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Post by Boomzilla on Jun 5, 2024 5:26:13 GMT -5
Correct me if I’m wrong, please.
I have always read that the input impedance of any power amplifier is essentially halved when you’re using its XLR (balanced) inputs. So the single ended (RCA) inputs are half the sensitivity but twice the input impedance. Is this right?
If so, then is it also fair to say that, all other things being equal, the XLR inputs require twice the current from the preamplifier as the RCAs?
Normally, this is not an issue. Any properly-designed, AC-powered preamp has robust output buffers and current to spare. But might this become an issue when driving the power amp(s) from a USB-powered DAC? If the source USB port has current limitations, and you’re trying to drive low-impedance XLR inputs on the amp, might the DAC struggle to supply the needed current?
I’m currently driving the XLR inputs of my Emotiva PA-1 power amps from an AudioQuest Dragonfly (a USB-powered DAC). It works, but I’m having to run it with its volume turned almost all the way up to get sufficient volume. Would I do better to run the power amps single-ended? Or would the higher-impedance input load be offset by the lower amp sensitivity?
Enquiring minds want to know.
Thanks - Boom
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KeithL
Administrator
Posts: 10,077
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Post by KeithL on Jun 5, 2024 11:39:03 GMT -5
Actually no... It's rather more arbitrary than that. On most modern amplifiers the balanced and unbalanced inputs use what amounts to different input circuitry. Therefore the input impedances and gains of both are simply set by the designers. The input impedance on each line is set by the value of a resistor... and "anything between about 10k and about 47k is normal". (There are minor reasons why the designers may go one way or the other in a particular design... but they really are pretty minor.) An unbalanced input has a single signal input... signal(+). A balanced input has two signal inputs... signal(+) and signal(-). It's pretty common these days for all three of those lines to have the same input impedance on a given piece of equipment. THERE'S SOMETHING WORTH NOTING HERE...
Back in the days of transformer coupled inputs and outputs impedance matching was somewhat important.Transformers tend to not act properly, or to deliver a good quality signal, unless they are matched to the proper impedance at the other end of the wire ("proper termination"). This was true for a lot of gear back in the days of tube gear... Pro gear also continued to use transformer coupled inputs and outputs for a while after they stopped being used in consumer gear... Back in the early days there were distinct benefits to using transformers for balanced inputs and outputs. However, these days, most of those benefits no longer exist - especially for line level signals. And so you will almost never find transformer coupled line level inputs or outputs these days. (You still find a few transformers in microphones and on the inputs of a few microphone preamps.) NONE of this is true for modern gear with solid state line level inputs and outputs. The rule of thumb for modern gear is that "the output impedance on the output should be significantly lower than the input impedance of what it's connected to". You will sometimes see specific numbers like 5x or 10x mentioned... although those are not necessarily requirements. Also note that "the minimum recommended load" is NOT the same as "the output impedance"... The simple reality is that, with modern solid state gear, input and output impedances are just plain not a concern. The outputs of pretty well any solid state preamp or DAC can drive the inputs of pretty much any solid state power amp or other device. In fact, the outputs of most solid state devices can cheerfully drive the inputs of multiple solid state devices. (The outputs on any of our gear can drive at least three or four inputs on any other gear of ours through passive splitters with no problem at all.) And, as far as output levels and input levels, there is a sort of de-facto industry standard that... - line level outputs should be able to deliver 1V or 2V or a bit more - line level inputs on things like preamps should be happy with input levels of 0.5V to 1V or a bit more - power amps often require a bit more drive level to reach full output (but all preamps will pretty much have no problem driving any power amp) It's also worth pointing out that, with most equipment, things like maximum output levels are also really arbitrary. The only exception is that SOME USB-powered devices are limited by the capabilities of the USB supply voltage. Likewise the output voltages available from the outputs of some battery operated devices like phones and tablets tend to be limited. (Some internally step up the USB voltage to a higher +/- voltage, but some are limited to the 5V swing of the supply provided by USB, or the 3.7V swing of a single battery.) I think you'll find that, on the Dragonfly, the maximum output voltage is not a limitation so much as a design choice. (And, to be honest, I forget whether one leg on the balanced input will give you more or less gain than the unbalanced input on the PA1... so you'll have to try that.) H OWEVER, I can tell you that the inputs on any solid state amp are NOT "putting a significant load" on the outputs of the Dragonfly or any other solid state device. That output voltage is simply being limited by "whatever the designers designed it to put out at full volume". (And none of that has to do with the current capabilities of the USB output.) Correct me if I’m wrong, please. I have always read that the input impedance of any power amplifier is essentially halved when you’re using its XLR (balanced) inputs. So the single ended (RCA) inputs are half the sensitivity but twice the input impedance. Is this right? If so, then is it also fair to say that, all other things being equal, the XLR inputs require twice the current from the preamplifier as the RCAs? Normally, this is not an issue. Any properly-designed, AC-powered preamp has robust output buffers and current to spare. But might this become an issue when driving the power amp(s) from a USB-powered DAC? If the source USB port has current limitations, and you’re trying to drive low-impedance XLR inputs on the amp, might the DAC struggle to supply the needed current? I’m currently driving the XLR inputs of my Emotiva PA-1 power amps from an AudioQuest Dragonfly (a USB-powered DAC). It works, but I’m having to run it with its volume turned almost all the way up to get sufficient volume. Would I do better to run the power amps single-ended? Or would the higher-impedance input load be offset by the lower amp sensitivity? Enquiring minds want to know. Thanks - Boom
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Post by Boomzilla on Jun 5, 2024 13:10:53 GMT -5
Thanks KeithL - What I needed to know!
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Post by leonski on Jun 5, 2024 15:45:33 GMT -5
I just looked at the Pass Labs 30.8 stereo, pure 'A' amplifier. Input impedance for SE / Bal is listed as 50 / 100. (presume Kohms?)
But that is the TOTAL for balanced. Typically, input impedance is 1/2 what they call for balanced PER LEG, , but the rating is TOTAL......
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Post by Boomzilla on Jun 5, 2024 16:49:13 GMT -5
Today's discovery - I'd ordered a mechanic's stool on wheels for the audio rack from Wal-Mart yesterday (so I wouldn't have to crawl around on the floor to revise wiring). Got notice of delivery today. Went to the corner UPS Store to pick it up - wasn't there. Checking online order details, Wal-Mart's driver delivered it to the UPS Store at the LSU Union building. I can't pick it up there without getting a parking ticket from the campus cops. Notified Wal-Mart; asked for a replacement; told me they couldn't. Got refund instead. Ordered anew (this time from Amazon). Lesson learned - Don't deal with Wal-Mart! Plan B - Currently have audio gear on a 3-shelf high, double-wide rack. IF (ah say IF) I were to reconfigure the rack to a six-shelf, single-wide, vertical rack, I could access the gear from a standing position without needing to crawl around anymore... Wire routing might be a slight challenge, but nothing I can't handle.
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Post by marcl on Jun 5, 2024 18:07:23 GMT -5
Today's discovery - I'd ordered a mechanic's stool on wheels for the audio rack from Wal-Mart yesterday (so I wouldn't have to crawl around on the floor to revise wiring). Got notice of delivery today. Went to the corner UPS Store to pick it up - wasn't there. Checking online order details, Wal-Mart's driver delivered it to the UPS Store at the LSU Union building. I can't pick it up there without getting a parking ticket from the campus cops. Notified Wal-Mart; asked for a replacement; told me they couldn't. Got refund instead. Ordered anew (this time from Amazon). Lesson learned - Don't deal with Wal-Mart! Plan B - Currently have audio gear on a 3-shelf high, double-wide rack. IF (ah say IF) I were to reconfigure the rack to a six-shelf, single-wide, vertical rack, I could access the gear from a standing position without needing to crawl around anymore... Wire routing might be a slight challenge, but nothing I can't handle. And then there's what I did ... I clamped a semicircular shelf that I had extending out from the regular shelves so i could just walk around and get to all the wiring. the only pain is that huge Outlaw 7500 five-channel at the bottom that weighs a ton, but I rarely have to pull that out.
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Post by Boomzilla on Jun 5, 2024 18:19:39 GMT -5
Whoa! That's cool. Did you make that or buy it?
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Post by leonski on Jun 5, 2024 18:27:52 GMT -5
Marcl, I THOUGHT you looked familiar! Gene Krupa, right?
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Post by marcl on Jun 5, 2024 20:06:55 GMT -5
Whoa! That's cool. Did you make that or buy it? April Fools Day 2004 I started working for IBM. I was home-based ... imagine, in 2004! So I had to set up a home office, and I searched and found the desk I wanted. It had this shelf on the left side. A couple years later (I worked for IBM 7 months and quit!) I moved the desk downstairs to the "padded cell". I had bigger monitors so I didn't need that curved shelf ... so I got this idea ... And leonski ... I was always more of a Buddy Rich kinda drummer ... here's the current kit next to the shelf ...
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Post by leonski on Jun 6, 2024 18:47:24 GMT -5
Aren't you glad Ringo Starr didn't come up?
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Post by Boomzilla on Jun 7, 2024 5:27:03 GMT -5
My subscription has expired. Before automatically renewing, and since things have probably changed in the interim, it is time to ask the question again; Tidal or Qobuz?
Pertinent factors:
I’ll be running Roon as my music player and want integration into the Roon interface. Specifically, when I do a search in Roon Remote, I want both content from my local library and my streaming service to be displayed.
I primarily listen to classical and rock but with some jazz, blues, and soul. I’m interested (sometimes) in new releases, but don’t generally listen to internet radio.
I don’t care about high-rez, MQA, or DSD.
And, of course, I want the broadest selection for the best price.
Suggestions?
Thanks!
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cawgijoe
Emo VIPs
"When you come to a fork in the road, take it." - Yogi Berra
Posts: 4,955
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Post by cawgijoe on Jun 7, 2024 7:02:00 GMT -5
My subscription has expired. Before automatically renewing, and since things have probably changed in the interim, it is time to ask the question again; Tidal or Qobuz? Pertinent factors: I’ll be running Roon as my music player and want integration into the Roon interface. Specifically, when I do a search in Roon Remote, I want both content from my local library and my streaming service to be displayed. I primarily listen to classical and rock but with some jazz, blues, and soul. I’m interested (sometimes) in new releases, but don’t generally listen to internet radio. I don’t care about high-rez, MQA, or DSD. And, of course, I want the broadest selection for the best price. Suggestions? Thanks! This is probably not going to help, but… I’ve had both Tidal and Qobuz and went with Qobuz. It’s less expensive and in my mind sounds better. I don’t use Roon, so no help there. I do care about hi-rez and Qubuz delivers.
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Post by Boomzilla on Jun 7, 2024 7:53:18 GMT -5
Awesome, cawgijoe - Thanks for the feedback. I'm leaning that way too. On an unrelated topic - I had an appointment with my ENT doctor yesterday. He said that in 2020, I had the hearing acuity of a 20-year-old (unusual for a 68 year old man who had worked around noisy machinery for 25 years). But in 2023, my high frequency haring had declined significantly. He said that presbyacusis normally didn't change one's hearing that quickly, and that the 2023 test may well have been affected by other factors. I may have had sinus problems that day, or one of the medications I was taking might have affected the test. I go next Wednesday to repeat my hearing test. The doctor told me to take a Claritin the morning prior to the test. We'll see what we get...
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Post by marcl on Jun 7, 2024 8:37:09 GMT -5
Awesome, cawgijoe - Thanks for the feedback. I'm leaning that way too. On an unrelated topic - I had an appointment with my ENT doctor yesterday. He said that in 2020, I had the hearing acuity of a 20-year-old (unusual for a 68 year old man who had worked around noisy machinery for 25 years). But in 2023, my high frequency haring had declined significantly. He said that presbyacusis normally didn't change one's hearing that quickly, and that the 2023 test may well have been affected by other factors. I may have had sinus problems that day, or one of the medications I was taking might have affected the test. I go next Wednesday to repeat my hearing test. The doctor told me to take a Claritin the morning prior to the test. We'll see what we get... I posted these before, but relevant to your experience ... hearingtest.online/www.headphonesty.com/2024/04/old-ears-hearing-age-test/Maybe not as accurate as the ENT test, but useful to look at trends and to connect bodily symptoms to audible effects. My Dr told me to use FloNase daily to keep down the congestion that I'm aware of in my right ear. I do hear better when I use it. My use of these tests shows some variability. But still not bad for being a 69+ year old drummer A couple weeks ago I did the first test using my Sennheiser HD280Pro headphones (left) and again using my Bose QC20 wired earbuds (right). Maybe the response curves of the phones are different. But I also know my ear canals are narrow, and so maybe the earbuds represent what my ear hears when not obstructed by the narrow canal. BTW ... Sean Olive posts often on FBook about his headphone testing, and he recently said they JUST got a new audiometer to use when screening listeners for hearing loss before doing listening tests .... it works to 20KHz while previous models only worked to 8KHz. The tests linked above only work to 8KHz but I know from using a signal generator in my room that I can hear SOMETHING up to 12-13KHz. So speaking of proverbial Harman curves ... I actually put a slight RISE of a couple db above 4KHz on my L/R Dirac target curve based on what I see in the test results.
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Post by leonski on Jun 7, 2024 17:20:49 GMT -5
Above posts about hearing 'acuity' are interesting. I was at an airshow (LOUD....than LOUDER!) and between flyovers, was speaking with a guy at a booth. HIS claim, after I asked about dads running around with kids on their shoulders and NO HEARING PROTECTION, was that the American Man in his 40s had worse hearing than a South African Bushman (Kalahari) in his 60s..... or older.
This rings true, if you'll pardon the expression.
ME? I wore fitted earplugs and gave the soundproof cans to the wife.
In general? Western and 'Industrial' countries, especially in Urban areas, are IMMERSED in a constant sea of NOISE. One good and loud rock concert? A 4th of July fireworks show? Even your gas powered Lawnmower or chain saw? ALL work against long term hearing acuity.
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Post by Boomzilla on Jun 7, 2024 18:43:13 GMT -5
Yeah - noise is killer for ears. I see a generation driving around in boom-box cars - they’ll need hearing aids before they’re 50!
I did have an interesting conversation with my ENT doctor about the future of hearing therapy. I suggested to him that advances might be made in the circular canals that would cause broken cilia to regrow, to flush broken debris from the canals (think “oil change for the ears”), or to make the auditory nerve more sensitive. He agreed that each of those ideas had potential, but that we weren’t there yet with current medicine.
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Post by Zombie on Jun 7, 2024 19:14:37 GMT -5
Yeah - noise is killer for ears. I see a generation driving around in boom-box cars - they’ll need hearing aids before they’re 50! I did have an interesting conversation with my ENT doctor about the future of hearing therapy. I suggested to him that advances might be made in the circular canals that would cause broken cilia to regrow, to flush broken debris from the canals (think “oil change for the ears”), or to make the auditory nerve more sensitive. He agreed that each of those ideas had potential, but that we weren’t there yet with current medicine. While I don’t really listen to music that loud now and honestly never have, whatever hearing loss I’ve had has been attributed to my drum playing. Particularly the crack of the snare drum. About 50% of my playing has been wearing over-the-ear headphones but the other 50% of the time I wore nothing. My hearing isn’t that bad but I have noticed the loss of higher frequencies in recent years. I don’t think it’s a real problem but my wife will occasionally ask me “did you hear that?” Usually my response is “no” but I think it’s more attributed to ignoring her than actual hearing loss. My drums have allowed me to have selective hearing and get away with it. 😊
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Post by leonski on Jun 7, 2024 19:29:40 GMT -5
Zombie? many years ago in my apartment days, I would play music probably TOO loud. But my scam was to convince my NEW neighbors that I was partially DEAF and that was the only way I could hear my music. I cooled it in the evenings and never before 1100 or noon.......Only worked when MOVING INTO a new place..... Faking Non-Hearing is good acting. Practice pays off!
I've been thinking along the lines of Boom for new medical treatments. Some for of NanoBots with VERY specific missions may help. I'm think initially for DENTAL work to clean and dispose of various Plaques / Decay or perhaps in the bloodstream to attack (another plaque) deposits in blood vessels.......
I'm certain many other uses for such useful machines could be found.
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Post by Boomzilla on Jun 7, 2024 21:09:38 GMT -5
We are in the dark ages of auditory medicine. Things will be different for our great grandkids.
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Post by leonski on Jun 7, 2024 22:40:42 GMT -5
Just my OPINION but in the majority of instances of hearing loss? I suspect a lifestyle / enviromental connection. If you lived in a quieter manner? Hearing should be very good and for many more years.
Disease and other loss agents are real, however, just like a non-smoker with excellent diet and no enviromentals will sometimes get lung cancer.
When I took woodshop, I was virtually the ONLY person to use earplugs when operating tooling. Teacher, a fairly young person had hearing loss which I ascribe to simple use of loud equipment over tens of years. Noise / Level concerns were NEVER addressed in ANY classroom session or materials.
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