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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georgehifi's avatar
georgehifi
8,556 posts
Mr. Modjeski seems to endorse passives
Yes his amps are loved by passives and with my customers that use them.

My power amp is a CJ Evolution 2000 its input impedance is 100k ohms, and input sensitivity is 900 mV to full output.
It should also love passives, with that 0.9v input sensitivity. And that 100k input impedance you could of had a 20k Alps passive, not just 5k,

A 20k Alps pot would have been fine for just about any source then, which by the way you have not told what you have as the source.?? because if it has high’ish output impedance it won’t be comfortable with that 5kohm Alps pot as it will load down it's output and also create a voltage divider.

Cheers George
krelldreams
52 posts
Sorry, I had mentioned my sources in a previous post, but this thread has many, many posts by many people! I primarily listen to LPs, but I do have a DAC (Cambridge DacMagic Plus), and an Audioquest Beetle to stream Spotify over Bluetooth. I initially entered this thread to ask Roger his opinion about using a tube amp with my Maggies, but realized, after considering my system, that my preamp is likely the weak link. That realization lead me to learn more about improving the switching and level control functions... whether by a traditional preamp, or by using the combination of a passive device with a dedicated phono preamp. I had a passive in a different system, so I tried it in the main system to check it out. 
krelldreams
52 posts
@ieales. 

Thanks for the link.. I’ll check it out. My comment regarding the phono preamp with aux inputs and level control was made selfishly because I am very much interested in outstanding LP playback, and only listen to my digital sources casually (for background music, or if I’m not in the mood to flip records). Therefore a high quality phono preamp with a couple auxiliary inputs and a volume control is very attractive to ME 
georgehifi's avatar
georgehifi
8,556 posts
krelldreams
I primarily listen to LPs, but I do have a DAC (Cambridge DacMagic Plus)
What would your phono stage be, hopefully I can find it’s output impedance and if it has capacitor coupling and if that’s big enough, to work into a 5kohm Alps pot., if not it will roll off the bass prematurely, "creating a leaner sound"

As far as the DacMaigic goes (at<50ohm output impedance) there’s no problem for it to see, your 5kohm Alps pot. But it has an output coupling cap also and with the 5kohm Alps pot that coupling cap has to be at least 5uf in size to be -3db at 10hz if smaller than this it could prematurely roll off the bass also, "creating a leaner sound".

Cheers George
almarg's avatar
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almarg
9,670 posts
What would your phono stage be, hopefully I can find it’s output impedance ....

George, I was wondering the same thing, so I took a look at Krelldreams’ posts earlier in the thread and it appears he is presently using a Schiit Mani phono stage (op-amp based, 75 ohm nominal output impedance, $129), but is looking into alternatives.

While I understand that the Mani has received a lot of praise, and is certainly considered to be an excellent value at its very low price point, I can’t help but wonder if his finding that...

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.

... is simply due to the output of the passive preamp accurately reflecting what the Mani is providing to it.

So it seems to me that it may be wise for Krelldreams to defer addressing the preamp question until an upgraded phono stage has been purchased and is in use.

Best regards,
-- Al

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