A single series string of 105 series LEDs gave a noise of about 2uV over 22Hz-22kHz (ref Valve Amplifiers, 4th ed). Not sure how many this amp used, but let's say 10. So that would correspond to roughly 0.6uV before paralleling. The noise of the paralleled strings would reduce as the square root of the number of parallel strings, so you could drop that by a factor of 2 or 3. So the noise is comparable to an ideal (zero excess noise) 270R at room temperature (which a cathode resistor is unlikely to be).
All moot, of course: the tube is far noisier.
All moot, of course: the tube is far noisier.
OK, so about 0.5uV Possibly a bit less because Morgan had a dodgy solder joint which contributed to his noise measurement. Eother way, errrr, lost in the noise. 😀
Thanks for the clarification.
Thanks for the clarification.
Looking at the Johnson noise from a 270 ohm resistor at room temperature: Vnoise(rms) = root(4kTRB)
k= boltzmanns' constant
T= abs temperature (293 degr Kelvin)
R= resistance
B= bandwith
4kT= 1.62 x 10~-24, times 270 ohms, times 21,980 Hz= 9.6 X 10~-18
Vnoise = 3.1 x 10~-9 = 0,003 microvolt/Hz~-1/2
That would be less than the LEDs. Is this white noise on the cathode complete harmless or can it lead to 'listening fatigue'? I have no clue how to implement these figures but some preferred the simple cathode resistor for prolonged listening while others preferred the immediate gain in weight on the bassnotes and stronger attack (not faster) with LEDs. Perhaps it's a case tot case study, how it mixes in with other shortcomings of our audio creations 😀
k= boltzmanns' constant
T= abs temperature (293 degr Kelvin)
R= resistance
B= bandwith
4kT= 1.62 x 10~-24, times 270 ohms, times 21,980 Hz= 9.6 X 10~-18
Vnoise = 3.1 x 10~-9 = 0,003 microvolt/Hz~-1/2
That would be less than the LEDs. Is this white noise on the cathode complete harmless or can it lead to 'listening fatigue'? I have no clue how to implement these figures but some preferred the simple cathode resistor for prolonged listening while others preferred the immediate gain in weight on the bassnotes and stronger attack (not faster) with LEDs. Perhaps it's a case tot case study, how it mixes in with other shortcomings of our audio creations 😀
I am talking about substituting RC with LEDs.
The best way would be to compare apples with apples, i.e. measure the noise from R or RC in the similar conditions compared to LED tests.
As to calculations you should take 820 ohm resistor @ say 320 K. This will roughly give 0,02 uV/Hz. Is this difference significant to hearing? I don't know. I am a cello player with some orchestral experience, so I always try to compare real sound to what is reproduced. I perceive LED bias (vs. RC) more real.
CCS's for C3g plate mounted.
An externally hosted image should be here but it was not working when we last tested it.
After having read a post on connecting g3 of C3g (to either cathode or anode/plate) while g2 connected via resistor, say, 220 ohm to plate, I am in doubt. Which one is ...
Source: http://audioroundtable.com/GroupBuild/messages/1999.html
Source: http://audioroundtable.com/GroupBuild/messages/1999.html
I started thinking if there was a relation between DC across coupling cap and transferring signal via such polarized cap. DC voltages in fixed and cathode biases across a coupling cap may be significantly different.What is an impact on sound?
Started a thread in PARTS.
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My cat (Rudy) is checking the progress.
An externally hosted image should be here but it was not working when we last tested it.
I dont know, but when you have located the grid(signal in), isnt the two other always crossing each other, so to speak 😕😛
They are between g1 and a. But there is the question of how each of them interacts with electron flow while differently biased. I don't know. Staying with "classical" i.e. g3-k, g2-a.
After some power test I may be tempted to change.
After some power test I may be tempted to change.
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thought you had it triode coupled ?
but I seen the size/value of resistor to anode debated a lot
but I seen the size/value of resistor to anode debated a lot
btw, DHT Rob have a schematic with C3g-50 amp on his site
seems he connects g2 and g3 together, and then to anode with 100R
is it different because of the IT
seems he connects g2 and g3 together, and then to anode with 100R
is it different because of the IT
I haven't found any measurements of triode connected pentodes with both g2 and g3 connected to anode. At another forum I have found a sound description of C3g with g2 connected to plate and cathode respectively. That is of personal taste, however.
IMHO, IT use does not imply connection presented in DHT Rob's schematic.
Datasheet reads U3=0V i.e. connected to cathode.
http://www.4tubes.com/DATASHEETS/SCANS-Original/A--C/C3g-TFK.pdf
http://www.4tubes.com/DATASHEETS/SCANS-Original/A--C/C3g-TFK.pdf
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