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Chip Amps Amplifiers based on integrated circuits

LM1875 transconductance amp
LM1875 transconductance amp
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Old 24th April 2015, 11:40 AM   #11
kp93300 is offline kp93300  Malaysia
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speaker impedance is 7 R
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Old 24th April 2015, 12:40 PM   #12
padamiecki is offline padamiecki  Poland
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so you can use 2*1 Ohm 1W resistors in parallel (=0.5 Ohm) instead of 3 (=0.33 Ohm) for current sensing
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Old 6th May 2015, 04:05 PM   #13
kp93300 is offline kp93300  Malaysia
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Thanks to Pawel.
This is my build of the amp.
There is too much bass with the markaudio 12p in superpensil. The bass notes are not well controlled.
I change the input cap from 10 uf to 0.7 uf and still too much bass.
i close off the outlet of the speaker with foam and is much better.
Otherwise, mid , high and soundstage are all very good.
Vocal is the best i have heard in my set up.
Piano and guitar are very nice and natural .
The high frequency is very refined like tubes.

Is there any other adjustment to tighten the bass ??
thanks

kp93300
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Old 6th May 2015, 04:07 PM   #14
kp93300 is offline kp93300  Malaysia
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Quote:
Originally Posted by bimbla View Post
Hello again,

I finally built a current drive based on TDA7293. Big amp really for my needs...
A non-inverting configuration with DC blocking RC input filter and the loudspeaker with the sense resistor forming the gain components. No R-C across the output.
I added a DC servo loop to keep the output DC in check.
I tested it with as many full-range loudspeakers, in sealed enclosures, that I had.
The results are simply fantastic. Each one of them sounded as if it was 4 times as big and 4 times as expensive.
I confidently shorted the output much to the amusement of the watchers.

Bass, Mid-range and treble associated with dialogues, music and effects, whether listening to music tracks or watching a movie all get placed correctly.

It seems like a per-equalized system.

Without the current drive, the same content becomes unbearable, dull and lifeless, so beware.

All audio DIYers must do this at least once.

can you share your schematic ?
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Old 6th May 2015, 04:22 PM   #15
thiagomogi is offline thiagomogi  Brazil
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Location: São Paulo, Brasil
To control the low, try resistor in parallel with the driver. Start with 30ohms
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Old 7th May 2015, 05:11 AM   #16
kp93300 is offline kp93300  Malaysia
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thanks thiagomogi for the suggestions .
What about raising the value of the resistor from speaker negative to ground? I have 0.5 R now.
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Old 7th May 2015, 06:57 AM   #17
padamiecki is offline padamiecki  Poland
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Default superb!

Quote:
Originally Posted by kp93300 View Post
The bass notes are not well controlled.
Is there any other adjustment to tighten the bass ??
thanks
kp93300
I wrote about this, this amp has very high output impedance, so resonances in the speaker are not damped.

you can build active eq knowing parameters of your speakers: section Bass equalization Transconductance amplifier project | Current-Drive - The Natural Way of Loudspeaker Operation
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Old 7th May 2015, 07:03 AM   #18
padamiecki is offline padamiecki  Poland
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Quote:
Originally Posted by kp93300 View Post
thanks thiagomogi for the suggestions .
What about raising the value of the resistor from speaker negative to ground? I have 0.5 R now.
because your speakers are 7.2 Ohm dc resistance you can put for example 0.68 Ohm resistor but not higher, 1875s are not so stable...
This will create more nfb factor, less distored sound but not cause more controll on bass resonance.

I think in your case mechanical damping of speakers enclosure is the best way to damp bass resonance frequency.
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Old 7th May 2015, 08:00 AM   #19
arcgotic is offline arcgotic  Romania
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Hi Pawel,

I want to buid this amp too. For a Visaton BG20 in open baffle, Rdc=6.3 ohm, should i change something in your schematic? I plan to use +- 24V Dc power supply.

The sistem is 3 way active, so this speaker will be crossed 120hz LR4 HighPass.

Thank you!
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Old 7th May 2015, 08:09 AM   #20
padamiecki is offline padamiecki  Poland
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Quote:
Originally Posted by arcgotic View Post
should i change something in your schematic?
no, it should work as it is!

but please read about the safety: Joe Rasmussen "Trans-Amp" - 40 Watt Transconductance "Current Amplifier"
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