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Chip Amps Amplifiers based on integrated circuits

LM1875 transconductance amp
LM1875 transconductance amp
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Old 14th May 2015, 12:32 PM   #31
arcgotic is offline arcgotic  Romania
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Is 4700uF/rail enough as power supply filter for this amp?
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Old 14th May 2015, 01:38 PM   #32
sreten is offline sreten  United Kingdom
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Variable Amplifier Impedance

Hi, the above is worth a read, rgds, sreten.
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Old 15th May 2015, 05:37 AM   #33
padamiecki is offline padamiecki  Poland
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Quote:
Originally Posted by kp93300 View Post
Is a speaker relay the only option?
I think so...
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Old 15th May 2015, 05:38 AM   #34
padamiecki is offline padamiecki  Poland
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Quote:
Originally Posted by arcgotic View Post
Is 4700uF/rail enough as power supply filter for this amp?
yes, I used only 3300uF
but better supply = better sound
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Old 18th May 2015, 08:35 AM   #35
arcgotic is offline arcgotic  Romania
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Would this amp be OK and not destroy my Selenium D220ti drivers directly connected, without any condensator or resistor? The driver has Re=6 ohm and will be actively crossed LR4 @ 1450Hz.

I ordered a 150VA toroidal transformer.

If i use it for both L and R, each channel with its own rectifier and filter, could it be a problem?
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Old 18th May 2015, 08:55 AM   #36
padamiecki is offline padamiecki  Poland
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Quote:
Originally Posted by arcgotic View Post
Would this amp be OK and not destroy my Selenium D220ti drivers directly connected, without any condensator or resistor? The driver has Re=6 ohm and will be actively crossed LR4 @ 1450Hz.

I ordered a 150VA toroidal transformer.

If i use it for both L and R, each channel with its own rectifier and filter, could it be a problem?
in general should not be a problem, please follow general rules from Joe's thread: Joe Rasmussen "Trans-Amp" - 40 Watt Transconductance "Current Amplifier"
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Old 22nd May 2015, 12:14 PM   #37
Andonio is offline Andonio  Italy
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Default an interesting application

Ive found on this old book: Linear and Interface Circuit Application Volume 1 (Texas Instruments 1986) an intersting circuit tuned to this thread, with a very exhaustive and complete description. (why the semiconductor-companies don't make any more these nice applications gifts?)

"Most audio amplifier circuits today are voltage output devices which apply a voltage to the terminals of the speaker. Large changes in speaker impedance with frequency yield poor frequency response with the high-frequency output falling off rapidly as the speaker impedance increases. It should be noted that the speaker cone displacement is proportional to the current in the voice coil rather than the voltage across the speaker terminals. The current is the primary mover of the voice coil.
The single speaker amplifier circuit shown in Figure 3-31 uses current feedback rather than the more popular voltage feedback. As shown, the feedback loop is from the junction of the speaker terminal and a 0.5Ω resistor, to the inverting input of the NE5534. Sensing the current through the speaker and feeding it back provides better speaker damping than obtainable with voltage-drive systems.
Note the unusual grounded output pin on the NE5534 op-amp. When the input to the amplifier is positive, the power supply supplies current through the TIP32 and the load to ground. Conversely, with a negative input the TIP31 supplies current through the load to ground. The gain in this case is set to about 15 (gain = SPKR 8Ω / 0.5Ω feedback). The 0.22F capacitor across the speaker rolls off its response beyond the frequencies of interest. Using the 0.22F capacitor specified, the amplifier output is 3 dB down at 90kHz where the speaker impedance is about 20Ω. The Quiescent output stage collector current is determined by the 130 Ω resistors that connect each transistor base to the appropriate supply rail, the output transistor VBE, and the 1Ω emitter resistors. To set the recommended class 'A' output collector current, adjust the value of either 130Ω resistor. An output current of 50 to 100mA will provide a good operating midpoint between the best crossover distortion and power dissipation.
The 0.1 F bypass capacitors on each rail may be mylar or ceramic disk. The 2.0 F should be a nonpolarized capacitor while the 0.22F across the speaker should be mylar.
Figure 3-32 shows the frequency response of the amplifier with a 2.0F input capacitor. This response is very flat with the -3.0dB point on the low frequency end at 45 Hz. The -3.0dB point at the high frequency end occurs at 80kHz. Total Harmonic Distortion (THD) is 0.01% at 6.25W rms output into an 8 Ω load with 18V on the supply rails."
Attached Images
File Type: jpg TI current ampli 1.jpg (10.4 KB, 637 views)
File Type: jpg TI current ampli 2.jpg (13.0 KB, 616 views)
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Old 22nd May 2015, 12:28 PM   #38
padamiecki is offline padamiecki  Poland
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Quote:
Originally Posted by Andonio View Post
Ive found on this old book: Linear and Interface Circuit Application Volume 1 (Texas Instruments 1986) an intersting circuit tuned to this thread, with a very exhaustive and complete description. (why the semiconductor-companies don't make any more these nice applications gifts?)

"Most audio amplifier circuits today are voltage output devices which apply a voltage to the terminals of the speaker. Large changes in speaker impedance with frequency yield poor frequency response with the high-frequency output falling off rapidly as the speaker impedance increases. It should be noted that the speaker cone displacement is proportional to the current in the voice coil rather than the voltage across the speaker terminals. The current is the primary mover of the voice coil.
The single speaker amplifier circuit shown in Figure 3-31 uses current feedback rather than the more popular voltage feedback. As shown, the feedback loop is from the junction of the speaker terminal and a 0.5Ω resistor, to the inverting input of the NE5534. Sensing the current through the speaker and feeding it back provides better speaker damping than obtainable with voltage-drive systems.
Note the unusual grounded output pin on the NE5534 op-amp. When the input to the amplifier is positive, the power supply supplies current through the TIP32 and the load to ground. Conversely, with a negative input the TIP31 supplies current through the load to ground. The gain in this case is set to about 15 (gain = SPKR 8Ω / 0.5Ω feedback). The 0.22F capacitor across the speaker rolls off its response beyond the frequencies of interest. Using the 0.22F capacitor specified, the amplifier output is 3 dB down at 90kHz where the speaker impedance is about 20Ω. The Quiescent output stage collector current is determined by the 130 Ω resistors that connect each transistor base to the appropriate supply rail, the output transistor VBE, and the 1Ω emitter resistors. To set the recommended class 'A' output collector current, adjust the value of either 130Ω resistor. An output current of 50 to 100mA will provide a good operating midpoint between the best crossover distortion and power dissipation.
The 0.1 F bypass capacitors on each rail may be mylar or ceramic disk. The 2.0 F should be a nonpolarized capacitor while the 0.22F across the speaker should be mylar.
Figure 3-32 shows the frequency response of the amplifier with a 2.0F input capacitor. This response is very flat with the -3.0dB point on the low frequency end at 45 Hz. The -3.0dB point at the high frequency end occurs at 80kHz. Total Harmonic Distortion (THD) is 0.01% at 6.25W rms output into an 8 Ω load with 18V on the supply rails."
very fine proposition, I simmed this topology but is seems that is very prone for the oscillation.
I had to tammed LT1022 with 47n cap!
People who built this agreed the same.
Attached Images
File Type: png sch.png (17.9 KB, 622 views)
File Type: png sinew.png (18.7 KB, 607 views)
File Type: png fft.png (7.1 KB, 588 views)
Attached Files
File Type: asc transcond Elektor lt1022 bd244.asc (2.6 KB, 60 views)
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regards, Pawel
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Old 22nd May 2015, 05:49 PM   #39
Andonio is offline Andonio  Italy
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Thanks, padamiecki,
Do you know if even with NE5534 OpAmp and Tip31-32 transistors the circuit transforms itself into an oscillator? I think it's worth the effort to try it, because at that time (1986) serious companies with a prestigious name (as TI) tested the circuits before publishing.
Regards. Luigi
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Old 23rd May 2015, 01:40 AM   #40
kp93300 is offline kp93300  Malaysia
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Hi pawel,
How does the sound of circuit in post 38 compared to the Lm 1875 amp?
regards
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