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.


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alexberger
905 posts
 
Hello @atmasphere ,

Thank you a lot for your reply.

I know some people like to put chokes between output and drivers B+.
It adds better isolation on high frequencies between power supplies.
But what do you think does it have any real effect?

What do you think about separate power  supplies between left and right channels for 300B SET amplifier? Does it do a significant difference?

Regards,
Alex. 

atmasphere's avatar
atmasphere
11,807 posts
 
I’m sure you misspoke when you referred to pi-squared. The 6.28 factor you referred to is of course correct, but that is 2 x pi, not pi-squared
Yup- thanks for that. My medication is a bit too powerful today...
It adds better isolation on high frequencies between power supplies.But what do you think does it have any real effect?

What do you think about separate power  supplies between left and right channels for 300B SET amplifier? Does it do a significant difference?
A choke is helpful as it can be used to help filter out the 60Hz sawtooth waveform that is part of the rectification process. They can be quite helpful in that regard, as to do it with resistors and filter caps essentially requires more filter caps and also means a bigger voltage drop in the power supply, where voltage might be at a premium. IOW you can have a fairly low voltage drop across the choke due to a low DC resistance, yet still filter out noise in the supply.

Separate supplies is not a bad idea at all, although in a class A1 SET you shouldn't have a lot of noise in the supply. If you have separate supplies though, you could also have separate chassis for left and right. This would give you the ability to run shorter speaker cables, which is really helpful when working with amps with a higher output impedance such as an SET.

The trick is that when things stereo share a common power supply its possible for them to talk to each other (the term is 'crosstalk') and essentially interact unless great care is taken to deal with the power connections and ground connections correctly.  Otherwise you can increase IM distortion and IM needs to always be kept as low as possible. 

cardiffkook
12 posts
 
Thanks for offering to answer questions!

Here is one nobody seems to have asked yet...

What is the role and importance of significantly upgraded power cords in component design? It seems to me that the PC is a fundamental part of the electronic device and that the manufacturer should optimize the cord for the device in building it. What are your thoughts on the matter as someone who actually builds electronics?
bdp24's avatar
bdp24
9,795 posts
 
@noromance, I respect Roger’s directive to keep this thread focused on amplifier design, and questions about that topic alone. I brought up Harvey Rosenberg and the Decca only in response to tomic601’s (who has a close relationship with Roger, if I'm not mistaken) mention of mentoring. I’m happy to share what Harvey had to say to me about the Decca, so I’ll start another thread dedicated to that subject. Let me find my notes and collect my thoughts, and I’ll lay it on ya! I know you have a Decca or London, and are therefore very interested in what Harvey had to say about them.
bdp24's avatar
bdp24
9,795 posts
 
@cardiffkook, I’m sure Roger will get to your question, but in the meantime you should know that he does NOT share your feeling that "the PC is a fundamental part of the electronic device", and does not "optimize the cord for the device in building it." He infact includes NO cord with his power amps! Further, he says his reason for doing so is that everyone has a spare computer power cord laying around ;-) . Anyone wanting a 'better" pc can get a 3’ long 10g Signal Cable one for $59.
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