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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@ramtubes. 

You mentioned, that in the RM 9, two KT120 or KT150 output tubes could be substituted for four EL34s in each channel. Is there an advantage to using fewer higher output tubes as opposed to using double the number of lower output power tubes, or vice versa? In other words, is the former following a “simpler” path than the latter?
@atmasphere. 

Great comment (on hearing)! I believe our hearing mechanism is somewhat of a “moving target”, so to speak. I’ve wondered why sometimes music through my system sounds great to me, and other times, not as good. Even when playing the same recordings at the same volume. The disparity is occasionally such that I think something is “broken”. Fortunately it sounds good much more frequently than it does not. 
I have for years heard accusations from audiophiles about TAS and now Stereophile requiring advertising from any company wanting one of their products reviewed. I have never seen any proof of that, and have to point of that though I have never seen an ad from Music Reference in Stereophile, a review of the RM-200 by Michael Fremer has twice appeared in the mag; once of the original version, a second of the Mk.2. That the Arma-Sphere M60 and/or MP-3 have not been reviewed is ridiculous. They review all kinds of over-priced status symbols, why not some high-value mid-priced pieces (the stuff most of us are interested in owning)?
@fsonicsmith 

 not all things that matter are amenable to testing.


Indeed we cant test for everything. However we can test for the big three and include that information in our listening. For instance if one amplifier produces a lot more bass from a speaker which amp is right. If the person prefers more bass then he buys that one. However usually when there is more bass the bass is not as good. Its uneven, boomy, the extreme being the "one note" bass. Now if we measure the amp with more bass and find it has poor damping we can say to the first order that is due to the poor damping. 

What gets interesting is when we have two very good measuring amps that sound fairly alike and one is tube and one is SS then we have to start wondering as Charlie did, What is it tubes do differently?

I hope someday I make a better amp than what i have made so far. An RM-9 is hard to beat. So are all the Marantz tube amps. Perhaps I have equaled the Marantz 8B, Saul's favorite. Perhaps I have better bass because now we have much larger filter caps than he had. Other than that not much has changed. BTW Saul told me that around the shop they firmly preferred a pair of Mono 8s to the famous Model 9. 


@krelldreams   You mentioned, that in the RM 9, two KT120 or KT150 output tubes could be substituted for four EL34s in each channel. Is there an advantage to using fewer higher output tubes as opposed to using double the number of lower output power tubes, or vice versa? In other words, is the former following a “simpler” path than the latter?


The advantage lies in fewer tubes to fool with, a little less heater draw so the power transformer will run cooler and you get away from the tight matching of 4 tubes. The path is the same. The idle current will be the same. Might have to shift the bias a little. I know the 120s work. We have had several people do it. If I get a chance I will give the 150s a try in an RM-9. Might look cool having 4 x 150s in the front row.