Power Supply Preference - Page 3 - diyAudio
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 4th December 2012, 04:05 PM   #21
MarianB is offline MarianB  Romania
diyAudio Member
 
MarianB's Avatar
 
Join Date: Jul 2011
Location: Romania
Send a message via Yahoo to MarianB
@AndrewT with all do respect, nothing you have sayd there has answeared my question, it is just unnecessary complicated stuff, to make it simple from 35Vcc you can only obtain an amplified AC/audio signal of about 24V maximum, now 24V on 4 Ohm load ( witch i think could be the case here ) is about 140W of power, this not taking in consideration the amplifier losses witch as far as i know in class D are much smaller, now if let say you require about 150W power from the supply then 150/70=2,2A, or let say the worst case scenario, about 30% losses as it is with class B, 140/0,7=200W, that would be the power needed from the supply, and with 70V rai to rail that is about 2,9A, and something like 6A for 2 Ohms load but as i say i doubt that is the case, well from 6 to 20A is qouite a difference, so as i sayd 20A for just 35v is too large of a current.

@jlind54 i think that first you need to be sure what audio power you need for the speakers and what is theyr load, i mean are 2 Ohms or 4 Ohms, then a more correct specs could be drawn for the supply.
__________________
Trance Session Live by Dj Marik
  Reply With Quote
Old 4th December 2012, 04:36 PM   #22
jlind54 is offline jlind54  United States
diyAudio Member
 
Join Date: Nov 2012
Location: Kansas
Subwoofer is an 18" 4 Ohm. I'm looking to drive it with near 70 volts which is how I decided +-35 and at 4 ohms that equates to an approximate 17.5 amps correct? I figure being 20 amps allows some wiggle room with speaker impedance change at given freq./box combinations. Am I thinking incorrectly here. Perhaps the voltage should be bumped up a bit like say shot for 80 which would give +-40? or does my supply need to truely be +- 70 instead of 35 as I've outlined above?
  Reply With Quote
Old 4th December 2012, 04:47 PM   #23
MarianB is offline MarianB  Romania
diyAudio Member
 
MarianB's Avatar
 
Join Date: Jul 2011
Location: Romania
Send a message via Yahoo to MarianB
@jlind54 i ask again: how much power do you need for that sub? if you mean you want a 70v signall for the load then it would be about 1,2Kw of power, now with 35v per rail you cannot get anywhere near that much power, 70vac signal would mean at least 98Vcc per rail ( that is +/-98Vcc ) and that is not taking into account the power devices losses, so maybe the power supply unit would need something like +/-100Vcc, that is much more than you have come to.

I think the reason for your mistake could be a poor understanding of what's going on on a power amplifier so that is why i think you have much to studdy before you can start working at a SMPS with that high voltage outputs.
__________________
Trance Session Live by Dj Marik
  Reply With Quote
Old 4th December 2012, 04:56 PM   #24
jlind54 is offline jlind54  United States
diyAudio Member
 
Join Date: Nov 2012
Location: Kansas
Could 70 volts not be achieved using a full bridge topolgoy in an amplifier output design making +-35 volt rails capable of the 70volt ac signal I'm desiring?
  Reply With Quote
Old 4th December 2012, 05:10 PM   #25
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
i doubt it would require that large current for just 35V rails... tell me please @AndrewT am i wrong in believing this?
that appears to be your question.
I answered it rather comprehensively.
20Apk is not a large current, irrespective of whether the supply rails hold up at only +-35Vdc, or are +-100Vdc. I gave a detailed derivation of typical worst case transient currents for a 2ohms speaker driven from regulated +-35Vdc supply.
Quote:
from 35Vcc you can only obtain an amplified AC/audio signal of about 24V maximum
I disagree on this conclusion.
I would expect at least 30Vpk from an amplifier sitting on regulated (SMPS) +-35Vdc supply rails, if ordinary followers were used. If common emitter/common source is used I'd expect at least 33Vpk from +-35Vdc.
I think it was ampguru that did a design based on common source (vert mosFET) and there are others. Dr Cherry recommends this topology over the much more common follower topology (common collector=emitter follower).
__________________
regards Andrew T.

Last edited by AndrewT; 4th December 2012 at 05:27 PM.
  Reply With Quote
Old 4th December 2012, 05:18 PM   #26
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by magnoman View Post
Andrew
Do these 3-5 multipliers apply as well to sub's with very limited bw?
The converters bw could potentially also keep up with these slower signals (limiting droop but would have to be correspondingly rated for the peak power).
probably not as a gut reaction to an actively driven bass only speaker.
Maybe 1.5times to 2times, but this is only my guess, since I cannot reproduce the original testing for real music into actual speakers.
A well resourced builder/designer should be able to determine a current factor for a reduced bandwidth speaker without a passive crossover between it and the driving amplifier. I have not seen this style of test reported in this Forum, but my adopted 3times is based on the Forum report that I have referred to a few times. I do wish some members would get together and expand that original report to other speaker types that we typically use.
I guess (again) that many have not realised the importance of meeting speaker current demand and thus little priority is given to finding design data that would help with selecting amplifier and PSU topologies.
__________________
regards Andrew T.
  Reply With Quote
Old 4th December 2012, 05:53 PM   #27
MarianB is offline MarianB  Romania
diyAudio Member
 
MarianB's Avatar
 
Join Date: Jul 2011
Location: Romania
Send a message via Yahoo to MarianB
@AndrewT you cannot speak of Vpk when an AC sinus signal ( like audio signal ) is involved, on the load you speak of Vef, and from an DC current that can be considered Vpk you can only get and AC signal of Vcc/1,41, that is a well known fact, on the other hand when calculating the VA ratings of a PSU for an amplifier, you do not take into account the transients cus you can never exactly predict them, you think about the continuous current needed, and that is the current you design the PSU to deliver, it is cind of ridicoulus to make a PSU of 20 amps for just 35v just cus of the transients, what about for +/-100Vcc then? how much transients is involved here and how much more current you need to supply? with only 20A as it is as you say for 35v it would be a 4Kw PSU, for only 1,2-1,5Kw max audio power amplifier? that is beyound real, so again with all do respect you are wrong, and you need to better learn the difference between DC and AC, specially for sine wave ac.

@jlind54 it seams you do not know verry well the difference between AC and DC, so for example mains Ac current ( like audio signall as well ) is a sine wave with 2 ratings: Vpk and Vef, at AC state you measure the Vef witch is Vpk/1,41. Transforming this into DC is done with rectifiers and filter caps, the rectifiers allow the current to flow in only one direction so it makes the DC, and the filter caps raise rthe measured voltage at the Vpk. On the other hand the power amplifier ( it's final stage ) puts one side of the load alternatively at + than at - rails, never do both of them are at the same time on the load, so that means the load can only receive signall from one rail at a time, so if 35Vcc per rail that is the DC that will be delivered as Ac to the load, and as i stated above you can think of the DC as the Vpk, and you get the Vef that will always be the measured voltage on the speaker by Vpk/1,41 and 35vcc/1,41=24,8vac, in reality it is a bit smaller cus a few V drops on the power devices.

Now knowing all that, how do you calculate how much Vcc per rail you need for a wanted signall at the load? simple, for 70 as you stated, it is 70*1,41=98,7Vcc, you make sure you add some aditional volts needed for the power devices so you come up with at least 100V per rail, and as there are 2 rail ( positive and negative ) the supply needs the outputs to be +/-100Vcc, that is 200V rail to rail.
__________________
Trance Session Live by Dj Marik

Last edited by MarianB; 4th December 2012 at 05:59 PM.
  Reply With Quote
Old 4th December 2012, 06:36 PM   #28
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by MarianB View Post
you cannot speak of Vpk when an AC sinus signal ( like audio signal ) is involved,
Yes, I can. I can see Vpk on a scope, it exists. I can measure Vaverage with a DMM, yes, it exists. I can meausre Vrms with a better DMM. Yes, it exists. I can use any of these to describe a voltage
Quote:
........ AC signal of Vcc/1,41, that is a well known fact,
Agreed.
Quote:
..............you do not take into account the transients
No. Just because we cannot predict a transient is no reason to ignore the existance of current transients.
Quote:
.......................it is cind of ridicoulus to make a PSU of 20 amps for just 35v just cus of the transients, what about for +/-100Vcc then? how much transients is involved here and how much more current you need to supply? .............................
A linear PSU with enormous capacitance (by smps standards) is easily able to meet enormous current demands put out by the connected speaker. That is one of the advantages of using a linear supply. It CAN meet very high transient demands that a speaker makes on the PSU.

I think the reason you are not accepting (and we are having this extended argument), that transient demand exists and transient capability is required is because the SMPS has by comparison a relatively small output capacitance. That topology requires that the transient demand must be met by other means.

It is not sufficient as a design exercise to say that the transient demand does not exist, just because the SMPS will have to be designed with different priorties if one were to admit that transient current capability is a necessary PSU requirement.

I off to the dancing, not back till tomorrow.
__________________
regards Andrew T.

Last edited by AndrewT; 4th December 2012 at 06:39 PM.
  Reply With Quote
Old 4th December 2012, 06:51 PM   #29
jlind54 is offline jlind54  United States
diyAudio Member
 
Join Date: Nov 2012
Location: Kansas
MarianB yes I somehow forgot the fact I would be creating an ac signal and there for taking what you said makes perfect sense now. So yes in general I would be shooting for the +-100 volt range. As for the amperage there would be no need to really increase to achieve 1200 watts of sinewave output correct?
  Reply With Quote
Old 4th December 2012, 07:24 PM   #30
jlind54 is offline jlind54  United States
diyAudio Member
 
Join Date: Nov 2012
Location: Kansas
Ok... thinking about this a bit more woudn't I only require +-50 volts to be able to achieve the 100 Vpk which would get me around 70 Vref? please let me know if my thinking on this is flawed.
  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
Making Symmetric Power Supply from Single with 4x ATX power Supply? lupetalo Power Supplies 11 20th November 2012 12:51 PM
Listening preference.... Harlan Tubes / Valves 34 5th November 2011 06:58 AM
preference between 5842 and 6c45pi dsavitsk Tubes / Valves 0 8th December 2006 10:43 PM
Matlab or Mathematica -- which is your preference? rif Everything Else 7 11th May 2004 06:34 AM


New To Site? Need Help?

All times are GMT. The time now is 12:35 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