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Old 9th April 2013, 08:26 PM   #8801
mjona is offline mjona  New Zealand
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Quote:
Originally Posted by dvv View Post
No opinons, no experience, no comments?

Doesn't every CCS also inject some noise into the circuit? Possible zener noise?
Hello DVV,

There were a couple of interesting articles by Walt Jung on low noise CCS in AudioXpress in 2007. If you have not read these they are now on his website.

The first article link is http://waltjung.org/PDFs/Sources_101_P1.pdf

I have been happy with the CCS as per figure 4A that Jung describes as having "moderate performance at low cost".

R1 can be a split resistor load with a capacitor from the split to the positive rail - as per Self.

Alternatively you can replace R1 with a constant current load as done by Pass.

In existing equipment the simplest solution is to replace R1 with a constant current diode.

Re the BFW16A MC preamp article from Elektor. If you do find it I will be interested to see it again.

I did build the board in anticipation of buying a MC cartridge when I could afford one. That never happened because I bought a Phillips CD player at a mark-down price.

Ten years ago I moved house to another city and a lot of magazines had to go as did a lot of junked electronics projects. I salvaged what I could - including the BFW16A's.

Michael J
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Old 10th April 2013, 07:13 AM   #8802
dvv is offline dvv  Serbia
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Many thanks for the link, Michael. Now it's study time again.

H/K, for example, holds dear to their heart Walt's 3a version.

Like you, I also tend to use the model under 4A, albeit a bit more evolved, but basically, that's it, the difference being that I tend to use a zener diode. I find that the sound is a bit more lively (or so it appears to me) when the base of the CCS transistor is at around 5V or a bit more. Typically, I'll use a ZPD 5V6 zener (0.5W, +/-5% tolerance, easily available), Goldmund loves the 8.2V version.

Add one more 1N4148 diode and another transistor and you have a cascode CCS.

Thanks again.
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Old 10th April 2013, 07:41 AM   #8803
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The LED CCS is rather impressive considering the simplicity . Self vaguely says about it and to me dams it with feint praise . LM 334 also is very good . I have no great experience with the LED CCS , any idea how good the behaviour is over a wide voltage range ? A LM317 is almost rock solid over a very wide range . The two transistor CCS not very good .

Thank you Michael .
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Old 10th April 2013, 08:10 AM   #8804
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Quote:
Originally Posted by nigel pearson View Post
The LED CCS is rather impressive considering the simplicity . Self vaguely says about it and to me dams it with feint praise . LM 334 also is very good . I have no great experience with the LED CCS , any idea how good the behaviour is over a wide voltage range ? A LM317 is almost rock solid over a very wide range . The two transistor CCS not very good .

Thank you Michael .
The LM317 is not very good at high frequencies
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Old 10th April 2013, 08:41 AM   #8805
dvv is offline dvv  Serbia
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Quote:
Originally Posted by nigel pearson View Post
The LED CCS is rather impressive considering the simplicity . Self vaguely says about it and to me dams it with feint praise . LM 334 also is very good . I have no great experience with the LED CCS , any idea how good the behaviour is over a wide voltage range ? A LM317 is almost rock solid over a very wide range . The two transistor CCS not very good .

Thank you Michael .
The two transistor CCS could be very good, but in a different configuration.

Yes, the LED version is good, but I find it not so good for rail voltage above say +/-30V - no idea why.

Some use it "as is", simple LED on transistor base, resistor to ground, but some do add a lower value capacitor, say 22...47 uF. I wonder how much sense that makes, after all, LEDs are supposed to all but noise free (as component noise goes).

Some Brits mainly divide the resistor value to the ground into two and stick that capacitor right in the middle between the series mounted resistors.

Although, truth be told, also some Brits do use the two transitor version in more or less modified forms (e.g. Arcam, Cyrus, Tag McLaren, etc).
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Old 10th April 2013, 09:28 AM   #8806
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Originally Posted by davidsrsb View Post
The LM317 is not very good at high frequencies
It is a great device to get a design up and running . I use them in industrial power supplies where high frequency noise is less of a problem . I often use them in audio designs to simplify the task . I fight very hard to improve upon them in reality when looking at the scope . I never use them in audio more out of pride than conviction .


I used one in a valve cathode recently ( KT88 ) . Mostly to protect the valve whist on a journey of the unknown . Instantly the distortion tumbled . It took me days to beat how well it worked .
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Old 10th April 2013, 10:26 AM   #8807
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by davidsrsb View Post
The LM317 is not very good at high frequencies
Jung shows 317 enhancements that become very good at HF.
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Old 10th April 2013, 10:28 AM   #8808
AndrewT is offline AndrewT  Scotland
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Originally Posted by dvv View Post
Yes, the LED version is good, but I find it not so good for rail voltage above say +/-30V - no idea why......................
would adopting a cascode alleviate this problem?
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Old 10th April 2013, 11:06 AM   #8809
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Quote:
Originally Posted by AndrewT View Post
Jung shows 317 enhancements that become very good at HF.
Hi Andrew , thanks for that . I read sometime ago you were looking at an isolation transformer to put near the incoming supply . A friend asked me recently about using one . I suddenly realized I knew very little about them . Especially where earthing is concerned and RCBO's . I have accepted in the past a 115 - 0 - 115 V output with 0 to earth to be a reasonable thing to do . Reading the thread it seemed there are many problems . I can get a 2000 VA unit made for him quite easily . Don't want to go ahead without understanding the advisability .

I can bond neutral to onside of the output as the mains usually would be . If so it defeats any reason to do it . I will put in some differential filtering ( 1 uF ) . I suspect that best not done to earth as I still think that requires class Y2 caps and I see it as serving no purpose ( live to earth rated ) . The transformer will have an electrostatic shield .


Anyone with anything to say about the sonic performance ? I felt in the past it was a downgrade if the transformer below 1000 VA . One guy in the thread was getting a mysterious 60 V between his various earths ! . I will have the transformer made as best I can with symmetrical windings so as to make capacitance to earth equal . That might help I guess ?

240Vac mains isolation transformer

Last edited by nigel pearson; 10th April 2013 at 11:18 AM. Reason: add link
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Old 10th April 2013, 11:13 AM   #8810
AndrewT is offline AndrewT  Scotland
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I still have my 3kVA 110Vac site transformer sitting unused in the garage.

I recently bumped into a post that linked to safe wiring up of an isolation transformer.
I can't remember where I saw it.
Big mistake. I should have copied it !!!!
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