Go Back   Home > Forums > >

Is a single capacitor psu possible
Is a single capacitor psu possible
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
Old 6th May 2021, 06:15 AM   #1
goodguys is offline goodguys  United Kingdom
diyAudio Member
 
Join Date: Feb 2011
Default Is a single capacitor psu possible

Hi thanks for reading.

I built a simple psu for my amplifier consisting of a 12v 15 amp transformer, followed by a bridge rectifier, then a 47,000 uf cap.
There was a lot of noise coming through the speaker so i inserted another 47,000uf and the noise went down. I kept inserting caps, the noise kept lowering, until i reached 135,000 uf and the noise disappeared completly.
I figured 135,000 uf was the perfect value so i took out the six caps and replaced with a single 150,000uf cap which is the closest value i could find, but some of the noise came back.
Why is that. Is it because the first cap smoothed the ac from the bridge rectifier, the second cap smoothed a little more, until it reached the sixth cap and was further smoothed to clean out the ripple totally, something a single cap cannot do.
Or is it the six caps being paralled connected had lower esr esl values which aided the smoothing process.
From this is it possible to build a power supply with just one smoothing cap or is this going too far.

Thanks.
  Reply With Quote
Old 6th May 2021, 06:42 AM   #2
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Is a single capacitor psu possible
What is the amp and how much current does it draw? If it is a repurposed car amp that is meant to be supplied from a car battery then you might be underestimating the current draw and the supply is sagging dues to reasons other than cap value.
  Reply With Quote
Old 6th May 2021, 07:01 AM   #3
klasdiy is offline klasdiy  Sweden
diyAudio Member
 
Join Date: Oct 2014
Is it important that the number of capacitors should be equal to 1? If so, you can probably make it by consider the large capacitor to have higher impedance than the parallelled smaller. Use brute force and try an even larger. If not you can use the common CRC technique and begin with 47 mF - R 47 - mF. The value of R depends on the current throug the amp. Calculate for a voltage loss under 1 V. There is a easy tool for PSU simulation where you can measure the noise, voltage losses and many other things: PSUD2 at duncanamps.com/psud2.
  Reply With Quote
Old 6th May 2021, 07:01 AM   #4
NickKUK is offline NickKUK  United Kingdom
diyAudio Member
 
Join Date: Dec 2019
Caps and PSUs have many different purposes.

1. You can calculate the cap required for a certain current draw to give a certain ripple.

2. Having a resistance and then capacitance to ground is a low pass filter - for example a 5.1ohm followed by 6000uF of capacitance (450V) for a valve amp is a 0.5Hz low pass filter.. 6000uF is hideously large for a valve amp.. for 450V+ caps it's also hideously large physically.

3. in parallel reduces ESR and increases available ripple current capability. perhaps less important for linear PSUs but for SMPS low ESR is something that needs consideration in the design. In a SMPS valve amp booster 48V->300V+ I had 8 low ESR electrolytic 100V 330uF caps in parallel. Compare that to the output caps at 0.03ohm ESR DC link non-electrolytic (on 80uF and one 20uF). Sizewise the film caps are massive compared to the equivalent electrolytic. It all depends on the purpose.

4. The point that mooly made about sag and current draw - you'll want to understand the peak current draw otherwise in overload the PSU will probably generate more noise, the voltage may sag and you will then find the amp design (things like the operating points of the amp chips/valves) then move causing additional distortion.

5. Adding more caps means more inrush stress without inrush control - typically they're designed for a specific energy rating (joules) so they can limit just enough. Without causes stresses on the power supply on startup.

Edit: I see it's linear More coffee needed!

Last edited by NickKUK; 6th May 2021 at 07:06 AM.
  Reply With Quote
Old 6th May 2021, 07:38 AM   #5
goodguys is offline goodguys  United Kingdom
diyAudio Member
 
Join Date: Feb 2011
It's a small diy class-a amp that i put together myself. There is no sag issue. The psu can deliver 15 amps.



This might sound weird but the more caps i put into the psu the more the sound changes, becomes inaccurate when compared against a single cap.

Caps add a certain colouration of their own, the more caps the more the colouration, the more inaccurate the music sounds.

Searching around i've read a ton of threads wherein people say things like elna caps sound different / better than nichicon, nichicon sound different to panasonic, panasonic sound different to mundorf. There too much evidence to think i am making a mistake or imaging it.
Just am disliking the sound of multiple caps and all the different colourations messed up the experience for me. Sorry for being so picky

For the six paralled caps I used two fischer caps, two elna made for audio, one nichicon, one panasonic.
What should i do next, try a bigger cap. What about small bypass caps across the transformer, bridge rectfier and large electrolytic.
Many thanks.
  Reply With Quote
Old 6th May 2021, 08:00 AM   #6
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Is a single capacitor psu possible
You have a number of things to consider.

Firstly you should have a look with a scope and see what the actual power supply voltage looks like in terms of ripple content.

Bigger caps cause problems of their own, the transformer and bridge will see massive current demands but only for a short time period each cycle. I suspect the noise is actually some other issue being masked/modified by you altering the PSU.

You have to do measurements in the first instance to see what is happening, what the supply looks like and what this 'noise' looks like at the amp output.
  Reply With Quote
Old 6th May 2021, 08:30 AM   #7
TonyTecson is offline TonyTecson  Philippines
diyAudio Moderator Emeritus
 
TonyTecson's Avatar
 
Join Date: May 2003
Location: Maybunga, Pasig City
Quote:
Originally Posted by goodguys View Post
Hi thanks for reading.

I built a simple psu for my amplifier consisting of a 12v 15 amp transformer, followed by a bridge rectifier, then a 47,000 uf cap.
There was a lot of noise coming through the speaker so i inserted another 47,000uf and the noise went down. I kept inserting caps, the noise kept lowering, until i reached 135,000 uf and the noise disappeared completly.
I figured 135,000 uf was the perfect value so i took out the six caps and replaced with a single 150,000uf cap which is the closest value i could find, but some of the noise came back.
Why is that. Is it because the first cap smoothed the ac from the bridge rectifier, the second cap smoothed a little more, until it reached the sixth cap and was further smoothed to clean out the ripple totally, something a single cap cannot do.
Or is it the six caps being paralled connected had lower esr esl values which aided the smoothing process.
From this is it possible to build a power supply with just one smoothing cap or is this going too far.

Thanks.
ripple voltage is directly proportional to load current and inversely to C or filter capacitance....the law is kept...
  Reply With Quote
Old 6th May 2021, 08:43 AM   #8
TonyTecson is offline TonyTecson  Philippines
diyAudio Moderator Emeritus
 
TonyTecson's Avatar
 
Join Date: May 2003
Location: Maybunga, Pasig City
goodguys, you can look at this too.....have fun.....Capacitance Multiplier Power Supply Filter
  Reply With Quote
Old 6th May 2021, 08:52 AM   #9
peufeu is offline peufeu  France
diyAudio Member
 
peufeu's Avatar
 
Join Date: Mar 2001
Location: Lyon, France
Quote:
Originally Posted by goodguys View Post
This might sound weird but the more caps i put into the psu the more the sound changes, becomes inaccurate when compared against a single cap.
What is the PSRR vs frequency of the amplifier?

Did you put a snubber on the rectifiers?
  Reply With Quote
Old 6th May 2021, 09:04 AM   #10
indianajo is offline indianajo  United States
diyAudio Member
 
indianajo's Avatar
 
Join Date: Jan 2010
Location: Jeffersonville, Indiana USA
I found I got rid of the last hum by making a pi filter. 470 uf, 2 ohms, then 470 uf. The one or 2 ohms between sections performs an important function. 470 because it was an op amp mixer, low current.
2nd the advice on the snubber on the rectifiers. Even .01 uf across the output of the bridge can help a lot. This hum transmits by radio, has high frequency RF occuring at twice AC frequency. .01 uf series 5 to 10 ohms even better, but difficult to solder directly across the bridge. If you put the snubber away from the bridge rectifier, the wires from bridge to snubber act as transmit antennas.
__________________
Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey PV-1.3K, MMA-81502, Herald RA88a mixer, Steinway console, Wurlitzer 4500, 4300
  Reply With Quote

Reply


Is a single capacitor psu possibleHide this!Advertise here!
Thread Tools

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 Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Smallest possible simplest possible 7W amp for 2.2 ohm load? BAED Solid State 24 1st May 2021 06:55 PM
Use balancing capacitor in filter capacitor of psu yeuclassa Power Supplies 9 25th April 2018 09:29 PM
Single and Split Supply from 1 PSU... Possible? shredhead Power Supplies 7 18th February 2016 06:49 PM
ino, a possible single-ended push pull amplifier st r Pass Labs 9 6th September 2015 07:38 AM
Passive balanced volume control using a single attenuator? Possible? ewildgoose Solid State 17 5th September 2004 09:58 PM


New To Site? Need Help?

All times are GMT. The time now is 03:02 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio
Wiki