MS275 question

NewOldStock · Post by **NewOldStock** » Sat Nov 21, 2009 10:16 am

Hey, I just got my first old PG amp... I am STOKED to finally be able to use it. I couldnt ever afford them when I was younger and now that I can... they are hard to find!

Anyway...

I picked up a decent looking MS275 on trade from one of my 4x4 buddies... its in "ok" shape... maybe a 7/10... the fins have been damaged all along one side, but otherwise it looks good and sounded great in his truck.

my question is this: Inside the amp there is a little switch, one side yellow and one side red ... What does that switch do? The friend I got the amp from has no idea, he bought it years ago, installed it and never thought about it again.

Thanks for the input everyone - I tried to search for it but havent been able to find any info on it - and I am afraid that even if I did see something on it, I dont know what its called so I may have just missed it.

Post by **Rold Gold** » Sat Nov 21, 2009 10:23 am

WELCOME to the Phorum..........

Before you do ANYTHING yer gonna have to replace the capacitors in the amp. Since it's old enough to drive, the caps tend to leak onto the board and can cause fire and thus literaly burn up the amp. I don't know what the switch is yer askin about.

NewOldStock · Post by **NewOldStock** » Sat Nov 21, 2009 10:30 am

Thanks! I have been a fan of the old PG stuff since I was a kid but like I said, I couldnt afford them.

good to know about the caps, any suggestions on where to send it to get them replaced?

Here is the picture on AmpGuts:

Its the little switch right there, center-left, by the cluster of 3 caps

In that picture its set to yellow - but now I am REALLY curious what the red-side does! lol

Thanks!

Post by **Rold Gold** » Sat Nov 21, 2009 10:34 am

Ya might PM ericD about a cap swap...... An d he can tell ya what the switch is also.

NewOldStock · Post by **NewOldStock** » Sat Nov 21, 2009 10:37 am

lol - finally got the picture to load - right after you responded!

Thanks! I'll send him a message!

marko · Post by **marko** » Sat Nov 21, 2009 11:39 am

the swich is for when your running 2ohms, it lowers the rail voltage iirc..

NewOldStock · Post by **NewOldStock** » Sat Nov 21, 2009 12:26 pm

lowers the rail voltage - so it puts out more power or so that it puts out less heat?

I am afraid I dont (obviously by the look of confusion on my face) know what that would do for/to the amp.

I downloaded the manual from PG, but there is nothing about the switch in the manual.

marko · Post by **marko** » Sat Nov 21, 2009 12:30 pm

it will make it run cooler and give it an easier life at 2ohms..

NewOldStock · Post by **NewOldStock** » Sat Nov 21, 2009 12:38 pm

Gotcha!

So lowering the rail voltage will make life easier on the amp - but will also lower the amount of output the amp produces at 2-ohms right?

Assuming I remember my high-school physics correctly. Not sure that it matters, I will probably be running the amp at either stereo 4-ohm loads or bridged 4-ohm loads...

depends on if I can get an MS2150 to match

NewOldStock · Post by **NewOldStock** » Sun Nov 22, 2009 9:42 am

in case anyone ever searches and finds this post - here is the FAQ on the MS/MPS amps:

http://webfaq.phoenixphorum.com/MS_MPS.htm

Misfire · Post by **Misfire** » Sun Nov 22, 2009 10:35 am

Welcome to the Phurom! I asked this question as well. Here is the link to the answers.

http://phoenixphorum.com/eric-d-whats-t ... 11450.html

brenzbmr@sb · Post by **brenzbmr@sb** » Sun Nov 22, 2009 1:50 pm

All MS275s have a two-position switch in the middle of the circuit board with a red dot on one side and a yellow dot on the other. At the factory, the switch is set to the yellow position. The red position will limit the power supply voltage and allow for more output current. This can improve thermal performance when the amplifier is driving low impedance loads (2 ohms bridged). This offers an alternative to installing cooling fans.

right off the page it self

NewOldStock · Post by **NewOldStock** » Sun Nov 22, 2009 9:21 pm

excellent!

I love you guys!

Thanks!

Post by **Eric D** » Mon Nov 23, 2009 11:05 am

I don't want to get too technical here, but the switch is more of a band-aid than a real solution.

The transformer inside the power supply of an amplifier is wound at a ratio which delivers an optimum rail voltage. The rail voltage is what feeds the output section of the amp and that directly powers your speakers. When you flip the switch in these MS amps, it lowers the voltage seen by the controller of the amps power supply. The power supply controller then changes its driving signal to the transformer for less output voltage. You end up loosing some efficiency. So the amp will produce less heat into 2 ohms mono for example, but the power supply will be less efficient, so really the better solution would be a 4 ohm load or an amp more optimized for the 2 ohm load.

Post by **mhyde71** » Mon Nov 23, 2009 11:16 am

what if we are driving 2ohm stereo and havent flipped the switch- just runs warmer than it should be or could be?

Post by **Eric D** » Mon Nov 23, 2009 11:27 am

I would not flip the switch to drive 2ohm stereo, that is an easy load for the amp. (Not as easy as 4-ohm stereo, but still plenty easy)

NewOldStock · Post by **NewOldStock** » Mon Nov 23, 2009 1:58 pm

mhyde71 wrote:what if we are driving 2ohm stereo and havent flipped the switch- just runs warmer than it should be or could be?

Good question

Eric D wrote:I would not flip the switch to drive 2ohm stereo, that is an easy load for the amp. (Not as easy as 4-ohm stereo, but still plenty easy)

Thanks again Eric!

brenzbmr@sb · Post by **brenzbmr@sb** » Mon Nov 23, 2009 8:14 pm

to be honest i ran that amp tri linear two ohms bridged to two 15s and two ohms stereo on cmponants all passive x overed.

i left that switch in the regular mode and tht amp banged. put a x flow fan on it and never had a problem with it.