Chip Amp Photo Gallery - Page 97 - 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 2nd March 2009, 03:42 PM   #961
troystg is online now troystg  United States
diyAudio Member
 
troystg's Avatar
 
Join Date: Apr 2004
Location: In a dream... Please don't wake me.
Quote:
Originally posted by Igla
Why are you all so worried about a few mV of DC offset?
21mV DC offset means nothing to you loudspeakers. Even 50 or 100mV offset won't harm your loudspeakers or make them sound worse.
Igla-

For my own information, what would be considered the level to start being concerned with?

I always "assumed" <50mV was acceptable.


All-

This is purely a question to gain personal knowledge NOT to debate or start any "x is better than y" bashing.
__________________
Troy
Thinking positive doesn't make things better, it makes you a better person.
  Reply With Quote
Old 2nd March 2009, 06:40 PM   #962
diyAudio Member
 
Join Date: May 2008
Quote:
Originally posted by Igla
Why are you all so worried about a few mV of DC offset?
21mV DC offset means nothing to you loudspeakers. Even 50 or 100mV offset won't harm your loudspeakers or make them sound worse.
It will not harm a woofer or full-range speaker. That might be different, if you use such an amplifier for the tweeter in an active speaker.

While 100 mV is an accepted offset with chipamps, for solid state amplifiers it would be considered highly unacceptable.

I wonder, if it will not affect the sound. It heats the IC unnecessarily and decreases the headroom. People report that they hear the unmeasurable differences from one capacitor to another. Depending on the rail voltages 100 mV will probably mean something around 1 % less headroom. Plus the headroom reduction that comes from the higher IC temperature. That could have a notable effect.
__________________
If you've always done it like that, then it's probably wrong. (Henry Ford)
  Reply With Quote
Old 2nd March 2009, 07:49 PM   #963
Igla is offline Igla  Slovenia
diyAudio Member
 
Join Date: Jun 2003
Location: Slovenia
troystg;
Pass Labs amplifiers states in their users manual (if I recall it right), that DC ofsett is less than 100mV.
I have on all my gainclones (LM1875, LM3875,TDA2050) about 30-50mV offset; I have tried to lower the offset to 0 with capacitor to ground in the feedback loop but the sound was much worse as without capacitor. The same goes for input cap. So I have no input cap and no cap to ground in the feedback loop.
I couldn't find any exact recommendations, how high DC offset is still acceptable. I can just say that your opinion is the same as mine: 50mV or less is acceptable.

pacificbilue;
DC offset for sure decreases the headroom (much more, if you are on the edge) but I can live with that a lot easier then with all those caps - they just mess the sound.
I did try to lower the offset with layout and wirings (without the caps at input and feedback) but I couldn't get lower then 30mV so I can't compare if 30mV sounds worse then 0mV DC offset.
  Reply With Quote
Old 2nd March 2009, 11:32 PM   #964
star882 is offline star882  United States
diyAudio Member
 
star882's Avatar
 
Join Date: Mar 2007
Quote:
Originally posted by pacificblue

It will not harm a woofer or full-range speaker. That might be different, if you use such an amplifier for the tweeter in an active speaker.

While 100 mV is an accepted offset with chipamps, for solid state amplifiers it would be considered highly unacceptable.

I wonder, if it will not affect the sound. It heats the IC unnecessarily and decreases the headroom. People report that they hear the unmeasurable differences from one capacitor to another. Depending on the rail voltages 100 mV will probably mean something around 1 % less headroom. Plus the headroom reduction that comes from the higher IC temperature. That could have a notable effect.
Such a small offset is not a problem for driving speakers. 100mV of offset will result in just over a milliwatt of extra dissipation in an 8 ohm speaker, which is not a problem. (IIRC, the offset of my friend's hybrid amp is 10mV.)
For certain test and measurement uses, however, such an offset can skew the results. In that case, add a trimmer to remove the offset. Or better, use a circuit (digital sample and hold based) to rezero the output on command.
__________________
"Fully on MOSFET = closed switch, Fully off MOSFET = open switch, Half on MOSFET = poor imitation of Tiffany Yep." - also applies to IGBTs!
  Reply With Quote
Old 3rd March 2009, 02:34 AM   #965
sasmit is offline sasmit  India
diyAudio Member
 
Join Date: May 2006
Send a message via Yahoo to sasmit
didn't want to start a debate...was just wondering whether 21mV offset was fine ? I was never concerned about offset earlier..I have been building STK series and other chipamps for arnd 10 years now, my current amp has 2 *TDA1514A sounds pretty good never bothered measuring it's offset ...only after I read some of the posts here tat I started to think of it..and decided to measure.
  Reply With Quote
Old 3rd March 2009, 02:51 PM   #966
diyAudio Member
 
Join Date: Feb 2009
Quote:
Originally posted by Beftus
Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.
Here's my first ever chip amp using the PCBs from BrianGT (chipamp.com). I finished both monoblocks yesterday. They sound great, a wide and detailed soundstage. Much to the dismay of my wife I can hear the difference to my Cambridge Audio 540A amp...

The design is far from original, I've seen more people use these aluminium enclosures, but I really like their look.

Specs:

- 2x Amplimo toroids 2x22V 80VA
- all 0.1 uF caps Vishay-Roederstein MKP1837
- all electrolytics from Panasonic (FC and TS)
- MUR820 rectifier diodes (couldn't find 860's locally)
- all resistors are metal film types

I hooked up the PSU and amp boards using 0.6mm (approx. AWG 23) solid core wire. For the signal output I used 1.4mm (approx. AWG 15) solid core wire.

Measurements taken after completion:
- DC rail voltages left & right channel: 30.3V & 30.8V
- DC offset left & right channel: 1mV & 0.4mV (may not be very accurate, measured with a dirt cheap DMM)

I may improve the aesthetics by replacing the front plate with a piece of wood (oil finished oak from a leftover piece of floorboard). To improve the WAF there's not gonna be a power LED.

WRT the rail voltages, do I need to worry about the little difference? DC offsets appears to be very low, I might check DC offsets again with a real DMM.

Next project will be a matching passive preamp/source selector. At the moment I use the preamp out of the 540A amp.
You should use much thicker wire for the PSU to amp hookup. You are saying that you are using .6mm for that link, yet using much thicker cable for the amp output... the PSU links are supplying that current you are so carefully trying to NOT limit using that thick cable at the output. You need to make the psu links as big, or even thicker, otherwise their resistance will limit your current from the psu to amp, and in the same vein, where is the earth return from the amp modules to the PSU?


  Reply With Quote
Old 3rd March 2009, 07:14 PM   #967
diyAudio Member
 
Join Date: May 2008
Quote:
Originally posted by Igla
I did try to lower the offset with layout and wirings (without the caps at input and feedback) but I couldn't get lower then 30mV so I can't compare if 30mV sounds worse then 0mV DC offset.
The datasheet specifies 10 mV as typical and 100 mV as maximum value for the input DC offset. The feedback cap does not remove it, but only reduces the gain at DC to 1. In other words you get the same DC offset at the outputs as at the input. If you want to get rid of DC offset, you can use a potentiometer/trimmer or a DC servo.

Quote:
Originally posted by star882

Such a small offset is not a problem for driving speakers. 100mV of offset will result in just over a milliwatt of extra dissipation in an 8 ohm speaker, which is not a problem.

Yet there are people out there (and out here), who claim to hear the difference between a carbon film and a metal film resistor in the feedback path. Guess what they must make of the destructive influence of 100 mV offset.
__________________
If you've always done it like that, then it's probably wrong. (Henry Ford)
  Reply With Quote
Old 4th March 2009, 12:23 AM   #968
diyAudio Member
 
Join Date: Feb 2009
Quote:
Originally posted by pacificblue




Yet there are people out there (and out here), who claim to hear the difference between a carbon film and a metal film resistor in the feedback path. Guess what they must make of the destructive influence of 100 mV offset.

its them carbon atoms! little buggers!!
  Reply With Quote
Old 4th March 2009, 01:44 AM   #969
diyAudio Member
 
FastEddy's Avatar
 
Join Date: Jun 2006
Location: North Californie
" ... people out there (and out here), who claim to hear the difference between a carbon film and a metal film resistor in the feedback path. ..."

You can see it on a 'scope or distortion analyzer ... but I can no longer to claim an auditory difference ... too old = 64+

" ... 100mV of offset will result in just over a milliwatt of extra dissipation in an 8 ohm speaker, which is not a problem ..."

" ... Guess what they must make of the destructive influence of 100 mV offset. "

= 1/10 Volt ! seems like a lot. Unless that is the voltage required to maintain a transistor in a "turned on" state ... depends on the circuit I suppose.

As long as it is a constant (DC) voltage, the speakers will simple dissipate it as heat, and not much at that ( into 8 Ohms )

From V=IR where R = 8, V = 0.1 then I = 0.0125 Amps ... for power V (Volts) * I (Amps) = P in Watts = 0.00125 = not much, heat or otherwise.

IF, on the other hand, the 100 mV were measurable as a changing sine wave in the audio range, any human could easily hear it, even me.
  Reply With Quote
Old 4th March 2009, 04:24 PM   #970
Igla is offline Igla  Slovenia
diyAudio Member
 
Join Date: Jun 2003
Location: Slovenia
pacificblue:
Wrong;
Ci capacitor in the feedback loop lowers the output DC offset - when I add Ci cap to the feedback the offset lowers from 30-50mV (depends on the input potentiometer position) to 1-2mV at the output. The sad thing is that Ci cap influence the sound.
So...the sound with Ci caps (Philips, Chemicon, Jamicon or Epcos) in the feedback loop is much worse then without the caps and 30mV DC offset at the output.
Still; never had chance to try the famous BlackGate caps


About the difference between carbon and metalfilm resistors and if you like - the difference in sound with and without 8 pieces of 5cm brass binding posts...
well, perhaps some other day.
Attached Images
File Type: jpg prikljucki_1.jpg (97.9 KB, 1114 views)
  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



New To Site? Need Help?

All times are GMT. The time now is 12:39 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