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Old 11th February 2011, 07:38 PM   #31
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Originally Posted by AuroraB View Post
How does the monolithic duals MAT02/03 fit in this picture.....?
Seen them used in some very low noise instrumentation preamps.
Quite expensive, but still made, AFAIK..........

"Sort of OK" is the answer. The history of the MAT 02 is involved.
Essentially SSM2210 ( and the pnp SSM2220 ) were an invention of Precision Monolithics who were bought by Analog Devices who replicated them as MAT 02 and MAT 03 ( there is a MAT 04 quad but each tranny has half the numbers! ). Nat Semi then replicated them as LM 194/394.
rbb' is variously quoted as 30R or 40R.

BUT they do not have a very high fT. Internal capacitance is highish and the PNP is a dreadful mismatch to the NPN, the PNP has a low Beta. So clever bias current cancelling circuits do not work and hf stability needs to be watched.

I have a very small bucketful of each and every variety rescued and unused.

Positively. The NPN variety have a very high Beta such that in is quite low and at around 1mA or so with about 100R or so source they make a decent low noise amplifier. The device matching is top class and they have very close to theoretical characteristics and so for logarathmic circuits such as multipliers they are all but irreplaceable or for posh current mirrors or for speciality opamp input replacement long tailed pairs etc.

For MC cartridge preamps or other very very low Rs transducer amplifiers, they no longer have any special characteristics. An AD 797 op amp with a similar en of 0.9nV sqrtHZ plus a well designed back end end with mega load drive capability and at less than 5 or $5 a pop makes them redundant.

I have the greatest respect for Analog Devices, I have been using their products since 1976. The reason that 2SB737 etc are not made any longer by Rohm or whoever is that an AD797 is the worlds very best low noise amp at low Rs. It meets strategic needs and anything else is a US military secret, and needs liquid helium to keep it at almost absolute zero.

HEY GUYS...If you could cool your preamps and the MC cartridge to about 2 or 3K then noise would never be a problem. The noise of the cooling systems out in the back garden might intrude!!!
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Old 11th February 2011, 08:09 PM   #32
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"HEY GUYS...If you could cool your preamps and the MC cartridge to about 2 or 3K then noise would never be a problem. "

One little problem. Semiconductor amplifiers don't operate at that temperature. I have an article on the design of a low noise amp for a cryogenic photodetector (liquid helium cooling) used in astronomical work and they had to keep the amp portion at about 70 degrees kelvin or it stopped working. Those poor electrons and holes in the fets and bjts would just freeze to death at a lower temperature.
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Old 11th February 2011, 09:13 PM   #33
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[QUOTE=Blackjack8635;2465415
HEY GUYS...If you could cool your preamps and the MC cartridge to about 2 or 3K then noise would never be a problem. The noise of the cooling systems out in the back garden might intrude!!![/QUOTE]

Hm... wouldn't 77K be enough......?
Many years ago, I operated an IR spectrometer through some winter seasons, topping up the detector coloumn with liquid nitrogen from a jug, every afternoon.......
Could be way cool to start an evening music session with some LIN fog in the living room.......
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Old 11th February 2011, 10:13 PM   #34
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YES!. I said..."If you could cool your preamps and the MC cartridge to about 2 or 3K then noise" etc. and the preamp does indeed need cooling and the transducer does need cooling also, in which case preferably to less than absolute zero But then if that were possible the transducer would also stop working.

I suppose that the minimum effective temperature depends on a.) your desired bandwidth and b.) the mobility of your charge carriers
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Old 11th February 2011, 10:13 PM   #35
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I have not read all this thread so I may be out of line or going over old material but the late John Linsley Hood used a pair of medium size power transistors as low noise input transistors in a number of his MC (and MM) pre-amps. Cica 1985/95. They were BD438//BD437. The circuits are easily accessible at Paul Kemble's collection of JLH schematics. Just Google "Linsley Hood Paul Kemble" and it should turn up.

EDIT: There are two separate schematics. One is about 2/3 of the way down the page and the other close to the end.
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Last edited by Jonathan Bright; 11th February 2011 at 10:17 PM.
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Old 11th February 2011, 10:30 PM   #36
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I have not read all this thread so I may be out of line or going over old material but the late John Linsley Hood used a pair of medium size power transistors as low noise input transistors in a number of his MC (and MM) pre-amps. Cica 1985/95. They were BD438//BD437. The circuits are easily accessible at Paul Kemble's collection of JLH schematics. Just Google "Linsley Hood Paul Kemble" and it should turn up.

EDIT: There are two separate schematics. One is about 2/3 of the way down the page and the other close to the end.
Yes, indeed, and he also designed one or two MC preamps looking somewhat similar but using the transistors in common base mode ( cascode ). Medium power transistors as you suggest do have some of the required characteristics, but also potential problems.

1.) 1/f ( flicker noise) is not usually specified for medium power trannies.
2.) they normally have a low Beta which implies a high in current noise. However a correspondent mentioned the ZTX 653/753 and others in the old Zetex range that are medium power but also have a high beta and so they are indeed worth consideration.
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Old 12th February 2011, 07:31 AM   #37
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" have the greatest respect for Analog Devices, I have been using their products since 1976. The reason that 2SB737 etc are not made any longer by Rohm or whoever is that an AD797 is the worlds very best low noise amp at low Rs."

Blackjack, I think the real anser to this is much more mundane! From the early eighties, integrated solutions began to emerge, and ultra low noise transistors found themselves in the company of IC's, even though the IC's were clearly inferior in noise terms.

I've had the great fortune of working in the consumer electronics industry here in Japan ( as a semcinductor supplier) for the past 4.5 years, and I can tell you the drive to get component costs down is absolutely tremendous. Ditto the computing industry out of Taiwan. As to whether IC solutions are a bit noiser . . . If the system cost came down by using an IC, but the noise went up 3-6dB the IC wins.

Having said that, the AD797 is in a class of its own, but I don't think it was the reason the Rohm part was discontinued . . . .
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Old 12th February 2011, 01:45 PM   #38
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Here is a pic of the MC stage currently in use.
The thin black/red cables left are outputs. The thin cables to right are symmetrical inputs. Clip-Leads black=ground, red=pos.rail, white=neg.rail.

Hartmut

IMG_7906_MC_stage.jpg
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Old 12th February 2011, 03:07 PM   #39
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Originally Posted by Bonsai View Post
" have the greatest respect for Analog Devices, I have been using their products since 1976. The reason that 2SB737 etc are not made any longer by Rohm or whoever is that an AD797 is the worlds very best low noise amp at low Rs."

Blackjack, I think the real anser to this is much more mundane! From the early eighties, integrated solutions began to emerge, and ultra low noise transistors found themselves in the company of IC's, even though the IC's were clearly inferior in noise terms.

I've had the great fortune of working in the consumer electronics industry here in Japan ( as a semcinductor supplier) for the past 4.5 years, and I can tell you the drive to get component costs down is absolutely tremendous. Ditto the computing industry out of Taiwan. As to whether IC solutions are a bit noiser . . . If the system cost came down by using an IC, but the noise went up 3-6dB the IC wins.

Having said that, the AD797 is in a class of its own, but I don't think it was the reason the Rohm part was discontinued . . . .
I am sure your assertion is spot on.
I have just scrapped a Pioneer CD player recorder that was an award winning design in its time. It has 4558 opamps in the output.
And replaced it with a Marantz SA-KI Pearl lite, purchased just yesterday for 700 ( I know this is slightly off topic ) and it sounds very nice. The point is I chose it over a 270 Marantz CD6003 and even my genuinely poor hearing could detect a world of difference.

The point is, what on earth is the difference in component quality?. A 4558 might cost a manufacturer 5 pence where a nice 5532 might cost 12p or 15p. To get a toroidal mains transformer with a flux band one has to pay 700 retail. There is a manufacturing conspiracy to cheapen products unecessarily and then wrap it all up in mumbo jumbo. oxygen free silver capacitors and audiophile grade wire, with special polywhatsit capacitors rolled carefully on a dusky maidens thigh.

Back on topic. I am just playing with a simple discrete MC input preamp cct. design and will use the 2SA1085's that I have to hand, I will then strap the input with resistors from 3R upwards, put some serious gain on the output and use the audio test set to measure noise at different bandwidths. Next step to put it through an RIAA filter, still with a null input, and do some simple listening, ie. can I hear a rustling sound?.

Should also be able to do a battery power versus conventional LM317 regulator supply.
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Old 12th February 2011, 04:03 PM   #40
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ie. can I hear a rustling sound?.
The sensitivity of your loudspeakers and your system's total voltage gain and listening distance plus background quietness will play a major role in that test. Noise in applications is always relative. Best engineering goal should be 'adequate' noise level in any specific application than absolute minimum IMHO.
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