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
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
krelldreams
128 posts
 
What I’m hearing is a thinning of the midbass range. The lower bass is coming through. There is also the etched character I hear in the higher frequency range. These are slight, but obvious changes in the sound which, together, render the music “less” pleasing to listen to. Still a good listen, but not as good, overall, as through the preamp. Maybe the Mani on its own is a bit lean and a little bright, and the tube preamp is adding some bloom and rounding off the rough treble edge..? Complimentary distortions? I used to be able to find complimentary components via trial and error, and a lot of listening. That method has been made impractical due to the sparsity of brick and mortar shops to deal with. Thus I’ve been following this discussion to learn what electrical/design properties can cause some of the differences in what we hear from our component systems. I have painstakingly tweaked the positioning of my speakers, the set up of my turntable and cartridge, the paths of my cables, seating location, room treatments, etc. Everything I can do myself to take advantage of what I already own. I believe my turntable, speakers, and power amp are of very good quality, and I’d been mostly happy with the preamp choice... until I inserted that “almost free” Mani, and it noticeably improved the sound of my LPs! I will absolutely seek out a higher quality phono stage, but I want that quality to be allowed to pass mostly undiminished to the amplifier.
bdp24's avatar
bdp24
9,868 posts
 

@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?

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