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
ramtubes's avatar
ramtubes OP
460 posts
 
Hey Roj, Its Verastarr Mikey..

Id like to know when we roll tubes and hear differences that are so different and unique even when its the same exact tube type, how and what exactly are we hearing ? Lets take 2 6sn7GT for instance, that for the purpose of this question have near identical electrical characteristics.
Thanks man !


First how many of the characteristice are near identical. Mu, Gm, Rp and bias point. These vary widely. With 6SN7s microphonics can play a large role.

I cannot comment on what you are hearing. If you want to be sure of what you are hearing it takes two identical circuits for the two tubes, an A/B switch, matched levels. We find with many listeners that the difference we hear rolling tubes are small enough to disappear. One cannot just swap a tube, we have found the sonic memory to be too small.

I did a strict A/B for 50 people in the SFAS. They looked at me and said. Hey these all sound the same, where are the differences.

Given that they want differences, we are repeating the test this saturday and will not A/B. It takes away all their fun when thinigs sound the same Sorry, but good equipment sounds good.

Because I test a lot of tubes, use them in off book applications I get to see some real measurable differences but then the tubes are actually different on the test gear too. A curve tracer will tell you a lot. 

The question I have is why do you want these differences?

If you could design your own preamp wouldnt that be more rewarding than swapping parts?


atmasphere's avatar
atmasphere
11,901 posts
 
The LP cutter head is fed a signal powerful enough to allow it to cut a groove on the surface of the lacquer which is an aluminum disk coated with lacquer.

The amps that drive it are just regular power amps although they are typically bandwidth limited to 40KHz or so. It is impossible to clip the amps; they can usually make about 10x more power than the cutter head can withstand.


The signal sent to them has the RIAA pre-emphasis. It is the inverse of the RIAA playback equalization curve. No other EQ is applied (although typically there is compensation for individual cutter head response, so the electronics are trimmed to match the head with which they are used).


So there you have it.
ramtubes's avatar
ramtubes OP
460 posts
 
@ atmasphere

So what is the cutting curve? Can you show us please?
ramtubes's avatar
ramtubes OP
460 posts
 
@atmasphere 

Does anyone find this interesting or alarming that we call the RIAA curve the big one and not make much mention that it is for velocity transducers only?

Ralph please explain your comment below.
No. Its well understood that is the case. There has been some controversy over other types of transducers as you point out, won't be properly equalized. IMO/IME the producers of such cartridges should offer their products with an equalizer to set things right.


Would readers care to comment that this is news that the RIAA curve is only 12 db not 40 db bottom to top.

Producers of amplitude cartridges do provide EQ, they have to in their box that powers the cartridge. Sao Win tried to EQ mechanically with little success. I built the equipment so he could measure his cartridges (which he did not before). Soon after he gave it all up from frustration of lack of uniformity. 
 
A year or two ago the Panasonic cartridge was reviewed with its"box" and there were great errors found in the resulting frequency response. The reviewer was a bit disappointed that these people could not get it right. 
atmasphere's avatar
atmasphere
11,901 posts
 
There have been a few other strain gauge cartridges offered with similar issues.
So what is the cutting curve? Can you show us please?
Yes. The RIAA pre-emphasis is the algebraic sum of the ordinates of three curves, each expressed in dB:

A parallel L/R network with a TC of 3180 milliseconds

A series RC network of 318 milliseconds

A parallel RC network of 75 milliseconds

From top to bottom the range is a bit over 35 dB.
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