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 3rd July 2007, 12:34 AM   #1
nhuwar is offline nhuwar  United States
diyAudio Member
 
nhuwar's Avatar
 
Join Date: Jan 2007
Location: Cypress Texas
Default Input impedance

I'm curious what's a normal line level input z for the average tube amp? I was thinking around 15k is this a good number or to low?

Thanks

Nick
  Reply With Quote
Old 3rd July 2007, 01:04 AM   #2
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Hi Nick,
Depends on what you want to use to drive it, 15K is a pretty tough load for most tube pre's excluding transformer coupled designs. Fine with solid state. I typically use 70K - 100K on power amplifier inputs, and 100K on pre-amplifier inputs. (Essentially the dc resistance of my stepped attenuators.)

Higher impedance inputs reduce the need for very large output coupling capacitors in the preceding component, both a cost and performance benefit.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 3rd July 2007, 01:08 AM   #3
mcs is offline mcs  Denmark
diyAudio Member
 
Join Date: Aug 2003
Location: Denmark
I would go with 50-100k. Old amps often had very high input impedances (250k to 1M), but with modern source equipment and preamps there's no reason to go that high.

Best regards,

Mikkel C. Simonsen
__________________
My personal electronics website
Remote control kits website
  Reply With Quote
Old 3rd July 2007, 11:14 AM   #4
nhuwar is offline nhuwar  United States
diyAudio Member
 
nhuwar's Avatar
 
Join Date: Jan 2007
Location: Cypress Texas
It is a transformer and I think it's 15k resistance not z now that I really look at it.

Nick
  Reply With Quote
Old 20th July 2007, 09:41 PM   #5
diyAudio Member
 
Join Date: Mar 2003
Location: florida
Assuming the input stage is class A, the grid resistor determines the input.
  Reply With Quote
Old 20th July 2007, 09:56 PM   #6
nhuwar is offline nhuwar  United States
diyAudio Member
 
nhuwar's Avatar
 
Join Date: Jan 2007
Location: Cypress Texas
Nope not class a it's a driver stage in push pull. But I dont think I am going to use a transformer on the input.

Just for clarification doesn't the interstage transformer act as a phase shifter?

Nick
  Reply With Quote
Old 20th July 2007, 11:07 PM   #7
diyAudio Member
 
Join Date: Mar 2003
Location: florida
Yes many amps use transformers for phase inverters.

I think you would be better off with a cathode follower driver. The transformer would degrade the low frequency performance.
  Reply With Quote
Old 20th July 2007, 11:25 PM   #8
nhuwar is offline nhuwar  United States
diyAudio Member
 
nhuwar's Avatar
 
Join Date: Jan 2007
Location: Cypress Texas
Oh I didn't know that. I was under the impression that transformers only effected the high frequency response.

Nick
  Reply With Quote
Old 21st July 2007, 12:02 AM   #9
jnb is offline jnb  Australia
diyAudio Member
 
Join Date: Dec 2006
If the impedance of a winding is too low, it attenuates the lows. This is because it forms a voltage divider with the source impedance, and as the winding is an inductance its impedance falls with frequency.
  Reply With Quote
Old 21st July 2007, 12:40 AM   #10
nhuwar is offline nhuwar  United States
diyAudio Member
 
nhuwar's Avatar
 
Join Date: Jan 2007
Location: Cypress Texas
So if the inductance of the primaray is to low I will get roll off.

Is this dependent on the inductance in relation to the driver tube anode impedence or just the inductance in relation to frequency?

Nick
  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
Input Impedance Bengali Analog Line Level 7 15th August 2007 10:24 PM
How much input impedance is enough? Russ White Chip Amps 5 13th April 2005 07:25 PM
ZV7 Input Impedance. gl Pass Labs 0 15th February 2005 10:54 PM
input impedance bbksv Chip Amps 2 13th February 2004 11:58 PM
JLH input impedance hlyytine Solid State 12 1st February 2004 07:00 PM


New To Site? Need Help?

All times are GMT. The time now is 02:10 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