When the silicon diodes switch off the tube rectifiers will stay on until 0volts, may damp transformer ringing. Could be the thinking behind this idea?
^^ Good point. That way you would not get much in the way of commutation noise, but the higher voltage output of solid state rectifiers and the tube would last a really long time.
But since the supply Voltage is more than the pinch off from the diode, then this conduction to 0V is a bit academic. The tube diode is redundant and serves no purpose, apart from burning heat.
Certainly, but it's a very expensive ~60 ohm resistor used for damping (compared to a snubber). When the silicon stops conducting, there is still a rather steep rise in dynamic resistance though of course not 'infinite'.
Couldn't agree more!. It also eliminates the need for and inductor and a zobel filter on the output. I have also found it allows minimal compensation which allows greater bandwidth, better slew rate and no need to over compensate the amplifier just so you Can have marginal security with say an esl panel and it's highly capacitive load wreaking havoc on the stability of the gain stage 🙂.
Colin
That's a huge accusation! Did you actually see this for yourself? If so it's disgusting and please post details - the company should be exposed. This would almost certainly be considered false advertising and illegal under the consumer code in my country. If you buy a "nuvistor" amp you expect the amplifiying to be done by nuvistor tubes right? It'd be kind of like buying a V8 and finding a turbo-charged 4 cyl inside the engine casing with a secondary audio system that makes V8 noises, no? 😡
If not though, what you're saying is probably opening the door to some legal action and I wouldn't blame them one bit for it if it happens.
That LED thing is fairly common with semi-pro guitar and recording gear.
Usually the tube is in circuit to provide euphonic distortion but to save money and enable the use of generic wall warts they do not run at the proper voltage.
So they fake the warm glow with an orange LED.
This is usually pointed out in reviews.
VladimirK "Is GNFB perfect and what could be wrong with it? Many people subjectively find that there is "a fly in the ointment", speaking about GNFB story. But nobody can proove it strictly.
One skilled mathematician, who became interested in audio, tried to understand audible effects of GNFB for himself (I red his posts at forum). In the most general assumptions, he considered the feedback quadripole. The most common result is that a quadripole with any kind of feedback is always a generator. In the case of positive feedback - we know what the generator is. In the case of a negative - the generation fades exponentially. If one wants to minimize the generation decay process (settling) - try to achive maximum speed at feedback loop. Therefore, for amplifiers with GNFB it is good to have more than megahertz passband. For amplifiers without GNFB, it is not necessary.
Another finding was, "be careful with spectral analysis". "Better care of time locations of extremes of a signal as a function of time". "Linear distortions could harm more than nonlinear"."
--Class D amps only have 350kHz passband and use global negative feedback, some models have insane amount of loop gain.
john curl "lad, your math guy may be on to something important. We are constantly looking, but our test equipment screens out what we are looking for. The subjective results is virtually always: Higher bandwidth, or better yet, no global negative feedback."
The words "subjectively" and "subjective results" have a big meaning in this case, That means the subject is comparing sound to his imaginary ideal of what is right without knowing what has happend in the recording process a small change in the mic position changes stereo image massively, The subject is comparing his vague memory of sitting in the audience space while the recording is done on stage with stage mics mixed with ambience mics, even if it is done only in the audience space both M/S and X/Y technics don't sound like you are sitting in the audience everything sounds different from the get go and then the engineer will tweak it to sound acceptable on all devices.
Just because the subject wants the records to sound softer on the top end and more fat in the middle and no feedback adds a little of this kind of distortions the subject boldly declares that is better,
If you really want to test the amp quality put it inside your listening chain after the preamp and hook a load on it, tap the signal from the output into your familiar power amp and listen with the test amp in and out of your audio system if you can't hear change then your amp is good if you can then your amp is not simple as that.
In my experience the low distortion high feedback type pass the test and the no feedback fancy artisitic amps always change the sound in some way.
Be scientific about it not believe in faires, ghosts and goblins.
One skilled mathematician, who became interested in audio, tried to understand audible effects of GNFB for himself (I red his posts at forum). In the most general assumptions, he considered the feedback quadripole. The most common result is that a quadripole with any kind of feedback is always a generator. In the case of positive feedback - we know what the generator is. In the case of a negative - the generation fades exponentially. If one wants to minimize the generation decay process (settling) - try to achive maximum speed at feedback loop. Therefore, for amplifiers with GNFB it is good to have more than megahertz passband. For amplifiers without GNFB, it is not necessary.
Another finding was, "be careful with spectral analysis". "Better care of time locations of extremes of a signal as a function of time". "Linear distortions could harm more than nonlinear"."
--Class D amps only have 350kHz passband and use global negative feedback, some models have insane amount of loop gain.
john curl "lad, your math guy may be on to something important. We are constantly looking, but our test equipment screens out what we are looking for. The subjective results is virtually always: Higher bandwidth, or better yet, no global negative feedback."
The words "subjectively" and "subjective results" have a big meaning in this case, That means the subject is comparing sound to his imaginary ideal of what is right without knowing what has happend in the recording process a small change in the mic position changes stereo image massively, The subject is comparing his vague memory of sitting in the audience space while the recording is done on stage with stage mics mixed with ambience mics, even if it is done only in the audience space both M/S and X/Y technics don't sound like you are sitting in the audience everything sounds different from the get go and then the engineer will tweak it to sound acceptable on all devices.
Just because the subject wants the records to sound softer on the top end and more fat in the middle and no feedback adds a little of this kind of distortions the subject boldly declares that is better,
If you really want to test the amp quality put it inside your listening chain after the preamp and hook a load on it, tap the signal from the output into your familiar power amp and listen with the test amp in and out of your audio system if you can't hear change then your amp is good if you can then your amp is not simple as that.
In my experience the low distortion high feedback type pass the test and the no feedback fancy artisitic amps always change the sound in some way.
Be scientific about it not believe in faires, ghosts and goblins.
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That's a huge accusation! Did you actually see this for yourself? If so it's disgusting and please post details - the company should be exposed. This would almost certainly be considered false advertising and illegal under the consumer code in my country. If you buy a "nuvistor" amp you expect the amplifiying to be done by nuvistor tubes right? It'd be kind of like buying a V8 and finding a turbo-charged 4 cyl inside the engine casing with a secondary audio system that makes V8 noises, no? 😡
If not though, what you're saying is probably opening the door to some legal action and I wouldn't blame them one bit for it if it happens.
A tech who worked at that company posted on this forum a few years ago.
He was deeply unimpressed and specifically called out the issue we have been discussing here. There are a few other comments floating around. I'll leave it at that.
There are several headphone amps floating around with dual triodes running at 16V at the inputs, the tube is lit by some bias LED's but it is used in the signal path.
IIUC Scott, the triode anodes have 16 volts on them but the heater is not used (LED is used to simulate heater glow). How is the tube in the circuit? Is the input just connected to the cathode and from there to the real amplifying device?
I've yet to see or hear of anyone doing that; unless you include the fact that many audiophiles like to see the tubes while the unit is playing. When we made our first amps the tubes were in the back- the most common complaint we got was 'why are the tubes not in the front where we can see them?'
LEDs are frequently used in the cathode circuit to bias small signal triodes. Don't you guys keep current on trends in tube design? 🙂 This topic is discussed in great detail on this very site.
Well I've searched here and on google and cannot find anything, so please give us a link to this as it's well hidden. I've found a few comments on the X series being a reet pain because of the stacked construction but nothing on actual fraudulent use of tubes.
I was at a McIntosh demo where they used LEDs to bottom-light the tubes. When I asked if they were functional, I was assured they were- they change color when the amp is warmed up. The guy from Mac was horrified when I asked him if they were used in the active circuitry. "Of course not!"