Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Chip Amps Amplifiers based on integrated circuits

eBay mono LM1875 kit
eBay mono LM1875 kit
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 Today, 06:26 AM   #401
rabbitz is offline rabbitz  Australia
diyAudio Member
 
rabbitz's Avatar
 
Join Date: Jul 2003
Location: Newcastle, Australia
Quote:
Originally Posted by chermann View Post
i found the low input cap at your board - on my compare amps they were different too:

i had at the green the 10F nichicon UES and at the other the 4,7F Wima - now i use this super big 10F foil. - for me the different in sonic bass is notable and important - so i have to ask you : Are really happy with your 1F at the input??

chris
The answer is yes. My favourite DIY amp, the AKSA 55, used a 470nF with Zin=47k IIRC and was more than satisfactory as was my reference / baseline. If my calculations are correct, a Zin=22k with a 1uF cap gives a corner frequency of 7.23Hz and this amp will be used with speakers with an F3 no lower than 60Hz.

I did spot this in a post (I think from lineup) which is handy:
My rule of the thumb is using ~50 uF kohm.
uF x kOhm = 50
----------------------
Input impedance is 10 kohm, I will go for 50/10 = 4.7 uF MKP
Input resistor is 22 kohm, I will go for 50/22k = 2.2 uF
Input resistor is 47 kohm, I will go for 50/47k = 1.0 uF
Input impedance is >47 kohm, I will still go for = 1.0 uF MKP


Ideally 2.2uF may be better but 1uF will suit the application. My other eBay PCB uses 2.2uF but had none available for this build.

Also mentioned in the same thread as the quote, if you use a bipolar electrolytic as an input cap, then multiply the film cap size by 10.

What is interesting is we have both gone down different paths. I've gone for small power supply decoupling and input caps where you have gone the other direction but on this PCB, we both have had results that we find satisfactory and put a smile on our face. Been a good kit whether built as is or modded.
__________________
If there are no dogs in Heaven, then when I die I want to go where they went - Will Rogers
  Reply With Quote
Old Today, 06:41 AM   #402
rabbitz is offline rabbitz  Australia
diyAudio Member
 
rabbitz's Avatar
 
Join Date: Jul 2003
Location: Newcastle, Australia
Quote:
Originally Posted by chermann View Post
Hi Rabbitz and others

I see at the LM3875 datasheet that this chip is more powerful but the current is still 4Amps max - so its comparable with the LM1875.
the THD and the PSRR is much better.
I know you are experts at chip amps + you (rabbitz) own a Arcam A19.
Can you "confirm" that a powerful chip sounds at lower power /volume level better then e.g. LM1875??

chris
Firstly, I am not an expert and know very little about amplifiers but get by with the experience I've gained over the years.

I can't say I've compared amps at low volumes as it is not how I listen. I will check over the next few days and put up a LM3886 P19, LM3875 against the LM1875.

Low volumes becomes an issue due to the Fletcher Munson Curve and the only amp I've had with a decent loudness circuit was that from Yamaha as it's variable. I do have an active BSC that I could try with it as well.
__________________
If there are no dogs in Heaven, then when I die I want to go where they went - Will Rogers
  Reply With Quote
Old Today, 06:54 AM   #403
rabbitz is offline rabbitz  Australia
diyAudio Member
 
rabbitz's Avatar
 
Join Date: Jul 2003
Location: Newcastle, Australia
Quote:
Originally Posted by chermann View Post
i am asking because in generally i planned to use a other chip in the next future to compare with the LM1875 - but i want to try composite + parallel LM1875 first...so a lot of work
chris
Parallel can be fun or a hassle as did try that with a LM4780 a decade ago. The DC offset went through the roof but I believe if you closely match the feedback network resistors so you get identical gain in both amps, the outcome is improved. I think there is some info on it in the LM4780 datasheet. The output current sharing resistors (Rout) I used were 0R15 3W and were supplied in the Audiosector kit.

I've attached the parallel info I got for the LM4780.

Peter
Attached Files
File Type: pdf RZlm478020amp.pdf (184.1 KB, 2 views)
__________________
If there are no dogs in Heaven, then when I die I want to go where they went - Will Rogers
  Reply With Quote
Old Today, 07:07 AM   #404
chermann is offline chermann  Austria
diyAudio Member
 
Join Date: Jan 2017
Location: Vienna
Quote:
Originally Posted by rabbitz View Post
Firstly, I am not an expert and know very little about amplifiers but get by with the experience I've gained over the years.

I can't say I've compared amps at low volumes as it is not how I listen. I will check over the next few days and put up a LM3886 P19, LM3875 against the LM1875.

Low volumes becomes an issue due to the Fletcher Munson Curve and the only amp I've had with a decent loudness circuit was that from Yamaha as it's variable. I do have an active BSC that I could try with it as well.

Thanks rabbitz


Sorry rabbitz...i mean with low level music...no boom boom... i measured it at home at my listening level "normal" = floating the room with enough energy = 1-3 Watt continuous and peaks about 15 - 30 Watt at 8R. depending which music you are listining
chris
  Reply With Quote
Old Today, 07:10 AM   #405
chermann is offline chermann  Austria
diyAudio Member
 
Join Date: Jan 2017
Location: Vienna
Quote:
Originally Posted by rabbitz View Post
The answer is yes. My favourite DIY amp, the AKSA 55, used a 470nF with Zin=47k IIRC and was more than satisfactory as was my reference / baseline. If my calculations are correct, a Zin=22k with a 1uF cap gives a corner frequency of 7.23Hz and this amp will be used with speakers with an F3 no lower than 60Hz.

I did spot this in a post (I think from lineup) which is handy:
My rule of the thumb is using ~50 uF kohm.
uF x kOhm = 50
----------------------
Input impedance is 10 kohm, I will go for 50/10 = 4.7 uF MKP
Input resistor is 22 kohm, I will go for 50/22k = 2.2 uF
Input resistor is 47 kohm, I will go for 50/47k = 1.0 uF
Input impedance is >47 kohm, I will still go for = 1.0 uF MKP


Ideally 2.2uF may be better but 1uF will suit the application. My other eBay PCB uses 2.2uF but had none available for this build.

Also mentioned in the same thread as the quote, if you use a bipolar electrolytic as an input cap, then multiply the film cap size by 10.

What is interesting is we have both gone down different paths. I've gone for small power supply decoupling and input caps where you have gone the other direction but on this PCB, we both have had results that we find satisfactory and put a smile on our face. Been a good kit whether built as is or modded.



Thank you rabbitz for sharing your experience -i just tried the UES caps in the input and maybe i am biased with this - now i have and my other amp (blue decoupling cap and wima 4,7F at the input) +at my "best amp part" the foil cap. i have to try more with foils or others.
chris
  Reply With Quote
Old Today, 07:48 AM   #406
chermann is offline chermann  Austria
diyAudio Member
 
Join Date: Jan 2017
Location: Vienna
Quote:
Originally Posted by rabbitz View Post
Parallel can be fun or a hassle as did try that with a LM4780 a decade ago. The DC offset went through the roof but I believe if you closely match the feedback network resistors so you get identical gain in both amps, the outcome is improved. I think there is some info on it in the LM4780 datasheet. The output current sharing resistors (Rout) I used were 0R15 3W and were supplied in the Audiosector kit.

I've attached the parallel info I got for the LM4780.

Peter

Thanks rabbitz. yes i read about parallel amps - its not easy....DC offset is a killer.
chris
  Reply With Quote

Reply


eBay mono LM1875 kitHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
LM1875 Ebay dual channel pcb question nenad88 Chip Amps 11 30th August 2018 12:21 AM
Chinese Mono LM1875 Board Twil Chip Amps 54 23rd April 2018 09:04 AM
ebay lm1875 pcb asuslover Chip Amps 7 27th August 2016 04:58 AM
Running two LM1875 mono amp from single psu si82 Chip Amps 21 2nd June 2014 04:32 PM
Just fired up my new dual mono lm1875 Gainclone. Shoog Chip Amps 5 19th January 2004 07:09 PM


New To Site? Need Help?

All times are GMT. The time now is 12:26 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki