Hi Vincent, watched all your videos on your products which are great. I noted your comments about using opamps. But as you noted, the circuit requires to be matched to the input impedance and sensitivity of the (pre) amp and all those variables change the “voice” of the unit considerably. Therefore I thought it might be an interesting excercise to try.
In one of your videos you go through the various caps and settled on a reasonably priced copper foil cap. Could you share the brand or link to those? I’ve found a few that look the same on Aliexpress but these are still around $50 or more each.
Re your calculations for the size of these caps, I think the lower frequency would lie too high when using a 0.22uf cap, as the calculation of 14.47hz yiu showed in the vid, I think represents the -3db point of the slope, not the 0db point. This means that the 0db or starting point of the slope starts at approx 100hz (-0.1db at 45.75hz), which is well above where you would want it to be. Using the suggested 10uf values is probably overkill given your impedance of 50k, but something between 1uf = 31.8 hz and 4.7uf = 6.8hz would likely provide a better bass curve. Additionally these smaller cap values will start to introduce larger phase shifts in the bass region, with the 0.22uf having potentially more than 15deg phase shift, 1uf = 9deg and 4.7uf = 2deg, which is more acceptable. Anyway, just my 2 cents worth
Yes, you’re right about the bass response. But my tube amp has an input impedance of 100K and my bookshelf speakers (and tube amps) cannot reach that low frequency, 0.22uF can meet many applications. Of course it would be great to have a higher capacitance value but as you already mentioned, these caps are very expensive. As far as I’m happy with the bass (in fact the bass response is stronger and well-controlled than other DAC), I can only make a trade-off (P.S. physical size is another consideration).
You’re also right about the impedance matching and sensitivity. As what I showed in the video, not all of the output transformers are suitable for the DAC, even if they have the similar frequency response. Some have very low input impedance which leads to heavy distortions (TDA1541 cannot deliver enough current).
Regarding the coupling caps, they were purchased from the small local workshop. The brand name is “Pan Ocean” and I just Googled it and saw someone is selling them at AliExpress:
Thanks for watching my video! I’m still new to TDA1541(A) and learning every day. Working on a new streamer with dual TDA1541A and will share the result later on.
Hi Vincent,
I appreciate your approach. Especially your search for characteristic like “no fatigue” or if one wants to keep listening. I would add “volume” – how low can it be.
Almost a decade we played around with PSUs on the first DAC HATs for the Pi
Now we seem to have time again and want to get into multibit DACs which brings us directly to the output stage. First passiv, later I would like to try what Lampizator page index is talking about.
On your 10K:60K output transformer do you use an I/V resistor on the secondary windings?
Any recommendation where to get those transformers from?
Thanks
Thanks.
In fact, I’m not a fan of “volume control” because it sits on the audio path and the quality of the volume control affects the sound quality very much. I’d prefer to control the volume via software. Anyway, the I2S signal contains the volume data which can be configured by the system.
I don’t have the I/V resistors on the 2nd windings of the 10K:60L output transformers, they should be placed right after the DAC. I got mine from a local shop but I found them available in AliExpress:
Note the as the voltage is amplified the current becomes smaller, it is more susceptible to EMI. In my latest project I use 10K:40K instead because now I have two DAC (so that I don’t need a large voltage gain).
Hi Vincent, I’ve put the DAC together and works like a charm. The only difference I notice is that volume output to the preamp is lower then what my external DAC delivers. Is there a way to give it some more gain?
Yes, it’s true that the output levels are lower than modern DAC because ProtoDAC ultlizes a passive I/V stage. However, the ProtoDAC delivers ~2Vpp with an 400R I/V resistor which should good enough for most of the power amps. You may either use an active pre-amp, or an output transformer in the link above. An 10K:40K output transformer doubles the output voltage.
Hope it helps.
Unfornately there is not enough space inside STEALTH V3.
Please also note that you may encounter an impedance mismatch problem if the secondary impedance is too high.
As you’re using a pre-amp, I think the output level shouldn’t be problem to you?
I have a passive preamp, but it’s acceptable. What i notice is a sort of clipping when using a crossfeed setting like the Bauer 700Hz/4.5dB (FusionDsp plugin Volumio). I wanted to test that to crank up the volume. Why is that happening? It does not clip with my external DAC.
Where do you position this DAC if you compare it with others? Do you have some measurements? Wish you all the best for 2025 and keep the innovation going, greatly appreciated!
I’m not familiar with the DSP (not a fan), not sure what leads to clipping but does this happen to some other I2S DAC HAT such as HiFiBerry? Probably a software issue I suppose.
Unfornately I don’t do measurement. Figures or data on paper cannot reflect the sound performance. I’d say this DAC is my 2nd favorite (note that it’s very personal and I love vocals), my most favorite is still TDA1541 (w/o A).
I believe the ones that I have are genuine but I had seen a different silkscreen printing due to the different lots and production factories.
Someone said inside the fake TDA1541(A) there are few TDA1543 or TDA1387 packed together but I can tell the difference among TDA1541(A), TDA1543 and TDA1387.
@Vincent_Fong
The Toroid Inductor in your design shown in “TDA1387 Schematic A5.PDF” shows a 40mH inductance. I am not able to find or source that part anywhere. Could it be that it should be 40uH instead? I would like to know what amperage the inductor have too :).
If not, could you perhaps give some pointers to where one could source them?
I just tried to filter out the high frequency noise from the Pi or power supply with a CLC filter as much as possible. The choke/inductor is tailor-made, probably you cannot find it in the market. But you may replace with anything you had. As the DAC does not consume much current, anything choke >100mA can do.
Hope it helps.
