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Sound Quality Vs. Measurements
Sound Quality Vs. Measurements
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Old 7th November 2014, 10:15 AM   #16941
PMA is offline PMA  Europe
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Sound Quality Vs. Measurements
So, you would not care about added wire inductance to capacitors, resistors, about unshielded wires capacitively coupled to anything in the neighborhood, right? Yes you have PCB trace inductances as well, but they are under control and repeatable, and capacitive coupling is effectively shielded by ground planes.
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Old 7th November 2014, 10:38 AM   #16942
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Old 7th November 2014, 11:02 AM   #16943
nigel pearson is offline nigel pearson  United Kingdom
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I would go further. The inductance is a very big friend. As long as we measure everything it is an option. Valve guys actually buy inductors to make a Pi filter. We can have a Pi filter out of the problem. One that helps exactly where it needs to ( LW MW SW ). Natuarlly one must bend wires just like it was a 1970's TV front end.

Dejan and I both favour oversized low Z decoupling and I spend money there more than on the big dustbins inside the PSU. If the dustbins have high Z so much the better. All they need is ripple ratings above the usual for long life.

What you and others are saying is make the problem go away. This is like exhaust gas. It is a problem, or an energy source? Turbo or no turbo? The main question is can the decouplers do the job and will the refresh rate be OK ? It is like the house plumbing. Does the water from the company fill the tanks quickly enough?

I would say a PCB power amp module is probably a good idea. Keep it very simple and try to make it into a Kirkhoff problem . The Hypex is hard to beat. It loves linear PSU's if large enough.

Alex Kitic's RH amps are very simple. I feel they are OK but can be improved. What I do like about them is they are Kirkhoff amps. Two valves joined by shunt feedback. Valve one cathode to 0V with a resistor, valve two cathode to 0V with resistor and capacitor. And that is mostly it.
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Old 7th November 2014, 11:09 AM   #16944
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Sound Quality Vs. Measurements
Quote:
Originally Posted by nigel pearson View Post
I would go further. The inductance is a very big friend.
Enough, to me. You like capacitor RLC resonances, you like unpredictable behavior of resistors. Do you ever measure these effects, or is it just your "philosophy"?
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Old 7th November 2014, 04:04 PM   #16945
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Originally Posted by nigel pearson View Post
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AR 94 bi-amp. Should be easy. One way is build an active tweeter amp. Personaly I would use capacitor coupling as the device will be filter No1 and protection in one ( you might need more poles ). A high grade 10 uF can be 100 V polyester or whatever is better. Build the amp with a bootstraped input to make it have a very high input Z. If classA the bootstrap should be benign . It goes between op amp minus and 2 x 10K on the input. Usually a series resistor and capacitor ( 5 K at 1 kHz - 3 dB ? ). The the little amp can be in paralell with the preamp output. I am assuming an OPA2604 with booster transitors. Myself I would use complimentary feedback pairs with 200 mA standing current. I would not have the outputs in the feedback loop as the tweeter will not upset the working and will stay in class A well enough. After listening tests feedback can be tried. The op amp will have traditional feedback, be it direct or via the output stage. Can have 50/50. OPA 2604 was very stable used this way.
Not going to happen, Nige. I keep them out of love only, but they cannot keep pace with my standard 1041 monitors - which can be bi-, tri-amped and eventually brought up all the way to a fully active status.

Now, THAT may happen yet.
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Old 7th November 2014, 06:41 PM   #16946
nigel pearson is offline nigel pearson  United Kingdom
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An idea I had a long time ago was to have a buffer amp feeding off of the main amp. By removing the tweeter more might be won than lost. The load coud be 1K at > 2 kHz with the tweeter removed. This would allow almost class A preformance from class AB amps ( most like high resitance loads ). The buffer would be class A and frequency tailored to the tweeter. The beauty is it changes very little of an existing set up and can adapt to many speakers. My Dynaco A25's should be one to try. I would use my OPA2604 amp. I found out 2 x 1N4007 with a small resistor ( 4R7 ) gave results no different to the Vbe bias. Tweaking the 1N4007 current will help make it lower bias. These old drawings of mine are my notes to myself. One can add filters just like you would to an OPA2604/604. I did feed the signal in via op amp -ve input. Can't say it sounded different. If the loop feedback is removed and placed at the op amp output the distortion is virtually identical. Sound it very different.
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Old 7th November 2014, 07:14 PM   #16947
nigel pearson is offline nigel pearson  United Kingdom
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Here again in single supply. Not an option I think that needs trying. If wondering why the low 1.5 mA it is as a simple amp is often drawn in text books. All I did was replaced the BD135/136 or whatever with a high gain pair. The idea being suddenly it becomes a super amp and it does. The two purple resitors are typical of a 1960's amp. They are fine if the heat sink is correctly sized. As it is class A bias only needs to be ball park. If the two reistors are 0R it becomes more or less the text book idea. One can play with the current as one pleases. Note how the distortion is non existant, Even at 65 kHz it wasn't much worse.

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Old 7th November 2014, 07:20 PM   #16948
dvv is offline dvv  Serbia
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Where are you going with this, Nige?

You still need to add active crossovers, and they are a bitch to make them sound right. If you go for them, I suggest you use new high speed (> 100 V/uS) op amps for filter functions. It really does make a difference.
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Old 7th November 2014, 07:37 PM   #16949
nigel pearson is offline nigel pearson  United Kingdom
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It just shows how easy it is to get strated if a tweeter. Sometimes just the output cap is good start ( try 6.8 uF perhaps ). 8 watts is more than enough for a tweeter. I doubt one needs 0.8 amps standing current ( 0.2 ? ) . This amp was built dead bug. It can be done. The filter cum output cap is what I would call the worlds most sophisticated protection circuit. For the worst case it is actually the dream solution. Being high grade the sound is not degraded.

I think the main reason active is diffiuclt is the whole game has changed. Suddently the tweeter is seeing the amp and is under that amps control. The removal of the global feedback might resolve that a bit. You will struggle to measure anything except with your ears. It will sound different and will measure the same. I kid you not. If someone says damping factor I will say yes but not how one should think of it. Remember most tweeters are resistor attenuated so that means worse damping.

Putting extra poles both into the op amp and arround it are easy. That means 4 poles if you want. Myself, two passive poles seems better. It is a shame to use an op amp if not considering using it's tallents. The complimentary feedback output stage is almost a zero distortion option unlike a Darlington or FET. Thus feedback is optional. How cool to have what peoploe call zero feedback amp that is also zero distortion. When class A and - 70 dB it is zero distortion.
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Old 8th November 2014, 07:44 AM   #16950
dvv is offline dvv  Serbia
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True, but we both know it takes a LOT more, don't we? If you want something decent, that is.

I was amazed at the prices some driver manufacturers want. Putting together a decent driver complement makes the cost of two amps such as you have shown a drop in the ocean. Just take a look at Wilmslow Audio prices, but do take a sedative before you do, I don't want you fainting.

It's easy enough for me only because I had the good sense to envisage my own speakers on a clear upgrade path straight away, so they have all it takes right now. To go fully active, I simply need to disconnect the respective parts of the crossover and rewire straight down to the binding posts. However, not many have that fortune.
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