Does anyone care to ask an amplifier designer a technical question? My door is open.

Re: Beveridge
Hi, Roger,
You'd worked on the Bev DD amps for my Model II's when you were situated in Santa Barbara.  Unfortunately, Rick was unable to complete the restoration process and my panels require attention.  Can you assist?
Thanks for the attention.
Vbr,
Sam

Roger, thanks for your time.
Some of the technical talk on this thread is way over my head so I’ll have to bone up on my tube electronics, which I learned over 50 years ago in college, then became a computer jock so I forgot about them until recently.
I am sold on tubes for analogue audio but am confused by all of the information on power. I see from many posts that tube power need not be very high or as high as the speaker manufacturer claims as a requirement, i.e. a 200 WPC SS amp is needed to drive a speaker with 85db sensitivity (the manufacturer requires a minimum of 75 WPC, but likes at least 100 WPC), yet I have used a tube power amp with 40 WPC on the speakers and it sounds terrific. I have read that it is in the output transformers and SS amps are generally direct coupled.
Will you please explain this phenomenon?

Thanks. Rollin

Well, that just figures, doesn't it? Living way out here in Wyoming, my chances of having a conversation about this is more than rare. Then in the last few weeks, I have an opportunity to tap into 3 different audio engineers, electronic engineer, amp designer. It's funny how that can be.
  So here is something that probably has been asked before, but there are just too many pages for me to go through. Why shouldn't decent tone controls, and maybe even loudness controls come back in fashion? For it is simply that I need them at times, being 61. Now, mind you, I have bought many a product in the past that had such controls that were not worth the solder. Then, I got ahold of a low cost Yamaha integrated that changed my mind about such things. When it came to a loudness control, they chose NOT to increase the bass/treble, but instead to reduce the midrange. Cool idea. Other companys were spot on in the thinking tone controls whose turn over frequency for that particular control could switched to a more desirable frequency to start the correction. So if you were to use the bass control, you might have a choice of adjustment starting at either 100 hz or lower, at 60 hz, for example. The fact that these could be switched out of circuit when not needed, is enough for me to buy such a product.

  Your thoughts...

I hope that Roger will step in at some point and address some more questions but currently there are a couple projects occupying a lot of his time. So he’s had to take a little break from here.

@4krow - Roger has often talked to me about the difficulty in doing tone controls right. I know there are some C4 preamps of his out there with tone controls that owners have found very useful. He was often asked how to use the controls and his stock response was use the setting that sounds best to you.

In addition, Roger designed and for a while offered the two knob EQ for speakers that lack bass in the 320, 160 or 80 Hz range. You could choose between these frequencies and dial in exactly how much you want to boost, up to + 6 dB if I recall. Roger designed it in part because he listens to a lot of Leon Redbone and noticed the vocals never quite sounded right on most of the speakers he listened to. So the EQ corrected for that. He’s one of the few people I know that consistently uses the bass control on his RM3 crossover. Me, I’m set it and forget it with my RM3, but Roger fiddles with his to get the sound to his liking.

@c1ferrari (it’s been a while Sam, we met at Newport in my room there as you had interest in demoing the Lightspeed attenuator). I will talk to Roger about your situation and see what we can do to help (same for you Baranyi). We do stock the mylar for the panels if you need some.

I am sold on tubes for analogue audio but am confused by all of the information on power. I see from many posts that tube power need not be very high or as high as the speaker manufacturer claims as a requirement, i.e. a 200 WPC SS amp is needed to drive a speaker with 85db sensitivity (the manufacturer requires a minimum of 75 WPC, but likes at least 100 WPC), yet I have used a tube power amp with 40 WPC on the speakers and it sounds terrific. I have read that it is in the output transformers and SS amps are generally direct coupled.
Will you please explain this phenomenon?

@rollintubes
With all amplifiers its all about frequency response and distortion as to how they are going to sound. Solid state amps tend to have the flattest frequency response, but the difference between that and a good tube amp is slight and on many speaker loads may not even be measurable. Yet the solid state amp often sounds brighter and harsher, even though its got flat frequency response.

The reason is distortion. Our ears detect sound pressure by detecting the presence of higher ordered harmonics in any sound (likely because pure sine waves are extremely rare in nature). Solid state amps typically make more of these higher ordered harmonic distortions than tube amps do.

So when you are trying to make power, this really comes into play in a number of ways. As you push an amplifier towards full power, tubes and transistors behave differently- at clipping (anything over full power) transistor amps produce a large amount of higher ordered harmonics. Tubes don't, until they are over-driven really hard (and thus their distortion becomes audible as break-up).

So a smaller tube amp can act like its a lot bigger than it seems compared to a transistor amp. This is because music has lots of transients, and the distortion may only be showing up on the transients. The ear interacts with these distortions, telling you that the sound is louder. But the tube amp tends to do this in a way that is less noticeable, so essentially its giving you false loudness cues (this is particularly true of SET amplifiers, which is why they are often cited for being so 'dynamic' for how little power they have).


The other thing that comes into play is decibels. A 3db (decibel) increase is not very noticeable to the ear, but it takes twice as much power to do it. Your solid state example of 200 watts is just a little over 6 db more powerful than your 40 watt tube amp. That's not a huge increase volume-wise, so the additional distortion the tube amp makes at or near full power is able to fool your ear.


In a nutshell, tube amps have a more pleasant overload character so you can push them into overload and not even know it. That is why tube power **seems** more powerful than solid state power. Its not, but you might need a sound pressure level meter to see what is happening.

Why shouldn't decent tone controls, and maybe even loudness controls come back in fashion?

@4krow

A really nice tube preamp that had excellent tone controls was the Harmon Kardon Citation 1. If you can find one and have it properly refurbished, problem solved (so long as you don't need low output moving coil capability, although you could solve that with a stepup transformer). It employed switches to execute the tone controls, so when set to flat it really was flat. Its tricky to build a good tone control circuit (which requires an additional gain stage) that does not color the signal beyond the effect of the tone control itself, which is why tone controls went the way in the quest for greater transparency.