Yes, but you ran with your own interpretation and I could no longer get a word in.
Yes, really.
As I said, "The frequency components of the pulse get ever so slightly changed in magnitude and phase and the bridge greatly magnifies this. Nothing there but tiny fractions of a dB and a few degrees of phase." , but that just didn't cause any controversy.
Last edited:
Richard will be happy to read this
Not only "NOT evil", but as it help us to get rid of DC offset adjustments, with all the evils of the adjustable potentiometers, it save time (money) and bring a better reliability over the long term.
In fact, the only annoyance of servos is the need of +-12V DC rails to power the IC.
No need to servo or use DC blocking caps in the feedback path of a CFA. Both the nx and sx amps are DC coupled and the drift and offset are exemplary. With the diamond buffer you have 1 st order cancellation of the delta Vbe so imeadiately are into low drift territory. Close physical proximity also helps. I use an offset adjustment pot - but with a servo you need a power supply, decoupling not mention an opamp as well so the pot is hardly excessive in that context.
You can not get away without DC blocking or a servo on most blameless or balanced bipolar input VFA's. As for JFET inputs . . . You will need to match and use a servo or DC blocking.
Last edited:
But they are SO cool !
I can screw up , and my servo "saves me" ,
Any devices for Q1-4 , you can get real "sloppy" on this circuit.
I Modifed one of my creations - listening to the (below) "abomination".
For a true entry level build , it just works. My last CFA , BTW.
PS - having the same semi's for Q1-4 - almost no thermal drift.
Output slowly cycles +/- .1mv (not as good as the simulation).
R6/9 are different - running Q2 20% more Ic than Q1 for laughs !
OS
Attachments
If you look to the diamond VSSA i published, you will find some advantages.
In the original VSSA, there is some additional gain provided by the input stage. That was clever. It helps to reduce open loop distortion, while keeping the schematic as simple as possible. The cap increase the feedback at DC to 100%. The drift at the output will be only the one of the input stage.
The servo i suggested brings some obvious advantages, specially on an industrial point of view, by suppressing the need of any fine tuning of the DC offset. And you can set its gain to go even further, decreasing the offset, simplifying the temperature coupling of the input devices.
Yes, it adds complexity, but, once the board is designed, it is only few components more to add to the circuit, and their overall price and size are lower than the original Lytic CAPs. Too It dont brings audible evils of those awful devices, with a relatively short life, full of DA etc. ;-)
Too, there is two advantages to set the input filter were i did. It kills the natural instability at very HF of the diamond and it makes the FC of the input filter not sensitive to the source impedance.
About powering tthe IC of the servo, yes it need an effort to power-it. But you can set an additional +-15V power supply that you can share with a protection circuit, like the one in my signature. And even build the preamplifier in the box, powered by the same PSU...
I have an interesting question.
If I've figured this out correctly, one reason resonant tweeters sound bad is because they keep radiating for some time after the input signal has passed. So for short bursts of treble, on average the treble is actually louder because it lasts longer. So, is it possible that resonant tweeter can also increase hearing loss?
If I've figured this out correctly, one reason resonant tweeters sound bad is because they keep radiating for some time after the input signal has passed. So for short bursts of treble, on average the treble is actually louder because it lasts longer. So, is it possible that resonant tweeter can also increase hearing loss?
Interesting, indeed. But, if you look to waterfalls of speakers, you will see that tweeters usually resonate less longer than other speakers.
My point is more that, once excited by any frequency, they resonate at a frequency with is often in the most sensitive range for our ears.
Reason why i always preferred my two way system, crossed at 700Hz, limited at 16KHz without tweeters than the same with the help of any super tweeter ?.
Last edited:
But this also works the other way: in a highly resonant system, amplitude needs some time to build up. You need to accumulate a sufficient amount of energy to be able to release it later.
C'mon Esperado . . . Let's at least be honest here and not concoct fairytails about the benefits of servos and caps. Throw the damn things out and be done with it!
That makes sense, but a loudspeaker in practice is abysmally inefficient. As I understand the efficiency is greater at the resonant frequency, thus more power, which would show as either longer ringing or a peak in intensity, or both.
I think servos are the way to go and that the need for an offset pot is a disadvantage, not to mention the necessary matching of transistors. An amplifier with a given gain, on the order of 20-30, when dc coupled, will have about the same offset without a pot, for a given degree of input transistor matching, be it CFA or VFA. A CFA has no fundamental matching benefit over a VFA. Moreover, a VFA built with a single monolithic NPN dual matched pair can provide very good offset performance.
I prefer a power amplifier to have less than 20mV offset at the output, and the dc servo is the best way to accomplish this without an offset pot or a lot of transistor matching (if you don't want to use a capacitor in the feedback network).
A good dc servo is quite simple and takes up very little board space, and is probably less expensive than an good-quality dc offset trim pot.
Cheers,
Bob
You disappoint me. And your comments make-me think you are not serious.
Instead of using terms like "fairy tails" better to *demonstrate* were i'm technically incorrect (if i was).
I don't said anything strange about caps neither. Lytics are not totally transparent, everybody noticed-it. And you have to change them, let say, all the 10 years ?
A servo just allow to use film caps instead. Better and long lasting.
The main negative point with a servo is the output noise of the IC.. ahah, reduced by -54dB in my example, go figure !
And all my other arguments are valid, including the time to tunne DC and evils of the trim pots with years, oxidation etc.
Last edited:
- Status
- Not open for further replies.