Chipamp request for Bi-Amp with SS amp, 40+40v supply rails - diyAudio
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Old 14th June 2007, 09:30 PM   #1
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Question Chipamp request for Bi-Amp with SS amp, 40+40v supply rails

Hello !!

I'm needing a Bi-Amp configuration, and my Solid State amp works with 40+40v. Would be excessive and expensive put another one huge amp to drive the tweeter, so I thought about use an Chipamp to drive the Tweeter.

What about the TDA7293 ? How does it sound?

Any other suggestion?

The loads are 8 Ohms. Woofer is 92Db, and tweeter 95Db, so the tweeter will work with -3db attenuation on the signal, before the amp. The frequency cut is 1800Hz, 24Db/oct


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Old 15th June 2007, 07:31 AM   #2
AndrewT is online now AndrewT  Scotland
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Hi,
Quote:
frequency cut is 1800Hz, 24Db/oct
are you talking about active Bi-amping and not passive bi-amping?
The increase in sensitivity of the tweeter will allow a half power amplifier to achieve the same SPL as the mid/bass driver.
Some would try a much lower power for the tweeter amplifier, but I always suggest matching maximum (peak) SPLs. This helps avoid clipping of the very fast transients that get sent to the tweeter.
But if you want to build a dual channel amp that has a mix of half power and full power amplifiers inside you then need two different voltage PSUs. It is much cheaper and simpler to use the same voltage to power both amplifiers and then you end up with the same voltage drive to each driver. An adjustment of the sensitivity control on the input to the tweeter amp allows setting of the treble you prefer to hear.
The type/duration of signals sent to the respective drivers is very different. You may achieve some economy by reducing the continuous power output of the tweeter amp. Smaller faster capacitors will go some way, discrete gives even more flexibility here but not in this thread.
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Old 15th June 2007, 06:20 PM   #3
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Yes, the crossover will be active, and two amps are necessary to drive both transducers.

I'll power both amplifiers with the same PSU, but as the tweeter is +3Db sensitive, I'll attenuate 3Db on the tweeter's amp input. The easyest way I think.

I was wondering what would be better, I think that despite the thoughts, only a good listening test will show which option is the best.

1- Two TDA7293 amps. One for woofer, one for tweeter. -3Db on the signal input of the tweeter's amp.

2- One SS amp (symasym), and one LM3886 amp (with LM338 voltage regulator, as the supply rails are too high to the LM3886 handle), again -3Db on the signal input of the tweeter's amp.

3- This would have the best damping factor and power dissipation.

Two paralel TDA7293 to drive the woofer (just to optimize the power dissipation and damping factor), and one TDA7293 to drive the tweeter, of course with a -3Db attenuation on the signal input.

That's what I must decide.

The SS amp is Symasym, an wonderful amp. LM3886 is also good sounding for HIGHS. Symasym is more dynamic and alive.

So, if I decide to go with Symasym because of the sonic quality, I'll use LM3886 for highs that is also good sounding.

Theoretically, the best "enginering" option would be go with TDA7293's.


What you think?
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Old 16th June 2007, 09:26 AM   #4
AndrewT is online now AndrewT  Scotland
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Quote:
SS amp is Symasym, an wonderful amp. LM3886 is also good sounding for HIGHS.
this seems odd.
I would expect the symasym to outperform the chipamp at all parts of the frequency spectrum.

BTW,
forget about damping factor, use this ONLY when designing your speaker. Even then the DF effect is quite small and can be more dominated on what is between the PCB output and the driver input.
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Old 16th June 2007, 06:34 PM   #5
MikeB is offline MikeB  Germany
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Quote:
Originally posted by AndrewT
this seems odd.
I would expect the symasym to outperform the chipamp at all parts of the frequency spectrum.
I haven't compared myself, but all who have, tell that symasym plays at another league than chipamps.


Nando, if you have an extra amp only for trebles, you might consider ClassA, nothing beats ClassA for highs.
Why not building another pair of symasyms?

Mike
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Old 16th June 2007, 06:41 PM   #6
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Hi MikeB ! Your answer is always well come !

I think that would be a waste build another symasym just to drive the tweeter, much more expensive than a chip-amp. LM3886 when well implemented, performs pretty well with highs, and Symasym would drive the woofer, that is what express that wonderful dynamic, voices, pianos etc.

I can consider Class A. The tweeter only needs a half of the woofer power, as it is 3Db more sensitive. How many watts would you expect to drive the tweeter very well with a class A amp?


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Old 16th June 2007, 06:47 PM   #7
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A 20W class A amp dissipates about 110W, wow, not possible
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Old 16th June 2007, 06:49 PM   #8
MikeB is offline MikeB  Germany
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You might need an extra power supply for the ClassA, +/-20V would be a good guess, giving ~20W into 8ohms. A DoZ might be interesting, quite simple and can be easily modified to symetrical powersupply skipping the outputcap.
Dissipation would be ~40watts.

Mike
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