Xmas Amp - Dibya's TDA7293 by Jhofland

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#202
Hi Folks,
Just a reminder that the boards will be arriving soon but only a fraction of people who signed up have sent me payment for the shipping. Here is the list so far from the Swap Meet thread for the logistics.

Here is the list of people who have sent me shipping payment:

Jlevro
Astromo
Nautibuoy
kp93300
Signal lost
Chermann
Twocents
Invaderzim
Francois G
Tubesguy
Sixto
Angchuck
Click to expand...

Dibya’s TDA7293 Xmas amp by Jhofland - Giveaway
 
#205
Hi X, that's a very helpful diagram. I agree with all the comments about isolating grounds... I am mostly unfamiliar with the buffer (whether it's an off-the shelf or custom item - essentially how to buy or make one?)... also i have not previously seen using a second NTC and 22 uF MKP in parallel connecting the clean ground form the secondaries to chassis. (see red dashed outline added to your diagram) I understand the use of GLB's everywhere else, just haven't seen an NTC used in this way before.

Thanks! - Six.

xrk971 said:
It’s not a trick but a fortunate case that adding a buffer in between my signal source and amp cleaned things up. The buffer has a ground loop breaker to isolate dirty vs clean ground (as do all the other circuits). The buffer happens to have its own separate wall power supply and an isolated DCDC step up dual rail PSU (Murata). Here is sketch of my setup.
Click to expand...
 

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#207
Sixto said:
Hi X, that's a very helpful diagram. I agree with all the comments about isolating grounds... I am mostly unfamiliar with the buffer (whether it's an off-the shelf or custom item - essentially how to buy or make one?)... also i have not previously seen using a second NTC and 22 uF MKP in parallel connecting the clean ground form the secondaries to chassis. (see red dashed outline added to your diagram) I understand the use of GLB's everywhere else, just haven't seen an NTC used in this way before.

Thanks! - Six.
Click to expand...

The NTC (8D-20 or CL-60) provides a nominal 8ohm to 10ohm resistance when cold. Just like a resistor. However, if there is a catastrophic fault and full current needs to shunt to ground, the NTC heats up and is about 0.5ohm to allow the current to safely get dissipated. Alternatively, two anti parallel diodes conduct when voltage is greater than 0.6v and allow more current to flow. The 22nF (or 100nF) cap is there as an RF shunt to reduce radio noise. You will need really big diodes to handle 10A currents and the single NTC is more cost effective and compact way to do this.

Someone else posted the link to the buffer.
 
#209
Elna Silmic II

Dibya said:
Secret Sauce in the recipe:

Want a 50W Tube like Amp to drive your bookshelf speaker with less than 1% THD?

* Use Desktop Class A or Pocket Class A Headphone amp by XRK971 as a
Preamp
* Replace C5 and C11 with Elna Silmic II 100uf 50v ( I still have no explanation how PSU cap effect sounds)
Click to expand...

Hi Dibya and other builders,

Mouser does not have any of the Nichicon 100uF 50V caps for C16 in stock at present. Can I use the Elna Silmic II caps in the above quote for all caps C16, C5, C6, C9, C11 even though C5, C6, C9, C11 are supposed to be 220uF. I just happen to have these caps on hand.

Thanks for the help,

Myles
 
#211
Kokanee said:
Hi Dibya and other builders,

Mouser does not have any of the Nichicon 100uF 50V caps for C16 in stock at present. Can I use the Elna Silmic II caps in the above quote for all caps C16, C5, C6, C9, C11 even though C5, C6, C9, C11 are supposed to be 220uF. I just happen to have these caps on hand.

Thanks for the help,

Myles
Click to expand...

Hi Myles,

Go ahead , give 100hrs of burn in as otherwise silmic may sound bit muddy reason I prefer Muse caps as they don't require ingredient called patiance, you can't buy patience from mouser, digikey and rs components unfortunately.
 
#217
Ok, got it Dibya. Thanks :up:

As for the DC servo:
In the #1 post it is written "Note that if populating the DC servo, C17 and C2 should be replaced with jumpers."
In the build shown in the #171 post, C17 is not replaced by a jumper.
What would be the best practice?
 
#218
C17 is a bypass cap for C2.
C2 has a jumper installed which negates any effect C17 would have.
X just hasn’t removed the film cap yet. 😀

With a fresh unpopulated board, a jumper in C2 is sufficient. Leave C17 empty.
 
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