|
|
Post by Boomzilla on Dec 12, 2015 21:17:23 GMT -5
When you hook it up to a 4-ohm load. I know that in theory the wattage output doubles (ohm's law), but only if the power supply is sufficiently robust to deliver the extra current.
Most amplifiers can NOT deliver that much current, so their four ohm output is less (sometimes significantly less) wattage than the theoretical 2x the 8-ohm output.
Which brings up the next question. Since the power supply may already be "sagging" with 4-ohm loads, what does this do the the SOUND of the amp?
Is there less bass control? Do the output transistors change their frequency response curve due to the higher operating temperatures?
I realize that there are too many variables to give any absolutely factual answers, but assuming a standard A/B-class amplifier configuration, what should the listener be aware of to determine whether or not the amp is under stress. For purposes of this question, please assume operation WELL below the clipping range.
Thanks - Boomzilla
|
|
|
|
Post by jackpine on Dec 12, 2015 22:03:30 GMT -5
I know the damping factor drops in half. It is a ratio of the amps output impedance to the speakers impedance. Most newer solid state amps have very high damping factors so it shouldn't too big an issue.
|
|
|
|
Post by deltadube on Dec 12, 2015 22:44:43 GMT -5
When you hook it up to a 4-ohm load. I know that in theory the wattage output doubles (ohm's law), but only if the power supply is sufficiently robust to deliver the extra current. Most amplifiers can NOT deliver that much current, so their four ohm output is less (sometimes significantly less) wattage than the theoretical 2x the 8-ohm output. Which brings up the next question. Since the power supply may already be "sagging" with 4-ohm loads, what does this do the the SOUND of the amp? Is there less bass control? Do the output transistors change their frequency response curve due to the higher operating temperatures? I realize that there are too many variables to give any absolutely factual answers, but assuming a standard A/B-class amplifier configuration, what should the listener be aware of to determine whether or not the amp is under stress. For purposes of this question, please assume operation WELL below the clipping range. Thanks - Boomzilla clipping ... u push the amp to limits it clips the signal.. blow your tweeters 1st... smoky smell... .. get an emo amp !!! |
|
|
|
Post by garbulky on Dec 13, 2015 0:40:20 GMT -5
On your speakers it will sound shouty. And the mids will have a suck out. And the sound will be somewhat thin. It won't be warm.
|
|
|
|
Post by vcautokid on Dec 13, 2015 0:51:30 GMT -5
Amplifiers that show that they are about at their limit have trouble resolving, and run into audio compression. Also harshness happens too. If you have a high current swing amplifier, even if it doesn't do the half the impedance double the power, aka as the perfect voltage source, you would be fine. Lots of better things to lose sleep over. There is a great primer in the Emotiva Videos about how much amplifier do you really need. This might be a good refresher too. My mantra is that there is never too much good clean power. No speaker was ever harmed with good clean power.
|
|
|
|
Post by Boomzilla on Dec 13, 2015 5:17:04 GMT -5
...My mantra is that there is never too much good clean power... Yes and no. There is no such thing as free lunch - in economics or in audio. I'm familiar with the conventional wisdom on how much power one needs. I'm also familiar with the fact that musical crescendos, and even transients, require many, many times the "steady state" power requirements. What I'm absolutely NOT convinced of is the completely unproven, but often voiced theory that "more power is better." I see. vcautokid. that you've qualified your statement with "good, clean power," but I'd still question the veracity of the core concept. What does more power really cost? I'm asking the question not from an economic standpoint, but from a sonic one. When you go to multiple output devices (for a conventional amplifier, pairs of NPN-PNP transistors), you get a choir singing - not a soloist. Every one of those transistors has a tolerance range with slightly differing, overlaid transconductance curves. The less expensive the transistors, the wider the tolerance range. The more output transistors, the bigger the choir. The above paragraph is descriptive of best-case brand new transistors. When the transistors heat up, their tolerances become wider. As the transistors age, their tolerances become wider, and diverge in random directions. Is it audible? To most, apparently not. But the purest music I've heard has always come from lower-powered amplifiers that used fewer output devices. Coincidence? I don't think so. So I politely partially disagree with your power statement. I completely agree that if you're stupid enough to clip your amplifiers (regardless of power), you put your speakers at risk. So, if you're even occasionally a headbanger, then more power is always better. But for those of us who listen at perpetually lower volumes, then there's sound quality to be gained by listening to lower-powered amplifiers. As to damping factor, KeithL has said that the concept is overrated, and I agree. After all, transformer-coupled, vacuum-tube output stages have relatively low damping factors due to their inherent transformer impedance, but still manage to have tight bass. At the clipping limit, or with poorly-designed driver circuitry, I can see where bass control would be poor, but that rarely happens these days. So back to the original question - Assuming a sufficiently robust power supply, and further assuming that the amplifier will not be driven to clipping, what should one expect when a solid-state amplifier (no output coupling transformers) is played into a 4-ohm speaker? garbulky says "... it will sound shouty. And the mids will have a suck out. And the sound will be somewhat thin. It won't be warm." In short, exactly the sound most often produced by AV receivers. Most AVRs aren't rated for 4-ohm loads, and their power supplies are meager (to meet their price points). I couldn't have put it so succinctly! So my take-home from this conversation is: If you're going to run four-ohm speakers, then you'll also want an amplifier with a high current power supply. For me, this rather changes the idea of using a Chinese or British integrated amplifier for four-ohm speakers. Most integrated amps don't have the power supply for high current (there are exceptions - Krell comes to mind). So, with my 4-ohm speakers, I may be better served by keeping muscular mono block power amps and just live with the extra componentry. Zilloid |
|
|
|
Post by Gary Cook on Dec 13, 2015 5:37:17 GMT -5
if you want to hear what a speaker really sounds like, then DON'T listen to it on a tube amp. ALL tube power amps with output transformers have a very low damping factor (compared to almost all solid state amps). This means that most modern speakers, which are designed to be used with amps that have a relatively high damping factor, will sound muddy with most tube amps. For example, by definition, any amplifier with a low damping factor WILL interact with the differences in load impedance common to typical speakers, so a tube amp with a damping factor of 5 is virtually guaranteed to sound different on every speaker you connect to it, while a solid state power amp with a damping factor of 500 is unlikely to be affected measurably (or audibly) by slight changes in the impedance of the load. The tubes in a power amp are operating under much more trying conditions: they're being asked to supply lots of current and dissipate a lot of power. Now, we take the output from those tubes, and send it through a transformer, which adds distortion, other nonlinearities, and is a "very interesting load" in terms of impedances and phase shifts that vary with frequency, and other similar complications. And the output of that transformer has a relatively high output impedance, which means that it doesn't control the speaker very well (low damping factor), which is where you get the less well controlled bass. Tube amps in general tend to have very low damping factors; while virtually all modern solid state amps have very high damping factors (which allows them to control the woofer very well). While their low damping factor means that the bass performance of tube amps will vary wildly depending on what speaker you connect them to, in general they produce weak, boomy, or muddy bass when you connect them to a speaker designed to work with modern high-damping-factor amplifiers. Cheers Gary |
|
|
|
Post by Boomzilla on Dec 13, 2015 9:42:02 GMT -5
Hi Gary Cook -
Thanks for the info! I'm not advocating tube power amplifiers (although they do work well with some speakers). And your quotes from KeithL are correct - he believes that more damping factor is better. Someone else here, then, posted about "there really wasn't much difference between a damping factor of some low number and a damping factor of above that number, provided that the lower number was "enough" for the speakers. In other words, damping factor is vitally important until you have enough - and after that more doesn't specifically get you much "better."
This contradicts KeithL's comments, so since I can't remember who said it (or evaluate the credibility), let's just toss it out & say that high damping factors are good.
This would argue strongly (for those who like tube sound) that a tube-SS hybrid amp would be the best of both worlds. Tube sound (from the preamp section) with high damping factor from the solid state output section. This is consistent with what my ears tell me. Qinpu makes an A-6000 integrated with tube inputs & a 16.5 WPC solid state output module. It's intended as a headphone & desktop amp, and it sounds wonderful!
Cheers!
|
|
DYohn
Emo VIPs 
Posts: 18,494
|
Post by DYohn on Dec 13, 2015 10:14:52 GMT -5
|
|
|
|
Post by audiobill on Dec 13, 2015 10:54:42 GMT -5
if you want to hear what a speaker really sounds like, then DON'T listen to it on a tube amp. ALL tube power amps with output transformers have a very low damping factor (compared to almost all solid state amps). This means that most modern speakers, which are designed to be used with amps that have a relatively high damping factor, will sound muddy with most tube amps. For example, by definition, any amplifier with a low damping factor WILL interact with the differences in load impedance common to typical speakers, so a tube amp with a damping factor of 5 is virtually guaranteed to sound different on every speaker you connect to it, while a solid state power amp with a damping factor of 500 is unlikely to be affected measurably (or audibly) by slight changes in the impedance of the load. The tubes in a power amp are operating under much more trying conditions: they're being asked to supply lots of current and dissipate a lot of power. Now, we take the output from those tubes, and send it through a transformer, which adds distortion, other nonlinearities, and is a "very interesting load" in terms of impedances and phase shifts that vary with frequency, and other similar complications. And the output of that transformer has a relatively high output impedance, which means that it doesn't control the speaker very well (low damping factor), which is where you get the less well controlled bass. Tube amps in general tend to have very low damping factors; while virtually all modern solid state amps have very high damping factors (which allows them to control the woofer very well). While their low damping factor means that the bass performance of tube amps will vary wildly depending on what speaker you connect them to, in general they produce weak, boomy, or muddy bass when you connect them to a speaker designed to work with modern high-damping-factor amplifiers. Cheers Gary Oh my, I'd better get some solid state asap!!! LOL!!! |
|
|
|
Post by mgbpuff on Dec 13, 2015 11:15:03 GMT -5
Why we can not get a definitive answer regarding damping factor, power required, etc. is this simple fact - an amplifier / speaker set up is an open loop system. This means that for the speaker to respond as close as possible to the input signal, we are dependent on some uncompensated characteristics to be just right to get optimum sound. Friction, air pressure and accompanying associated losses all combine to give an output (sound) that is dependent to a varying degree to things that we are not controlling. Some sort of cone position or sound pressure feedback would be required to make sound reproduction controllable and therefore impervious to uncompensated external force influences. I don't believe anyone has come up with such a system save for some unusual sub woofer designs. So in the mean time we debate whether this or that is better with little agreement because many external influences are not being controlled.
|
|
|
|
Post by geebo on Dec 13, 2015 11:19:01 GMT -5
define 8 ohm amp. Is it an amp that's not recommended with 4 ohm loads?
|
|
|
|
Post by Boomzilla on Dec 13, 2015 11:25:04 GMT -5
define 8 ohm amp. Is it an amp that's not recommended with 4 ohm loads? Yes - The manufacturer specifies output power at 8 ohms only & gives no indication whether or not the amp is suitable for 4 ohm loads (much less power output / distortion at that load). |
|
|
|
Post by Boomzilla on Dec 13, 2015 11:28:26 GMT -5
Thanks, DYohn - a VERY good article. |
|
|
|
Post by geebo on Dec 13, 2015 12:45:12 GMT -5
define 8 ohm amp. Is it an amp that's not recommended with 4 ohm loads? Yes - The manufacturer specifies output power at 8 ohms only & gives no indication whether or not the amp is suitable for 4 ohm loads (much less power output / distortion at that load). Well if it is not recommended to connect 4 ohm loads then it's protection circuit might just shut it down and the end result is no sound at all.  |
|
|
|
Post by vcautokid on Dec 13, 2015 13:02:57 GMT -5
if you want to hear what a speaker really sounds like, then DON'T listen to it on a tube amp. ALL tube power amps with output transformers have a very low damping factor (compared to almost all solid state amps). This means that most modern speakers, which are designed to be used with amps that have a relatively high damping factor, will sound muddy with most tube amps. For example, by definition, any amplifier with a low damping factor WILL interact with the differences in load impedance common to typical speakers, so a tube amp with a damping factor of 5 is virtually guaranteed to sound different on every speaker you connect to it, while a solid state power amp with a damping factor of 500 is unlikely to be affected measurably (or audibly) by slight changes in the impedance of the load. The tubes in a power amp are operating under much more trying conditions: they're being asked to supply lots of current and dissipate a lot of power. Now, we take the output from those tubes, and send it through a transformer, which adds distortion, other nonlinearities, and is a "very interesting load" in terms of impedances and phase shifts that vary with frequency, and other similar complications. And the output of that transformer has a relatively high output impedance, which means that it doesn't control the speaker very well (low damping factor), which is where you get the less well controlled bass. Tube amps in general tend to have very low damping factors; while virtually all modern solid state amps have very high damping factors (which allows them to control the woofer very well). While their low damping factor means that the bass performance of tube amps will vary wildly depending on what speaker you connect them to, in general they produce weak, boomy, or muddy bass when you connect them to a speaker designed to work with modern high-damping-factor amplifiers. Cheers Gary This is why everyone has better ears than me if it is MOSFET, Bipolar, and how many? I don't know about if I could tell the difference in a good quality amplifier today, maybe care that much. I have heard some amps that the Mini X will swamp. Just saying. Of course your mileage may vary. |
|
|
|
Post by Boomzilla on Dec 13, 2015 15:32:54 GMT -5
Well if it is not recommended to connect 4 ohm loads then it's protection circuit might just shut it down and the end result is no sound at all. The manufacturer does NOT say 8-ohms only or "not suitable for lower impedances." Instead, they say nothing at all. It's a Yaqin VK-2100 and it came without an owners manual. Google doesn't seem to provide one either. The amplifier's specs: ●TUBE: 12AU7 * 2 12AT7 * 2 (Voltage amplifiers and drivers) ●Output Transistors: 2SA943 x 2 and 2SC5200 x 2 (Toshiba Japan) ●Maximum Output: 85W per channel ●Output Impedance: 8Ω ●Input Sensitivity: 0.25V ●Distortion: ≤0.5% (1KHz) ●Frequency Response: 10Hz ~ 100KHz (-2dB) ●Signal-to-Noise Ratio: 85dB (A weight) ●Power Supply: 110v/220V AC 50/60Hz Not very good, but the sound may be better than the specs (or not). With 8-ohm speakers, the thing may do well, but my gut feeling is that it'll be stressed severely by 4-ohm loads. At this price, I doubt that the thing even has protection circuits. We'll see... |
|
|
|
Post by garbulky on Dec 13, 2015 15:39:47 GMT -5
|
|
|
|
Post by Boomzilla on Dec 13, 2015 15:50:52 GMT -5
Thanks, garbulky - They, in fact, DO specify that it's OK from 4 to 8 ohms, but the only distortion or power specs provided seem to be at 8 ohm loads. Presumably, things go downhill from there. What the heck - If they blow my tweeters then I've learned something. I'm going to fire it up! |
|
|
|
Post by Axis on Dec 13, 2015 15:53:35 GMT -5
if you want to hear what a speaker really sounds like, then DON'T listen to it on a tube amp. ALL tube power amps with output transformers have a very low damping factor (compared to almost all solid state amps). This means that most modern speakers, which are designed to be used with amps that have a relatively high damping factor, will sound muddy with most tube amps. For example, by definition, any amplifier with a low damping factor WILL interact with the differences in load impedance common to typical speakers, so a tube amp with a damping factor of 5 is virtually guaranteed to sound different on every speaker you connect to it, while a solid state power amp with a damping factor of 500 is unlikely to be affected measurably (or audibly) by slight changes in the impedance of the load. The tubes in a power amp are operating under much more trying conditions: they're being asked to supply lots of current and dissipate a lot of power. Now, we take the output from those tubes, and send it through a transformer, which adds distortion, other nonlinearities, and is a "very interesting load" in terms of impedances and phase shifts that vary with frequency, and other similar complications. And the output of that transformer has a relatively high output impedance, which means that it doesn't control the speaker very well (low damping factor), which is where you get the less well controlled bass. Tube amps in general tend to have very low damping factors; while virtually all modern solid state amps have very high damping factors (which allows them to control the woofer very well). While their low damping factor means that the bass performance of tube amps will vary wildly depending on what speaker you connect them to, in general they produce weak, boomy, or muddy bass when you connect them to a speaker designed to work with modern high-damping-factor amplifiers. Cheers Gary It has been a very long time since I heard a good Tube system and it was so Yummy. I am sure Keith is spot on and you really need the right speakers for the job. I am thinking some klipsch Heritage series speakers may do the job but before I die I want to have a good Tube system just for old time sake. |
|
