Mod a Pa amplifier - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

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
Reply
 
Thread Tools Search this Thread
Old 22nd July 2005, 09:06 AM   #1
diyAudio Member
 
Join Date: Sep 2002
Location: north of Italy
Question Mod a Pa amplifier

To move a sealed sub whith LT i have buy an used QSC RMX 1450.
Yesterday i have open the case amp and dowloaded the schematic from qsc site:
http://www.qscstore.com/rmmodaschan21.html

Now i want to do some mod.
First one i want to add more capacitant, 6600uF for a rail of a channel is not to much; the second mod is to add best decoupling cap for the 2 opamp.
The third mod is to add 2 pair of transistor fo channel (1943/5200) to have more current capability at heavy load.

The questions are:
Which is the acceptable ammount of capacitant for this amp? (for a rail of a channel)

Can i add 2 pair of 1943/5200 for channel whithout any other modifications?

After that modification must i do reset bias current?

Is this amp in class AB?

Thanks for any reply
regards
D.N.
  Reply With Quote
Old 22nd July 2005, 11:42 AM   #2
Villaw is offline Villaw  Cyprus
diyAudio Member
 
Join Date: Feb 2005
Location: Ni
You can carry out all the mods you ahve suggested.
If I was to modify that amp I would,
1. change the caps to better quolity metalised polyprops
2. add more capacitance in the PSU should space allow and by pass them with polyprops
3. change (if possible) the opamps to burr browns.
4. change the fets to bipolars (difficult)


Have fun.
__________________
Nick
  Reply With Quote
Old 23rd July 2005, 05:51 AM   #3
diyAudio Member
 
Join Date: Sep 2002
Location: north of Italy
Quote:
4. change the fets to bipolars (difficult)
mmmm.... i don't understand.........2sa1943 and 2sc5200 are bipolars, i don't see fet in this amp.

regards
D.N.
  Reply With Quote
Old 23rd July 2005, 03:51 PM   #4
Villaw is offline Villaw  Cyprus
diyAudio Member
 
Join Date: Feb 2005
Location: Ni
yes yes my mistake. I got used to seeing fets that haunt my dreams...
__________________
Nick
  Reply With Quote
Old 24th July 2005, 10:46 AM   #5
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
the output bias controller will deliver the same voltage to the extra output pairs. The doubled up output pairs will now dissipate twice the heat. Have a think about running temps and heatsink capacity.

The doubled up outputs will run at reduced current into the SAME loading and REDUCE the load on the drivers due to improved current gain in the outputs.

BUT you want to increase the low impedance capacity. This WILL increase the loading on the drivers. You need to check carefully the SOAR of the drivers into your proposed worst loading conditions. I recommend a substantial increase in driver heatsinking to extend the driver SOAR when under severe load.
Another alternative would be to double up the drivers as well.

I recommend PSU caps @ +-2mF for each amp of peak output current into your proposed new load. e.g. 40Vpk into 8R needs 10mF, 56Vpk into 4R needs 28mF. Smaller // caps have less inductance and higher ripple capacity so 4 times 6.6mF is better than 26.4mF, but not everyone agrees with this view.

All your mods make sense. I would add one more, increase the onboard decoupling and bypass with PP(MKP) and ceramic.
__________________
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
Wanted: DIY amplifier builder with experience. I need a 0.7 ohm stable amplifier Audiophilenoob Swap Meet 34 16th May 2005 11:58 PM
Questions about how to decrease the PASS A-40 amplifier into a class AB amplifier. novtango Pass Labs 2 21st October 2002 01:50 AM


New To Site? Need Help?

All times are GMT. The time now is 09:00 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