.

EDIT: 14 not 16. I just looked at my PCB file, and it's 1U, not 2U. Sorry.

Thanks for the replys

I'm really a noob at design so I would appreciate some help at incorporating the pad, P48 and gain knob. Would you just use the design showed on page 7 in the ina217 datasheet?

Do you have any idea who could do the pcb?

Thanks again

I have about 60 Tamura mic-input transformers that I was thinking of doing something with them. If you consider transformer input then I could do something single opamp based.

Otherwise yes the fig 4 on page 7 is a complete mic-amp.

Pardon the promotion, Expat Audio have the "Eden" Mic Pre's based on the INA163. Very *very* clean pre's.
http://www.groupdiy.com/index.php?topic=50419.0

Each channel is 2" x 2.5". 8 will stack side by side in 1U.

We also have controllers etc for the phantom and pad etc.
If you're onboard for a number of Mic Pre's, then I may be able to design a controller for your front ends too.

drop me a PM if your interested.

Cheers

Rochey

Warning... whenever you put more than two mic preamps in a single chassis, customers ASSume they are inferior to stand alone preamps.  ;D ;D ;D

JR

So... one INA217 in 2U rack sounds much better than 12 in 1U rack?

JS

joaquins said:

So... one INA217 in 2U rack sounds much better than 12 in 1U rack?

Click to expand...

Oh, my, yes, especially if you can add a toob to the circuit board.

=-a

Do you think it's possible to fit 16 ch + a power supply in a 2U rack? XLR inputs and DB25 outputs, a gain knob and a

@Sahip: It's not that I don't want the transformers, but with that many channels I guess it will be quite costly, but if you have any ideas, please let me know.

@Rochey: PM'ed

Best
Jakob

Clemen said:

Do you think it's possible to fit 16 ch + a power supply in a 2U rack? XLR inputs and DB25 outputs, a gain knob and a

Click to expand...

Yes, normally 16x XLR's can be put accross a 1U box. If you stack 8x2 in a 2U enclosure, then you'll still have half the case left over for DB25's and power.


Also, Clemen, I copy and pasted some of your questions from your PM (if that's okay). I don't think there's anything particuarly sensitive in your question:
[quote author=Clemen]BY PM:
How will it work, is it assembled and will each board have gain, P48 and pad knobs? What about a power supply for the 32 channels, will that be included as well?[/quote]
The Mic Pre is split into different sections - Control (buttons, led's etc), Front End (switched relays etc) and Preamplifier (where the signal is amplified).
Have a look at page 9 of http://expataudio.com/diy/edenmicpre/Eden%20Microphone%20Preamplifier%20PG20.pdf
The blocks in blue show the boards available from expat audio.

The Eden's will come preassembled and tested.
The Digitally Controlled Mic Pre FE will be sold as PCB's. You'll need to buy the parts online and solder yourself.
The 3 button switch controllers come as a PCB and an IC. You will need to buy the other passive components on the board.
The Uber PSU comes as a PCB only. You will need to buy the other passive components on the board.

32channels is a big project. You'll probably need 2, maybe 3 Uber PSU boards (can be fed from the same toroidal transformer).

I'm working on audio samples, however, as you can see on page 2 and 3 of http://expataudio.com/diy/edenmicpre/Eden%20Microphone%20Preamplifier%20PG20.pdf
the frequency response of these amplifiers is super flat in the audio range, and the distortion is very, very low (Distortion is measured in %-Y Axis, Frequency by Hz-X Axis). At 30dB of gain (average) your THD is near the noise floor. In fact, your microphone may only just be that low. At 60dB (higher gain), then the distortion is still very low (~0.03% THD).

This really does let you commit the cleanest possible sound to your DAW, then run it through whichever "flavor" plugin you want to use. (that's why I personally LOVE the Eden design - it gives me options after recording).

abechap024 said:

http://www.ti.com/lit/ds/symlink/ina217.pdf

you'd be surprised how many commercial products have these little buggers at their heart. Look on page 7 for a schematic. The sound is going to be super clean!!

Click to expand...

im also looking in at making a large count of pres, probably 2 2U racks of 12. these things look pretty sweet. not trying to hijack your thread Clemen, but could someone help me out with how i would supply power to each module evenly? i have never really designed something like this before. i call myself more of an assembler haha

the smallest I have seem is the all in one mic pre chip made by that corp. that chip is way tiny and a complete balanced I/O mic pre, cost for the chip is like 6 dollars a chip. Worth checking into.

that 1570 is the chip#

berkleystudios said:

abechap024 said:

http://www.ti.com/lit/ds/symlink/ina217.pdf

you'd be surprised how many commercial products have these little buggers at their heart. Look on page 7 for a schematic. The sound is going to be super clean!!

Click to expand...

im also looking in at making a large count of pres, probably 2 2U racks of 12. these things look pretty sweet. not trying to hijack your thread Clemen, but could someone help me out with how i would supply power to each module evenly? i have never really designed something like this before. i call myself more of an assembler haha

Click to expand...

Have a look at the uber power supply at expat audio. Its exactly what it was designed for.

You can run a few in parallel if you must.

Frankly, if you consider yourself an assembler, Eden is ideal.

"Gain Range 15dB to 60dB (easily modded) "
Is the mod to get more gain ie 80db to work with ribbons or very soft program material

We can sneak up to around 70dB by changing the smd resistor on the eden board.

Careful though, up at that end, you will start to distort a little

you get another vote for the Eden pre here.
For a noob build, these come ready to go and tested.  So it would make your life way easier.  There is no one else making super small formats like that.  Maybe JLM baby animals or something like that.

BR said:

you get another vote for the Eden pre here.
For a noob build, these come ready to go and tested.  So it would make your life way easier.  There is no one else making super small formats like that.  Maybe JLM baby animals or something like that.

Click to expand...

That's real kind! Thank you!

I just fit 8 api type preamps int a 2u chassis and am thinking of adding 4 more. You could do 24 channels in 2 spaces. With cinemag xfromers. The 8 channel project came in roughly 1.2k. But 8 of these preamps in a single box has changed my life.
-s