Preamp Micstasy Style

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rkn80

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Joined
Sep 20, 2009
Messages
410
Location
Germany
Good evening, GDIY-community,

it has been a while since I presented my last project here, but no I think, it is time again to do it again. And here we go:
My newest project is a mic preamp similar to the RME Micstasy but a little bit extended. Actually, I always wanted to design a mic preamp like this, but there was never a trigger. Now a friend o me needs such a thing, so I accept the challenge. Like al of my project it will be a free time project and I will consider to make it open source.
These are the specifications/requirements we are talking about:
8 mic preamp inputs
85 gain, 0.5dB steps
8 balanced outputs on Sub-D
Built-in premium AD converter from ESS or TI or Cirrus (I don't trust that AKM will be back on stage soon)
USB Interface with USB Audio 2.0 compliant operation up to 192kHz sampling rate
ADAT output for all channels up to 96kHz
Wordclock I/O
Fully remote controllable
LED or OLED Level meter on front, all settings can be made via knobs on the front in case you don't want or you can't use the remote software for some reason.
So far so good.
I made already the design of the mic channel. It is built around a PGA2500. It has of course the standard features like Phantom power and Pad (both switched by relays) in front of the PGA2500. Behind the PGA250 there follows a second amplification to make the final max. gain of +85dB. The PGA2500 can only give +65dB. This second stage can be switched between +19.5 and +20dB. So we can make 0.5dB steps together with 1dB steps of the PGA2500 and the -20dB Pad in front of the PGA2500.
Well I have to say I don't know how RME made that in their Micstasy but I think it will be something like this, therefore I call this Micstasy-style. RME please forgive me if I am wrong.

Next step now is to design the ADC part.

What do you think? Your thoughts on this are welcome.

Raphael
 

ruffrecords

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Joined
Nov 10, 2006
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13,931
Location
Norfolk - UK
Cool. That is the first time I heard of the PGA2500. Looks like a good choice for digitally controlled mixer designs.

Does anyone really need 85dB of gain these days?

Cheers

Ian
 

rkn80

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Joined
Sep 20, 2009
Messages
410
Location
Germany
That's ok. ;-)
I used the combo connectors for XLR and 6.35mm jack. The analog input supports line input. I am not sure wether a metal version of the combo connectors exists?

Raphael
 

MidnightArrakis

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Joined
Sep 25, 2015
Messages
131
I don't know, but cool to have it.

Here is a pic of the analog preamp part, that I made today.
GOOD JOB!!! What 3D CAD-program did you use to create your image? LOOKS GOOD!!!

I just took a look on the NEUTRIK website and I didn't see any - metal - COMBO Jacks listed. However, and knowing NEUTRIK, I am more than certain that they have designed and manufactured their plastic COMBO connectors to be robust enough to withstand the rigors of the Rock'N'Roll life!!! But, perhaps Ian has some better and/or deeper insight about this. I once worked with "one of the largest concert sound-reinforcement companies in the world" and some of the equipment in our racks, all made by leading "Pro-Audio" companies, had NEUTRIK XLR and COMBO connectors on them and we never had any issues with anything ever happening to any of them. But, that's just me.....

It is difficult to see accurately because of the image being at an angle, but it appears to me that the XLR's all need to be moved closer to the edge of the PCB so the connector flange or lip will extend out far enough to mate and be within the metalwork panel. If your CAD-program can output either an " .igs " or a " .stp " file, I could review your design more closely. Or, should you happen to be using SolidWorks, you could run a "Pack & Go" routine and send me that file for a review. I would be more than happy to help out.

I was also wondering, did you perform all of the placement of the components just once and then do a copy for the other 7 channels? (In SolidWorks, that is called a "Linear Pattern" copy command). And.....where did you get all of the 3D CAD-models for all of those parts? GOOD JOB!!!

While I am guessing that you probably have all aspects of your project already under control, on the off-chance you -- might -- need some assistance in the areas of PCB design, mechanical design and/or the "Electronics Packaging" of your project, you may contact me for any help. The attached PDF files will show you some of my handiwork just to give you a bit of a reference. > I AM NOT SELLING ANYTHING!!! < I am merely offering assistance. (NOTE: I just helped another member on this forum upgrade the GERBER files of a PCB design he had sent to me (I have a professional GERBER editing program). At the same time, not only did I remove several errors in his GERBER files but also corrected some errors in his N/C Drill file. And.....all of the hours I spent working on his PCB files didn't cost him a single penny or in your currency: 0.0084764384 Euros)!!!

/
 

Attachments

  • JBW-Designed - RACK STUFF -- Assemblies-Chassis-Enclosures-Panels-Systems.pdf
    6.2 MB · Views: 27
  • JBW-Designed -- Various PCB Designs - 2D & 3D.pdf
    2.5 MB · Views: 14

rkn80

Well-known member
Joined
Sep 20, 2009
Messages
410
Location
Germany
Good evening,

today I added ADC (I decided to go with ES9842PRO or ES9840), analog output, and ADAT.
First I wanted to go with the good old AL1401 (and its CoolAudio replacment) but then I recognized, that they don't support SMUX. Therefore, I am using a CPLD instead. Well writing an ADAT encoder in VHDL is not that difficult, receiving/decoding is the challenge. Yet CPLDs are currently hard to get due to the semiconductor crisis. We will see...

@MidnightArrakis: I am using KiCAD. The 3D-rendering is made with KiCAD, too. The 3D-Models I get either from 3dcontentcentral or from the manufacturers. Many of them have the step models on their website. I am sure, I will come back to your reviewing offer.

USB-Interface is the next step.

Raphael
 

Attachments

  • micamp.png
    micamp.png
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MidnightArrakis

Well-known member
Joined
Sep 25, 2015
Messages
131
Good evening,

today I added ADC (I decided to go with ES9842PRO or ES9840), analog output, and ADAT.
First I wanted to go with the good old AL1401 (and its CoolAudio replacment) but then I recognized, that they don't support SMUX. Therefore, I am using a CPLD instead. Well writing an ADAT encoder in VHDL is not that difficult, receiving/decoding is the challenge. Yet CPLDs are currently hard to get due to the semiconductor crisis. We will see...

@MidnightArrakis: I am using KiCAD. The 3D-rendering is made with KiCAD, too. The 3D-Models I get either from 3dcontentcentral or from the manufacturers. Many of them have the step models on their website. I am sure, I will come back to your reviewing offer.

USB-Interface is the next step.

Raphael
[I will come back to your reviewing offer] -- 10-4, Good Buddy!!!

/
 

rkn80

Well-known member
Joined
Sep 20, 2009
Messages
410
Location
Germany
Added the USB2 interface, Wordclock IO and Phantom Power. Phantom power is made from a +12V input.
I am now looking into the main power supply for the PGA2500 and the Opamps. So I need +5V and -5V. I would like to generate these supply voltages from a single +12V input. That would give some additional choices for the power supply (external wall power supplies etc...).
The placement of the functional groups is not final yet. I will refine it once all groups are finished.
 

Attachments

  • micamp.png
    micamp.png
    250.1 KB · Views: 41

mhelin

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Mar 12, 2005
Messages
561
Location
Tampere, Finland
Regarding the AL(or V)1401 it does support SMUX as transport but it doesn't do the job of splitting the data from for an example a 4ch 96kHz stream into a 8ch 48kHz one for you. For that it would be easier to fit the design into any programmable logic chip. I think Wavefront had an application note for SMUX which used one of their DSP for that purpose. See
 
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