Audiosector LM3875 - Volume Control / Preamp options

batdan · 12th December 2010, 03:43 AM

This was posted on the chip amps forum, however it was suggested I post here also.

Hi all,

I have built the LM3875 Dual Mono Premium Kit successfully and have used an ALPS 50k log pot on the input side, however the music sounds "restrained" on playback.

But, if I use the preamp section of my receiver (Yamaha RXV1900) and turn the pot all the way up on my LM3875's I get the sound I am wanting. My source is a Gigawork DAC.

So, what is the best way to move forward? Will changing the ALPS out for something else be OK, or do I need a preamp? Is my ALPS at 50K to high? How do I calculate the correct value? If the preamp route is the way to go, can anyone point me in the direction of a suitable kit?

Thanks,
Dan

Peter Daniel · 12th December 2010, 05:39 AM

Regarding schematic posted here: Audiosector LM3875 - Volume Control / Preamp options the 47k series resistors seem a bit high, I would rather not go over 10k. How far you turn the pot at normal listening?

batdan · 12th December 2010, 06:15 AM

Quote:

Originally Posted by Peter Daniel

How far you turn the pot at normal listening?

Hi Peter,

One quarter turn for normal listening.

Thanks,
Dan

batdan · 14th December 2010, 06:44 PM

So is it worth trying a 10K pot instead of my 50K? Can anyone point me to somewhere that shows how best to calculate what value to use, or is it a matter of trial and error?

Thanks,
Dan

Peter Daniel · 15th December 2010, 01:09 AM

If you are using fixed series resistors shunted by a pot, it doesn't matter what value is a pot, for a given required attenuation the pot will be always set to a same shunt resistance value, no matter if it's 50k or 10k.

However, it's still worthwhile to try smaller value series resistors, like 10k suggested previously. And it looks like you need a lot of attenuation, so if 10k series resistors work better, most likely you will need to go with 10k pot indeed, to get more control over attenuation range.

batdan · 2nd January 2011, 05:59 AM

Hi,

I bought a 10K "21 Step Attenuator Potentiometer" from Ebay seller Gigawork for $10 and replaced the 50K ALPS. The sound now is perfect, exactly what I am after. Thanks for the great kits.

Daniel

charlesbahr · 20th April 2011, 02:54 PM

Hi,

I have two questions about what potentiometer to add to my Lm3875 kit. I was originally planning to take the headphone-out of my iPhone, send it directly into the LM3875, and put the output into my old Stax electrostatic headphones. I was going to use the volume slider on the iPhone to control the sound level.

But then I started thinking about a pot for a more flexible design of the chipamp... and then as I was trying to find out about the output voltage and impedance of the iPhone jack, I thought - maybe I should be using the line-out?

I think I should be able to take a headphone-out into the chipamp, but I would like advice from the experts. And then - what is an acceptable pot to get. I've looked at the recommendations -- ALPS RK27? 20K ohms? The resistance just limits the "off" level in the way it's wired in the diagram above, right?

Peter Daniel · 24th April 2011, 05:00 PM

I would suspect that line out from the iPhone should be superior to headphone output.

20K or similar value pot should be fine.

iPod and iPhone Line Out Cable with USB

charlesbahr · 25th April 2011, 11:50 AM

Peter,
Many thanks! I may get that adapter you referred to.
Charlie

syklab · 5th June 2011, 10:21 AM

Hi Peter,
I have a Elma 24 step ladder type 100K volume contrl from my old tube pre-amp, will that be suitable for use on your LM3875 GC kit?

Thansk

12th December 2010, 03:43 AM	#1
batdan diyAudio Member Join Date: Oct 2009	Audiosector LM3875 - Volume Control / Preamp options This was posted on the chip amps forum, however it was suggested I post here also. Hi all, I have built the LM3875 Dual Mono Premium Kit successfully and have used an ALPS 50k log pot on the input side, however the music sounds "restrained" on playback. But, if I use the preamp section of my receiver (Yamaha RXV1900) and turn the pot all the way up on my LM3875's I get the sound I am wanting. My source is a Gigawork DAC. So, what is the best way to move forward? Will changing the ALPS out for something else be OK, or do I need a preamp? Is my ALPS at 50K to high? How do I calculate the correct value? If the preamp route is the way to go, can anyone point me in the direction of a suitable kit? Thanks, Dan

12th December 2010, 05:39 AM	#2
Peter Daniel diyAudio Member Join Date: Jul 2002 Location: Toronto, Canada	Regarding schematic posted here: Audiosector LM3875 - Volume Control / Preamp options the 47k series resistors seem a bit high, I would rather not go over 10k. How far you turn the pot at normal listening? __________________ www.audiosector.com “Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC

15th December 2010, 01:09 AM	#5
Peter Daniel diyAudio Member Join Date: Jul 2002 Location: Toronto, Canada	If you are using fixed series resistors shunted by a pot, it doesn't matter what value is a pot, for a given required attenuation the pot will be always set to a same shunt resistance value, no matter if it's 50k or 10k. However, it's still worthwhile to try smaller value series resistors, like 10k suggested previously. And it looks like you need a lot of attenuation, so if 10k series resistors work better, most likely you will need to go with 10k pot indeed, to get more control over attenuation range. __________________ www.audiosector.com “Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC

20th April 2011, 02:54 PM	#7
charlesbahr diyAudio Member Join Date: Apr 2011 Location: New Jersey Blog Entries: 1	iPhone/headphone or line-out and potentiometer Hi, I have two questions about what potentiometer to add to my Lm3875 kit. I was originally planning to take the headphone-out of my iPhone, send it directly into the LM3875, and put the output into my old Stax electrostatic headphones. I was going to use the volume slider on the iPhone to control the sound level. But then I started thinking about a pot for a more flexible design of the chipamp... and then as I was trying to find out about the output voltage and impedance of the iPhone jack, I thought - maybe I should be using the line-out? I think I should be able to take a headphone-out into the chipamp, but I would like advice from the experts. And then - what is an acceptable pot to get. I've looked at the recommendations -- ALPS RK27? 20K ohms? The resistance just limits the "off" level in the way it's wired in the diagram above, right?

24th April 2011, 05:00 PM	#8
Peter Daniel diyAudio Member Join Date: Jul 2002 Location: Toronto, Canada	I would suspect that line out from the iPhone should be superior to headphone output. 20K or similar value pot should be fine. iPod and iPhone Line Out Cable with USB __________________ www.audiosector.com “Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC

14th December 2010, 06:44 PM	#4
batdan diyAudio Member Join Date: Oct 2009	So is it worth trying a 10K pot instead of my 50K? Can anyone point me to somewhere that shows how best to calculate what value to use, or is it a matter of trial and error? Thanks, Dan

2nd January 2011, 05:59 AM	#6
batdan diyAudio Member Join Date: Oct 2009	Hi, I bought a 10K "21 Step Attenuator Potentiometer" from Ebay seller Gigawork for $10 and replaced the 50K ALPS. The sound now is perfect, exactly what I am after. Thanks for the great kits. Daniel

25th April 2011, 11:50 AM	#9
charlesbahr diyAudio Member Join Date: Apr 2011 Location: New Jersey Blog Entries: 1	Peter, Many thanks! I may get that adapter you referred to. Charlie

5th June 2011, 10:21 AM	#10
syklab diyAudio Member Join Date: Jul 2009	Hi Peter, I have a Elma 24 step ladder type 100K volume contrl from my old tube pre-amp, will that be suitable for use on your LM3875 GC kit? Thansk

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Audiosector LM3875 - Volume Control / Preamp options	batdan	Chip Amps	9	13th December 2010 05:36 PM
X-preamp volume control	MBK	Pass Labs	45	3rd July 2008 09:14 PM
i need preamp schematics w/o tone control or volume control	hernanstafe	Parts	7	30th January 2008 03:12 AM
Volume control for lm3875 amp	Arx	Chip Amps	10	23rd September 2007 09:25 PM
Passive volume control options for the Behringer DCCX	RyanC	Digital Line Level	10	10th June 2004 12:58 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read