ppi epx 205, interesting crossover (to me, at least) - diyAudio
Go Back   Home > Forums > General Interest > Car Audio

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 February 2008, 03:11 AM   #1
ppia600 is offline ppia600  United States
diyAudio Member
 
Join Date: Jun 2007
Location: Louis y ana
Default ppi epx 205, interesting crossover (to me, at least)

I was able to find the right sized allen wrench today to remove the front and back covers on it today and found something interesting inside. Of course the crossover is designed around the phantom power +/- voltage setup using the din cables directly to the ppi amps, but it also has a tiny power supply section for someone who wouldn't use the crossover on ppi amps.
Now I noticed there is only one transistor in the power supply, it is a to220 style and on the primary side. Then there are of course diodes on the secondary side that I assume feed the audio circuits. What I am wondering is:

1- WHY on earth would they use only one transistor to drive the transformer? That would seem to be a little more difficult to make smooth dc with. (would that be to punish people that aren't using ppi amps with a little extra noise.. to motivate them to buy the ppi's to get better sound??? )

2-If the power supply isn't noisy, WHY would every other power supply I've seen besides this one have two tranistors with opposite polarities driving the primary side? I mean, if it is possible to use only one polarity transistor, why use opposing polarity ones in everything else that requires two different voltage rails?

4-If it would be possible to use only one polarity transistor in a power supply that could produce two opposite polarity voltage rails on the secondary side (in a high powered audio amp for example) , would it be too inneficient at that power level?


Now I'm starting to think I should have kept it and not put it up on ebay, lol. Someone please explain this crossover's power supply and make it seem less special to me so I won't feel so bad when it sells for next to nothing.
__________________
Don't worry... you can always turn the gain down!
  Reply With Quote
Old 25th February 2008, 05:35 AM   #2
djQUAN is offline djQUAN  Philippines
diyAudio Member
 
Join Date: May 2004
Location: manila
Send a message via MSN to djQUAN Send a message via Yahoo to djQUAN
1. Audiocontrol does the same thing. they use a regulated supply for low level circuits. assuming the supply has output inductors and the board layout and circuit design is well made, noise is not an issue.

2. it is much easier and cheaper to use push-pull designs.

3. where's three?

4. some pro amps use a flyback switching supply (ask eva) and they work fine. same answer as #2.

there's my 2C.
  Reply With Quote
Old 25th February 2008, 05:50 AM   #3
Eva is offline Eva  Spain
diyAudio Member
 
Eva's Avatar
 
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
Congratulations, you have discovered flyback SMPS. This is the most widely used topology in low power supplies, it uses a single switch and can produce positive and negative voltages. The outputs are always regulated unlike in almost every small push-pull and the ripple from the 12V supply is not fed directly to the outputs unlike in push-pulls. It's just that most car audio designers are stuck to unregulated push-pull even for tiny power supplies because they don't know anything else. Some people just do electronics design as cookbook copy and paste. Designing a flyback requires some more math and magnetics knowledge than a plain push-pull, and you have to design the frequency compensation of the feedback loop too. Of course flyback has drawbacks but they only show up when high currents are involved.
__________________
I use to feel like the small child in The Emperor's New Clothes tale
  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
Interesting... fredos Class D 3 26th November 2007 06:45 PM
interesting amp & interesting problem m6tt Tubes / Valves 9 14th August 2007 06:28 PM
Interesting crossover question Fast1one Solid State 7 17th February 2007 08:04 PM
Can you hear the crossover point of a speaker with a well-designed crossover? 454Casull Multi-Way 11 2nd April 2004 05:48 AM


New To Site? Need Help?

All times are GMT. The time now is 08:11 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