M44 True RMS Voltage

[jammer750]

Is that because the power supply side will not be able to keep up ?
I just picked up a super clean black ZX500v2.

Are the power supplies in the M/MS series more up to the task ?

[pdelgadinho]

How are you getting the 900W for the ZX500? What is the calculation to go from 30V to 900W?

Edit: Trying to answer my own question...

4ohm stereo
V squared / Ohm = Wattage
30 * 30 / 4 = 225W x 2 channels

4ohm bridged (voltage is doubled)
V squared / Ohm = Wattage
60 * 60 / 4 = 900W x 1

Is this right?

[jammer750]

Ohm's law.
The ZX500 is outputting 30 volts per channel.
When you bridge a bridgeable amp you get a + & - 30 volt swing = 60volts.

Your numbers are right, but it does not mean the amp will actually do that.

With a test tone, you won't get 900W from a ZX500. With music, and some capacitance on the input to the amp, you will get peaks of 900W.

Eric,
So I guess these are rated pretty spot on from Phoenix then. Kind of like my A/D/S amps. They do rated RMS. With a dynamic headroom of approx. double.

[Eric D]

I thought the ZX500 was rated at 150W x 2. 30V a channel would get you 900W mono (60V), which is a lot more than rated.

Both the power supply and the output section of the amp are a limiting factor. I think each output transistor is rated at 130W thermal capacity. If you cut that in half (Class A/B), you are down to 65W each. There are 8 of them in all, so that is only 520W of thermal capacity total. (these are just estimates).

As for the power supply, there are 8 MOSFETS, each rated at 55A I think. I don't know what the thermal capacity is though. So, there should be plenty of current, but thermally the parts could not handle the sustained load.

[jammer750]

Yes, It is rated at 150 x 2 or 600 x 1
Your thermal calculations must be close
Hence the 600 x 1 RMS rating.
So, to me it would seem that it will to rated continues power of 600 x 1
But have dynamic headroom of 900 x 1
Does that sound correct ?
I am new to this and I am still learning
And appreciate all the help an knowledge on this site.

[Eric D]

I agree with what you have come up with.

Most people can hear distortion, but few (if any) can hear distortion related to clipping as well as an oscilloscope can "see" the clipping.

If you set your amplifier for max output with no load, you will set it to these voltages. Then listen too it with your chosen music. If you hear clipping related distortion, you will have to back off on the gains. You may have to back off as far as the rated specs of the amp (24.5V a channel in the case of the ZX500). Chances are you will find the ZX500 will sound great set to the higher voltage. Most music is dynamic enough to not stress the amp far enough.

This is really the big benefit to PG amps over say Rockford amps, if you ask me. Most RF amps (old school ones I am familiar with) are built to produce just over their rated voltage output, but do it with a test tone. If you buy a 100W x 4 amp from RF, it will do 100W x 4 with a sine wave of any frequency, into its rated loads.

Well, with PG, the amp will produce far more output voltage than the rating, but it does not have the capacity to sustain this with a sine wave. This is the reason I personally found a PG ZX450 to have more output (play louder) than my PAIR or old RF Power 250.2C amps (rated at 125W x 2 each). Plus the PG did this while sounding a heck of a lot better as well.

You can verify this with an oscilloscope. Once hooked up and with a load on the amp, you can play music, you will be able to see the "jumps" in the signal and if it is clipping or not.

[Eric D]

Here are some additional numbers...

MS2125 = 38V rails (+ and -), with 24V RMS output prior to clipping

MS275 = 36V rails (+ and -), with 22.75V RMS output prior to clipping

MQ430 = 26V rails (+ and -), with 3V RMS output prior to clipping (not a typo)

After modifying the preamp section of the MQ430 I got 16V RMS output from it.

Here are some photos of the results...

This is the output of the MQ430 stock. Notice the scale is 2V per division, so the output is swinging from about +4.4V to -4.4V.

MQ430 Prior to Mod 3V.JPG (33.72 KiB) Viewed 7392 times

After I modified the preamp section, the amp now swings from about +24v, to -24V before it clips. (10V divisions on the screen)

MQ430 After Mod Clipping.JPG (33.73 KiB) Viewed 7392 times

And here is the output reduced to just under clipping, which gave me 16V RMS.

MQ430 Output After Mod 16V.JPG (33.39 KiB) Viewed 7392 times

[todd217]

wow thats disappointing on the ms2125.

[ttocs]

what modification did you do to the 430?

[Eric D]

what modification did you do to the 430?

http://phoenixphorum.com/viewtopic.php?f=22&t=20577

[jammer750]

Do you think a similar mod would work on the preamp section of the MS2125 ?

[Eric D]

Do you think a similar mod would work on the preamp section of the MS2125 ?

No, the preamp section of all the rest (or so I think) of the MS amps are not broken.

In every PG amp I have come across, the output section will clip before the preamp section does. This is as it should be. You don't want the preamp clipping, as you introduce a ton of distortion, and you never get to reach max output power.

In the case of this MQ430 (and I am guessing all other MQ430s), the preamp section clips well before the output section does.

No matter what you do to the other MS amps, their rail voltage is what limits their output voltage. To get more you need to rebuild the power supply for more voltage.

[freshkryp69]

Do you think a similar mod would work on the preamp section of the MS2125 ?

No, the preamp section of all the rest (or so I think) of the MS amps are not broken.

In every PG amp I have come across, the output section will clip before the preamp section does. This is as it should be. You don't want the preamp clipping, as you introduce a ton of distortion, and you never get to reach max output power.

In the case of this MQ430 (and I am guessing all other MQ430s), the preamp section clips well before the output section does.

No matter what you do to the other MS amps, their rail voltage is what limits their output voltage. To get more you need to rebuild the power supply for more voltage.

Eric, can & will you work on a 2125 to raise the output voltage to that of a 2250 since they have the same boards, on request? i suppose the torrids would be the major rework issue? Also, I've seen you bypass the gain section on a Ms amp, & tookout the caps inline with the signal, & got rid of the low freq cut off that the caps created, & raised the preamp input v to accommodate late model decks/processors with hi v preamp outputs..
I have a level control on my 9255 for each channel, so i can rework the preamp side and gain that tiny bit of sq due to less circuitry required when the opamp is removed and use the decks outputs to drive the pre-driver transistors? I have done rail/PS caps, bigger PS fets, and want to take my Ms amps to the highest level possible and understand the gains are small for the work required to achieve them.
Can i get all the possible options from you, on what can be done to my 2125's (twrs & midbass) & 2250 (sub). After this, i have 3 Orion nt's i need done.
thanks.
Brad

Ps..i have shrouds for cooling the Ms's.

[jammer750]

Do you think a similar mod would work on the preamp section of the MS2125 ?

No, the preamp section of all the rest (or so I think) of the MS amps are not broken.

In every PG amp I have come across, the output section will clip before the preamp section does. This is as it should be. You don't want the preamp clipping, as you introduce a ton of distortion, and you never get to reach max output power.

In the case of this MQ430 (and I am guessing all other MQ430s), the preamp section clips well before the output section does.

No matter what you do to the other MS amps, their rail voltage is what limits their output voltage. To get more you need to rebuild the power supply for more voltage.

Well. do you think that they designed the MS2125 for best sound quality then ? It seems with that output that none of the components will be stressed.
It is surprising that the MS275 has nearly the same output. And over 500watts bridged

[Eric D]

The MS2125 will do high current / low impedance better than the MS275. The MS275 is a 500W amp, the MS2125 is a 1000W amp.

The MS2250, MS2250TA (MAC500), MS2125, and MPS2500 are all 1000W amps. They just do 1000W at different loads.

Upgrading a MS2125 to a MS2250 is not cost effective. It requires replacing so many parts, it is better to start with a MS2250TA and go from there.

[Mr. Wild]

The MS2250 is rated at 1000Wrms @4ohm bridged. It has a shroud. 2ohm brideg is a no no.

The MS2125 is rated at 500Wrms @4ohm bridged. If it had a shroud it could do 1000Wrms@2ohm bridged. Am i right?

The MPS2500 is rated at 500Wrms @2ohm bridged. If it had a shroud it could do 1000Wrms @1ohm bridged. Am i right or would it reduce rail voltage before hitting 1k? Being stable into 1/4 ohm loads MUST mean this one reduces its rail voltage.

I assume the MS's don't reduce rail voltage.

[Eric D]

None of these amps reduce rail voltage by choice. Their rail voltage is a ratio of input supply voltage. If you load them down too much, then the input current will climb, and this may lower voltage at the amplifier's input terminals (due to resistance in the power cable). If the voltage stays constant at the input terminals, and you load the amp down, its rail voltage may sag when you reach the max the power supply can handle.

[Mr. Wild]

M-series amps are current limited ie they reduce rail voltage. I thought this to be the case with MPS amps and their crazy 1/4 ohm capability.

So loading an MPS with 1/4 ohm load just makes the power supply sag so much that it doesnt melt down. Interesting.

[Eric D]

Who said anything about it not melting down?

I don't know of any PG amp which limits its current. M amps included. They do detect the demand, and can warn you (overload light), but they will go a long way prior to doing this.

[Mr. Wild]

Well you know what i mean. Limiting the rail voltage limits the power (and current) output.

Its clearly explained in the PG vintage products FAQ

M-series, XS-series, ZX&ZXti-series.