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Old 15th April 2004, 09:14 PM   #1
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Default current amplifying phono stage

Hi all,
Some time ago, there was quite an interesting debate on the asylum concerning current sensing phono stages (for MC, that is).

http://db.audioasylum.com/cgi/m.pl?forum=tweaks&n=72458

It is mainly an I/V Converter with some (remarkable) tweaks.

I understand that some of the protagonists posting here as well.

How might such a design rate against some highly regarded actual projects around here?

I understood, that the current sensing part is discussed in papers like that (Fig. 2(b)):
http://focus.ti.com/lit/an/sboa034/sboa034.pdf

Together with the hints Jon Risch gave in the asylum it should'nt be too hard to track things down

I happen to have two trashed DL103's with working coils, so a balanced version with frozen assembly would be doable.

I would be glad to get some respond,

Rüdiger
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Old 16th April 2004, 01:00 AM   #3
BrianL is offline BrianL  United States
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Check out the patent on Dynavector's circuit. A bit vague, but
will give you some info. Some searching of the USPTO web site
using their search engine should yield the patent.
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Old 19th April 2004, 12:05 PM   #4
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Hi,

unfortunatley, I did not find any information on the dynavector patent.

I made a quick sketch from jon's announcements, what do you think, might it work?

Click the image to open in full size.


Rüdiger
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Old 20th April 2004, 03:02 AM   #5
BrianL is offline BrianL  United States
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OK, since you couldn't find it for yourself.

www.uspto.gov the patent is # 4,644,517

I'll leave it to you to print out.


The circuit you show has too many moving parts. All that
stuff connected to the "+" inputs of the OPA2604's is
probably unnecessary.

Also, to do the frozen coil thing, it looks like you'll
need at least two dead cartridges. I believe tat Risch
said you could get by with just having one of them
in one "side" of the circuit, but maybe more is merrier.
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Old 20th April 2004, 06:45 PM   #6
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Hi,
Quote:
www.uspto.gov the patent is # 4,644,517
I'll leave it to you to print out.

OK, I did not get that the searching machines covered different timeframes... Thanks

Quote:
The circuit you show has too many moving parts. All that
stuff connected to the "+" inputs of the OPA2604's is
probably unnecessary.
True if offset is no problem.
Quote:
Also, to do the frozen coil thing, it looks like you'll
need at least two dead cartridges.
Yes, I have two...

Hm, I'm wondering a bit about the low interest this thread provokes. Do you think, that the current sensing approach is crap? Old stuff not worth trying? Anything Else?
Rüdiger
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Old 20th April 2004, 08:18 PM   #7
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Quote:
Hm, I'm wondering a bit about the low interest this thread provokes. Do you think, that the current sensing approach is crap? Old stuff not worth trying? Anything Else?
I personally think it's great. My only doubts involve the input opamps. IME opamps do not seem to provide the perfect interface for MC carts. No idea why, but transformers or discretes seem to work better at these low levels. Not to mention that good sounding regulators for MC amps seem to exclusively consist of batteries . Still, the current approach may be different. As this is quite a simple project it's definitely worth building.

As a matter of interest what do you use at present?
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Old 20th April 2004, 09:11 PM   #8
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Hi,
Recently, I finished (?) my version of the la bohème stage
www.klaus-boening.de

It sounds great, and it is more the success that encourages me to try something else/further than an actual discontent.

I'm open minded to tranformer-based solutions, discrete, valve and so on, but Klaus Böning, or Blue Amp or Horch are proving that one can achieve great results with op-amp based/involved solutions as well.

Rüdiger
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Old 20th April 2004, 09:21 PM   #9
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Quote:
but Klaus Böning, or Blue Amp or Horch are proving that one can achieve great results with op-amp based/involved solutions as well
Maybe not a good example as your input circuitry is discrete. I am not surpised you like the sound.
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Old 20th April 2004, 09:22 PM   #10
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Some guys at MIT 20 years ago were convinced that this was the final answer in terms of vinyl reproduction. They used discreet npn's and pnp's (I can't give away their circuit even though they never went anywhere with it). They thought that you got mechanical damping on the cantiliver that greatly reduced mistracking, I have no evidence that this is true. For geometry mistracking it obviously can't be true. BTW some of what Mr. Risch said in that asylum thread is wrong, you do not need low current noise for this circuit. The TI/BB app note is about photo diode amplifiers for CAT scanners and is also not particularly relevant and could lead you astray.
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