Xmas Amp - Dibya's TDA7293 by Jhofland

Yes, All Cee’s are in there.

In the future, I am not going to do anymore special orders of mixing / combining shipping. It’s too difficult to track and breaks the mindless work flow, thereby multiplying time involved by 3x.

Now I know why when you order something from Mouser, if you have a “change request” they will cancel the old order and make a new order.
 
After trying to figure out where all that mains noise was coming from, it seems that adding a OPA1656/LME49724 balanced/SE buffer (which has a 5kV isolated DC/DC converter for making the +/-12v rails) between the source and amp, and grounding the buffer's on-board GLB to earth ground helped things. For good measure, I also switched to Victor's ppb 1kHz oscillator. Things look better now and it would appear that I had a small ground loop somewhere that is now broken by the buffer. The 60Hz peak is about -93dB now, very acceptable result as that is basically same as noise floor of CD format. Also, the higher order harmonics of the 60Hz seem to also be controlled. For a typical 8Vrms into 10ohm case, the THD is now 0.0013% and H2 and H3 are about the same but higher orders are monotonically descending:

X: are you advocating that the BTSB buffer be part of the normal build to achieve the best possible sounding amp?

Hope you’re digging out..


Thanks, Pete
 
Hi Pete,
As much as I would like to say using the BTSB will make it sound better (it might) I only used it in trying to break the ground loop that I had. If you need a little more gain or if you are using a balanced source, the BTSB can reduce noise pickup. It really is a handy little preamp.
 
Hi Pete,
As much as I would like to say using the BTSB will make it sound better (it might) I only used it in trying to break the ground loop that I had. If you need a little more gain or if you are using a balanced source, the BTSB can reduce noise pickup. It really is a handy little preamp.

So your ground loop issue shouldn’t be a common issue with the building of this amp, i.e., the BTSB unit isn’t a necessity? I already have a dedicated preamp (Akitika PR-101).

Thanks

Pete
 
No, the ground loop has to do with one’s particular setup with regards to the source and how things are wired. Vunce, for example, did not have an issue. Generally, using a single PSU has more potential for ground loops on the input signals. Going to a dual mono PSU and amp is generally better.

The ground loop was still relatively low at -65dB (acceptable to many people) and only audible with ear pressed to the speaker cone. With the balanced source into the BTSB, it was maybe -97dB basically inaudible.

Besides good ground wiring topology schemes (star ground and use GLBs between analog ground 0v and dirty ground/chassis ground), sometimes ground loops come down to the types of opamps we have in our preamps or front end. FET based input stages have essentially zero current and thus less prone to ground loops compared to BJT input gates.
 
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Besides good ground wiring topology schemes (star ground and use GLBs between analog ground 0v and dirty ground/chassis ground)

Thanks X. Yup, star grounds are part of my routine building behaviors and have had to use GLBs on occasion when nothing else seemed to work. I went ahead and ordered 5 sets of boards made so you might as well as pull my name from the freebie list. I’ll order the BTSB SMD board if any noise issues can’t be solved any other way. I use SE in & out.

Regards & dug out,

Pete
 
Here are the final design files with the following changes:...

New and final board layout (107mm x 65mm):

Hi,
Looks like the board was made using kicad (?). What is the recommended way to import/open the gerber files?
Newbie here, tried with the import function in eagle but got weird results with some lines/traces going completely off the board.
As far as I understood, 'F' files are for the top layer, 'B' for the bottom one.
Shall I install kicad instead?
Thanks in advance for the info.
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