help with preliminary calculations - 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 6th April 2013, 01:28 AM   #1
diyAudio Member
 
tenderland's Avatar
 
Join Date: Jul 2004
Location: us
Default help with preliminary calculations

Hello ,

After a few tube amp projects I have decided to build a solid state amplifier.
The speaker handles a RMS power of 5 W. Here are the calculations I came up with.

P(with reserve)= 15W
Vrms=11v
Vpk= 15v(aprox)
Irms (1ch)= 1.37A

This gives me a rail supply of +/- 15V

Do these calculations look accurate ?

Thanks
J
__________________
"If every one is making wheels , why make wheels ? " Steve Jobs
  Reply With Quote
Old 6th April 2013, 01:33 AM   #2
diyAudio Member
 
Join Date: Jun 2011
8 ohm speaker? OK.
__________________
Now I am Become Death, the Destroyer of Words
  Reply With Quote
Old 6th April 2013, 01:42 AM   #3
diyAudio Member
 
tenderland's Avatar
 
Join Date: Jul 2004
Location: us
Default Input stage

Thanks ! Yes 8 ohm.

Iam working on the Input stage ( actually bouncing all over)

I will have a cc source feeding a diff pair loaded by a current mirror.
Where I am running into some confusion is how I determine how much current is needed(gm) flowing from the collector of the diff pair. From what I have read the diff pair and all the other transistors generally have a beta of 100.
__________________
"If every one is making wheels , why make wheels ? " Steve Jobs
  Reply With Quote
Old 6th April 2013, 07:18 AM   #4
glennb is offline glennb  Australia
diyAudio Member
 
Join Date: May 2004
Location: Melbourne
Quote:
Originally Posted by tenderland View Post
Hello ,

After a few tube amp projects I have decided to build a solid state amplifier.
The speaker handles a RMS power of 5 W. Here are the calculations I came up with.

P(with reserve)= 15W
Its arguable that the power amp should be rated at LESS than than the speakers.

Quote:
Vrms=11v
Vpk= 15v(aprox)
Irms (1ch)= 1.37A

This gives me a rail supply of +/- 15V
You need to allow a few volts for losses, power supply regulation and OPS saturation.
__________________
Glenn.
  Reply With Quote
Old 6th April 2013, 07:33 AM   #5
Boscoe is offline Boscoe  United Kingdom
diyAudio Member
 
Join Date: Feb 2010
Location: England
Quote:
Originally Posted by glennb View Post
Its arguable that the power amp should be rated at LESS than than the speakers.
Please ignore this, it's total utter rubbish. Ignore the speaker power rating it means nothing when it comes to music, you want to get an amplifier as powerful as is reasonable otherwise they just clip sound harsh and dull.
__________________
I thought about it once, but then thought again.
  Reply With Quote
Old 6th April 2013, 08:30 AM   #6
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Speakers can pass a very low power when it is DC.
When the signal is constant amplitude single frequency sinewave they can pass a lot more power, at least double the DC power rating.
If the power is delivered as brown noise or pink noise or white noise, then you will find that the maximum power that can be passed is nearly double the constant sinewave.

If the power is delivered as a single event pulse, the peak power of that pulse can be nearly four times the constant sinewave power.
The ratio of maximum peak power to DC power can easily exceed 10 times.
This makes it difficult to determine exactly what amplifier power rating to use, prior to hearing the result with real music and speech signals.

Manufacturers will use any of these power definitions for rating their speakers.
The honest manufacturer will specify which power rating they are using.

The dishonest just adopt any power value that they think will attract uninformed buyers.

That 5W could be a sinewave or a noise power rating. It might work with a 1W amplifier without blowing up, equally it may survive many decades being driven sensibly by a 50W amplifier.
__________________
regards Andrew T.
  Reply With Quote
Old 6th April 2013, 01:03 PM   #7
diyAudio Member
 
tenderland's Avatar
 
Join Date: Jul 2004
Location: us
Default Power

Thanks all,

After reading the replies and initial gut feeling.
IVe decided to make it 30 W/ch. This will match well
With my skill level and budget . Thanks for the input
This is much more difficult than building a tube project.


J
__________________
"If every one is making wheels , why make wheels ? " Steve Jobs
  Reply With Quote
Old 6th April 2013, 03:24 PM   #8
diyAudio Member
 
Join Date: Jun 2011
Recall that beta is not a reliable parameter of transistors, it varies greatly. Therefore design procedures are aimed at developing designs which do not depend on this parameter.

The LF gain of the amplifier does depend on beta, but we ignore this as long as there is sufficient gain to eliminate LF distortion by NFB.

I'll try and get back to you about the collector current in the diff. pair, I'm a bit busy ATM.
__________________
Now I am Become Death, the Destroyer of Words
  Reply With Quote
Old 6th April 2013, 05:51 PM   #9
godfrey is offline godfrey  South Africa
diyAudio Member
 
Join Date: Nov 2009
Location: Cape Town
Quote:
Originally Posted by tenderland View Post
From what I have read the diff pair and all the other transistors generally have a beta of 100.
Most small signal transistors have beta higher than that. e.g. BC547C (NPN) and BC557C (PNP) have beta > 400. It's generally a good idea to use high-beta transistors for the input diff pair.
  Reply With Quote
Old 6th April 2013, 06:59 PM   #10
diyAudio Member
 
tenderland's Avatar
 
Join Date: Jul 2004
Location: us
Default great help

Thanks all,

I will try to keep my questions minimal. I have the three popular books by Sloan, Self and Cordell. I am pooring over them.
__________________
"If every one is making wheels , why make wheels ? " Steve Jobs
  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
New Jordan driver - preliminary details Colin Full Range 221 14th January 2014 06:59 PM
Preliminary info about a TQWT to build giralfino Multi-Way 7 6th April 2013 02:23 PM
6LR8 Amp Preliminary Questions wrenchone Tubes / Valves 8 6th January 2007 03:26 AM
3 way design preliminary proposals for comment nutcake Multi-Way 0 19th June 2006 06:34 AM


New To Site? Need Help?

All times are GMT. The time now is 05:07 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