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
charnich
10 posts
 

Hi, Im working on a JVC JA-S31 which I acquired from fleabay. Although it functions I feel that the left channel lacks a little clarity and low end as compaered to the right. Also the heatsinks stay cool to the touch at idle and during a listening session. I felt that a good place to start was to adjust bias. The problem is that there aren't bias pots on the board. Is it possible to insert one and be able to adjust it as easy as that? If so Im assuming that I would replace a resistor with the pot. If so, which ones would I replace. Would I replace  one of the R637/R639 pair and one of the R638/640 pair? Also when taking my bias measurements where do I connect the leads? I am a newb to this and I know someone is going to flame me and say if I don't know then shouldn't be messing around with it etc , but I need to learn somehow and I bought the amp the specific purpose of doing so. Its just the way I learn. The schematics are at https://www.hifiengine.com/manual_library/jvc/ja-s31.shtml  I would greatly appreciate any input to get me started in the right direction. Thank you
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fleschler
2,021 posts
 
I had the Acoustat Xs back in the early 80s.  They sounded very good with their built in high voltage amps (dangerous things).  However, they looked like coffins (my late wife's terms) and had lost all its highs above the speaker height, about 4' high.  Stand and you would hate the sound.  I replaced them within a year with Acoustat 2&2s, very superior overall.  
iamasif
19 posts
 
Hi @ramtubes  
Recently I added a power-amplifier Monoprice monolith to my audio/video gear and it is connected to Panamax M5300 power conditioner. Btw these all these equipments are in my basement.

When units are powered on I hear a very mild hum noise from the amplifier unit, if connect amplifier directly to the wall outlet I don't hear any hum noise. If I do the similar setup other side in the basement I don't hear any hum when connected to wall outlet or thru panamax power conditioner.

What might be the issue?
atmasphere's avatar
atmasphere
11,850 posts
 
Isn't the presumption with most speakers that they will be driven by a voltage source? And by assuming that, isn't it consequently presumed that the amplifier will provide the current according to the impedance while driving the voltage regardless?
Yes and yes. But emphasis on **most** speakers; not all speakers expect the amp to be a voltage source. Examples: Coincident Technology, Lowther, Audiokinesis, Pure Audio Project, Spatial Audio, Classic Audio Loudspeakers, pretty much any speaker that is used with an SET (so most horns); high end audio is a diverse community.

Aren't the output stages of amplifiers typically followers? If so, that would make them voltage sources, wouldn't it? If you operated the output devices in a mode that provided both current and voltage gain than I suppose you could call the amp a power source, but that's rare and any reactance in the speaker will exacerbate nonlinearity, wouldn't it?

Not all amps have followers for output sections. Most transformer-coupled tube amps for example do not. Most OTLs however do. Yet both transformer coupled and OTL tube amps can behave as a voltage source if sufficient feedback is applied. IOW its all about the design.
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