Help with Capacitor selection for amp - 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 17th April 2005, 01:31 AM   #1
gengis is offline gengis  United States
diyAudio Member
 
gengis's Avatar
 
Join Date: Feb 2005
Location: Midwest--IA
Question Help with Capacitor selection for amp

Hi, All,
I am building a amp with 50V-0-50V AC recommendation.
I have (2) 500VA, 45V tap transformer, and I have bunch of 80V capacitor laying around.
Is it advisable to use the 80V capacitors, or should I buy 63V capacitors?

Thanks.
  Reply With Quote
Old 17th April 2005, 01:54 AM   #2
tool49 is offline tool49  Canada
diyAudio Member
 
tool49's Avatar
 
Join Date: Apr 2003
Location: Montreal
The 80V would be totally appropriate here. I would use them because with regulation factors and everything, the 50V transfo is going to give you 75VDC rails at idle.

Hope this helps!
Sébastien
  Reply With Quote
Old 17th April 2005, 06:55 AM   #3
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
your 45-0-45 transformer will give about +-67Vdc after the rectifier and caps at standard mains voltage and about +-71Vdc when mains is running @ +6%.
Do not use anything less than 75v for smoothing caps and decoupling. Some designers who want very good long term reliability and low warranty claims might even specify 100V here.
The 50-0-50 transformer is probably aiming for about 200w / 8R power output but you will have about 160w / 8R (-0.9db).
To improve your output slightly you can add 2 low current (500mA) windings onto the toroid and rectify these. About 5Vac will give about 7Vdc. add these to the + & - rails to give +-74Vdc off load and use these higher volts to power the input and driver section. If you want you can go even higher and then regulate the driver rails down again (might improve sound quality).
hope this helps.
__________________
regards Andrew T.
  Reply With Quote
Old 17th April 2005, 07:03 AM   #4
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi again
forgot to add, the Vrail voltage will fall to about +-62Vdc when on full load,i.e. when driving about 7R.
Your 500va will drive 8R all day no problem and give good short term power into 4R when on music type signal but will run a bit warm if you drive 4R really hard e.g. disco, PA, sine wave drive to industrial etc.
__________________
regards Andrew T.
  Reply With Quote
Old 17th April 2005, 05:08 PM   #5
K-amps is offline K-amps  United States
diyAudio Member
 
K-amps's Avatar
 
Join Date: Nov 2003
Location: Indiana
This is hilarious... one guy says 75 vdc, the other says 67vdc... you will be scratching your head by the time you read the posts.

45vac is 63.63DC ( 45 * 1.41414) and taking the rectification losses approximately 62.5vdc per rail unloaded .

Although you can get away with a 63v cap, it is NOT advised. If you have fluctuations on the mains, you will blow your caps pretty fast. I'd say 75 vdc is ok or even 80 vdc depending on what is available.

Also some Toroids actually measure MORE at idle so you may end up with your toroid actually being 47-0-47 in which case your unloaded rails are a tad over 65vdc after rectification losses.

With this supply and a 500 VA Toroid, you are looking at approx 180 watts 8 ohms with dynamic headroon of 230 watts or so. The better the PSU regulation, the higher your output.

K-
  Reply With Quote
Old 17th April 2005, 05:53 PM   #6
gengis is offline gengis  United States
diyAudio Member
 
gengis's Avatar
 
Join Date: Feb 2005
Location: Midwest--IA
Default 80VDC capacitor

Thanks all for the reply.

K-amps--you are right, the toroids have a 6% load flutuation.
But I am going to use both of the toroid for the amp, a dual mono.

I am thinking of using 72000uF (six 12000uF) or 90000uF (six 15000uf). I have space on the board for six of them. Just was not sure of using the 80VDC capacitors (higher V rating than input).

I have 80V capacitors on hand, I will have to purchase 75V if that is elected. I am leaning toward using on hand stuff now.
  Reply With Quote
Old 17th April 2005, 06:24 PM   #7
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
It's always OK to use higher voltage rated parts, just not the other way round! It's a 'max' rating not a 'needed' rating. So even 100V caps would be great.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 17th April 2005, 10:06 PM   #8
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
I hope you have the info you need, I have reviewed the various posts and ALL seem to be correct or very close. But you will need to read each response in context.
I do not know if one of our contributors was trying to wind me up but this is all the comment I will make on this thread.
__________________
regards Andrew T.
  Reply With Quote
Old 18th April 2005, 03:58 AM   #9
Account Disabled
 
Join Date: Aug 2004
Location: Earth
gengis,

Let's start at the beginning. Your project amplifier recommends a 50V-0-50v AC secondary transformer. No power rating was given, right?

Transformer manufacturers rate their transformers AT FULL RATED LOAD (any that don't, should, to conform) in other words if it's a 300W (VA) transformer it will be at a draw of 3A! Now, that will only occur when the amplifier, assuming Class AB not Class A, is flat out! At idle the transformer will be some X% higher than the 50V per side. This is called the regulation and usually around 6%for 300VA toroids, and around 4% for 500VA toroids.

So for a 300VA with 6% regulation the idle supplies will be about 50x1.414x1.06- 0.6 = 74V assuming nominal mains and negligible ripple at idle.

Ideally, you should use 80V caps to allow for higher than nominal mains noting that a further surge voltage (short term) allowance is built in for extreme surges.
  Reply With Quote
Old 18th April 2005, 04:16 AM   #10
Account Disabled
 
Join Date: Aug 2004
Location: Earth
Having said that I'd suggest you don't consider the 500W 45V tapped tranny, unless it's 45-0-45. Assuming it is and it has 4% regulation then your supplies would be 65V and you could use 75V caps or if desperately penny pinching use 63V caps with 3 power diodes in the feed. But they would be on their limit with quality of manufacture their only saving grace.

Considerable amplifier power would be lost as a result of perhaps 8V of loaded supply. A 150W amp -> a 100W amp! If the topology of the amplifier proper is designed with very high PSRR then the lower VA tranny and higher supply will allow a sizeable dynamic headroom and you could have effectively a 250W amplifier in a 150W guise.

A 150W/ch amplifier as above can be designed using a 300VA toroid! Utilizing the crest factor of typical full range musical programme, it would consume probably 80W while audibly clipping at the peak equivalent of 250W/ch.
  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
Coupling capacitor selection DcibeL Chip Amps 23 18th July 2011 04:20 AM
PSU shunt capacitor selection oshifis Tubes / Valves 1 21st January 2008 10:31 AM
PSU capacitor selection phreeky82 Parts 3 28th June 2006 09:33 AM
Capacitor selection, an engineering choice Christopher Everything Else 141 27th July 2003 10:48 PM
Aleph4 capacitor selection Jmertz Pass Labs 3 3rd May 2002 06:48 PM


New To Site? Need Help?

All times are GMT. The time now is 09:15 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