Phoenix Gold MPS-2240

[azvrt]

Hi,

I just purchased my first ever PG amp, a MPS-2240.
I tested it today and was very impressed.
Sonically I don't think it would be my number 1 choice on tweeters, but I absolutely love it on my mids.

Correct me if I am wrong, the MS-275 is basically the same amp (same for MPS 2500 and MS-2125), the main difference being the MPS was a cheater amp and has less power at higher impedances.
My question is: Do they sound the same ?

I think the comparison can be made between Soundstream Class A 3.0 and Ref 300 (same for 6.0 and Ref 500).
The Class A's are cheater amps and less powerful at higher impedances. However, in Soundstream's case, for the cheater amps a high-bias scheme was chosen (hence the 'Class A') which resulted in the amps sounding noticably different from the regular Refs, even though they were not real Class A amps of course.

I do not think this is the case with MPS and MS, or is it ? Do they sound the same (except for differences caused my power/headroom differences obviously) or different ?

Does anyone here have the schematics for the MPS-2240 ?

Would anyone know how to (easily ?) modify its 2 volt gains into (approx.) 5 volt gains ?
My Eclipse HU has 8 volt pre-outs, the Soundstreams and BLT's that I am working with have 5 volt gains and with help of Genesis I just modified my Genesis Series 2 Q-90X from 3 volt gains to 5 volt gains.

I'll have a look at the board this week, check the caps. If I understand well the power supply caps must be thoroughly checked or even replaced ?

Thanks !

[Eric D]

Yes the caps need to be replaced ASAP. I have never found any of these amps with original capacitors to not have them leaking. And trust me, I have worked on MANY of the MPS and MS amplifiers over the past several years.

I am sure plenty of people here will passionately argue against me on this, but the MPS2240 and MS275 do sound the same. They are physically identical amps, using identical parts, other than some changes to the power supplies. The only way a MS275 will sound different is for example on a pair of 8 ohm speakers, the MS275 will be able to play them to comfortable levels, whereas the MPS will probably clip on this load, or come close to clipping just to get any sound out of it. So yes, under these conditions the MPS will not sound as good.

If you setup an A-B comparison between a MPS2240 and MS275 on 4 ohms speakers, at say 10V output (match the amps gains), I am confident no human on Earth would be able to consistently tell them apart.

As far as your points on the Soundstream amps, I could not agree more. The Ref amps sound great, but the Class A line is indeed a cut above. I personally prefer the Class A amps, to most PG amps, but I feel the PGs are better built (all just my opinions though).

[soth]

From what i've seen and observed Eric is spot on.

I've got a mps2240 also, but will need to get it fixed sometime in the future. Green light just keeps blinking and doesn't put any power out.

Overall I love the mps and ms series amps. They look plain but have a wonderful sound to them.

Kevin

[azvrt]

Thanks guys.
I am also having an interesting conversation regarding this amp here:
http://www.diyaudio.com/forums/car-audi ... ost2739365

If I understand correctly the idle current could be set on this amp which might imply it is a high bias amp ?
I'll await this person's reply as I find this very interesting.
I did find it strange that I saw 3 ampere idle current mentioned somewhere while mine only draws 0.9 / 1 ampere.
If the idle current can be altered and on the 275 it cannot, then it's a second 2240 I'm after, not a 275.

[Eric D]

Both of those amps have a bias control which is used to adjust the bias current to get rid of the crossover distortion present in the output. The crossover distortion I am referring too is where the signal "crosses over" from the positive half cycle to the negative, or the other way.

On a Class B amp there will be a little horizontal spot in the output signal, which could be audible. The whole point of Class A/B is to eliminate this. If a Class B amp is run with enough feedback though, you will find this crossover distortion nearly vanishes. Class B amps can be great, my only guess why they are not popular is simply marking making a lot of people think they are junk.

I once spent a while listening to a MS amp with the bias all the way down (effectively Class B). This amp had almost no idle current. I could not tell the sonic difference between it, and it with its bias correctly adjusted. The amp had enough feedback to filter out the crossover distortion. Only on a lower impedance load would there start to be a change.

So, I would not say any MS or MPS amp were a "high bias" amp. Maybe the ZPA amps are, but even then I really doubt it.

The Soundstream Class A amps are the only high bias amps I am familiar with. I am sure there are plenty of other designs out there which are as well, but I have not come across them yet.

[azvrt]

Is 1 ampere idle current normal for these amps ? I read somewhere on the web they have a 3 ampere idle current ?

Would anyone happen to know exactly where to measure the bias for each channel. How many mVDC must the bias be set to ?

On the speaker outputs (terminals) I measured 37 mVDC on the right channel and 28.4 mVDC on the left. Is this bad ?
No speakers or RCA wires were hooked up to it.

The caps have not leaked

[rolandk]

Bias on MS/MPS amps is 100uV (not mV) measured across the big grey output resistors with the amp cold and no load or input signal. Your amp should idle at ~1A.

[azvrt]

Thanks for the information, though it is kind of worrying
The person with whom I am having a discussion on DIYAudio was telling me otherwise (higher bias)
Also, a repairman who I am acquainted to told me otherwise.
You might be right though, as the bias we measured at the locations you mentioned was very low.
We set it to over 25 mV and the amp now idles at 2 ampere. The person from DIYAudio is telling me it can safely idle up to a maximum of 3 ampere, so I thought we should be on the safe sife with the the 2 ampere. By the way we set it at 14 volts.

We tested the amp aftwerwards with a 100 Hz and 2 kHz test tone and everything seemed fine, it only clipped when we sent it a very strong signal.
With music it sounded fine also.

[stipud]

rolandk was PG's head tech for a decade or so, so I would trust him on that

[rolandk]

Its been 5+ years since I worked on those amps and now that I thought about it a little more I believe the official spec is 50uV, not 100uV. The only PG amps that idled at ~3A were the ZPA's.

[marko]

I'm sure my original ms2250's idle at 4amps, been a while but that figure stuck in my head for some reason..

[Mr. Wild]

I have a ZX450 V1 that idles at 2.5 amps cold. But then again it is a 4-channel amp.

[Xtian]

Hi guys, i have a MPS 2240 and a MS 2125 and i wanna swap the caps on both..
Is it any good for the sound to use some caps like the NICHICON Fine Gold in the PSU and the Mundorf M-lytic on the rails??

http://www.hificollective.co.uk/compone ... on_fg.html

http://www.hificollective.co.uk/compone ... ic_ag.html

I'm also looking for endplates for both (MPS2240 white and MS2125 grey)

[Eric D]

The big caps in these amps are just used to keep the voltage steady in portions of the power supply. Replacing them with better caps would never hurt, but it will not improve the sound of the amps. To improve the sound you need to change parts which are in the signal path of the amplifier.

[Xtian]

Thx for the reply Eric..

ok, then i don't have to spend too much money on these..

and how about increasing the capacitance?
I was planning on keeping the same capacitance for the four big ones
but increasing the twelve smaller ones to 4700µf 16V each, is that ok?

[Eric D]

I use these caps, which are 5,600uF...

http://search.digikey.com/us/en/product ... -ND/589284

[Xtian]

Thx alot...
these have four times the ripple current in comparisation to the ones i had in mind.