ProtoDAC TDA1387 X8 project

[hifinet]

Recently I built a 6N16B Russian subminiature tube output in SRPP configuration as output stage of the TDA1387 DAC with MoOde 9.0.6. Fun and very cute. This is the Mikrolampizator by Lukasz Fikus of Lampizator. Highly recommended to any DIYer.

https://www.youtube.com/watch?v=cg9WqhtLzhI

In my experience, the subminiature tubes are excellent, both US and Soviet variants. They sound great, and they are very inexpensive compared to the miniature counterparts. Thank you for sharing.

[hifinet]

One comment on the Lampizator circuits is regarding the bypass cap (100uF) across the cathode resistor. If the added gain is not needed, I think it generally sounds better without the cap. The audio signal is essentially passing through the electrolytic capacitor, which adds coloration (the same applies to cathode bias in the power amp output stage; fixed bias sounds better). Also, without the cap, there is some local feedback, which reduces distortion.

[Skip Pack]

Hello @hifinet,

I'm curious if you or any of our fellow ProtoDAC constructors have used Abraxilito's Dark LED Filter I/V conversion board with a ProtoDAC. I understand that his board may need some adjustment to accommodate the higher current from the 1387 X 8 compound board used in the ProtoDAC. Your knowledge and impressions are most welcome.

Thanks,  Skip

[hifinet]

I have no experience with the project. What sounds good to me is the "grounded base (discrete) cascoded stage" and the "passive I/V followed by a single-ended output buffer". I will pass on the "9th order LC filter", since it's unnecessary. I can't hear anywhere close to 24.1kHz or higher. Why do I need a 40dB attenuation filter at 24.1kHz? I already have two.

Quote from the Burr Brown PCM56 datasheet page 7:

"A low-pass filter is required after the PCM56 to remove all unwanted frequency components caused by the sampling frequency as well as those resulting from the discrete nature of the D/A output. This filter must have a flat frequency response over the entire audio band (0-20kHz) and a very high attenuation above 20kHz. Most previous digital audio circuits used a higher order (9-13 pole) analog filter. However, the phase response of an analog filter with these amplitude characteristics is nonlinear and can disturb the pulse-shaped characteristic transients contained in music."

I have a great deal of respect for Abrax. He is an actual EE, and his products have quite a following. In a brief interaction with me, he did make this statement: "Having recently done comparisons between NOS without filter and with filter I hear clear differences. I guess I can only attribute them to images being heard indirectly via intermodulation as I can't think of another explanation. Perhaps its that my amps are more susceptible than others' to IMD as there are guys on this forum who hear nothing wrong with NOS DACs without an anti-imaging filter."

[hifinet]

In this post, he says three TDA1387 will drive the IV stage to maximum output.

In this post, he suggests using a "series and shunt combination of resistors", provided the DACs output compliance isn't exceeded. Or limit the digital volume.

Reducing the Vdd from 5V to 3V will decrease the output current of each TDA1387 from 1mA to 0.6mA.

[Skip Pack]

Thanks for your impressions. My observations, though with much less understanding, are similar. I suspect his board would help some amp/speaker combinations but make little difference or slightly degrade others. I wouldn't try it soon (this year), but I'll follow this thread.

[springle19]

Folks

Very happy with my protoDAC build, and great instructions to work to. Lovely, rich, and clear sound thru my 43 year old Rotel 820BX and Tannoy Mercuries. But, by God, was doing the soldering hard work - my eyes are a fraction of what they used to be! 

One minor point. I do hear a minor 'click' thru the speakers when I press 'play' in moode, a fraction of a second before the selected track starts playing. I think this is protoDAC related.  Annoying rather than fundamental, and no evidence the issue persists once the track is up-and-running

Any thoughts on why I have got this and a possible fix?

Best, Simon P

PS Mark W - HiFi Collective came good on the Charcrofts . . .

[hifinet]

Folks

Very happy with my protoDAC build, and great instructions to work to. Lovely, rich, and clear sound thru my 43 year old Rotel 820BX and Tannoy Mercuries. But, by God, was doing the soldering hard work - my eyes are a fraction of what they used to be! 

One minor point. I do hear a minor 'click' thru the speakers when I press 'play' in moode, a fraction of a second before the selected track starts playing. I think this is protoDAC related.  Annoying rather than fundamental, and no evidence the issue persists once the track is up-and-running

Any thoughts on why I have got this and a possible fix?

Best, Simon P

PS Mark W - HiFi Collective came good on the Charcrofts . . .

Hi Simon P,

Thank you for the kind words.

I think the click is module related. Probably one chip on the module. The fix is to replace the module. Not an easy thing to do, unless you have excellent desoldering equipment. Do you get a click before each track in the playlist, or just at the beginning of the first track?

Mark

[springle19]

Folks

Very happy with my protoDAC build, and great instructions to work to. Lovely, rich, and clear sound thru my 43 year old Rotel 820BX and Tannoy Mercuries. But, by God, was doing the soldering hard work - my eyes are a fraction of what they used to be! 

One minor point. I do hear a minor 'click' thru the speakers when I press 'play' in moode, a fraction of a second before the selected track starts playing. I think this is protoDAC related.  Annoying rather than fundamental, and no evidence the issue persists once the track is up-and-running

Any thoughts on why I have got this and a possible fix?

Best, Simon P

PS Mark W - HiFi Collective came good on the Charcrofts . . .

Hi Simon P,

Thank you for the kind words.

I think the click is module related. Probably one chip on the module. The fix is to replace the module. Not an easy thing to do, unless you have excellent desoldering equipment. Do you get a click before each track in the playlist, or just at the beginning of the first track?

Mark

Mark

Thanks for the prompt reply

The click diagnosis is a bit tricky, at least toggling forwards/backwards in short order (with 4 or 5 seconds per track) using a short test playlist . . .

Under these circs, I get a click (on both left and right channels) at the start of maybe every third of fourth item, but the click does differ in intensity. If I didn't know better, I'd say it sounded like a bit of static or a needle going down on an LP (NOTE: am using test tracks from a flac-ed CD)

Possible soldering issue to revisit/check? If I have to go down the module replacement route, that should be pretty hassle free given I used a mount for the module, so can pop it out.

So far, I can't hear clicks within tracks, only as tracks initiate playing, so I need to keep some proportion . . .

Your thoughts appreciated

[hifinet]

I think the clicks might be due to a noncontinuous DATA I2S stream. So the click happens at the start of the DATA stream. If the tracks are played gapless, then the DATA stream is continuous, and there are no clicks (or the chance of a click is greatly reduced) at the start of the next track. I can occasionally get a tick (small click) at the end of the playlist. The modules are now very inexpensive, and if yours is socketed, I would just try another.

My TeraDak TDA1387*8 consistently made a sound of a record skipping a couple of grooves at the beginning of play.