Transformer for LM3886 - Page 3

marcusdeming · 19th July 2007, 08:10 AM

What is LTP?

How about if i apply the same sort of connection to another amp, what will it affects? As in the 22r crossing from the left chaneel to ground and the right channel, another 22r to the ground.

AndrewT · 19th July 2007, 11:26 AM

LTP=long tail pair.

it is not 22r from output to ground.
It is an attenuator and the resistance from output to ground is 1000+22r=1022r or 1k0//1k0+22r=522r or 1k0//1k0//1k0+22r=355r.
Take your pick.

marcusdeming · 19th July 2007, 11:37 AM

I think i get it finally(OMG)

1000+22r=1022r or 1k0//1k0+22r=522r or 1k0//1k0//1k0+22r=355r
its for a single channel right, no crossing over the left or right channel, basically as a load to reduce gain/ amplitude.

marcusdeming · 20th July 2007, 08:57 AM

out of curiosity i am just wondering how is a combination like this different from just a single resistor itself at say 355r or 522r

AndrewT · 20th July 2007, 09:09 AM

The single resistor dissipates the total power.
You may end up having to use a wirewound.
I chose 1k0 because Pd=V*V/R=20*20/1000=400mW when the amp is delivering 50W into 8ohms.
Short term excursions to around 400mW will not cause any long term damage to a 600mW metal film resistor.
Even peak voltages of 24Vac when only driving the headphone attenuator will bring Pd to about 576mW. This may cause long term degradation of the resistor.
If you think that you may drive your chipamp that hard into headphones then select 1k5 rather than 1k0 as your parallel dropper resistors.
The only difference that choosing 1k5 will be that more are required in parallel to raise the volume at the headphones if they are too quiet.

marcusdeming · 10th January 2008, 01:44 PM

I am finally going to get to working on the lm3886, all the parts are ready and I am going to have a headphone output, can i confrim that using the configuration will not damaed my headphones, in which they range from 16ohms - 600 ohms.

19th July 2007, 11:26 AM	#22
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	LTP=long tail pair. it is not 22r from output to ground. It is an attenuator and the resistance from output to ground is 1000+22r=1022r or 1k0//1k0+22r=522r or 1k0//1k0//1k0+22r=355r. Take your pick. __________________ regards Andrew T.

20th July 2007, 09:09 AM	#25
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	The single resistor dissipates the total power. You may end up having to use a wirewound. I chose 1k0 because Pd=VV/R=2020/1000=400mW when the amp is delivering 50W into 8ohms. Short term excursions to around 400mW will not cause any long term damage to a 600mW metal film resistor. Even peak voltages of 24Vac when only driving the headphone attenuator will bring Pd to about 576mW. This may cause long term degradation of the resistor. If you think that you may drive your chipamp that hard into headphones then select 1k5 rather than 1k0 as your parallel dropper resistors. The only difference that choosing 1k5 will be that more are required in parallel to raise the volume at the headphones if they are too quiet. __________________ regards Andrew T.

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19th July 2007, 08:10 AM	#21
marcusdeming diyAudio Member Join Date: Oct 2006	What is LTP? How about if i apply the same sort of connection to another amp, what will it affects? As in the 22r crossing from the left chaneel to ground and the right channel, another 22r to the ground.

19th July 2007, 11:37 AM	#23
marcusdeming diyAudio Member Join Date: Oct 2006	I think i get it finally(OMG) 1000+22r=1022r or 1k0//1k0+22r=522r or 1k0//1k0//1k0+22r=355r its for a single channel right, no crossing over the left or right channel, basically as a load to reduce gain/ amplitude.

20th July 2007, 08:57 AM	#24
marcusdeming diyAudio Member Join Date: Oct 2006	out of curiosity i am just wondering how is a combination like this different from just a single resistor itself at say 355r or 522r

10th January 2008, 01:44 PM	#26
marcusdeming diyAudio Member Join Date: Oct 2006	I am finally going to get to working on the lm3886, all the parts are ready and I am going to have a headphone output, can i confrim that using the configuration will not damaed my headphones, in which they range from 16ohms - 600 ohms.

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