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Old 10th November 2009, 02:36 AM   #91
Bonsai is offline Bonsai  Taiwan
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Lumbar, it no good saying a design approach is 'non=negotiable' without listing the defects. What exactly are your objections? The spec looks pretty good to me and I don't doubt it probably sounds good as well.
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Old 10th November 2009, 03:16 AM   #92
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A common base stage does not have an input impedance that is zero ohms, at least not in the open loop case. With shunt feedback it can be much reduced like the PhonoClone design but lets talk about the common base stage.
So the common base stage is also amplifying the voltage. I like common base input stages because they have a "natural" input impedance that matches a low impedance MC quite well and does not suffer from early effect so is high speed without the need of high feedback or series cascoding.
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Old 10th November 2009, 03:42 AM   #93
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Joachim,
exactly. Using the nice Hitachi devices you get pretty close to zero Ohm. The common base stage only amplifies voltage. Choosing grounded collector topology here reflects a total lack of judgment.
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Old 10th November 2009, 05:21 AM   #94
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Bonsai,
despite pretty good looking specifications, you get noticeably more opaque sounding tsuri-daiko, den-den daiko, shime-daiko, kakko, taiko, ikko and sasara.
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Old 10th November 2009, 05:39 AM   #95
Bonsai is offline Bonsai  Taiwan
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#A common base stage does not have an input impedance that is zero ohms, at least not in the open loop case. With shunt feedback it can be much reduced like the PhonoClone design but lets talk about the common base stage.
So the common base stage is also amplifying the voltage. I like common base input stages because they have a "natural" input impedance that matches a low impedance MC quite well and does not suffer from early effect so is high speed without the need of high feedback or series cascoding. "

Why is early effect an issue when the amplified output signal is still only a few mV? OK I can understand it if we were swinging a few volts, but a typical MM input is 3-5mV, which is what the head amp is supposed be converting the mc input to. If early effect is an issue, you can always cascode the 1st stage.

I see you mention the low input impedance as being good on the common base design . . . but why do you then load the mc cartidge with 100 Ohms or some other low value? surely the value of a low impedance input is of no significance if you then stick a 100 ohm resistor across it.

Now, I can imagine from the noise point of view, you can possible argue that at LOW frequncies where the cartridge impedance is very low, the transistor noise might be an issue, but what happens at say 10KHz when the cart z is much higher? The current noise contribution then becomes an issue.
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Old 10th November 2009, 01:37 PM   #96
syn08 is offline syn08  Canada
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Originally Posted by Bonsai View Post
Now, I can imagine from the noise point of view, you can possible argue that at LOW frequncies where the cartridge impedance is very low, the transistor noise might be an issue, but what happens at say 10KHz when the cart z is much higher? The current noise contribution then becomes an issue.
Exactly, and more:

- It is not obvious that MC cartridges should be loaded with a low impedance. Manufacturer specs are within a wild range.
- A high impedance input can always be lowered, not the other way around. Only low impedance is useless for (e.g.) high output MCs.
- Non degenerated common emitter and common base have exactly the same input impedance (Beta/gm) and transconductance gain (gm).
- My main problem with Hiraga or any other similar approach is the required power supply. To place the devices in the minimum noise area, you need to run them pretty hot (some 10mA) so batteries are not really an option. The requirements (hum, noise, etc...) for a power supply to feed the Hiraga thing are huge. As usual, it is very bad engineering to move the stringent requirements from the signal stage to the power supply, it's kinda sweeping the dirt under the rug.

Now, if input current is really an issue, using a bias current cancellation technique is pretty straightforward. This is just another servo, and I was able to bring down the input current to the nA levels, close to a JFET input... Unfortunately, it is thermodynamically impossible to cancel the input bias current without impacting the noise. How large the penalty is, depends on the cancellation technique. My best was about 0.3nV/rtHz (by using low noise opamps, discretes could do better, at the price of complexity).

It is really funny to watch how opinionated the GEB team can be, in particular without showing any practical implementation or results. It reminds me of simulation afficionados, but at least those did some efforts to support their opinions.
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Old 10th November 2009, 04:54 PM   #97
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I have probably heard and measured more phono stages then you can imagine. Some of them sounding great with a high impedance loading. So i do not like to be put into the GEB team. I could also accuse you to be opinionated because you simply can not beat me in terms of experience with other peoples creations. For example I owned and measured several versions of the Connaisseur that sounded great with a high impedance fet input stage. I own several versions of the Essex equalizer and was a Hiraga dealer so again heard and measured several incarnations of Le Pre-Pre. I own Phonostages by Trigon, Bladelius, Hoer-Wege, Ultee, Convergent, Lorycraft, LC Audio you name it. On shows i worked with Mark Levinson, Krell, Rowland, Aesthetics, Aire, Burmester, Pass to only name a few. I have usually a good relationship to the designers and know a lot about the technologies they are using. I have experience with tubes, fets, bipolars, opamps and a mix of it with currentfeedback, voltagefeedback, LCR RIAA etc. etc. That is exactly the reason because i like your designs without even hearing them. They breeze some fresh air into a szeene that is basically stuck in the past. I only want to help if i can and think your designs are great. I really would like to listen to one of them on my system. I also did some simulation concerning loading and will present them here in some days.
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Old 10th November 2009, 05:00 PM   #98
syn08 is offline syn08  Canada
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Originally Posted by Joachim Gerhard View Post
I have probably heard and measured more phono stages then you can imagine.
Sorry, I have no problems with your position and experience. It's the Spambot team that's slightly irritating in it's sufficient ignorance.
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Old 10th November 2009, 05:24 PM   #99
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Quote:
Originally Posted by Joachim Gerhard View Post
A common base stage does not have an input impedance that is zero ohms, at least not in the open loop case. With shunt feedback it can be much reduced like the PhonoClone design but lets talk about the common base stage.
So the common base stage is also amplifying the voltage. I like common base input stages because they have a "natural" input impedance that matches a low impedance MC quite well and does not suffer from early effect so is high speed without the need of high feedback or series cascoding.
Exactly this observations I get by some evaluations and comparing of different circuit topologies.
But the exactly reason I haven't find out, because I don't find p-spice parameters of moving coil cartridges, that have internal DC resistance <20 ohms
Here two schematics, that outperform the most others regarded sonic quality (not necessarily regarded signal to noise ratio - for me purely cosmetic parameter).
Hiraga MC Preamp
Attached Files
File Type: pdf C_Mark Levinson JC-1DC_ckt.pdf (51.8 KB, 239 views)

Last edited by tiefbassuebertr; 10th November 2009 at 05:27 PM.
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Old 10th November 2009, 05:29 PM   #100
syn08 is offline syn08  Canada
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Originally Posted by tiefbassuebertr View Post
Here two schematics, that outperform the most others regarded sonic quality (not necessarily regarded signal to noise ratio - for me purely cosmetic parameter).
Horror! The ML preamp uses emitter followers at the input!
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