Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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

Can I replace the 1M volume pot with a 100K one in my HK A300?
Can I replace the 1M volume pot with a 100K one in my HK A300?
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
Thread Tools Search this Thread
Old 18th March 2007, 02:01 PM   #1
Bing Yang is offline Bing Yang  United States
diyAudio Member
Join Date: Dec 2003
Location: Houston
Default Can I replace the 1M volume pot with a 100K one in my HK A300?

I have a HK A300. The circuit is very traditional. I modified it to bypass tone control and balance. Since the old 1M volume pot was not well balanced after cleaning, I replaced it with a 100K cheap volume pot. It worked for a while but shorted out one day. The volume was loud even at the lowest dial.

This volume pot is between the selector switch and the 12AX7 input amplifier. I did add a 500K grid resistor to the ground and hoping that it will compensate the smaller value pot. I also listened only CDs.

After I learned more and obtained a record player, I rebuilt the phono stage. The phono section was a very simple two stage 12AX7 with feedback. Then I found out that I need a 1M pot to match the impedance. So I put the pot back and suffer the balance problem.

My questions are:

1. Can I replace the pot with 100K if I only listen to CD? Could it be possible that my cheap pot was destroyed because a 100K pot cannot be used in front of a 12AX7? I do have a blue 100K ALPS pot that is quite expensive. I would prefer to use it instead of buying a new 1M pot. They are difficult to find.

2. If the first answer is yes, can I add a MOSFET follower right after my phono preamp 12AX7 output and before the output capacitor? This should lower the output impedance so that I can use the 100K pot. Is it true?

3. Since the phono section gain is low, I can also use the empty tube space for tone control to add a one tube gain stage with low plate resistor value. This will give more gain and lower output impedance. I think a simple 12AU7 should do the job. Any suggestions?
Bing Yang
  Reply With Quote


Can I replace the 1M volume pot with a 100K one in my HK A300?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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Alps Blue Velvet 100k volume pot For Sale nikolas812 Swap Meet 1 5th June 2009 11:56 PM
FS - Toroidal trafo (25V/300VA) and Noble volume pot (100K) - UK mubeen1983 Swap Meet 6 25th October 2008 10:16 AM
Adjustable power supply to replace volume control Leolabs Solid State 8 11th July 2007 05:43 PM
lm3875 inverted layout with 100k pot, not enough volume? rocktboy Chip Amps 11 12th January 2006 06:44 PM
WTB: Alps Blue Velvet mono 100K volume pot Derrick Swap Meet 0 16th October 2003 11:41 PM

New To Site? Need Help?

All times are GMT. The time now is 07:17 AM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 16.67%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio