RC-M70 12VDC jack

[Transistorized]

Rather than open a new thread, since this section pertains to M70 Voltage and power consumption, I wanted to ask here.

My parts M70 (which works) always seemed to my ears to be more powerful. Today I just noticed that its a RC-M70W not a RC-M70JW. The voltage selector on the M70W has 110V versus the M70JW which is 120V. Likewise the wattage consumption of the W model versus the JW model is 47W versus 40W.

I measured the wall voltage at my home and got a fairly steady 121.3V.

So am I correct that when powering my 110V 47W (M) coded M70 on 121.3V that it would push the amp chips a little harder than on my (JW) coded boxes and sound louder with harder hitting bass?.....or is this still all in my head?

 

[docs]

I think you are correct.

 

[Transistorized]

I think you are correct.

Thanks docs. My ears can be deceiving sometimes

 

[JVC Floyd]

Its like the m90 c versus the m90 jw , the jw is 61 watts and the m90 c is rated at 70 watts.

 

[Radio raheem]

what i don't get is the victor m90 is rated at 30w but it's as loud as any of them

 

[Superduper]

This wasn't ever an issue before about 20 years ago when eBay and the internet in general made importing stereos from abroad common. Back then, models that had different power requirements and specifications stayed in the country or region for which that product was intended. Now, we have all kinds of power input specs from 100V, 110V, 120V and 220/240V because stuff is coming from everywhere else but never intending to be used here. Essentially if you feed more voltage than what was intended, you will end up with more voltage to the circuitry. Anyone who's ever read a component datasheet for the amp modules knows that the power output that the chips are capable of increases with higher voltage (up to a point, before they go poof). Take for example the amp chip of the M70, the AN7145k (H). On the (H) chip only, the datasheet says absolute maximum is 24v (WITH NO SIGNAL). For the non-H chip, the datasheet says 20V operating voltage is max.

There is a fallacy that certain versions of the same boombox is more powerful (louder). This is true if you plug the boombox into higher voltage than it was intended for. If you plug the victor boombox (100v) into 120v, you'll get even more volume but it's not true that it's any more powerful, only that you are over-powering the unit. Now, if these things didn't blow up at that voltage, you'll get really loud boombox if you plug a 120v unit into 240v, but usually, if it even emits any sound at all, it might be nothing more than a peep before it emits smoke.

Now, if you go and measure the output at the M70 power supply (proper version for the region) when plugged in, I'll bet you'll find about ~18.5 volts +/- with no load which should drop with a load since the power supply for the amp module is unregulated. However, if we take the equation 120/110=1.09, that tells us that this boombox will experience 9% greater voltage from the transformer mismatch (to the mains). This boombox which normally has (18.5V) at the outputs of the PS when plugged into 110v will now see 20.18V if plugged into 120v. If your boombox has even more than 18.5v normally, you could begin to live dangerously. The components at greatest risk of overvoltage is probably the amp chips and the capacitors in that unregulated rails. In fact, there is another thread right now which stated his GF-9000 boombox, a 120v version was overpowered by 240v. Unquestionably in that case, the amp chips likely has fried. Much of a boombox circuitry is protected by voltage regulators so they possibly might survive, but if you double the voltage, forget it, something gonna go.

In short, is this 110v unit in trouble by plugging into 120v? Maybe, not, it's a 9% increase in voltage, and it's still likely barely within range of the component max, but it's on the fringe of recommended operating voltage. And it's not just the amp chips. Even the regulators will be stressed more because these regulators produce heat based on how much voltage is dropped. Ok, it's not really voltage that regulators are typically rated at, it's usually in watts sinked but there is a relationship. For example, if a tuner circuit requires 8v and the normal circuit voltage is 15v, the regulator will "sink" 7v. 7V x current consumed = watts, which is converted to heat. If the circuit voltage is 18v instead, it is now sinking 10v, which will result in greater watts (or heat generated). This introduces stress into the regulator and at higher voltages, at some point, the amount of heat generated will cause the regulator to fail unless heat management is taken into consideration (such as heat sinks, fans, etc). The problem is that whether or not any of these techniques are utilized depends on the original design, and in every case, the design will be for the power normal for that region.

So ideally, power your boomboxes using the proper voltage and if it's slightly off, use the boombox in moderation or retrofit the power supply to supply the proper output voltage.

 

[baddboybill]

Very interesting information!!! That is why I will never plug a 100v unit into our 120v and properly use my 120v-100v converter

 

[Radio raheem]

This wasn't ever an issue before about 20 years ago when eBay and the internet in general made importing stereos from abroad common. Back then, models that had different power requirements and specifications stayed in the country or region for which that product was intended. Now, we have all kinds of power input specs from 100V, 110V, 120V and 220/240V because stuff is coming from everywhere else but never intending to be used here. Essentially if you feed more voltage than what was intended, you will end up with more voltage to the circuitry. Anyone who's ever read a component datasheet for the amp modules knows that the power output that the chips are capable of increases with higher voltage (up to a point, before they go poof). Take for example the amp chip of the M70, the AN7145k (H). On the (H) chip only, the datasheet says absolute maximum is 24v (WITH NO SIGNAL). For the non-H chip, the datasheet says 20V operating voltage is max.

There is a fallacy that certain versions of the same boombox is more powerful (louder). This is true if you plug the boombox into higher voltage than it was intended for. If you plug the victor boombox (100v) into 120v, you'll get even more volume but it's not true that it's any more powerful, only that you are over-powering the unit. Now, if these things didn't blow up at that voltage, you'll get really loud boombox if you plug a 120v unit into 240v, but usually, if it even emits any sound at all, it might be nothing more than a peep before it emits smoke.

Now, if you go and measure the output at the M70 power supply (proper version for the region) when plugged in, I'll bet you'll find about ~18.5 volts +/- with no load which should drop with a load since the power supply for the amp module is unregulated. However, if we take the equation 120/110=1.09, that tells us that this boombox will experience 9% greater voltage from the transformer mismatch (to the mains). This boombox which normally has (18.5V) at the outputs of the PS when plugged into 110v will now see 20.18V if plugged into 120v. If your boombox has even more than 18.5v normally, you could begin to live dangerously. The components at greatest risk of overvoltage is probably the amp chips and the capacitors in that unregulated rails. In fact, there is another thread right now which stated his GF-9000 boombox, a 120v version was overpowered by 240v. Unquestionably in that case, the amp chips likely has fried. Much of a boombox circuitry is protected by voltage regulators so they possibly might survive, but if you double the voltage, forget it, something gonna go.

In short, is this 110v unit in trouble by plugging into 120v? Maybe, not, it's a 9% increase in voltage, and it's still likely barely within range of the component max, but it's on the fringe of recommended operating voltage. And it's not just the amp chips. Even the regulators will be stressed more because these regulators produce heat based on how much voltage is dropped. Ok, it's not really voltage that regulators are typically rated at, it's usually in watts sinked but there is a relationship. For example, if a tuner circuit requires 8v and the normal circuit voltage is 15v, the regulator will "sink" 7v. 7V x current consumed = watts, which is converted to heat. If the circuit voltage is 18v instead, it is now sinking 10v, which will result in greater watts (or heat generated). This introduces stress into the regulator and at higher voltages, at some point, the amount of heat generated will cause the regulator to fail unless heat management is taken into consideration (such as heat sinks, fans, etc). The problem is that whether or not any of these techniques are utilized depends on the original design, and in every case, the design will be for the power normal for that region.

So ideally, power your boomboxes using the proper voltage and if it's slightly off, use the boombox in moderation or retrofit the power supply to supply the proper output voltage.

im ok Norm as i converted my victor to 240v as i had a spare 240v m90 power supply

 

[Transistorized]

Wow! Thank you Norm and to all who have responded.

I knew something was up. I kept shaking my head on how my beat up glued together parts box seemed to be blowing my minty M70's out of the water... It has a non working left meter probably from being operated on too high of voltage prior to receiving it. It makes sense it could be damaged since it reads operating voltage when selected on the top. I am willing to bet it pegged over with 120V by a previous user and fried it. Also, there is something up with the circuitry when playing a tape. If you select ALC for recording you get a helicopter pulse that comes and goes on the speakers and I have sprayed the living h*ll out of the record bar but this remains unchanged. If you select manual record level it's fine. So it's a beater but otherwise works okay. The back and handle are glued together so....yeah....it's had a rough life. I got it really cheap and decided to give it a little love because it seemed to want to live.

All of you who are planning on entering a battle with your box, now you know how to get a slight edge on your competitor ....albeit at the risk of blowing an amp chip or various other components. But if it's a beater box and you want to get that slight edge with the risk of letting out the blue genie smoke...well...

I have a step down transformer that takes 120V down to 100V but unfortunately nothing 110V. I could use on batteries. I have plenty of those.

Because this is a beater, and if I were to choose between the two (with neither being optimum), I wonder which would be less stressful? 100V or 120V? Obviously I would think 100V but I know enough to know that sometimes under volting can be equally stressful in other ways to some circuits. Sorry, I'm not as good with current flow characteristics but I'm smart enough to heed advice from those that do know.

So far, the chips have handled this increased voltage like a champ as we would expect....but for how long will they work on the edge? That's the question that I keep coming back to in my head after reading. It appears that I have slightly abused this box...because I have but at the same time I feel bad for cracking the whip on a senior survivor. I keep looking left and right. Devil to my Left / Jesus on my Right. Which way should I go?

I welcome opinions. If you had 3 of these and your beater was being pushed to its limits, would you throw caution to the wind and let 'er rip or go easy on the old girl?

 

[Superduper]

Is your 120v M70’s not loud enough for you at full tilt? Because while your beater 110v M70 might “sound” more powerful at the same volume slider position, the practical volume limit might be no better if you factor in distortion. I’m curious to know, if you blast both at max volume, does the beater one sound better to you? If yes and you got it for cheap anyway & you need that extra oomph, then blast it til it doesn’t anymore haha.

 

[Transistorized]

Very interesting points Norm. This prompted me to do a study Heck I'm already half deaf so why not

So I did a little test with my mid grade box and the beater. One is designed for 120V and fed the correct voltage and the other running at +10V higher capacity. Also as a side note, these two boxes in this test have properly working tone boards so that wouldn't skew the test on the volume output, etc..

I am not using my minty M70 that superduper repaired the tone board on. That machine will not be getting abused. So here we go.....

What I noticed is exactly what you described Norm. The beater hit higher levels on my decibel meter (and I am sure higher wattage output) but the sound would probably only appeal to those who like fingernails on a chalkboard They both started to break up at the same loudness decibel level (peak RMS) but at different points on the volume scale (as expected). Basically once both chips topped out RMS wattage the slightly overpowered chips just shouted their distortion signal louder with more volume travel to the max...haha.

In conclusion, you will get a louder distorted (crappy) sound sooner on the volume dial of the over powered box. It will go louder however, it's only an illusion when it comes to CLEAN power as both chips will still only output RMS cleanly at their rated spec output and perspective volume levels. Only if you were looking at decibels and total loudness would you win a battle. If you were looking for cleanest sound wide open it would go to the unit operating on its proper voltage. As far as clean output they're still the same at the same decibel output but again, at different points on the volume dial.

I took into consideration that the volume sliders and component specs (capacitors, chips, etc..) will vary from machine to machine but the results I got seemed to favor what superduper was saying.

Shifting gears a bit, I have noticed this same type of behavior with new modern sports tunes. Most cars today have a potentiometer for a gas pedal versus a cable. What some of these "performance tunes" do is just change the sensitivity of the throttle to where when you press half way on the pedal it opens the engine throttle more than stock giving the illusion that you gained more power with their tune chip. In reality, dyno numbers are still the same.

This test on the M70 reminded me of this and therefore has lead me to make my ultimate decision. There is no need to push the chips too hard. It's just smoke and mirrors....no pun intended...