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Re: input voltage drop in amplifiers
开云体育A typical linear power supply powered audio amp (!00% SAE) consist of a transformer, bridge rectifier and huge energy storage capacitors which provide two functions. 1) Smooth the rectified DC into filtered DC suitable to power the Amplifier electronics. 2) Provide an uninterrupted supply of on demand energy storage over the entire 20Hz to 20KHz audio range o satisfy the musically related peak audio demands which are most often strong bass notes or drums. ?Signals that have no relationship to the incoming AC power. ?Satisfying #2 is often done by maximizing the size of the capacitors to store the most energy that is well beyond the minimum capacitance value needed to satisfy requirement #1. ?Hence the specmanship discussion of the amount in Joules of energy that is stored by these capacitors. If you ever had an amplifier without protection relays, you may have noticed that it can play music for a very long time well after the power has been shut off from JUST the amplifier. ?My point is that the energy available in these capacitors will last well beyond the brownout you see on the AC side. So putting this together, Let assume the amplifier is on and not playing music to keep this simple. ?The capacitors are charged to peak voltage (Power) since there is no demand. ?When the brown out occurs. the amplifier electronics never skips a beat because the capacitors have more than enough energy to keep the amplifier going without any negative consequence over the duration of the brown-out. ?So there is no harm or foul happening to the amp. You may say, “But I See the lights that light up the big VU meters get dim”. ?That is true. ?The transformer 100% see the AC voltage power sag. ?The big VU meters are running on 6.3VAC directly off a winding from the transformer. ?So if the primary see the voltage sag, so does the secondary. ? But the Secondary winding the power the amp have one more step in the process. ? A bridge rectifier that the bulbs do not have. ?The bridge rectifier only allows energy to charge the capacitors. ?I will not allow the capacitor to discharge due to the drop in the secondary voltage. ? The capacitors keep the amp alive and running during the entire event preventing the amp from seeing the brown out. When some other device that is on the same AC circuit powers up and draws high inrush current, the AC voltage will sag. ?The sag will only last about 200mS or so. ? How low the voltage goes has multiple variables. ? Lets talk a SAE amp turning on for example. The current drawn will be a function of the resistance and impedances involve in the current path chain. 1) Capacitor ESR. ?ESR stands for Equivalent Series Resistance which includes DC resistance of the metal conductors plus ion flow resistance in the capacitor’s eletrolyte. 2) Bridge Rectifier forward voltage at the given current. ?No true resistance but we can treat it as so. 3) Internal AMP Secondary power wiring resistance feeding both the bridge rectifier and the capacitors. 4) Transformer Secondary winding wire resistance. 5) Transformer Power Rating 6) Transformer Primary winding wire resistance. 7) Internal Amp AC wiring resistance all the way up to the AC plug 8) House AC power wire resistance that feeds the AC outlet. All of resistance are in series with the current flow. ? Each drop some voltage as the current flows. ?Most case the resistance is low enough under normal conditions that the corresponding voltage drop is negligible. The capacitors is different in that it become 100% of the load on turn on. ?It has to store energy like a battery. ? You have to charge a capacitor just like a battery. ? The capacitor represent a short circuit when it has a charge voltage that is less than the charge voltage. ?On startup, the voltage is zero. This means the transformer secondary will see the short circuit. ?The secondary voltage drop will be a function of the peak secondary current that transformer can provide times the resistance of items 1-4. The transformer will attempt to provide all the power (Current) ?the secondary side need to address the load.. ?However, when the magnetic core of the transformer starts to saturate, the secondary current will become clamped and peak limited. ?This is reflected back to the primary side but with a reduced current level by the turns ratio of the transformer. ? ?The reduced peak current time the resistance of items 6-8 will result in the value of the AC voltage drop from it nominal level. ? How low can the primary AC voltage drop? ?To any level it wants based on the peak current the transformer demands. ? The onlything stopping this from blowing up is: 1) The circuit breaker's "time delay" before it says to much and trips. 2) The amount of energy that will be needed to charge the capacitors. ?The bigger the capacitors, the more time it will take to charge them up. When the time it take to fully charge the capacitor exceeds the time delay of the circuit breaker, that is when the circuit breaker will trip. Many of the biggest amplifier will install inrush limiting circuits where a large value resistor is intentionally inserted in series with the primary with a bypass relay. ? I could be electronic too. ? The point is the relay limit the peak primary current to a level that will not trip a 15A circuit breaker. ? It also means it will take the amp a bit longer to become fully charged and ready to run. ?Once the capacitors are full, the resistance is bypassed and not the transformer is directly connected to the AC mains as normal.
Best Regards, Mark Gurries Electrical Engineer DCC Website & NMRA DCC Clinics: |
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Re: SAE A105 Sub amp
开云体育20-200Hz range does not answer the question. ?It could well be the upper frequency limit of the amp for all I know. The question of the crossover frequency which is a single frequency value. ?It is the frequency where the incoming audio is split up into subwoofer frequencies and those tare defined to be above subwoofer frequencies. ?Any audio frequencies below the crossover frequency is sent to the subwoofer. ?Those that are above are passed on to the main amp that driver the normal speakers. Typically subwoofer crossovers operated in the 80 to 120Hz range. ? But it is a single value within that range. ?200Hz is way beyond what is classified as subwoofer frequency range. If the crossover frequency was set to 100Hz, the sub would play 100HZ in down and the main speaker will play 100Hz on up.
Best Regards, Mark Gurries Electrical Engineer DCC Website & NMRA DCC Clinics: |
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Re: SAE A105 Sub amp
The SAE A105 subwoofer amp is a re-badged DBX XB140 unit. According to the owners manual, the frequency response is 20-200Hz @ 70W Regards Jim On Sunday, July 22, 2018 2:36 AM, "Mark Gurries gurriesm@... [SAE_Talk]" wrote: A non response typically mean no one knows. ? But If I had to guess, it would be someplace between 80 and 120 Hertz. A105 was made long after the SAE we normally talk about went out of business. ?It was made by DAK in Korea using the purchased SAE name.
Best Regards, Mark Gurries Electrical Engineer DCC Website & NMRA DCC Clinics: |
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Re: SAE A105 Sub amp
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On Jul 22, 2018, at 2:36 AM, Mark Gurries gurriesm@... [SAE_Talk] <SAE_Talk@...> wrote:
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Re: SAE A105 Sub amp
开云体育A non response typically mean no one knows. ? But If I had to guess, it would be someplace between 80 and 120 Hertz. A105 was made long after the SAE we normally talk about went out of business. ?It was made by DAK in Korea using the purchased SAE name.
Best Regards, Mark Gurries Electrical Engineer DCC Website & NMRA DCC Clinics: |
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Re: input voltage drop in amplifiers
开云体育
Perhaps a larger concern is when the A/C cycles off as there is likely a brief over-voltage surge. If that's the case, some sort of power surge protection would be a good idea. I'll bet that your Monster Power unit does this for you, but a page flip of the manual might be reassuring.
In my house the micro has a weird split neutral circuit with the garbage disposal unit. But it's a 20 amp circuit with nothing else on it. The A/C is on its own 240 Vac circuit. I had a similar problem running a shop vac and table saw simultaneously from a 15 amp circuit. Lots of nuisance tripping resulting in silence and darkness while trying to cut wood. I eventually solved the issue by installing two 20 amp circuits independent of the lighting. Sorry for the novella, but I hope this helps. Regards, Rob |
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Re: input voltage drop in amplifiers
开云体育Hi Rob, I believe Jim’s reference to AC is a Air Conditioning unit. If I am wrong then I would like to know the answer.The power drop in voltage that the Air Conditioning unit draws ( unfortunately on the same circuit breaker) as my stereo system. I am running a Monster Power Pro 3500 before my sound system. Does the same rules apply in your below answer to a heavy appliance draw such as a Air Conditioning unit or say a Microwave oven. With my Air unit on and then turning on the Microwave I blow the breaker every time….?
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Re: input voltage drop in amplifiers
By input, I assume you mean 120 Vac power input. I would expect the AC power line voltage to drop momentarily when you turn the amplifier on as there is considerable inrush current to charge the main filter capacitors. This event lasts no longer than 1-2 seconds. This is generally not damaging for the amplifier although some designs may experience eroded switch contacts over time. Also, if you increased the capacity of the main filter caps then the inrush current will increase which may stress the bridge rectifier diodes or transformer. Replacing an old 18 AWG power cord with a 14-16 AWG cord might help. Plugging the amp directly into the AC outlet rather than an extension cord or power strip might help, too. If the voltage drops whenever there is a musical peak, e.g., the lights dim when a bass drum is hit, then that particular power circuit is either heavily loaded or is far from the circuit distribution panel. The heavy current draw is causing the AC power line voltage to sag a bit. It's possible for the amp to clip more easily in those circumstances. If this is happening and it bothers you, consider putting the amplifier on a different AC circuit. The gold standard would be its very own 20 amp circuit. Regards, Rob |
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Re: input voltage drop in amplifiers
If I read your message correctly you are asking the effects of a power line sag.? The root cause for this is the innate resistance of the wiring in your home coupled with the high inrush current required to start the compressor.? It's not a big deal to the amplifier at only 5 Volts difference.? If it was a significantly larger number the amplifier would go into clipping far earlier and make damage to the speakers more likely if driven hard.? Every well designed electric/electronic device has to deal with these situations gracefully(TV's, radios even refrigerators).? In short 5 volts is pretty insignificant especially due to the fact that the line recovers within a few seconds.? If you are looking for something to worry about this is not it!
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Re: input voltage drop in amplifiers
No, this is a result of the load drawn by the amp as the filter capacitors charge.? You'll probably also find the input voltage drops as the overall volume level (power drawn) increases.? Low line voltage is typically around 103-104 VAC, while typical is 115-120 VAC. Ed? From: "jim albert [email protected] [SAE_Talk]" To: "Yahoogroups" Sent: Friday, July 20, 2018 10:15:00 AM Subject: [SAE_Talk] input voltage drop in amplifiers
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Hi All Hopefully I am able to articulate my question in a manner that makes sense. When an amplifier running and has an input 120 volts and then the a/c comes on and the ampplifier input voltage drops to 115 volts or so and then recovers back to 120 - what actually happens internally inside the amp? How does it impact amp function - mehanically and/or sonically? If this is a re-occurring situation, could the amp suffer damage? Thanks to all Jim |
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input voltage drop in amplifiers
Hi All Hopefully I am able to articulate my question in a manner that makes sense. When an amplifier running and has an input 120 volts and then the a/c comes on and the ampplifier input voltage drops to 115 volts or so and then recovers back to 120 - what actually happens internally inside the amp? How does it impact amp function - mehanically and/or sonically? If this is a re-occurring situation, could the amp suffer damage? Thanks to all Jim |
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SAE 2401 - advice needed
Hello SAE lovers and I am looking for some advice from anyone familiar with SA 2401. - can it handle a load of just one ohm when driving multiple speakers? - looks like it has short circuit protect, yes/no?, does anyone know when this kicks in? If anyone has a link to specification of 2401 that would be most useful I will be extremely grateful if anyone can help with this |
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SAE A105
I recently purchased an SAE A105 Sub amp which seems to be a nice little amp but I can’t find info on it. My questions are what is its crossover point to the sub, does it rll off the mains at that point and how much input power is required to properly operate the system. If anybody knows I’d sure like to find out. Thanks
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Re: P101 or P102
开云体育The P101 suffers from relays that did not have gold plated contacts. ?Connection goes intermittent after some time. ?If if you managed to clean the relays and restore contact, the problem will return. ? Good relay have gold contacts to prevent these type of problems. You would be better off with the P102 when all is said and done. ? But you give up some of the feature and control options that the P101 had. ?But if you never used those features, then it will not matter.
Best Regards, Mark Gurries Electrical Engineer DCC Website & NMRA DCC Clinics: |
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Re: SAE Mark IVD
Hjalmar Scheibler
Thank you Craig !!! Very helpfull !!!
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Am 10.07.2018 um 19:22 schrieb Craig Tathwell llwhtt@... [SAE_Talk]: ? |
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Re: SAE Mark IVD
Offset is set by R54 on each channel measured at the speaker terminals, set for 0VDC.? Quiescent current adjust, R22, is used to set the "bias" of the Voltage Amplifier Stage, VAS. Measured across either R24 or R25, 62 Ohm resistors. Set for 1.24VDC which is 20ma quiescent current. The output stage bias is best set with a distortion analyzer, .03-.04 THD at 1W at 20KHz into 8 Ohms using R40 which is under the main board. If you don't have a distortion analyzer you can measure the voltage across the collectors of the drivers, Q9 and Q10, set for 2.1VDC using R40. Craig
On Tuesday, July 10, 2018, 10:05:53 AM PDT, Hjalmar Scheibler jahalama@... [SAE_Talk] wrote:
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SAE Mark IVD
Hjalmar Scheibler
Hello,
I have a SAE Mark IVD amp I want to recap and restore. How do I adjust offset and bias ? I have downloaded the schematic. Is bias set by measuring across the emitter resistors R41/R42 ? Where is the test point for offset ? What does "quiesent current adjust" mean ? Thank you Hjalmar |
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P101 or P102
Background: I have a P101 that I took in years ago for a non working tape monitor.? The tech thought he fixed and told me "by the way I found a bad ground and fixed it"? He didn't fix the tape monitor, but he added a ground hum.? Took it back and the owner found a stuck relay for the tape monitor, but couldn't fix his techs work without a schematic.? I've been using a Harmon Kardon preamp I bought in the meantime. I'm trying to decide whether to send the P101 to one of the recommended repair shops on here or buy a P102 off eBay.? I can recoup some of what I spend by selling my RS-101 if I buy a P102.? FYI, the power is supplied by an A501 and I also have an SAE tuner.? I have no idea of the difference between the P101 and P102 other than the added bass and treble controls and loss of speaker switch (via RS-101). All comments and opinions are appreciated.? Thanks. |
Scott Svare
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