Go Back   Home > Forums > Amplifiers > Power Supplies

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 21st December 2005, 04:07 PM   #1
K-amps is offline K-amps  United States
diyAudio Member
 
K-amps's Avatar
 
Join Date: Nov 2003
Location: Indiana
Default How much power will I get?

I am re-rigging an old Adcom 555 to run a 4 ohm bridged load.

For that I am lowering the rails to about 45vdc. Using a 1000va Plitron with 33-0-33secs. Will use two 68,000uF Caps per channel, what power can I expect from the setup per channel, bridged into 8 ohm / 4 ohms?

Again in bridged mode, each channel will have 68,000uF per rail so about 136,000uF per channel or 272,000uF for the entire amplifer.

In terms of joules, I am guessing I will be within 20% of the stock cap wihich is 15000uF (at 85v) vs. 68000uF (at 45v).

My guess is I will get 300w bridged into 8 ohm and 500w into 4 ohm.

In stereo mode I might get 80-90 watts per channel.
  Reply With Quote
Old 22nd December 2005, 02:17 AM   #2
Eva is offline Eva  Spain
diyAudio Member
 
Eva's Avatar
 
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
You are halving supply rails and then bridging the amplifier, so you will probably end up with the entire modified amplifier providing just as much power as each channel of the unmodified amplifier would provide now.

Why would you want to do such a modification?
  Reply With Quote
Old 22nd December 2005, 03:04 AM   #3
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
Quote:
How much power will I get?
Freaking too much power!
__________________
lineup
  Reply With Quote
Old 22nd December 2005, 07:55 AM   #4
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi Kamps,
for your stereo high impedance calculation try subtracting about 5V from your supply rails. The sinusoidal test signal will now give a peak voltage into your 8ohm load of about 40Vpk.
e.g. 45Vdc-5V=40Vpk. Rms power = V*V/2/R = 40*40/2/8 = 100W.

For a lower load subtract a larger voltage from your supply rails. This takes account of rail droop and losses in the output and driver stages. For 4R subtract about 8V giving rms power = 171W. This is very approximate. For a 2ohm the losses are much worse and I should not try to guess but maybe -12V giving rms power = 272W.

For dual channel your big transformer will probably manage to keep the 8ohm loads well supplied say -6V, but as you reduce the load the transformer droop will get worse and these same droops will apply to bridged mode.

Now you can estimate the bridged mode power.

The formula for bridged mode is double the power into double the load impedance.

So your 16ohm load (-6V) will have 190W, the 8ohm load (-9V) will have 324W and the 4ohm load (-14V) will have 480W. All these numbers are based on the difference between unloaded PSU DC voltage and sinusoidal Vpk. You will need to actually measure this in your final amp and you will find a big variation from my guesstimated figures. These are an approximate guide to indicate if the project is worth doing, but it also indicates where the losses are worst and may guide you in choosing appropriate loads. 4ohm is not a nice bridged load!!!!

good luck and voltage guessing.
__________________
regards Andrew T.
  Reply With Quote
Old 22nd December 2005, 01:05 PM   #5
K-amps is offline K-amps  United States
diyAudio Member
 
K-amps's Avatar
 
Join Date: Nov 2003
Location: Indiana
The top ten reasons:

1) It will be used to drive one bass unit only.
2) At 4 ohms, the old 555 would croak as the heatsinks were slightly undersized (they fixed it in the Mk.ii)
3) By lowering the rails and bridging the amp, I am utilizing the real estate better. Also I get more power.
4) At 4 ohms stock, I get 325 watts, at modified rails and bridged I get about 480 watts... not the same Eva
5)The 480 watts will be dissipated over 2 heatsinks as opposed to one, thereby aging the amp in a linear manner
6) I have always felt that lower rail amps (same topology) sound better.
7) Lower rail amps are typically more reliable.
8) Lower rail amps can be more readily converted into a pseudo class-A amplifier by merely increasing bias. In this case, I could get a 10w class-A amp with 10 dB class-B headroom
9)Ability to drive 2 ohm loads with no issues.
10) All this without redesigning the whole thing and spending about 10 hours or so.


The stock Adcom with 82 vdc rails was rated to deliver 850 watts into 4 ohms bridged. Now as ludicrous as that claim was, Lowering the rails to half while driving the same load is surely less ludicrous.

The OP stage uses 4 pairs of TOS's famed 2sd424/b554 pairs. The devices were rated at 180vce though some folks have used them with +/- 125vdc rails (Me I just tested the Adcom with +/-100vdc rails and the amp survived... However, at 45vdc rails I am sure the SOAR will be very robust. Each device is rated at 150 watts so with an OP stage worth 1200watt devices should be able to give me at least 200-250 watts with 45v rails... granted these are mere approximations but I bet if you looked at the SOAR, I could get much more.

Sorry Eva but this is my opinion and I am sticking with it.

Andrew thanks for the info, I kind of figured the ballpark but hoped for a second opinion, appreciate it.

Cheers Mate.
  Reply With Quote
Old 22nd December 2005, 06:26 PM   #6
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi Kamps,
I have just run 4 pair 2sa1943/c5200 with 4.5% regulation & +-68mF through Bensen's SOAR spreadsheet.
4ohm 60 degree phase angle and Tc=45degC are just inside the SOAR limit. It predicts 170W into 4r.
2ohm 45degree phase angle is right on the limit at 303W. This would lead to a bridged output of 606W into 4 ohm also at 45degree phase angle but somehow you have to keep Tc<45degC while delivering this.
I think these numbers are a bit optimistic but the guidance appears to show it's possible but also that 4ohm is as difficult as I suspected (phase only 45degrees indicates the output stage is starting to rebel). As the load goes lower the permitted phase angle falls off rapidly.

Using these calcs I suspect that the Adcom claims were for very short term loading maybe 10mS or less and on a low duty cycle to give the junctions time to recover.
__________________
regards Andrew T.
  Reply With Quote
Old 22nd December 2005, 08:29 PM   #7
K-amps is offline K-amps  United States
diyAudio Member
 
K-amps's Avatar
 
Join Date: Nov 2003
Location: Indiana
True,

Or the regulation was just not there because at clipping into 8 ohms (290 watts or so resistive) the rails did drop from 82 to about 64v on the stock PSU.

Thank you for your numbers, they help a lot.

Also I suspect the driver along with a 4mH Aircore in series will add 1 ohm or so to the load, so we should be ok.

K-amps.
  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
40A 250V Schottky Power Diodes- Has anyone use in Power Amp to replace Diode Bridge? dtm1962 Solid State 10 15th September 2011 07:38 PM
LTspice tool for power amp power supply component evaluation andy_c Software Tools 2 23rd August 2009 05:10 PM
Power transformers versus amplifier output power..what is your option? destroyer X Solid State 38 9th May 2009 05:23 PM
Amplifier 3000 Wats Rms Power + Smps Higcht Power Bestiality MARAVILLASAUDIO Class D 1 5th November 2004 04:06 PM
power output calculations, rated power and required power output metebalci Tubes / Valves 7 22nd February 2004 05:49 PM


New To Site? Need Help?

All times are GMT. The time now is 11:28 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