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
krelldreams
128 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
10,312 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

krelldreams
128 posts
 
Gentlemen, thank you for your advice. I actually never intended for either the Axiom passive, or the little Mani to take up residence in my main system, however I decided to try them, which lead to my interest in replacing my preamplifier. What started this for me was the purchase of the Mani for another system in the house, where I would like to set up an old Sonographe turntable, which lacks a phono input. Upon receiving the Mani, I thought I’d see how it compared to the phono stage built in my Rogue preamp. To my surprise it sounded better in every way. That prompted me to not only look for a better phono preamp, but also had me questioning the rest of the preamp! A call to Rogue revealed that they hold the tubed line stage in higher regard than the included, solid state phono stage. So now I am actively looking to address both (line and phono). Since LPs are my primary source, I thought maybe it would make sense to get as transparent a source-selector/level control as possible, while putting a larger part of the budget toward the phono preamp. This is veering a little off the topic of the thread, but I wanted to explain my presence here. I hope it’s not too far off...
georgehifi's avatar
georgehifi
10,312 posts
 
almarg
 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
Think I found it.
Output impedance of the Mani at 75ohms is fine, but if you have a look (linked) there does look to be 2 x Wima output coupling caps on the Mani 's board, I say by the look of them maybe 0.47uf.
These into a 5kohm load of the the passive Alps would give a -3db already at 67hz, and could very well be the leaner sound being heard.
https://ibb.co/WsFNvhk

Could even be the same with the DacMagic.

Cheers George
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