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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bdp24's avatar
bdp24
9,788 posts
 
@ieales, agreed, but the Modulus pots (Noble?) were not that precise. I have no interest in resetting the channel balance every time I adjust the volume!
ieales's avatar
ieales
1,201 posts
 
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.
analogluvr
859 posts
 
I can’t imagine living without my dual Kozmo pots now that I have them. I will never own another preamp without some sort of balance, preferably dual volume pots. 
atmasphere's avatar
atmasphere
11,785 posts
 
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.
Some volume controls in DACs are actually far more than subtle in their operation. Stripping bits isn't the best way to control volume. For that reason the buffered volume control that can be in an active line section could be more neutral.


One thing is certain: when it comes to preamps, passive volume controls or running direct, because there are so many different products and approaches to this problem no generalization about the matter could be seen as true.
ramtubes's avatar
ramtubes OP
460 posts
 
@bdp24  I also remember The RM-5 and the Audible Illusions Modulus 2 were considered THE bargain tube pre-amps to choose between. I found the AI Mod's 30dB of line stage gain unfortunate and ill-advised, as well as it's dual-mono volume controls. The Modulus is still in production (in updated form, of course), so Roger, any thoughts of offering a contemporary RM-5 type pre?

Thanks for the memories... who sung that?  The Modulus and RM-5 present a great example of dueling designers. Art did not put feedback around the line tube as I did. I also made it variable with dip switches for many gain settings from 0 to 30 dB which is the full gain of the tube. He later put a cathode bypass disconnect to lower the gain but that is a Very bad idea as it raises the output impedance to about 10K. The feedback in my line stage lowered the output impedance to about 1K. Im surprised people didnt hear the difference more easily. Again, that would have showed up in an A/B which is just not done is it?

Where I did volume and balance Arthur liked his dual controls. Other than that the preamps were pretty except for the power supply. His blew up, mind didnt. 

Problem was, Arthur was not an engineer and the preamp was the work of many people. I think he bought the company from Bruce Moore. Hope Im not bragging on mine too much, just the facts Madam. 

He claims in the TAS book to have sold 25,000 units.  His tech, Meserve. was my tech in the 1980s and said theres no way. We sold 960 over the 15 years we made it. All sonically and ciruits wise the same.. Only thing that changed was the jacks as better ones came alone. If you can find a MKIV that was the nicest as we put on a phono tube off switch, heavier metal, nicer jacks. We only made 50 so good luck. The MKIII is more available and just as good except for those two things. 
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