Power amp under development
 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

 Solid State Talk all about solid state amplification.

 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
quasi
diyAudio Member

Join Date: Sep 2004
For Upupa Epops;

Quote:
 Originally posted by Upupa Epops Have you any detailed pic of square wave ( 10 kHz ) into eight Ohm ? Or eight Ohm with parallel 100 n cap ? 3 dB bellow clipping ?

Hey Upupa Epops;

Piccy of square wave response at 1khz into 8 ohm resistive load taken at near rail to rail swing.

Cheers
Attached Images
 1khz square wave response.jpg (20.1 KB, 4188 views)

quasi
diyAudio Member

Join Date: Sep 2004
Aother pic

Piccy of square wave response at 10khz into 8 ohm resistive load at near rail to rail swing.

Cheers
Attached Images
 10khz square wave response.jpg (21.4 KB, 4094 views)

 11th December 2004, 12:00 PM #103 Upupa Epops   diyAudio Member   Join Date: Aug 2003 Location: Prague,Czech Republic To quasi : Have you connected amp with generator by line with correct characteristic impedance ? I see on input small overshoots .
quasi
diyAudio Member

Join Date: Sep 2004
Hey Upupa Epops;

Quote:
 Originally posted by Upupa Epops To quasi : Have you connected amp with generator by line with correct characteristic impedance ? I see on input small overshoots .
No I didn't. I just connected the output of my signal generator to the power amp input so the signal is just terminated by the input impedance of around 33kohms.

Is there a better way?

Cheers

 11th December 2004, 12:57 PM #106 Upupa Epops   diyAudio Member   Join Date: Aug 2003 Location: Prague,Czech Republic Look at output impedance of generator and the same impedance give on input pins of amp, but in parallel ( typical output impedance of generators is 600 Ohm or 50 Ohm.
 13th December 2004, 08:57 PM #108 Nexus   diyAudio Member   Join Date: Aug 2003 Location: The Netherlands Hello JWB: In reply to: post #57 http://www.diyaudio.com/forums/showt...269#post505269 can you post a schematic of the protection part which is on the pcb in this post? Thank You in advance. Nexus
quasi
diyAudio Member

Join Date: Sep 2004
Unhappy Quasi

Quasi is unhappy;

Well I have spent (wasted?) a lot of time trying to get this amp to clip symmetrically by using split & higher rails to the driver stages.

The problem I had (maybe common to all quasi-comp MOSFET amps) is that the positive signal swing clipped around 4 to 5 volts before the negative swing.

Well I succeeded in fixing it. I thought by using a higher rail for the driver stages (particularly the positive rail) I now have the negative rail clipping some 10 volts before the positive swing. and the clipping isn't as clean.

What gives??

The amp runs best with common rails all tied together (even with the positive signal swing clipping first).

Do any of you learned gentlemen and ladies have any thoughts?

One thought that had was shifting Q8's collector from the output rail to positive rail.....but this will double the voltage across it.

This is the latest cct.
Attached Files
 schematic design_ n-mos3.pdf (33.4 KB, 1697 views)

 14th December 2004, 12:10 PM #110 richie00boy   Did it Himself diyAudio Member     Join Date: Nov 2003 Location: Gloucestershire, England, UK keypunch, IRFP250N has about the same SOA as the older IRFP240. A single pair of these will give you 120 watts into 8 ohms. If you can get IRFP250 (not N version) that will give you even more. I'm talking genuine IR parts only. Ciss is the capacitance figure you should be concerned about. Also check Qg which is gate charge. You want this to be as low as possible and it's a better thing to use than input capacitance, which is quite non-linear. quasi, Your amp is having problems when you use higher driver section rails because the lower half of the output stage has a little gain (yes, I know the feedback results in overall unity gain) thus can swing almost to the rail. So if you move the operating point for the driver of the lower rail to a higher voltage it begins to saturate the MOSFET much earlier as it's referenced to a higher point, as you have found. The only solution with this output topology is to use a higher positive rail only. If you move the collector of Q8 to the positive rail you ruin the whole feedback around the driver/op and end up with an unstable (both thermally and electrically) amp.

 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         Aussie Amplifiers         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 New To Site? Need Help?

All times are GMT. The time now is 03:41 AM.