TDA7293 parallel design DIY

[hydrovac]

I have the thing up and running... sounds pretty good (mono so far, haven't put in the other channel). I've been testing it using a variac supplying power to the 32-0-32 tranny with input voltages of +/- 35 volts up to +/- 42 volts to the amp. I've used 8 and 4 ohm loads havent pushed the 4 ohm loads too hard.

The chips are running for a month here at these rails, definitively the chip can handle it. The only thing to make sure is, not dissipating more than 50W on the chip... can't find any formula to compute this dissipation though.

For amps, I'd distrust anything that has the power supply on same board. The "included" power supplies are normally minimum "get by" designs that fit into the smallest space possible, which makes the board cost lowest possible, also at the cost of least possible audio quality.

So, I like small double-sided amp boards + separate power supply boards.
A 30-0-30 VAC 400Va transformer and a split rail power board, is pretty much standardized for this amplifier separate rectifiers and smoothing circuit, is the least I would like to use.

DIY power supply board:

7293 chips, decoupling (Elna) and filter caps:

30-0-30 toroidal 13Amps:

Also made a single chip PCB, just in case might come in handy for three way actives:

will start the build tomorrow.

 

[captrajesh]

Congratulations Hydrovac. Hope the amp would be ready in time when I visit Hyderabad next.

 

[GeorgeO]

Excellent going so far, hope things evolve as planned. Good luck!

 

[saheb11123]

Waiting to see the end result eagerly

 

[hydrovac]

Congratulations Hydrovac. Hope the amp would be ready in time when I visit Hyderabad next.

Thanks capt!
I will try to complete the build by that time

Excellent going so far, hope things evolve as planned. Good luck!

Yes George,
Things seem to be going as planned (leaving the time component out!) Thank you.

Waiting to see the end result eagerly

@saheb11123
Here goes,

Both the populated amp boards ready:

PSU boards assembled:

Amp and PSU board modules on heat sink:

Chassis with transformer and connectors:

 

[keith_correa]

What is the reason for mounting the PS board on the heat sink? Convenience?

And, no heat sink for the rectifier?

Also, I just noticed that the back of the TDA's are not flush with the edge of the board, so, are you getting complete surface contact with the heatsink?

Edit: I took a look at a previous pic of the board with heatsink and see that you have used a "spacer" sheet to fill in the gap.

What did you use to calculate the optimal total capacitance needed for the reservoir caps in the PS? Where are the Zypher Labs Sonocaps available? Cost per cap?

Nice build, BTW!

 

[lifewater]

Hi Krishna Sir,

Lovely professional looking stuff. Great finish.... Do keep up the good work.

Best wishes,

Lifewater

 

[saheb11123]

Wow!!
Looks very neat and good.
I bet it sounds great too.
What will be the tonality compared against a discrete deaign?

 

[hydrovac]

What is the reason for mounting the PS board on the heat sink? Convenience?

And, no heat sink for the rectifier?

Nice build, BTW!

Inconvenience in mounting it elsewhere in the cab. :sad:

35Amp bridge for only 6Amp load... the rectifier's metal casing will suffice. However, as there is a provision for heat sink, i will mount one.

Nice compliment! Thanks

I am trying to squeeze the whole thing in this old chassis I had.
Internal dimensions: 30Wx21Dx15H cm

Heatsinks on rectifiers:
available source of heat sinks and price not known!

 

[hydrovac]

Hi Krishna Sir,

Lovely professional looking stuff. Great finish.... Do keep up the good work.

Best wishes,

Lifewater

Wow!!
Looks very neat and good.
I bet it sounds great too.
What will be the tonality compared against a discrete deaign?

Thanks Pranjal and saheb for your encouragement... will be posting listening impressions.

 

[saheb11123]

The cabinet looks faboluous. The sinks are huge and looks nice.

 

[hydrovac]

Also, I just noticed that the back of the TDA's are not flush with the edge of the board, so, are you getting complete surface contact with the heatsink?

Edit: I took a look at a previous pic of the board with heatsink and see that you have used a "spacer" sheet to fill in the gap.

What did you use to calculate the optimal total capacitance needed for the reservoir caps in the PS? Where are the Zypher Labs Sonocaps available? Cost per cap?

I admire your keen observation for minute but important details
The chip mounting surface is offset by 3 mm from the edge of PCB, so I had to use a spacer bar machined nicely to mirror finish on both sides,
and tether it to the heat sink, (Applying heat sink compound) for optimum surface contact.
Direct mounting on the heat sink is more desirable if possible.

There are many different methods about calculating values of capacitors for various applications. There is no one size fits all rule for caps.
This whole matter is a bit of an art form... I wish there were a simple formula, but there isn't one.

How I'd do it an easy to recon old school formula of 500-800 uF/Watt as a general rule of thumb, and as my pocket book permits.
I am not sure if is that what you want, since there are all sorts of situations using decoupling/filter capacitors. I only mentioned because it is a common application.

But, what if your requirements are different? What if you want to run a pure class A amplifier, or you want a 150W/8 Ohms amp using higher than usual bias levels?
It depends on the situation where do you want to use it. Please, be more specific Post a circuit diagram, so we can help.
In short, theory is nice, but nothing beats hard practice.

Look for http://www.ti.com/lit/an/slta055/slta055.pdf from TI that gives a pretty good explanation about capacitors.
I hope all this has cleared up some points and perhaps helped you learn a few interesting details.

As of now there are many projects on hand, and the subject capacitors are from one of the various sources I procure the components from, for my DIY hobby.

Good luck with your knowledge quest... It will take some time but as you gain experience, things will get clearer.

Cheers!

 

[saheb11123]

@hydrovac
I am coming to your house to loot the caps!!
WOW!! Its cap heaven..

Also on another note, is there a sonic difference with different caps i.e, for example sprague vs elna vs nichicon vs samwha etc.

 

[GeorgeO]

Krishna

Time overrun is normal, cost over run is what hurts :sad:, where did you source the RCAs and binding posts? I'm interested since I've got an amp build in the pipeline.

Thanks

 

[hydrovac]

George, the binding posts and RCA sockets are from neighborhood MX shoppe...

Basic concept:
A compact amplifier is particularly interesting for anyone who wants more than simple stereo operation- in other words, anyone who wants to configure a system with bi-amplification, active speakers or multiple channels.
Such systems sound best when all amplifiers have the same construction. That's how the P7293 came about. The amp uses 2 TDA7293 per channel.

Assembly time! Dual Mono block:
In this simplest case, a complete two channels and power supply are built into a single enclosure, resulting in a small, ready-to-use amp.
As stated, by using a 30vac 400vA transformer to run at 42vdc, it can provide 100W into 8ohm, or 150W into 4ohm...
Apparently cheap and common, these chips can provide enough juice for active systems and the quality should be more than adequate.

Sec voltage

Nice and steady VDC

Dual rail voltage

Full amplifier:
If we place a selector switch and a potentiometer ahead of the inputs of a stereo version of our amplifier, we have a miniature version of a full amplifier.
The gain of the compact final amplifier is fully adequate for a high-level signal source, such as a CD player. If more gain is needed, a small op-amp preamp stage can be added to the configuration.

Listening Impressions:
I'm prepared for it to be utter rubbish two TDA7293 makes a wonderfully robust, single ended amp in parallel mode, the chip sounds very different.
Transients seemed to be accentuated more than with the other chip amps. Details at the rear of the soundstage seemed more defined assuming the use of an adequate power supply and good-quality components,
the versatile amp is distinguished by a warm, vivacious sound image. In bi-amping or active-loudspeaker operation, it can compete with amplifiers having much greater output power.

Gear used:
Arcam Delta 270 CDP, DIY preamp, Boston Acoustics A26 book shelf, Monster Audio 12 gauge sp cable, Mogami 2803 Amphenol rca ICs DIY.

Mission accomplished... thanks for reading

 

[flat_listener]

looks good Hydrovac,

Are you going to silk screen component mask and maybe sell on some extra boards for those that might want? any moq to make the PCB?

What active option are you attempting? DSP pre amplifiers or just 3 way internal speaker crossovers?

best luck!

 

[lifewater]

looks good Hydrovac,

Are you going to silk screen component mask and maybe sell on some extra boards for those that might want? any moq to make the PCB?

What active option are you attempting? DSP pre amplifiers or just 3 way internal speaker crossovers?

best luck!

Worth a thought Krishna..

 

[hydrovac]

@flat_listener,
@Pranjal,

Thanks for your interest in the project;
I didnt use the silk screen because this amp is intended for my personal build... building your own amplifier and optimizing price/performance is generally mutually incompatible. The solder-in parts may seem to have an attractive price,
but by the time you obtain the circuit board, heat sinks, power transformer, enclosure box, connectors and all the rest, you will find that build-it-yourself amplifiers are about fun, not saving bucks.

In building your own stuff... apart from the hard work; you also need to know what exactly you're doing. Otherwise one might end up damaging something due to negligence of basic safety design features
(I'm talking about the enclosure, not the circuit board). I am not aware of your DIY skills though.

I will be using a Sherbourn PT-7020A pre/pro for signal processing. Couple of sp formats under consideration will figure out the rest, once that is finalized.
As for selling the PCB, I have no intention to do so however if you are really interested, let me check if I can spare a pair of boards for you.

 

[saheb11123]

Great build looks wonderful.

 

[captrajesh]

I and my friend John found the datasheet of TDA7293. This IC can run up to 100V, low distortion, and can easily be paralleled.

I was discussing with someone about this project. He said that it is very difficult implement a design paralleling chips, especially this one. Is it so?

Congratulations Hydrovac. Hope the amp would be ready in time when I visit Hyderabad next.

Thanks capt!
I will try to complete the build by that time

Looks like I'm not going to visit Hyderabad anytime soon. As discussed, you may consider an amp tour, starting with me.

I guess this one is heavy. May be you can consider the single chip version. That will do as the sound signature would be similar.