Carlos's Low value res config with 3875

pwan · 26th June 2006, 08:09 AM

Hi,

The original Carlos's proposal on the low value res config (2K / 100 Ohm for feedback res) is to LM3886. I wonder if anyone ever try this with LM3875 (whose current output is much lower than 3886 in Carlos's design) ?

Thanks.

peranders · 26th June 2006, 08:32 AM

If you have different resistor values you will also get different properties like noise and output offset. To me this seems to be a bit below optimum.

sangram · 26th June 2006, 09:37 AM

I tried with 4766 and it worked fine (4.7K/220). DC-offset is very low (less than 5mV per channel).

I don't like the sound, but it could be any number of things. I suspect it's the chip that doesn't sound good, but I'm going to experiment with different values and then with different resistors before I blame the chip, the resistors, or the values.

Just FYI, I liked the LM4780 best when connected with high value resistors (220K/10K) but in that case even the resistors used were different and the offset was too high. I don't believe in resistor sound too much, but knowing the horrible components we get in our country, I'm not ruling anything out...

frank1 · 26th June 2006, 11:30 AM

Quote:

Originally posted by sangram
I tried with 4766 and it worked fine (4.7K/220). DC-offset is very low (less than 5mV per channel).

I don't like the sound, but it could be any number of things. I suspect it's the chip that doesn't sound good, but I'm going to experiment with different values and then with different resistors before I blame the chip, the resistors, or the values.

Just FYI, I liked the LM4780 best when connected with high value resistors (220K/10K) but in that case even the resistors used were different and the offset was too high. I don't believe in resistor sound too much, but knowing the horrible components we get in our country, I'm not ruling anything out...

How about measuring the performance so you can quantify "doesn't sound good"?
The PC sound card is a very powerful tool for audio testing. There are some very good audio spectrum analyser tools available (free). Some even contain a tone generator.
Personally, I use TrueRTA (there is a free but limited version) for testing my amps.

What's audible should also be measurable!

Frank

pwan · 26th June 2006, 11:54 AM

Quote:

Originally posted by peranders
If you have different resistor values you will also get different properties like noise and output offset. To me this seems to be a bit below optimum.

Perander,

What do you mean "To me this seems to be a bit below optimum."?

PS: Thanks frank, sangram.

analog_sa · 26th June 2006, 12:23 PM

Quote:

Originally posted by pwan

What do you mean "To me this seems to be a bit below optimum."?

Maybe that noise will be too low

sangram · 26th June 2006, 12:27 PM

Quote:

Originally posted by frank1

What's audible should also be measurable!

Frank

I agree. I actually have a full suite of test tools downloaded some time ago, including a distortion analyser, tone generator, etc. My recording software has a spectrum analyser built in as well, and I have Speaker workshop as well which works well.

Never got around to using any of it though...

Maybe I'm just lazy!!!

Edit: I think what P-A was saying is that the resistor values need to be higher than 2.2K/100 ohm. I guess I agree.

pwan · 27th June 2006, 11:34 AM

OK I will try it soon.

Thanks all for your comments.

26th June 2006, 08:09 AM	#1
pwan diyAudio Member Join Date: Apr 2006 Location: Earth	Carlos's Low value res config with 3875 Hi, The original Carlos's proposal on the low value res config (2K / 100 Ohm for feedback res) is to LM3886. I wonder if anyone ever try this with LM3875 (whose current output is much lower than 3886 in Carlos's design) ? Thanks.

26th June 2006, 08:32 AM	#2
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	If you have different resistor values you will also get different properties like noise and output offset. To me this seems to be a bit below optimum. __________________ /Per-Anders (my first name) or P-A as my friends call me Tube Buffered Gainclone in work \|Thread

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
Carlos! This is my amp	thanh	Solid State	11	9th August 2005 04:07 AM
Carlos grounding Scheme	kestrel200	Chip Amps	17	20th May 2005 11:20 PM
Carlos regulated PS pcb	antomas	Chip Amps	0	18th May 2005 03:21 PM
PA100 or Carlos Improved NIC	sith	Chip Amps	0	10th May 2005 07:58 PM

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


	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

26th June 2006, 09:37 AM	#3
sangram diyAudio Member Join Date: Sep 2002 Location: India	I tried with 4766 and it worked fine (4.7K/220). DC-offset is very low (less than 5mV per channel). I don't like the sound, but it could be any number of things. I suspect it's the chip that doesn't sound good, but I'm going to experiment with different values and then with different resistors before I blame the chip, the resistors, or the values. Just FYI, I liked the LM4780 best when connected with high value resistors (220K/10K) but in that case even the resistors used were different and the offset was too high. I don't believe in resistor sound too much, but knowing the horrible components we get in our country, I'm not ruling anything out...

27th June 2006, 11:34 AM	#8
pwan diyAudio Member Join Date: Apr 2006 Location: Earth	OK I will try it soon. Thanks all for your comments.