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Old 4th August 2009, 06:27 PM   #891
shmulik is offline shmulik  Israel
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you should consult someone who really understand these things, but if you look in the data sheets of the drv134 you will notice a 10KOhms input impedance. this means that when connecting a potentiometer at the input (taking from the variable tap to the drv input) the source will not see the same impedance in different volume settings. I think the actual impedance would be between 5K (at full volume) to 10K (complete silence) and somewhat non linear behavior even if the potentiometer is linear. the common practice is to use a potentiometer in front of an operational amplifier (input impedance of 1e13 Ohms which is completely swamped by the potentiometer's resistance) or using some other type of active buffering.

this "build it for my sister" thing annoys me to. it starts with a "no problem, very easy, no bother!" and ends as a lifetime project you don't know how to gracefully end...
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Old 4th August 2009, 09:48 PM   #892
Cobra2 is offline Cobra2  Norway
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Quote:
Originally posted by shmulik
---
this "build it for my sister" thing annoys me to. it starts with a "no problem, very easy, no bother!" and ends as a lifetime project you don't know how to gracefully end...

Oh boy, we have been there...

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Old 4th August 2009, 10:16 PM   #893
juluska is offline juluska  Ukraine
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Quote:
Originally posted by shmulik
you should consult someone who really understand these things, but if you look in the data sheets of the drv134 you will notice a 10KOhms input impedance. this means that when connecting a potentiometer at the input (taking from the variable tap to the drv input) the source will not see the same impedance in different volume settings. I think the actual impedance would be between 5K (at full volume) to 10K (complete silence) and somewhat non linear behavior even if the potentiometer is linear. the common practice is to use a potentiometer in front of an operational amplifier (input impedance of 1e13 Ohms which is completely swamped by the potentiometer's resistance) or using some other type of active buffering.

this "build it for my sister" thing annoys me to. it starts with a "no problem, very easy, no bother!" and ends as a lifetime project you don't know how to gracefully end...
My sister knows it's difficult for me to build this amplifier because i'm just learning. I'm an architect and i'm about to get back to university to begin my electronics engineering studies while i'm working. It doesn't matter the duration of the project, the finality is learn in the path.
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Old 5th August 2009, 08:49 AM   #894
logical is offline logical  Romania
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@juluska: if you want to keep it very simple, you can use a simple pot as a passive preamp, but it has to be logarithmic...

but, as stated in the DRV134's datasheet, TI recommends using an active preamp, that is a simple opamp (but something of good quality, like the OPA2104 for better sound, minimum noise).

a very interesting active preamp with tone control is found here: http://sound.westhost.com/project97.htm

You could use just the figure 4 circuit (also, lose the capacitors on the right because you already have an input capacitor on the PA150 boards)
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Old 5th August 2009, 11:23 AM   #895
AndrewT is offline AndrewT  Scotland
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Hi,
if the DRV is between the passive pot and the amplifier then the DRV is not driving the pot.
The DRV is driving the power amp and whatever impedance/resistance you have built into the power amp's input.

What is before the pot?
Can that source/s drive a 5k or 10k passive pot?
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Old 5th August 2009, 06:03 PM   #896
juluska is offline juluska  Ukraine
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Quote:
Originally posted by AndrewT
Hi,
if the DRV is between the passive pot and the amplifier then the DRV is not driving the pot.
The DRV is driving the power amp and whatever impedance/resistance you have built into the power amp's input.

What is before the pot?
Can that source/s drive a 5k or 10k passive pot?
A switch, cd player, radio... I don't know if these sources can drive a 10k pot. How can i know it?
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Old 5th August 2009, 06:09 PM   #897
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Originally posted by rhysh
Update: The rest of the parts will be going to Per-Anders early next week, using DHL again. This should hopefully not cause a delay as PA has stated he will be away.

And again, a huge thanks to Per-Anders for helping me out

Any updates on this Rhys?
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Old 5th August 2009, 06:41 PM   #898
juluska is offline juluska  Ukraine
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WHAT ABOUT USING THIS PROJECT FOR BRIDGING THE PA150 PCBS?
IS A BETTER SOLUTION THAN DRV134 OR THAT 1646?
http://sound.westhost.com/project14.htm
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Old 5th August 2009, 07:13 PM   #899
AndrewT is offline AndrewT  Scotland
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the DRV is reputed to not sound the best for audio.
Could someone suggest a good audio line driver?
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Old 5th August 2009, 08:45 PM   #900
udailey is offline udailey  United States
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If you read Alex' website you will find that he gave up on the DRV and moved to using a transformer based solution instead. Thats Alex88. He is the guy who designed these boards.
Uriah
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