Re: [SlimDevices: Audiophiles] output inpedance of the TP
Phil Leigh;292171 Wrote: surely the speaker is wired in parallel across the amp output? Maybe this diagram will help: [image: http://upload.wikimedia.org/wikipedia/commons/8/88/Source_and_load_circuit_Z.png] Z_S is the output impedance of the amplifier. Setting Z_S to zero doesn't cause any problem - on the contrary, it's desirable (so long as there is some other protection against accidentally shorting the amp). It maximizes the efficiency and minimizes the distortion caused by differences in the impedance curve between Z_S and Z_L. -- opaqueice opaqueice's Profile: http://forums.slimdevices.com/member.php?userid=4234 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
Wireless, I did not use the built-in attenuators in the TP, because I am running balanced ics and the built-in attenuators only work w/RCA. -- Shredder Shredder's Profile: http://forums.slimdevices.com/member.php?userid=11380 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
opaqueice;292390 Wrote: Maybe this diagram will help: [image: http://upload.wikimedia.org/wikipedia/commons/8/88/Source_and_load_circuit_Z.png] Z_S is the output impedance of the amplifier. Setting Z_S to zero doesn't cause any problem - on the contrary, it's desirable (so long as there is some other protection against accidentally shorting the amp). It maximizes the efficiency and minimizes the distortion caused by differences in the impedance curve between Z_S and Z_L. Ah - yes oops - another schoolboy error... should have realised that as I was typing (it had been a long day) - of course you are correct, the internal resistance/impedance is in series with the load (doh!). Anyway, the point is... source = 0.1xload is a good heuristic in all active circuits. Thanks, Mr. O. -- Phil Leigh You want to see the signal path BEFORE it gets onto a CD/vinyl...it ain't what you'd call minimal...SB3+Stontronics PSU - Altmann JISCO/UPCI - TACT RCS 2.2X with Good Vibrations S/W - MF X-DAC V3/X-PSU/X-10 buffer (Audiocomm full mods)- Linn 5103 - Linn Aktiv 5.1 system (6x LK140's, ESPEK/TRIKAN/KATAN/SEIZMIK 10.5), Townsend Supertweeters, Kimber Chord cables Phil Leigh's Profile: http://forums.slimdevices.com/member.php?userid=85 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
seanadams;291893 Wrote: That's wrong - below radio frequencies, you want a low source impedance and a high load impedance. 100R into 10K is a good (and typical) arrangement for audio. Obviously, the theorem is not wrong http://en.wikipedia.org/wiki/Maximum_power_theorem but I'll take your word on the desired relative impedances being the best. Why is this and from there how do you reconcile a speaker's typical impdendance with a typical SS amp's output impedance (high back to low)? regards, David -- wireless200 wireless200's Profile: http://forums.slimdevices.com/member.php?userid=11887 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
wireless200;291953 Wrote: Obviously, the theorem is not wrong http://en.wikipedia.org/wiki/Maximum_power_theorem I think Sean was probably referring to the doesn't bode well part of your post when he said it was wrong. Read the second paragraph of the wiki article you linked to and you'll see why. Why is this and from there how do you reconcile a speaker's typical impdendance with a typical SS amp's output impedance (high back to low)? Reconcile what? In both cases the source impedance is much lower than the load, as it should be. -- opaqueice opaqueice's Profile: http://forums.slimdevices.com/member.php?userid=4234 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
wireless200;292026 Wrote: TP (100 ohms) into Amp (10k ohms) vs Amp output (~4 ohms) into speakers (~4 ohms). In one case the impedance is not matched in the other it is. I assume this is because the speaker is a physical transducer and you'd need maximum power transfer but again I'd like to hear a designer's perspective. Eh? What kind of SS amp has an ouput impedance of 4 ohms? Mostly they're well under .1 ohms (usually expressed in terms of the damping factor). An amplifier with an output impedance close to the impedance of the speaker it's connected to will audibly distort. Yes, this is a whole 'nother matter - LC effects. Not really wanting to get into that at this time for my purposes. It's -not- another matter - it's one of the main reasons you need the output impedance much less than the input impedance. -- opaqueice opaqueice's Profile: http://forums.slimdevices.com/member.php?userid=4234 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
Take the highly regarded Brystons as an example. Their pre-amps have an output impedence of 110 ohms, and their power amps an input impedence of 50k ohms. 100 ohms or so is pretty much a standard value for pre-amps, and matches the output of the TP. Therefore this is a technical non-issue in your case. I hope that puts your mind at rest. -- bigfool1956 David Ayers Music is what counts, hifi just helps us enjoy it more bigfool1956's Profile: http://forums.slimdevices.com/member.php?userid=13782 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
wireless200;292047 Wrote: The Mcintosh mc402 gives 2, 4, and 8 terminals as output load impedance. Yes: that's the required LOAD impedance, ie. the input impedance of the device you're driving (the speakers). The output impedance of the amplifier itself (the SOURCE impedance) will be significantly smaller - as opaqueice says, probably less than 0.1 ohms. wireless200;292047 Wrote: Again as stated earlier I think it's to generate maximum voltage across the input. But if that were absolutely the case then speakers impedances should be as high as possible. The physical machinations required of a woofer or tweeter must account for this difference. High impedances mean that less current gets passed, which of course means lower power. Speakers need to have a fairly low impedance so that sufficient current will pass that you'll get a usable loudness. And in turn, this means the output impedance of the amp must be extremely low. -- cliveb Transporter - ATC SCM100A cliveb's Profile: http://forums.slimdevices.com/member.php?userid=348 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
wireless200;292026 Wrote: Well I think NewBuyer had it right: you want maximum voltage across the target but I wanted to hear Sean's explanation. I want to use the TP as a pre-amp and avoid buying a separate pre-amp. That's why I'm asking these questions. Although it's good information I don't really want to hear other's are doing it... I like to know what the pros and cons are from a technical perspective. An MC402 by itself is pricey and if I've got to buy a pre-amp too then I've got to take that into account for my budget. regards, David Hello David, You asked a question and for advice. Sean answered it (the designer of SB). Then you turn around and disagree with him with some lame wikipedia link. Wikipedia is a large general information source. It is not the exact or absolute answer to a very specific question you posed. From source to driver device we are not looking for maximum power out (power as in watts), we are looking for maximum efficiency as in signal voltage gain transfer without causing distortion of the audio signal. The wikipedia was describing in general terms maximum power transfer of power in watts to an output device. As in an RF amplifier to an antenna load where impedance mismatch causes output power to be lost in the form of heat. As for the outputs on the Transporter, they are well-designed line level outputs. The unbalanced RCAs have 2Vrms output and the Balanced have 3Vrms (8.5Vpp). Any amplifier with a properly designed input gain stage and 29dB of overall gain is going to be loud enough for most people not to need a pre-amp. More to the point is trying the Transporter alone, if it is not loud enough for your taste, buy or use a pre-amp. A good dealer would most likely let you try this at the shop. If the TP alone does not get loud enough for you, then there is always the Mac I-Amp Model MC6900. Last but not least, what are you trying to drive that needs 400 watts per channel? Most people never use more then the first 25 watts of their amplifier unless they have very inefficient speakers. The Mac MC252 has 250 watts and plenty of dynamic headroom. Yes I have 300 watts per channel. My room is fairly large and my speakers are not the most efficient, but having said that, I would never be able to use more then 2/3 of the power. Turning the pre-amp gain past Two Oclock would cause permanent hearing loss. I would have bought 200 watt mono blocks, but Charles only makes 300 watt mono blocks. -- iPhone iPhone Last.FM http://www.lastfm.com/user/mePhone Media Room: Transporter, Vandersteen Quatro Signature, Ayre MX-R Mono Blocks, VTL TL-6.5 Signature Pre-Amp, VCC-5 Reference Center Channel, four VSM-1 Signatures, Runco 710, RAM Oppo DV970HD, VeraStarr 6.4SE Living Room: SqueezeBox Duet, Vandersteen Model 3A Signature, Two 2Wq subs, VCC-2, Two VSM-1, ADCOM GTP-870HD, Cinepro 3K6SE III Gold Bedroom: Squeezebox 3, Thiel 2.3, NAD C370 iPhone's Profile: http://forums.slimdevices.com/member.php?userid=13622 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
opaqueice;292032 Wrote: Eh? What kind of SS amp has an ouput impedance of 4 ohms? Mostly they're well under .1 ohms (usually expressed in terms of the damping factor). An amplifier with an output impedance close to the impedance of the speaker it's connected to will audibly distort. It's -not- another matter - it's one of the main reasons you need the output impedance much less than the input impedance. The Mcintosh mc402 gives 2, 4, and 8 terminals as output load impedance. Musical Fidelity Kw550 specs a 50 ohm output load loop impedance. Of course LC effects will distort the waveform (or even eliminate it at certain frequencies due to filtering effects). I guessing if there were no LC effects, then there would still be valid reasons for the relatively different impedance values between source and target. Again as stated earlier I think it's to generate maximum voltage across the input. But if that were absolutely the case then speakers impedances should be as high as possible. The physical machinations required of a woofer or tweeter must account for this difference. -- wireless200 wireless200's Profile: http://forums.slimdevices.com/member.php?userid=11887 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
Don't try and compare line level situations with speaker load situations, as there is more to take into account in the case of speakers. In the line level situation, which you asked about initially, the connection is made using voltage bridging (AKA impedence bridging). Maximum power transfer is not required, and this configuration is more resistant to noise. In the case of a power amp to speaker connection, you need to be able to a number of things. You need to be able to generate a serious amount of power to move the speakers, and you need to be able to control these mechanical devices, particularly around the area of their mechanical resonance. For these reasons, speakers have a relatively low impedance, to enable good power delivery, but the power amp will, as opaquiece states, typically have an output impedance of around 0.1 ohms. While the lower output impedance does not optimise the power transfer, it does increase the damping factor. The higher the damping factor, the better controlled the speaker will be. Thus there is a trade off between power delivery and control. Also, you misunderstand the labelling of the output terminals on the MacIntosh. When they say 2, 4, or 8 ohm output load impedence, they are talking about the nominal impedance of the speakers, and not the the output impedance of the amplifier itself. -- bigfool1956 David Ayers Music is what counts, hifi just helps us enjoy it more bigfool1956's Profile: http://forums.slimdevices.com/member.php?userid=13782 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
I'd recommend that you get the amp/speakers you want and hook up the TP directly to the amp and give it a listen. If you don't like what you hear, then add a pre-amp. I wouldn't budget for one right out of the box. Having said that, I ended up using one because I like the way it sounds. I'm using an SB3+Dac and adding a preamp brought the lower frequencies to life. I also like the tube sound in my preamp. You may not experience any of this with your equipment combo, so I think it makes sense to give it a listen and go from there. -Ben -- Ben Diss 'SB3' (http://www.slimdevices.com/pi_squeezebox.html) - 'Lavry DA10' (http://www.lavryengineering.com/productspage_da_10.html) - 'BAT VK-31SE' (http://www.balanced.com/products/line/Vk-31SE/index.html) - 'Halo A21' (http://www.parasound.com/halo/a21.php) - 'BW 803D' (http://www.bowers-wilkins.com/display.aspx?infid=1156) Ben Diss's Profile: http://forums.slimdevices.com/member.php?userid=4289 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
David - power transfer is irrelevant in the context of audio (generally speaking). It is very important in power stations and radio transmitters. Amplifiers and pre-amps have active devices in them - transistors and valves - that amplify the voltages. Power transfer is only relevant where we are trying to minimise losses in passive circuits like power lines etc. In line-level audio, we care about voltages rather than power. Optimum voltage transfer occurs with low source and high sink impedance so that the sink does not load the source. For speaker to power amp matching (and this differs slightly between valve amps with output transformers and tranny amps) the issue is that the PSU can only deliver so many volts (say 40) before it distorts. So, the output transistors vary the voltage between 0-40 volts (max). The speaker impedance is say a fixed 8 ohms (lets ignore reactance here) and the output impedance is usually lower - say 2 ohms. The output transistors do the work of varying the voltage to deliver the requisite power to the speakers. This is the opposite to mains wiring or antennas where we want to lose as little power as possible along the line - there are no amplifiers to compensate for the power loss along the way. The downside (if you can call it that) of having a low internal or output impedance of an amp is that more power is lost as heat within the output devices...that's why amps get hot. As an example, if your power amp can swing 40V from its PSU rails, has an impedance of 2 ohms and is running into an 8 ohm speaker, the max voltage the amp could deliver to the speaker would be: 40*(8/8+2) = 32 volts The power the amp could deliver into the speaker would be (39.5*39.5)/8=128 watts and the power lost inside the amp by heating up the heatsinks would be (32*32)/2= 512 watts of heat That's roughly 25% efficiency. This is for a Class A amp with full power delivery at all times (not class B!!!) If the impedance of the amp was 8 ohms: volts to speaker= 40*(8/(8+8)) = 20v power to speaker = (20*20)/8 = 50 watts power lost to heat = (20*20)/8 = 50 watts That's 50% efficiency...but the amp can only deliver 40% of the power of the other example. Given that the maximum volt swing from the PSU is a fixed thing and the speaker impedance is a fixed thing, the amp designer only has one choice...if he wants to deliver more power, he has to sacrifice overall efficiency and lower the impedance of the amp... I hope I haven't confused things? ...dons flame-proof suit, waits for attack by real electronics engineers :o) -- Phil Leigh You want to see the signal path BEFORE it gets onto a CD/vinyl...it ain't what you'd call minimal...SB3+Stontronics PSU - Altmann JISCO/UPCI - TACT RCS 2.2X with Good Vibrations S/W - MF X-DAC V3/X-PSU/X-10 buffer (Audiocomm full mods)- Linn 5103 - Linn Aktiv 5.1 system (6x LK140's, ESPEK/TRIKAN/KATAN/SEIZMIK 10.5), Townsend Supertweeters, Kimber Chord cables Phil Leigh's Profile: http://forums.slimdevices.com/member.php?userid=85 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
Thanks Phil and others I think I've got a better understanding of what's going on there. Actually I understand the Wiki article just fine. I derived the theorem in 2nd year EE and have an MSEE. It's covered in every Circuits 101 class. Actually I think opaq is a little confused about what it says because the reason the theorem doesn't apply for my question wasn't due to the parts about power transfer or efficiency. Of course thankfully others stepped up with very good clear-headed explanations as to what was going on. Thanks to Phil and others for that. There were some very good replies. As far as needing 400 watts. I have inefficient speakers. Aerial 7Bs (rated 86 dB but measured less in Stereophile). They drop to 4 ohms in the bass region. I thought about getting an MC252 but the MC402 was reommended for my speakers. But probably either one would work. Follow the old adage for cars - get the biggest engine you can in the model you want to buy. :) I've owned a 400 watt Krell and a 300 watt Musical Fidelity with these speakers and, yeah, they could get loud but I don't think they were overkill by any means. Also of course it has to do with delivering peak power when it's needed. Certainly the Aerials swallow the 100 watt Marantz I have hooked up to them now. It'll get loud too but you can tell they need something with more power or ability to deliver power when needed. Also nothing meant against Sean by quoting that link. No need for me to go and re-explain the theorem when a link would do. I was looking for a little more explanation and others nicely stepped up. regards, David -- wireless200 wireless200's Profile: http://forums.slimdevices.com/member.php?userid=11887 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
opaqueice;292064 Wrote: Actually the wikipedia article is fine - he just needed to read (and understand) past the first two sentences. Maybe that was too much to expect. Actually understanding the article - standard fare in any circuits 101 class - isn't the issue. The article doesn't say anything about what is best for audio quality does it. Obviously there's more to it than power transfer and efficiency. I think that's where you're getting confused. -- wireless200 wireless200's Profile: http://forums.slimdevices.com/member.php?userid=11887 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
Wireless, not sure you need all that power for the Aerials. FWIW, I have Aerial Model 9s-pretty similar to the 7bs except with more bass. When I first got them, I powered them with a 150 watt Classe intergrated. Sounded teriffic. However, I had been told by numerous sources that the 9s would only really sing with more power. I then purchased 2 350 Classe monos off of Audiogon. Not a great purchase. The bass may be a little punchier, but all in all not a significant improvement. I have heard the Aerials w/Mac gear and that is definitely a good match. Perhaps relevant to your original question, I run my TP directly into my power. Without attenuators, my amps had way way too much gain. Added Endler stepped attenuators and am now happy as a clam. Good luck. -- Shredder Shredder's Profile: http://forums.slimdevices.com/member.php?userid=11380 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
wireless200;292136 Wrote: I think that's where you're getting confused. Confused about what? -- opaqueice opaqueice's Profile: http://forums.slimdevices.com/member.php?userid=4234 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
Shredder;292146 Wrote: [...]Perhaps relevant to your original question, I run my TP directly into my power. Without attenuators, my amps had way way too much gain. Added Endler stepped attenuators and am now happy as a clam. Good luck. Shred, why didn't you adjust the jumpers inside the TP? Do you not want to open it up? regards, David -- wireless200 wireless200's Profile: http://forums.slimdevices.com/member.php?userid=11887 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
I've come to understand that less 'rated power' can -in principle- confer an advantage. Every active component has a dynamic range and that includes power amps. This means a lower rated amp -can- have an advantage conferred to it against a bigger amp whose dynamic range stays mostly unused even at maximum usable volume. I am talking about comparing differently powered models of the same amp design e.g. FPB200 vs FPB600. (Clearly, amps of different basic design have different current delivery into hard or complex loads and better load handling is in principle a good thing, but that's an aside to my point.) So bigger isn't automatically better. It depends! Darren -- darrenyeats SB3 / Inguz - Krell KAV-300i (pre bypass) - PMC AB-1 Dell laptop - JVC UX-C30 mini system darrenyeats's Profile: http://forums.slimdevices.com/member.php?userid=10799 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
Actually, I -am- confused about Phil's post. Phil Leigh;292086 Wrote: As an example, if your power amp can swing 40V from its PSU rails, has an impedance of 2 ohms and is running into an 8 ohm speaker, the max voltage the amp could deliver to the speaker would be: 40*(8/8+2) = 32 volts The power the amp could deliver into the speaker would be (32*32)/8=128 watts and the power lost inside the amp by heating up the heatsinks would be (32*32)/2= 512 watts of heat That's roughly 25% efficiency. This is for a Class A amp with full power delivery at all times (not class B!!!) In your examples you treated the amp as a voltage source and the output impedance as if it were in -parallel- with the load. But (regardless of the class) I thought output impedance is defined as the part of the internal resistance that's in -series- with the load (again, treating the amp is a voltage source, as you did). If that's right, an amp with an output impedance of 2 ohms driving an 8 ohm speaker will only lose (40-32)*(40-32)/2 = 32 watts of power, not 512, and the efficiency goes to 1 as the output impedance goes to zero. The reason class A amps have low efficiency is because they have an output transistor which dumps current to ground even when the signal is zero. Right? -- opaqueice opaqueice's Profile: http://forums.slimdevices.com/member.php?userid=4234 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
opaqueice;292163 Wrote: Actually, I -am- confused about Phil's post. In your examples you treated the amp as a voltage source and the output impedance as if it were in -parallel- with the load. But (regardless of the class) I thought output impedance is defined as the part of the internal resistance that's in -series- with the load (again, treating the amp is a voltage source, as you did). If that's right, an amp with an output impedance of 2 ohms driving an 8 ohm speaker will only lose (40-32)*(40-32)/2 = 32 watts of power, not 512, and the efficiency goes to 1 as the output impedance goes to zero. The reason class A amps have low efficiency is because they have an output transistor which dumps current to ground even when the signal is zero. Right? erm... surely the speaker is wired in parallel across the amp output? - thats why if you wire 2 identical speakers in parallel to an amp their impedance halves and the power delivery doubles...at least until the amp psu gives up! when the internal impedance of an amp hits zero that's a short circuit and the amp blows up! My example was VERY simplistic. AFAIK the amp is a voltage source in most cases. That's what the transistors do - they they act as a tap for the PSU voltage. I'm happy to be wrong... -- Phil Leigh You want to see the signal path BEFORE it gets onto a CD/vinyl...it ain't what you'd call minimal...SB3+Stontronics PSU - Altmann JISCO/UPCI - TACT RCS 2.2X with Good Vibrations S/W - MF X-DAC V3/X-PSU/X-10 buffer (Audiocomm full mods)- Linn 5103 - Linn Aktiv 5.1 system (6x LK140's, ESPEK/TRIKAN/KATAN/SEIZMIK 10.5), Townsend Supertweeters, Kimber Chord cables Phil Leigh's Profile: http://forums.slimdevices.com/member.php?userid=85 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
I always thought that Musical Fidelity does a good job explaining the benefit of reserve power in their amps - they focus on dynamic range and performance with musical transients, rather than a sustained db level performance. '_Here_is_one_such_explanation_from_them_' (http://www.musicalfidelity.com/products/supercharger/dynamicrange.html), and from there, also be sure to click on their System Diagnostic link to see an interesting interactive graphic... -- NewBuyer NewBuyer's Profile: http://forums.slimdevices.com/member.php?userid=7862 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
O is correct - when we speak of the impedance of a source, we are talking about what is effectively a series resistance in the source. For a power amp driving speakers, you want it as low as possible. See diagrams here: http://www.kpsec.freeuk.com/imped.htm. Also, highly recommend reading: The Art Of Electronics. But getting back to the subject of line-level audio, there's an example here if we suppose we're using passive attenuators, i.e. a resistor divider. Let's say you have a typical 100 ohm source and you want to divide its output voltage level in half. One way to do this would be to put a resistor divider on the output, say two 500 ohm resistors (for a load of 1K). Now you have an output with a higher impedance because the source is not as stiff, it's going through this high resistance that you've added in order to create the voltage divider. However, it's not exactly half, because the divider itself is also acting like a load, pulling down on the source's 100 ohm impedance. The voltage division is effectively as if you have a 600 ohm resistor and a 500 ohm resistor. But also, the new output after the divider has a higher Z because the load is being driven through that additional resistance of the divider. Alternatively, since there is some impedance in the load, you could just hang a single resistor to ground on the output, and this will create a voltage divider in conjunction with the source's 100 ohm impedance. But now the source is working much harder because it has to drive that relatively low impedance, not just the amplifier's high Z of 10K ohm. This will significantly increase the distortion level of an op-amp output. If you've followed all this so far it should make sense why you'd want a low source Z and a very high load Z for a line level signal. You're not trying to transmit gobs of power as with a speaker output, nor are you trying to deal with reflections as with a high-frequency signal. Instead, you are just trying to get signal information (a voltage level) from A to B as accurately as possible (low noise, low distortion). This is best achieved by a stiff or strong (ie low Z) source feeding a high Z load. The reason line-level sources have a 100ohm impedance instead of close to 0 is to provide some short-circuit protection for the output. And in Transporter, this impedance is in fact provided by a series resistor. By contrast, for speakers, you are trying not just to move information, but to actually get work done, and for that to happen your load must have a fairly low impedance: a few ohms, instead of many Kilo-ohms. Otherwise, the voltage required to make the load do anything would be ridiculously high. Also, now that you're dealing with significant power transfer, you want a source impedance as close to zero as possible, because otherwise a bunch of energy is being wasted in the source. -- seanadams seanadams's Profile: http://forums.slimdevices.com/member.php?userid=3 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
As to why impedance _matching_ (in the proper sense of the term) of amps and speakers is usually NOT desirable: basically the reason is that the efficiency is very poor. Let's suppose you have a power amplifier with an output Z of 0.1 ohms, and you want to get maximal power out of it. It might seem that this would deliver the most power into a 0.1 ohm speaker... and you could make a 0.1 ohm speaker by tying a bunch of regular speakers in parallel. The problem is that for this to work, the amp would need to be able to deliver enormous quantities of current at a very low voltage, and it's not feasible to design one that could do that. Conversely, let's say you have a 8 ohm speaker. For a given source voltage, maximal power would be delivered to the speaker when the output also has a 8 ohm internal impedance, but the problem is that under that condition you are burning an equal amount of power in the source: a lot of work is getting done by the load, but the system as a whole is only 50% efficient. In practice you are better off designing for efficiency, and upping the voltage. At first it is not really obvious why it works like that, but if you imagine the two extremes of the situation it makes more sense. If you put a short circuit (using a very large wire) across a battery, the battery will heat up but the wire will not. No work has been done outside the battery, so the system is 0% efficient. Now consider an infinitesimally tiny load attached to the battery. Efficiency is now 100% - the battery will not get hot because it isn't strained, but not much work is being done either, because the load is insignificant. It should be more intuitive now that the maximal power transfer would happen when the load is being driven as hard as the source can push, but this is not the same thing as maximal _efficiency_. Since solid state amps naturally have a very low Z, it does not make sense to put an additional resistance at the source - that would just waste power in the amp. Instead we enjoy higher efficiency by using a 4 to 8 ohm load, and use higher voltages to reach the output power levels desired. So that is why if an amplifier says it has 4 ohm outputs what they're really saying is this output can make voltage and current levels suitable to power a 4-ohm load, not this output has a 4ohm impedance. -- seanadams seanadams's Profile: http://forums.slimdevices.com/member.php?userid=3 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
100ohms, from http://www.slimdevices.com/pi_transporter.html -- radish radish's Profile: http://forums.slimdevices.com/member.php?userid=77 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
Hmmm, that's interesting... the TP has a 100 ohm output impedance and the McIntosh has a 10k ohm input impedance (20k ohm balanced). What does this mean as far as sound quality. Matching impedances result in maximum power transfer so this doesn't bode so well, does it? I don't know exactly. -- wireless200 wireless200's Profile: http://forums.slimdevices.com/member.php?userid=11887 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
wireless200;291846 Wrote: Hmmm, that's interesting... the TP has a 100 ohm output impedance and the McIntosh has a 10k ohm input impedance (20k ohm balanced). What does this mean as far as sound quality. Matching impedances result in maximum power transfer so this doesn't bode so well, does it? I don't know exactly. You are fine here - you want maximum voltage (not power) transfer in line-level audio, so making sure the load input impedance is at least 10 times the source output impedance is the guideline here when using unbalanced connections. I believe it is the same when using balanced connections - anyone know otherwise? -- NewBuyer NewBuyer's Profile: http://forums.slimdevices.com/member.php?userid=7862 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
Re: [SlimDevices: Audiophiles] output inpedance of the TP
wireless200;291846 Wrote: Matching impedances result in maximum power transfer so this doesn't bode so well, does it? That's wrong - below radio frequencies, you want a low source impedance and a high load impedance. 100R into 10K is a good (and typical) arrangement for audio. -- seanadams seanadams's Profile: http://forums.slimdevices.com/member.php?userid=3 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 ___ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
