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.


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ramtubes OP
460 posts
 
@krelldreams   Roger asked for specs... the only spec I know of is “1.2k” hand written on the bottom of the case. This was only a test anyway since I’d need more than the single input this one provides. I was not aware that Music Reference made passive devices (?).

 I am considering both tubed and solid state phono preamps. Any design parameters that I should be paying attention to? Any designs to avoid? I currently only need one for a high-output MC cartridge (MM gain and loading), but I plan on trying other cartridges in time as well. I’m not opposed to getting a step up device if a cartridge I get in the future needs one.


BTW, i looked up the Axiom. If you have an ohm meter just connect it to the input jack and output jack and get some numbers. Non of them are good for long runs as we all know. If yours is 1.2 K ohms thats a rather low number unless the source is much lower. 

For  you preamp you need to focus on S/N ratio and RIAA accuracy and distortion which should be nill. If you find a measured review I will look at it. You want at east 60-70 dB signal to noise ratio at the output of YOUR cartridge. 

We might build a few phono preamps on special order. The one I have developed for Clio has is all tube start to finish, 3 gains, 12 loadings, tape EQ available (he likes 15 ips tape). It uses only 4 tubes which I am rather proud of as most will use more and give you more trouble. 

I tried a FET front end some years ago and just did not like it. A Low noise FET is about the same noise as a SLN 6922, so there is no noise advantage there. You can get the lowest noise with transformer inputs, but then you have to deal with placement issure and the sound of the transformers. 


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almarg
9,670 posts
 
@prof, I'm sure Roger would take this into account, but keep in mind that since the CJ Premier 12 and the Eico HF81 are both tube amps and have output transformers, they should not be operated unloaded while they are being provided with a signal. So a suitable switchbox would apply load resistors to whichever amp is not selected.

Best regards,
-- Al 
wolf_garcia
6,712 posts
 
I'm another who has compared garden hose sized power cables to more modest but appropriately sized "stock" cables and found that both work fine with no audible differences. I do use a relatively gigantic PS Audio AC cable for a REL sub, but that's simply to impress people although no people have yet to be impressed...still...it wasn't expensive since it was "previously owned"...gotta say it looks cool...maybe thickness isn't so important after all (really? you're thinking THAT?).
pryso
1,939 posts
 
Roger, "What exactly is A-B-A?"

I've seen multiple comparisons where some/many were prepared to offer conclusions after a single switch from an original component (A) to something different (B).  For several reasons I don't feel that is meaningful without at least going back once to the original.  I also thought that was a standardized label but apparently not.
fleschler
2,021 posts
 
That's interesting information concerning the 6SN7 tube.  My power amps use them (NOS 1948 Raytheons) as cathode followers and the 6CG7 as a pair as input tubes.

Now if the 6SN7 is not really a good audio tube, why does VAC use it on the entire line of amps as input tubes?   He could have used a 6SL7 or 6CG7 or variant.
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