ProtoDAC TDA1387 X8 project

[thomaschan]

@thomaschan This reminds me of a favorite FET preamp from Audio Amateur in the 70's. A single stage FET common source amplifier is essentially a single ended triode, without the heater supply. THD will be in the 0.1-0.2% range, and with the proper part, mostly H2. The best sounding tubes have low THD, almost all H2 and virtually no H3. THD with the FET circuit can be lowered by increasing the supply voltage with excellent voltage regulation.

The output of TDA1387 X8 is up to 800mV with a 100 ohm I/V resistor. I wonder if that is high enough to be fed directly to the MBL6010 based preamp. Does it have enough sensitivity, gain and is it low noise?

In the D1 thread, the consensus was that the best sounding circuits have the lowest parts count with the shortest signal path. In that circuit, they used high output MOSFETs in a simple circuit and cranked the voltage up to +45/-45V to get lowest THD.

In my limited experience with 3 different tube output and FET output with TDA1387 x8, I had to change the I/V resistor value to have better sound quality. In all 3 cases with tube, I had to reduce the resistor value in order to avoid clipping. 

I have yet to connect the  FET output to the 6010 preamp. I'll let you know afterwards.

[thomaschan]

@thomaschan The BF245B circuit with the 820 ohm source resistor is biased for a TDA1541A. The TDA1387 X8 will have a different bias point. I think the TDA1541 sinks about 4mA current at idle. The TDA1387 X8 produces about 4.5mA current at idle (based on 1.9V/420 ohm I/V resistor). After the 1541, the voltage on the gate with 100 ohm I/V is -0.4V. With the 1387 it is +0.45V (you can confirm and measure this voltage at the gate with a DMM). With the 820 ohm source resistor, I think the BF245B is under biased. To achieve the same bias point as the 1541, the value of the source resistor should be increased to 1000 ohms. You could try it and see if it sounds better.

I am using 92 ohm I/V resistor. I'll do some measurements this weekend and let you know.

[speedy210]

Hello, can anyone tell me where I can get the circuit boards for the TDA1387? 

[hifinet]

I don't know. If you find out or get the Gerbers, let me know.

Assembled modules are here .

[speedy210]

So far I haven't found anything anywhere. Otherwise I'll be happy to get back to you. Yes, I recently ordered two modules from the Ali-store.

[hifinet]

You could ask the UK eBay seller kinkin0000 if he sells the TDA1387 X8 PCBs. He designs his own PCBs. His ProtoDAC PCB looks very well designed. $4 each for the preassembled modules on Ali is already pretty cheap. The DAC chips are pretty cheap, but I'm not sure you could construct the modules yourself for much less.

The schematic is very simple, since it is just eight chips in parallel with 100nF decoupling and 1uF pin 7 caps. Only 7 active pins on the DIP 28. I am pretty sure it is a two layer PCB. diyA @Kleinhorn could probably whip out the PCB design in KiCAD in very little time, with the proper incentive...

[speedy210]

The question is whether these might not be better?

http://kwlhk.en.seekic.com/product/integ...A1387.html

Yes, they are more expensive, but if the quality or the audio sample is better, then they are worth it.

[Tim Curtis]

The question is whether these might not be better?

http://kwlhk.en.seekic.com/product/integ...A1387.html

Yes, they are more expensive, but if the quality or the audio sample is better, then they are worth it.

They are probably sourcing them from the same overseas chip-pull industry as the manufacturer of the 8-chip module.

AFAIK there isn't any New Order Stock TDA1387 left in the world.

[speedy210]

Thanks @Tim, yes of course that could be the case. If you want to be on the safe side, you could remove the 1381 from an old device. That's what I wanted to do with a TDA1541.

[hifinet]

Creative Labs Soundblaster Cards circa 1995. One chip per board. I'm sure almost all ended up in China for harvesting or the landfill. No CD players that I am aware of. It came along at the end of multibit DACs. Delta sigma DACs killed it spec wise. That was the end of it.

TDA1387 Creative_Labs_Soundblaster_AWE64_Gold_CT4390

TDA1387 Creative_Sound_Blaster_AWE32_PNP_CT3990

What would make a difference is to change the 1uF ceramic caps to acrylic, if it will fit.