TDA7294 + Power Transistors AMP (TDA7293 to come also)

I need help !! I built both the amplifier with a single tda7294 and the bridged 2 x TDA7294 with 2sc5200/2sa1943. The one with the single TDA7294 works flawlessly. The one with bridged 2xTDA7294 it sounds very weird and off and doesn't amplify much. For the bridged version of TDA7294 I used 4 transistors (2 x 2sc5200, 2 x 2sa1943), 2 pairs for the 2 outs

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The red resistors are 0.15 ohm / 10w, the blue resistors are 6.8 ohm / 10w and the orange resistors are 22k. What am I doing wrong ??
 
Xerpenter, The configuration you have shown won't work.
You need to drive each section with a separate signal that is out of phase from the other section, a "Balanced" signal.
The bottom amp will not swing any voltage as its input is grounded and it's output is just working against the upper amplifier.

In order to use the method you are trying to do by feeding part of the output of the top amp in to the bottom amp they should be of equal gain.
Typically Inverting configurations are used for both amps in such a configuration.
You are using a non-inverting on the top and trying to feed the bottom one in a inverting fashion.
A non-inverting amp has a gain of X+1 and a inverting amp if configured the same will have a gain of X.
Also the bottom amp now has two DC ground references, one at the non-inverting input and one at the inverting input of the same opamp and these too are fighting against each other.

FWIW

jer :)
 
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Addum as I ran out of editing time,

It is hard to say as you don't specify what the other resistor values are.
It would be easier to just create a balanced signal with a DRV134 or a dual opamp or even single stage gain of 1 inverting opamp feeding one of the two otherwise identical amplifiers.

Here are just a few examples,

http://www.diyaudio.com/forums/analog-line-level/228601-balanced-line-driver-drv134.html#post3357278

Balanced Line Driver & Receiver

http://www.diyaudio.com/forums/chip-amps/76419-ad815-beefy-balanced-line-driver.html#post876810

http://www.diyaudio.com/forums/solid-state/123951-audio-distribution-balanced.html#post1560504

I like to use this configuration,

http://www.diyaudio.com/forums/chip-amps/190936-tda7293-bridge-parallel-circuit.html#post2608127

jer :)
 
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Hey guyz, I almost finished this legendary amp pointed out by dr.Frost.
I used a case from an old Technics, it has two 300VA toroids 25-0-25, two bridged TDA7293+2sc5200/2sa1943 transistor modules, will have 40.000uF per channel (80.000 uF total), power meter and heatsink (from Technics), two 92mm cooling fans. I still need to add speaker delay relays cause of the pop noise when turning on, it has no pop noises when turning off.
One of the toroids was 32-0-32 but I decided to unwind it to match the other rather that winding more wires on the one with lower voltage. The reason was the size of the heatsink. When this power amplifier is driven with +-50V DC, it heats up like a toaster :) but don't worry, with 25-0-25 it gives enough power but does not heat up. You can listen to it on mid power without using the cooling fans.
I am impressed by the sound quality, would not think that the sound will remain so clear, and it stays clear when driving the speaker on high power.
For now I am driving a two 4 ohm coiled Pioneer champion series speakers using bridge and one 4 ohm speaker coil. The speaker is 1400W max and 400W nominal and this amp pushes it like a boss.
I put some speakon connectors for the speakers also left the Technics amps originl connectors so you could choose if you want to have 4 channels or 2 bridged.

Enough talk lets see the pics :)
An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


I used this schematic:
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Yeah, that could be done sure. With 2 jumpers, one to disconnect the 2nd inverted amp input from the ground, and 2nd to disconnect the 22k resistor from the feedback loop. Im ny case i can use 1x bridge or 2x mono (per channel). For subwoofers mono is enough, this amp will be used only for subs. But for stereo applications its a good idea.
 
Yes the jumper way is an option but i prefer to have a dual opamp at each pair TDA729x, this way you only have to wire the speakers up like you need, can add a small switch to link left and right together on the input side so you don’t need Y phone cables like you use on a car, and this way you have TONS of usages, from 2 Subs/stereo speakers to 2 speakers & mono sub or 4 channel surround (best surround if you ask me, just 4 BIG speakers)
 
Will try with LM3876... max supply voltage of 45V unregulated... or 33,31V AC with 0 load
Will be using it for 4 ohm subwoofer.
Has zobel, star grounding, 22k 1k 47uF FBN, 2 pairs of outputs.
some pics:

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Blown feedback resistor: :D

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direct upload
 
Jesus Christ! I desoldered the chip...
As I tought it was blow :( It wasnt!
I missed one thing... that ground pin was disconnected.
As I remember the design of my stereo LM3875 boards I didnt connect the ground pin (7)
Now, I found the PCB design I made for 3875 in the beginning of the summer...
I found it and rebuild it, now The current amplification board is separated from the HVOpamp board, minimal radiation and noise Id say. Not sure tho :D

I MUST CLEAN THOSE PCBs They look like they came from fluxwar :(

I also didnt had new spade connectors so... :(

I may design PCB for LM3886,76,75 But I will probably never build it.
Just for the sake of knowledge, and I love to design PCB's even if im bad at it :D
Sorry for bad quality, got sphone only. 720p..

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.
 
A question for dr frost dk or kebbz !! Does the TDA 7293/7294 bridged mode amplifier have included inverter or do I need to disconnect the second input from the ground and feed them 2 types of signals separately (0 and 180) ?? Someone here told me I would need a separate phase inverter for this. I completed kebbz's schematic with TDA7294 pair in my case, but it sounds very weird and has low volume. It sounds right for about half a second just as the current from the caps is about to be depleted completely. Later I discovered that V- was not connected to the second TDA7294, but by then I completely gave up on the transistors and just stuck with the normal TDA7294 as I knew those would work for sure by themselves. I haven't tested it since I corrected the V- issue. The question is, does this schematic work, do I need a phase inverter for bridged config ??
 
Hi dr frost dk ,
thanks for sharing this amplifier, it is awesome.

My only question is does this amp need preamp?

I've seen some people using LM741 and others in front of their chip amps, some don't. I never did that. With only TDA 7294 I get around 30W, not 70W like in datasheet. My voltage is ±28V on 4 ohm load. For my sub I am doing the same amplifier but with ±50V supply.
 
Hi dr frost dk ,
thanks for sharing this amplifier, it is awesome.

My only question is does this amp need preamp?

I've seen some people using LM741 and others in front of their chip amps, some don't. I never did that. With only TDA 7294 I get around 30W, not 70W like in datasheet. My voltage is ±28V on 4 ohm load. For my sub I am doing the same amplifier but with ±50V supply.

It depends on your source. Output on devices like MP3 players, tapes, receivers, is pretty much whatever the manufacturer wants to have within loose limits. It can be anywhere from ~.5V to 1.5V.

Using your own design preamp/op amp gives you some control over input levels and some bonus features like tone controls. It is easy to build a things like frequency controls for doing bi amp or subwoofer at that stage rather then a speaker crossover network in the speaker. A LOT cheaper too. Couple of small capacitors/resistors can replace pounds of inductor and huge caps in the speaker.