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Dirty-South Blues Harp forum: wail on! > Effect of Bias Settings on Harmonica Tone?
Effect of Bias Settings on Harmonica Tone?
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463 posts
Oct 19, 2022
10:18 AM
My friend installed a bias adjustment kit in my '95 Fender Blues Deluxe. I want to play with the bias settings, now that I can. I can adjust the setting to be higher or lower.

Here is my question:
What is the effect of various bias settings on the tone of your harmonica as it is played through an amp? I'm looking for reports from people who have experimented with different bias settings.

(I know I could simply experiment with different settings on my Blues Deluxe and listen to the results. I will, one day).

In the meantime, though, I'd like to hear the experiences of harp players who have tinkered with bias settings and noted differences in amplified harp tone those changes have produced.

So it's clear:
I'm not looking for theory. I'm not looking for opinions. I'm not looking for advice that "too high a setting will shorten tube life".

I'm looking for real life experiences from those who have played with bias settings and noted a definite change in their amplified harp tone as a result of changes in the settings.

Your homework:
What were those changes to your harp tone? Describe them as best you can.


wolf kristiansen
7078 posts
Oct 19, 2022
4:19 PM
It’s been a while but as I recall, I adjusted my Hot rod Deville bias pretty cold and it was a different kind of break up. I think it broke up earlier, as in at a lower volume, wasn’t quite as feedback prone but also was not so loud. The bass seemed to break up earlier. This was ok, but in a band setting I think it was ‘muddy’. I noticed on recordings that the harp sound was always this kind of same thing.
Eventually I started to run the bias hotter, and I think it made for a tighter sound. I could still get plenty of break up but I could get a tighter, cleaner sound.
That’s just how I remember what I was thinking about it.
464 posts
Oct 30, 2022
2:17 PM
Thank you, SuperBee, for your response. I've been running my Blues Deluxe bias pretty hot. Based on your experience, I think I'll stay with that. I like the sound well enough.

If I ever get ambitious enough to play with the bias settings, and give extended listening to the sound with each setting, I shall report the result.


wolf kristiansen
413 posts
Apr 25, 2023
1:44 PM
Some brands of tubes like it hot and some sound good cold. JJ sound best and smooth at 70% diddipation. Sovtek 5881WXT sound quite good when you run them very very cold. 10 years ago i modified some bassmans after Mark Burness ideas and make some very brutal amps with huge bass and even louder than HarpKing amps. One of the thing we modified was the adjustable fixed bias pot. Some people prefered about 10-15 mA to get more bass, more crunch more volume and less feedback.
I get tired of that sound & too loud amps. Nowadays i build amps with cathode bias.

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