Ridiculous. "Opposite of engineering" - really???
So amp manufacturers who use lots of power devices in their output stages are also working "opposite of engineering"?
Your thesis illustrates that assumption is the mother of all screwups (no insult intended, just parapharising). The reason is simple - you never bothered to ask under which conditions do those transistors operate? As it happens, they operate under double pure class A conditions, meaning that they are biased at twice the current the maths say they will realistically need even with less effcient headphones. Since my available heta sink are is limited, I need such devices which can take the stress and work for decades without failure. I coukld have gotten away with it using smaller devices, like say BD 139/140 or some such, but I'd have to increase the size of the heatsink for safe operation.
And indeed, under normal operating conditions, ambient temp 25 C, they will work non stop for days without overheating, delivering 22.5 V peak to peak, into an 8 Ohms load.
They can actually drive my loudspeakers, but obviously to small power levels only, as limited by the +/- 16.5 V PSU.
You can call it whatever you like, I call it a job decently done. I am not aware of ANY dynamic headphones it cannot drive to ear splitting levels.
Much to my embarassment, the schematic shown is wrong. I noticed that later on, when Federico Paolini of Analog Audio warned me, sent Lucio the corrected one and asked him to swap them, but appearently he never did.
Later on, I was shown a Texas Instruments schematic which was pretty similar. I never made it, so I couldn't compare the two.
Still later on, "Elektor" published a design where this configuration, with an added pair of Darlington power devices, acted as a decent power amplifier. It was billed as a "100W amplifier" into 4 Ohms. I am not sure how you can actually squeeze 100W of power from a single pair of relatively lower powered devices (125W each, if memory serves).
But it seems to be catching. For example, Marantz bills one of their prestigious integrated amp, using 200W devices, as delivering 200 Watts. Either they know something I don't, or some copywiter got carried away.
The latest fad seems to be quoting 1 mS impulse power outputs. To me, 1 mS is a completely useless specification regarding an audio amplifier. I am not happy with IEC standard of an impulse being 20 mS either, I think it's too short, to me, anything below 50 mS is too short. That's the delay time I put in my protection circuits.
Only if you want to cheer him up with a so-so sound at best.
I tried it and was not very happy with what I heard. Sure, it works flawlessly, and does its job as advertised, but the sound quality was to me below par. To start sounding decent, it needs headphones with an impedance of 220 Ohms or more, works well with Beyer's 600 Ohm cans. Unfortunately, most headphones these days fall into the 30-100 Ohm impedance slot.
My Sennheiser HD 598 for example sounded aenemic, even if bass is not their key selling point.
Unfortunately, the OPS is about the only serious problem area for many IC amps.
Here we are just looking for the absolute lowest thd numbers as it is a test instrument --- signal generator.
He can try it and see if the numbers are sota or not into a low z. Do you have lower thd OPS/buffer to recommend for driving low z loads? Would like to see -140dB, if possible.
THx-RNMarsh
Here we are just looking for the absolute lowest thd numbers as it is a test instrument --- signal generator.
He can try it and see if the numbers are sota or not into a low z. Do you have lower thd OPS/buffer to recommend for driving low z loads? Would like to see -140dB, if possible.
THx-RNMarsh
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I was reading a paper recently (I can’t remember which, sorry) and it was shown there that AD797 scores high as an RFI immune device even among the special “EMI hardened” modern ICs
George
As you are fond of German and classic stuff : www.sac-gmbh.de/sac/Files/Download/Prospekte/pa50T-b.pdf
110W/4, from a single pair of 130W A1294/C3263.
With AD797 in the last decade of manufacture (YeeY, mr. Wurcer).
And not even Sanken manufacture power devices, but Made in China ISC copies. Mr Fuchs believes they 'sound' better than the Japanese originals.
'Squeezing' 100W/8 continuous output power out of them would be harder, but plenty 'classic' Japanese examples for that.
The Texas Instruments IC, linked to by JCX, can really deliver 2 x 1A.
Fully driven, your TO-92 complementary pair buffer would die trying, and not even come close to 1/10th of that figure (with common rail voltages for a line stage).
(means you're OK with the text in the TNT article ?)
I guess you didn't follow Barrie Gilbert's article? His analysis was for and ideal buffer output stage.
To be fair to the other contributors (there have been many) overcoming the issues of using small signal op-amps has been the subject of literally dozen's of threads here for quite a few years, this is not new. They have contributed a lot of complete designs that work. I don't think it reflects well that you roll the calender back every few weeks and act like nobody has contributed anything that maters.
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-130dB involves the entire signal chain including every aspect of supply coupling and grounding scheme.
This is definitely a case of ten builds will all measure differently.
I am not a German audio freak, but I do have much respect for some audio companies and for German engineering in general. Mostly through personal experience, everything I have which is German made still works today as it did then. I know of this company, but have not heard antything by them in action.
As for what op amps are declared for, I am aware of what the Data Sheet says, but I'm equally aware of what happens when you do add a simple pair current buffer. You do not HAVE to use the mentioned transistors, you could directly connect a pair of BD 139-16/140-16 and get even more current. I find that for line level applications not expected to go below 600 Ohm impedance, a pair of said to-92 will do just fine.
By adding a pair of BD 139/140 drivers and a pair of 2SC5200/2SA1953 to the output of a simple BB 2604, you can build a very good power amp of 22-24W/8 limited only by the PSU line voltage. And so forth.
Anyway, there's no point in arguing this, since most people will probably never try it for whatever reason. Their loss.
Just as I will not trust any op amp to deliver currents of 1A or above. The problem of heat scares the hell out of me.
I have increased total capacitance in my phono preamp Blowtorch-like raw power supply from 4700 micro to 6800 same brand and type of capacitors.
I left 24hours for burn-in. But sonic results are not good-sound is degraded with lack of precision , loss of fine details and with a false body of instruments.
It seems that Pavel is right when he suggesting not to go over the top with capacitors in preamps power supplies. He uses humble 1000 micro in his regulated power supply. Perhaps some people like coloration which high value capacitors provide-it reminds me of microphonic valve type of coloration.
I left 24hours for burn-in. But sonic results are not good-sound is degraded with lack of precision , loss of fine details and with a false body of instruments.
It seems that Pavel is right when he suggesting not to go over the top with capacitors in preamps power supplies. He uses humble 1000 micro in his regulated power supply. Perhaps some people like coloration which high value capacitors provide-it reminds me of microphonic valve type of coloration.
Helping the guys tweak the demo card Friday, as I was saying they farkled to grounding scheme.
Can-you simulate and publish the bandwidth/phase curves at the input of the VAS in closed loop ?
The best FT that I'm able with very fast CFAs is around 10KHz, by habit.
It's detailed in the sx-Amp write up on my website with the loop gain plot.
Yes. -130 dB is not achievable with a casual approach.
-126 dBV is already 0.5uV.
I have not found anything like this (or bandwidth curves of open loop).
I'm sure you have a sim file for your amps: it is so easy to trace the bandwidth at the input of the VAS, closed loop. !
Well, i don't believe it is possible to do a lot better, unless using a lot of local feedback, so very low GNFB ratio.
Flat up to 60KHZ ? i don't believe-it.
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