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Old 16th May 2013, 01:12 AM   #9031
qusp is offline qusp  Australia
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coppertop, RF from GSM and various other spill, being rectified by bipolar junctions in opamp input/output stages and various other devices, then folded down as DC error, modulating the voltage across PCB traces and planes etc is a very real problem that will only get worse with the advent of power over wifi among other advances.
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Old 16th May 2013, 01:54 AM   #9032
4Torr is offline 4Torr  United States
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Off the topic a little...
I've found that pop music of the 60's and early '70's music sounds best to me when played by an AM music station on a mono dipole speaker radio. That's how I remember hearing it back in the day and how it moves me most.
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Old 16th May 2013, 02:17 AM   #9033
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Originally Posted by 4Torr View Post
Off the topic a little...
I've found that pop music of the 60's and early '70's music sounds best to me when played by an AM music station on a mono dipole speaker radio. That's how I remember hearing it back in the day and how it moves me most.
Made in a recording studio with your radio in mind, you're the audience, it's a live performance.

For hi-fi, you might record it with microphones in your room, and then play it somewhere else, so you can fuss over quality of reproduction.
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Old 16th May 2013, 07:57 AM   #9034
dvv is offline dvv  Serbia
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That cumulative RF interfearence IS a problem is hardly news. However, I would remind one and all that beisde looking at the phenomenon as such, you also need to remember the relative POWER of cell phones, wireless phones, TV and radio waves, etc.

A nice home grown test is to activate your phone (cell or wireles) and bring it near to your audio. If nothing untoward happens, your problem is small. If any audible interference does occur, then you do have a pronounced problem.

Especially nice is leaning the phone right on to your MC input, or your tuner's front end (puting it on the case right above the front end). Again, if nothing untoward happens, you're all right.

More prone to this sort of thing are the wild bandwidth amplifiers, espeially those of yore, such as say Sansui or Kenwood/Trio models from the late 70ies, which were allowed to do 500 kHz unhindered. Mind you, I also advocate wide bandwidth, do make it go above 300 kHz for good phase response, but do install a band limiting filter at its input, as people like reVox and Sony usually do. Sony even advertises internal and external slew rate, i.e. without and with the band limiting input filter.

Lastly, this is one of the reasons why one must pay a great deal of attention to as good decoupling as possible of the PSU lines. Typically, three unit, obe larger cap of say 100 uF, a smaller around 4,7-1 uF and lastly a 100 nF ceramic cap. In respect to the price of the whole shebang, this isn't really a great expenditure, and it certainly cannot hurt.
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Old 16th May 2013, 08:26 AM   #9035
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Off the topic a little...
I've found that pop music of the 60's and early '70's music sounds best to me when played by an AM music station on a mono dipole speaker radio. That's how I remember hearing it back in the day and how it moves me most.
Simple . Great turntables . Simple audio chain . Good amp . Sometimes 10 kHz bandwidth .

I even get good sound on my Sony SW ( ST 3950 ) . No way is it 2.5 kHz as some say .

Naim even claimed long range AM ( Australia ? ) was best ever sound . There was even stereo I was told with a +/- 20 Hz dead band to give a centre reference ( double SSB stereo = mono ) . 10 kHz top end . On researching this there is no limitation placed on HF ( especially long wave ) . The 4.5 kHz stated is typical . Distortion would be about like SE valve amps . Noise 50 dB on a good day .

Most of that music sounds great on a Garrard 401 ( Lenco 75 ) . Goldring 1042 or better . NAD 3020 as pre amp ( not bad ) . DIY power amp . Speaker to your taste . CD players , yet to hear one I like .

Last edited by nigel pearson; 16th May 2013 at 08:31 AM.
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Old 17th May 2013, 10:03 AM   #9036
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I renewed my acquaintance with Quad ESL 63 yesterday . Smaller than I remembered . I took a 200 mile round trip to Nottingham to try out my SE valve amp . So good to hear a speaker that tells the truth . The truth was very acceptable and plenty loud enough ( too loud to talk ) . The great advantage being that no feedback amps are fine with the Quads as is 8 watts ! Bass is very good and as I remembered . As my friend commented when correct the Quads do not sound dull . The amps below 1 % distortion up to 5 watts and mostly second harmonic . Just below clipping the harmonics are in suspension bridge reduction . The frequency response 15 Hz to 47 kHz - 3 dB and 20 Hz to 20 kHz -0.7 db ( related to 1 kHz and 8R ) . The amp is optimized for 6R .

On CD the total system distortion will be less than 1 % typical . At times 0.1 % Hiss and hum inaudible . It didn't make me a total convert to valves . I would run a very discrete subwoofer from 15 to 100 Hz with transistors . I like the hard incisive quality of a big paper cone speaker and transistor amp . Something like Holliman perhaps ?
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Old 19th May 2013, 04:07 AM   #9037
qusp is offline qusp  Australia
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Originally Posted by dvv View Post
More prone to this sort of thing are the wild bandwidth amplifiers, espeially those of yore, such as say Sansui or Kenwood/Trio models from the late 70ies, which were allowed to do 500 kHz unhindered. Mind you, I also advocate wide bandwidth, do make it go above 300 kHz for good phase response, but do install a band limiting filter at its input, as people like reVox and Sony usually do. Sony even advertises internal and external slew rate, i.e. without and with the band limiting input filter.

Lastly, this is one of the reasons why one must pay a great deal of attention to as good decoupling as possible of the PSU lines. Typically, three unit, obe larger cap of say 100 uF, a smaller around 4,7-1 uF and lastly a 100 nF ceramic cap. In respect to the price of the whole shebang, this isn't really a great expenditure, and it certainly cannot hurt.
agree completely and thats how I design too, except for the obligatory and somewhat arbitrary decoupling scheme, which will not touch (well not much) higher power common mode GSM location chirps. the above is not news to me, rather what i'm working to improve on. its possible to improve rejection of common mode by up to 30-40dB over the above with combination common mode/differential filters for example x2y, as I mentioned

Last edited by qusp; 19th May 2013 at 04:10 AM.
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Old 19th May 2013, 04:40 AM   #9038
hpeter is offline hpeter  Europe
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The only time RF affects my brain is when I have been working inside a TV transmitter building. These give us headaches. The field strength from these is above safety limits and you do not hang around. The public never goes near these field levels
quite soon is planned wireless solution to wired standards, it works ~60ghz
people will be beamed not only by wifi at home
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Old 19th May 2013, 06:37 AM   #9039
a.wayne is offline a.wayne  United States
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We're looking for the same Holy Grail, fas42. If only we knew why.

I know lots of Jamaicans, and not one has any conception of what I think we generally mean by "hi-fi". Most Jamaican music...several entire genres...is mostly played on systems we would consider appalling, cobbled together and messed about with until they sound right.

Who am I to argue? It's their music, so they get to define what hi-fi means. They add plenty, and are especially fond of rattling bass bins. Adding stuff may be OK if it's the right stuff. Perhaps hi-fi is whatever the music expects?

Little Richard sounds wrong on my system, and I pine for my old Dansette. Arguably, every hi-fi enthusiast should have an American car radio, too, and an American car to go with it. OTOH, "River Deep, Mountain High" was a flop in America because those radios couldn't resolve it, so it sounded like a wall of noise.

I'm with you on the "whatever first impressed" theory, fas42. That was when we were into the first rush of listening to contemporary music as a social activity, and we heard it on the best equipment of the time. That time, for me, was pretty much the dawn of available hi-fi, and we and our mates got into the kind of sophisticated music that made use of it. We were an elite in that respect. Perhaps we hanker still for that feeling?

The idea of having a system that is better than everyone else's is narcissistic, surely? Music is a social thing, so what's best cannot legitimately be private.
Those Jamaicans you know are into "sound Systems" not HiFi , different genre to those into HiFi , the ones into HiFi are as serious as any ...
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Old 19th May 2013, 07:48 AM   #9040
dvv is offline dvv  Serbia
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agree completely and thats how I design too, except for the obligatory and somewhat arbitrary decoupling scheme, which will not touch (well not much) higher power common mode GSM location chirps. the above is not news to me, rather what i'm working to improve on. its possible to improve rejection of common mode by up to 30-40dB over the above with combination common mode/differential filters for example x2y, as I mentioned
I bought into serious decoupling with Otala's texts. He used, as the last before the output trannies, a seris resitor of 1 Ohm and xxx nF capacitor to the ground, naturally on all power amp supply lines.

At first, I didn't think too much of it, but later on, it tickled my imaginaton. So I did some experimenting. To cut a long story short, I found that virtually all power amps could benefit from it, some more, some less. Since it really gets rid of residual inductance from the PSU (non reguilated, just apssive caps), I was not really surprised to note that low quality amps, with low quality power supplies, benefitted the most.

The trick is in the tuning. I'm sure there are ways to calculate it fairly precisely, but that's boring. Much more fun listening for it, start with a very low value like 220 nF and work your way up. Anyway, there aren't that many steps up to 680 nF which is the largest value I ever used. You know, try 220 nF, then the first next value and so forth for as long as you can hear any difference, even if minimal. Once you cannot, go back a step, and that's it. A wonderful excuse to tell your good wife why you simply must run the system at a power level hgher than usual.

And odd things can happen. With Toshiba 2SC5200/2SA1943 trannies, rated at 150W, once I couls ghear some "birdies", literally like chirping birds. Very low level, but it was unmistakably there. On a whim, I took the Toshes out and replaced them with Motorola/ON Semi MJL 3281/1302. Nominally, a very similar transistor, both being based on Toshiba's 2SC3281/2SA1302. Just replaced them one on one.

Chirping gone. But that's only half of it. I now had a smoother (so to speak) midrange and better treble, more life-like. Since everything was the same in both cases, I was a bit caught out with that. So I checked and double schecked, got in some well hearing friends, and we all agreed, the difference was small, but it definitely WAS there.

From their Data Sheets, I note Toshiba says collector output capacitrance is "200 pF TYPICAL", while Motorola says "600 pF MAXIMUM". So I picked up both lots and went to see some friends with an excellent lab nearby. About 10 pairs in each lot. The AVERAGE value for Toshiba was 320 pF and for Motorola 390 pF. That's close enough on two output pairs that I seriously doubt that was the reason for any differences.

What we must never forget is that while two nominally same trannies from two sources may well satisfy all Data Sheet requirements, but they will always be products of two different technologies, quite simply no two manufacturers have the same technological process, so it stands to reason that their products will be at least slightly different - whether that's enough to cause audible differences we cannot know any other way but to try them both.

While I suspect the effect will vary in different circuits and in its extent, I submit that these small, subtle differences WILL produce some differences in sound. As such, I feel this is a variable which also needs to be taken into account during designing.
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