It is plainly to be unusual, I know that much.
My goal is also to achieve low noise and high fidelity through research and development. This is why I keep modifying the idea to get better and better.
To start, all I was using was the 324 on its own with a filter network in its feedback loop. It actually worked very well if you can forget about the horrendous amount of noise.
I'm consistently trying different discrete ideas and just basically experimenting with it; that's all.
My goal is also to achieve low noise and high fidelity through research and development. This is why I keep modifying the idea to get better and better.
To start, all I was using was the 324 on its own with a filter network in its feedback loop. It actually worked very well if you can forget about the horrendous amount of noise.
I'm consistently trying different discrete ideas and just basically experimenting with it; that's all.
The patent number on the phono preamp with the emitter follower input stage is 4,312,060. Here is a
the link to it. http://patft.uspto.gov/netacgi/nph-...1=AND&d=PTXT&s1=4312060&OS=4312060&RS=4312060 .
Regards,
Ray
the link to it. http://patft.uspto.gov/netacgi/nph-...1=AND&d=PTXT&s1=4312060&OS=4312060&RS=4312060 .
Regards,
Ray
Noisy.
I owned a prototype unit and a production unit for many years; the noise drove me crazy and I finally ended up modifying the design to convert the first stage to a cascode and use quieter tubes and FETs.DB was quite in love with grounded grid circuits. The noise was a penalty paid for bandwidth and freedom from capacitive loading of the cartridge. In later preamps, the source follower to grounded grid was replaced by a cathode-coupled amp.
http://www.pat2pdf.org Good service mentioned by someone (forgot who)
Interesting solution but I wonder how good it is in real life.
Interesting solution but I wonder how good it is in real life.
It's good to get some theories first so you won't energy on things you can't improve. The noise is set to a certain level on all signal sources and a MM cartridge has a rather high noise. Less noise than 4 nV/Hz like a NE5534 is not needed. So it's useless to strive for less noise than that. National had an good application note about cartridge noise and how to calculate it. Forgot the number though but I'm sure someone can get it. It's a rather low number AN-??Duo said:
peranders said:
I wonder if that's still true now that neodymium magnets are available? The same developments that have suddenly enabled hugely efficient ribbon tweeters could be used to drastically reduce the number of turns needed in the coil of an MM or MC cartridge (reducing their resistance), turning accepted wisdom on its head.
Would it really make a difference?
I don't know if MM cartridges have yet taken advantage of neodymium (I know some MCs have), but I would have thought that it could enable a reduction in turns by a factor of four, and even with the same gauge of wire, that would give an improvement in noise of 3dB. If you made the wire thicker, but kept the total coil mass the same, you would gain another 3dB. Further, a lot of RIAA stage noise pronouncements are made using 70s data and referring to the Shure M75ED (a notoriously high source impedance).
On another point, it's as well to remember that although bipolar input ICs sound impressive with their low nV/sqrt Hz figures, it's the current noise that predominates, so the source impedance of the cartridge become even more significant.
I don't know if MM cartridges have yet taken advantage of neodymium (I know some MCs have), but I would have thought that it could enable a reduction in turns by a factor of four, and even with the same gauge of wire, that would give an improvement in noise of 3dB. If you made the wire thicker, but kept the total coil mass the same, you would gain another 3dB. Further, a lot of RIAA stage noise pronouncements are made using 70s data and referring to the Shure M75ED (a notoriously high source impedance).
On another point, it's as well to remember that although bipolar input ICs sound impressive with their low nV/sqrt Hz figures, it's the current noise that predominates, so the source impedance of the cartridge become even more significant.
LTspice has a circuit example of a phono preamp. Several years ago I used that circuit and added a simulated Shure V15V (1K in series with 0H5). To my surprise, the noise decreased with frequency and the low frequency (voltage) noise was dominant. I expected the noise to increase with frequency because the cartridge impedance will increase and also the current noise, but instead it decreased. The current noise didn't seem to be a significant factor.
Regards,
Ray
Regards,
Ray
I thought the noise would increase because the cartridge impedance would increase 1000 times from 20 Hz to 20 kHz but the gain would only decrease by 100 times. However, I forgot the 47K load resistor shunting the cartridge would limit the impedance to 47K maximum no matter how much the cartridge impedance increased.
Regards,
Ray
Regards,
Ray
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