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 !
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 !
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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.
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.
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
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
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.
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.
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.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.
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.
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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.
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.
The MS-275 and the MS2240 are the same audio channel wise, with the only difference being the bias setup for low ohms and the power supply rails are lower voltage < I.E. different power supply toroid windings >, and the last op-amp stage on the front end has a different gain to drive the amp correctly for low ohm operation as I recall. Personally i would use the MS-275 for your 4 ohm loads, and bias it to your liking as long as you don't exceed the factory max spec of three amps at 12.0 VDC. The MS-275 will give you slightly better headroom then the low ohm amps will due mostly by design the low ohm amps were made for very low ohm loads, so they turn on into 2 and 1 ohm loads very well. but if your running 4 ohms I don't see why you need the low ohm capability. The MS-275 has the 2 ohm/ 4 ohm switch so you can optimize it for 2 ohms if need be.
Optimum SQ:
Well start by using a scope to see your sine waves. Then if your not exhibiting a any glitches near the zero crossover point then your good to go for that sort of distortion issue. Next I would try to make sure both channels have the same amount of Bias, while not observing any crossover notches on the scope. Then you can raise then as you like as long as you don't exceed the factory spec, and or observe the bias cause the idle current to peg you power supply, then your way too far high. If you decide to run high bias on any amp you should bench test it for a day under load to make sure you have not exceeded any safe margins. The amp you might save might be your own in this case. here again if your not comfortable doing these things ask questions, or search the web for info and advice. I am not the final word here, You and you willingness to learn and search for info set your limits.
Resistors mentioned:
All of this era of PG amps used VI limiting < Voltage-Current Limiting on their output stage. It was there to keep the amp in its sweet spot or SOA so it would survive some of the things people do when no one is looking. Some folks say they can hear VI limiting in the audio when it is operating limiting the amp from destruction. Hence why I am not sure if the resistor mod is for SQ or reliability. but is only on the low ohm amps as far as I can tell. < so it might be SQ, or it might be Survival at load... I have not taken time to test the change using Spice modeling to see it results >...
Bias:
Biasing outputs is not a big deal, but it is important if you want the amp to run correctly and not have crossover distortion at the output. You can measure the V drop across each of the large gray resistors near the outputs of your amp. They pretty much should all read the same. If not you may have issues. On a amp like this where one set of output pairs are used its really not a big deal unless your N and P transistors draw different bias voltage drops. As I said above they should read pretty much the same. If not then your outputs may not be well matched as a pair.
In amps like old PPI, SoundStream, and Orion where you got dozens of outputs all banked together then this voltage measurement becomes critical to the survival of the amp.
SoundStream would measure each V drop across each Emitter resistor to find where the output stage did not balance properly, and would swap even good reading outputs till a balanced / matched output stage was gained. Current sharing on amps with more then one set of output devices is important as all the output devices should carry a even share of the load or the amp will die a short and sudden death, even fresh off the bench.
If your not sure how to set bias Voltage and read V drop voltage then ask or search for info till you feel good about going this deep into this or any amp.
DC Offset:
Your DC offsets are beyond my limits of acceptability for a repair coming off my bench. But your amp is still functional, so its your call weather or not to clean them up to my level of expectations or not. It is most likely the transistors I mentioned above, and is completely repairable for less them $10.00 US in parts.
The last M-100 I did had been damaged while it was being tested by XXX. All that failed was a set of Diff Input pairs. And these parts are widely still available from MCM, Digi-Key, Mouser etc..I suggest you use Octopart to search for your needs online, I do...
Marko , my friend, How be you my brother? I am still typing as you can see. trying to spread my seeds as much as possible
...It's nice to hear from Marko, you know how to reach me so don't be shy.....CThank you once more for the information, I appreciate it.
Regarding the bias setting, here is a picture of how to set measure and set the bias for one channel of a Ref Picasso.
I have done it many times on several SS amps such as Renoirs, Picasso's, 10.2's etc.
In some caes the bias was somehow way off.
Could you please indicate where to measure it on this picture of a MS-275 ?
I guess it should not be that much different for a MPS-2240 ?
I did indicate the right pots, right ?
Regarding the resistors, if I understand correctly mine has 6.8 kOHms while some revisions have 2.7 kOhms ? Should I leave it this way ? I'll try and find more info on the matter, but you seem very knowledgeable.
Regarding DC Offset:
The parts you mentioned would be the "input Diff pairs 2SC2389 and 2SA1038" and the "first large transistor pairs 2SC 4323 and 2SA1360". Replacing these might solve the matter ? Would you happen to have the schematics of this amp ?
Thanks again.
Regarding the bias setting, here is a picture of how to set measure and set the bias for one channel of a Ref Picasso.
An externally hosted image should be here but it was not working when we last tested it.
I have done it many times on several SS amps such as Renoirs, Picasso's, 10.2's etc.
In some caes the bias was somehow way off.
Could you please indicate where to measure it on this picture of a MS-275 ?
I guess it should not be that much different for a MPS-2240 ?
I did indicate the right pots, right ?
An externally hosted image should be here but it was not working when we last tested it.
Regarding the resistors, if I understand correctly mine has 6.8 kOHms while some revisions have 2.7 kOhms ? Should I leave it this way ? I'll try and find more info on the matter, but you seem very knowledgeable.
Regarding DC Offset:
The parts you mentioned would be the "input Diff pairs 2SC2389 and 2SA1038" and the "first large transistor pairs 2SC 4323 and 2SA1360". Replacing these might solve the matter ? Would you happen to have the schematics of this amp ?
Thanks again.
Your pictures did not load well and when blown up they simply went too blurry to do much with.
But from what i could make out the bias pots on the MS amp are pointed to. So your correct there.
If you look under the big speaker cables you will see the only 4 large resistors to be seen near the outputs they are the resistors you need to read Bias Voltage off of. Careful with your meter probes the gold circuit board will short easily if your probes slips, I like to use the wires on the resistor as test points to avoid flash marks, or simply use test clips of a suitable size and clip on to measure the V drop.
I uploaded a simple file from a old friend of mine. You might recognize the circuit design. Please no names in this matter. The voltmeter probes placement will tell you the total bias for both the outputs of that pair only. You must measure each pair and or each device individually, I measure each resistor independently to qualify that each device acts the same. This should guide you well enough on ANY amplifier you work on.
DC offset:
yes you have the correct transistor info and the course I would go about resolving your high DC output from the amp channels.
As I said before I have not qualified the resistor mod to the VI limiting it was simply marked on the info I do have access to. So play with this factory info at your own risk. Or simply just ignore it if your happy with what you have.
As for schematics:
Well I am not guessing about all this info, but I have been servicing these amps since they hit the market. During my many encounters over the years with many of the manufacturers any info I may have picked up came at the cost of a promise of not distributing it around the world or on the web. I am still bound by this promise, and I hope you understand....
I did find this hand drawn schematic of a MS-275 over on a forum located In England as I recall, perhaps you can find it helpful. It's not copyright to my knowledge as so it is safe to post it openly on the web as i found it on the web. It's close enough to guide you thru most any MS amp you might look at since they were all laid out on the same topology. Please be advised that PG made critical changes in certain component values between each amp design so don't hold the resistors values to the highest degree of integrity. As i explained in the earlier post the power toroid windings will be different along with the rail supply voltage, and the gain of the last op-amp stage just before the main discrete amp channel....Hope this helps some, its the most I can post without angering the wrath of the many friends I made over the years.....C
But from what i could make out the bias pots on the MS amp are pointed to. So your correct there.
If you look under the big speaker cables you will see the only 4 large resistors to be seen near the outputs they are the resistors you need to read Bias Voltage off of. Careful with your meter probes the gold circuit board will short easily if your probes slips, I like to use the wires on the resistor as test points to avoid flash marks, or simply use test clips of a suitable size and clip on to measure the V drop.
I uploaded a simple file from a old friend of mine. You might recognize the circuit design. Please no names in this matter. The voltmeter probes placement will tell you the total bias for both the outputs of that pair only. You must measure each pair and or each device individually, I measure each resistor independently to qualify that each device acts the same. This should guide you well enough on ANY amplifier you work on.
DC offset:
yes you have the correct transistor info and the course I would go about resolving your high DC output from the amp channels.
As I said before I have not qualified the resistor mod to the VI limiting it was simply marked on the info I do have access to. So play with this factory info at your own risk. Or simply just ignore it if your happy with what you have.
As for schematics:
Well I am not guessing about all this info, but I have been servicing these amps since they hit the market. During my many encounters over the years with many of the manufacturers any info I may have picked up came at the cost of a promise of not distributing it around the world or on the web. I am still bound by this promise, and I hope you understand
....I did find this hand drawn schematic of a MS-275 over on a forum located In England as I recall, perhaps you can find it helpful. It's not copyright to my knowledge as so it is safe to post it openly on the web as i found it on the web. It's close enough to guide you thru most any MS amp you might look at since they were all laid out on the same topology. Please be advised that PG made critical changes in certain component values between each amp design so don't hold the resistors values to the highest degree of integrity. As i explained in the earlier post the power toroid windings will be different along with the rail supply voltage, and the gain of the last op-amp stage just before the main discrete amp channel....Hope this helps some, its the most I can post without angering the wrath of the many friends I made over the years.....C
Together with my father we did the bias check and set yesterday.
Thanks for pointing out the large resistors, and the diagrams you provided were also helpful.
The amplifier drew about 0.8 ampere. When measuring the bias in mVDC, it was very low.
We raised it to about 26 mVDC for each channel. Mathing it for each channel was not easy as the pots were very sensitive. The bias keeps raising slowly but surely for a longer period of time while the amp warms up, so the 26.5 mVDC probably ended up higher.
Anyway, with these settings, instead of idling at 0.8 ampere, the amplifier starts up with drawing about 1 ampere, and steadily rises to 2 ampere where it stops rising.
This is at 14 volts (we set the bias at 14 volts to be sure we don't set it too high), though the idle current doesn't differ that much between 12 or 14 volts. Above 14 volts, it does affect idle current much more, but in the trunk voltage will probably never exceed 14 volts, probably a little less.
I think with the 3 ampere max idling you mentioned, we should be on the safe side with our 1.9 / 2 ampere. We checked with the oscilloscope and a 100 Hz and 2 kHz test tone, no clipping could be detected in 4 ohms stereo until the amp reaches it's max rated power, of course.
I think I will receive the MS-275 this friday / saturday and will repeat the procedure.
We had to be very careful not to cause any short circuit with our multimeter's grippers on the resistors on this particular board, but all went well.
Soon I might also own a MS-2125 with one channel not producing sound, so prepare yourself
Thanks again for your invaluable help. I might leave the gains the way they are as the noise floor on my Altec speakers is acceptable, so I can simply turn the fader of my Alpine ERE-G190 down for this particualr amplifier, so I don't have to raise the gains of my 5 volt gains amplifiers to match this one. If the noise floor is as low as it was when I checked it yesterday (had to put my ear very close to the speaker to detect it), it'll be fine in the car.
I'll check the DC offset for the 275 once I receive it, and again on this 2240 with the new bias settings (don't know whether that affects the DC offset but I'll soon find out), and I'll probably replace all parts you mentioned to put the amp(s) back into tip-top condition.
Thanks for pointing out the large resistors, and the diagrams you provided were also helpful.
The amplifier drew about 0.8 ampere. When measuring the bias in mVDC, it was very low.
We raised it to about 26 mVDC for each channel. Mathing it for each channel was not easy as the pots were very sensitive. The bias keeps raising slowly but surely for a longer period of time while the amp warms up, so the 26.5 mVDC probably ended up higher.
Anyway, with these settings, instead of idling at 0.8 ampere, the amplifier starts up with drawing about 1 ampere, and steadily rises to 2 ampere where it stops rising.
This is at 14 volts (we set the bias at 14 volts to be sure we don't set it too high), though the idle current doesn't differ that much between 12 or 14 volts. Above 14 volts, it does affect idle current much more, but in the trunk voltage will probably never exceed 14 volts, probably a little less.
I think with the 3 ampere max idling you mentioned, we should be on the safe side with our 1.9 / 2 ampere. We checked with the oscilloscope and a 100 Hz and 2 kHz test tone, no clipping could be detected in 4 ohms stereo until the amp reaches it's max rated power, of course.
I think I will receive the MS-275 this friday / saturday and will repeat the procedure.
We had to be very careful not to cause any short circuit with our multimeter's grippers on the resistors on this particular board, but all went well.
Soon I might also own a MS-2125 with one channel not producing sound, so prepare yourself
Thanks again for your invaluable help. I might leave the gains the way they are as the noise floor on my Altec speakers is acceptable, so I can simply turn the fader of my Alpine ERE-G190 down for this particualr amplifier, so I don't have to raise the gains of my 5 volt gains amplifiers to match this one. If the noise floor is as low as it was when I checked it yesterday (had to put my ear very close to the speaker to detect it), it'll be fine in the car.
I'll check the DC offset for the 275 once I receive it, and again on this 2240 with the new bias settings (don't know whether that affects the DC offset but I'll soon find out), and I'll probably replace all parts you mentioned to put the amp(s) back into tip-top condition.
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Hmm I was saying we tested the amp in 4 ohms stereo with a test tone and checked for clipping with the oscilloscope. I don't know how my mind came up with 4 ohm stereo as no load was hooked up to the speaker output besides the oscilloscopes probes. What would the impedance be, then, in such a circumstance ? Just being curious.
Someone at the PhoenixGoldPhorum just told me where the bias should be measured on these amps, same location as you mentioned. But he mentioned 100 uVDC (0.1 mVDC) and that the amp should idle around 1 ampere. When we first measured the bias, before setting it, the bias was indeed very close to 0 mVDC and idling current was close to 1 ampere (0.8). Having set the bias over 25 mVDC, idling at 2 ampere, this information is kind of worrying now
Won't the amplifier damage itself at the bias we set it to, or would it already (immediately) have done so if it truly was to high ?
Someone at the PhoenixGoldPhorum just told me where the bias should be measured on these amps, same location as you mentioned. But he mentioned 100 uVDC (0.1 mVDC) and that the amp should idle around 1 ampere. When we first measured the bias, before setting it, the bias was indeed very close to 0 mVDC and idling current was close to 1 ampere (0.8). Having set the bias over 25 mVDC, idling at 2 ampere, this information is kind of worrying now
Won't the amplifier damage itself at the bias we set it to, or would it already (immediately) have done so if it truly was to high ?
Who are you talking to from the other forum ? If his advice is to your likely please do as he says.
Also I did not tell you to bias your amp at 25 MVDC. High bias is just about anything above what is required for the output stage to not exhibit crossover distortion across the 20 to 20K bandwidth and not exceed its distortion spec's, and deliver its rated power into load..
This amp was made to take heat loads of very low ohm's and since your not running it at those loads it should run fine. if not it will thermal cycle off to protect itself.
I quoted PG's info and amp brochure directly about the 3 amps draw at 12 volts DC test voltage. This is their MAX hot rated bias idle current draw. Hot rating requires a test load and a signal source to run the amps temp up to typical operating temps.
As for the spec of 0.1 to 0.2 MVDC of bias well if you have a scope and get 20 to 20K rated power and 250 Milli-Watts outputs with NO crossover distortion then so be it. You have successfully low bias'ed the amp at it minimum limits.
If you over bias the amp it will thermal cycle shutdown as it is designed to do that. If that person worked for PG then please take his advice. If he did not work for them please consider disregarding his input as not valid.
Also I did not tell you to bias your amp at 25 MVDC. High bias is just about anything above what is required for the output stage to not exhibit crossover distortion across the 20 to 20K bandwidth and not exceed its distortion spec's, and deliver its rated power into load..
This amp was made to take heat loads of very low ohm's and since your not running it at those loads it should run fine. if not it will thermal cycle off to protect itself.
I quoted PG's info and amp brochure directly about the 3 amps draw at 12 volts DC test voltage. This is their MAX hot rated bias idle current draw. Hot rating requires a test load and a signal source to run the amps temp up to typical operating temps.
As for the spec of 0.1 to 0.2 MVDC of bias well if you have a scope and get 20 to 20K rated power and 250 Milli-Watts outputs with NO crossover distortion then so be it. You have successfully low bias'ed the amp at it minimum limits.
If you over bias the amp it will thermal cycle shutdown as it is designed to do that. If that person worked for PG then please take his advice. If he did not work for them please consider disregarding his input as not valid.
No I fully trust you in this matter and have left the bias the way it is, resulting in the 2 ampere idle current. But you can imagine I got scared for a minute when I received contradicting information. I've been told in the past that with Soundstream amps, too high of a bias can result in damage and I just got nervous there.
But again, I appreciate your help a lot and will keep running the amp at this higher bias, especially since I do not plan running it any other way than in 4 ohms stereo.
I could probably lower the bias without having any distortion, but I like to have a high idling current, it fools me into thinking I have somewhat of a Class A amp
I'll probably receive the MS-275 tomorrow and will let you know the DC-offset on that one, and I will set the bias so that it draws about the same idling current as this one.
But again, I appreciate your help a lot and will keep running the amp at this higher bias, especially since I do not plan running it any other way than in 4 ohms stereo.
I could probably lower the bias without having any distortion, but I like to have a high idling current, it fools me into thinking I have somewhat of a Class A amp
I'll probably receive the MS-275 tomorrow and will let you know the DC-offset on that one, and I will set the bias so that it draws about the same idling current as this one.
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