Cmoy layout. - Page 2 - 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 11th December 2008, 09:54 PM   #11
gfiandy is offline gfiandy  United Kingdom
diyAudio Member
 
gfiandy's Avatar
 
Join Date: Jul 2003
Location: Cambridge UK
Hi,

I have to admit I only skimed the data sheet, this was the point I saw that lead me to belive you would get current limiting at 26mA.

Short-circuit current
Sinking current, VO = 5 V
25C
26
mA

If you are running ar 12V then the situation is only slightly better.

Short-circuit current
Sinking current, VO = 12 V
25C
31
mA

this is in the typical operating characteristics.

However having taken a more carefull look you are right the Absolute Max current is indeed listed as 80mA. However operating parts at absolute max they may be operating outside there specified range. i.e the load regulation is undefined all you can say is that it won't be destroyed. This means the output 0v may start to move. Also operating near max power reduces there operating life (and with two channels of 40mA each you could be peaking at 80mA).

If you put a large caps on the output then the caps would be able to supply the transients. But I didn't see any on your design and you only mentioned putting small caps on the back.

In my experience average power has little to do with transient performance, with low crest factor music I am sure you will get plenty of noise. However if you want to capture the dynamics of more complex music you don't want the headphones to start to clip that early. The current limit will cause a transient to be cut off, its not about the average power which is a different issue. I used to use a 5V headphone amp in my designs this would happy drive 2.2V peak into 32 Ohm headphones, but still I got complaints from customers about dynamic perfomance and even volume from some people. I ended up with BUF634 OPA2134 compound design to deliver the current.

Its clear from other peoples comments that this design works. I guess I am just a pedant and don't like to see things that arn't designed to work inside there operating parameters, not right on the edge. Bottom line, if one of my engineers came to me with this design I wouldn't let it out of the building, but that is for comercial use and I guess as a DIY project its just fine.

Regards,
Andrew
  Reply With Quote
Old 12th December 2008, 02:11 AM   #12
diyAudio Member
 
Join Date: Mar 2007
Ok Andrew, you have compelled me.
I don't think it is possible to have too much capacitance. However, it is certainly possible to have too little.

One question though. I don't think that the polarity of the highlighted cap is right. Should it be the other way around?
Attached Images
File Type: png cmoyrev1.1.png (13.7 KB, 601 views)
  Reply With Quote
Old 12th December 2008, 05:14 AM   #13
diyAudio Member
 
Join Date: Mar 2007
something about that didn't look quite right to me so I made a few changes to where the power is connected. I'm still not really sure about the orientation of the cap on the V- rail to ground. I believe it should be the other way around, no?
  Reply With Quote
Old 12th December 2008, 05:36 PM   #14
diyAudio Member
 
kuldeepsingh's Avatar
 
Join Date: Aug 2006
Location: Chennai, India
Send a message via MSN to kuldeepsingh
Arrow Paralleled / Bridged CMOY

IS paralleled or bridged operation possible in Cmoy designs for getting better power drive for headphones?

Using OPA4134, this bridging or parallel operation could be easy..
__________________
. . .. ... ..... ........ ............. ..................... ..................................
My Blog
  Reply With Quote
Old 12th December 2008, 06:51 PM   #15
gfiandy is offline gfiandy  United Kingdom
diyAudio Member
 
gfiandy's Avatar
 
Join Date: Jul 2003
Location: Cambridge UK
Your not alone, I grind my engineering team down just as much:-) Seriously for the cost of a couple of extra caps I think you will find the improvement well worth it.

You are right the -ve terminal of the cap should be connected to the -ve power supply and the positive should be connected to ground.

It will be very unhappy if you leave it like it is, it may even let the magic smoke out :-)

Kuldeepsingh - with this design the limiting factor is the rail splitter so it would be the first place to improve performance. Putting the outputs of opamps in parallel requires that they are isolated with some resistance. But it could be done, a better approach would probably be a high current output opamp or a buffer. A bridged design won't benefit you in this case as the design is current limited not voltage limited and a bridged design will increase the volatage available but not the current.

Regards,
Andrew
  Reply With Quote
Old 12th December 2008, 06:58 PM   #16
diyAudio Member
 
theAnonymous1's Avatar
 
Join Date: Feb 2004
Location: Anonymityville
Rail splitter limitations aside, you can easily triple the output current drive by using another op-amp such as the THS4032 or AD8397. Another benefit of the AD8397 is that it's a rail-to-rail op-amp.

Here is one I built using the AD8397.

http://i33.tinypic.com/2nhhkr9.jpg
  Reply With Quote
Old 12th December 2008, 11:13 PM   #17
diyAudio Member
 
Join Date: Mar 2007
Issues fixed so far. Hopefully I haven't created any new ones.
Attached Images
File Type: png whole.png (15.0 KB, 532 views)
  Reply With Quote
Old 12th December 2008, 11:54 PM   #18
diyAudio Member
 
Join Date: Mar 2007
I have added the Gerber files from Diptrace in case anyone wants a closer look. I place no restrictions on them. Use at your own detriment! I mean discretion!
Attached Files
File Type: zip cmoy1.2fixed.zip (13.2 KB, 36 views)
  Reply With Quote
Old 13th December 2008, 12:54 AM   #19
diyAudio Member
 
Join Date: Mar 2007
See I was right! That pack of files had a screwed up trace. Now it should be right.

Could a moderator please remove the last attachment.
Attached Files
File Type: zip cmoy1.3fixed.zip (13.3 KB, 80 views)
  Reply With Quote
Old 13th December 2008, 12:05 PM   #20
diyAudio Member
 
Join Date: Jan 2008
Looking good - definitely a good idea adding those caps - http://tangentsoft.net/elec/vgrounds.html#output-cap gives a bit of information about it, if you're interested. Tangent mentions there that the MINT, which has the same ground setup shown here, originally had issues with when the TLE2426 was stretched beyond its limitations which were solved by adding those two capacitors.
  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
Eagle vs. Sprint-Layout for PCB design/layout hollowman Parts 11 12th January 2014 09:01 PM
Cmoy Pcb Layout Angel-Baby Chip Amps 32 11th December 2008 06:08 PM
new cmoy amp inox Solid State 7 11th December 2005 10:15 PM
CMOY Help? sbelyo Chip Amps 2 3rd July 2004 10:14 AM


New To Site? Need Help?

All times are GMT. The time now is 12:34 PM.


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