Author Topic: Sansui Amplifiers (Read 109986 times)

karipas · « **Reply #60 on:** Sep 16, 2006 at 06:56 PM »

Quote from: Lord Foo on Sep 14, 2006 at 06:20 PM

The Red Protection lamps of my Sansui AUD707Decade kept blinking when I am using it and the source CD sends powerful bass to the amp.

The red pilot lamp would flicker and the audio ouput would cut out. After a while, the output would cut in again.

I realized later that i was using a 120 volt black step down transformer. When I replaced it with a 400 watt 100 volt transformer i bought from the Pier, the amp didn't encounter problems again.

foo.

Sir, thanks also, I will try to measure the voltage in my outlet and the output voltage from my step down transformer. Will the same problem occur if my stepdown transformer is supplying lower than 100V?

.....And to everyone, thanks for the valued information and help, I hope I can correct the problem very soon.

av_phile1 · « **Reply #61 on:** Sep 16, 2006 at 07:50 PM »

Quote from: karipas on Sep 16, 2006 at 06:49 PM

Hello Sir AVPhile, I think this is something I can also do or ask somebody to solder it for me. The top mark on my transistors are SK A1386 70P and SK C3519 77P. Do you have an idea how much is these transistors and where can i buy an original part?

Are you sure the power transistors are the culprit? Did you have it checked by a reliable techie?

If so, check out Deeco electronics in Raon and ask if they have these transistors (drop the SK label) or exact replacements (the A and C prefixes indicate matched complementary pairs for typical push pull class AB types, so are B and D) As far as price is concerned, it's been more than 20 years since I changed those Sansui power transistors so I am out of touch.

karipas · « **Reply #62 on:** Sep 17, 2006 at 09:54 PM »

Quote from: av_phile1 on Sep 16, 2006 at 07:50 PM

Are you sure the power transistors are the culprit? Did you have it checked by a reliable techie?

Hi Sir AvPhile, Maraming salamat po. I have not ask anybody yet to check my amp as I worry that it might do bad than good I have to know first the causes before I send it out for repair. I had an experience kasi with my sub hanggang ngayon e still under repair pa din due to parts unavailability. I enjoy using this amp very much than with my 7.1 ch that is why I am very cautious.

Anyway this is what I found out this afternoon and tonight. My Alpha 707 is rated at 360W , my AC outlet delivers 220V, I am using before a computer AVR rated at 110V, 100W but when i measured the output voltage it is only 85V in the afternoon and 90V in the evening. In this AVR, I enountered the same problem the I have with the current stepdown transformer I am using rated at 110V, 1000W (I changed it becuase I thought the problem is when I played out loud, the AVR cannot suport the power needed by the amp hence I changed it to an Xformer with higher wattage), but when I also measured the voltage it is only at 75V in the afternoon and 80V in the evening. Could this be the source of the problem (undervoltage), or something really went wrong with my amp becuase I used 110V AVR and transformer? If this is the case that i am uising 110V, what will be the normal section of the amp will be damaged?

Sir aHobbit, may amp has a cd in, kaya pwede na natin siguro i-rule out as a possible cause. Now I am really worried that I damaged my amp using 110V.

Thanks.

sandawa · « **Reply #63 on:** Sep 18, 2006 at 03:49 PM »

I'm just curious, is your amp Sansui A707 or Sansui AU-Alpha 707? Reason for asking is I'm monitoring rare Sansuis that arrived here and Alpha 707 is comparatively rare outside Japan and Europe. Also, the Apha 707's power rating in the original version is 130wpc and 320 watts power consumption. If you have the 240V version released in Europe, it may have a higher power consumption figure.

I'm not a technician, more a listener, but if your measuring equipment is accurate, and it gives you over 10% variation in your voltage rating, you should file a complaint with your power company. Those figures would damage most of your appliances, not just the stereo system.

av_phile1 · « **Reply #64 on:** Sep 18, 2006 at 04:03 PM »

Your AVR's undervoltage is below 10% of the expected values and AFAIK they can have detrimental effects on some appliances. If you measure them at 90VAC without load, expect the voltage to further drop when loaded.

I think there's also such a thing as undervoltage shutdown or lock-out in power amps if the input voltage falls below a certain value. This is entirely theory for me though as I have not experienced severe undervoltage conditions where I live. I heard that feeding motors with lower than required voltage can cause them to run overly hot as increased current is forced to compensate for prolonged voltage sag.

I would think that any undervoltage in the amp's voltage rails will have the same effect as reducing the speaker load impedance. And that is to extract more current that could cause the protection circuit to engage when it could no longer produce the needed current to amplify the signal.

But since you are using Automated Voltage Regulators, they are supposed to output the correct 100v or 110v, as the case may be. The input household voltage sag must be so severe to cause more than 10% reduction in the AVR output . See if you can up their output voltage to the proper level or borrow another that does, and if your problem recurs despite this, then it's time to turn to a repair center.

aHobbit · « **Reply #65 on:** Sep 18, 2006 at 06:11 PM »

I think your amp can not easily be destroyed by under voltage - the only thing you can do to validate if your amp is still in good condition is to try to plug it in the correct voltage and operate it and observe.

rascal101 · « **Reply #66 on:** Sep 19, 2006 at 09:07 AM »

Undervoltage condition at the input or output in my opinion is as dangerous as overvoltage because although voltage is low amp maintains same power. As such, the current increases. If it exceeds current rating of the semiconductors they will get damaged.

aHobbit · « **Reply #67 on:** Sep 19, 2006 at 02:29 PM »

Quote from: rascal101 on Sep 19, 2006 at 09:07 AM

Undervoltage condition at the input or output in my opinion is as dangerous as overvoltage because although voltage is low amp maintains same power. As such, the current increases. If it exceeds current rating of the semiconductors they will get damaged.

AM sorry, what power does an amp maintains?

I have made an amp ... it can be biased from 18V - 32V .. depending on how much peak power you want from it

... the only problem you may encounter with low voltage is that your amp will clip earlier (DC output) which is probably why sansui will trigger it protection circuit too early (because at low voltage, clipping can occur at low volume), without the engaging of protection - amp may destroy your speaker ... not your amp ...

Typically, voltage sags during amp operations ... and low voltage can be interpreted by your amp as typical voltage sag (premature that is) ...

still need to digest what you mean 'mantains what power' thingie ... peace

bumblebee · « **Reply #68 on:** Sep 19, 2006 at 02:43 PM »

Ano bang voltage ang pinag-uusapan nyo? Yung galing mains or yung galing psu?

rascal101 · « **Reply #69 on:** Sep 19, 2006 at 03:16 PM »

Quote from: aHobbit on Sep 19, 2006 at 02:29 PM

AM sorry, what power does an amp maintains?

I have made an amp ... it can be biased from 18V - 32V .. depending on how much peak power you want from it ... the only problem you may encounter with low voltage is that your amp will clip earlier (DC output) which is probably why sansui will trigger it protection circuit too early (because at low voltage, clipping can occur at low volume), without the engaging of protection - amp may destroy your speaker ... not your amp ...

Typically, voltage sags during amp operations ... and low voltage can be interpreted by your amp as typical voltage sag (premature that is) ...

still need to digest what you mean 'mantains what power' thingie ... peace

Say your appliance is having input power of 20W at standby position (meaning to say audio source is paused or just on). For 220Vac operation, this means input current of 91mA. When input voltage sags to 150Vac appliance will automatically draw 133.3mA to maintain standby operation. This is 42.3mA above current when input voltage is at 220Vac. This current is drawn by the appliance to maintain regulated voltage and biasing currents.

This is actually what is happening to any appliance when input voltage fluctuates. If the rectifier diodes is rated for 100mA operation only then you can expect to have them damaged in a short time without your undervoltage protection circuit.

jhunB! · « **Reply #70 on:** Sep 19, 2006 at 08:19 PM »

sir rascal... y di na u nag-mail??....

karipas · « **Reply #71 on:** Sep 19, 2006 at 09:10 PM »

Quote from: sandawa on Sep 18, 2006 at 03:49 PM

I'm just curious, is your amp Sansui A707 or Sansui AU-Alpha 707? Reason for asking is I'm monitoring rare Sansuis that arrived here and Alpha 707 is comparatively rare outside Japan and Europe. Also, the Apha 707's power rating in the original version is 130wpc and 320 watts power consumption. If you have the 240V version released in Europe, it may have a higher power consumption figure.

I'm not a technician, more a listener, but if your measuring equipment is accurate, and it gives you over 10% variation in your voltage rating, you should file a complaint with your power company. Those figures would damage most of your appliances, not just the stereo system.

Hello Sir, it is an AU Alpha 707 (I just cant recall if its 320 or 360W power consumption), I have to check the back again and i will let you know, I bought it from a friend who also bought it from Pier. Sir the fluctuation is coming from my AVR and step down transformer and not directly from the outlet. The voltage from my outlet is in the range of 220V to 230V.

Thanks.

karipas · « **Reply #72 on:** Sep 19, 2006 at 09:22 PM »

Quote from: av_phile1 on Sep 18, 2006 at 04:03 PM

But since you are using Automated Voltage Regulators, they are supposed to output the correct 100v or 110v, as the case may be. The input household voltage sag must be so severe to cause more than 10% reduction in the AVR output . See if you can up their output voltage to the proper level or borrow another that does, and if your problem recurs despite this, then it's time to turn to a repair center.

Hi Sir Avphile, I have the same feeling, I have to borrow or invest a good one. Anybody can suggest a good but not expensive brand? Hopefully this will fix my problem.

Hello Everyone, Thanks for the valued inputs.

rascal101 · « **Reply #73 on:** Sep 20, 2006 at 09:03 AM »

Quote from: jhunB! on Sep 19, 2006 at 08:19 PM

sir rascal... y di na u nag-mail??....

OT, kumusta sir? hehehe Bawal gamit kong proxy sa office and di pa ako nagbabayad tel sa bahay. Anong balita?

sandawa · « **Reply #74 on:** Sep 20, 2006 at 09:35 AM »

Quote from: karipas on Sep 19, 2006 at 09:10 PM

Hello Sir, it is an AU Alpha 707 (I just cant recall if its 320 or 360W power consumption), I have to check the back again and i will let you know, I bought it from a friend who also bought it from Pier. Sir the fluctuation is coming from my AVR and step down transformer and not directly from the outlet. The voltage from my outlet is in the range of 220V to 230V.

Thanks.

Thanks for the reply. You're lucky, konti lang meron nyan. That's an excellent amp unless you got a defective one. The other I mentioned, A-707, was the Saudi-type component amp once common here, yung mga binebenta sa international market nuon that accept speakers 8 to 16 ohms only. Ang alam ko marami dun nasunog na.

I was thinking the mains was your problem since undervoltage was common to your AVR and transformer. I'm using several AVRs and transformers now and measuring outputs on a monthly basis. Since I started buying Jap vintage hifi 5 years ago, I have limited my AVR and 100V transformer choices to two brands, Zebra and Panther, but there maybe better and cheaper brands now.

ATJr. · « **Reply #75 on:** Sep 20, 2006 at 09:56 AM »

Quote

Undervoltage condition at the input or output in my opinion is as dangerous as overvoltage because although voltage is low amp maintains same power. As such, the current increases. If it exceeds current rating of the semiconductors they will get damaged.

wow, you have loaded the bases too much here!!!

can't make heads or tails with this statement. wonder what this can really mean.

Quote

Say your appliance is having input power of 20W at standby position (meaning to say audio source is paused or just on). For 220Vac operation, this means input current of 91mA. When input voltage sags to 150Vac appliance will automatically draw 133.3mA to maintain standby operation. This is 42.3mA above current when input voltage is at 220Vac. This current is drawn by the appliance to maintain regulated voltage and biasing currents.

This is actually what is happening to any appliance when input voltage fluctuates. If the rectifier diodes is rated for 100mA operation only then you can expect to have them damaged in a short time without your undervoltage protection circuit.

now where did you get this idea? you are way off......

Quote

The other I mentioned, A-707, was the Saudi-type component amp once common here, yung mga binebenta sa international market nuon that accept speakers 8 to 16 ohms only. Ang alam ko marami dun nasunog na.

yeah, i repaired lots and lots of them, that is why we call them, "SANSUNOG".

rascal101 · « **Reply #76 on:** Sep 20, 2006 at 10:15 AM »

Quote from: TonyT on Sep 20, 2006 at 09:56 AM

wow, you have loaded the bases too much here!!! can't make heads or tails with this statement. wonder what this can really mean.

now where did you get this idea? you are way off......

yeah, i repaired lots and lots of them, that is why we call them, "SANSUNOG".

You say loaded the bases and say off then what is the correct one?

Pls explain the relationship between transformer pri and sec voltages and currents. Also, why does bulk ripple increase with load?

How will I compensate for low input line voltage? Will I decrease/increase duty cycle to maintain bulk voltage?

ATJr. · « **Reply #77 on:** Sep 20, 2006 at 10:31 AM »

sorry, but comparing your posts with the topic at hand, i'd say yours wandered off....

when discussing audio electronics, sad to say, your knowlegde about smps have no place in it...

to set the records straight, ohms law states E= I x R, voltage is equal to the product of resistance times the current passing thru it. i learned that in high school physics and had stuck in my head since. i do not know that that law has been changed.....

rascal101 · « **Reply #78 on:** Sep 20, 2006 at 10:41 AM »

The question being asked is about the consequences of undervoltage so I tried to explain what is happening on the PSU. Doesn't matter if linear or smps.

Linear of SMPS, you still need a PSU in your amp and same principles apply.

I know that you have great experience with amps, I don't question your knowledge here but at the same time you seem to put down SMPS. Why what is so different about SMPS and amps? An SMPS designer cannot make amps and vice versa?

JojoD818 · « **Reply #79 on:** Sep 20, 2006 at 10:47 AM »

Quote from: TonyT on Sep 20, 2006 at 10:31 AM

to set the records straight, ohms law states E= I x R, voltage is equal to the product of resistance times the current passing thru it. i learned that in high school physics and had stuck in my head since. i do not know that that law has been changed.....

that's what I also learned from our hs Physics teacher (Bless her), but what got stuck in my head was something else.

Kirchoff's Law that is.

I also remember her saying "Volta" instead of "Volts".

rascal101 · « **Reply #80 on:** Sep 20, 2006 at 10:59 AM »

Sir TonyT, JojoD,

Let get things straight, am not questioning Ohms Law. I have been answering what happens when input line voltage becomes low. To maintain input power so as to provide sufficient voltage and current to load, what will PSU do? This is not an Ohms Law question.

Kapag tinanong ba pangalan mo sasabihin mo taga Paranaque ka?

av_phile1 · « **Reply #81 on:** Sep 20, 2006 at 12:02 PM »

Quote from: rascal101 on Sep 20, 2006 at 10:59 AM

This is not an Ohms Law question.

Oh, isn't it? And I thought that was the basis of your assertion that current will increase if you go undervoltage.

rascal101 · « **Reply #82 on:** Sep 20, 2006 at 12:06 PM »

To show you guys what I mean, on your amp or appliance monitor your input line voltage and current. You will require a voltmeter and ammeter. What happens to your input current when your input line voltage increases? What happens to your current when input line voltage decreases?

scofield · « **Reply #83 on:** Sep 20, 2006 at 12:09 PM »

O.T. P = E x I ata yung formula ni sir rascal101. di ko na maalala kung ohms law yun. hehehe

bumblebee · « **Reply #84 on:** Sep 20, 2006 at 12:16 PM »

Ohm's Law was never questioned at all.

rascal101 · « **Reply #85 on:** Sep 20, 2006 at 12:20 PM »

Isa pa nga,

For example on your amp,

Input power = 100W, Output power = 50W (standby)

Assuming input line voltage = 220Vac, input line current = 454.4mA, power factor = 1.

The equations are:

1. Efficiency = Pout / (Pin x power factor)
2. Power = voltage x current

Note: Pout = output power, Pin = input power

When input line voltage = 180Vac, what will be input line current to maintain output power of 50W?

scofield · « **Reply #86 on:** Sep 20, 2006 at 12:30 PM »

555mA?

rascal101 · « **Reply #87 on:** Sep 20, 2006 at 12:39 PM »

Very good! Correct!

Now will we see an increase in current if our input line voltage drops eg from 230Vac to 210Vac? To find out for yourself, do the experiment I mentioned.

av_phile1 · « **Reply #88 on:** Sep 20, 2006 at 01:48 PM »

Quote from: scofield on Sep 20, 2006 at 12:09 PM

O.T. P = E x I ata yung formula ni sir rascal101. di ko na maalala kung ohms law yun. hehehe

Ah ok, that seems more like it.

I think this is Joule's law.

JojoD818 · « **Reply #89 on:** Sep 20, 2006 at 11:27 PM »

rascal,

you are correct, things are straight as they are.

My name is Jojo and I'm from Valenzuela, not Paranaque.

J/K

Oh well, speaking of high school Physics, I now miss my Biology teacher.