I'm looking for info about tube amps (1 Viewer)

[John Morris]

If the "switcher" knows the identitity of the product being tested, it's not a DBT.

Most times, the trial is not unblinded until it is finished. Sometimes, though, as the trial progresses, you can guess which choice the subject is getting just by how they respond to the choice.
A while back, my wife was involved in a NIH trial and after awhile it wasn't unusual for us to get phone calls in the middle of the night from a frantic wife who was crying that her husband was unconscious and not breathing. In these cases, the blind needed to be broken immediately so that she could advise the paramedics if the patient was on study drug or placebo. Almost always, they were on study drug. Shortly thereafter, as more and more patients who were on drug died, the study was stopped and unblinded fully. It seemed that in this specific situation, the drugs commonly used to treat this problem was actually leading to increased mortality and morbidity, rather than helping. The only way that we could have known that this accepted treatment was harmful was to run this randonized, double blinded, placebo controlled trial.
Thank goodness that our use of these DBTs isn't so serious or important!
Oh and Larry, it was CAST.

 

[Saurav]

Hey, no apologies needed. I was being just as pedantic as you

 

[Larry B]

Merc:

Thus, encainide and/or flecainide were the offenders?

Larry

 

[Larry B]

Saurav:

I was being just as pedantic as you

Damn, you and I should be used as models for forum politeness!

Larry

 

[Ken Situ]

Where are we going from here?

 

[John Morris]

Thus, encainide and/or flecainide were the offenders?

Larry: Yup. And to a non-significant extent moricizine. Of course, a bit later, Dupont withdrew moricizine as well. Completely opened our eyes to late term pro-arrhythmia.
Wow! Sorry for getting so way, way, off topic!

 

[John Sully]

I believe that in a matter of a couple of months, the VAST majority of the issues many have posted here against tubes will be moot. TubeDriver BLUE tube output technology is so revolutionary that EVERYONE will be not only be able to enjoy all the benefits of tubes without the limitations but they will be the most affordable tube technology available.

I'd like to know what makes these amps so revolutionary. Guys like Hafler and MacIntosh developed wide bandwidth, low distortion, high power tube amps in the 1950's. Is lighting the tubes with a blue LED the hot thing? How do you make a tube amp live in the high vibration environment of an auto sound system? If the amp is so revolutionary, why wasn't a patent applied for for the entire topology?

BTW, it is considered bad taste to post a content free post extolling the virtues of your own company.

 

[Larry B]

John:

BTW, it is considered bad taste to post a content free post extolling the virtues of your own company.

I agree. Would it be reasonable for me to suggest that we all simply ignore the post, rather than getting into a pissing match with the poster?

Larry

 

[Ken Situ]

I will just stick to my Dynaco's, EICO's, the McIntosh's...etc, than some kind of blue light thingy.

 

[RichardMA]

Not at all. There are many manufacturers of tube audio equipment today. They mostly exist near the upper end of the price spectrum, because the average user today isn't interested in tubes. If you're looking for something cheap, you'll probably have to try out DIY. There are a few companies that produce budget tube gear - Jolida and ASL come to mind first. I'm using ASL amps which cost $200 for a pair of 8W monoblocks.

Those monoblocks are excellent! Auto-biased. I'm using

one as the tweeter driver in my centre channel in

a bi-amp application. It produces more natural sounding

human voices than my Adcom or Marantz THX solid states.

For $99/ea, I can't believe Antique Sound Labs could build them.

 

[chung]

Those who want an engineer's perspective on tubes vs solid state might want to look at this fairly old article:
http://www.trueaudio.com/at_eetjlm.htm
Note that some of the single-ended triode tube amps can generate more even harmonics when driving low-impedance speaker loads. Trueaudio also markets PC based signal generators, distortion analyzer and spectrum analyzers. You can use their tools, which are inexpensive, to generate test tones for your amps, including tube amps, and look at the resultant distortion across your speakers (or simulated speaker loads made of resistors, capacitors and inductors). The tube sound is actually very well understood.

 

[Saurav]

Looks like an interesting article, I think I'll read it in more detail tonight. Is it primarily focussed on tube guitar amps though? I would think that the design requirements would be quite different for tube hi-fi/audio and guitar/keyboard amps. As someone once put it, "it's the difference between fighting the distortion and working with it" - I would think that neutrality would be the goal of tube audio gear, while guitar amps would require higher levels of controlled distortion. The same 12AX7 would be biased very differently in a stereo preamp and a guitar amp.

Of course, maybe this is discussed in that article, I just skimmed over it for now.

 

[Andy Anderson]

Hey y'all--

I've been considering some tube amps, and the offerings from ASL look to be a great deal. I'm considering their little pre with the waves, and also the 1003 integrated push-pull. Now, the waves are "auto-biasing", and the new 1003 has a "bias pot" with a "bias meter" on the front.

My question to y'all is, what is "biasing"? I've seen the term used a few times, and don't really understand it. Can anyone help me out?

Andy

 

[Saurav]

Think of it as a control that sets the.... well, the optimum operating point of the amplifier, so to speak. Basically, all the voltages and curents need to be at specific values for the tube to sound its best. As the amp ages, the values of resistors (and maybe capacitors too) drift a little, and the operating point changes. So, for a vintage amp, it's usually recommended to check the bias around once a year.
Another possible application for using a bias control could be to tune the sound of the amp, by choosing adifferent bias setting. Also, if you swap the tubes and put in a different brand, that may have a different optimal bias point.
AFAIK, biasing isn't unique to tubes, transistors need to be biased too. However, the bias controls aren't usually available to the end user.
I think an EE would be able to give you a much better response... it was precisely when we got to the chapters on transistor biasing and feedback that I decided I was going to be a software engineer. All those equations made my head hurt

 

[Ken Situ]

Bias is used to set the operating point of a tube. Since all components degrade over time, especially tubes, therefore, a Bias pot is used to adjust the operating point of a tube.

In an output stage of a push pull configuration, you can use separate bias for each tube to more or less eliminate the need for a matched pair, electrically speaking.

 

[Andy Anderson]

Cool. So:
ASL's AQ1003DT
..on that amp, what does the bias meter actually read?
Also, on a model-specific note, I'm considering this amp to use with a DIY sub and DIY speaks I plan to build. Here's my game plan--let me know if I'm out of line:
I plan to put together a Shiva-based sealed 54L sub using a Hypex HS200 amp as offered by Adire Audio. Now, signal runs from source to AQ1003DT, and I run RCAs from the pre-outs of the AQ1003DT to the HS200, which uses a high pass filter to cut out the top end. Then I run speaker line from the AQ1003DT to the speaks. Simple as that, or is there a better way?

 

[Saurav]

Simple as that, or is there a better way?

Precisely simple as that, assuming the 1003 has preouts and speaker connectors You could do more elaborate things if you want to remove the low bass from even reaching your integrated, but I don't think it's worth it. I tried it, with an op-amp based high-pass crossover between my preamp and my mains, set to 25Hz to cut off the very low bass. It certainly didn't sound any better, and I thought it sounded worse, though that may be psychological (throwing opamps between two tube stages).

 

[John Morris]

I am actually excited about the ASL Twin Head amp. It is both supposedly a fantastic headphone amp AND a simple tubed preamp in one... for only about $1K. I think I gotta test this sucker!

 

[Larry B]

Saurav:

It certainly didn't sound any better, and I thought it sounded worse, though that may be psychological (throwing opamps between two tube stages).

Do you conduct a DBT each time you try a new circuit, change a capacitor, etc.? And by the way, have you verified your preference for vinyl over CD, and tube over solid state, using a DBT? If we are to accept the opinion put forth by Chung (and Jaleel, where ever he is these days), wouldn't any conclusions drawn without such tests be meaningless?

Larry

 

[Saurav]

If we are to accept the opinion put forth by Chung (and Jaleel, where ever he is these days), wouldn't any conclusions drawn without such tests be meaningless?

I really don't care, because the only conclusion I have drawn is that I prefer the vinyl experience to the CD experience. That does not apply to anyone else on this planet, and I'm not interested in justifying it beyond just "my preferece".