phoenix gold mps-2240 schematics - diyAudio
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Old 7th October 2011, 08:41 PM   #1
azvrt is offline azvrt  Netherlands
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Default phoenix gold mps-2240 schematics

Hi guys,

Looking for the schematics for this amp.

Thanks.
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Old 8th October 2011, 02:27 AM   #2
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Why, whats wrong with yours ? Let me know your issues and I will help guide you as much as possible...C
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Old 8th October 2011, 08:55 AM   #3
azvrt is offline azvrt  Netherlands
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That's very kind of you, I appreciate it !

There should be nothing wrong with, just purchased it. Haven't tested it yet, though.
But I like to have schematics of all amps I own, though it's not certain whether I will keep this one. With amps, I promised myself to stick to two brands only, in my case Soundstream and Genesis, as I am afraid that if I buy one from another brand and I like it, I will might buy more (did anyone say MPS 2500) ?
I always wondered about these amps though, and I was able to buy it for a great price. Plus I like it's high idling current.

I might keep it, as when I paid the seller and grasped the amp we immediately bonded haha (not me and the seller). I like its weight, feels sturdy.

Anyway, if I do keep it, I'll probably want to modify the 2.0 volt gains to 5 volt gains, same as my mid/late-nineties Soundstreams. With help from Genesis, I modified the 3.0 volt gains of the DLS Genesis Series 2 Q-90X to 5 volt gains as well. Had to change some resistors and small capacitors. Maybe you could tell me whether this is (easily) possible ?

Also, I will have a look at the board and check the caps. Or should I replace some right away ?
Are there any (easy) modifications that can be done on this amp, not requiring more advanced soldering skills like op-amps do ?

Thanks !

Last edited by azvrt; 8th October 2011 at 08:57 AM.
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Old 8th October 2011, 03:23 PM   #4
azvrt is offline azvrt  Netherlands
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Tested it today, and I like it ! Definitely a keeper. Wouldn't use it on tweeters, but sounds great on mids. It will probably end up driving my front 4.5 inch Altec Lansing carbon speakers in my 3-way setup, on a 120 Hz Hz high pass and 2.5 kHz low pass.

I don't know why I saw 3 ampere idle current mentioned somewhere on the web, it draws about 0.9 / 1 ampere at idle.
Current-draw wise, it's not very efficient. It draws a little more current than I am used to at certain listening levels. That doesn't bother me at all, though, especially on its intended mid-range use in 4 ohms stereo.

Would definitely like to modify the 2 volt gains into approx. 5 volt gains if possible.
Also, does anyone sell the gold (speaker) screws for these ? I am missing one and one other is not in good condition.
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Old 8th October 2011, 11:02 PM   #5
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Well it sound like you have a keeper. Bias is max rated at 3 amp at 12 volts supply and this is in high bias SQ mode. You can live with it at 1 amp if there is no distortion on a scope, and the SQ is acceptable to you. Higher bias will equal higher heat on the sink. Your call though...

To change the input voltage you will need to either alter a feedback resistor in the input gain circuit to change its overall gain or just build a simple voltage divider across the input. First op-amp is input buffer only, second stage is 0 to 20 DB gain with adjustment to the feedback of the op-amp, and the last op-amp stage is bass boost and output buffer to the main amp thru a 33 ufd 16 volt cap. The input RCAs also have a 33 ufd 16 volt cap just behind the RCAs.

There is a VI limiting mod for these requiring that R138, R139, R238, and R239 be changed to 2.7 K ohm. You might want to check yours to see if it is there or not. Original part call out is 6.8 K ohm. I have no reference to weather this was for SQ or reliability. Sounds like you could figure that out though.

PG used Panasonic FC caps but they still leaked on the input 12 volt side. A simple white paper under the cap should show you if its leaking or not. Or just be safe and replace them every two to five years of service. You can try higher voltage caps to see if it helps some like 25 or 35 volt versions. PG used 16 volts versions and I feel this is a bit low although functional I feel a 15% margin is advisable at minimum. so add 15% to the 16 or 25 volts is the next voltage range up. PG ran exact ratings on most all their power supply caps, so if it was rated at 35 it most likely saw 35 volts in normal operation. I am a fan of 15 to 25% margins on caps, but this is just my opinion and my training long ago.

I suggest you find stainless set screws and be done wroth the search for them. They are metric as i recall but you may have a early addition and they were US standard inch measurement.

Check your DC offset voltage across the speaker terminals with no RCAs and signal and no speakers. And let me know what you read in DC milli-volts. I am partial to seeing less then 10.0 MVDC for my personal choices of acceptable. But it is not uncommon to see 25 MVDC on these with age. It is usually the input Diff pairs 2SC2389 and 2SA1038, and you can also find leakage issues with the first large transistor pairs 2SC 4323 and 2SA1360. The later run rather warm to the touch and I like to move them to underneath the PC board with kapton insulators so they rest against the sink body. They also track the amps heat better this way and you will usually see marked improvement with DC offset track with heat loading.

Well that's enough to start you with for now. Re-post any findings you have and I will do my best to help you out....C
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Old 9th October 2011, 08:42 AM   #6
azvrt is offline azvrt  Netherlands
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Thank you for this huge amount of information. I will definitely get back to you on the DC offset.

I find the first part very interesting but I do not fully understand. You refer to high bias SQ mode. Are there different 'modes' on this amplifier ? Is it a high bias amp such as the Soundstream Class A ?
On the SS amps I can set the bias. Are you telling me I could raise the idle current on the MPS for even better sound quality ? Sound quality is what I am after, not power.

This amp will be run in 4 ohm stereo on some 4 inch mids so I doubt it will get too hot, even at a 3 ampere idle current. I might be using fans anyway since I will be using high bias amps from Genesis and Soundstream along with this one. Please tell me how to proceed !

I am planning to buy a second PG as I like to have spare amps of the ones I am using. I thought of buying a MS-275 since it will have more power in 4 ohm stereo. Lower impedances are not interesting to me on my mids.
But if the 2240 is a high bias amp, the MS-275 might not sound the same. Someone at the PG forum is telling me that they do sound the same (except for differences caused by power/headroom differences, obviously).

I'll definitely have a look at those caps and try and replace them with higher voltage caps. Would it be useful to use caps with more uF's ?
The screws might very well be metric.

I have a hard time understanding the technical information you provided regarding the input gains. I'll let my father read through it, he'll probably understand better.

Thanks again for all the information, I really appreciate it. Please get back to me on that bias/idle current/SQ thing I am REALLY interested to know more.
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Old 9th October 2011, 09:06 AM   #7
marko is offline marko  United Kingdom
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as always a very good read and very good in depth explanation from Cecil (how are you by the way?)

Fred, I think I can slowly convert you to a PG fanatic
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Old 9th October 2011, 09:14 AM   #8
azvrt is offline azvrt  Netherlands
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Quote:
Originally Posted by marko View Post
Fred, I think I can slowly convert you to a PG fanatic
You already have, Luke, you already have...

I have decided to use the Soundstream Class A's on my highs, bass and sub.
For my mids I will be using Genesis Series 2 Class A and this PG.

If it turns out I can set the idle current ot this MPS, then I shall truly be in heaven.

Marko,
I am thinking of replacing my Boston Pro mids and Dynaudio MW160 midbass by Altecs and go for a full Altec install, except for the Dynaudio tweeters and Kef sub, of course. But I might leave the Bostons and Dyns in there and just use Altecs for my front mids and rear ovals. Little off topic sorry.
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Old 9th October 2011, 04:14 PM   #9
azvrt is offline azvrt  Netherlands
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Right speaker output 37.1 mVDC
Left speaker output 28.4 mVDC

I saw some orange adjustable potentiometers for each channel. Does this mean it is a high bias amp such as some of the Soundstreams ?

The idle current is 1 ampere, like I mentioned. How exactly do I get the idle current up for optimum SQ ?

I also saw the S4 switch was never installed, S3 is there. What are they for ?

The R138/139/238/239 are 6.8 kOhm.

Last edited by azvrt; 9th October 2011 at 04:28 PM. Reason: additionial information
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Old 9th October 2011, 08:44 PM   #10
azvrt is offline azvrt  Netherlands
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Ah I see from pictures of boards on the internet that the MPS-2240 does not have the S4 switch in the center of the board, the MS-275 does.

I can currently buy a MS-275 over here for a pretty good price. Does it sound the same as the MPS-2240 ? I'd like to have a spare amp with near-identical sound.
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