Sound Quality Vs. Measurements

[simon7000]

Originally Posted by scott wurcer

When the wiper lifts the gain is very low, that was my point.

Scott,

The issue is not when things work right, it is real world abuse. Assume the 1000 uF capacitor has a leakage of say .01 uA per uF x V. For even an 8 volt unit that would be 80 uA across 100K that would be .1 volt and across 10K .01 volts. The gain at maximum would be 60 dB. at minimum maybe 30 db. so that .09 volts would become 2.844 volts of pop! Now if the gain structure were set wrong you might be able to damage a speaker. But if the gain structure is set so you clip around 7 to 12 volts, then you will hear noise but most likely no damage.

E.S.

[dvv]

[QUOTE=nigel pearson;3013111]

Originally Posted by dvv

Nige, I would strongly suggest you try one of these.

ref Booster circuits .

Thanks everyone who looked at the mic amp circuit . Many studios do use similar circuits even now . I was told today D V V that studios upgraded from your early OPA series you like to NE 5532/4 ! Also the boosters , Option 2 goes down the pub to discuss as it is intriguing . Thanks

You were not kidding when saying about your amps . Amcron have a serious rival in current delivery . Sound I am sure also .

Intrigued by 0.165 R in PSU between stages ( 0.330 x 2 ) . I also noticed 22 nF diode suppression on bridge rectifiers . In Germany a customer removed similar from my amps and insisted it sounded more open . Opinion now says fit RC snubber ., Some use 470 R and about 4n7 . 10 nf suppressor and 100 R + 68 nF snubber as the ultimate combination. These where for a specific transformer . I suspect they will be useful to try . I think I can find the maths somewhere .

Frankly Nigel, I don't see moving from OP 37 to NE as an upgrade. The only caveat of OP 37 is that since it is a decompensated version of OP 27, it is stable with gains of 5:1 and over. If you need unity or smaller than 5:1 gain, this can be a problem, you have to compensate it and fool around with it a bit, but that's all.

If you use current boosting, I think it will still come out as one of the best ones out there, which is a feat, given that it is hardly a new one, now around 28 to 30 years at large (off hand).

Snubbers can work, I agree, but experience tells me that this will not happen every time. It seems they are most useful with really sensitive stuff, like phono and mic preamps.

On the other hand, since I use shunt power supplies for everything but the main power amp, after several attempts, I came to the conclusion that there's no difference with or without them in my particular case. This could be attributed to the construction of the shunt stabilizer, who knows.

If one is using simpler forms of stabilization, like 3 point stabilizers, I would say there is a positive difference.

Option 3 is for those cases when you need a lot of current boosting. If you choose for your output transistors say BD 139/149 (easily available, dirt cheap), you can drive 50 Ohm loads no problemo. If you use say MJE 15030/15031, which are 50W devices, you can build a simple but very effective say headphones amp, eaisly capable of driving sub-8 Ohm loads, let alone over 30 Ohm loads. And in true, pure class A mode, but for that, you will be needing some serious heat sinks.

For a true power amp, use say BD 139/140 as drivers, and say 2SC5200/2SA1943 as output devices. If you are feeling melancholy, use BD 249/250 C as output devices for that distinctly sweet, vintage sound, but since their gain is not exactly stellar, use more powerful drivers, say BD 239/240 C. On the other hand, their current capability is outstanding, 25A continuous, 40A in impulses (50A if from SGS-Thomson), so you could end up with an amp which is a Current Monster.

[nigel pearson]

[IMG][/IMG]

D V V . I think the boosted op amp idea is great . Alas my notes on my circuit are lost although so much like what you did to be not worth showing ( No 3 ) . This version would drive a 4 ohms speaker . The results were what one would get working from theroy alone . All the better rules applied I should say ( decoupling , gain etc ) . This was a class A design running approximately 1 A . It used simple diode and resistor bias ( vbe was tried for bias also ) .

Notice how both op amps are loosely speaking generics of 741 . Notice also how 5534 is unhappy . Better op amps were tried with startling differences . The 5534 problems are easy to cure with comp cap . However.....

The LF 351 N was kept as control during tests . It was much better than expected . TLO71 measured almost the same , it sounded different and to me less good .

The test also shows how the 5534 marginally had a higher output . I reran these tests and can say they are representative . Note all op amps had a surplus of current to drive the output stage .

The amp works well with no output stage feedback to the op amp . This is shown with feedback .

I was going to design a discreet op amp after this and never got far . A blameless TDA2050 if you like .

These are just my workshop notes .

[john curl]

Come now, we can do better than this, certainly? '-)

[nigel pearson]

Hi John . Shame I lost the circuit , it was simple and nice . The buffer proved very useful for comparing op-amps . I was supporting D V V and saying it is a good idea . Two modest op amps representing in miniature the whole debate . It is 2 minutes work to try another op-amp and opinions on op-amps is another matter .

Last night by semi-chance I visited the streets where two of our greatest audio people lived . Plantation Road and Walton Well Road . Two minutes walking distance apart . Percy Wilson and Michael Gerzon . I hope they knew each other ? How facilitating to have been there if they had . Michael I am sure would have written on this forum if he had lived into the age of broadband . As many will know his patents cover much of how modern digital works ( loss-less encoding ) .


Packing It All In

BTW. Alan Blumlein was dyslexic . I doubt he would have been on this forum . Michael is likened to Blumlein .

http://community.klipsch.com/forums/...Phonograph.pdf

[john curl]

Michael Gerzon was a genius, on the level of Richard Heyser. In fact, I got the two of them to get along with each other, about 30 years ago. Some tension, at first. Two very smart guys suspicious of each other, but as I knew them both, I knew they would get along, once they personally met each other. In my life experience, they were the two most innovative minds that I ever knew personally. Alas, both died young, before their time.

[scott wurcer]

Originally Posted by simon7000

Scott,

The issue is not when things work right, it is real world abuse. Assume the 1000 uF capacitor has a leakage of say .01 uA per uF x V. For even an 8 volt unit that would be 80 uA across 100K that would be .1 volt and across 10K .01 volts. E.S.

I still don't follow you. I don't see how you would get more than 10's of mV across the cap.

[scott wurcer]

Originally Posted by nigel pearson

As many will know his patents cover much of how modern digital works ( loss-less encoding ) .

He might have been a great engineer but that is a bit of an overstatement. The concept of signal entropy came from Shannon, and in any case the predominant lossless format (FLAC) is free.

[nigel pearson]

Originally Posted by john curl

Michael Gerzon was a genius, on the level of Richard Heyser. In fact, I got the two of them to get along with each other, about 30 years ago. Some tension, at first. Two very smart guys suspicious of each other, but as I knew them both, I knew they would get along, once they personally met each other. In my life experience, they were the two most innovative minds that I ever knew personally. Alas, both died young, before their time.

You know if Jesus had made a secret visit to earth I would believe it to be Michael . He was the kindest man I ever knew . Very dignified and giving . If you are an atheist one should still accept how a person is said to be important .

My teacher for many years was another Oxford audio man . Unknown to all . 20 Lathbury Road which is also near the other two . I would guess Michael knew him .

Oxfordshire Blue Plaques Scheme

[nigel pearson]

Originally Posted by scott wurcer

He might have been a great engineer but that is a bit of an overstatement. The concept of signal entropy came from Shannon, and in any case the predominant lossless format (FLAC) is free.

Audio was Michael's hobby gone wrong . I had the privilege of mildly discussing maths with him . A friend and I were convinced Michael would be the greatest mathematician who every lived . Alas this bloody hobby we all love got hold of him .