sr1200

Re: THATDIP Preamp - THAT1570/5171 Digitally Controlled Mic Pre [PICS]
« Reply #60 on: February 27, 2012, 07:59:31 PM »
ahhh i see what youre gettin at there.... yeah a typo... should i let avid know? lol :evil grin:
MEI Studio - Long Island, NY: http://www.meirecords.com


promixe

Re: THATDIP Preamp - THAT1570/5171 Digitally Controlled Mic Pre [PICS] New
« Reply #61 on: March 01, 2012, 12:57:35 AM »
=)

UPDATE: As I'm about to order the revised THATDIP Lucidity Preamp boards I have a question. The entire system (preamp / front panel controller / remote boards) was initially designed around a 12-pin (2x6) interconnect (header+cable). But recently, while looking for a suitable cable assemblies and bulk ribbon cable supplies, I realized that oddly enough the industry standards are either 10-pin or 14-pin IDC interconnects... Why did they skip on 12-pin? Have no clue. But I decided to base my whole design on a 10-pin IDC connectors because they just turn up in searches a lot more, i.e. are more available to a general DIY crowd. =)

That leads to the question at hand. I have 10 remote MIDI boards and 10 UMPC front panel PCBs with the old 12-pin headers on them. Would people here be opposed to purchasing these and soldering the cables between them manually (i.e. bypassing the 12-pin headers)? I will post detailed graphical explanation on how to do that. The reason is that I, quite frankly, don't have enough cash to reorder the MIDI and Front Panel boards with the new 10-pin standard headers until I generate some sales of the existing stuff I have. The end-user functionality of the design is completely unaffected by this header mismatch issue.

I can discount the front panel and the MIDI PCB price because of this inconvenience. Please let me know whether or not this is a huge issue for the DIY people here. =)

Thanks!
« Last Edit: January 01, 2013, 10:21:22 PM by promixe »

promixe

Re: THATDIP Preamp - THAT1570/5171 Digitally Controlled Mic Pre [PICS] New
« Reply #62 on: March 01, 2012, 08:49:30 AM »
As I'm working on the MIDI remote board I'm running into some undocumented protocol quirks... After implementing the basics described by sr1200 on page 3 I still can't get PT to recognize my device. It appears that PT is also sending a 0xA1 0x00 0x00 message along with the heartbeat message, which contradicts their 0xBx status byte format and isn't documented anywhere. And my proper heartbeat response is not pleasing PT as it keeps telling me there isn't a preamp connected to it... =\

sr1200, maybe you could relay this message to your contact at Av1d and ask for more information? Otherwise I have to go through THIS and I already smell a dead end there... =)

Thank you!!!

UPDATE: Looks like I got it to recognize my MIDI board finally. It seems that MIDI-OX (my MIDI monitor program) takes exclusive control of my computer's MIDI IN port and while displaying all incoming messages nicely it doesn't let PT see them. =) But the 0xA1 messages from PT are still there and I don't know their purpose. Back to work... Oh, first some sleep. =)
« Last Edit: January 01, 2013, 10:22:01 PM by promixe »

promixe

Re: THATDIP Preamp - THAT1570/5171 Digitally Controlled Mic Pre [PICS] New
« Reply #63 on: March 04, 2012, 05:46:28 AM »
UPDATE: Revised PCBs are ordered - huge thanks to Frank (12volts)! Should be here in about a week and a half. =)

Also, I redesigned the preamp and MIDI boards so that they can work with up to 16 (!!!) channels in a single chassis. I'm still working on the firmware to make this happen, but the idea is that in PT you select that you have TWO preamps connected on consecutive MIDI channels, even though the physical connection is just to a single UMPC MIDI board. It recognizes which MIDI channel should talk to which group of preamp channels inside a single rack. Basically PT thinks you have 2 Av1d PREs, but you actually have one 16-channel custom-brewed super-clean goodness. =)

And I'm beginning to work on the metering system for this project that will be able to send the levels over the network into a remote control app (OSX / iOS first, Linux / Win with help from others) through my upcoming OSCAR (OSC Audio Remote) design. It'll be a little while until it's in beta, but hopefully the MIDI remote can sustain your happiness for a while. =)

I also ran some tests on the current boards I have and the EIN has improved a bit over previous versions of the preamp - it is now -128dBu @75dB gain with 150Ohm termination, 20-20k BW, flat weighted. Pretty high-end if you ask me. But I have a question about this if anyone knows what FFT size the industry uses to measure the EIN. I use very large FFT size (131072+) but have noticed that if I decrease it to 32768 or less the EIN figure improves dramatically (up to 3dB), which makes this a theoretically noiseless preamp on paper with -131dBu EIN (the thermal noise floor of the terminating resistor that is). =)))

More updates to come.
« Last Edit: January 01, 2013, 10:23:24 PM by promixe »

promixe

Re: THATDIP Preamp - THAT1570/5171 Digitally Controlled Mic Pre [PICS]
« Reply #64 on: March 04, 2012, 02:18:15 PM »
As a side note: I just randomly visited THAT's website and they've just released 5173 digital chip!!! It appears to be 5171's smaller variant with 3dB steps and 5x5 QFN24 package. The specs are really good, very similar to 5171 especially at higher gains. Hmm.. =) Let's see how much it costs...

Looking at the datasheet, however, there are some major differences on the digital side, both good and not so. The cool feature is that they now support GPIO changes on zero-crossings, in addition to gain. But to take advantage of this the GPIO switching has to be a lot faster than what relays offer... Another cool thing is that the gain now DIRECTLY matches the PT MIDI protocol described on page 3 here. =) The thing I don't dig as much though is that it is now daisy-chainable, and not addressable as the 5171 is. It is basically controlled the same way PGA2500 is. The SPI addressing is a major convenience to me personally, as I can minimize SPI traffic significantly and the code is cleaner that way. But daisy-chained fashion is not a complete deal breaker, just not my personal preference. =)

But I suspect it will be about 1/3 cheaper than the 5171, if not more. We'll see. =)

loicm

Re: THATDIP Preamp - THAT1570/5171 Digitally Controlled Mic Pre [PICS]
« Reply #65 on: March 12, 2012, 05:17:24 AM »
Dear Promixe,

Quote
if anyone knows what FFT size the industry uses to measure the EIN. I use very large FFT size (131072+) but have noticed that if I decrease it to 32768 or less the EIN figure improves dramatically (up to 3dB), which makes this a theoretically noiseless preamp on paper with -131dBu EIN (the thermal noise floor of the terminating resistor that is). =)))

I think you should integrate the signal up to 20 KHz in your FFT. If you increase the size of the FFT, you will get the noise of the high frequency. This will lead to poor results. 
It's normal that the noise change according to the bandwith of your analysis.

To do a FFT, you define a temporal window and the number of point in this window (the size I guess in your software).
This number of point will give you the bandwidth of the analysis. If you increase this value you will get the high frequency in the spectrum.
The more point you have in the FFT, the more high frequency and noise you will get in your spectrum.
The noise is the integration of the spectrum curve. I think you should integrate up to 20 KHz for this measurement.

Also the EIN change a lot according to the gain you have. There is an ANSI recommendation to make the measurement.
http://us.sonici.com/ctrldocs/ResearchPapers/5000445.C-IsEINAnAdequateMeasureofACN.pdf

Also, it is very important to terminate the input.

EIN = max gain + 22~22k hz bandwidth RMS S/N


All resistors generate noise from thermal agitation. A mic pre will also add
voltage and current noise. But an open input is like a very high resistance,
and high resistance generates giant noise.

If you short input pin 2 to pin 3 you will just measure the pres voltage noise mostly. If you use a standard resistor like 150 ohms you will measure the resistor noise as well as the pre voltage and current noise. There will be a limit no matter how quiet the pre is.

An example...

a very quiet 1nV/sqrt Hz EIN density pre will contribute about the same random noise component as a 50 ohm resistor. So with a 150 ohm load connected it actually makes most of the noise rather than the pre.

To get input spectral noise density measure output RMS, divide by gain,
then divide by SQRT of frequency range (sqrt 20kHZ=141). You must band limit the signal you are measuring to get meaningful results.

One problem you will get using a simple meter...it's likely that most of the noise you measure will be hum harmonics rather than random noise (hiss) so you may get much poorer results than expected.

Here is a good thread about this : http://www.gearslutz.com/board/geekslutz-forum/598851-how-can-i-measure-ein.html

And this from RANE :

EIN. Equivalent Input Noise or Input Referred Noise
What is tested? Equivalent input noise, or input referred noise, is how noise is spec'd on mixing consoles, standalone mic preamps and other signal processing units with mic inputs. The problem in measuring mixing consoles (and all mic preamps) is knowing ahead of time how much gain is going to be used. The mic stage itself is the dominant noise generator; therefore, the output noise is almost totally determined by the amount of gain: turn the gain up, and the output noise goes up accordingly. Thus, the EIN is the amount of noise added to the input signal. Both are then amplified to obtain the final output signal.

For example, say your mixer has an EIN of -130 dBu. This means the noise is 130 dB below a reference point of 0.775 volts (0 dBu). If your microphone puts out, say, -50 dBu under normal conditions, then the S/N at the input to the mic preamp is 80 dB (i.e., the added noise is 80 dB below the input signal). This is uniquely determined by the magnitude of the input signal and the EIN. From here on out, turning up the gain increases both the signal and the noise by the same amount.

How is it measured? With the gain set for maximum and the input terminated with the expected source impedance, the output noise is measured with an rms voltmeter fitted with a bandwidth or weighting filter.

Required Conditions. This is a spec where test conditions are critical. It is very easy to deceive without them. Since high-gain mic stages greatly amplify source noise, the terminating input resistance must be stated. Two equally quiet inputs will measure vastly different if not using the identical input impedance. The standard source impedance is 150 ohms. As unintuitive as it may be, a plain resistor, hooked up to nothing, generates noise, and the larger the resistor value the greater the noise. It is called thermal noise or Johnson noise (after its discoverer J. B. Johnson, in 1928) and results from the motion of electron charge of the atoms making up the resistor. All that moving about is called thermal agitation (caused by heat -- the hotter the resistor, the noisier).

The input terminating resistor defines the lower limit of noise performance. In use, a mic stage cannot be quieter than the source. A trick which unscrupulous manufacturers may use is to spec their mic stage with the input shorted -- a big no-no, since it does not represent the real performance of the preamp.

The next biggie in spec'ing the EIN of mic stages is bandwidth. This same thermal noise limit of the input terminating resistance is a strong function of measurement bandwidth. For example, the noise voltage generated by the standard 150 ohm input resistor, measured over a bandwidth of 20 kHz (and room temperature) is -131 dBu, i.e., you cannot have an operating mic stage, with a 150 ohm source, quieter than -131 dBu. However, if you use only a 10 kHz bandwidth, then the noise drops to -134 dBu, a big 3 dB improvement. (For those paying close attention: it is not 6 dB like you might expect since the bandwidth is half. It is a square root function, so it is reduced by the square root of one-half, or 0.707, which is 3 dB less).

Since the measured output noise is such a strong function of bandwidth and gain, it is recommended to use no weighting filters. They only complicate comparison among manufacturers. Remember: if a manufacturer's reported EIN seems too good to be true, look for the details. They may not be lying, only using favorable conditions to deceive.

Correct: EIN = -130 dBu, 22 kHz BW, max gain, Rs = 150 ohms

Wrong: EIN = -130 dBu


I'm still in the project ! I will do some measurement with the spectrum analyzer we have here.

Best regards,
Loïc

promixe

Re: THATDIP Preamp - THAT1570/5171 Digitally Controlled Mic Pre [PICS] New
« Reply #66 on: March 22, 2012, 03:44:11 PM »
UPDATE: The boards are ready to go. I'm in the process of preparing initial documentation/BOMs for everything and putting them up on my website (which will hopefully launch this week).

The DIP adapters will be BTO (Built To Order) for a while to gain momentum, so there will be a delay of several days between receiving an order and shipping them out.

- DIP adapters are $40/ea
- Lucidity Preamp Channel PCBs are $20/ea  (and $15/ea if you order over 7pc.)
- UMPC Front Panel Kit (PCB+uC) is $40  (single kit needed for 1-8 channels)
- UMPC MIDI Remote (PCB+uC) is $35 (single kit needed for 1-16 channels)
- PSU v1 PCB is $20. Customers ordering 8 or more channels will get the PSU board for free (while I have this edition of the PSU board in stock).

There are various configurations possible: MIDI remote only (headless, i.e. black front panel), MIDI + Front Panel, Front Panel only with no MIDI, etc...

I will post links to BOMs ASAP. In general, to build the preamp channel it's around $30 in additional components here in the US for top quality, most expensive being relays. You could build it for less if you wanted to. So, the full cost of a single channel is around $95 or less (with PCB, DIP adapter, remaining components).

If you would like to place an order please PM me with your shipping address and what you would like to order and I'll send you my Paypal address and a quote. Thanks!

More to come!...
« Last Edit: January 01, 2013, 10:26:58 PM by promixe »

promixe

Re: THATDIP Preamp - THAT1570/5171 Digitally Controlled Mic Pre [PICS]
« Reply #67 on: March 29, 2012, 12:01:40 AM »
The new preamp boards are beautiful in white! =)



BOM's are up online:

THATDIP Preamp v3e
UMPC Front Panel v4e
UMPC MIDI Remote v2e
UMPC PSU v1

For US customers note the "ORDER BOM" links at the bottom - this should save you guys some time! =)
Intl. customers - similar functionality is coming...

Basic documentation is coming up ASAP.. +)


mrcase

Re: THATDIP Preamp - THAT1570/5171 Digitally Controlled Mic Pre [PICS]
« Reply #69 on: March 30, 2012, 06:29:58 AM »
indeed! looks great! you`ll get an order from me soon.


promixe

For 2012 update on this project please visit my site!

For build/support thread click HERE



Thank you all for your participation in this thread!

rmaier

Congratulations on your site and on getting things to this point - this looks like a fabulous project, and I'll be in touch with an order as soon as time and finances permit. Very much looking forward to hearing how things come together for people working on these.
"Even if you don't know where the destination is of the sounds that you originate, it's worth getting it right at the start." - Rupert Neve


 

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