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.


128x128ramtubes
ramtubes's avatar
ramtubes OP
460 posts
 
@almarg  . I recently changed to a Pass XA25, which is specified as a class A amplifier rated at 25 wpc into 8 ohms and 50 wpc into 4 ohms. Per JA’s measurements, though, it is capable of 80 and 130 wpc into those impedances. I presume that most of that increase represents the amp’s capability after leaving class A, although per JA’s comments some of the increase apparently reflects differences in the distortion percentages the ratings and measurements are based on.


I have a different take on the reason for the power disparity... simply heat. The amp got hot at 1/3 specified power of 25 watts. At 1/3 of 80 is would have shut down. I think I saw a "more later" on that from JA, but cannot now find the quote. Perhaps you can. 

I think what Pass Labs did is a sensible way to get around the FTC power test procedure.  Perhaps 25 watts is the class A region however the amp does just fine out of class A and I cannot see anything in the distortion plots that concerns me when the amp leaves class A to AB. 

Too much has been made of Class A amplifiers. Most dont know what class A involves. You could call this amp a 25 watt class A amp though its really an 80 watt, high bias AB amp that just wants to get around the FTC rule.
ramtubes's avatar
ramtubes OP
460 posts
 
@bdp24  The J’s midrange (provided by the available-separately Model 80) was great by itself (unusually transparent for a cone speaker)


Thanks for reminding me the model number of the 80. For others who dont know the 80 was a full range speaker, woofer and tweeter as I recall, doing its best at being a full range, small, economical speaker.  Fulton made good sounding stuff. I don't know how but I always assumed him to be a compentent engineer with great listening skills.

He told the monkey story with a totally straight face like, Hey this really happened. We bought his wire. 

It appears you have owned some fine equipment. Nothing like we are faced with today, which is mostly marketing, jewelry and auto body finishes.  oh and bad specs. 
ramtubes's avatar
ramtubes OP
460 posts
 

@fsonicsmith   And while a solid state input stage may very well offer better measurements, where is the proof that it sounds better? At the end of the day, isn’t it indisputable that it is cheaper to produce and less complicated?


Are you saying a solid state input stage is not a good idea, or doesnt sound as good, or you would not buy an amp with one?
krelldreams
128 posts
 
@bdp24 That's actually a good suggestion, and easy for me to do, and I have no good reason why I haven’t. I had a Forte model 4a for awhile as well (50 w class A), but never tried that on Maggies either. I have different systems in different areas of the house, and typically don’t mix them (?). I did try a passive preamp in the main system recently and did Not like how it made the system sound. Maybe my preamp isn’t too bad after all... I will try the Dynaco with the Maggies this weekend. Thank you for taking an interest in my quest for sonic nirvana! Lol
ramtubes's avatar
ramtubes OP
460 posts
 
@kellydreams   . I did try a passive preamp in the main system recently and did Not like how it made the system sound

Not knowing the passive and what is was driving, including cables I would say this: 

I have no problems with passives. If one thinks of it as the volume control on an integrated that is somewhat separated physically the question becomes: What is in the way? What might be loading the passive? Generally the problem is cable capacitance or output/input impedance problems  (I wont say mismatch). 

Heres the way I look at it. In an RM-10 the input is right to the grid of the tube. In a preamp its the same thing. Why should it sound any different?

People do like preamps for other reasons, many of which may be imaginary. I made lots of preamps. Of course you need one for phono.

Bill Johnson told me they sell twice as many preamps as power amps. Seems people like to play with preamps more. Some say because its the thing you touch. 

In my system i got tired of the cables from the pre to the crossover. I wanted something really simple.

Because the RM-3 crossover has two knobs for high and low output I decided I needed only one, the bass and so made the treb pot into a volume control. Reduces cables and connector problems.

Now I think the way to make a crossover is with several line inputs, volume and bass level. So simple. I adjust the volume and sub level (100 Hz and down) on most every CD.

If you care to share the specs on the passive, cables and power amp we might figure out what was happening?
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