Audiosector LM3875 - Volume Control / Preamp options - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 11th December 2010, 09:06 AM   #1
batdan is offline batdan  New Zealand
diyAudio Member
 
Join Date: Oct 2009
Default Audiosector LM3875 - Volume Control / Preamp options

Hi all,

I have built this kit successfully and have used an ALPS 50k log pot, 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
  Reply With Quote
Old 11th December 2010, 07:45 PM   #2
diyAudio Member
 
Join Date: May 2008
The 50K Dual Log Alps Blue with a 47K metal film shunt resistor should be perfect for your LM3875. I use that configuration to great effect in my Audiosector LM3875 premium kit.
  Reply With Quote
Old 11th December 2010, 08:03 PM   #3
jonners is offline jonners  United Kingdom
diyAudio Member
 
jonners's Avatar
 
Join Date: Jan 2007
Location: Cheltenham
Dan -

If you post your question in the appropriate thread in the Audio Sector Vendor Forum you will likely get some advice from Peter D. himself. I think he recommends a pot in the 10-20k range.
  Reply With Quote
Old 11th December 2010, 08:36 PM   #4
diyAudio Member
 
Join Date: May 2008
Here is the schematic of my passive attenuator. It is a dual input/dual output. It also contains a single ended class A MOSFET headphone amplifier. I use a CDP direct into the pre as my primary source. I have a tuner as my second source, and although the output voltage is less than the CDP, it still sounds very good (imo).

I tried 20k and 100k before I settled on the 50k/47k shunt option. In my opinion, it gives the most natural presentation.
Attached Images
File Type: jpg Passive Schematic.jpg (152.8 KB, 761 views)
  Reply With Quote
Old 12th December 2010, 01:04 AM   #5
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
wire the volume control correctly and remove the added series resistors.
__________________
regards Andrew T.
  Reply With Quote
Old 12th December 2010, 03:37 AM   #6
batdan is offline batdan  New Zealand
diyAudio Member
 
Join Date: Oct 2009
Quote:
Originally Posted by AndrewT View Post
Hi,
wire the volume control correctly and remove the added series resistors.
Andrew - Not sure what you mean by this post? Can you be more specific. My ALPS pot is wired on the input, no added resistors.

Zebra - so adding a 47K resistor on my inputs is all I would need to try?

Will also put a post in the Audiosector forum

Thanks,
Dan
  Reply With Quote
Old 12th December 2010, 09:42 AM   #7
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
My comment was referring to Zebra's pic, the preceding post.
__________________
regards Andrew T.
  Reply With Quote
Old 12th December 2010, 10:23 PM   #8
diyAudio Member
 
Join Date: May 2008
Quote:
Originally Posted by AndrewT View Post
Hi,
wire the volume control correctly and remove the added series resistors.
I actually prefer it in the shunted configuration. I tried it with the pot wired correctly, and the volume got very loud, very quickly. Despite the loudness, it also sounded quite lifeless and dull.

Regards,

Chris.
  Reply With Quote
Old 12th December 2010, 10:28 PM   #9
diyAudio Member
 
Join Date: May 2008
Quote:
Originally Posted by batdan View Post
Zebra - so adding a 47K resistor on my inputs is all I would need to try?
It's worth a try. The 2 resistors cost me about 0.25GBP.

Regards,

Chris.
  Reply With Quote
Old 13th December 2010, 05:36 PM   #10
diyAudio Member
 
Join Date: Dec 2004
Location: Parisian suburbs
Quote:
Originally Posted by batdan View Post
Zebra - so adding a 47K resistor on my inputs is all I would need to try?
Adding resistors at the entry is right if you dont forget to also modify the configuration of the pot as per the Zebra100 schematic : the pot output is not at the variable pin (pot wiring detail)

I tried this setting on my own Audiosector LM3875 amp and found the sound to be a little bit clearer than with standard alps pot, particularly at low volumes.

Now, there is a negative side : to work fine, pot and resistance must have about the same value, so even at full level this is a divider where you lose half of the sensitivity of the amplifier...
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
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
Preamp volume control?? Craig405 Tubes / Valves 7 10th September 2005 10:32 AM
Passive volume control options for the Behringer DCCX RyanC Digital Line Level 10 10th June 2004 12:58 AM


New To Site? Need Help?

All times are GMT. The time now is 05:06 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2