Capacitor tolerance - 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 24th May 2009, 04:50 AM   #1
diyAudio Member
 
Join Date: May 2009
Default Capacitor tolerance

I'm working on the steve bench phono pre circuit and am trying to figure out sourcing for the riaa network caps. The values to go for according to salas are 6500pf (1800||4700) and 11400 pf (1000||2200||8200). What I'm wondering is, how tight do the tolerances need to be for these. I found them on mouser.com in silver mica 1% (except the 8200pf which is non-stocked - 2% is in stock). However, it would be over 50 bucks just for those caps, so I'm wondering if I can go wider on the tolerance and/or find a better deal elsewhere.

Ben
  Reply With Quote
Old 24th May 2009, 05:38 AM   #2
diyAudio Member
 
Join Date: Apr 2006
Location: Minnesota
I'm not an expert on this, but I think it is OK to go with +/- 20% parts. They should be a lot less expensive.
  Reply With Quote
Old 24th May 2009, 07:55 AM   #3
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
For RIAA you need the closest tolerance parts you can get. RIAA is incredibly sensitive to errors because you are trying to cancel out one steep curve with another to get a flat response. 2% tolerance is not good enough. Try looking for polystyrene instead of silvered mica.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 24th May 2009, 08:50 AM   #4
diyAudio Member
 
Join Date: Jan 2004
Location: Toronto, ON, Canada
Might be cheaper to invest in a good LC/LCR meter and get a bunch of high-tolerance caps.
  Reply With Quote
Old 24th May 2009, 11:03 AM   #5
diyAudio Member
 
Geek's Avatar
 
Join Date: Sep 2004
IMO, 2% is just fine.

I have measured tubes drifting spec. over their lifetime more than that, making any cap tighter than 2%, moot.

Now a SS RIAA, yeah, go with 0.5% or whatever you can afford.

Cheers!
  Reply With Quote
Old 24th May 2009, 02:50 PM   #6
diyAudio Member
 
Join Date: May 2009
Quote:
Originally posted by Geek
IMO, 2% is just fine.

I have measured tubes drifting spec. over their lifetime more than that, making any cap tighter than 2%, moot.

Now a SS RIAA, yeah, go with 0.5% or whatever you can afford.

Cheers!
Right, if I didn't need 500V caps this would be a whole lot easier.
  Reply With Quote
Old 24th May 2009, 03:53 PM   #7
diyAudio Member
 
Join Date: May 2009
Quote:
Originally posted by EC8010
For RIAA you need the closest tolerance parts you can get. RIAA is incredibly sensitive to errors because you are trying to cancel out one steep curve with another to get a flat response. 2% tolerance is not good enough. Try looking for polystyrene instead of silvered mica.

Where do you suggest looking for these? Searching mouser, allied, and digikey failed to yield anything in 1% tolerance at the voltage spec I need.
  Reply With Quote
Old 24th May 2009, 04:11 PM   #8
diyAudio Member
 
Join Date: Sep 2002
Location: VA
As someone else mentioned get a LC/LCR meter and hand pick your own. I feel its as if not more important for the caps and resistors in each channel to match each other so you don't notice a difference in tonal balance between channels. ie; if one cap is at one end of its 10% tolerance in one channel and the same cap in the other channel is at the other end of its 10% tolerance you will likely hear it..

Dave
  Reply With Quote
Old 24th May 2009, 05:43 PM   #9
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
There's two schools of thought on RIAA accuracy. One is, "make each channel be as tight to RIAA as possible." The latter is, "absolutel conformance is nice but channel-to-channel matching is most important." My own views tilt toward the latter. I want each side matched to better than 0.1dB.

You can use an LCR meter, but a better way (considering tube and stray tolerances) is an inverse network (same network used in both channels' measurements) fed from a very flat generator or flat input and accurate AC voltmeter measurement of the output. Undersize the caps a bit, then trim to spec with smaller caps.
__________________
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 24th May 2009, 07:57 PM   #10
diyAudio Member
 
Geek's Avatar
 
Join Date: Sep 2004
Hi,

Quote:
Originally posted by boxerboxer
Right, if I didn't need 500V caps this would be a whole lot easier.
A trick for that is have a larger value DC blocking capacitor (0.1uF to 0.47uF @ 630V is easier to find than RIAA valued ones) in series with your accurate cap. 50V is fine for the accurate cap because there's no way any AC value in an RIAA stage will (or should) exceed the RMS rating.

Cheers!
  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


Similar Threads
Thread Thread Starter Forum Replies Last Post
RN65C / E 10KB - what tolerance ? Bernhard Parts 1 21st April 2007 09:10 PM
WTB: 2x 3mh 20AWG inductors, 20% tolerance owdi Swap Meet 2 28th July 2005 05:50 AM
900% Vas tolerance? Otter Subwoofers 1 10th May 2005 12:16 AM
0.01% tolerance 10 and 100 ohm resistors SkinnyBoy Swap Meet 2 26th November 2003 10:38 AM
1% tolerance resistor spreadsheet MRehorst Parts 1 16th December 2002 03:38 PM


New To Site? Need Help?

All times are GMT. The time now is 02:52 PM.


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