Reducing gain of a WE91 type amp - 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 22nd April 2013, 12:42 PM   #1
rtsang is offline rtsang  Hong Kong
diyAudio Member
 
Join Date: Aug 2005
Default Reducing gain of a WE91 type amp

Just want to ask what is the best way to reduce gain of a 300B amp with a pentode driver followed by a cathode follower to drive the 300B. Way too much gain for my volume control in the preamp to manage. I am already using a passive transformer volume control.

I had thought of several options, want to see the pros and cons of each.

1. Add a potential divider in front of the input.
Not sure if there is any down side to this.

2. Remove the cathode bypass cap of the pentode.
This may increase the output impedance of the driver, though this should be buffered by the cathode follower.

3. Reduce the anode load of the pentode.
This may decrease the voltage swing of the driver.

4. Add feedback.
Probably not my cup of tea.


Thanks in advance.

Ray
  Reply With Quote
Old 22nd April 2013, 03:39 PM   #2
diyAudio Member
 
Palustris's Avatar
 
Join Date: Aug 2006
Location: Cape Cod
Remove the preamp and mount the transformer volume control at the input of the amplifier. The preamp simply adds noise and distortion and is unnecessary.
  Reply With Quote
Old 23rd April 2013, 12:34 PM   #3
rtsang is offline rtsang  Hong Kong
diyAudio Member
 
Join Date: Aug 2005
The preamp is a passive preamp with a selector and a transformer volume control. Unfortunately there is not enough space in the amp to add a few RCA sockets, a selector and put the transformer volume control in it to convert it to a integrated amp.

I had kept the interconnects short so not much noise should be added by this passive preamp.
  Reply With Quote
Old 23rd April 2013, 06:50 PM   #4
diyAudio Member
 
Palustris's Avatar
 
Join Date: Aug 2006
Location: Cape Cod
Well, if you have a passive preamp, then there may be a problem with your transformer volume control. What is the input sensitivity of the amplifier and what is the slope of the volume control, e.g. is it an audio taper or linear taper? It sounds as if your volume control doesn't give you enough control at the lowest settings. A voltage divider at the input will serve to reduce the input voltage, but that seems like a bandaid repair rather than an engineering fix.
  Reply With Quote
Old 23rd April 2013, 09:09 PM   #5
chip647 is offline chip647  United States
diyAudio Member
 
chip647's Avatar
 
Join Date: May 2011
Location: The South
Default "Pentode Driver"

Well, there is your gain problem. Your pentode has too much gain. Try a lower gain pentode or, gasp, a triode. The buffer means that the tube is not driving any load of significance so a triode will not be harmed.

Your amp likely has full power with 0.1 volt input. You never want to throw away more signal than you have to. This is a system mismatch problem.
  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
F4 Type amp but with gain fab Pass Labs 13 7th August 2009 09:00 PM
reducing system gain slr 5000 Solid State 28 30th August 2008 10:05 AM
Reducing preamp/amp voltage gain? Stubb Solid State 1 1st November 2004 08:35 PM
Reducing the gain with an inverting gainclone Bricolo Chip Amps 10 1st December 2003 04:58 PM
Reducing gain on Bride of Zen? Yochim Pass Labs 12 13th September 2002 02:18 PM


New To Site? Need Help?

All times are GMT. The time now is 02:17 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