Did you see the pics page48? Yes they are. The hum is about the same as when i had 'wrong' voltage divider till popiilin adjusted it. That's why i'm thinking maybe it's the centertap. I tried some small things, rearrange n so on but still same.
The red wimas and blue jantzen caps are gonna be replaced to some smaller sized. Took what i had
Dc heater? Lt1085, some caps n resistors? If i use chassie as sink? Maybe after cap change i can squeeze it in?
The red wimas and blue jantzen caps are gonna be replaced to some smaller sized. Took what i had
Dc heater? Lt1085, some caps n resistors? If i use chassie as sink? Maybe after cap change i can squeeze it in?
Hi,
If I may say so you're using way too thick wires where there really is no need to. More metal equates higher stray field.
You could replace all of the heater wiring for 0,6mm twisted copper solid core. Nothing fancy needed.
Next thing I'd do is loose that fat run of Oelflex and replace that with a twisted pair as above.
Push all the AC carrying wire, mains and heaters against the chassis top.
Don't tie other wires together with mains carrying wires, shielded or not.
Never cover resistors in tape, they'll heat up and may catch fire.
With proper lay out and grounding there really is no need for DC heaters on this level.
Try lifting the "Common" ground from the chassis and see what that does.
Try the hum bucking resistors across the heater xformer as popillin suggested.
Don't know why you changed that again....
Hire an octopus to hold the soldering gun....
Ciao,
If I may say so you're using way too thick wires where there really is no need to. More metal equates higher stray field.
You could replace all of the heater wiring for 0,6mm twisted copper solid core. Nothing fancy needed.
Next thing I'd do is loose that fat run of Oelflex and replace that with a twisted pair as above.
Push all the AC carrying wire, mains and heaters against the chassis top.
Don't tie other wires together with mains carrying wires, shielded or not.
Never cover resistors in tape, they'll heat up and may catch fire.
With proper lay out and grounding there really is no need for DC heaters on this level.
Try lifting the "Common" ground from the chassis and see what that does.
Try the hum bucking resistors across the heater xformer as popillin suggested.
Don't know why you changed that again....
Hire an octopus to hold the soldering gun....
Ciao,
Try to answer you...
The Oelflex is gone except to powerswitch. Did anyone look at the last pics?
Heater wiring is 0,8 solidcore or 1.0. Colour BLUE! See pic!
Rest of the wiring is 0,3 - 0,6 (blue n red)
The tape is not going to be there 'forever' and it's also 3Ms heat resistant tape we used in owens at work 850degress. cost 30-40e each role free for Mr Max anyway know you know that.
Everything is mounted upside down and i was just little scared it would fall down. I have not yet permanently secured caps etc
The hum buck res is gone cuz of the new pt that contains a Centertap. Popiilin said that remove those 2x100 and insert ct between voltage divider, so i did!
How much can i lift common ground? Like with 12R ?
Can anyone look at the ground cables how i linked it together and see if it's ok?
I tried my best.
/J
The Oelflex is gone except to powerswitch. Did anyone look at the last pics?
Heater wiring is 0,8 solidcore or 1.0. Colour BLUE! See pic!
Rest of the wiring is 0,3 - 0,6 (blue n red)
The tape is not going to be there 'forever' and it's also 3Ms heat resistant tape we used in owens at work
850degress. cost 30-40e each role free for Mr Max anyway know you know that.Everything is mounted upside down and i was just little scared it would fall down. I have not yet permanently secured caps etc
The hum buck res is gone cuz of the new pt that contains a Centertap. Popiilin said that remove those 2x100 and insert ct between voltage divider, so i did!
How much can i lift common ground? Like with 12R ?
Can anyone look at the ground cables how i linked it together and see if it's ok?
I tried my best.
/J
I have now soldered in those 100R from 6,3V AC down to voltage divider and centertap of pt is hidden away.
Also moved coupling caps little bit further away from sockets.
The groundlug is moved down directly to chassis without going thrugh a long bolt. It feels like a better connection atleast. Let's listen (for hum)
Also moved coupling caps little bit further away from sockets.
The groundlug is moved down directly to chassis without going thrugh a long bolt. It feels like a better connection atleast. Let's listen (for hum)
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I have now soldered in those 100R from 6,3V AC down to voltage divider and centertap of pt is hidden away. Also moved coupling caps little bit further away from sockets. Let's listen.
I checked my storage, I seem to have all components here to make a dc heater (Pete Millets design) Problem is space. Ok, let's see how it goes with AC first
You cannot easily get good DC out of a 6.3V AC winding and you would need quite large filter caps to do it. You really are walking into a heap more trouble even considering it.
Let me tell you, AC heaters correctly applied with a correct star ground will not make a hum at line level. I have made three very good preamps with some outrageously messy wiring which are whisper quiet. The only two times I have ever had serious hum issues were both attributable to an underspec's transformer spewing out stray magnet field and building into a two small case where it was impossible to get enough distance between the transformer and the signal circuit.
I presume all the twisted blue wires meeting in the middle over the caps are your star ground - how do the RCA's and the Pot attach to it. Minute deviations from a single star ground point can have big impacts on hum. I usually implement mine by having a single bolt through the case and all earths clamped to it using tabs. I generally have two of these, one for the power supply earths and one for the small signal. I then take a thin wire from the small signal to the power supply. Finally I take the power supply earth to the socket.
You may want to attempt to move the choke to see if it has any impact on the hum. I would expect one channel to be worse effected than the other if that were the case, can you confirm before doing anything.
Don't panic - persevere until you get it cracked.
Shoog
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If you look at the pic you see a red wire going down to ground on the ALPS. That red wire is connected to the black and that is soldered with earth/screen which goes back to rca sockets. Ground for cathode goes separately also with similar red wire down to star ground. I was thinking this is part of signal so i keep it apart from psu ground
OK thx Shoog.
Do you have any pic or diagram how you exactly did with star ground? I feel little bit unsure right now.
When you did get problem, was pt mounted like mine /with cover or inside like mine before?
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Don't like that, take the pot earth straight to the star ground with its own seperate wire. Similarly a seperate wire from the RCA to the star ground. Even if this doesn't solve the issue - it will not hurt. Remember that the source you attach the preamp to and the power amp may all be at different earth potentials. By sending the RCA earth through the screen of a signal wire you maybe generating a considerable current flow due to even a small difference in earth potential between your components. This will be injected straight into you signal wire by inductance.
I have successfully used discrete single core wires for all signal runs within amp bodies without issues of hum pick up - dirty earthed screens can be far more problematic.
Shoog
Go back to the centre tap - its doing the same thing with less components.
No picture without opening up a case. If it comes to it I will, but not yet.
Shoog
I gotta buy you a beer someday Shoog! 
After this small mod it is suddenly almost quiet! I can hear it slighty (no traffic outside now) when sitting down writing this about a 1m away. There is little noise but it can also be some little from my KT88 amp.
THE funny side of this is exact same concept as I used here is implented in my Yaqin poweramp so i guess after same mod there it's gonna be even more silence from my kt88 amp....
Now i'm thinking, do i dear to change back to CT (had little more tractor hum with that)
A idea: What about one separate cable from each cap to groundstar? (totally six)
After this small mod it is suddenly almost quiet! I can hear it slighty (no traffic outside now) when sitting down writing this about a 1m away. There is little noise but it can also be some little from my KT88 amp.
THE funny side of this is exact same concept as I used here is implented in my Yaqin poweramp so i guess after same mod there it's gonna be even more silence from my kt88 amp....
Now i'm thinking, do i dear to change back to CT (had little more tractor hum with that)
A idea: What about one separate cable from each cap to groundstar? (totally six)
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