"However you can also consider the fuse to be a common denominator in the AC chain, in that you might use the same fuse while auditioning different power cords, and still be able to hear differences between"
I would just LOVE to do a real blind test on this!! I sold stereo for seven years, and we did blind tests all the time after work. Oh what fun, and NO, I was almost always "wrong" on what was what on wire, cords, stands, rock weights, and if my pet rock really loved me. |
I spoke to Richard Brown (Brown Electronics Labs, BEL) many times over the years having owned a (Richard Brown updated) BEL 2002 and two BEL 2001 Power Amplifiers. He steadfastly insisted that his amps should be shut off EVERY time after a listening session because he believed that the startup capacitor charging was critical to proper continued operation of his amplifiers. He felt that restoration to full capacity for critical listening would take less than 20 minutes after a startup. If any one wants to challenge this electrically for whatever reason that's fine, I'm just sharing the personal opinion of one of the most innovative and brilliant amplifier designers of the 20th century.
I've long regretted my sales of these amps. Nothing I've owned since has quite matched them. Not to say there isn't something better but I haven't had the opportunity to experience it yet.
An interesting thread. |
Rower30, I do not blame you for taking that position, and no doubt this is why there are a number of 'HiFi' fuse products now available.
However you can also consider the fuse to be a common denominator in the AC chain, in that you might use the same fuse while auditioning different power cords, and still be able to hear differences between the power cords.
IME, the better the AC wall wiring is (including the outlets), the easier it is to hear the effect of the power cord. That might seem counter-intuitive, but the the wall wiring is in bad shape and has losses of its own that will see the equipment having a lower AC voltage delivered.
|
Let's see...we see a big voltage drop across the power cord, but ignore that TINY little device called a FUSE that EVERYTHING power related goes through!
Wow,I guess a $200.00 Rotel integrated amp would be simply crazy good if we bypass the fuse. Why spend more and risk blowing something nice up with no fuse! The change would be so dramatic that spending more would seem silly.
Seriously, it's hard to look at 10 AWG wire and ignore the worst link in the chain. The fuse IS THE CIRCUIT for all practical purposes unless someone knows something about a series circuit I don't. The voltage drop will pick on the worst component in the chain. |
This entire question falls into the category of:
It sounds like, or it seems like, it sure ought to be true and, Yeah that sounds right.
A solid state amp does all its going to do in seconds, except get hotter once under load. |
Plants run THHN wire in flexible and solid conduit all day and night. It's SAFER than ROMEX run bare inside your walls! Yes, flexible conduit is UGLY in your house, but the NEC, which the fire marshal follows, allows this circuit.
People confuse flex life with flexibility. They are not the same. SOLID THHN wire in flexible conduit will last just fine based on the conduit's self limiting min bend radius. Of course, SOLID WALL conduit has to be FIXED service because it will kink when it is bent and pinch the wires.
Some circuits REQUIRE SOLID wire so it is either "good" or "bad" (fire alarm wire). When solid wire is "bad" it's an open or very high resistant "touch" circuit that can be tested for. Stranded wire can lose strands over it's life and burn off when full rated current is drawn after the wire ages and strands break. Stranded wire is responsible for the majority of fires for this reason.
I just bought a used PASS LABS XP-10 pre amp, and it does have a "stand-bye" mode, which powers off a good part of the circuit. But, a 10 watt draw is pretty light. Circuits that draw VERY small levels of power would be designed accordingly, and to the typical junction temps of those circuits. There is no magic in circuit temperature stability.
I'm not talking about circuit life, but "sound quality" after thermal equilibrium. Shoot, most of you change stuff before a layer of dust gets on it! I buy half my stuff used and have no fear at all with SS equipment. My Apt 1 amp is 30 YEARS OLD and still fine driving 1979 B&W 801's! The APT 1 amp has no power switch, you plug it into the wall. No, it isn't for 24/7 "sounds better" it's because a SWITCH is GARBAGE and over rides every piece of wire in the power circuit, so he took it out.
I'm still amazed at how little the IEC plugs, wall outlet plugs and power switches are really looked into. They are the predominat part of the circuit. But, we may silly money for "wire" and ignore the critical plugs and switches. |
ROMEX is 100% soft annealed copper, it is simply the AWG size that limits flex. Its solid wire. Even if it were 20 gauge it can still break... You can run equivalent AWG stranded copper cords straight from the box (hard-wire, no connectors)to your device. AC is 60 cycle, it only knows resistance (AWG size). Don't let the fire marshal see that installation... |
ROMEX is 100% soft annealed copper, it is simply the AWG size that limits flex. You can run equivalent AWG stranded copper cords straight from the box (hard-wire, no connectors)to your device. AC is 60 cycle, it only knows resistance (AWG size).
You can ALSO run ROMEX in adhered ridgid EMT or unadhered flexible EMT conduit to your device and, with the suitable conduit interconnects. So it can be done, safely, with ROMEX in conduit. Done all day long in industrial plants to REMOVE crappy connections anywhere possible, THOSE are fire hazards! |
I run two 15' lengths of JPS Labs In-Wall cable from two 20 amp dedicated circuits on my main AC panel directly to my mono amps using Furutech IEC plugs at the amp end. No outlets or power cords. I noticed a pronounced drop in noise. I do the same with a third circuit to my Equi=Tech balanced conditioner for my front end rack.
I turn my amps on about an hour before I listen and the sound seems smoother, with less harshness in the highs compared to listening without a warm up period. There also seems to be very slightly less noise resulting in a bit more clarity. My phono amp and pre amp remain on 24/7. |
I turn my amp on about 30 minues before I start to listen an when I finisch listening I turn my amp of. Any amp that breaks down because you turn it on or of is designed wrong. |
Solid state amps get better over days. Some people rather having them on 24/7...problem is on countries with power fluctuations, high voltage may kill your amp. |
"Can you tell me why it is dangerous and where it says it is not legal?"
Fire Hazard. The solid copper is not soft annealed and will break after too few flexes. It is rated for in wall use only. NEC states that NM cable (Romex) should be used in protected areas only (walls, floors etc). |
Atmasphere
Can you tell me why it is dangerous and where it says it is not legal? |
Rower30, Take a look at my comments about power cords 1/2 way back in this thread.
Your power conditioning can be the best in the world but if there is significant voltage drop in the power cord a problem is being introduced that does not have to be there. I would expect romex to work quite well but it is not legal to use as a power cord- such use is dangerous. |
In my experience, when SS amp has been on for at least an hour, it sounds best. I have no idea why. The exception is my BR system's bel Canto S300 power amp. Sounds the same from minute #1 to hour #1. Again, I have no idea why.
Neal |
We had a customer actually bury 9/16" SOLID copper rod in his wood floor to his speaker terminals from the power amp. And, he ran the ROMEX into his power supply. Way cheaper than the silly cord. If you have a power conditioner, the power cords make even less sense. Cords have no active way to condition the power at all. AC is AC regardless of the phase angle when it is rectified to DC. Noise on the line? Sure, a big old bank of capacitors can eat that up.
I haven't seen a correlation to what's on the transistors DC V+ bias voltage showing in the audio path. Not to say the data isn't trere, I haven't seen it shgown in an output signal test. Power supply ripple is pretty darn low anymore. |
"This supports bringing the ROMEX right into you amp's transformer leads (many do this)."
I've never heard of anybody doing that. I'd love to see a pic. |
Yep, and the IEC plug is rated at just TEN amps. Count them; 1,2,3,4,5,6,7,8,9,10 AMPS! That's all you get. A far cry from what people realize. The conductors in the cord are NOT dropping the voltage you are measuring. Can't be true. You are measuring the terminations, like it or not. This supports bringing the ROMEX right into you amp's transformer leads (many do this). Two terrible connections GONE!
A power cord cannot reconstruct what should be there, it has no idea what "should" be even is. It can only "change" it into something else yet again. Not a bad reason to convert it to DC is it? Screw the A/C other than connections, make sure the DC is done right. Most people use power conditioners to offset crappy DC power supplies. There is no other reason. True DC has no master other than the potential to do work. |
No, a power supply cord is in SERIES with the ENTIRE ROMEX lead and all the way back to the power station. An insignificant voltage drop and even less so if the lead is equal to the ROMEX in AC resistance. So if you use a 12AWG cord you're NOT going to see appreciable voltage drop across the cord. Its probably more accurate to say the power cord is in series with the house wiring and the transformer that feeds it. However I am not theorizing here at all- the measurement I mentioned was quite real. To compensate for the power cord losses, I used a variac and measured the AC voltage drop across the cord, IOW at the output of the variac and the AC input of the amp itself. Now I am not saying the the other wiring, in the house and outside on the line does not have an effect. But for this measurement they remained a constant. A 12 gauge cord will have less voltage drop- but part of the issue are the connections at either end of the cord. If they are heating up it does not matter what the gauge of the cord is! |
Well, I hit a hot button for discussion it seems. Do mean this to be a "learning" experience, not arguments. Sorry for any flames going any direction on this, even if I'm just a catalyst to it all!
First order filter should be 6dB / octave not 3dB. It is a VOLTAGE amplitude drop. So it goes 6, 12, 18, 24 dB ETC as you gang filters in series. So, you have to be careful to use 20LOG and 10LOG in the right places. I was thinking optical cable half POWER bandwidth point, which is measured at -3dB. Wow, sorry about that!
"These effects can be quite measurable!! For example, I have seen a 3-volt drop across a 6 foot power cord cost a tube amp of about 35% of its total output power. If you want a reason to look for, that one is pretty basic!"
No, a power supply cord is in SERIES with the ENTIRE ROMEX lead and all the way back to the power station. An insignificant voltage drop and even less so if the lead is equal to the ROMEX in AC resistance. So if you use a 12AWG cord you're NOT going to see appreciable voltage drop across the cord. Do a voltage divider rule to the ENTIRE DC circuit! The AC circuit could care less about what we just paid for the cord. What you WILL find, is CRAPPY wall and IEC sockets that are independent to the cord used. THAT is what you measured. The wall outlet has a limit of 20 amps, no getting around it. You can only get so much continuous DC from that. LARGE filter caps can leverage power gained over time, to the SAME net power over a shorter time. Some call this dynamic power or "high current". But the TOTAL power over time has to be the same.
All things being the SAME (dielectric and conductor size and type - stranded or solid), a 150-ohm twinaxial (two coaxial in parallel) will ALWAYS have half the capacitance per foot. The shield is taken into account when you set the insulation thickness or, you would NOT have a 150-ohms cable would you? Of course not. Yes, if you buy a 120-ohm twinaxial cable the capacitance is not half, but it isn't apples to apples on the "root" insulated conductor. And, the conductor spacing will be twice the spacing or MORE with the same root single ended conductor impedance.
RCA leads do NOT "shield" magnetic "hum" at all. This type of interference is diffusion coupled clear through the shield and non-magnetic (foil or copper) shields. So, to get rid of magnetic coupling requires a TWISTED pair and differential mode transmission with common mode rejection - sometimes called CMMR. The "shields" on audio cables are RF only, and really do very little at that since most inputs use a RF filter cap to ground to strip off RF. It's more show than go at audio. That, and it is CHEAP to do over balanced lines. Power cord have shields to mostly BLOCK crap going INTO the A/C grid FROM your equipment (PC monitors ETC). Collapsing electric fields across a resistive connection throws off RF (lightening and AM radio). Magnetic lines cancel at ninety degrees, but it's impractical to be always ninety degrees and go "forward" to the amp! Sooner or later, you have to turn the cable.
The only other method to block AC hum, is to use ferrous or "magnetic" type materials that intercept and reroute the flux lines around what's inside the shield.
Poor audio circuits can be swamped out with RF, which is terribly inefficient to amplify. So terrible sound can be rooted in RF leakage into the gain stages, clipping the circuits and throwing the audible band into chaos. Super wide band amplifier stages can simply amplify the RF, and NOT clip the audio levels so much. It doesn't matter where clipping happens, it goes all the way through at the audio level after the stage.
Still, I'm NOT a taker on amplifiers ideally needing to be "warm" to sound good (The P/N junction are actually HOT as heck by nature, and run better when COLDER. The new Macintosh amps are set-up to be COOLER running to IMPROVE reliability AND sound. Sure, old school amps are biased to be hot since they didn't take the time to design around a COOLER thermal equilibrium, and the amp was ONLY at design attributes when it was warm. But, THAT point is static after about twenty minutes or so. Transistors like to be cooler to work well, and last a long time. COLD is good, it's just that the DESIGN can not keep the circuit cooler that FORCES a higher thermal stability inflection point. Designers don't WANT that. There isn't a SINGLE attribute on a transistor, inductor, resistor or capacitor that likes HEAT to be better.
You guys and gals go ga-ga over your low loss leads, but never give to the notion how inefficient a HOT transistor is? HEAT is HIGHER resistance everyone! That means you need MORE gain to offset the HEAT, which leads to more circuit paths, and LESS purity of the signal. Sooner or later, the HEAT offsets the GAIN, and the amp design collapses in on itself.
So what you "hear" is an amp that need twenty minutes to be at the DESIGN values of all the components using contemporary (older?) circuit designs.
As for 24/7? Sorry, I don't buy it, and my ears don't buy it and I don't want to buy the electricity to buy it! After twenty minutes my DNA-225 is SILLY hot. I'll turn the radio on for twenty minutes and catch the news, than listen to music to forget all about the news!
Oh, I still contend that speakers, cable / amps are heavily interrelated due to back EMF and how the amplifier's output stages are effected. The amps damping factor with respect to frequency, complex amplitude and phase cancellation does indeed alter what you hear. Each amp likes a different cable to alter the negative effects of the speaker, and itself. But, you can't change your amp or speaker, so we change cables. Some argue (DynAudio) that speaker leads should be CONSTANT impedance at audio. But, some amp and speaker combinations may not like that "ideal" world since the amp and speaker aren't ideal. No ideal LOAD (the speaker) throws a signal BACKWARDS to the amp! So much for ideal circuits.
The pre amp leads, not so much. HIGH impedance terminations and LOW current don't interact as badly. The do have "issues", (there is current) just not so much.
So of all the discussion, I 100% agree on speaker leads contributing to sound (I can hear it). Power leads and pre-leads, no, not so much. I haven't heard it. And, on pretty good stuff; Benz Micro Ruby 3 with Vandersteen Quatro SIG wood series II speakers.
Good stuff everyone. |
Your car will run a little better if you leave it on all the time, snow will never stick to the windows, and in the summer the AC will insure your car is always cool...sure it wastes gas, but so what? Waste is OK if the results make you feel good and you can afford it...nothing else matters. |
With the second part I agree. I don't know what he was thinking but it's just not true. After 20 minutes the amp still sounds cold and that cannot be good. |
I found it in the manual for my Quatros:
"Once broken in, modern power amplifiers sound good after only 20 minutes of warm-up. Leaving the amplifier on all the time exposes the speakers to possible damage from power line anomalies or electrical component failure when the system is unattended."
So he just says "sound good" not "sound its best". Notice the emphasis here is on preventing damage to the speakers. |
20 minutes is certainly bullshit. In my experience with SS one hour is minimum, two is a little better, and I cannot hear a difference past that. |
I thought I remember reading something from Richard Vandersteen to the effect that "modern" equipment only needs 20 minutes to sound its best, but I can't find it now. |
There is no 24 hour warm up period required for my class SS Amps (Pass XA-100.5). They sound great in only an hour. In fact Pass recommends you put them in standy mode when not in use. Little current consumption when they are in standby. |
Paperw8 wrote: "i would have thought that the power supplies in these devices were a regulated a bit better than your comments would lead me to believe."
- most of power amplifiers have unregulated power supplies. |
09-14-11: Paperw8
09-14-11: Kijanki
Voltage ratio in electronics is, and always has been 20log(v2/v1). Pretty much anything other than power is always 20dB(k2/k1) including sound pressure, sound level etc.
-3dB of voltage means 0.708 of a value. i see; so in your mind a 3dB reduction in power "has always" meant that power if reduced to 0.708 of it's original value and not 0.5 of it's original value.
ok...i can see that when you drill down, there is much inconsistency among the dB equation citing crowd. you're not even consistent with almarg; at least he realizes (i think) that a 3dB reduction in power means that power has been reduced to 0.5 of it's original value.
Paperw8, Kijanki said that a reduction in VOLTAGE to 0.708 corresponds to a 3db reduction, which is the same thing that I said (although I rounded off differently, to 0.707). Obviously, for a given load a reduction in voltage to 0.708 corresponds to a 50% reduction in power, which in turn corresponds to the same 3db. There is no inconsistency among what I, Kijanki, Atmasphere, and JeffreyBehr have said on the db and filter rolloff issues. when you say that a first order filter falls off by 6dB/octave, that is a statement of how the power levels change. As I have tried to explain multiple times in different ways, it is a statement, for a given load, about how both the power levels AND the voltage levels change. It means that in one octave the voltage level has been reduced by a factor of 2, and the power level has been reduced by a factor of 4. Is that not clear? Regards, -- Al |
Paperw - My statement about -3dB clearly said voltage and also said before "other than power". Please read carefully before you post. Are you still arguing your 10log idea for voltage in spite of what I told you about common agreement in all measuring equipment?
I'm not sure what you question with the circuit breaker? Home circuit breaker won't respond to 1ms pulses - it is to slow for that. It will respond to average value base on duty cycle within each 16.6ms period.
Frequency of occurrence and frequency content of pulse are two completely different things. Lightning, for instance, is a single even that is very short meaning it is carrying very high frequency content. Because of that lightning rod wire has to be pretty straight (no sharp corners) to keep low inductance and effectively drain high frequency current to ground. |
09-14-11: Atmasphere
Paperw8, the amp I mentioned in my example draws 500W from the wall at full power.
i've got light fixtures that draw more power than that, so 500w is not a ridiculous power draw.
09-14-11: Atmasphere
If you dig around on this forum, you will find that the idea that the stereo sounds better late at night is a fairly common experience. IOW you are right that other loads on the AC line do indeed affect the sound of many stereos.
if you're telling me that audio equipment makers are selling equipment where the power output swings wildly as a result of only a few tenths of a volt difference in power from the wall, that i would say that some pretty shaky equipment is being sold at top dollar prices. one of the things that i appreciate in your comments it that it helps me understand how very challenging it is to design a power amplifier - in fact, it seems to me that that might be the most challenging device to design - but all the same, i would have thought that the power supplies in these devices were a regulated a bit better than your comments would lead me to believe.
09-14-11: Atmasphere
Finally, with regard to the posts you are trading with Al, if you have ever heard of a first-order crossover in a speaker, that is a filter that is as simple as they get. A first-order crossover is of course 6db/octave. I don't think I have ever heard of a 3db/octave filter, but such a filter would actually need *more* parts to make it happen.
here's the problem: referring to the henry ort reference, ort is correct, dB is, strictly speaking, a ratio of power levels. the problem is that it is true that people have also (and admitted incorrectly if you want to be a strict constructionist about it) used dB to refer to ratios of other quantities. that has led to confusion. when you say that a first order filter falls off by 6dB/octave, that is a statement of how the power levels change. to give you an example of the confusion, if you look at a bryston schematic, where they have the balanced inputs, they use a resistor ladder to reduce the voltage by 1/2. they refer to the reduction as a 3dB reduction in the schematic. if you use the 20log(v2/v1) equation, you would get a 6dB reduction. i suppose the proper course of action is to maintain the strict construction of what a dB is; i.e. that it is only used to inform on what is going on with power levels and nothing else. |
Atmasphere - sorry for using word "waste", since filament makes it all work, and overstating losses. With my tendencies to exaggerate 50% error ain't bad at all. |
09-14-11: Kijanki
Voltage ratio in electronics is, and always has been 20log(v2/v1). Pretty much anything other than power is always 20dB(k2/k1) including sound pressure, sound level etc.
-3dB of voltage means 0.708 of a value.
i see; so in your mind a 3dB reduction in power "has always" meant that power if reduced to 0.708 of it's original value and not 0.5 of it's original value. ok...i can see that when you drill down, there is much inconsistency among the dB equation citing crowd. you're not even consistent with almarg; at least he realizes (i think) that a 3dB reduction in power means that power has been reduced to 0.5 of it's original value.
09-14-11: Kijanki
As for power cord. What you describe is average value. Amplifier might take 10A on average but it will be taken in narrow spikes of 100A or more, causing 10V drop on your 0.1ohm power cord equivalent to 20% drop in max power.
you would blow your circuit breaker if you tried to send a 100A surge through a power cord. audio equipment is not designed for use in industrial settings, they're used in homes for the most part.
09-14-11: Kijanki
Capacitor inside is not discharging faster. The problem is that it discharges very little. If voltage drops from one peak of 120Hz full wave to the next only 50mV (ripple voltage) and amplitude is 50V then charging will be done only in arccos((50V-50mV)/50V)=2.6deg. Charging pulse will be 16.6ms*2.6deg/360deg=0.12ms. Pulses will be a little wider because of all inductance in the circuit but as Atmasphere said - in millisecond range.
i think you misunderstood my point. i was not commenting on the *length* of a pulse, i was commenting on the *frequency* of pulses. as i read atmasphere's comments, he was saying that these pulses occured at a high frequency. what i was saying is that the pulses only occur once per second - hardly what i would call high freqeuency. |
Paperw8, the amp I mentioned in my example draws 500W from the wall at full power.
If you dig around on this forum, you will find that the idea that the stereo sounds better late at night is a fairly common experience. IOW you are right that other loads on the AC line do indeed affect the sound of many stereos.
Kijanki is correct in his comments about the double duty I mentioned: the cord has to manage to supply power for the filament circuit of the amp as well as its DC supplies. He is incorrect on the 90% figure we see in his previous post however. But it is still a lot of current- about 45% of the total draw. The high frequency content, despite being once per 60Hz cycle, comes from the fact that the pulse is narrow and square. Anyway you look at it that requires some bandwidth to not current limit.
Finally, with regard to the posts you are trading with Al, if you have ever heard of a first-order crossover in a speaker, that is a filter that is as simple as they get. A first-order crossover is of course 6db/octave. I don't think I have ever heard of a 3db/octave filter, but such a filter would actually need *more* parts to make it happen.
If you want a simple rule of thumb, double a voltage, that's a 6db increase. Double the power, that's a 3 db increase. The 3db figure of power doubling is why small, incremental increases in amplifier power have been known in the past as 'gold plated decibels'. This term has also been used in the radio broadcast industry. |
Paperw8 -
Voltage ratio in electronics is, and always has been 20log(v2/v1). Pretty much anything other than power is always 20dB(k2/k1) including sound pressure, sound level etc.
-3dB of voltage means 0.708 of a value. 12dB means ratio of 4, 20dB i ratio of 10 etc. All electronic equipment is scaled that way (oscilloscopes, multimeters, oscillators, dividers etc.). When you press +20dB button on the oscillator output will always jump tenfold. ALWAYS. I've never seen another definition and I'm long, long time in this business.
Also first order has always been 6dB/octave (20dB/decade). That's how every signal filter is defined etc.
As for power cord. What you describe is average value. Amplifier might take 10A on average but it will be taken in narrow spikes of 100A or more, causing 10V drop on your 0.1ohm power cord equivalent to 20% drop in max power.
Capacitor inside is not discharging faster. The problem is that it discharges very little. If voltage drops from one peak of 120Hz full wave to the next only 50mV (ripple voltage) and amplitude is 50V then charging will be done only in arccos((50V-50mV)/50V)=2.6deg. Charging pulse will be 16.6ms*2.6deg/360deg=0.12ms. Pulses will be a little wider because of all inductance in the circuit but as Atmasphere said - in millisecond range.
Width of the pulse depends on the ripple (voltage drop) and ripple depends on the load. It is in a sense fixed frequency switching power supply that is polluting mains. Current spikes have high frequency content that propagates thru voltage drops to every other component on the same mains. Shielding and filtering becomes extremely important.
Jeff Rowland talks a little about it here: http://jeffrowlandgroup.com/kb/questions.php?questionid=144
As for tubes - I built 100W EL34 amp when I was 15 but vaguely remember that tubes need to be heated. This is the double duty Almarg mentioned and can be demanding one - at this moment Atmasphere ears are getting red because his amps (one of the best in the world) waste 90% of power on filament of current hungry tubes (2.5A per tube and there is a lot of them). If not for that, I would buy this amp in a jiffy. |
if power is reduced by half is that a 3dB reduction or a 6dB reduction. I'm sure Kijanki will answer the part of your question that was directed to him, but in the meantime I'll state that if power is reduced by half that is a 3db reduction. That same 3db reduction also reflects voltage being reduced to 0.707 of its original value. ort isn't saying that 20*log(v2/v1) is a voltage dB, what he is saying is that it is a power dB expressed as a ratio of voltages. I have tried to explain in my previous posts that it is incorrect to distinguish between a "voltage db" and a "power db." A db is a db. Regards, -- Al |
09-14-11: Almarg
The number "10" in all of your equations that I've quoted above should be "20," since you are computing the number of db based on a voltage ratio. I've explained it, Kijanki provided a proof of it, and Ott provided a proof of it.
kijanki, did you say what almarg says you said? if power is reduced by half is that a 3dB reduction or a 6dB reduction. the problem is that you're not clear on what ort is talking about. as to ort, when ort talks about dB he is talking about *power*. in the webite that you cited ort says "The dB is a logarithmic unit expressing the RATIO of two powers". what ort also says as an aside "Although the dB is defined with respect to power, it has become common practice to also use it to express voltage or current ratios". so while he is saying that some people compute dB for voltage, or current, ort feels that, properly stated, dB is a ratio of power levels. so when ort talks about dB, he is talking about a ratio of power levels. so when he refers to the 20*log(v2/v1) equation, the dB is a dB in *power*; that's why he calls it a "Derivation of dB as a Voltage Ratio". ort isn't saying that 20*log(v2/v1) is a voltage dB, what he is saying is that it is a power dB expressed as a ratio of voltages. in ort's view, it is not proper to talk of dB as a ratio of voltages, but he recognizes that many people do so. so what i would expect ort would say about my postings is that it is not strictly proper to talk of a dB in voltage but that it is commonly done even though the only proper dB computation is for power. thus, when you refer to the 20*log(v2/v1) equation, you have to be clear that, in ort's view, "This is only correct, however, when V1 & V2 (I1 & I2) are measured across the same value of impedance". |
09-14-11: Paperw8
v_dB=10*log(v_out(f)/v_in(f))
v_dB=10*log(1/2)/octave
v_dB=10*(-0.3)/octave
v_dB=-3dB/octave
that's the result; it's not subject to your opinion or my opinion, that's just what it is. As I said, you have a fundamental misconception which underlies all of the differences in our positions. The number "10" in all of your equations that I've quoted above should be "20," since you are computing the number of db based on a voltage ratio. I've explained it, Kijanki provided a proof of it, and Ott provided a proof of it. I've recommended multiple times that you do further research to convince yourself of it. Until you understand that the number 10 is the wrong number to use in converting voltage ratios to db, we will get nowhere. Regards, -- Al |
09-14-11: Almarg
Paperw8, the fundamental misconception you have, which ultimately leads you to incorrectly assert that first order filters roll off at 3db/octave, is the notion that the numerical db value describing the ratio of two signals applied to a given resistive load will be different depending on whether voltage or power is being considered.
while you have posted many informative comments on this forum, one of my criticisms of you is that you post references that you seem to have only half-read, and then draw conclusions that don't stand up to a closer reading of the reference. as to the first reference you cited, the writer presented a first order RC filter. he also showed the transfer function for the filter. so if you really do want to know the behavior of the circuit, don't take my word for it, just look at the equation and figure it out for yourself. if you look at the *asymtotic* behavior of that circuit shown (and by "asymtotic" i mean frequency>>RC), the transfer function is: v_out=(C/f)*v_in where C is a constant and f is frequency. let me first establish that an "octave" means a doubling of frequency. given that, for each doubling in frequncy, the output voltage v_out is reduced by half relative to v_in. so if you want to compute the decibel change in voltage for each octave: v_dB=10*log(v_out(f)/v_in(f)) v_dB=10*log(1/2)/octave v_dB=10*(-0.3)/octave v_dB=-3dB/octave that's the result; it's not subject to your opinion or my opinion, that's just what it is.
09-14-11: Almarg
I'll mention, btw, that early in my career as an electrical design engineer, a great many years ago, I had the exact same misconception, until my boss enlightened me.
The value of that number is one and same, whether voltage or power is being considered. For a given resistive load, reducing the applied voltage by a factor of 2 reduces power by a factor of 4 (as you agree), and the change in signal level is 6db. Period.
what "signal level" are you referring to? i've got a deal for you almarg, if you're so convinced that i am wrong, then rip an *unedited* copy of my postings and send them to henry ort and ask for his comments on them. that will be interesting... |
What the equation means is that when voltage is reduced to half it's original value, power is reduced to one quarter it's original value. Yes, of course. I stated that in my post here. Hold on, this goes to my previous comment: you can't just cite equations without understanding what the equations mean. first, the equation 20log(v2/v1) is a dB relationship in *power* not in voltage; a relationship which is true under certain conditions (which, btw, are articulated in the previously cited henry ort reference as well as in my previous comments). Paperw8, the fundamental misconception you have, which ultimately leads you to incorrectly assert that first order filters roll off at 3db/octave, is the notion that the numerical db value describing the ratio of two signals applied to a given resistive load will be different depending on whether voltage or power is being considered. I'll mention, btw, that early in my career as an electrical design engineer, a great many years ago, I had the exact same misconception, until my boss enlightened me. The value of that number is one and same, whether voltage or power is being considered. For a given resistive load, reducing the applied voltage by a factor of 2 reduces power by a factor of 4 (as you agree), and the change in signal level is 6db. Period. The db change in that situation if voltage is being considered is 6db; the db change if power is being considered is 6db; the db change is 6db, period. That is why the formula for db as computed from voltage levels includes the constant "20," while the formula for db as computed from power levels includes the constant "10." Otherwise the two numerical values wouldn't work out to be the same, as you'll agree. Kijanki's post provides an elegant mathematical proof of the equivalency of the two formulas, 10log(P1/P2) and 20log(V1/V2), as does the Ott paper, in a different way. But until you recognize that a db is a db, regardless of whether power or voltage is being considered, the other differences in our positions, including the issue of filter rolloff which started the discussion, will remain unreconcilable. Regards, -- Al |
09-14-11: Atmasphere
The reason power cords make a difference despite the limitations described in this statement has to do with voltage drop in the power cord. It also has to do with how DC power supplies work.
These effects can be quite measurable!! For example, I have seen a 3 volt drop across a 6 foot power cord cost a tube amp of about 35% of its total output power. If you want a reason to look for, that one is pretty basic!
i'm still not convinced of the significance of upmarket power cords, but at least your comments give me something to work with more than just "i believe". at least you articulate mechanisms which can be discussed. here my comments to which i would be interested in reading your reaction. first, i will address the issue of voltage drop across the power cord. while you didn't state the current draw the produced this 3 volt drop, i will assume a current draw of around 30 amps, a reasonable figure for a practical system that would be in a residential setting. in that case, the cord presents about 0.1 ohms of resistance; for a 6 ft power cord that would translate to a resistance of about 50-60 ohms/km. that to me seems like a realistic resistance for a wire. the thing is, even if you went to an upmarket power cord, that resistance is not going to go to zero. so even if an upmarket power cord improves the wire resistance by 10%, that amounts to only about a 0.3 volt difference. if your amplifier is sensitive to that small of a change, there are probably a number of problems with that amplifier. first, it would be sensitive to your turning on lights, or appliances, or a range of devices that would draw a current because the voltage coming out of your wall can be influenced by this kind of stuff. second, i would suspect that a bigger contributor (but more difficult) contributor to voltage loss would be due to resistances in transformers and diodes/active components within the power supply circuit. but real circuits don't operate under ideal conditions. that is why power supply regulation is so important. while your comments suggest that you are aware of the mechanisms for power supply regulation, the question in my mind is why wouldn't a designer of audio equipment have the same awareness? if you really are observing the dramatic changes in output power that you are reporting, then that would lead me to suspect that you have a real power supply reguation problem since it would appear that you have a extremely sensitive amplifier. if true, it just seems to me that your amplifier wasn't designed for the real world, in which case you would probably still have problems after you bought an upmarket power cord.
09-14-11: Atmasphere
But there is more. Most DC power supplies have a power transformer, a set of rectifiers and a bank of filter capacitors. The circuit draws its power from the filter caps, which are replenished by the transformer and rectifiers. Now its a simple fact that the filter caps are not seriously drained in between cycles, else the amplifier will not work very well. But the rectifiers will only turn on at a certain time- whenever the voltage from the transformers is higher than that of the filter caps.
This only happens at the peaks of the incoming AC power. IOW, the power supply is only doing its work in very short bursts of energy. Now in normal operation what this means is that the diodes are doing some fairly high frequency service; they may only be on for a few milliseconds per cycle. This is called commutation- the turning on and off of the rectifiers, and the current that might occur at these times can be quite prodigious depending on the circuitry of the audio device.
Meanwhile the power cord may be doing double duty, especially if the amplifier has a filament circuit.
Consequently you have two effects: voltage drop at 60Hz, and the current ability at a fairly high frequency. The greater the demand on the cord the greater the likelihood that its effects will be audible on this basis; OTOH the lower the current and the more regulation employed by the audio device the less audible it might be.
i get the part about the diode switching on and off, and i get the part about the on period being very short. but for a 60Hz ac line voltage, that on/off cycle should only happen once/second. so i don't see where the "fairly high frequency" stuff is coming from that you described. as i see it, for the diode on/off cycles to occur with the frequently that you suggest would imply that while the line voltage is in the declining phase, the capacitor is discharging faster than the line voltage is decreasing; that sounds like extremely bad circuit design. as far as the amount of current that is pumped through the diode to charge the capacitor, it depends on how tightly you need to limit ripple in the dc voltage. but even still, the current pumped through the capacitor is not the current drawn from the wall. i mean, it's not like the power cord is jammed into the circuitry straight-on; it goes through a transformer. i would expect that the transformer is going to do something for you such that the amount of current drawn from the wall is somewhat less prodigious than the current through the diodes. which would mean that the current through the power cord would be less than the current through the diodes. so if you used diode current as the basis for an estimate of voltage drop across the power cord, you would have an exaggerated figure.
09-14-11: Atmasphere
Meanwhile the power cord may be doing double duty, especially if the amplifier has a filament circuit.
i don't understand the "double duty" comment. this might be a concept related to tube amplfier designs, but i don't know much about tube circuits. i'm old enough to remember how great is was when they came out with transistor radios, so for me it's ridiculous to go back to tube devices. maybe younger people have a different perspective... |
09-14-11: Almarg
Kijanki, no problem with the beer. Thanks for your comment, which as I'd expect is totally correct, with P representing power and U representing voltage.
hold on, this goes to my previous comment: you can't just cite equations without understanding what the equations mean. first, the equation 20log(v2/v1) is a dB relationship in *power* not in voltage; a relationship which is true under certain conditions (which, btw, are articulated in the previously cited henry ort reference as well as in my previous comments). second, what the equation means is that when voltage is reduced to half it's original value, power is reduced to one quarter it's original value. |
Warm up in SS amps after 24 hrs is mainly due to the temperature of power transistors stabilizing, (with music playing).
The electrical characteristics of transistors are very temperature sensitive, and the heatsink/transistor thermal lag can very between different types of heatsinks.
This warm up (an hour usually) is audible, even if the amp has been on (idling) for 24 hours.
Well designed amps can be left on 24/7 for years without problems.
Temperature cycling of power transistors reduces the power transistor life, and that should be taken into account.
Power supply capacitor life is effected with excessive heat, over many years, but they are easily replaced.
I have always left my amps on 24/7 for years, with NO failures.
Life is too short to "wait" for good sound. I hate to listen to a cold amp come up to speed. Why waste time?
Leave the amp on 24/7! |
"they may only be on for a few milliseconds per cycle"
This current is not only huge but have very high rms to average ratio heating windings, while high frequency content heats up the core of transformer.
This huge current spikes' amplitude and time depend on ESR of capacitors. ESR of electrolytic cap increases with temperature making it more forgiving on transformer. Output current also closes thru power supply capacitors and is affected by ESR. It can take a while for temperature inside of big electrolytic caps to stabilize. |
Kijanki, no problem with the beer. Thanks for your comment, which as I'd expect is totally correct, with P representing power and U representing voltage.
Ralph (Atmasphere), just saw your post. Thanks also.
Best regards,
-- Al |
I'd like to do a blind test on power cords, too. Power goes all over the county on high voltage lines, step it down at ana xformer, goes through the house in 12-14 AWG ROMEX, through a gazillion dollar power cord that magically realigns the power (how it ever "knows" what it "was" when it left the plant I'll never know) and THEN goes into a CRAPPY IEC outlet, and THEN into the simple wires from the IEC outlet inside the amp to the power DC supply circuit block. Any decent DC block will turn all the AC to pure ripple free DC. If it doesn't, no power cord is going to change that. Since this comes from the OP, I will assume its fair game. The reason power cords make a difference despite the limitations described in this statement has to do with voltage drop in the power cord. It also has to do with how DC power supplies work. These effects can be quite measurable!! For example, I have seen a 3 volt drop across a 6 foot power cord cost a tube amp of about 35% of its total output power. If you want a reason to look for, that one is pretty basic! But there is more. Most DC power supplies have a power transformer, a set of rectifiers and a bank of filter capacitors. The circuit draws its power from the filter caps, which are replenished by the transformer and rectifiers. Now its a simple fact that the filter caps are not seriously drained in between cycles, else the amplifier will not work very well. But the rectifiers will only turn on at a certain time- whenever the voltage from the transformers is higher than that of the filter caps. This only happens at the peaks of the incoming AC power. IOW, the power supply is only doing its work in very short bursts of energy. Now in normal operation what this means is that the diodes are doing some fairly high frequency service; they may only be on for a few milliseconds per cycle. This is called commutation- the turning on and off of the rectifiers, and the current that might occur at these times can be quite prodigious depending on the circuitry of the audio device. Meanwhile the power cord may be doing double duty, especially if the amplifier has a filament circuit. Consequently you have two effects: voltage drop at 60Hz, and the current ability at a fairly high frequency. The greater the demand on the cord the greater the likelihood that its effects will be audible on this basis; OTOH the lower the current and the more regulation employed by the audio device the less audible it might be. The bottom line though is you do not have to look any further then these two phenomena to find something that is not only measurable but also audible and independent of anything upstream of the cord. With regards to warmup, I remember a Sanyo amp from the mid 1980s that had a passive freon heatsink. It sounded best cold (MOSFET output section)- as soon as it warmed up, the bass was gone. A fan on the heatsink really helped but it was at its best if you kept the amp outside during the winter. I do most of my work with tubes though, and these days it seems that if the amp/preamp needs more than about 2 hours to get to where its going to, it may well need new filter caps or the like. We have measured voltage differences between power supplies that are not broken in as opposed to those that are. This seems to have mostly to do with the filter caps forming up. While most of that happens fairly quickly, a cap might take a few weeks to really reach full efficiency, depending on how much use it gets during that time. The explanation we got from an engineer at Cornell Dublier was that there is a certain amount of water molecules that has to be chased out of the electrolyte by the operation of the cap. Sometimes that can take a while. |
dB=10log(P2/P1)=10log((U2^2/R)/(U1^2/R)=10log(U2^2/U1^2)=10log((U2/U1)*(U2/U1))=10log(U2/U1)+10log(U2/U1)=20log(U2/U1)
Al, Dave, please leave some beer for me. |
Dave, I'll go with the beers and the music. Further explanation seems pointless. JeffreyBehr, thanks for your comment, which of course is 100% correct.
Regards,
-- Al |
Should we explain the relationship between power and voltage again, or should we just open some beers and turn up the volume? |
09-13-11: Almarg
Paperw8, let me supplement the reference I previously provided with this one, supporting my contention that db = 20log(V1/V2), rather than 10log(V1/V2) as you have claimed. It was written by someone possessing technical credentials that are utterly impeccable.
i didn't read henry ort's biography, but i did read his explanation of the decibel. you may be surprised to read this, but i actually agree with with mr. ort has stated. but i don't agree with what you agree with what you have stated. the reason being that i think that you have misinterpreted what mr. ort wrote to support your conclusions. in fact, if you read mr. ort's explanation more closely you will see that my description follows what he wrote. |
Paperw8, let me supplement the reference I previously provided with this one, supporting my contention that db = 20log(V1/V2), rather than 10log(V1/V2) as you have claimed. It was written by someone possessing technical credentials that are utterly impeccable. See his biographical information here. With respect to your related erroneous contention, that first order filters roll off at 3db/octave, I suggest that you Google the terms "first order filter" and "6 db per octave," placing both phrases within the search term field, with the quotes. You will find countless references supporting the 6db figure. If after viewing all of that, as well as the reference I previously provided, you find yourself continuing to insist that db = 10log(V1/V2) and that first order filters roll off at 3db per octave, I will have no further comment. Regards, -- Al |
