Modular Subwoofer Amplifier build

QUAD 33-303 Pre & Power Amplifier
t.antony

t.antony

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This is an experimental project for my ported subwoofer as good plate amps need to be imported and a bit expensive to come by. This amplifier uses easier to get (and cheap) TDA7293 chips.

Before going further, I would like to thank Goldy Rathore for helping me in this project. As my experience in building an amp from scratch is limited to few veroboard experiments, his suggestions and the URLs he shared proved to be very valuable.

I came across this schematic (TDA7294 x 8 = 800w.jpg - 4shared.com - photo sharing - download image) in the web that uses 8 ics in a bridged-parallel way. Since my power requirement was a modest 200W, thought of modifying this schematic to better suit my needs. Goldy recommended 4 IC modular version by limiting output power to about 200w@4ohms and power supply to 320VA(25-0-25). He also suggested to design the PCB with an option for bridging two boards (bridged parallel mode) for combined output if more power if needed.

My main concern was the ability of the amp to provide sufficient gain in the lowest octaves, Which is addressed well in this article - Avoiding TDA7293 pitfalls. According to that article and as per the data sheet - TDA7293 Datasheet pdf - 120V-100W DMOS AUDIO AMPLIFIER WITH MUTE/ST-BY - ST Microelectronics (Page8), I have modified the schematic like below.

tda7293x4.gif


Its a simple modular application where the first IC is wired as master and the remaining 3 as slaves. Thought of posting it here for purview by knowledgeable members like Linuxguru
 
Last edited:
Antony,

This may turn out to be good in terms of performance. Does this operate in Class H? There may be ready made modules designed using the same chips and in a bridge configuration.

Cheers.
 
The schematic above is a parallel version. Unfortunately the datasheet of TDA7293 does provide (unlike the National app note AN-1192 which provides all the details for the Overture chips) the voltage for various combinations of no. of chips and load impedance :( .

Nevertheless, we can derive the same using the voltages specified for 4 ohms and 8 ohms. It turns out to be ~45volts dc for 200watts @ 4 ohms. The trafo would be 32-0-32 V AC.

The only concern here is that the IC is now near its 50v limit. A power surge may be disastrous.

Regards,
Goldy
 
I think you can save yourself some time and effort by getting one
of the ebay boards, unless you want to DIY it from scratch, of course.

TDA7293 Parallel 250W Mono Power Amp Board Kit NEW,Y25 | eBay
150W+150W TDA7293 X 4 BTL+Speakers protected board | eBay

You probably have see this link already -

http://www.quekky.com/PI7293.quekky

There appears to be some misleading info about slave mode.
The quekky link shows 2,3 to GND. But as per this link below, pins 2, 3, 4 (IN+, IN- and SGND) should
go to -Vs. Pls verify the proper one.

http://www.rotgradpsi.de/mc/amp51/amp51ref/tda729x_pitfall.html

Edit again: This seems to be the right way to use the TDA7293 in slave mode -

http://mdcs.elektroda.net/250wrms/250wrms.gif
(from this link here)
http://mdcs.elektroda.net/250wrms/250wrms.html
 
Last edited:
anilva said:
Antony,

This may turn out to be good in terms of performance. Does this operate in Class H? There may be ready made modules designed using the same chips and in a bridge configuration.

Cheers.
Click to expand...

Remember seeing Class G schematics using this IC and TDA7294. I think ready-made modules might be available as well.

Thought of taking this approach as it's relatively simple and less expensive.
 
goldyrathore said:
The schematic above is a parallel version. Unfortunately the datasheet of TDA7293 does provide (unlike the National app note AN-1192 which provides all the details for the Overture chips) the voltage for various combinations of no. of chips and load impedance :( .

Nevertheless, we can derive the same using the voltages specified for 4 ohms and 8 ohms. It turns out to be ~45volts dc for 200watts @ 4 ohms. The trafo would be 32-0-32 V AC.

The only concern here is that the IC is now near its 50v limit. A power surge may be disastrous.

Regards,
Goldy
Click to expand...

I am not sure if the BPA100, & BPA200 voltage ratings will apply in a pure slave operation like this.

The 250w mono ebay link provided by quad looks like a simple parallel application with 1 master and 2 slaves. They say 250w @ DC supply voltage of 30V. Since a 24-0-24 torroid can supply a DCV of about 33V, I think it's worth a try with the 3 slave version.

Also one more thing. In the 8ic version, the cap in the zobel circuit had a higher value. Not sure if that value is also dependent on the number of slaves :confused:
 
quad said:
I think you can save yourself some time and effort by getting one
of the ebay boards, unless you want to DIY it from scratch, of course.

TDA7293 Parallel 250W Mono Power Amp Board Kit NEW,Y25 | eBay
150W+150W TDA7293 X 4 BTL+Speakers protected board | eBay

You probably have see this link already -

quekky.com - PI7293 - 3 TDA7293 in parallel

There appears to be some misleading info about slave mode.
The quekky link shows 2,3 to GND. But as per this link below, pins 2, 3, 4 (IN+, IN- and SGND) should
go to -Vs. Pls verify the proper one.

Avoiding TDA7293 pitfalls

Edit again: This seems to be the right way to use the TDA7293 in slave mode -

http://mdcs.elektroda.net/250wrms/250wrms.gif
(from this link here)
http://mdcs.elektroda.net/250wrms/250wrms.html
Click to expand...

Thanks for the links. I am thinking of a DIY from scratch. As the chips are relatively inexpensive(Rs.75), it doesn't hurt much to smoke a few in the process :)

I will double check the pin wiring today evening. This is what the ST Datasheet says on slave mode

  • The master chip connections are the same as the normal single ones.
  • The outputs can be connected together without the need of any ballast resistance.
  • The slave SGND pin must be tied to the negative supply.
  • The slave ST-BY pin must be connected to ST-BY pin.
  • The bootstrap lines must be connected together and the bootstrap capacitor must be increased:for N devices the boostrap capacitor must be 22mF times N.
  • The slave Mute and IN-pins must be grounded.

And here is the slave wiring diagram as per the ST datasheet.

stmodular.gif
 
t.antony said:
Thanks for the links. I am thinking of a DIY from scratch. As the chips are relatively inexpensive(Rs.75), it doesn't hurt much to smoke a few in the process :)

I will double check the pin wiring today evening. This is what the ST Datasheet says on slave mode

  • The master chip connections are the same as the normal single ones.
  • The outputs can be connected together without the need of any ballast resistance.
  • The slave SGND pin must be tied to the negative supply.
  • The slave ST-BY pin must be connected to ST-BY pin.
  • The bootstrap lines must be connected together and the bootstrap capacitor must be increased:for N devices the boostrap capacitor must be 22mF times N.
  • The slave Mute and IN-pins must be grounded.

And here is the slave wiring diagram as per the ST datasheet.

stmodular.gif
Click to expand...

There's an updated version of the data sheet in the link below which states -

- Slave IN must be connected to Negative supply.

http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00001887.pdf
 
Just got email from HSU,they can offer VTF 1 only amp for $200 + S/H,
So local US price can be $250 (11.5k).
 
Thanks everyone for the inputs. Those links will be useful if this project did not pan out as expected :D

For the sub crossover I am planning to go with standard Linkwitz-Riley filters combined with a phase controller like this one - Project 103 - Subwoofer Phase Controller

Also want to experiment possibility of implementing these options as well.

1) Switchable cascaded filter sections to get 2nd, 3rd & 4th order slopes.
2) Switchable/adjustable crossover frequencies of 30, 40, 50, 60 & 70 Hz.
 
I think it's time I put an update before someone post another sub amp kit here :)

Filter ideas are evolving around the Universal Active Filter chip - UAF42 as it can be used to construct a second order high-pass filter with independently variable Q, resonant frequency (Fo) and Gain with minimal components.

Datasheet is here - http://www.ti.com/lit/ds/symlink/uaf42.pdf
Filter design guide - http://www.ti.com/lit/an/sbfa002/sbfa002.pdf

More information on the usage of this chip is available at Charlie's Audio pages; there is a spreadsheet to calculate the filter values as well - projectspage

Useful information on how to tailor the low end of a ported loudspeaker - Satellites and Subwoofers
 
t.antony said:
I think it's time I put an update before someone post another sub amp kit here :)

Filter ideas are evolving around the Universal Active Filter chip - UAF42 as it can be used to construct a second order high-pass filter with independently variable Q, resonant frequency (Fo) and Gain with minimal components.

Datasheet is here - http://www.ti.com/lit/ds/symlink/uaf42.pdf
Filter design guide - http://www.ti.com/lit/an/sbfa002/sbfa002.pdf

More information on the usage of this chip is available at Charlie's Audio pages; there is a spreadsheet to calculate the filter values as well - projectspage

Useful information on how to tailor the low end of a ported loudspeaker - Satellites and Subwoofers
Click to expand...

Looks like a good idea for a active filter. The chip makes it easier. Shouldn't be too much of a risk for a subwoofer crossover.

Cheers.
 
Hi Antony,

Just wondering whats the distance from the port entry to the rear panel within the cabinet. Recommended is 3" I think.
 
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