A portable digital multi-track recorder -- proto-pr0n

[jdbakker]

Status update:

I'm pretty much done with the board designs for the channel strips (PGA2500-based mic pre, CS5381 ADC, gain/P48/HPF switches, 56-LED VU meters, channel control processor) and a proto version of the HDD recorder. Will post schematics etc. when I get some time, right now I'm in "finish as many boards as possible before Christmas"-mode.

Left to do (in order of priority, highest first):
- clock/power distribution board, with power regulators, 24.576MHz clock, NiMH chargers and central control AVR
- digital peak/RMS meter board (to get measurements for the VU-meter)
- Schaeffer/Front Panel Express front panel
- Cohen/Green-like mic pre
- Transformer+DOA-based mic pre (probably Jensen Twin Servo -alike, possibly 312-inspired). I'm really excited about experimenting with hooking the mic pre output iron directly to the ADC.
- relay gain control board for abovementioned mic pres
- ADAT/SPDIF/AES I/O panel

Sadly it looks like I'll not make my Jan 19 deadline, as I lost three weeks when UPS and an unnamed Dutch governmental agency decided to play 'hide the parcel' with my Digi-Key shipment. "A NON-CUSTOMS GOVERNMENT AGENCY HOLD CAUSED THIS DELAY" is not a fun thing to see in the tracking display of a critical package...

On a more positive note, I've just had a very good e-shopping experience with http://www.audio-cube.nl/. They carry Elna Silmic II and Cerafine caps, which I wanted to audition for the input of my mic pres. There was a thread/META mentioning them on this board, but my Search-fu wasn't strong enough to find it or I'd have linked to it here. Anyway, I am always a bit hesitant when ordering from small web shops, since I've been burned before as it's way too easy for web shops to keep running long after their 'real world' owners have gone out of business. This time was a very pleasant exception: I had placed my order last Monday, and the caps arrived this morning!

Back to the PCB CAD program,

JDB.

 

[jdbakker]

Update: the PCB panels for the mic pre/ADC/VU channel strips have just arrived.



Top left is the PGA2500-based mic pre. The '2500 can be seen straddling the gap between analog and digital ground planes. To the right is the HPF, and the relays to switch between vanilla and HPFed signal.

Top mid is the ADC. Not much to see here, most of the circuitry is on the bottom of the board. U6 is a buffer that separates the ADC outputs from the capacitive ribbon cable.

Top right is a board with a 256-cell CPLD and 512KB buffer RAM, for the HDD recorder. The CPLD is a 0.5mm pitch part, so I decided to make this header board for if/when I should muck up the soldering. Apart from the HDD recorder proper this board is used for digital signal routing too.

The bottom board is the dual-channel strip control/feedback PCB. From left to right it has P48 injection, holes for the XLRs (since the Neutriks are deeper than the front panel to board clearance for this PCB), a Lorlin gain selector, a +20dB boost switch, channel/P48 switches, clip indicator and a 56-segment bi-colour LED VU meter. HPF/PFL/Phase switches are mounted over the empty area at the right edge.

I'll keep y'all informed on how this progresses.

JDB.
[rather later than planned, due to Mr. Murphy]

 

[jdbakker]

An update of the update: the PCBs were produced by http://www.eurocircuits.com/ . They have good prices, and contrary to other cheap board houses they allow multiple designs in one panel. The boards are silver-plated, and they look good to me. Had a bit of a bother getting them to accept my tool's flavour of Gerber, but other than that I'm quite happy with them.

JDB.
[pity their online price calculator is Internet Explorer-only, though]

 

[Rochey]

i'm writhing with envy...

 

[Carl_Huff]

Any progress to report? I find this project to be very interesting!!

 

[jdbakker]

[quote author="Carl_Huff"]Any progress to report?[/quote]
Waiting for parts. In the meantime I'm designing a simple S/PDIF output board so I can test the channel strips without the recorder backend.

Will keep this thread updated,

JDB.

 

[lagoausente]

Awesome really.
Definitely I think that intelectual ability is very bad distributed over the humanity.
My brain give off smoke trying to learn how to make a DC-DC Smps.

 

[just.sounds]

I hope this project is still alive! I just found it and it is very amazing!! I think it is too complex for me to begin with but i think this is a system where many location recordists are waiting for!! And i guess this is kind of a bump

 

[jdbakker]

It's still alive, just waiting for parts. The big holdup is that the main routing CPLD (100-TQFP on the top right of the PCB panel picture I posted earlier) is impossible to buy. When I designed the boards it was in stock @ Digi-Key, when I was ready to order it was out-of-stock with huge lead times. And naturally it's a part with no second source or pin-compatible replacement. So now I have to decide whether I keep waiting or re-do ~200$ worth of PCBs.

(The rumor I've heard was that this part was used by a large-volume customer which didn't keep track of RoHS requirements until the last minute and then suddenly found itself out of usable parts, followed by a buying frenzy which left distributors' pipelines empty. I have been informed that this is a regular list item and that it's expected to become available Real Soon Now).

JDB.

 

[just.sounds]

That is kind of a bummer! by the way, Goedemorgen leuk om te zien dat er meer Nederlanders aan het doe het zelven zijn .

 

[just.sounds]

PM'd

 

[lagoausente]

Haven´t tried the Mic pre section? I´m curious about your impressions of the PGA2500 based mic pre.

 

[jdbakker]

[quote author="lagoausente"]Haven´t tried the Mic pre section?[/quote]
Only very briefly. The mic pre board is designed to directly drive the ADC, and therefore doesn't swing to full line levels.

I have just sent some converter boards to be fabbed for the TI SRC4392 so I can at least test the channel strips standalone. Will report back once I have those running.

JDB.

 

[ChrisRoberts]

Whatever happened to this?