Seite 6 von 24
Verfasst: So Jan 27, 2008 12:18 am
von [silent:arts]
when I ever will do a rev2 board I will include it.
from my understanding the grid stoppers are there to prevent oscillation at high gain settings (like we have with the Sowter Output transformers)
try the potentiometer mod I did first, for the grid stoppers you would have to modify the PCB. worked for me.
and I can't remember any hum before, only the oscillation ...
Kubi would be the man to explain grid stoppers
Verfasst: So Jan 27, 2008 12:15 pm
von waldorfcave
ok i found a 22k pot and assembled it. gain range is better now, but hum is still there.
now i measure the voltage of the tube pins
Verfasst: So Jan 27, 2008 2:50 pm
von waldorfcave
..also did the grid stopper mod...nothing happens
highvoltages for the tubes:
v101: pin 1: 119
pin 6: 123
v102: pin1: 104
pin6: 230
v103: pin1: 94
pin6: 95
v104: pin5: 196
pin6: 76
i think they are in the normal range.
DAMM the comp works sound good but the fucking hum peak 105hz @ -74db is to loud.
i rewired my ground lines, pushed all transformers checked everything.
slowly i´m out of my nerves....
if nothing worx i will put a pad behind the output. so i have to use more gain but the humfloor will be less i think.
Verfasst: So Jan 27, 2008 2:59 pm
von [silent:arts]
putting out my unit out of the rack to compare at the moment ...
waldorfcave hat geschrieben:
DAMM the comp works sound good but the fucking hum peak 105hz @ -74db is to loud.
this is -74dBfs in your DAW, right ? what's your headroom ?
if it is -74dBu all is fine (mine is -67dBu at max gain)
will post my voltages soon ...
Verfasst: So Jan 27, 2008 3:17 pm
von [silent:arts]
mhm, most of my voltages are lower (and I only had a 5 minutes warm up):
v101: pin 1: 119 (mine: 93V)
pin 6: 123 (mine: 100V)
v102: pin1: 104 (mine: 91V
pin6: 230 (mine: 200V)
v103: pin1: 94 (mine: 73V)
pin6: 95 (mine: 73V)
v104: pin5: 196 (mine: 113V)
pin6: 76 (mine: 108V)
what Tubes are you using ? will try to find some normal ECC83 in my box (since I used NOS Telefunken ECC803S)
Verfasst: So Jan 27, 2008 4:09 pm
von waldorfcave
maybe this is an idea?
i use jj ECC803 and 12bh7 from electroharmonix all brand new
Verfasst: So Jan 27, 2008 5:26 pm
von [silent:arts]
Lars, I think we are on the right way
I checked different Tubes in the place of V101, and there were significant differences in overall noise, noise and hum spectrum.
sadly I can't do any FFT at home, but I used a Neutrik Minilyzer and my ears.
the Tubes I found and have tested are:
- Telefunken ECC803S (my "Stock" Tube in there)
- Valvo ECC83
- Siemens ECC83
- Sovtek 12AX7LPS
- JJ ECC83S
- JJ ECC83
- Japan 12AX7A
with the JJ ECC83S I had significant Hum and a Noise Floor of only -50 dBu. will be fun to do some real measuring at work with different tubes.
(but this will take some time ...)
do you have any other ECC83 to check ?
Verfasst: So Jan 27, 2008 5:32 pm
von waldorfcave
no ihave no different tubes
is - 50 dbu good or worse ?
ok. then i need new tubes, which should i prefer?
great volker
Verfasst: So Jan 27, 2008 5:46 pm
von [silent:arts]
waldorfcave hat geschrieben:is - 50 dbu good or worse ?
it is 17dB worse than -67dBu
waldorfcave hat geschrieben:ok. then i need new tubes, which should i prefer?
interesting thing is the JJ ECC83 was better than the JJ ECC83S in my little test. should be the other way in my understanding.
I have only used old tubes yet, don't know what I should recommend.
it is always handy to have some spare tubes ...
Verfasst: So Jan 27, 2008 5:51 pm
von waldorfcave
ok.
but what should i do now
Verfasst: So Jan 27, 2008 5:58 pm
von [silent:arts]
I will send you the V101 and V201 from my unit (but I want them back
)
this way we can make sure if the hum goes away with other tubes.
Verfasst: So Jan 27, 2008 6:33 pm
von waldorfcave
you make my day
Verfasst: Di Jan 29, 2008 11:19 pm
von [silent:arts]
ChuckD hat geschrieben:
I have 4 older Mallory Caps (silver cans) that someone gave to me for free. Send me you address and I will mail you 2 of them! I will use the other two on mine. I measured them with my Fluke MM and 2 came out as ~13uF and the other 2 came out as ~12uF so I will pair them up that way.
Not sure if they are good. They are new old stock but they were free ... so.
I will throw them in the post for you.
-ChuckD
received them today, thanks very much.
Verfasst: Mi Jan 30, 2008 2:42 pm
von waldorfcave
Hi Volker,
received your tubes....and i´m totally shocked
now i have some hum behind -98dbfs, this far enough for me.
changed my tubes yesterday also to electro harmonix, with result of -80dbfs hum. nearly ok.
But i need this telefunken tubes
maybe somebody know where i can buy them
- oh man this thing is really crazy for me. i´ve been looking for hours for some faults.
now i know what differences are in tube
Verfasst: Mi Jan 30, 2008 2:48 pm
von [silent:arts]
waldorfcave hat geschrieben:now i have some hum behind -98dbfs, this far enough for me.
good to hear - so it is not the PCB or your build
if you are looking for those Telefunken tubes:
ebay
ich sollte meine Altersvorsorge mal aus dem Sidechain entfernen, da tut es auch was anderes ...