Audio (Guitar) Power Amplifier, Power Supply Questions

Thread Starter

ICSvortex

Joined Apr 13, 2021
3
Hi!
It's my first post here, hope yall can help!

I want to build a compact mono audio (guitar) power amplifier to power my passive 4ohm 4x12 inch speakers for my guitar.
I looked into 2 TDA7293 boards to have around 200W output.

My question now is about the power supply.
I work in industrial automation so i dont have too much of a clue about audio electronics.
I heard that the performance of the power amp is highly dependent on the power supply, but i never got a suggestion to which PSU to use.
Since the boards are suggested to use double 32V ring cattle, i guessed i would use a transformer from mains (230VAC 50Hz) to 32VAC.

What i wanted to know is what size of transformer i need to use?
And also how i would have to wire the two TDA7293 boards together to generate the 200W of output (100W per board max)?
Also i would like to have a volume potentiometer and if possible a 3-band equalizer to but in there, are there any 3 band EQ boards out there that are widely available? And what value of potentiometer would i have to put in there to control the wolume on a line level signal?

It turned out to be more questions than i thought^^

Thanks anyway!
 

Ian0

Joined Aug 7, 2020
3,281
I tested the TDA7293 when it first came out, and found it to be very blowy-uppy. If you looked at it in a funny sort of way it would release the famous smoke and go the way of all silicon.
They might have improved it since then, but it seemed to have trouble recovering if it was driven into clipping. That would be OK for hi-fi, a bit dodgy for Public Address, but for guitar - there's nothing a guitarist likes more than to drive an amplifier into clipping. When it tried to recover from clipping, one MOSFET must have maximum voltage on its gate, and it couldn't get it turned off before it turned the other one on - it crowbar'd the supply and expired.

Secondly, the only way you could wire up two of them to drive a single load is as bridge-tied-load, but you can't with a 7293 as it won't drive 2Ω.
You could rewire your, 4x12 cabinet, which must have four 16Ω speakers in parallel, and make it a 16Ω cabinet instead of a 4Ω cabinet, then it might work.
 

Thread Starter

ICSvortex

Joined Apr 13, 2021
3
Secondly, the only way you could wire up two of them to drive a single load is as bridge-tied-load, but you can't with a 7293 as it won't drive 2Ω.
You could rewire your, 4x12 cabinet, which must have four 16Ω speakers in parallel, and make it a 16Ω cabinet instead of a 4Ω cabinet, then it might work.
The Cabinet has a 16Ω input, so that would be no problem.
But the problems with the TDA7293 seem frightening.
For context: i would be running my guitar modeler (line 6 helix) in front of the Poweramp so driving the poweramp into clipping wouldnt be something i'd want to do anyway.

But could you recommend me a different poweramp board then?
As for what it needs, i'd like it to have 100W+ output and be mono.

But thanks for your wisdom so far!
 

AnalogKid

Joined Aug 1, 2013
9,362
ebay has zillions of electronic modules for just about everything (including a 100 W audio amp), so I'm sure there is a 3-to-5 band EQ out there.

If you want 200 W out, then you need - wait for it - a 200 W transformer. Note that at 50-60 Hz, this is not compact. Or light.

AND - what is "double 32V ring cattle" - ? I assume you are talking about +/-32 V power supply output voltages, but - - - ???

ak
 

Audioguru again

Joined Oct 21, 2019
3,550
The old TDA7293 amplifier is not stocked by Digikey which is the largest electronic parts distributor in North America. Maybe nobody buys its problems anymore.
Its output is 110 Whats with horrible distortion or 50 real Watts with low distortion.
 

Audioguru again

Joined Oct 21, 2019
3,550
I think all guitarists are ancient (like me) but without hearing aids or are deaf to the horrible distortion they produce. To hear an electric guitar I hate distortion so I turn off my hearing aids that boost high frequencies.

All my amplifiers have plenty of headroom so they never produce clipping distortion.
The Pfizer Covid-19 vaccine gave me a little amount of tinnitus (shhhhh) in my hearing.
 

Kenmra150

Joined Apr 18, 2021
2
Hi!
It's my first post here, hope yall can help!

I want to build a compact mono audio (guitar) power amplifier to power my passive 4ohm 4x12 inch speakers for my guitar.
I looked into 2 TDA7293 boards to have around 200W output.

My question now is about the power supply.
I work in industrial automation so i dont have too much of a clue about audio electronics.
I heard that the performance of the power amp is highly dependent on the power supply, but i never got a suggestion to which PSU to use.
Since the boards are suggested to use double 32V ring cattle, i guessed i would use a transformer from mains (230VAC 50Hz) to 32VAC.

What i wanted to know is what size of transformer i need to use?
And also how i would have to wire the two TDA7293 boards together to generate the 200W of output (100W per board max)?
Also i would like to have a volume potentiometer and if possible a 3-band equalizer to but in there, are there any 3 band EQ boards out there that are widely available? And what value of potentiometer would i have to put in there to control the wolume on a line level signal?

It turned out to be more questions than i thought^^

Thanks anyway!
Hello ICS Vortex,
I compliment you for wanting to build your own amp. You may want to abandon the idea of slapping a couple of modules together, as the other folks on this thread have provided you with some real challenges to making that work. But if you want to build your own, I suggest a kit since you do not have a strong audio electronics background. Ceriatone makes a wide array of guitar amplifiers of various power ranges. I would suggest that unless you are a touring artist, there is little need for a 200 Watt amplifier; which is usually only useful for stage playing. Another avenue for guitar amplifier kits, is Antique Electronics or Tubes and More. They offer many kits that are perfect for beginning amplifier builders with explicit instructions. Ceriatone kits are a bit more difficult, but they are proven designs that you just have to pay careful attention.
Hopefully you can find an amp that suits your needs.
 

Kenmra150

Joined Apr 18, 2021
2
Heh, great suggestion GetDeviceInfo, three of my guitar amps are all "rescues", almost all of them just required recapping. Love those old Gibsons.
 

Thread Starter

ICSvortex

Joined Apr 13, 2021
3
Thanks for the suggestions, but i've come to the conclusion that i'll probably have to shell out those 500+$ for a poweramp that meets my specs.
I've thought about buying an old Marshall Valvestate and using the poweramp of that but as said, i dont really know whats going on in there if i trash the pre-amp part etc.
Would love to do a read up on the topic at some point but for now i'll stick with my automation knowledge and only repair electronics from time to time, as building and designing something seems to be out of my wheelhouse for now^^
 
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