7 Easy Pieces
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Pass Labs This forum is dedicated to Pass Labs discussion.

 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
 23rd June 2004, 07:05 PM #1 Nelson Pass   The one and only     Join Date: Mar 2001 7 Easy Pieces Just when you thought it was safe to go back to the work bench.... Here's 7 easy pieces for chip amps. www.passlabs.com/np/GC-VAR-INV-FDBK-1a.pdf You might find this a trivial circuit, but for those who don't know it, it can be very important. Chip amplifiers have enormous amounts of open loop gain (120 dB = 1,000,000) which can create stability problems when the circuit is set for low gain, say only 10 or 20 dB. This circuit places a resistor to ground at the negative input, which throws away some of the open loop gain, resulting in less feedback. In fact you can put a variable resistor here, and tune the amount of feedback to taste. www.passlabs.com/np/GC-VAR-BAL-FDBK-1a.pdf Does the same thing for a balanced input circuit. Generally you want the pots at equal value, but for the most perfect common mode input rejection, separate pots allow trimming. www.passlabs.com/np/GC-OUTPUT-BIAS-1a.pdf You say your chip amp needs more output bias? Here's an old trick. www.passlabs.com/np/GC-OUTPUT-BIAS-2a.pdf Here we see the same thing as GC-SS-3a, but without the SuperSymmetry jazz, just a pair of chip amps. The voltage sources will be low values, as will the output resistors, and additional output stage is provided by the DC difference in the output voltages across those output resistors. The load output sees the split value, so there's no DC seen there. You also get the advantage of delivering about twice the current as a single chip amp. www.passlabs.com/np/GC-BOOTSTRAP-1a.pdf What? You want your chip amp to behave as if it's seeing a higher impedance and also deliver more current? You can parallel chip amps equally, or you can set one up as a current bootstrap, relieving the load on the first amp, but also leaving it in control of the signal. Sort of like power steering. Watch how you set the current gain of the bootstrap. For this circuit, 50% is a good number. www.passlabs.com/np/GC-BOOTSTRAP-2a.pdf And of course you can go crazy and use a lot of them. In this case, the current gain would probably want to be set to divide the current equally between all the amps, including the first one. In the case of 4 bootstrap amps, each would probably want to be set at delivering 20% of the output current. www.passlabs.com/np/GC-ZEN-ALEPH-1a.pdf How can we resist not making a Zen amp with such a current source? Here we see that the Aleph current source is easily duplicated by a chip amp.
 23rd June 2004, 09:36 PM #2 uli   diyAudio Member   Join Date: Dec 2002 Location: Vienna, Austria Hihihi, dont shock people late in the evening! Uli __________________ 'Jazz is not dead, it just smells funny' F.Zappa
 23rd June 2004, 09:38 PM #3 rtirion diyAudio Member   Join Date: Nov 2000 Very nice examples. These will keep me busy for quite some time.
 23rd June 2004, 09:41 PM #4 karma   diyAudio Member     Join Date: Feb 2003 Location: hamilton,ontario same here gc zen hmm __________________ http://www.karmaelectronics.info
 23rd June 2004, 09:46 PM #5 roddyama   diyAudio Moderator Emeritus     Join Date: Jan 2002 Location: Michigan "You want me to hold the chip amp where?" __________________ Rodd Yamashita
 23rd June 2004, 09:54 PM #6 joensd   diyAudio Member   Join Date: Dec 2001 Location: Germany Anybody got a spice model for an appropriate opamp to simulate with? Think I need a cup of tea. Jens - already thinking a pot might be better
 23rd June 2004, 10:27 PM #7 Michael Rothacher   AudioMaker.Tech diyAudio Member     Join Date: May 2001 An homage to Feyneman... Nelson, you're one cool dude
metalman
diyAudio Member

Join Date: Jun 2003
Quote:
 Jens - already thinking a pot might be better
Metalman - Already thinking pot might be better!

In the last 24 hours my head has chipped exploded spun inverted balanced , bootstrapped and in true Pass fashion finished in a state of Zen

I'm sure I hurt something in there but what a ride

Thanks Nelson!

 24th June 2004, 12:29 AM #9 Nelson Pass   The one and only     Join Date: Mar 2001 My pleasure.
 24th June 2004, 12:46 AM #10 Mattyo5 diyAudio Member   Join Date: Aug 2002 Location: Farmington, CT Ok Nelson, i have to ask this, exactly how much time did you spend on those schematics? I knowing you, probably didn't take you long, but I'm curious later -Matthew K. Olson

 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 Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Holton Precision Audio         CSS         Dx Classic Amplifiers         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post antomas Pass Labs 10 29th January 2009 09:48 PM ErikdeBest Swap Meet 2 2nd June 2006 11:50 AM gengis Swap Meet 0 9th January 2006 01:27 AM hifi Swap Meet 1 31st August 2003 08:51 PM

 New To Site? Need Help?

All times are GMT. The time now is 03:57 AM.