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 25th August 2013, 12:09 AM   #21
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
I also left the simulated inductances of the power and ground rails, in the simulation schematic. It's set up so that you can specify the length of the rails, in inches, and it sets the inductors' values, and their parasitic resistances, automatically, based on the parameters for those, that you can also set.

Also, the AC Mains voltage supplies are parameterized, so you just set the RMS output voltage and the frequency, by editing the existing .param statements on the schematic, and it sets the actual values for both of them.

Likewise, the capacitances and voltage ratings of the four caps per rail are all set from two param statements. And then also, their ESRs are all calculated automatically, based on the capacitance and voltage rating, using an approximate formula.

The maximum time-step should be set to 10u (10 microseconds). It could be shorter, for better accuracy. But that makes it run more slowly. You can try making it larger until something changes for the worse, in order to get the best simulation speed.

Last edited by gootee; 25th August 2013 at 12:14 AM.
  Reply With Quote
Old 25th August 2013, 12:47 AM   #22
fas42 is offline fas42  Australia
diyAudio Member
 
fas42's Avatar
 
Join Date: Jun 2012
Location: NSW, Australia
Blog Entries: 9
Quote:
Originally Posted by gootee View Post
For that, we must place a very small (small physical package) cap, very close to the power connection of each output device, connected between power and ground. Connection lengths of more than a few mm will make this cap much less effective. So no axial-lead caps are allowed. Use radial-lead types or surface-mount. The cap value is usually anywhere from 0.01 uF to 1 uF. The small size of the package and the use of short connections matter more than the actual capacitance value. Ceramic or film caps will work.
Tom (gootee) and abraxalito are making excellent points about important aspects ... I might just throw in now some 'extensions' to what Tom has said here - I've realised that I gave the 'wrong' advice elsewhere about what combinations of cap types are 'safe, and I will do a full rundown in my blog shortly about such, : the film or ceramic should be around 1uF, preferably on the larger value side - anything smaller is close to being useless, a mosquito bite in its impact - in the smallest physical package that neatly spans the the connection points. Then, to ensure no nasty resonance problems, and improve overall bypassing as well, have the smallest physically sized electro cap of value 100-220uF, preferably low ESR, 'bypassing' the bypass cap, . There are plenty of tiny caps like this in the catalogues, any decent quality one will do ...
__________________
Frank . . . everyone knows what a 'bad' recording is - it's one that doesn't sound good on their own, very special system ...

Last edited by fas42; 25th August 2013 at 12:51 AM.
  Reply With Quote
Old 25th August 2013, 02:27 PM   #23
diyAudio Member
 
Join Date: Sep 2010
Location: Peppermint Grove Beach, Western Australia
Default Awesome

Thank you kindly.

I'll have a play and I look forward to learning a bit more about whats really going on on the psu side of life.

Thanks again!
  Reply With Quote
Old 25th August 2013, 02:53 PM   #24
diyAudio Member
 
KatieandDad's Avatar
 
Join Date: Nov 2011
Location: UK
Stripboard / Veroboard comes to the rescue here.

Most guys will agree that smaller caps improve the response of the amp. Bigger caps improve the bass.

Why not buy a nice long length of stripboard and a big bag of 1000uF Panasonics. At that value or even 470uF they are relatively cheap.

Aiming at around 10000uF, you can add caps a pair at a time to evaluate your own results.

Below 4700uF I would expect the performance to be mediocre, you can evaluate the audible gains above that for yourself.
  Reply With Quote
Old 25th August 2013, 04:25 PM   #25
John8 is offline John8  United Kingdom
diyAudio Member
 
Join Date: Dec 2005
Location: Nottingham England
Wrong (top) and right way (bottom) to wire power supply reservoir capacitors.
The correct way is to minimise the common impedance by making sure the common point for the input and output is as close to the capacitor as possible.
Any ripple voltage generated by the extra resistance and inductance is not then transferred to the output load.
This is of the utmost importance in switched mode power supplies where large circulating currents in common PCB tracks can cause increased ripple voltage on the output. It is also applicable to 50/60Hz power supplies with high values of reservoir capacitors producing large pulses of current from the rectifier diodes due to the very short conduction times. Any common impedance noise is transferred directly to the output and onto the supply rails of the amplifier. The same applies when the amplifier takes large 'lumps' of current from the reservoir capacitor on heavy bass, the voltage drop on the supply rail is minimised.
Attached Images
File Type: jpg Right and Wrong1.jpg (61.0 KB, 240 views)
  Reply With Quote
Old 25th August 2013, 07:20 PM   #26
KSTR is offline KSTR  Germany
diyAudio Member
 
KSTR's Avatar
 
Join Date: Jul 2007
Location: Central Berlin, Germany
FWIW, construction and impedance plot of a capacitor strip in the above manner (4x 2200uF + 4x100uF + some films in the 47nF to 2.2uF range). As we can see, there is room for improvement at around 1MHz but it would probably do well with any chipamp.

The impedance plot is referenced to 1Ohm=0dB(+-3dB or so of uncertainity), so -40dB is 10mR. Note this is a transmisson type of measurement. If I had attached the feeding line to the output (at the film caps) to get a true 1-point impedance plot the curve would look slightly different because the resistive and inductance geometries are changed a bit. The big caps were still hot from soldering which made the plateau at 6mR possible, it went up to 10mR after cooling down.
Attached Images
File Type: jpg cap_bank_#1.jpg (23.5 KB, 210 views)
File Type: jpg cap_bank_#1_imp.jpg (69.3 KB, 206 views)

Last edited by KSTR; 25th August 2013 at 07:30 PM.
  Reply With Quote
Old 25th August 2013, 08:31 PM   #27
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
Cool, Klaus!

It would be interesting to see it from the load end's point of view.
  Reply With Quote
Old 25th August 2013, 10:41 PM   #28
fas42 is offline fas42  Australia
diyAudio Member
 
fas42's Avatar
 
Join Date: Jun 2012
Location: NSW, Australia
Blog Entries: 9
Yes, KSTR's effort demonstrates what's possible if you really want to go to town with this strategy - in the end it becomes a battle to physically locate everything to have the required impact, a 3D sculpting exercise more than anything else.

The ol' law of diminishing's climbs on board - how much low impedance do you need, to how high a frequency ...?

10mR all the way is great, 100mR much, much easier to do - that range of values is the sweet spot, worth thinking about ...
__________________
Frank . . . everyone knows what a 'bad' recording is - it's one that doesn't sound good on their own, very special system ...
  Reply With Quote
Old 26th August 2013, 01:16 AM   #29
fas42 is offline fas42  Australia
diyAudio Member
 
fas42's Avatar
 
Join Date: Jun 2012
Location: NSW, Australia
Blog Entries: 9
Klaus, just noted your fine work in Network Analyser Measurements, hadn't chanced upon it earlier - nice to see theoretical and practical correlating well ...

Again, in the quest for better sound, the big 'workload' is finding out whether going to the n'th degree is useful or not, from an audible point of view. Personally, the effects of interference are such a headache to truly null that it probably makes sense pushing these sorts of performance results to at least a very high degree.
__________________
Frank . . . everyone knows what a 'bad' recording is - it's one that doesn't sound good on their own, very special system ...
  Reply With Quote
Old 11th September 2013, 05:34 AM   #30
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
Quote:
Originally Posted by gootee View Post
"A WHOLE LOT" of PSRR is called for, when music is playing.

The music IS THE CAP CURRENT, almost all of the time. And the cap voltage is proportional to the integral of the cap current. So the louder the music, the bigger the ripple, and the more PSR you need. (I attached part of the intro from the song "Highway to Hell", in an LT-Spice simulation of a power amp and PSU, showing the reservoir cap currents and the output voltage across the speaker. Very enlightening.)

For all but the very high frequencies, the reservoir and decoupling (at the chip) caps are seen as one capacitance, by the chip's power pins. So maybe Peter Daniel has more capacitance near the chip amps, to make up for the crazy-low value at the PSU.

You can't just pull the capacitance value out of the air, or base it on your "opinion" of "the sound", and expect to have an amp with the max rated output power that the rail voltage would be capable of providing. Too little capacitance and the output will clip, well before the rail voltage limit. You can and should calculate the minimum acceptable capacitance, for a desired max rated power. If you then decide to use less than that, then you have to calculate the new (lower) rated max power spec.

The peak voltage of the output signal can only go up to the point where there's still room for the ripple voltage and the voltage across the amplifier itself to sit between the signal peak and the max rail voltage. Higher than that and ripple-shaped chunks get gouged out of the output signal. That's the onset of clipping. Higher still and the entire top of the output signal will get sheared off. The spray of high frequencies inherent in the sharp edges has been known to burn up tweeters, and blow the ribbon tweeter fuses of my Magnepan MG-3.6/R speakers, unless a higher-rated amp is used, so that it isn't approaching clipping at the desired (high) loudness.

We can also easily prove, mathematically, that too little capacitance means that there is a bass frequency below which the capacitors will run out of charge, before the next charging pulse comes along. The capacitance value needed, to be able to reproduce down to a particular bass frequency, also depends on the rated maximum RMS output power, which defines the peak output signal voltage and current if a sine wave is assumed.

But as abraxalito mentioned, music doesn't usually look like a sine wave (except maybe when there's a flute solo).

The most bullet-proof way to calculate the MINIMUM required capacitance is to assume that the signal could be ANY shape, and could be anywhere up to the peak output voltage and current that are implied by the rated maximum output power. To do that, we should always assume that the output signal could be constant DC, at the peak value. Then the amp will never be able to clip, ever, and will be able to handle even the lowest bass frequencies without ever running out of current.

Once you know the max rail voltage (from transformer output voltage and rectifier voltage drop at max current) and the load impedance and the "Vclip" voltage for the amplifier itself (given in LM3886 and LM3875 datasheets, as a plot versus rail voltage), then the minimum required capacitance and the max rated output power are redundant, i.e. if you have one, you can calculate the other. And if one changes, then so does the other.

I attached the formula for calculating the absolute minimum reservoir capacitance.

But it's a whole lot easier to just let a spreadsheet calculate for you. So I attached the spreadsheet version of the formula. You can change any of the numbers in the BLUE cells, and see what happens. (Save the file with the ".txt" removed from the end of the file name.)

Cheers,

Tom
Attached is an updated/improved version of the PSU reservoir capacitance calculator spreadsheet that I put up with post 9.

Just change the filename by removing the ".txt" from the end, so that the file name ends with ".xls".
Attached Files
File Type: txt Reservoir_Cap_Requirements_Gootee_04SEP2013.xls.txt (114.0 KB, 53 views)
  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
Power Supply Resevoir Size Nico Ras Power Supplies 2061 16th July 2013 10:46 AM
Chip Amps and Pre Amps bcmbob Chip Amps 17 13th August 2010 09:38 AM
Chip amps vs class D amps lanchile Chip Amps 46 21st April 2010 04:38 AM
resevoir cap. replacments, recommended makes lt cdr data Parts 2 23rd December 2005 06:36 PM
Has anyone compared the Chip amps against Class T amps? soongsc Chip Amps 3 24th July 2005 11:50 AM


New To Site? Need Help?

All times are GMT. The time now is 03:51 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