Xmas Amp - Dibya's TDA7293 by Jhofland

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lykkedk

lykkedk

Member
Joined 2002
So i succesfully ordered all parts (not the PSU parts).

I'am also in luck that i recieved a discount from the Aisler pcb-house here in EU, so having ordered 3 pcs. of them the other day.
Anyway, what i'am searching for is a schematic of some psu with capacitance multiplier for this Xmas amp.:santa2:
Never tried one, so this time i will... I'am hoping someone here succesfully use one which to share?

Jesper.
 
lykkedk

lykkedk

Member
Joined 2002
So i digged down the capacitance multipler.

I found some very interessting articles along the way, and qouted directly from https://sound-au.com/project15.htm ::

If you are desirous of trying this circuit with a Class-AB amp, I would strongly recommend that the input to output voltage differential be increased (reduce the 12k resistor to do this). For optimum performance (depending on output voltage, the current variation, etc), I would suggest that a differential of 6V to 10V should be Ok, depending upon the power of the amp. Dissipation will need to be calculated (or measured), and remember that Class-AB amps can (and do) create peak currents which can be very high indeed. For the 20V (nominal) supply shown, peak current into an 8 ohm load is 2.5A (which was the design goal in the first place), but if the voltage is increased, peak currents increase in proportion.


As an example, consider a 100W amp (8 ohms). Peak current into a resistive load is about 3.6A, but when driven into a typical speaker load (whose impedance dips to (say) 3 ohms), the peak current will be 9.6A. This is not mere speculation, but reality - such peak currents are quite common - one of the reasons many manufacturers quote the peak output current of their amps. These specs can be as high as 40 Amps or more (for a 100W unit), which is overkill as it will never be used (40A requires a load that falls to 1 ohm - not a speaker I'd ever buy).


It must be remembered that this circuit acts in a manner very similar to a regulator - just without the regulation. If the output current is highly transient in nature, the circuit will allow hum to pass if the input voltage suddenly drops due to increased load (in the same way a regulator will).


Also note that the supply voltage to the power amp(s) will be modulated by the instantaneous current drain of the amp (which happens with 'conventional' supplies too). Maintaining a voltage differential sufficient to accommodate these variations is imperative.


When a capacitance multiplier is suddenly loaded, there may be some ripple 'breakthrough', because the voltage across the circuit is reduced when the load current is increased. If the voltage across the series pass transistor falls, there may not be sufficient reserve for the minimum value of ripple voltage (as described above). It is very uncommon to find capacitance multipliers used with Class-AB amplifiers, because their supply current is constantly changing.
Click to expand...

So i conclude that it's not necessary a good idea with AB amps.
I'am hoping someone here actually use some here, and perhaps show schematic/pictures of an successfully setup CMx

On the other way, if anyone have some good old psu setup, with the recommended capacitors (uF wise) and resistor size (CRC ?), or anything please show it :)
I'am still open for everything, and in no rush, just need some guidance to go the right path.

One more thing, how much current must i expect running it at some 8-5ohm speakers?

Jesper.
 
J

jimk04

Member
Joined 2018
Paid Member
Hopefully this will link to post #777
https://www.diyaudio.com/community/threads/xmas-amp-dibyas-tda7293-by-jhofland.365002/post-6815054

Showing my setup with a CRC. 10mF>1R>10mF per channel so 40000if in total. I do hear a slight hum at idle.

I have always wanted to try capmx in some different amp builds. I believe they are better in class A but I have a contact on here who tried one on a class AB and he reported a good improvement. I think you still want a reasonable bit of capacitance before the load, after the Capmx to cover you for those transients .
 
K

Keetesyflush

Member
Joined 2018
Hey y’all, just finished stuffing everything and a first power on. The dc offset was a bit too high and I realized I had started with 10k ohm at r15. Swapped it for 47k and I’m under 1mv now!

Initial listening on an old pair of infinity speakers I use in my garage for smoke tests is pretty good. I'm looking forward to boxing this up nice and finishing the build. Also spliced up an old computer power supply to reuse cable/connectors - completely hadn't even considered that until it was mentioned on this thread. I kinda like seeing "CPU" printed on the clips :D

IMG_6110.JPEG
 
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R

Roland968

Member
Joined 2020
xrk971 said:
Hi Folks,
Is there anyone in Germany that has a working Xmas amp? There are some folks on a German forum that might be interested in having a listening comparison with other amps. Please let me know if you are interested in a listening party.
Click to expand...
The boards are on their way to me, I have all the parts except for the LM317L/LM337L (could I just use the normal ones in the TO220 case?)
I then wanted to compare with existing amps, Sabaj A20a, Topping PA5, AIYIMA A07, German TDA7293 amp that was over 20 years old, HK 1200, NAD C320 BEE and Cyrus Two.
The Xmas amp should also serve as a basis for comparing power supplies (linear, with LT4230, cap multiplier, SMPS).
If someone comes from near Cologne with an interesting amp, a comparison would of course be interesting. Can you please send me the link to the forum or post it here?
 
xrk971

xrk971

Founder of XSA-Labs
Joined 2012
etsy.com/shop/XRKAudio
Paid Member
xrk971 said:
Hi Folks,
Is there anyone in Germany that has a working Xmas amp? There are some folks on a German forum that might be interested in having a listening comparison with other amps. Please let me know if you are interested in a listening party.
Click to expand...
@JPS64 will have more info on this amp shootout in Germany.

Yes, TO-220 voltage regulators can be used but the holes are small and for TO-92. You could solder smaller resistor legs to a regular one.

I just checked Mouser and over 400 TDA7293 in stock. Stock up while they last!

https://www.mouser.com/ProductDetail/STMicroelectronics/TDA7293V?qs=uepKQD%2BspxBrLGmEx5TjhQ==
 
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lykkedk

lykkedk

Member
Joined 2002
Hi all... and merry X-mas amp. ;) (Still waiting for the correct transformer from Poland)

Well, it won't be that long until i am ready to test some, therefore asking if it's just normal procedure when doing this, i mean:

All parts mounted, Input shorted, output with DMM (measuring DC-offset) and slowly turning up the variac looking for smoke, hot part's etc...
Right ?

Jesper.

IMG_4202.jpg
 
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Berlusconi

Berlusconi

Member
Joined 2019
Kay Pirinha said:
About a whooping USD 12 apiece
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For "whooping 12 bucks" you can buy yourself three cappucinos in any better european restaurant!
That's normal price at any trustworthy seller. Recently I've purchased at Mouser, Farnell and Reichelt at approximately the same price, 11 to 12 EUR. Purchasing at lower price is too expensive... if you allow for the risk, or should I say certainty of getting fakes.
 
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xrk971

xrk971

Founder of XSA-Labs
Joined 2012
etsy.com/shop/XRKAudio
Paid Member
lykkedk said:
Hi all... and merry X-mas amp. ;) (Still waiting for the correct transformer from Poland)

Well, it won't be that long until i am ready to test some, therefore asking if it's just normal procedure when doing this, i mean:

All parts mounted, Input shorted, output with DMM (measuring DC-offset) and slowly turning up the variac looking for smoke, hot part's etc...
Right ?

Jesper.

View attachment 1130359
Click to expand...
Nice work. Yes, measure output voltage DC offset. If that is high, something is wrong. Look for smoke or listen for strange sounds. It’s a pretty easy amp to startup if assembled correctly. Good luck.
 
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