Raspi 2 and HiFiberry DAC+ coupled to a LM3886T Gain Clone Amp

[tcpip]

I am envisaging a problem here. Since the media center is within the box, the power off may not always be controlled and also it may not be preceded with turning off the media center. The result maybe a corrupt database and that would leave Kodi unusable for next time...any thoughts? There are suggestions on super capacitors in some forum...there should be a better way to do this...

Are aware of audiophonics.fr?

They have a lot of inexpensive kits and modules to let you add features to an RPi based system. One of the things they've developed is a small PCB which can handle power cycling of the RPi. When you hit the power button, this PCB sends a signal to one of the GPIO pins of the RPi, and a daemon running on the RPi triggers a clean shutdown. It similarly also supports a clean startup.

All the pages are in French, so use Chrome to browse the site and translate each page into English with one click. The software for the daemon to do the shutdown is provided as free download, I believe. They have a forum where they answer DIYer queries.

 

[sunilmani]

To all the experts out there - need some help
1. I am trying to get the offset voltage to zero, but cannot get it below 6 mv. Let me know from the steps if i am missing something - Ref. diagram
a. With open input, I am adjusting RT2 and measuring voltage at OP2A pin 3. Once set to minimum possible, i move to next step
b. With open input, I adjust RT1 and measure voltage at OP1 A pin 3 and try and get the voltage to min.

When i do step a and check voltage at OP1 A pin3 , i find the voltage has increased considerably and vice versa after step b, voltage at OP2 A pin 3 increases considerably. So, i tried getting the same voltage at output of both the opamp. The voltage on pin 3 of both opamp OP 1A and OP 2A is 6 mv. Let me know if i am missing something here.

 

[sunilmani]

Hi Sunil. Very elegant cabinet. As a few forum members had mentioned earlier, the speaker connectors are too close to the AC mains. The cables from at least one of the channels will end up being close to either the AC socket or the transformer. Also, twist the wires to and from the transformer, and those from the bridge rectifier to the filter condensors.

An excellent guide to wiring was written by a member of diyaudio, called Bonsai: http://hifisonix.com/wordpress/wp-c.../How-to-wire-up-a-Power-Amplifier_Updated.pdf

Cheers,
~hp

Thanks HP. I could not get the heat sink of the size i desired. Also, the fabricator fellow tried to take short cuts. But yes, even then, it has come out well. Thank you.

On twisting the cable, will surely do that. As of now, i cannot increase the distance between the speaker terminals and Ac mains. Need to live with it and check if there is an impact due to it.

 

[jls001]

1. I am trying to get the offset voltage to zero, but cannot get it below 6 mv.

Short inputs and measure DC offset at the outputs.

 

[tcpip]

http://www.audiophonics.fr/en/raspb...nagement-module-for-raspberry-pi-p-11504.html

This is the power mgmt module I was talking about. This allows you to implement a power switch like on an ATX PC cabinet. Very cool. Can be used with any RPi project.

 

[Audiodoc]

6mv is not a large voltage if you are providing with the dc voltage at output with shorted input signal.

If you do a proper star ground you wont have any hum or ground loops.

Test on a cheap test speaker.

 

[sunilmani]

6mv is not a large voltage if you are providing with the dc voltage at output with shorted input signal.

If you do a proper star ground you wont have any hum or ground loops.

Test on a cheap test speaker.

Will check and post the results

 

[sunilmani]

Short inputs and measure DC offset at the outputs.

will be completing the wiring and then would be measuring and adjusting the offset.

 

[sunilmani]

AUDIOPHONICS PI Power Management / Power supply for Raspberry Pi - Audiophonics

This is the power mgmt module I was talking about. This allows you to implement a power switch like on an ATX PC cabinet. Very cool. Can be used with any RPi project.

Looks cool. Procuring it would be expensive.

 

[sunilmani]

I am at the input stage and wiring it to connectors using a 2 core sheilded cable. Going with connecting the shield to source ground as depicted in the diagram. Let me know if any issues seen.

The other option would be to use a pair of twisted wires for connecting to inputs

 

[sunilmani]

Short inputs and measure DC offset at the outputs.

I did this, the best i could do was 5.2 mv on one side amp and 5.9 mv on the other:sad:

 

[sunilmani]

6mv is not a large voltage if you are providing with the dc voltage at output with shorted input signal.

If you do a proper star ground you wont have any hum or ground loops.

Test on a cheap test speaker.

Thought the offset is 5.2 mv and 5.9 mv, thank fully there is no hum on speakers. Should i spend more time worrying about offset? Appreciate inputs here

 

[tcpip]

What are you complaining about? 6mV is excellent DC offset.

 

[sunilmani]

Wiring done last night and the amplifier was powered up. Can see the latest state in the picture. I know that the wiring path taken for the input circuit is not optimal, but i had to take that route after a lot of consideration. A direct path would have meant that the input wire would have gone close to the transformer and would have been in parallel to the speaker wires as well.
So, took that route, the good part being - as as suggested i tested with a throw away speaker; and there was no hum what so ever. Today i plan to test it out with speaker boxes.

Wish me luck.

 

[sunilmani]

What are you complaining about? 6mV is excellent DC offset.

I need not bother about it...yeah. Honestly i was worried about connecting the speaker boxes due to the offset. If 5.*mv is acceptable limit, then let me get rolling :yahoo:.

Thanks buddy!!

 

[jls001]

Even 10 mV will not cause harm, though lower is desirable. Congrats! on completing the build.

 

[tcpip]

Even 10 mV will not cause harm, though lower is desirable. Congrats! on completing the build.

Yes, 10mV is considered an acceptable limit by quite conservative builders. 5.x mV is totally cool.

 

[sunilmani]

Yes, 10mV is considered an acceptable limit by quite conservative builders. 5.x mV is totally cool.

:yahoo::yahoo:

 

[sunilmani]

Even 10 mV will not cause harm, though lower is desirable. Congrats! on completing the build.

This was the phase 1 of the build. I have planned for a phase 2 and a phase 3 as well...i know its a bit over the top; but yes, i intend to

The raspberry pi is to be powered up now. This was part of phase 2 plan for me.

 

[sunilmani]

And it sung....the voice was really sweet. Fruits of labor are sweet as they say ;-). The vocals were clean, the high notes were rightly touched, seems to lack depth though. I increased the volume and it kept going and going..to a point where i was worried of blowing up my speaker. Guess i need a new pair of speakers now

The IC's are not properly connected to heat sink as of now...as in no heat sink paste or heat sink silicon is used. will be applying the same before final assembly.

Need to make some mechanical assembly changes as well before i can put the cover on.