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


I closed the cable and fuse thread because the trolls were making a mess of things. I hope they dont find me here.

I design Tube and Solid State power amps and preamps for Music Reference. I have a degree in Electrical Engineering, have trained my ears keenly to hear frequency response differences, distortion and pretty good at guessing SPL. Ive spent 40 years doing that as a tech, store owner, and designer.
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Perhaps someone would like to ask a question about how one designs a successfull amplifier? What determines damping factor and what damping factor does besides damping the woofer. There is an entirely different, I feel better way to look at damping and call it Regulation , which is 1/damping.

I like to tell true stories of my experience with others in this industry.

I have started a school which you can visit at http://berkeleyhifischool.com/ There you can see some of my presentations.

On YouTube go to the Music Reference channel to see how to design and build your own tube linestage. The series has over 200,000 views. You have to hit the video tab to see all.

I am not here to advertise for MR. Soon I will be making and posting more videos on YouTube. I don’t make any money off the videos, I just want to share knowledge and I hope others will share knowledge. Asking a good question is actually a display of your knowledge because you know enough to formulate a decent question.

Starting in January I plan to make these videos and post them on the HiFi school site and hosted on a new YouTube channel belonging to the school.


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Haha... Nimble Tube-Roller Society! That exchange must have been just before I started buying stereophile (1986). I agree that having the freedom to choose different power tubes for the same amplifier is liberating from an owners standpoint (well, at least THIS owner!). It is also a very good point that buying something designed around a “single source” part is risky. I had an H.H. Scott LK-150 power amp (built in 1961) that I’ve used 6550, KT88, and now KT120 power tubes in. My son is using the amp now. That’s still a great amp (in my opinion). My point is that even though those tubes are from the same “family”, it was great to be able to try different flavors in the same amp. Regarding preamp tubes; I’ve had preamps that were built around different tube types, and they all had their strengths and weaknesses. I didn’t really attribute those differences to tube A vs tube B. But I knew not what made them sound the way they did. That’s why I wanted to take this opportunity to ask someone who has to make a decision about which to use. As you said, how can one compare between tubes used in completely different units?
@fsonicsmith

Let me ask you this Roger; other than one of Ralph’s amps, which modern era top-tier tube amps have you actually sat down and listened to with not just your own planar speakers, but also modern coned speakers across a decent spectrum?

Other than designing amplifiers Roger has a pretty robust repair business and is an authorized repair shop for Allnic. Lots of vintage and modern equipment, solid state and tubed, crosses his path. I know because for the last 3 years I have been the repair intake person. As he has mentioned previously, Roger also measures anything he can get his hands on and has notebooks full of test notes for equipment that spans the ages. Also, Roger does not design planar speakers, he designs electrostatic speakers, there is a difference, perhaps you might read up on that.

Are you living in a cave?
Actually he has quite a nice house with a very nice system.

When we’re bored we go visit local folks to hear their modern systems (this past weekend we heard Avantgarde horns with their associated electronics) and Roger is pretty active with the SFAS, with the responsibility for running the upcoming phonostage shootout in January. My point is that Roger is very up to speed regarding current designs and design "philosophies," but testing and measurements are still critical to producing quality components and the principles behind these measurements go back in time. Ohms Law is still Ohms Law after all. Unless I missed something it hasn’t been updated or modernized.

Same is true for balanced amplifier design. Today we see all sorts of designers referring to their equipment as balanced. In many cases the design is just balanced at the input, not throughout (then there are the pseudo balanced designs). The only person I know that has been doing true balanced tube designs consistently (and in adherence to the balanced standard) has been Ralph Karsten and he’s been at it for over 40 years. However, the concept is not so modern, in fact it wasn’t developed for home audio use, but rather first utilized by the phone company to drive long cable lines (although I am unclear if the phone company developed the standard which I have heard referred to as the 600 ohm standard).

So Fred Sonic Smith (I assume that’s what your handle references) perhaps you should leave us. You bring zero value, you do not possess the knowledge or credibility to refute anything Roger says and although their opinions greatly differ, at least Ralph has the credentials and reputation to partake in those discussions. Let him do so if he wishes, he needs no help from you.

I re-entered because I could not resist. I saw that your irascible behavior has continued and not just towards me, so I felt better about re-entering.

Actually that was your cue to leave and stay away. You re-entered because you enjoy trolling here.
(although I am unclear if the phone company developed the standard which I have heard referred to as the 600 ohm standard).
The 600 ohm aspect has to do with the spacing of the lines on telephone poles. You've seen them many times - that spacing causes the resulting transmission line to have a characteristic impedance of 600 ohms. This means that if terminated by a 600 ohm load, there will be no reflections at the termination in the transmission line- its not that the impedance of the transmission line is 600 ohms.
So output transformers driving a balanced line were set up to drive a 600 ohm load. When the balanced line system was brought into studio and radio station applications, the 600 ohm became a standard which stood for many years and many pro audio components still support it.


I’d like to add this: I appreciate the fact that there are two professionals contributing here, despite the fact that there is tension that’s been created by disagreement. I’m trying to read through the commentary to the points being made, the examples being given, and the facts. The reality is, there are many ways to arrive at the same destination. I’ve listened to, and owned A LOT of gear in my life, though none, so far, by either of these designers. Some products allow the music to communicate to you, some don’t, and a combination of components may speak to me, but not to you. I know this isn’t a technical question, but I felt compelled to write it nevertheless. 
Also, FWIW, I’ll mention that Keith Herron, whose company and products (especially his phono stage) are about as non-controversial and highly regarded as they come, suggests that with his particular phono stage no loading whatsoever will often be found to be preferable with LOMCs, regardless of the cartridge type. (The LOMC input of his phono stage is FET-based, and it applies a load resistance to the cartridge that is nearly infinite when load resistors are not connected externally, to RCA jacks that are provided for that purpose). And I have found that to be the case in my own system, with an AT-ART9 cartridge having a recommended load of "100 ohms minimum."

I am glad this has been brought up. I met Keith at an audio show (IIRC the last THE SHOW Las Vegas held at St. Tropez). He had his phono stage there and because I didn't see any loading capability on it assumed it was MM only. He quickly corrected me by pointing out the cartridge he was using. When I asked him why no loading feature he provided an eloquent response that went over my head, but after my own testing, from that day forward I have never loaded a MC cartridge, regardless of the cartridge manufacturer's recommendation. Keith added a loading feature in the next design iteration and continues to offer it today and we can probably guess why.