Linkwitz TXFM distorts(Pinging richie000boy) - diyAudio
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Old 12th January 2007, 11:29 AM   #1
mikee55 is offline mikee55  United Kingdom
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Angry Linkwitz TXFM distorts(Pinging richie000boy)

Hi all,

I have Rods Input mixer connected to a 24db lowpass xover and fed to the Linkwitz Transform. The mixer and crossover work fine, but when I pass the signal through the transform, the signal is somewhat distorted. The gain on the amplifier is cranked up,the Loudness circuit on and bass turned up( I know It shouldn't be) and it seems clearer. I had to use an NE5534AN instead of a TLO71, but pin out is identical. Oh and I can only drive the circuit with the headphone out on my PC speakers????

Any ideas, anybody, please.

Cheers mikee55

Update: Just took signal straight of the back of a DVD player and its distortion is realy loud now. Seems like an Impedance issue?
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Old 12th January 2007, 12:07 PM   #2
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Apart from the possibility that you simply overdrive it - there is also the danger of insufficient stability with this OP-AMP depending upon application.
So you might best post the dimensioning.

Regards

Charles
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Old 12th January 2007, 12:08 PM   #3
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The NE5534 will oscillate at gain less than 3 if compensation is not applied, see the datasheet.

Also can you post the schematic? Maybe some of your resistors are too low value.
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Old 12th January 2007, 12:35 PM   #4
mikee55 is offline mikee55  United Kingdom
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Talking Hi richie000boy

Just emailed you, Sir.
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Old 12th January 2007, 12:47 PM   #5
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At high frequencies the gain is determined by the ratio R2/R2=1 which is definitely too low for this op-amp to work without compensation.

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Charles
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Old 12th January 2007, 02:28 PM   #6
mikee55 is offline mikee55  United Kingdom
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Default What can I do?

Hi phase_accurate,

Should I go an swap it for the TLO71?

Mikee55
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Old 12th January 2007, 02:59 PM   #7
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This is one solution although the 5534 seems to be the better sounding one of both.

The other solution is to use compensation as required: 22 pF between PIN 5 & 8.

Regards

Charles
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Old 12th January 2007, 09:36 PM   #8
mikee55 is offline mikee55  United Kingdom
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Default Okay

I've swapped the op-amp for half a TLO72 and I get the same result????????????

cheers mikee55
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Old 13th January 2007, 12:12 AM   #9
gmikol is offline gmikol  United States
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Default Re: Linkwitz TXFM distorts(Pinging richie000boy)

Quote:
Originally posted by mikee55

Oh and I can only drive the circuit with the headphone out on my PC speakers????
...
Update: Just took signal straight of the back of a DVD player and its distortion is realy loud now. Seems like an Impedance issue?
Not an impedance issue, but possibly a gain issue. If the DVD player is putting out a 1Vrms signal, that's 1.41Vpeak. It looks like you have a low-frequency gain of about 8.4 (76/9). That means the output of the LT could be as high 11.8V peak. I don't know how high the NE5534 or the TL072 can drive, but 12V seems to be pushing your luck, even on 15V rails, so you're getting clipping out of the LT stage. It's also possible you're clipping the input stage of the amp. Try making R10 in the mixer circuit 47K or even 22K to see if it fixes anything. That should cut the signal level by a factor of 2 or 4. And don't forget to turn down the loudness and bass controls on the amp.

--Greg
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Old 13th January 2007, 01:45 AM   #10
mikee55 is offline mikee55  United Kingdom
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Default Doh!

Cheers Greg, but I found a cap with a broken lead. It works fine now. Its 2.45 am now so will wait till morning when I can listen properly.

Cheers

Mike
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