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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.


ramtubes
ramtubes's avatar
ramtubes OP
451 posts
 
@stereo5 

I have a question for you Roger:
What are your thoughts on Class D amps? I have listened to quite a few and always came away unimpressed with my ears aching. I am a Mac guy at heart marrying a Mac solid state amp with a Mac tube preamp. Perhaps I like a more mellower sound?

I heard your tube amps back in the 90’s at Sound II in North Dartmouth, Ma. Leo (RIP) was a huge fan of tubes and carried your line as well as VAC and Audible Illusions. I did a lot of listening and buying in that store. An added plus was there was a fantastic strip Joint right across the street from the store on Route 6. Really fun times!


I was making class D amps in 1990, before they were hardly known. Mac Turner brought me in to consult on his. What disturbes me about them is that they all get their sound from the IC in the front end. Perhaps some are discrete front ends but I have not seen any. 

The biggest problem is the output choke that is necessary to filter the switching waveform. If you look at Stereophile reports you will always seen one impedance that is flat while the others either peak or droop. 

They are going to be popular due to size, low cost, ridiculously high power that hardly anyone needs. I was interested back then as an engineering exercise but no desire to make any. Over 100 watts is only justified by either high listening levels or insensitive speakers or both together. Excess headroom is a myth. 

I have some Mac gear to be quite excellent. I have a post about that here. Just go to my profile to find it.


ramtubes's avatar
ramtubes OP
451 posts
 
@cakyol
Can you please tell me the purpose of resistors R1 -> R8 in the power supply shown below in the URL ? Is it to reduce the resonant frequency in case the supply oscillates with the stray inductance of the smoothing caps ?https://www.passdiy.com/project/articles/burning-amplifier-1


They are part of the RC filter of the power supply, to reduce ripple. A choke would be better but expensive and bulky. He is likely using multiple resistors to spread the heat and often reduce cost.

It is nothing to do with resonance or stray inductance. Those arent problemsl. Its simple AC ripple filtering.

They could be replaced by a single power resistor of sufficient wattage at 1/4 the value. They appear to be 1 ohm each which is rather low to do much. Nelson is a good guy we spoke together at Burning Amp 2018. http://http//berkeleyhifischool.com/having-fun-at-burning-amp-2018/  

In his earlier presentations he talks about the Amp Camp. It is once again available at DIY audiostore. Its not my kind of circuit but it is interesting.
ramtubes's avatar
ramtubes OP
451 posts
 
Roger, thank you again for your response. My ears have required long warm up times for almost all of the gear I have had over the years. Solid State as well as tubes, dacs, tuners, tape machines, etc. I suppose R. V. knew what I was talking about, the warm up problems. Is the forming switch the same as an amp having a stand by mode ? I assume it is this capacitor thing that I have been responding to. I am glad you are here posting, as I am greatly enjoying the information. Enjoy !


Glad you know your ears, many people dont. 

SS equipment can be very temperature sensitive because transistors themselves are much more sensitive than tubes as I have written here to another question. Therefore there may be a lot of variation over time. 

The forming switch is not like a standby switch. A standby switch, such as on a guitar amp, keeps the tube heaters on but cuts off the B+ to let the amp cool and extend tube life. However it is intended to be used by the player on breaks not longterm. Turns out long term, tubes do not like to have only their heaters lit without B+. Cathodes tend to get lazy. They learned this in the tube computers. So even overnight standby can start to be a problem and really has no sonic benefit. Standby on a Fender is so the player can go get a beer.

I designed my amplifiers to warm up to optimum pretty fast. I have worked on other amps, expecially ones with SS devices in the power supply, that take quite a while to come up to optimum.

ramtubes's avatar
ramtubes OP
451 posts
 
I have had many responses, good questions, no Trolls. If I missed your question please re-ask it again.
blueranger's avatar
blueranger
575 posts
 
Thanks for your expertise. I have a question about damping. You said a heavy gauge speaker wire would actually decrease damping. So a speaker gauge around 16 might exert more control over the woofers for deeper bass?
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