|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
75.82.52.72
In Reply to: RE: What should I do with it? posted by wheezer on August 20, 2012 at 12:00:28
I don't use any shielded wire inside my chassis.What is '23.5 chassis wire'?
Is that shielded?
"I also have some of their TWPR shielded cable to use from the Vpots > grids. "
What value is your volume control? How long is the cable? What tube?
Thanks
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 08/20/12Follow Ups:
I don't use any shielded wire inside my chassis.
...Not even for the phono?
What is '23.5 chassis wire'?
...Cardas Chassis wire. Litz and teflon jacketed. They do something else to the litz, can't recall.
Is that shielded?
The chassis wire isn't, but all the wire is so indicated as chassis or shielded when paired. Percy has a good selection.
The copper strands are enameled so it needs to be tinned first.
"I also have some of their TWPR shielded cable to use from the Vpots > grids. "
What value is your volume control? How long is the cable? What tube?
50K Vpot about a foot > 7308 AMP. PQ's
There's no AC in the preamp chassis except for the music and the on board MC set up transformers are run balanced (balanced tonearm cables also) so CMR is high.
The unshielded TWPR input wires of the set up transformers run straight to the panel jacks. The unshielded TWPR output wires run straight to the tube socket.
The reason I asked about the volume control and first stage tube has to do with Miller+cable capacitance vs. source impedance and the low pass filter that it creates.
With a 50k pot the worst case output impedance is 12.5k. With the 50pf of the 7308 you don't want to add much cable capacitance but with only one 1 foot it's probably not a problem.
Do you know the capacitance of the cable?
I've seen 250k pots with shielded cable and that's a recipe for HF roll off.
With unshielded cable I can't understand why the noise floor would change with a wire change.
With shielded cable, the cable with the most capacitance might be killing high frequency noise.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Tre' hi,
The pre doesn't have a step-up, so it's MM - for now.:-)
The pre has a PCB. w/a reg'd FET B+.
Linestage - plates in parallel and each (L,R)now, has it's own CCS. So output Z was around 1K6 stock.
The Phono - each (L,R tube) section has it's CCS.
There's only two wires (both shielded) that I've tried to replace. Both with unshielded wire first of course.
The Vpots> grid and one input from the back RCA> front selector.
RF has always been and issue.
When discussing this with the folks at Cardas, they suggested trying their "chassis" wire first, before going the shielded route.
As for the capacitance of the phono IC, I don't know, nor the stock or Cardas wire. This should be easily obtainable from Cardas.
I'd get the same RF shout with high output source components as well.
It could be the surrounds and not what's in-between the four walls of the chassis?
Your thoughts are most helpful. Bringing back the cobwebs of RF issues I've not visited in a good 10yrs.
Cheers,
Wheeze
It would be good to track down the source of the RF and maybe stop it at the source.
I'm a little embarrassed to say I missed that it is RF you are having a problem with.
I need to learn to read. :-)
Sorry.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
No problem.
Any of your experience would be appreciated.
Chasing RF can = chasing one's tail.
Probably why I gave up way back when....
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: