Sorry about that. I forgot what thread I was in. No more 600 from me. :)
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Curious, what version of the RCA Black plates do you have? I've been trying to decide which variation to buy, the one with side getters or the double D bottom getters. I can't find a consensus as to what the differences are between each, which to me means they both should perform very well.
My Leben has (2) matched pairs of the side getter version. I've never had the opportunity to listen to the double D's. The research I have read however, is pretty conclusive that the RCA Black Plate is the best valve for the CS-600 when configured for 6L6's.
Sorry man, did not mean to offend. The love of Leben HI Fi gear is shared by a relatively select few. Consequently, there is no dedicated CS-600 thread on Head-Fi. If you puruse all of the postings you will notice that the discussion began to include the CS-600 as more HF'rs purchased the unit. To my knowledge, you are the very first to complain.
Two different versions of the Leben CS300XS headphone output!
I asked Leben about why the HD650 (103dB) is humming on my Leben CS300XS, whilst my less sensitive Audeze (LCD-2rev.1/3 - 93db) and HiFiman HE500 (89dB) cans are not:
Here's the answer from Leben
This may be due to the headphone output power.
In the past there were two types of CS-300X, one has 1000mW headphone
output, and the other has 800mW for high efficiency headphones.
Your CS-300X should be with 1000mW headphone output for low efficiency
headphones, therefore, the noise shall be improved by reducing the
headphone output power from 1000mW to 800mW.
Please refer to the attached schematic diagram for CS-300X.
There is 270 ohms resistor at the headphone out.
By replacing this resistor by 1K ohms(30W) resistor, the headphone
output will be reduced to 800mW.
What this also implies is that one can, if one is willing to do so (or make someone capable do it for you) - actually make another headphone socket and have to sockets: One high and one low sensitivity output.
If anyone is interested, the fuse type for the CS300XS is slow, 6.4mm x 30mm, 2A. I swapped the stock fuse for a furutech and it does indeed make an appreciable difference - the sound is lusher with more immediacy and dimension. Although I find the furutech to be too warm in my system and I will try the hifi tuning fuse.
FWIR they are not the same specs etc. - but the 600 is a good performer with headphones, the headphones output i tapped from the output stage as with the CS600 an ran through resistors.
What headphones do you intend to use?
here's a happy CS-600 and LCD-2 listener..
I've read that CS600 is happier with higher impedance headphones due to unconfirmed high-ish output impedance (??).
The planar magnetic LCD-2, however, even though it is not high impedance, has a very flat impedance curve which makes it less dependant on impedance matching - which also corresponds to my own experiences.
The very low standard dynamic Denon DXXXX series seems to be less of a good match ( I read this several places)
My advice: Use the CS-600 with higher impedance headphones or planar dynamic hteadphones with flat impedance curves, Like the Audezes and Hifimans.
Another low impedance headphone which exhibits lovely synergy with the CS-600 is the AT W3000ANV. "Ethereal" is an adjective which conveys a sense of the experience.