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Old 13th April 2013, 10:23 PM   #371
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Ah, Kean's famous Srotsisnart Buffer! It fits chip amplifiers too? Wow, so much lower insertion loss and lower parts count than other solutions. Much less complicated than a chip based solution. Probably could fit it onto a dime size daughtercard to add atop the board. Of course I have almost no idea what component values or connections, except the clues in post#370 mention of LTP and power, and. . .
There is a schematic clue as well--Q14, Q15 on this Circlophone schematic.

Another tidbit of information that we do know: If your amplifier has limp bass because the source needs/lacks a buffer, then, in that case, a buffer will outperform an an equalizer, thoroughly. I think that adding the buffer could turn our nebulous 70 watts of something into a "safer bet" for level sounding audio. But, we need to decide before performing the labor fine tuning the amplifier's small signal area. Want a better bet with a buffer?
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Old 14th April 2013, 12:15 AM   #372
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Yep, R28, R29, R22, Q14, Q15 and C13 are the components. Take these, and connect the emitters to the +/- inputs of the given amp, or chipamp. I don't know if this will improve the circuit in question but I think it's a good bet and Dan seems pretty sure, so it must be worth a try.
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Old 16th April 2013, 10:20 PM   #373
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Quote:
Originally Posted by KSTR View Post
Let's not forget layout and wiring, Bob. Visually "small" design glitches can have big impact on the amp's perfomance additional to (if not even dominating) parts selection.
I agree. Check out this thread in this case:
Why are there only disastrous PCB Versions for TDA7293/TDA7294/LM3886 etc. available?
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Old 16th April 2013, 11:57 PM   #374
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Tiny size double-layer board avoids disaster layout from the mad pinout of the TDA729X, like this:
1pc x TDA7293 Mono Amplifier Board Official Standard 85 w Original B Board | eBay

I'd give those weak slippery screw terminals a fail because they're hazardous and reduce quality, and the components may be random values of bargain parts; however, the board itself looks quite good. SO, as soon as you de-solder those screw terminals, then you've got a non-disaster option available.
EDIT: Also found:
http://www.ebay.com/itm/TDA7294-65W-...-/200912855861
There's the TDA7294 version, conveniently in kit form so you can put on the components you want to use.
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Last edited by danielwritesbac; 17th April 2013 at 12:08 AM.
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Old 17th April 2013, 01:28 AM   #375
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Any good bridge schematic with mute removed.I wanna use for a subwoofer.
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Old 17th April 2013, 05:35 AM   #376
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Did you realize that the topic for this thread, is Not subwoofers?
Anyway. . .
To remove the mute, connect a 10k resistor from pin10 to pin7.
Power caps at/upon the amp board may be about 270u per rail.
Maximum transformer sizing is 200VA, and fuses are suggested.
The rest of the information is located here: TDA7294 Datasheet
However. . .
There are also good LM3886 Subwoofer Amplifiers, to consider.
More awesome. . .
Why not biamp for TDA729X mids & treble, with LM3886 bass?
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Old 17th April 2013, 05:53 AM   #377
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The thing is that there is a 22k R connected with one output to the other Vin .Because 22 k is so common.My feedback resistor is 61k not 22k,,so will it change.Couldnt we take common resistor for mute pins
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Old 17th April 2013, 07:55 AM   #378
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Right. The bridge resistor should be same value as your feedback resistors.
Quote:
Originally Posted by simply14prem View Post
Couldnt we take common resistor for mute pins
Yes!
For bridged and parallel applications:
Pin9 from one chip is cabled to the other chip, and Pin10 from one chip is cabled to the other chip. Not more parts than: 1 10k resistor for mute, 1 22k resistor for standby, 1 10u cap for standby, and 2 wires of course. The chips must operate mute and standby at same time, so you force that.

For more information, also see the TDA7293 datasheet (it has more clues).
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Last edited by danielwritesbac; 17th April 2013 at 07:59 AM.
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Old 18th April 2013, 03:07 AM   #379
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I think i need to parallel then coz bridging heats up a lot
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Old 18th April 2013, 06:01 AM   #380
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Quote:
Originally Posted by simply14prem View Post
I think i need to parallel then coz bridging heats up a lot
That's true!

Bridged:
If your speaker is 8 ohm and your amp is bridged, each chip sees a 4 ohm load, which reduces efficiency dramatically and sends a lot more power into the heatsink, and that gets hot. With two chips at twice the load, your heatsink would need to be four times bigger.
On powerside, you quadrupled the load, but it isn't safe to quadruple the transformer because you only doubled the number of chips and therefore may only double the transformer current. SO, this bridge amp idea operates starved for current, wastes a lot, and you've then got a big audio compressor with poor bass. In addition to those troubles, bridged adds an additional power amp to the chain, effectively doubling the amplifier distortion. And double distortion Plus straining outputs for much more distortion is audibly inferior. That is definitely not a home hi-fi, but it might make a fun and very loud guitar amp.

Parallel:
If your speaker is 4 ohm and your amp is paralleled, each chip sees a 8 ohm load. The number of chips is double, the transformer current may be double and the heatsink size is double. This all matches up nicely and works well.
The modern low inductance style speaker has a pair of 8 ohm woofers making a 4 ohm load, transducers in parallel has half LE, and the crossover coils are half size; and it is done with the purpose of a very clear and dynamic sound. These types are delightful to use with the Parallel chip amplifier. That plan effectively doubles the number of speakers and amplifiers, Without doubling the number of boxes and wires, and Without doubling the amount of strain on each woofer. With the parallel amp, the performance is usually excellent.

Basically, bridged makes a guitar amp, but parallel makes a hi-fi. Which one do you want?
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Last edited by danielwritesbac; 18th April 2013 at 06:08 AM.
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