MJOLNIR V 1.0(5 x TDA7293 IN PARALLEL)

[phoenix87]

Hi,
so i had recently built the mighty mini and designed the PCB , I am very happy with performance and simplicity of the chip TDA7293 , so I though why not make a parallel version of it to drive lower impedance loads .
I came up with a solution of using 5 TDA7293 in parallel in slave mode with a supply voltage of +- 40V to be driven down to 2E load.
Additional circuit for reliable operation
1. DC detect.
2. thermal over load
3. Click POP removal circuit that doubles up as a over-voltage protection ie it mutes the IC when the input voltage to the IC increases a certain predefined value.
Additional Features .
1. Added a preamp stage with variable gain.
2. Signal LED
3. Temp Controlled FAN speed controller.
4. Protect led
5. Fuses on power supply rails and output for added safety
6. Added bourchet cell to prevent oscillation
Estimated OUTPUT POWER

1. 80W @ 8E (+-40V)
2. 160W @ 4E (+-40V)
3. 320W @ 2E (+-40V)

i am yet to order the PCB, constructive criticism is most welcome.....

regards
Phoenix87

 

[CharlieLaub]

I have always been a fan of multiple paralleled (slave mode) TDA7293 chipamps. This is a pretty cool feature of the design for driving lower impedance loads. I think 5 in parallel is a good number since 2R is about the lowest load that will be encountered with home audio.

From my experience, one of the tricky points is the choice of capacitance for the bootstrap cap (use 20-50% more than datasheet recommends) and the tendency of the chip to explode if the negative rail is lost or does not come up before, and go down after, the other rails. For instance, if you fuse the negative rail and that fuse blows while the positive rail fuse remains intact, all the ICs will explode! Exciting, huh? But if you are familiar with these issues and know the usual ways to work around them you should be fine.

RE additional circuits: It wasn't clear to me if you were planning to integrate these into the PCB or provide additional standalone designs for these features. I don't think you will need the click and pop or DC detection circuits or fan speed controller. Access to the Mute and Standby mode pins for the master IC would be something that would be useful in case the user wants to control the amp behavior.

On the other hand, I think that it would be a good idea to build in a simple input gain (not really a preamp) circuit using an op-amp with 6-9dB of gain. You can then keep the amp gain around 28-20x and let the line level gain stage take care of the rest. The input sensitivity can be better controlled while reducing amp input resistance to reduce noise. With only a single op-amp in play and the max rail voltages known, and the op-amp current consumption known, you could implement the op-amp PS right from the rails using only a voltage divider and a one or two RC filtering stages to bring ripple under control as PSRR is only 75dB@100Hz.

 

[phoenix87]

the issue with the IC exploding , can be dealt by fusing only the positive rail , but explosion is a event of catastrophic failure ,if the fuse rating is done correctly both the fuses should blow at the same time .I have implemented the mentioned additional circuits in the PCB, the DC detect circuit is given to protect the speakers if anything goes wrong with amp it is a fail safe kept to protect the speakers . and as mentioned earlier the Click pop removal circuit actually doubles up as over voltage protection , the TDA7293 can survive +-60 with no signal , so the Click pop removal circuit actual mutes the TDA7293 if the power supply voltage goes above a predetermined value , this will particularly come in handy if some one plan of the using the amp close to its limits say 45-50V the amp will protect it self .And the fan control circuit is kept if some one uses a small heatsink ...a fan might just help.
And yes i have added a simple gain stage on the input i wrongly called it as a preamp ...

thanks charlie ...for the pointers I would be very happy if you would give some more .....

regards