Non-Inverted Gainclone Clipping - 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 24th July 2007, 10:19 PM   #1
mwl6m is offline mwl6m  United States
diyAudio Member
 
Join Date: Nov 2006
Default Non-Inverted Gainclone Clipping

I have recently built a gainclone using the pcb from Peter Daniel, but when I apply a sine wave of amplitude 1 and frequency 1000Hz the amp shows a clipping of the lower portion of the output waveform. I have used the schematic that Peter Daniel supplied, but am unsure of why this is occurring.

When I power up the amp with a signal source from a Microsoft Zune, the amp sounds great (very low distortion that I can discern), but I am trying to do some performance calculations, and this is throwing me for a loop. Any help would be greatly appreciated. Thanks.
  Reply With Quote
Old 24th July 2007, 10:26 PM   #2
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
Use a smaller-amplitude input waveform.
  Reply With Quote
Old 24th July 2007, 10:46 PM   #3
mwl6m is offline mwl6m  United States
diyAudio Member
 
Join Date: Nov 2006
Yes it shows no clipping at an amplitude of around .7 V. Does this mean anything bad about the amplifier since it clips at such a low voltage, or is that inherent in the gainclone design? Thanks.
  Reply With Quote
Old 25th July 2007, 08:49 AM   #4
juma is offline juma  Germany
diyAudio Member
 
juma's Avatar
 
Join Date: Nov 2005
Location: Berlin
The clipping point is determined by:

1. the gain of the amplifier (determined by ratio of values of resistors in feedback network), and

2. Maximum voltage swing (determined by power supply voltage and amplifier's internal design).

For example, if feedback network resistors are Ra=22k and Rb=680 R, the gain is = Ra/Rb + 1=33.35 which means that for 1V input you should have 33.35 V on output, but it won't happen because the voltage swing is limited by power supply voltage (usually +-24V), so the amplifier will go into clipping.

All of this can be easily understood by carefully reading the datasheet of the chip (LM3875, LM3886...).
  Reply With Quote
Old 25th July 2007, 10:52 AM   #5
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
clipping with 0.7V output or with 0.7V input.
Is this voltage AC waveform (RMS) or peak?

Peter's version runs from 1500uF on the chip amp and no smoothing at the rectifier.

This will have serious ripple on the supply lines. Can you measure the troughs in the ripple to ground voltage fed to the chipamp supply pins when you carry out your test?
Or measure the average voltage at the pins and measure the ripple voltage. Then, Vavg-[half ripple peak to peak]~=voltage ground to trough of ripple.

The output starts clipping when the troughs start to approach the peak output voltage.

Are the ripple and average voltages different on the +ve & -ve sides?
__________________
regards Andrew T.
  Reply With Quote
Old 25th July 2007, 03:58 PM   #6
mwl6m is offline mwl6m  United States
diyAudio Member
 
Join Date: Nov 2006
It is clipping with a sinwave of an amplitude of 1V. Your answer makes sense because I was testing the amplifier using a +/-25V lab power supply. So that would mean that a 1V input would need 33V of swing, which is not possible with a power supply of +/-25V.

Any suggestiong on what type of smoothing caps to use for the power supply? I have a 25-0-25 secondary transformer, and would like to use this for the power supply. Can the rails be brought up to +/-35V? Any help would be appreciated. Thanks a bunch.
  Reply With Quote
Old 25th July 2007, 04:34 PM   #7
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
what is the regulation of the 25Vac transformer?

I'll assume 7% for this example.

Open circuit output voltage is [1+regulation]* Vac=1.07*25=26.75Vac
after passing through the rectifier the multiplier square root (2) must be applied and subtract 0.7V for the diode voltage drop giving [26.75*1.414]-0.7=37.8-0.7=37.1Vdc. Way above your target.

The smoothing caps must be rated for maximum mains input voltage to the transformer primary.
If your tolerance on mains is 6% then that 26.75*1.06 becomes the input for the rectifier and the maximum voltage across the smoothing caps is 39.4Vdc. This is a bit close to a 40V rating so you may feel safer using 50Vcaps.

Once you connect a load to the smoothing caps the voltage falls slightly at a low bias setting and more when the bias is higher.
Expect the chipamp to see a nominal 1V less than the open circuit voltage or about +-36Vdc from your 25V transformer.

Under load expect the PSU voltage to collapse. Maybe as little as 3V lost at maximum output power if your PSU is well specified or as much as 10V lost if instead you go for puny.

Now find out your mains tolerance and the transformer regulation and do the numbers for your installation.
__________________
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
GainClone Design -- PSU, which chip, grounding, clipping queries wes-ninja250 Chip Amps 5 19th August 2005 07:08 AM
My first non-inverted gainclone circuit eranrund Chip Amps 21 19th June 2005 08:24 AM
PCB for Inverted Gainclone 2Bak Chip Amps 8 19th February 2004 10:09 AM
Gainclone and clipping (may also be appliable to other high feedback amps) Bricolo Chip Amps 8 26th November 2003 02:46 PM
Non-inverted Gainclone jpask Chip Amps 1 29th March 2003 09:01 AM


New To Site? Need Help?

All times are GMT. The time now is 08:12 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