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Old 15th March 2014, 07:28 PM   #1
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Smile Raspberry Pi, TDA1541A, PMD100, discrete IV

Thought I'd share what I've been dabbling with of late.

Still unfinished, but works well.
Essentially a Raspberry Pi with Koalo's I2S driver, fed by an old, badly implemented Kwak clock, feeding I2S to my old PMD100 circuit (resurrected from my previous DAC). This inturn feeds an 8x oversampled I2S signal to a TDA1541A, which feeds a discrete IV stage (a BJT equivalent of Nelson's D1 - very crude at the moment, but works well).

The pi is powered by a dedicated linear PSU, via a USB hub, which also powers a USB (well, SATA) HDD.

It needs a bit of a tidy up, a rebuilt clock and IV stage but I'm very happy with it. No doubt, there are various ways I can tweak this. I'll be busy for years.

Runs MPD nicely, playing FLAC and internet radio, can control it via my phone, and has a shutdown button, so I can run it completely headless.

Seriously toying with an SSD for it - not that it's very noisy at the moment.
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Old 15th March 2014, 09:02 PM   #2
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Fantastic!

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Old 18th March 2014, 01:26 AM   #3
kp93300 is offline kp93300  Malaysia
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Quote :
Still unfinished, but works well.
Essentially a Raspberry Pi with Koalo's I2S driver, fed by an old, badly implemented Kwak clock, feeding I2S to my old PMD100 circuit (resurrected from my previous DAC). This inturn feeds an 8x oversampled I2S signal to a TDA1541A, which feeds a discrete IV stage (a BJT equivalent of Nelson's D1 - very crude at the moment, but works well).
unquote


I am also interested in such a project. I have most of the parts from the diyparadise monica project with TDA 1545.
Can you elaborate more on the PMD 100 circuit ?
I would like to interface the pi with the TDA 1545 chip directly.

thanks

kp93300
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Old 18th March 2014, 01:33 AM   #4
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I've tried the TDA1545 (or it might have been TDA1387 which is very similar) and it sounds better run NOS than with oversampling. I compared 2X OS vs NOS and NOS won out with less 'greyness' to the sound. Bear in mind TDA1545A (original TDA1545 isn't available any longer) doesn't use I2S, rather EIAJ.
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Old 18th March 2014, 09:10 AM   #5
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Thanks for the compliments!

kp, I basically used Guido's circuit for PMD100, but used a set of jumper switches instead of a PIC: DIYHiFi.org • View topic - PMD100 to TDA1541
It's possible, if I could be bothered that I could now use the pi instead of a PIC to program the filter chip using I2C.

(I think there's a diyaudio thread about 7220, where I account my move to PMD100, I think it's easy to find).

I do recall that I did have to modify the driver slightly to get it to work with the PMD100 - I can't quite recall but it was a couple of register pokes to setup an external clock to the pi and to tweak the frame size of the I2S output. I think it's (sort of) detailed in the raspberry pi thread somewhere: Raspberry Pi • View topic - I2S: Anyone got it running? (answer is yes!)

(I do want to update the kernel and rebase my mods, but I'm not in a hurry to do so at the moment).

Abraxilito, 2x NOS is probably not going to make a huge difference. What digital filter did you use? The 4x 7220 was ok, nothing to shout about in my opinion to the 100 for instance. However, you get interesting electrical issues when you start playing with higher frequencies.

When I have access to a scanner, I shall post my IV stage - although it's a work in progress.
I also have more fun with the PSU lined up, an enclosure to sort out and I really want to do something about the clock.... Won't happen overnight though.
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Old 18th March 2014, 01:08 PM   #6
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2X OS was done on an LPC1114 or LPC1313 (can't recall which) with a quasi minimum-phase FIR I designed myself. SAA7220 is a very electrically noisy chip taking as it does about 1W of power - tends to need extra-special care to PSU regulation. In contrast the LPCs (ARM Cortex M0 and M3) take about 40mW or so.

Incidentally how did you feed 8X I2S to the TDA1541A?In my understanding it only accepts data that fast in a mode with two data pins.
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Old 18th March 2014, 03:49 PM   #7
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Correct, 8x i2s straight to tda1541a, so 4 wires.
Clk, bclk, datal, datar.
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