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
 
@prof    Actually, the talk of switchers raises another question I'd like to direct to Robert:

I have more than one amp I like to use for my system. It's a minor pain to switch the cables, but it sure would be nice to have a switcher where I could switch between amplifiers to the main stereo speakers. (So interconnects would lead from one output of my preamp to my main amplifiers, and out the other output to a second amp. Depending on which amp I wanted to use I'd just flip a switch.

At one point I did a bit of research and saw some candidates, but for the most part they looked awfully cheap, which left me hesitant.

Would you say a fully transparent switcher of the type I'm describing could be built?


Yes we have one, can make you one with a volume control to balance the gain of the two amps so they play the same loudnes. They, God willing, you flip back and forth, on the same speaker please, and hear of not hear the differences between the two amps. This is exactly what we are doing.

Then you can invite your friends over and really have some fun. You will likely find what we have found.. Some amps sound very similar with differences too small to be sure they are real and some amps let you know pretty quickly what they are up to. We find good correlations with measurements.

What are your two amps.
prof
3,479 posts
 
@ramtubes

You’re gonna hate me: My amps are Conrad Johnson Premier 12 monoblocks and an old Eico HF81.

BTW, since you asked about hearing "the other side" for power cords:

I was cured of power-cord-fever early on. I had been given a selection of Shunyata power cords to try, from their least expensive to very expensive. I didn’t think I heard any difference between the less expensive Shunyata cables and my 15 dollar power cable (On CD players, etc). But I thought the most expensive cable seemed to obviously change the sound. (Darker, smoother, more lush). To double-check I had a pal help me do a blind test between that cable and the 15 dollar cable. Once I didn’t know which cable was being used, all the "obvious" sonic differences I thought I was hearing vanished and I couldn’t tell them apart. Saved a bunch of money there! I haven’t worried about pricey cables since. (I’ve gone on to blind test other components, sometime identifying differences, sometimes not).

ramtubes's avatar
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
6,723 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?).
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