LM3875, need for preamp?

mac-attack · 7th October 2005, 08:48 AM

I'm about to build a power amp and I'm currently looking at Peter Daniels (www.audiosector.com) LM3875 based amp.

I would like to know if it is possible to drive such an amp directly from my DVD player (a Marantz DV4500) only using a passive pot for volume control? I understand that the LM3875 amp has a 22K input impedance, unfortunately the output imp of my source is unknown to me. Can someone please eleborate on the pros and cons of this approach? Also, what would an input buffer do for me when driving the amp directly from the DVD?

I have tried to search the forum for answers to my questions, but so far without any luck. Please let me know if there are threads handling my questions already.

M.A.

evo · 7th October 2005, 10:11 AM

Hi mac-attack,
I've built the 3875 kit and have used it with a Meridian206/Pioneer DV535 and a passive pot with no problems at all.
Although i believe driven by a pre-amp it will sound better.

This is well regarded and there's loads of info as well:

Nuuks Site

HTH
evo

GaryB · 7th October 2005, 10:36 AM

I've got an LM3875 amp similar to the audiosector kit and I have driven it from a DVD player though a simple 10K passive preamp and it sounded fine. This was in a fairly modest system.

I've also taken the amp to the house of various friends and gotten some interesting feedback saying that it sounds good but not great when driven by the wrong preamp but amazing with the right preamp. Examples of the "wrong preamp" include the 10K passive preamp and a tube preamp with relatively high output impedance. Examples of the "right preamp" were a transformer volume control preamp or a transformer coupled tube preamp. Both of these have pretty low output impedance so I'd draw the conclusion that is the key to getting the best out of an LM3875 amp.

---Gary

skyraider · 7th October 2005, 10:56 AM

preamp is not necessary for gainclone unless you are driving long cables, or just want to color the sound. It works fine from a cd output.

javven · 23rd October 2005, 07:50 AM

Earthdawn player?

Not hijacking the thread, so back to the program...

Any specific concerns with enclosing the preamp section in the same chassis as the power-amp section?

skyraider · 24th October 2005, 02:53 AM

Quote:

Any specific concerns with enclosing the preamp section in the same chassis as the power-amp section?

even better so you can reduce signal cable. Just make proper isolation for transformers..

7th October 2005, 08:48 AM	#1
mac-attack diyAudio Member Join Date: Mar 2004 Location: Sweden	LM3875, need for preamp? I'm about to build a power amp and I'm currently looking at Peter Daniels (www.audiosector.com) LM3875 based amp. I would like to know if it is possible to drive such an amp directly from my DVD player (a Marantz DV4500) only using a passive pot for volume control? I understand that the LM3875 amp has a 22K input impedance, unfortunately the output imp of my source is unknown to me. Can someone please eleborate on the pros and cons of this approach? Also, what would an input buffer do for me when driving the amp directly from the DVD? I have tried to search the forum for answers to my questions, but so far without any luck. Please let me know if there are threads handling my questions already. M.A.

7th October 2005, 10:36 AM	#3
GaryB diyAudio Member Join Date: Sep 2002 Location: Silicon Valley	a good preamp helps I've got an LM3875 amp similar to the audiosector kit and I have driven it from a DVD player though a simple 10K passive preamp and it sounded fine. This was in a fairly modest system. I've also taken the amp to the house of various friends and gotten some interesting feedback saying that it sounds good but not great when driven by the wrong preamp but amazing with the right preamp. Examples of the "wrong preamp" include the 10K passive preamp and a tube preamp with relatively high output impedance. Examples of the "right preamp" were a transformer volume control preamp or a transformer coupled tube preamp. Both of these have pretty low output impedance so I'd draw the conclusion that is the key to getting the best out of an LM3875 amp. ---Gary

7th October 2005, 10:56 AM	#4
skyraider diyAudio Member Join Date: Jan 2004 Location: malaysia	no preamp is not necessary for gainclone unless you are driving long cables, or just want to color the sound. It works fine from a cd output.

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
Preamp for an LM3875 amp (mono)	purpf	Chip Amps	0	25th June 2009 10:53 AM
LM3875 and preamp... and more...	danbli	Chip Amps	9	26th October 2008 07:21 PM
Tube Preamp Popping on Source Input Change (?) / 6DJ8 Preamp On Chip Amps	MartyM	Tubes / Valves	3	16th October 2008 04:52 AM
LM3875 T or TF?	TooManyToyz	Chip Amps	1	25th November 2007 07:18 PM
Easy Tube Preamp to Front LM3875 GC?	CarlosT	Instruments and Amps	27	1st February 2007 11:58 AM


	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

7th October 2005, 10:11 AM	#2
evo diyAudio Member Join Date: May 2004 Location: England	Hi mac-attack, I've built the 3875 kit and have used it with a Meridian206/Pioneer DV535 and a passive pot with no problems at all. Although i believe driven by a pre-amp it will sound better. This is well regarded and there's loads of info as well: Nuuks Site HTH evo

23rd October 2005, 07:50 AM	#5
javven diyAudio Member Join Date: Oct 2005	Earthdawn player? Not hijacking the thread, so back to the program... Any specific concerns with enclosing the preamp section in the same chassis as the power-amp section?

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

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