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Old 6th December 2010, 12:09 PM   #3801
SY is offline SY  United States
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Quote:
Originally Posted by soongsc View Post
Self made or known brand?
I'm unfamiliar with commercial offerings, but my preamp, His Master's Noise, can be found in the "Articles" column on the right side of this site's home page. Likewise, Morgan Jones features a balanced design in his book "Valve Amplifiers." I don't know if Vacuum State does, but I wouldn't be surprised.
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Old 6th December 2010, 03:28 PM   #3802
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Originally Posted by Flodstroem View Post
Yes I have figured out this could be e great problem. But think of it in this way, there is no 12 ch, its only 2 ch and 12 frequencies. To my help are the fact that those outputs could be leveled control by 15 dB. Also Im going to do some matching of the series LDRs by a resistor paralleled over the LEDs (10k-1M) This helps damping the most sensitive LDRs (in the "start" region), but not the shunted LDRs Those I had to match in another way.

And finally, this is for a big x-over system and there are 6 frequencies per ch and Its interesting to see how this is going to work together.
Hmmm, Im quoting myself here just to go back to topic (my topic )
and for to refresh your memory
I now have a second approach/ for my 12 ch circuit
I have realized that matching all those 12 + 12 pcs of LDRs was not an easy thing that could be overlooked for to get a simple solution. I have learnt the lesson.
But how to match a such a bunch of LDRs? Buy 1000 pcs and try to find 12 + 12 matching each other...... no thats impossible
But,
My solution for to day looks like this and its not a simple solution as first thought:

Each LDR are controlled by its own trimable circuit consisting of two trim potentiometers including an 1/2 OP290
This means I can use what ever LDRs that came to my hand without any matching at all (of the LDRs).
Instead Im using the electronic circuit for each of the LDR and then I can match them "active".
This solved a big problem and that was to get all LDRs to act in the same time, paralleled with my vol. potentiometer.
When using my new circuit I can set the zero-level to be equal for all LDRs in the circuit and I can also trim the "span" or the angel of the resistance change (e.g a change of the OP-amps gain individually) for to get the LDRs to have the same/equal resistance increases or decreases with different vol. pot settings.
Of course, if the LDRs characteristic isnt linear then I will not have a total match but I could trim a part of the differences to become less pronounced.

Though, Im able to match the pair of LDRs for each OP290, INCLUDING that I also have the possibility to match each pair of LDRs to each other.

With the new circuit I can match all LDRs to each other in a 6 ch. set up, both the 6 series and the 6 paralleled LDRs and then steer those 12 LDRs by a single (cheap) stereo potentiometer only.

OK, I will need much more active circuits, a power source, including PCBs (but I make them myself in the kitchen ) But I already have all the components stored.

The costs for to build this active circuit does however not became as expensive as what a 2 x 6 ch. high quality potentiometer would cost.

I have done some testing and there was no problem matching two totally different LDRs to become a well matched pair.

I should come back soon with some drawings
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Old 6th December 2010, 07:25 PM   #3803
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Originally Posted by ondesx View Post
even if it's a bit irritating to be always undeservedly corrected, [/url]

I bet your 2 foot tall with a little person complex.
Nearly all phono leads that come from a turntable have an RCA on the end not an XLR. The shield/earth runs on the outside of the RCA what does this leave, one single centre connection that can only carry one wire not two for balanced, hence it is single ended.

Now please I ask the moderators to get this thread back on line, as the banter here, has nothing to do with the Lightspeed Attenuator.

Cheers George
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Old 6th December 2010, 07:42 PM   #3804
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Quote:
Originally Posted by georgehifi View Post
I bet your 2 foot tall with a little person complex.
...
That sort of thing doesn't help. Consider this an official warning.

If you want to talk about your attenuator, please do so without the personal comments. If you're not interested in engaging other members who have technical criticisms, you're under no obligation to do so.
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Old 6th December 2010, 07:53 PM   #3805
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Originally Posted by georgehifi View Post
I bet your 2 foot tall with a little person complex.
Nearly all phono leads that come from a turntable have an RCA on the end not an XLR. The shield/earth runs on the outside of the RCA what does this leave, one single centre connection that can only carry one wire not two for balanced, hence it is single ended.
Whether you like it or not, I don't care: there are two kinds of balanced lines: one is called "floating balanced" that is used in current mode for this phono preamp...

And it is also this "floating balanced" that I used for my balanced version of LS shown in posts #3703 and #3705 with only three LDRs per channel instead of 4... Then we still are speaking of LDRs, isn't ? I ask you again: calm yourself and verify all your affirmations before posting...

Last edited by ondesx; 6th December 2010 at 08:06 PM.
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Old 6th December 2010, 07:54 PM   #3806
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Nearly all phono leads that come from a turntable have an RCA on the end not an XLR.

Sneaking in before any moderator wields his/her axe, may I draw attention to the late 1980s Audio Synthesis ADEQ RIAA pre-amp? It used the SSM2016 as the first stage, worked with MM and MC devices and could be configured for balanced or unbalanced operation.

Balanced working required any earth tag on the cartridge to be removed and for the tonearm-to-amp leads to terminate in XLRs. I've used this setup for over 20 years and it still works just fine. My input leads are made from lightly twisted "wire-wrap" cable with no screen - there is not a trace of hum.

As George suggests, it's not a common approach. It's worked well for me but, who knows, it might have every bit as good unbalanced. Had it made that big a difference, I'm sure it would have been copied.

A bit like the Lightspeed, come to think of it. (It's amusing how many people come to this list and start by lecturing one and all here on the need to reinvent the wheel before they even know how to use one. But it seems they soon go.)
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Old 6th December 2010, 09:45 PM   #3807
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[QUOTE=Ryelands;Balanced working required any earth tag on the cartridge to be removed and for the tonearm-to-amp leads to terminate in XLRs. I've used this setup for over 20 years and it still works just fine. My input leads are made from lightly twisted "wire-wrap" cable with no screen - there is not a trace of hum.

As George suggests, it's not a common approach. It's worked well for me but, who knows, it might have every bit as good unbalanced. Had it made that big a difference, I'm sure it would have been copied.

)[/QUOTE]

Just giving the facts SY and trying to stop misconceptions being aimlessly formed

Yes you are right, 99.99% of cartridges end up being single ended when they get to the rca's sockets on the phono stage.
I have myself only come across one early (Mark Levinson Phono Stage) that had a true balanced input but this required a rework of the cabling inside the tone arm and the flying leads leaving the turntable.
Unfortunately Decca cartridges with their 3 pin output did not work balanced successfully with this, also a lot 4 pin cartridges which have their blue and green pins connected internally inside the cartridge.

Cheers George

Cheers George
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Last edited by georgehifi; 6th December 2010 at 09:48 PM.
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Old 6th December 2010, 10:15 PM   #3808
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Actually, every tonearm I've seen has twisted wire in the arm-tube, so that can be left alone. All that needs to be replaced is the coaxial interconnects (easy). Some Shures need to have the strap cut- every other cartridge I have had on hand (Grado, Stanton, Audio Technica, Panasonic/Technics, Linn) separated the blue and green so were balanced-ready. The only cartridges I've seen that don't work balanced are Deccas.

I checked and indeed Vacuum State's preamps are balanced in on the phono, so it's not just Morgan, me, and a few others. But whether or not that's popular commercially (and it isn't!), it's the right way to run things, it's pretty easy to do, and since we're all diyers, we can do it.

No misconceptions.
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Old 6th December 2010, 10:21 PM   #3809
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I'm not arguing it's the right way, I said it's not the done way, to prove this put an ohm meter across both l/r of the turntable rca outer body flying leads when attached to the phono stage and you will get continuty in 99% of cases. Not balanced.

Cheers George
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Old 6th December 2010, 10:32 PM   #3810
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Allen is in minority with his later balanced phono stages, but even he used for a long time the standard way (attached) single ended circuitry that 99% still use today.
Cheers George
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File Type: jpg Allen's Phono Stage.jpg (46.5 KB, 308 views)
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