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.


ramtubes

Showing 8 responses by atmasphere

atmasphere's avatar
atmasphere
12,099 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.
atmasphere's avatar
atmasphere
12,099 posts
 
I'm sure someone can understand my prior answer. I know you can, therefore to your first question, 'yes'.

To the second, also 'yes' but the question you asked didn't have a simple answer- some questions are like that :)


To the third, a correct answer requires a correct question- the **response** is not raised; the **pre-emphasis** is, and by about 5 db (so the simple answer is thus 'no'). Remember that the curve is just that and is the amalgam of three timing constants. The range of frequencies to which you refer is the area where the response is relatively flat compared to the rest of the curve. It isn't flat because of the ordinates of the timing constants. So its a gentle curve in that range, and the **pre-emphasis** is 'lifted' by about 5 db over that range, not 12.


There are plenty of images on the web.  Fig. 2 of the article at the link below is pretty good- you can see the 5 db or so rise in the pre-emphasis in the range of frequencies about which you asked:


https://www.stereophile.com/features/cut_and_thrust_riaa_lp_equalization/index.html



atmasphere's avatar
atmasphere
12,099 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.
atmasphere's avatar
atmasphere
12,099 posts
 
Thanks for the link. It is clear to me that above and below 1 KHZ there is 6 dB of EQ on either side of the red line, making a total of 12 dB as stated before.
I think you might be misinterpreting something- The red line is not the EQ curve. If you look at the actual curve, at 500Hz it only rises about 3 dB to 1Khz and then about 2 1/2 dB to 2KHz. The scale on the left is 5 dB per gradient.


I've seen a number of older console and stand-alone components that had networks installed for the ceramic cartridge inputs. Loading of ceramic cartridges is pretty critical if you wan them to work right.


Strain gauge cartridges seem to be the high quality version of a constant amplitude device in that they can track at 'normal' tracking pressures and have decent bandwidth. But its always bothered me (nor am I alone in this by any means) that they are often sold without proper compensation. I went to hear one back when CES was still at the Alexis Park and brought an LP that I knew quite well since I recorded it. You could tell it was the same music but the tonality was definitely off. The manufacturer was claiming that it needed no EQ... I thought about offering to do an equalizer for it but with his remonstrations it seemed an uphill battle. I think your comment about the Win hit the nail on the head- there's a bit of a consistency problem.
atmasphere's avatar
atmasphere
12,099 posts
 
µs, not ms
75 µs, 318 µs and 3180 µs
<facepalm>Correct!</facepalm> 
atmasphere's avatar
atmasphere
12,099 posts
 
One major variable that usually seems to be overlooked in such discussions is the criticality of the design of the printed circuit board itself, including where the chips are placed, how signals are routed within the board, and how power and analog and digital grounds are distributed and "decoupled" (loose translation: "kept pure").
My take on it is layout. A single misplaced trace can shoot down your design because of the noise it can make. And Al is correct- this is merely the tip of the iceberg.
atmasphere's avatar
atmasphere
12,099 posts
 
No- I liked the styling of the Marantz. I was also influenced by ARC. Both of these can be seen on the front panel of our old M-50 amplifier. But people wanted the tubes on the front, so we turned the chassis around when we introduced the MkIIs. The MA-2s still have a front panel though.


We still do our anodized finishes at the same place ARC used to do them.

I think the model 8 was a better sounding unit too. The 9 IMO only worked acceptably in Triode mode. Side note: when I was first showing my employees what I wanted for hand-wiring quality, I showed them the insides of a model 8b we were renovating at the time and told them this was the quality of workmanship we had to meet and beat.
atmasphere's avatar
atmasphere
12,099 posts
 
This is also confirmed by graph you presented from Stereophile.

I am simply trying to tell readers that the high end of a disc is cut 12 dB higher above 2200 Hz. Also that the RIAA playback curve they are accustomed to seeing is for a magnetic (velocity) cartridge and the one for a displacement (strain gague) would be only 12 dB top to bottom as apposed to 40 dB.

How can you disagree?
The graph shown by Stereophile is correct, and it shows **less than 6dB rise between 500 and 2KHz**. Again, the gradients of the graph are 5dB increments, and at 500Hz is only about 2.5dB down from where it is at 1KHz. And a similar amount up at 2KHz.

With regards to the rise above 2Khz; at 20Khz its about a 15db rise; but the disk cutter is not limited to 20KHz so the pre-emphasis goes all the way up until reaching the cutter amp’s bandwidth limit. To prevent phase shift, the playback should have bandwidth with attendant EQ to at least the same frequency and most of them do (and most LOMC cartridges have the bandwidth as well).

However, constant amplitude transducers like the strain gauge and ceramic cartridges aren’t properly equalized as you point out unless some additional EQ is applied. This isn’t a problem for most people though (because strain gauge cartridges are so rare that statistically they don’t exist, having so many zeros as significant digits that any numbers to the right of the decimal point that aren’t zeros are probably a figment of someone’s imagination; my respects to Douglas Adams)  so really isn’t much of a concern, except for the new strain gauge cartridge guy that thinks he’s going to make a million bucks on his new entry into the market. If he doesn’t have that equalizer sorted out, he likely won’t be selling his cartridge for very long. Panasonic seemed to be the only one that really had this sorted to any degree and even they bailed on it.



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