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Old 16th December 2013, 09:14 PM   #41
gpapag is offline gpapag  Greece
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I have written that I have observed some HF radiation issues around coil L1 at the 2x4 miniDSP board
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Originally Posted by gpapag View Post
Using my spare old 2x4 MiniDSP board (v1.3), I decided to investigate the issue a bit in detail. (*)
The board takes a DC Input from 4.5 to 24V.
This DC is fed to the onboard DC-DC stepdown buck switching regulator built around LM2841Y which is switching at 1.25MHz
The converter outputs 3.3Vdc
http://www.ti.com/lit/ds/symlink/lm2841.pdf
I supplied the board (stock, no added capacitance at the DC-In) through a bench stabilized variable PSU and monitored the input current, the magnetic field around L1 and the 3.3Vdc at the supply pins of the ADAU 1701, the DSP IC of the board http://www.analog.com/static/importe...s/ADAU1701.pdf
(The +3.3V is routed to and is identical with that of pins #22, #23 and the GND at pin #26 of Expansion Connector #2).

The result of the observation is that there appears pulses of 1.25MHz (and it’s higher harmonics) at the input current, the magnetic field around L1 and at the 3.3Vdc.
The effect becomes more pronounced when the DC-In voltage increases.
It is minimum at 5Vdc and goes to maximum at 24Vdc.
The harmonics really take off from 8Vdc and up.



George

(*) I have an oscilloscope that has a –3db bandwidth of 20MHz only, so the collected data (and the lousy photos) are somehow misleading at high freq harmonics both in amplitude as well as on details due to not so good triggering of the scope.
Attached Images
File Type: jpg 1 DC-In Diagrams.JPG (70.7 KB, 123 views)
File Type: jpg 2 Combo 5V.JPG (150.1 KB, 118 views)
File Type: jpg 3 Combo 8V.JPG (143.4 KB, 115 views)
File Type: jpg 4 Combo 12V.JPG (140.0 KB, 112 views)
File Type: jpg 5 Combo 18V.JPG (139.1 KB, 108 views)
File Type: jpg 6 Combo 24V.JPG (148.2 KB, 10 views)
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Old 16th December 2013, 09:16 PM   #42
gpapag is offline gpapag  Greece
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I would say that it would be better to feed the board with 5-6Vdc, no higher.

The same DC-DC switching voltage regulator is used on the newer (v1.8) MiniDSP board I have (with some peripheral component values differing), as well as on MiniDIGI and MiniAMP boards. Therefore the issue is of interest to me and I am working on it.

George
Attached Images
File Type: jpg 7 PSU current 5V.JPG (146.4 KB, 11 views)
File Type: jpg 8 PSU current 8V.JPG (138.8 KB, 7 views)
File Type: jpg 9 PSU current 12V.JPG (142.6 KB, 4 views)
File Type: jpg 10 PSU current 18V.JPG (145.7 KB, 3 views)
File Type: jpg 11 PSU current 24V.JPG (139.7 KB, 4 views)
File Type: jpg 12 V pick-up.JPG (427.0 KB, 25 views)
File Type: jpg 13 H-Field probe over MiniDSP board.JPG (349.3 KB, 34 views)
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Old 26th December 2013, 08:36 PM   #43
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Quote:
Originally Posted by gpapag View Post
MiniDIGI jumper settings and Input selectors connection

George
Hello George

After many hours of research I found in your article almost all the answers I needed for my project... my only difference is that instead of 2 MiniAMPs I want to route the I2S data from the MiniDSP to 2 CurrymanDACs...

Also I have the USB streamer and not the MiniSTREAMER...

Can you give me some advice on connecting the 2 CurrymanDACs to the MiniDSP?

Also it would be very nice to know what switch or correct specs of the switch you used for toggling between the 4 digital inputs on the MiniDIGI... so I can print it and try to find one near my home.

Congratulations for the project! Hope to hear from you soon...
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Old 27th December 2013, 12:58 AM   #44
gpapag is offline gpapag  Greece
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Thank you Andre

Regarding the connection to the CurrymanDACs, I would agree with Curryman’s post without adding anything different.
MiniDSP :: Topic: USBStreamer>MiniDSP>Curryman DAC (2/3)

Regarding the switch, I used a simple and cheap 3 pole- 4 position rotary selector. I utilised one pole only.
It has to be a “Brake Before Make” type, which means that the moving toggle should come clear from one position to the other without shorting (electrically connecting) them while in transit.

George
Attached Images
File Type: jpg selector.JPG (32.6 KB, 28 views)
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Old 27th December 2013, 01:08 AM   #45
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Hehe Nice to know you were also following my post on the other fórum.

Much thanks for your help, I will tomorrow search in some stores if I can get this part... Should I take care trying to find the rotary switch of higher quality for no interference on áudio signal?
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Old 27th December 2013, 08:29 AM   #46
gpapag is offline gpapag  Greece
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I did a search for CurrymanDAC because I didn’t know it and I found the response of Curryman to your question. (This is a nice DAC).

Ref selector, I would care for a good, stable force between the toggle and the contact points.
For now, other “qualities” of the selector (contact point details like kind of metal ect) are for me not essential.

George
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Last edited by gpapag; 27th December 2013 at 08:54 AM.
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Old 4th January 2014, 01:42 PM   #47
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Thank you very much for your help! I already have the rotary switch

Would it be possible to connect from USBStreamer to MiniDIGI using Toslink but not through optical connection? I mean similar to what you did with the SPDIF soldering cables below the boards on the pins of the SPDIF connectors?

What would be the disadvantages of not using the optical vs using an "electrical" toslink connection?
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Old 4th January 2014, 04:14 PM   #48
gpapag is offline gpapag  Greece
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For the USBStreamer, I have seen they solder a cable below the board at the data pins of the TOSLINK connector.
If you connect the other end of that cable to the SPDIF-IN of the miniDIGI, I think that there will be no disadvantage (compared to an optical connection) because there are two isolation transformers there, one for each SPDIF Input.

George
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Old 4th January 2014, 06:31 PM   #49
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Hmm só no problem. But you mean TOSLINK IN on the MiniDIGI (?)


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Old 4th January 2014, 11:00 PM   #50
gpapag is offline gpapag  Greece
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This time I meant what I wrote.
I wrote SPDIF-IN of the miniDIGI.

George
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