Help with first GC project - 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 3rd January 2008, 06:56 AM   #1
diyAudio Member
 
Join Date: Jan 2008
Default Help with first GC project

Hello everyone,

I came accross this forum almost by accident a few weeks ago. I was surprised to find the following the LM38XX amplifiers have. I thought they would have sounded like a radio shack alarm clock.

My NAD751 recently went t**s up so now I'm looking for an amp to replace it. As I used it primarily (almost exclusively) for music I figured a chipamp might fit the bill. My speakers are B&W DM602s which are bi-ampable so I think I'd like to try biamping them with a pair of chipamps each. I expect the advantages of biamp won't be as great in this case since they will still be going through the speaker crossovers and not crossed over before the amp.

So here is what I would like to know about building my first chipamps:

I was thinking of buying the chipamp.com kits. They seem fine to me, are there any issues with the kits? I'm sure I could not design and fab (professional PCB fab that is) a system cheaper, especially considering my time. Are there any other sources fro chipamp kits?

What do I use for volume control? I will be using the amps with a CD player, and possibly MP3 player but no phono. Do I need a preamp? Or can I simply feed the line outs through a stepped attenuator then into the amps? Where is a good place to get the stepped attenuators? What impedance should I use?

Where can I find the toroidal power transformers for a decent price? What is the reccomended secondary voltage for 8ohm speakers?

Are there any advantages of using parallel amplifiers for moderate listening levels? About the loudest I'd go in my house is turning my 35W (100+ peak) NAD304 up halfway.

How can I expect the chipamp performance to compare with my NAD304? If I do end up building a chipamp I'll probably do some back to back tests.

Any and all feedback is welcome. Feel free to get technical. I am an electrical engineer, though most of my experience is with embedded systems. I find it interesting to look at some of the PCB designs, its a bit of a change from all the 4layer 7mil feature size PCBs I've designed.
  Reply With Quote
Old 3rd January 2008, 09:14 AM   #2
Nuuk is offline Nuuk  United Kingdom
diyAudio Member
 
Nuuk's Avatar
 
Join Date: Feb 2003
Location: Somerset, SW England
The first thing you should do is measure the voltage output of the transformer in your NAD. I suspect this may be suitable to power your chip amps. Voltage rails up to around +/-37 volts will be fine for 8 ohm loads so you want a transformer with a maximum output of 25 VAC.

Not only could you use the transformer but the case as well!

The chipamp.com kits are fine. And bi-amping (even with the existing passive crossovers) won't do any harm!

You may or may not need an active buffer stage or pre amp between your CD and the chip amps.

I would be very surprised if the chip amps didn't sound better than the NAD.

May I suggest that you do as much research on this forum as you can as all of your questions have been answered somewhere. Also this site and the others on the Gainclone ring link will provide you with all the information you need to complete your project.
__________________
The truth need not be veiled, for it veils itself from the eyes of the ignorant.
  Reply With Quote
Old 3rd January 2008, 09:22 AM   #3
diyAudio Member
 
gainphile's Avatar
 
Join Date: Dec 2007
Location: Melbourne the sunny city!
Yeah.. the first time I read about gainclones 4 months ago I thought exactly the same thing, until reading reviews and forums. Now I have a 4-channel gainclones driving a pair of speakers actively and not sure how to top the quality
__________________
http://gainphile.blogspot.com
  Reply With Quote
Old 3rd January 2008, 10:53 PM   #4
diyAudio Member
 
Join Date: Jan 2008
I had thought about taking the transformer from the NAD. There are two reason why I don't want to do this. First of all there the power section of the NAD still works. if I buy a new receiver I may just patch it into the NAD power section. Secondly the NAD uses a standard (non-toroidal) transformer. I was always under the impression that toroidal transformers are better. Is this true?
  Reply With Quote
Old 3rd January 2008, 10:57 PM   #5
BWRX is offline BWRX  United States
diyAudio Moderator Emeritus
 
Join Date: Jan 2005
Location: Pennsylvania
Just because a transformer is a toroid doesn't mean it's good! There are lots of good transformers that aren't toroids, probably including the one in your NAD receiver.
__________________
Brian
  Reply With Quote
Old 4th January 2008, 02:26 AM   #6
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
Quote:
Originally posted by drproton
I had thought about taking the transformer from the NAD. There are two reason why I don't want to do this. First of all there the power section of the NAD still works. if I buy a new receiver I may just patch it into the NAD power section. Secondly the NAD uses a standard (non-toroidal) transformer. I was always under the impression that toroidal transformers are better. Is this true?
Hi drproton,

I think that the ONLY (electrical) way that toroidal transformers are better than other transformer types is that they have relatively lower-strength radiated EM fields, which are also concentrated basically around only one axis. Toroidals are usually worse than E-I types at filtering garbage out of the AC mains, for example.

Maybe you could just leave the entire NAD power supply completely intact, and use it for your chipamps! What existing DC rail voltages does it have?
__________________
The electrolytic capacitors ARE the signal path: http://www.fullnet.com/~tomg/zoom3a_33kuF.jpg
  Reply With Quote
Old 5th January 2008, 01:06 AM   #7
diyAudio Member
 
Join Date: Jan 2008
Thats not a bad idea. There is one other problem with the NAD transformer. It won't fit in the enclosure I want to use. I've done some more research. It seems like (anecdotally at least) preamp/buffering the chipamps give better quality sound. I would guess this is due to impedance issues, and higher level outputs like headphone outs or sound card outs don't suffer the same. Now that I think of it my NAD 304 has separable preamp/poweramp sections. I can use this to test the preamp thing. As a test I can also use my bench supply which is capable of +/- 50v @ 5A. I'd still run this through the power supply caps as this supply is a switching type and might be prone to noise.

I found a couple preamp designs in my searching, but the only ones I found that are available as a kits are the twisted pear amps. I these okay? Are there any other kits out there? How about kits for active crossovers?

What does the term "balanced" mean as it pertains to audio? I know I learned this one before, but I can't remember it now.
  Reply With Quote
Old 6th January 2008, 04:24 PM   #8
BWRX is offline BWRX  United States
diyAudio Moderator Emeritus
 
Join Date: Jan 2005
Location: Pennsylvania
Quote:
Originally posted by drproton
What does the term "balanced" mean as it pertains to audio?
Balanced means you have two signals (one non-inverted and one inverted) and a ground.
__________________
Brian
  Reply With Quote
Old 6th January 2008, 08:49 PM   #9
diyAudio Member
 
Join Date: Jan 2008
That was my guess, seeing as how "balanced" sources are used to feed bridged amps.

On another note, I fixed my NAD 751. It turns out the root of all the problems was, quite typically, a defective electrolytic cap. Once I saw that the line marked "DC8V" was about 6volts DC + about 6V of sawtooth I tracked it back and found a slightly bulged cap. I replaced that and everything was good.

I think I will still build the gainclone. I'm also probably going to make a set of speakers for my computer. The ones hooked up to it now cost me $0 and sure sound like it.
  Reply With Quote
Old 7th January 2008, 09:59 AM   #10
AndrewT is online now AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally posted by BWRX


Balanced means you have two signals (one non-inverted and one inverted) and a ground.
no,
balanced = same impedance on both the inverting and non-inverting inputs.
Same impedance implies the same resistances and the same reactances.
__________________
regards Andrew T.
  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
CDPRO2 Group Project (open source project) BrianGT Digital Source 147 8th August 2008 11:37 AM
My OLD Project....... cheap tube audio project!!! tube-lover Tubes / Valves 4 8th May 2008 09:26 PM
first project ceebmoj Full Range 5 23rd January 2008 07:51 AM
My first project, cool project. sorinsistem Solid State 3 19th January 2006 05:08 PM


New To Site? Need Help?

All times are GMT. The time now is 08:30 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