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tda1387 dac pcb "front end"
tda1387 dac pcb "front end"
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Old 25th March 2018, 08:37 AM   #141
abraxalito is offline abraxalito  United Kingdom
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No dual supply is needed, just a single rail. Its only 1VRMS output after all.

I think a JG buffer might well work fine - you don't need the inductor though (from memory it has an LC filter before the JFET) as the filtering already built in is plenty fierce enough. But if you leave it in there won't be a problem.

As for the magic you should be able to find out fairly soon, once I've finished building the last couple of boards I'll then give them a final test and get them out. You'll need a single low noise supply of 8 to 9V to power it all. In total with the buffer configured to drive headphones it'll take about 160mA, for line driving we can reduce the current requirement a little bit.
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Old 25th March 2018, 01:23 PM   #142
mmerrill99 is online now mmerrill99
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@abraxalito - neat & professional looking modular stack, DAC, filter & buffer.
Sorry if this has been covered already but what is the required input signal, I2S?
What are the dimensions?
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Old 25th March 2018, 02:00 PM   #143
abraxalito is offline abraxalito  United Kingdom
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Yes its I2S input though plans are in the pipe to develop a digital interface board with the same form factor. PCB dimensions are 5 * 5cm - because that's a really cost-effective option from PCB vendors here, we can panelize 4 boards into 10 * 10cm which is the largest size board which goes for a cheap price.

The height of the stack depends on which board options are chosen but typically PCBs are spaced no more than 2cm apart, the top board which sports the amp is taller (up to 3cm potentially) if higher valued output caps are chosen (for lower impedance cans).
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Old 25th March 2018, 03:16 PM   #144
randytsuch is offline randytsuch
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Originally Posted by abraxalito View Post
No, its all single supply, 8-9V. I sometimes use a boost converter from an 18650 cell.
What boost converter did you use? Anything special?
That would make it pretty simple, just need to change the 18650 cell with 3.3v and connect up the boost.

Thanks
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Old 26th March 2018, 12:38 AM   #145
randytsuch is offline randytsuch
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So I ended up just using one 5V reg and one pair of batteries to supply power to the allo reclocker and the dac board.

Took a headphone amp I was no longer using, and used the board for mounting the dac.

Letting it run in some, but initial impressions were good.

SW is PiCorePlayer audio version. I have LMS running on another pi.

Randy
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Old 26th March 2018, 11:01 AM   #146
nige2000 is offline nige2000  Ireland
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Originally Posted by randytsuch View Post
So I ended up just using one 5V reg and one pair of batteries to supply power to the allo reclocker and the dac board.

Took a headphone amp I was no longer using, and used the board for mounting the dac.

Letting it run in some, but initial impressions were good.

SW is PiCorePlayer audio version. I have LMS running on another pi.

Randy
a guy from a battery manufacturer told me that for series charging they need to be matched to be anyway predictable

individual cell float charging gives great piece of mind
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Old 26th March 2018, 03:10 PM   #147
randytsuch is offline randytsuch
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a guy from a battery manufacturer told me that for series charging they need to be matched to be anyway predictable

individual cell float charging gives great piece of mind
If I had more than 2 in series, I'd worry about it more. I'll monitor them, and see how balanced they are over time. If they do go unbalanced, I can add 2 isolated PS's at that time. For now, this was a real quick and dirty way to get sound out of this card.

Listened some last night. Not sure if its broken in yet, and probably want to upgrade some caps, but it sounds good, much better than it should for the price. Didn't compare to my soekris yet, will give this some time to run in before I do that.

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Old 26th March 2018, 09:27 PM   #148
stellarelephant is offline stellarelephant  United States
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Can anybody explain this noise? I made a video.
YouTube

Let me explain that I am GREATLY exaggerating this DAC's noise level by pumping it through a microphone preamp into an old guitar amp line input. That was the only way to get it audible enough for the video. In normal use through speakers or headphones, the noise is pretty soft.

In the video I do four things. First I play with the proximity effect of my hand near the output caps (a la theremin ). Then I touch some metal parts with my hand. Next, I try a wire direct to ground. Finally I use the winner--the ground pin of my Mac's power brick. What???

I am quite baffled as to why this works so darn well. I have found that it only works when the other end of the power brick is connected to my Mac AND my Mac is connected to my monitor, AND the power cord of the monitor earthed via its own ground pin on the cord. If I disconnect the monitor, the Mac PSU alone only attenuates the noise a little bit. I can also work this in reverse--I can earth the Mac power brick and touch the monitor cord's ground pin to the DAC, and get the same perfect silence. In both scenarios, it does not matter if the Mac or monitor are switched on or off via the power strip...the result is the same. The way I originally discovered this effect was by accident...the same connections were being made indirectly when I hooked the new RPi DAC to a source selector box along with a Firewire DAC connected to the Mac.

BTW Randy, I am guessing you hold the Soekris in high regard? It will be interesting to read your comparison as well as any cap rolling you try. Is your new DAC more or less silent with the battery power?

Last edited by stellarelephant; 26th March 2018 at 09:35 PM.
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Old 26th March 2018, 09:38 PM   #149
pcgab is offline pcgab  United States
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tda1387 dac pcb "front end"
StellarElephant,
I don't have a good idea re: the noise, but the YouTube link says video unavailable.
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Old 26th March 2018, 10:05 PM   #150
stellarelephant is offline stellarelephant  United States
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StellarElephant,
I don't have a good idea re: the noise, but the YouTube link says video unavailable.
Oops. Believe it or not this is my first Youtube upload, ever. Thanks for the heads up. I had forgotten to hit the publish button. Please try the link again.
YouTube
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