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The Leben CS300XS Thread - Page 125

post #1861 of 2087
If I go for a target of the stated load (8 Ohm), then I will use a 10 Ohm resistor in parallel and the (50 Ohm) headphone will then get 2 Watt. This is actually enough, but a little more would probably be nice.
post #1862 of 2087

I spoke with my tube amp guru today, he has a long experience of designing and repairing tube amps. He didn't believe that driving HE-6 direct from the speaker outputs would damage the amplifier, but could not give a guarantee. He said that it is safe with a parallel resistor and also could be an advantage because the impedance (total impedance of the parallel circuit) is closer to what the amp is designed for. The resistor could be between 10 and 20 ohm, 5 W. If I understand it correctly a higher value than 10 ohm would deliver a larger part of the output power to the headphone (with an impedance of 50 ohm).

 

I also asked about the choke and he said that is a good idea. It can reduce noise and improve sound quality, probably a slight improvement but definitely not night-and-day. Raaf, he wondered where you put the choke? It could be on the power supply to the screen of the tube or to the anode and it could be useful to know which. The main problem should be to find a choke that is small enough to fit in the amplifier.

post #1863 of 2087

I will start off with a 10 Ohm, 10W ceramic resistor. This I got cheap and it will allow me to get an impression of how it performs via the speaker outputs. I have been playing with the idea to use a higher value because it will let the HE-6 have more of the power, as your tube-guru also says, but at the moment I haven't received an answer from Leben regarding how high an impedance is safe to use.

 

Since the amp is 12W, a 10 Ohm resistor will let the HE-6 get 2W, but if I use for example a 16 Ohm resistor, the HE-6 will receive 2.9W, while the amp will "see" a 12.2 Ohm load ... if I calculated correctly biggrin.gif

 

I expect a load of about 12 Ohm, when using the 8 Ohm setting, will be fine, but I want Leben to confirm the highest safe impedance. It may be higher.

 

Another advantage using speaker outputs is the much lower output impedance. Since my CS300 has a 270 Ohm resistor on the headphone output, I expect the difference will be huge.

post #1864 of 2087

I am very interested too in reading what Leben has to say about the HE-6s

 

Thanks!

post #1865 of 2087
Quote:
Originally Posted by Anders View Post

 

I also asked about the choke and he said that is a good idea. It can reduce noise and improve sound quality, probably a slight improvement but definitely not night-and-day. Raaf, he wondered where you put the choke? It could be on the power supply to the screen of the tube or to the anode and it could be useful to know which. The main problem should be to find a choke that is small enough to fit in the amplifier.

 

A picture says more than words :

 

I have placed the choke in series with the 2.7K resistor.

The choke is a little old transformer out of a old  "wallsocket powersupply".

I have used only the primary (230 V.) side.

It was small enough to slide it in between the AC and speaker terminals, I wraped some tape around it so it fits exactly.

 

Of course it's no big improvement, the Leben is well designed, but there was a slight humm with the volume full open with no music ,

and that has gone , my CS300 is completely silent now.

 

All the little improvements you make in a set-up add up, my approach to audio is to get the powersupply's as clean as possible and to keep the chain as short as possible, less is more wink_face.gif

 

And of course I'm a tube fanatic, the opamps of my dac have gone and have been replaced with tubes, that was a great improvement.

Have a look at the Lampizator website for how-to's : http://www.lampizator.eu/

post #1866 of 2087

Here is a small choke at low cost that should fit.  It is sold at Allied Electronics.

I use these all the time.

I don't know why expensive amps like these have such a cheep power supply.

 

http://www.alliedelec.com/search/searchresults.aspx?dsNav=Ntk:Primary|70218148|3|,Ny:True,Ro:0&dsDimensionSearch=D:70218148,Dxm:All,Dxp:3&SearchType=0&Term=70218148

post #1867 of 2087
Quote:
Originally Posted by 2359glenn View Post

I don't know why expensive amps like these have such a cheep power supply.

 

Makes me wander too, the extra cost of a choke is allmost  nothing compared to the rest of the components .

But ty to tell that to a manager wink_face.gif

post #1868 of 2087
Where is the power supply in that picture?
post #1869 of 2087

I used to work for Harman Kardon in the 70s and Engineering would come out with a good product.

After the office got through with switching to cheaper components the stereo usually ended up

a piece of crap.
 

post #1870 of 2087

BINGO!

Here is what I stumbled on when I searched the net (with added bold & italics to the interesting part):

Quote:
(...) the CS-300 was shortly followed by an improved version CS-300 X (Limited), where some changes were introduced (photo nr. 7). The output terminals used were better, there was an additional choke in the power supply, some passive elements were exchanged to better ones, but most of all the output tubes were exchanged to rare Mullard NOS.

Link:  http://www.highfidelity.pl/@main-135&lang=en

 

In other words, the standard/original CS300 does not have a choke in the PSU, but the later/upgraded versions has! This is in other words an "official mod" by the manufacturer.

 

The noise I hear with LCD-2 is in fact mostly a humming, which most likely is caused by the trafo inside the amp.

 

Edit:

I need to add this from the above article:

Quote:
A choke in power section, in the anode circuitry, is a “holy grail”, and is used by many tube device manufacturers. But like any other element, it has its problems.
(...)
... the choke, which was one of the biggest changes to the Limited version, is also gone.
(...)
... the HD800 are high impedance headphones - 600Ω – and they are not so forgiving, any error, any noise or hum can be heard immediately – just like with high efficiency loudspeakers. And with them, this hum was annoying. Mr. Waszczyszyn, like any scientist, systematically searched for the reason, and found out, that there is no choke in my unit, but only resistors, what increases noise slightly, and that the hum is a result of the chosen topology, with one channel closer to the power supply than the other. So it cannot be helped without reworking the whole amplifier. And I did not want to do that, because we could maybe improve on this one aspect, while destroying everything else, because architecture of elements is a part of the “magic” coming from years of experience. And I am sure Mr. Hyodo knew what he was doing. Well – this was probably a part of the compromise. There is nothing we can do with the loudspeaker output, but with the headphone output it is a different story. It was enough to solder a few resistors to the headphone socket, and that was it. Their values must be chosen experimentally, as it will depend on the impedance and efficiency of our headphones. At first the values were chosen too big, and needed to be adjusted, but now I can tell, that there is no hum at all! And no noise. This is the reason I recommend this simple trick to everyone – it is cheap and effective.

Edited by LarsHP - 8/9/13 at 4:19pm
post #1871 of 2087
Quote:
Originally Posted by LarsHP View Post

BINGO!

Here is what I stumbled on when I searched the net (with added bold & italics to the interesting part):

Link:  http://www.highfidelity.pl/@main-135&lang=en

 

In other words, the standard/original CS300 does not have a choke in the PSU, but the later/upgraded versions has! This is in other words an "official mod" by the manufacturer.

 

The noise I hear with LCD-2 is in fact mostly a humming, which most likely is caused by the trafo inside the amp.

 

Edit:

I need to add this from the above article:

 

I have a CS-300X version...but don't see any choke in the power supply. OR Am I seeing right through it?!

 

post #1872 of 2087

No choke indeed .

But from what I get out of the story, only the special custom build had one.

According to some tube gurus the best "sounding" powersupplies have a tube rectifier and a choke.

From what I experience and hear on my set , a choke has more pro's than contra's.

post #1873 of 2087

The choke on the CS-300X is located in the upper section of the amplifier, between the power supply and the transformers. I don't know how it is connected and the circuit, but it is probably wired differently than Raaf's choke.

 

post #1874 of 2087

That is not a choke Anders, I found this image earlier in this thread

 

post #1875 of 2087
@ Raaf
The custum built CS300 doesn't have a choke and neither the standard, but - according to the article - the X version(s) has.
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