TDA1387 continuous calibration dac

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At the risk of patronizing you, are you sure the polarity of the cap was correct? Positive to pin7, negative to ground? What kind of cap was it? Are you sure the cap is good?

Since I have hollowman on ignore I'll just point out here that the leakage of the cap could be an issue -a new cap might well take time for the oxide layer to form. With high leakage there will be little or no sound as the pin7 voltage will be lower than normal. I cannot explain the presence of hum - sounds like some wiring mistake was made in the process. I've shorted pin7 to GND (pin4) and the result was silence on my DAC, not hum.
 
I use 2200uF, and its sound good on my Orange Pi PC :D
 

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The red board you can see in this picture holds the CLCLC filter (left side) and the right side is the I/V stage. Because the filter needs a well-defined load, I bias the I/V transistor with more current (about 20mA) to get this particular load impedance. The extra transistors on the right are biassing current sources.
 

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Strange results...

Since I have hollowman on ignore I'll just point out here that the leakage of the cap could be an issue -a new cap might well take time for the oxide layer to form. With high leakage there will be little or no sound as the pin7 voltage will be lower than normal. I cannot explain the presence of hum - sounds like some wiring mistake was made in the process. I've shorted pin7 to GND (pin4) and the result was silence on my DAC, not hum.

Put same 1000uF Jamicon back in. Now: No hum whatsoever, with good sound (yes: improved over orig. 1uF). Weird!

Then, replaced 1000uF Jamicon with new Panasonic FM-series 2200uF/25v. Mild hum audible at max volume. In any case, SQ seems improved over Jamicon. Pana FM's take a few hours to break in. Hum may go away (??).
 
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Put same 1000uF Jamicon back in. Now: No hum whatsoever, with good sound (yes: improved over orig. 1uF). Weird!

Then, replaced 1000uF Jamicon with new Panasonic FM-series 2200uF/25v. Mild hum audible at max volume. In any case, SQ seems improved over Jamicon. Pana FM's take a few hours to break in. Hum may go away (??).

Hrm, that is interesting. Would you be willing to post the specific model numbers for those caps?

On my tda1387x8 DAC, I had quite a hum too. But I also did all kinds of hackery on that DAC, so I assumed I introduced a ground loop somewhere. And I didn't notice which mod caused the hum, as all along the way I had a pot (for volume control) between the DAC and amp. I'm not in the habit of listening at max volume, so keeping levels below the 50% mark or so totally masked the hum.

I can't remember which caps I used for pin7, I'll have to check later.

But your experience suggests there could be something about the characteristics of the cap that might introduce hum.

Oh, one more question: how is your device grounded? Particularly, are you grounding your pin7 cap directly to the tda1387 chip's pin4? Or are you perhaps using a separate ground plane? If you have other dedicated grounds available, that might be something else to try.
 
Magnavox CD2000 with TDA1387 (non-oversampling)

With my TDA1387-based project, a primary objective was to do as little work as possible. I.e., soldering, PCBing, parts-ordering, etc.

Several years ago, I posted on a weird late-80s Magnavox (Philips) CD2000 single-play CD player that used a TDA1543 fed by a SAA7210 decoder. That's right: Philips left out the digital filter in a 1989 model!

I removed the orig. TDA1543-- along with its Pin 7 resistor -- and added an I2S-to-EIAJ converter plus a TDA1545 (and its Pin 7 components). Sound quality marginally improved. Replacing this monstrosity with a TDA1387 improved sound further --but I can't say why: that I2s/EIAJ circuit was a mess!

I also replaced all the aging electro caps, added an AuriCap across the mains, replaced stock diodes with Vishay Sinterglass Avalanche diodes, etc., etc.

I played around with the I/V and output/filter opamps -- swapping them with OPA2132s, adding power-rail snubbers, etc.

The biggest improvement was bypassing all those opamps; and, Instead, using a modded version of Rudolf B's I/V stage (I think Rudolf has posted several versions here on DIYA -- way back in 2003/2004?).

In the images below you can see the discrete I/V with glowing red biasing LEDs. It's stealing power (13v) from output-opamp's socket. The I/V opamp was removed -- leaving an empty socket where I could plug in wire-ends from the Rudolf I/V. (a lot of modularity was incorporated into this project -- I want "quick access" to previous designs).

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.
 
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Oh, one more question: how is your device grounded? Particularly, are you grounding your pin7 cap directly to the tda1387 chip's pin4? Or are you perhaps using a separate ground plane? If you have other dedicated grounds available, that might be something else to try.
I dunno what's up the "cap hum"???

To answer your question:
Pin 7 cap (negative) to Pin 4. See above images I just posted. I trimmed the leads to keep them as short as possible. It looks ugly but path length matters!
 
my build for a friend is pin 7 left floating its improve tonality rather than using a cap on pin 7, but there is a background noise floor heard, mostly on high volume. btw i used super capacitor 33000uf and can not found the improvement compare to 1uf.

once i use the 6 x tda1387 to directly 150 ohm earbud with no IV, sound realy good.. i use around 5K pot to attenuate the out put through pin 7 but it to short i think..
 
I am using active I/V now and find there's no benefit from having a pin7 cap any longer. The bass is normally excellent without a cap. The pin itself is sensitive to radiated noise though - don't attach any wire or track to it - if you do, you'll definitely need that 1uF cap to shunt the noise to ground.
 
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Hello guys! Does anybody know what RMS level will I get from standard datasheet application (2k7 resistors, op amp I/V)? I mean full scale level (0dB)

In a private email, I asked Abraxalito virtually the same question. His response:

abraxalito said:
We begin with the output current swing of the DAC - a single chip powered from 5V has 1mA total swing (neg to pos peaks). The I/V resistor turns this current into a voltage swing, bearing in mind we need the voltage swing to be less than 3.5V due to the restriction of the DAC's output voltage needing to be <=3.5V. So with 2k7 we're fine and get 2.7V swing which is just a bit under 1VRMS.

The only caveat is this was not in the context of opamp I/V. I'm not sure how opamps affect that calculation.
 
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