2. amps-preamps
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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
jfuquay
109 posts
 
A good friend has your RM-200, which I’ve heard often. Wonderful sound. Thanks for sharing your experience. Here’s my question: What determines an amp’s “brightness?”
I broke my “hear it before buying” rule when I bought a Musical Fidelity M2si integrated amp (Class A front end/AB power per the maker) because I wanted more power (137 watts at 4 ohms) to drive a pair of Magnepan MMGWs in a living room setup. But while it has great energy and dynamics, the new amp is brighter than the compact Teac HA-01 ICE-powered Class D amp (43 watts at 4 ohms) I had planned to replace. The Teac has a Burr-Brown DAC chip, and I tried a Music Hall 23.5 DAC with a tube buffer and a Musical Fidelity V-90 DAC with the new amp. All too bright for me. And I’m really surprised because I built the Nelson Pass-designed amp camp power amp (Class A) and think it is so natural sounding. I just assumed anything Class A/AB would be warmer than Class D. Apparently not.
twoleftears's avatar
twoleftears
5,318 posts
 

@gnaudio I’ve had several amps over the years plugged in the same room in the same AC receptable. A 300B stereo power amp didn’t hum. My current solid-state monoblocks don’t hum. But a popular US-based, US-manufactured, relatively inexpensive, tube integrated did hum, not a lot, from *both* the transformers and through the speakers, enough that when combined the hum could be heard from listening chair when music fell silent.

I lifted the ground. I ran an extension cord from the other floor of the house. I turned off every breaker in the whole house save for the one receptable being used. I tried ground loop eliminators, like the Hum X. I tried DC blockers, like the HumDinger from AVA. I followed the "how to eliminate hum" instructions from the PS Audio webpage. I tried isolation transformers (Furman pro). I tried a PS Audio unit. I tried a variety of other power conditioners. The company blamed it on the sensitivity of my speakers. I tried different speakers, with same result. Eventually I gave up.

It’s not any kind of discovery that the quality of manufacture of transformers used in different amps varies a good deal (designing to a price point + variable QC), but this demonstrates clearly that what works in location A will not necessarily work in location B, and that makes/models that achieve considerable popularity will not work for everybody, always. Live and learn.

Because mild to moderate hum is not fun or glamorous or sexy or exciting, I suspect it's a problem that occurs more often than is reported or discussed.


unreceivedogma's avatar
unreceivedogma
985 posts
 
Why would triode sound better than pentode?

Why woukd my Altec Lansing 604Cs be better for my Julius Futterman OTL3s At 16 ohms rather than 8 ohms?

And, with regard to the great interconnect debate: do you know of any testing done that approaches that of scientific blind testing that shows that any given wire, if made out of a certain material, and wound in a certain way, and shielded in a certain way, will cause electrons to move in one manner as opposed to another that can be explained as doing so and that because of that movement can be explained as yielding sonic performance that is measurably and quantifiably superior, or even just different?
mapman's avatar
mapman
22,341 posts
 
OK so here’s some SPL measures using db meter pro app on iphone 6 . Disclaimer: I have no info on how accurate this tool is but the numbers I am reading seem reasonable.

So in a samplling of various "typical quality nothing special" CD resolution recordings over several minutes from my closer listening position, I hit peak spl of 99 db and averaged about 86 db. Very clear and amps never break a sweat which I take as a good sign

I would rarely go louder but can and have. I’ve used amps rated at 60, 120, 180 360 and current 500w/ch into 8 ohms. I view the 500w/ch with the big OHM 5s as my insurance policy against clipping at minimum and the current Bel Canto ref1000m amps are the best sounding overall by far especially at higher SPLs. I also seem to hear the correlation between amps with specs that better double power into 4 ohm and better performance overall meaning better sound at least with the big OHM F5s. Not as much with my other smaller OHMs (8" main driver) and even smaller monitor speakers (Dynaudio contour 1.3mkII) and very small Triangle Titus that I also run off same amps.

pryso
1,939 posts
 
Roger, 

Wow!  What a fast moving post.  Glad to see all the interest.

"There is a lot to this question so lets hear back from you and others."

First off, I suspect many of us non-technical types may not know much about clipping.  I've been aware of it a few times but suspect it occurred other times when I was not certain what was happening.  In my experience I've heard the sonics become thin, hard or harsh, even metallic (as opposed to musical) when pushed to loud levels but before the crack or pop of an actual clip.  I considered that a related but slightly different issue.

When listening for pleasure it is generally in the 80-85 dB range.  But I doubt my RS dB meter is accurate to identify actual peaks so I'm unsure of those.

Regarding amps > 100 wpc, for many years I enjoyed a large pair of Duntech speakers, rated at 90 dB.  John Dunlavy recommended 200 wpc for "full musical enjoyment".  I experimented with a variety of amps (tube and SS) rated from 30 to 300 watts.  I finally settled on a pair of VTL 300 monos for a few years.  That was until I heard Curl's Halo JC-1s, rated at 800 wpc into the speaker's designated 4 ohms.  That was the best I found - musically accurate, solid bass (determined by good recordings of acoustic upright bass), and effortless, unstrained sonics.  To be fair I don't believe the 90 dB efficiency was accurate with such a complex 1st order crossover.

I've since moved on from that system but continue to believe this question of headroom is very important.  Interestingly I remember hearing several times some years ago the idea that within a given line up of amps, the model with 60 to 120 watts was likely the best sounding.

I did have a RM-9 for a few years, one of those few components I was later sorry I sold.
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