Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

TNT SS PSU - Is it real or illusive?
TNT SS PSU - Is it real or illusive?
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 October 2005, 02:42 PM   #11
ilimzn is offline ilimzn  Croatia
diyAudio Member
 
Join Date: Feb 2005
Location: Zagreb
(continued)
A little trick that works very well with multiple parallel caps used instead of one large filter cap... Also, PS for the previous post, normally the load is located remotely from the load attachment terminals. If the amplifier uses a Zobel network or Boucherot cell at the output, it is important that it be attached as close as possible to the actual amp, in the place of the idealized load on the above schematic.
Attached Images
File Type: gif caps_current_path.gif (3.6 KB, 310 views)
  Reply With Quote
Old 21st October 2005, 03:04 PM   #12
ilimzn is offline ilimzn  Croatia
diyAudio Member
 
Join Date: Feb 2005
Location: Zagreb
Lets consider for a minute a simplified situation where two independant windings and rectifiers feed a filter bank ending with a common ground. Not a problem until you try to use a single rectifier.
Since one winding alternately charges one and then teh other rail, you get a comon charging current path and discharging current path. It may not be a major problem as long as you can truly guarantee that the connectioon point of R4 and R4' is truly a point. The only remaining problem is that if the return wires to the transformer center point are still separate, due to different charging paths and discharging paths, the cancellation of currents in the twisted wire loops is not complete. Still, good layout will minimize the consequences. This also holds if you only have C3 and C3', i.e. one single pair of filter caps.
Attached Images
File Type: gif dual_rect_caps.gif (3.2 KB, 293 views)
  Reply With Quote
Old 21st October 2005, 03:26 PM   #13
ilimzn is offline ilimzn  Croatia
diyAudio Member
 
Join Date: Feb 2005
Location: Zagreb
Proper approach with single rectifier - extra lines between caps form a filter that separates charging and discharging current loops...
Attached Images
File Type: gif single_rect_caps_1.gif (2.3 KB, 276 views)
  Reply With Quote
Old 21st October 2005, 03:34 PM   #14
ilimzn is offline ilimzn  Croatia
diyAudio Member
 
Join Date: Feb 2005
Location: Zagreb
An interesting variation that also works slightly better at eparating charging and discharging loops when there is only a single cap pair, C2 and C2' in the picture. Pondering a bit shows that a common path for charging and discharging closes around more resistors of a higher value. In a typical implementation, this is done by making a slit inside the metal piece or PCB copper that joins the caapcitor terminals. Still, analysis shows that you only get a couple od dB attenuation on the charging current spikes.
Attached Images
File Type: gif single_rect_caps_2.gif (2.5 KB, 273 views)
  Reply With Quote
Old 21st October 2005, 04:45 PM   #15
ilimzn is offline ilimzn  Croatia
diyAudio Member
 
Join Date: Feb 2005
Location: Zagreb
Final thoughts:
As can be seen, when rectification and filtering is completely independant, there is considerable freedom in wiring without compromising the ground reference. Ths is because it is simple to have all the various supplies connect only into on ground point.
This is particulairly useful if there are local caps on thea mplifier board, creating a local power ground. With completely independant rectification, this only means that you end up joining (or not, as you wish) the quiet grounds, where very little current flows. The only consideration left is inductive coupling, and this is theone area where your only good weapon is mechanical layout and shielding.

With a single rectifier, or more properly, common rectifier, things get difficult if it supplies multiple amplifiers. In theory, it is enough to keep the power ground point, where load and quiet ground split, common between both amps. In practise, this can ge VERY difficult, and in fact you may not be able to get a satisfactory solution if you have two or more amplifier boards with power ground points relatively far from each other. At first, one may not think this is a big issue - just use a common star ground. The problem arises when the distance is such that wiring to the star becomes long, in which case, power rail capacitors local to the power amp board may become ineffective due to increased effective inductance of the wire to the star ground. While in theory the wiring is faultless, you may get an oscillating amp, or one with severely increased load current induced hash on the power lines.

The usual solution lets the common point of the main filter caps become the star ground, from where two power ground lines go to each power ground point of the power amp boards. here is where the compromises begin. In separating the power ground, we now have separated clean grounds, when most sources have a common ground. Since the separated clean grounds galvanically conenct in the same point (star ground), and have separate paths, if they conenct at the oposite end, a low impedance voltage divider and a ground loop susceptible to inductive coupling, is created. This is always a problem, and the solution is usually a matter of compromise... usually, it will include a low value (10 ohms) resistor from te point where the local power ground and the local clean ground split, as well as careful consideration on where to put the feedback reference point of the amp. Some solutions I have seen even deliberately couple input lines with certain parts of the star to power ground connection to cancel out ground current or voltage differences. I will try to draw up some pictures early next week...
  Reply With Quote
Old 21st October 2005, 05:53 PM   #16
Tweeker is offline Tweeker  United States
diyAudio Member
 
Join Date: Dec 2004
Location: Cincinnati, Ohio
Leaving aside sound quality entirely, a dual bridge is that many more diodes to deal with inrush current if you dont have a soft start. With a 600VA 30V secondary transformer, a single bridge, and 60,000 uF capacitance, I get a peak inrush current of about 180 amps.
  Reply With Quote
Old 21st October 2005, 11:34 PM   #17
ilimzn is offline ilimzn  Croatia
diyAudio Member
 
Join Date: Feb 2005
Location: Zagreb
Quote:
Originally posted by Tweeker
Leaving aside sound quality entirely, a dual bridge is that many more diodes to deal with inrush current if you dont have a soft start. With a 600VA 30V secondary transformer, a single bridge, and 60,000 uF capacitance, I get a peak inrush current of about 180 amps.
This should not be a problem, in either case they have to be dimensioned to withstand it, you just use more of the same. In any case, for large trafos you really need a soft start circuit if nothing else to be able to protect the amp properly with a fuse. One that survives 'bare' inrush will probably also survive everything catching fire... one of those cases where, somewhere, in the burnt-down ruins of your house, you hear a 'flink' of the fuse going open, when the foul deed is already done...
  Reply With Quote
Old 22nd October 2005, 01:38 AM   #18
HiFiNutNut is offline HiFiNutNut  Australia
diyAudio Member
 
Join Date: May 2004
Location: Sydney
Please correct me if I am wrong. From the amplifying circuits' point of view, what they see from the PSU and the ground is the voltage, not current. We want to reduce the current loops and have individual current return paths of the PSU only because we want to reduce the voltage variations seen from the amplifying circuits because large current creates voltage variations due to the finite resistence of wires or conductors.

I believe what ilimzn said is very true. But I have been thinking about ways of reducing the problems ilimzn pointed out of which he has put in considerable efforts eliminating them. Refering to my 2nd and 3rd images, the way I layout the amp is to have an ample distance between the bridges and the amplifying circuits. With that sort of distance I don't think I need to worry about the radiation from the wires, twisted (good idea) or not. The radiation may influence the filter caps but that has far less consequence comparing to influence to the circuit board.

As for current returns, I use the big aluminium flat for the PSU common ground. Aluminium conducts very well and such large area of conduction will ensure that the resistence is at the minimum. Let's say a peak current of 10A is being returned to the bridge via the PSU ground. If we have a wire resistence of 0.001 ohm it will create a voltage of 10mV. But if the aluminium flat has a resistence of 0.0001 ohm the the voltage developed due to the ground returning current is only 1mV. This voltage is entirely within the PSU common. Since the signal common is far from the PSU common I really can't see I have to go through all the troubles of separating the grounds, due to the use of a large aluminium flat. Conceptually, if the resistence of the aluminium flat is so low in comparison to other wirings, electrically the entire aluminium flat can be regarded as a single point. In that case there is no separate current return paths to talk about.

So perhaps topology is one thing, while implementation makes it work.

Again, please correct me if I am wrong.


tlf9999,

Thanks for correcting me on the "cancellation" assumption. I fully agree with your points.
  Reply With Quote
Old 22nd October 2005, 05:28 AM   #19
thylantyr is offline thylantyr  United States
diyAudio Member
 
Join Date: Feb 2001
Location: Mars
You are thinking too much trying to solve an easy problem.

Do this;

Temporarily just wire up the system using standard methods
and you will be surprised that it works.

Think Apollo 13
  Reply With Quote
Old 22nd October 2005, 12:14 PM   #20
tlf9999 is offline tlf9999  United States
Account Disabled
 
Join Date: May 2005
Location: none
Quote:
Originally posted by thylantyr
You are thinking too much trying to solve an easy problem.
We are just trying to show how sophisticated a solution we can come up for an ultra-simple problem, .

As to your Apollo example: building an amp is far more complicated than flying some human beings to the moon. Haven't you figured it out yet?

  Reply With Quote

Reply


TNT SS PSU - Is it real or illusive?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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Getting into LP... for real! DragonMaster Analogue Source 56 26th September 2006 10:18 PM
A Real Sub mikee12345 Multi-Way 10 10th March 2003 02:03 PM
Combing effects: How real in "real" rooms? smeade1079 Multi-Way 3 10th March 2003 12:32 AM


New To Site? Need Help?

All times are GMT. The time now is 09:31 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki