Semi finished gainclone LM3875 - 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 13th September 2005, 07:47 AM   #1
diyAudio Member
 
enzedone's Avatar
 
Join Date: Nov 2004
Location: New Zealand
Talking Semi finished gainclone LM3875

Well here it is, itís taken a year and this is the second case that Iíve put it into. But as you can see itís nearly finished. Apart from one rear cover and a power cord to and from the power supply, plus some speaker connections.
The first case was just the run of the mill Perspex box, which after building didnít look so hot. So I decided to completely strip the thing down and start again. The base was gathered from a scrap metal yard, its 3mm stainless steel which is nice and heavy, but a right prick to work with. The sides are pine sanded and coated with a clear varnish. The tops, sides and rears are all Perspex which I salvaged from a plastics factory in Albany.



If you look at the second picture in, you can see the heat sink at the bottom of the amp case. This was attached to the base as I wanted to keep the case as small as possible without getting crazy. The CD was used as a reference to the size. It is possible to go quite a bit smaller but without some really good and accurate tooling, this was about my limit. And spending money on more tools was just not an option. As this was already not high on the DAF (Domestic Approval Factor) list in the first place, spending even more money was out of the question.

Was it all worth it?
Thatís a question that I keep asking myself. I have learnt a lot building this amp and the knowledge gain has been invaluable.
What does it sound like?
Not bad, not bad at all. I have class A Technics SU650 amp and it does sound good compared to this. Does it sound better? Hard to say as it was not run in long enough, as I ripped it out and started on the second case. But it doesnít sound any worse than my Technics, at $1000 in 1989. That was an expensive buy back then. This amp has cost about $200 NZ to build, of course there has been other miscellaneous items which I felt could not be directly linked to the amp, which I had purchased to get this finished.
Would I do this again?
Well I would, but the next one had better sound really good for all the time and effort Iíve put into it. But it was very enjoyable to work on.
Attached Images
File Type: jpg amp photos2.jpg (23.8 KB, 750 views)
  Reply With Quote
Old 13th September 2005, 07:50 AM   #2
diyAudio Member
 
enzedone's Avatar
 
Join Date: Nov 2004
Location: New Zealand
Here is another picture. Sorry if there's not a lot of pics, I don't own a digital camera so I had to take this to work to use one there. I wasn't about to pull the thing apart again
Attached Images
File Type: jpg amp photos1.jpg (32.3 KB, 652 views)
  Reply With Quote
Old 13th September 2005, 08:09 AM   #3
diyAudio Member
 
enzedone's Avatar
 
Join Date: Nov 2004
Location: New Zealand
Post Lm3875

The chips were ordered from Brian, it's the older one with the simple supply setup. Actually I was worried about that as I had read so much about the inportance of power supplies. But my speakers have incredilbe base on them, so when it was first hooked up I was surprised at the sound. It seemed quite nice, even with the very lack luster power supply. I am using a set of Image 416's, these are made in New Zealand, you can check them out here,
imageloudspeakers.co.nz. So maybe the balance was right. It will be interesting to get this finished and then let it run for a while and do another comparison with the Technics.

Something else I've learnt while doing this project; New Zealand is an extremely expensive place to buy parts in, and also a very small market. So it's very difficult to get supplies. So if your living in New Zealand check out all the second hand shops and scrap yards to get some really cheap stuff. And think carefully before rushing out to buy parts, because it all starts adding up very quickly, a few connectors here and there, some wire, before you know it you've spent $100.
  Reply With Quote
Old 13th September 2005, 08:39 AM   #4
ofb is offline ofb
diyAudio Member
 
Join Date: Oct 2002
Location: canada
Default Re: LM3875

cute & smart. very nice.

Quote:
simple supply setup
which one? single tx with dual secondaries to two bridges? what tx brand and VA?

is 'technics su650' a typo by any chance? i'm not finding that one on google. perhaps similar to something on vintagetechnics.com ?
  Reply With Quote
Old 13th September 2005, 08:44 AM   #5
diyAudio Member
 
enzedone's Avatar
 
Join Date: Nov 2004
Location: New Zealand
Default Technics SUV650

Sorry it's probably my one fingered typing.......

I am using a single 160va 25-0-25v Transformer. Single rectifier board.
Dual supply.

The Technics Amp is old..88,89. But very nice as it was instorage for about 7,8 years while I was overseas travelling, so it's still resonably new in hours of use.
  Reply With Quote
Old 13th September 2005, 09:30 AM   #6
evo is offline evo  England
diyAudio Member
 
evo's Avatar
 
Join Date: May 2004
Location: England
Very nice enzedone, excellent work-nice to see something different.
  Reply With Quote
Old 14th September 2005, 04:03 AM   #7
diyAudio Member
 
enzedone's Avatar
 
Join Date: Nov 2004
Location: New Zealand
Default Cheers

You know this could be seen as stirring, but I have noticed over the last twelve months that there seems to be a lot of people theorising about this or that design or layout.....talk, talk talk.
O.k, I'm no electronic wiz but at some stage you going to have to get something made and let your ears do the judging.
  Reply With Quote
Old 4th October 2005, 03:11 AM   #8
diyAudio Member
 
enzedone's Avatar
 
Join Date: Nov 2004
Location: New Zealand
Talking Finished

Finished and running
Finished about two weeks ago, and has been running ever since. There was 10mv on one side and and 20mv on the other. Which was good compared to the first case. I think it had something to do with the length of wires from the board to the interconnects?
And I tried to keep them the same length. I am using a pair of image loudspeakers which have amazing base so it seems to be well balanced, but i still think it lacks a bit in that department. the next one i make will definately have a bit more punch in the power supply area.
  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
LM3875 Kit Finished - Could use some more bass johan851 Chip Amps 91 31st March 2008 01:13 PM
LM3875-semi finished enzedone Chip Amps 17 16th February 2006 04:19 AM
LM3875 amp finished!! Photo's durxter Chip Amps 10 5th September 2005 10:05 AM
10" XLS semi-finished Dave Jones Multi-Way 8 25th May 2004 09:58 PM


New To Site? Need Help?

All times are GMT. The time now is 02:05 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