A Heretical Unity Gain Line Stage part II - Page 3 - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 19th June 2005, 06:28 AM   #21
Variac is offline Variac  United States
diyAudio Editor
 
Variac's Avatar
 
Join Date: Dec 2001
Location: San Francisco, USA
Shoes for the Dead!
  Reply With Quote
Old 19th June 2005, 11:58 AM   #22
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Hi, I'm Joe Beats....
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 19th June 2005, 05:44 PM   #23
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
I have observed the same effect with IEC power filters that Andy describes, and have heard this tale of woe from a lot of fellow DIYers as well. I have not investigated this issue in detail, so much to do - so little time.. LOL My only surmise is that the linearity of the inductors and caps in those filters are suspect at audio frequencies and perhaps in addition they raise the source impedance of the ac supply. I have built filters using hand wound common mode and diff mode chokes and good film caps and heard some significant benefit in a few cases.

Good project Sy!

Kevin
  Reply With Quote
Old 21st June 2005, 08:35 PM   #24
diyAudio Member
 
Join Date: Sep 2002
Location: VA
What chance does a deceased veteran have of getting that high paying job and that free mule hes been dreaming of. Think about it, then take off your shoes..
  Reply With Quote
Old 21st June 2005, 08:58 PM   #25
diyAudio Member
 
Join Date: Aug 2002
Location: sylmar, CA. USA
Default Extra resistor

The 1M from wiper to ground on the input volume pot is not needed.

Best
Robert Morin
  Reply With Quote
Old 21st June 2005, 09:06 PM   #26
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
As I mentioned earlier, it's there for reliability- I've had too many pots go funny in the wiper, and the resistor there keeps the pops and bangs away in event of that failure. But indeed, it's optional. At about $0.02, it's a cheap measure.

Dave: I saw them live about 10 years ago. Everyone in the audience was my age, +/- two years. As are you, apparently.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 23rd June 2005, 09:14 PM   #27
diyAudio Member
 
Join Date: Sep 2004
Location: Oregon
Hi RDF,
Sorry for the tardy reply been distracted by work. The difference I hear with no rfi filter compared to with rfi filter is the rfi filter seems to make everthing sound closed down. The highs aren't as clean and open sounding and the mids aren't as open. The bass with rfi filter doesn't seem to be as articulate.
Micro Henry size chokes in the high voltage supply really aren't large enough. You would need something very much larger to do a good job of filtering.

Andy
  Reply With Quote
Old 23rd June 2005, 09:59 PM   #28
rdf is offline rdf  Canada
diyAudio Member
 
rdf's Avatar
 
Join Date: Jun 2004
Location: big smoke
Thanks Andy. My experience with the uH coils somewhat echoes your experience, though I hear it as a suprisingly cleaner top end. To my ears the result is incredibly 'fast' for a tube amp over the speakers at hand (Jordan JX92s and 12" Tannoy Gold), albeit based on a sample of one so far.


Quote:
Originally posted by Andy Bartha
You would need something very much larger to do a good job of filtering.

Depends on the target. The coils are sized to do nothing at frequencies lower than the self-resonance of the ASC oil power supply caps, but at frequencies above ~200 kHz in combination with RC bypass shunts simulations suggest a very large improvement in suppression of RF from the mains. That's a topic for a new thread though.
Many thanks again for your input.
  Reply With Quote
Old 30th October 2005, 10:45 PM   #29
DougL is offline DougL  United States
diyAudio Member
 
Join Date: Feb 2004
Location: Wheaton IL.
Blog Entries: 30
Quote:
I havenít diagrammed input switching since that will vary a bit from installation to installation. Use a good quality switch; I used a surplus Cinema Engineering 5 position two deck rotary switch with shorting between positions for optimal isolation. The input grounds are all tied together and kept completely separate from the preamp ground
What would be the disadvantage of using a 4-pole switch and source switching both signal and ground?
My intuition says that if there are ground issues between sources, its best to not tie them together.
By the way, every time my intuition is wrong, I learn something.

This is a great pre-amp series and I am studying it and taking notes.

Doug
  Reply With Quote
Old 30th October 2005, 11:07 PM   #30
rdf is offline rdf  Canada
diyAudio Member
 
rdf's Avatar
 
Join Date: Jun 2004
Location: big smoke
For the last 15 years I've used a passive control/volume unit based on a 4 pole Greyhill. It switches grounds and only the selected source and pre chassis are connected to the amp while in use. It's a make before break with audio sources wired every second position. In between sources the hot side has 100 ohm resistors wired to the ground terminals, themselves always referenced to the RCA outs. The net effect is sources are momentraily loaded with 100 ohms during switching, in normal use the resistors short any switch capacitance to ground to very high frequency.

I have never heard even a hint of inter-source crosstalk in any system it's been used. The amp I'm using now has a great deal of gain and would expose any issues. The couple of times I measured it with an Audio Precision test set the interchannel crosstalk exceeded 120 dB, at a level where shifting internal wires had an effect.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 05:08 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2