Pioneer sx-1250 help needed

[SaturationPt]

Look at the Martin Logan spec above: they (each speaker) produce 89dB (Decibels, sound level) at 2.83V (volts) measured at 1meter away from the speaker, on-axis (straight in front).

So what this shows you is that voltage is sound level, a direct relationship.

Your volume knob setting is amplification, which is voltage output, So the same amplifier, set at the same volume knob level (lets say for illustration purposes the 9:00 position is 2.83V output which is the abovementioned 89dB) should give you the same amplification and same voltage output regardless of the speaker load, and if all speakers are the same efficiency then all will be 89dB at 9:00 on the volume knob. If a less efficient speaker (80dB for example), less volume.

This relates to watts in the following way:

To calculate power required, you need to know the load. A higher reactance (ohms) will give you a lower power requirement, so an 8ohm load will require half the current and therefore half the power (watts) to run at the same voltage as the 4ohm speaker.

If you have two speaker systems, which are both 89dB at 2.83V, one (the Marties) is a 4ohm speaker and the other an 8ohm speaker, the 4ohm speaker will require approximately twice the power (watts) at that voltage / sound level, but the same volume knob setting.

The amplifier's power rating is the maximum power that it can produce. A higher power amplifier usually has a higher voltage at its maximum setting (which is also a higher volume), and also a higher current (current times voltage equals watts or P=I x E). Thus an amplifier with higher current, higher voltage, or both will be rated at a higher wattage output.

Most amplifier/speaker pairings run out of current before running out of volume-knob rotation. You might hit your maximum clean output at the 12:00 (or less) point and anything above that starts to become clipped or distorted. Just having more volume knob rotation left doesn't necessarily mean that you have more power available if you are already at the current limit of your amplifier.

The Engineer's version is more complicated in all of the other factors involved, this is the simple version which I believe answers your question.

 

[joehernandez]

Look at the Martin Logan spec above: they (each speaker) produce 89dB (Decibels, sound level) at 2.83V (volts) measured at 1meter away from the speaker, on-axis (straight in front).

So what this shows you is that voltage is sound level, a direct relationship.

Your volume knob setting is amplification, which is voltage output, So the same amplifier, set at the same volume knob level (lets say for illustration purposes the 9:00 position is 2.83V output which is the abovementioned 89dB) should give you the same amplification and same voltage output regardless of the speaker load, and if all speakers are the same efficiency then all will be 89dB at 9:00 on the volume knob. If a less efficient speaker (80dB for example), less volume.

This relates to watts in the following way:

To calculate power required, you need to know the load. A higher reactance (ohms) will give you a lower power requirement, so an 8ohm load will require half the current and therefore half the power (watts) to run at the same voltage as the 4ohm speaker.

If you have two speaker systems, which are both 89dB at 2.83V, one (the Marties) is a 4ohm speaker and the other an 8ohm speaker, the 4ohm speaker will require approximately twice the power (watts) at that voltage / sound level, but the same volume knob setting.

The amplifier's power rating is the maximum power that it can produce. A higher power amplifier usually has a higher voltage at its maximum setting (which is also a higher volume), and also a higher current (current times voltage equals watts or P=I x E). Thus an amplifier with higher current, higher voltage, or both will be rated at a higher wattage output.

Most amplifier/speaker pairings run out of current before running out of volume-knob rotation. You might hit your maximum clean output at the 12:00 (or less) point and anything above that starts to become clipped or distorted. Just having more volume knob rotation left doesn't necessarily mean that you have more power available if you are already at the current limit of your amplifier.

The Engineer's version is more complicated in all of the other factors involved, this is the simple version which I believe answers your question.

Thank you very informative . Definitely gives me a better understanding . So if a amp says it's capable of 200 watts at 8 ohms it should mean that we will be giving more current and voltage to the speaker than with an amplifier rated at 100 watts at eight ohms .
Now why do some double down into 4ohm and some don't and is that what to look for to be able and tell which amp can really deliver more current and volts ? How it acts in 4ohms and lower impeadeance . Is there other specs I should look at to be able to tell what an amp is capable of in terms of power .

 

[SaturationPt]

Q1: If the amp is capable of 200watts at 8Ohms, it is capable. The power that it will deliver into a speaker is identical to the power that a 100w (capable/rated) amp will deliver at that same volume.

Look at it like a light bulb. The outlet is capable of a 1500watt bulb, how much power is delivered depends on the bulb, not the socket (a 100w bulb will draw 100w, a 40w bulb will draw 40w).

Q2: There are various reasons why an amplifier might have a significantly higher power rating at 4Ohms than it does at 8Ohms. In many cases it is a function of the amplifier's design, in other cases it's a function of the weakest link limiting the output. This gets into a much larger discussion involving how amplifiers are (and were) rated: some are rated for music (or pink noise) power, both channels driven simultaneously, continuous. Other amplifiers are rated in what I like to refer to as car-stereo watts: a very short 1000hz tone burst into one channel only. You can see that running both channels at all frequencies continuously will require a more stout power supply than a short burst on one channel which can pretty much be handled by a capacitor's stored energy, and the single frequency vs all music also is a cheat of sorts. Continuous output requires the entire chain of components to be able to produce the power and dissipate the heat continuously, a short burst will probably not overheat anything.

Where double the power at half the impedance is a good measure of an amplifier's current capacity in some cases and designs, it isn't always the rule.

An example that does NOT follow is transformer / autoformer outputs. In a tube amplifier, the output rating (watts) is pretty much the same regardless of speaker impedance, there are often transformer taps for 4, 8, and 16Ohm. Same goes for McIntosh solid-state amps that employ an autoformer output, ... same power rating on all taps / impedances.

An example that does follow is an Onkyo Integra amp I used to own which had roughly double the watt output at 4Ohms that it had at 8Ohms. That amp had a marvelous current capacity and was designed with a lower gain (less voltage/volume at full-volume knob setting) than other amps I have owned, but it would run low impedance loads very happily. Another example might be a pair of ADCOM GFA-535 amps I have which are rated 60wpc at 8Ohms, 100wpc at 4Ohms, ... and I am pretty sure that driving both channels doesn't affect the output since it has completely separate L&R power supplies.

So: yes, no, and maybe. Clear as mud?

 

[toxcrusadr]

Can u explain this better , 1.5 ohms at 20 kHz ?

Speakers have a 'nominal' impedance rating, 4 ohms, 8 ohms etc. but this is an average over the audio spectrum, or in some cases a minimum. The impedance will go up and down from 20-20,000 Hz. The important thing is that it does not dip too low, especially in places where a lot of power would be required for a high volume note - such as in the bass range. People talk about certain speakers being 'difficult to drive' and those often have a dip somewhere to a very low impedance.

I have not run into a speaker that has a dip that low at high frequency. Unusual. BTW 'difficult to drive' speakers are often the expensive high performance ones, and the designers figured that if you can afford the speakers you can afford a high power amp to drive them. So they are able to trade off an impedance dip for higher performance, whereas a mass market speaker should be a little more tame and able to work OK with a variety of amplifiers.

 

[markthefixer]

Thank you very informative . Definitely gives me a better understanding . So if a amp says it's capable of 200 watts at 8 ohms it should mean that we will be giving more current and voltage to the speaker than with an amplifier rated at 100 watts at eight ohms .
Now why do some double down into 4ohm and some don't and is that what to look for to be able and tell which amp can really deliver more current and volts ? How it acts in 4ohms and lower impeadeance . Is there other specs I should look at to be able to tell what an amp is capable of in terms of power .

BTW 'difficult to drive' speakers are often the expensive high performance ones, and the designers figured that if you can afford the speakers you can afford a high power amp to drive them.

Quite true.

We (and I) are talking about class AB power amps.

This can get technical and sticky quickly. But an amp designed to deliver the voltage and current loads expected using 8 ohm speakers, will dissipate tremendous amounts of heat when trying to deliver a much lower voltage at a much higher current into a very low ohmage speaker.

Quite frankly the amplifier must be matched to the load. A low impedance load is a current load, without needing a lot of voltage to push it across the wires. The extra rail voltage in the power amp needed to push that power up into 8 ohms in the same amp delivering it to 2 ohms has to be dissipated as heat.

I couldn't find an old thread that illustrated the extra heat dumped in the heat sinks when an 8 ohm load was switched to a 4 ohm load for the same power (like cutting in an extra set of 8 ohm speakers in parallel). It could easily overwhelm the internal heat sinking of some amplifiers, burning up the outputs if the load resistance dropped any lower (demanding even MORE current). No to mention that the current requirements MAY not be able to be met by the power transformer in the unit.

 

[joehernandez]

Q1: If the amp is capable of 200watts at 8Ohms, it is capable. The power that it will deliver into a speaker is identical to the power that a 100w (capable/rated) amp will deliver at that same volume.

Look at it like a light bulb. The outlet is capable of a 1500watt bulb, how much power is delivered depends on the bulb, not the socket (a 100w bulb will draw 100w, a 40w bulb will draw 40w).

Q2: There are various reasons why an amplifier might have a significantly higher power rating at 4Ohms than it does at 8Ohms. In many cases it is a function of the amplifier's design, in other cases it's a function of the weakest link limiting the output. This gets into a much larger discussion involving how amplifiers are (and were) rated: some are rated for music (or pink noise) power, both channels driven simultaneously, continuous. Other amplifiers are rated in what I like to refer to as car-stereo watts: a very short 1000hz tone burst into one channel only. You can see that running both channels at all frequencies continuously will require a more stout power supply than a short burst on one channel which can pretty much be handled by a capacitor's stored energy, and the single frequency vs all music also is a cheat of sorts. Continuous output requires the entire chain of components to be able to produce the power and dissipate the heat continuously, a short burst will probably not overheat anything.

Where double the power at half the impedance is a good measure of an amplifier's current capacity in some cases and designs, it isn't always the rule.

An example that does NOT follow is transformer / autoformer outputs. In a tube amplifier, the output rating (watts) is pretty much the same regardless of speaker impedance, there are often transformer taps for 4, 8, and 16Ohm. Same goes for McIntosh solid-state amps that employ an autoformer output, ... same power rating on all taps / impedances.

An example that does follow is an Onkyo Integra amp I used to own which had roughly double the watt output at 4Ohms that it had at 8Ohms. That amp had a marvelous current capacity and was designed with a lower gain (less voltage/volume at full-volume knob setting) than other amps I have owned, but it would run low impedance loads very happily. Another example might be a pair of ADCOM GFA-535 amps I have which are rated 60wpc at 8Ohms, 100wpc at 4Ohms, ... and I am pretty sure that driving both channels doesn't affect the output since it has completely separate L&R power supplies.

So: yes, no, and maybe. Clear as mud?

Ok let's see if Iam following correctly.

The amplifier is the outlet the speaker is the bulb , what determines the power required ?The volume set at and the type of music being played ?
Is It the type of music that causes the dips and power requirements ? Or is it the ohm rating of the speaker ?

Next , any amp employing transformer/autoformer keep same power rating regardless of speaker impeadeance .
Is this because you are able to match the impeadeance from the output of the amp with the impeadeance of the speaker ? So if it's a 200 watt amp , you get 200watts period 8ohm 200watts , 4ohm 200 watts ?

I always wondered how car stuff had such high ratings.

I feel like I'm missing something. I know speakers have different impedance but I also hear about drops to 2 ohms or from 8 to 4 ohms , what causes these fluctuations ?

 

[SaturationPt]

Wow, one at a time!

The bulb and socket analogy is with the same music, same volume, same speakers, ... on two different amplifiers. The point was that the power output of any amplifier will be the same in this situation.
But your new question is asking more. Yes more volume will require more power, yes some types of music (and passages) will require more power than others. The "ohm rating of the speaker" is also a factor, but that is more of a compatibility than a straight power requirement as efficiency plays a bigger part.

As far as I know all transformer/autoformer output amplifiers have one power rating regardless of which tap is used. However, I only have experience with a few tube amps and McIntosh solid-state, there might be someone out there that does not follow this rule, I don't know (and you should look at the specs of any amplifier specifically, not just general rules).

Car stuff, and cheaper home audio, even some low-line "pro" gear.

The nominal rating (ex: 8ohms) is what is usually published, some high-end speakers also publish minimum. Amplifier ratings are usually also nominal. The dips and fluctuations are complicated but for a simplified overview you need to understand that the speaker "ohms" are total impedance, not straight resistance. This includes the inductive reactance combined with the resistance, and this varies. If you measure the resistance between the speaker terminals you will likely get a number that is different than the rating because you are only able to measure DC resistance.
In a speaker assembly, you have 2, 3, or more speaker drivers. These drivers are put in parallel at crossover frequencies, which also contributes to the dips in impedance throughout the frequency range. Someone here likely has a graph of a speaker's impedance vs frequency which will help to illustrate this. Anyway, this is the short version and you can spend days reading speaker and crossover design papers to truly understand, ... I think I used to back in my Engineering days, ...

For speaker selection however, you simply match the speakers' nominal impedance to the amplifier's ratings and approved load impedance, and IMO it is usually good to go significantly higher in power rating than you appear to need (to prevent clipping and provide enough capacity for proper "headroom" and dynamics). Everyone has their opinion on this, mine is just one of those many.

 

[jobrewer1983]

I need to learn about specs better

We all had to do some research at one point or another, and as MTF said, others can wall/assist you through the process.

Im a member of other Audio threads, (Lansing, and a few others), but i have to say AK has been the most helpful in info gathering.

And the Pioneer thread is on point, do your research but also dont be hesitant to ask questions on the site!

Kind Regards,
John

 

[KingBubba]

The importance of understanding amplifier current and speaker impedance is because it can be very easy to destroy an amplifier if a very low impedance load is applied to it. I think of an automobile motor as a comparison. When a car's motor is run on its wheels and has a well designed exhaust system, the motor has the proper amount of load on it and will operate safely. If you were to remove the exhaust system and put the transmission in neutral and then start to rev the motor, the motor has nothing, in the way of a load on it, to keep from over revving it when a lot of pressure is put on the accelerator pedal. In this situation, with no, or very little load on the engine, the engine could just rev itself until it blew itself up.

With an amp, the less of a speaker load placed on the amp is like the motor which is in neutral with no exhaust. The amp could literally blow itself up, if you put too low a speaker load on it. Some amps are not able to handle a load as low as 4 ohms. The same would apply if you put an 8 ohm speaker on A and another 8 ohm speaker on B and ran them both at the same time, because two 8 ohm speakers equal a 4 ohm load. This is just an average of what the impedance will be because speakers are are a live load, not a static load, like a resistor. With a variable like music being sent to the speaker the amp will be seeing a variable load that is not possible to determine. Because of this variability, you have to be able be careful with the speaker load placed on the amp and make sure it is not two low for the capability of the amp. I hope this give a little clarity to a very complicated subject.

 

[joehernandez]

thx for all the info , need to do some reading up when I can

 

[deltalight]

One of the MOSFETs in the RF Front End is out. Could be the LO (local oscillator) as well.

 

[joehernandez]

One of the MOSFETs in the RF Front End is out. Could be the LO (local oscillator) as well.

So you think this is what's wrong with my unit ? Would you be able to show me these parts on a pic ?

 

[goat67]

One of the MOSFETs in the RF Front End is out. Could be the LO (local oscillator) as well.

This is at best a wild ass guess. Without checking voltages to the board how can you possibly say this is what is wrong?

To the OP I think you should look at getting someone to repair the power supply board as Mark suggested. Better yet have this unit service by someone who knows what he is doing.

I have a 5590 that I restored and I enjoy it greatly.

 

[joehernandez]

I should be able to check voltages without destroying anything I have a meter , just need to know where to check and what setting to put meter .

 

[zebulon1]

Have you checked any voltages yet?

This is also a good spot to mention (Which I've been wanting to for a time) a story of a friend: Well a colleague who goes through amps. He was explaining to me his Yamaha M-70, C-60 set up that he just dragged out of storage. Had it new while in the Service and said he liked it loud. The next week was complaining of the amp cutting out and finely never came back on. I said use my Phase Linear 400 until you get the M-70 fixed (I don't have time to mess with his stuff). He wanted me to come over and listen to the PL in operation, apparently he liked it. I stopped by and was floored at what he considered good sounding music! He had the PL 400 running with the meters at 3/4 throttle connected to three sets of speakers playing a Led Zeppelin YouTube video. Holy cow, the house was bouncing on the foundation. Said he had to have the house fan blowing on the back to help keep it from glowing. He would listen at that level for hours. By the way, the 400 is quasi, loaded with the MJ15024's and was an early version with the limited cooling fins. I didn't want to give him my good stuff.
This is first hand experience in what some these amps can do. I think we (Most of use here on these forums) baby our equipment compared to some.

 

[goat67]

I should be able to check voltages without destroying anything I have a meter , just need to know where to check and what setting to put meter .

Get the service manual. Read it. Then find the diagram and schematics of the power supply board. We can go from there.

 

[joehernandez]

Haven't had a chance to check voltages yet it's u will check manual and diagrams then I will get back.

 

[rcs16]

Unfortunately the tuner section is kaput , nothing at all ! fm and am don't work.

That should be your first clue. Check the 13.5VDC reg first, then trace your 13.5VDC supply through the switches. As MTF suggests, might need a PS rebuild.

The good: The 1250 is super easy to work on...

The RF front end is all hand assembled, point to point wiring, with no circuit boards. Difficult to repair if it is that. You have to determine where you lose the signal through the stages. Determine if the prob is the PS or the RF front end or IF. Lets hope it is just a PS/switch issue.

 

[joehernandez]

Quick update guys, I haven't bothered trying to restore tuner yet cuz I have been using my sonos / tune in radio for radio stations and that works great . Eventually I will get around to having it fixed but it's on the back burner for now since I basically have a tuner .
Also I recently purchased a rega planar 2 turntable it's a real nice table but If I put up the volume before I start playing any music , like almost halfway i hear hum ? So I don't really hear it while playing music , well at least not yet cuz I haven't cranked it but it bothers me knowing that's going on in the background and could possibly be a problem. Any suggestions on how to get rid of this ? I read somehwhere that rega uses the left rca I think for grounding