2. amps-preamps
  3. 140029-80294

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's avatar
ramtubes OP
451 posts
 
@stargazer3   OP do you believe in the burn in process of an amp that over time the sound will settle and finally focus on a cohesive musical experience or is it to your opinion all in our brain that is adjusting to the sound of the component? When I mention burn in process its regard to periods of 300hrs and more (eg Naim or Simaudio Moon amps).


Speakers for sure. The are mechanical devices that have to loosen up. I hook up my woofers and drive them hard for a few days and can measure the resonant frequency drop a few Hz.

Amplifiers, only the tubes. When it comes to electronics and wire I believe the listener is becoming accustomed to the change. 

For those who will likely disagree: If burn in exists in these devices why did we not know about it until recently. I find no references to burn in in the 50s 60s 70s.. when did it start? 

I know the manufacturers love the idea because it gives them a reason for you to get used to the product. They are certainly going to promote the idea. 

With digital devics I really have to wonder what is burning in. The digits?

We always burn in amplifiers to find infant mortality. We would rather have an amplifier break in our shop than in your home. This process is well documented and 24 hours usually does the trick. The failures are very rare and most often just a tube. We even cycle the amps on and off many times to temperature cycle the glass which is what usually fails but its just 1 out of 100 tubes.

With tubes  I always set the idle current (bias) 10 % low because I know it will come up a little in the first 100 hours. 


ramtubes's avatar
ramtubes OP
451 posts
 
@ieales 

minimize artifacts occurring from the interconnect cable between the preamp and amp.

A second reason is that a preamp can provide a fairly high impedance load for the source
Source output 22R, amp inputs 23k5 or 100K. Adding a preamp with attendant switching, circuitry, noise and additional cables is little more than a subtle tone control. It maybe different, but it may not be better.


I agree with ieales and not the answer given above his, but then you all know that. What are these artifacts, are they Egyptian?
ramtubes's avatar
ramtubes OP
451 posts
 

@apogee141516 apogee141516176 posts12-07-2018 5:25amThis is kind of an obtuse question, but why do some amplifier manufactures say to use a preamp between their amplifiers and the streamer when you are only using a streamer and power amp, no vinyl and no other sources. I understand the need for a volume control and to have the impedance's low for the streamer/DAC and high for the power amp. My streamer/Dac is <100 ohms and the power amp is 47K. There is an implication that the preamp does other things that affect the SQ. Any idea what those are? An Allegri+ addresses the impedance problem and give a volume control and is extraordinarily transparent on my Ribbon Speakers.  My amp and steamer is very high end. Is there more?
 

Perhaps the amplifier maker hopes you will buy his preamp. You are correct, there is no need for one.

Sorry this post is gonna look strange. The operation of this app is wonky, but its free.



 
ramtubes's avatar
ramtubes OP
451 posts
 

@bdp24


@ramtubes, Here's a question for you Roger regarding a matter that was being discussed amongst Maggie owners on The Planar Speaker Asylum forum yesterday. One poster said of hearing from tube amps something I too hear, and that is of a sound stage that begins in front of the loudspeakers.

I heard that for the first time when Bill Johnson played an LP of Holst's The Planets (in 1973 at Audio Arts in Livermore, after he finished setting up his complete system in the shops really good room), a recording made in a large hall. The front of the orchestra was clearly located between myself and the front plane of the Magneplanar Tympani T-I's, and the rear of the orchestra was waaay back behind the speakers, sounding as if it was actually further away than was the wall behind the Maggies. I could hear the delicate triangle in the rhythm section, elevated on risers, playing in the quieter sections of the piece. It was thrilling!

Prior to that experience, at Sound Systems in Palo Alto I had heard a pair of the original Infinity Servo-Static ESL's, powered by the then-new line of SAE electronics. Through that system I did NOT hear the image "thrown" forward of the speakers. I have subsequently heard the forward image (and great depth) from other systems (including my own), but only when the electronics are tubed.

So my question is, why is it tubes are able to do that? Is it a matter of tubes being lowest in distortion at lower-signal levels (where imaging resides?), and transistors in their curves highest?

Thanks for throwing the ball my way.  

I would like to say its a property of tubes but I rather think its a property of how well the system was set up. I dont feel ampifiers have much to do with imaging. I don't see how they can. However I think they sound better than SS and therefore the system sounds better. When the system sounds better all sorts of nice things happen.

If you want to hear great imaging like you have never heard before find someone with properly set up Beveridge ESLs., the Direct Drive ones. They have 180 degree dispersion at all frequencies and properly set up FACE each other sending sound directly to you, directly to the middle and directly to the back wall which must be at least 6 feet away. Not many rooms will allow these set up distances. Ideally the room is 11 ft wide and 24 feet long or longer. Then the back of the sound stage is 2x6 feet or 12 feet deep. Its really cool. 
ramtubes's avatar
ramtubes OP
451 posts
 
@krelldreams My verdict, with this passive unit, in my system is as follows: The system with the passive has clear high and mid frequencies, good space, and sounds spacious... but it is a bit brighter, a bit leaner, and is less pleasant to listen to than with the preamp. I’d call the sound with the preamp “smoother” and “warmer”. The vocals through the preamp were slightly veiled compared to the passive though, which annoyed me. So.. after this exercise, I believe that either a better quality passive, or a more transparent preamp, is what I’d want. What design elements could improve the sound of a passive device? Clio wrote about a phono preamp with passive level control and aux inputs. What a great idea!


We make those phono preamps with a aux for people who appreciate that kind of thing. One other advantage is that you only power the phono section when you need it. Otherwise it is completely off, thus saving the tube life.

From a pure business sense I should talk preamp up and passives down, however that is not my truth. Passives are a great solution when used properly which is: dont load them with a lot of cable and dont load the source. This is easy today with low impedance sources.

Of course an active preamp is going to add a little distortion. Typically you can count on about 0.1 % per volt of output if there is no feedback. We dont know how every preamp colors the sound because we dont know what the designer is doing inside, perhaps intentionally. Some designers cheat the game by intentionally making something colored. They know someone will love it. Dont go assuming all preamps are designed on a level playing field, especially these days.

As someone said here he likes the microphonics of his 6SN7 preamp and calls it euphonic. Microphonics can pay a large role in preamp sound. Go tap on some tube preamps and see what comes out.

The thing that intersts me is that most complain that the bass of passives is usually lacking. However the bass of passives goes to DC with no phase shift. Tube preamps do not go to DC and at 40 Hz will start to have some phase shift. Is the phase shift what they like?
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