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Post subject: How to set a Passive EQ ?
Posted: Thu May 02, 2013 1:55 pm
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Hello,

I know that most Fender amplifiers have passive EQs - at least mine, Hot Rod and Bassman.
That means that "flat EQ" sound is obtained by setting all EQs to 12 (max).

That leads me to a question:

What is the intended way to adjust EQ settings :
- set everything on 12 (flat) and then cut what's too much
- OR set everything on the middle position and "boost" what's missing and cut what's too much, as most people do?

Does the amp sound best with all EQs on 6.5 or on 12 ? is it the same (that would be surprising)?

Any engineers here maybe?

Many thanks!


Last edited by theredled on Thu May 02, 2013 3:10 pm, edited 1 time in total.

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Post subject: Re: How to set a Passive EQ ?
Posted: Thu May 02, 2013 2:22 pm
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theredled wrote:
Hello,

I know that most Fender amplifiers have passive EQs - at least mine, Hot Rod and Bassman.
That means that "flat" sound is obtained by setting all EQs to 12 (max).


Wrong.

Here is the frequency response of the original 1959 5F6A Bassman:

Image

The green trace is B/M/T all set to 6.5.

The yellow trace is B/M/T set to 12.

The red trace is B/M/T set to 0.

The blue trace is B set to 0, M set to 12, and T set to 0.

theredled wrote:
That leads me to a question:

What is the intended way to adjust EQ settings :
- set everything on 12 (flat) and then cut what's too much
- OR set everything on the middle position and "boost" what's missing and cut what's too much, as most people do?

Does the amp sound best with all EQs on 6.5 or on 12 ? is it the same (that would be surprising)?

Any engineers here maybe?

Many thanks!


There is no "intended" way to set the tone controls. You can use any method you like to get the sound you want. I start with all controls at 6 and adjust from there. Buddy Guy sets his Presence, Treble, and Middle controls to 12 and Bass to 0. he also uses the Bright channel. :shock:

Here are some You Tube examples of other settings:













Yes, I am an engineer (BSEE by degree, Systems Engineer by profession).

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Post subject: Re: How to set a Passive EQ ?
Posted: Thu May 02, 2013 3:08 pm
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Thanks a lot for your detailed answer.
bluesky636 wrote:
Wrong.

Here is the frequency response of the original 1959 5F6A Bassman:

By "flat", I don't mean flat frequency response, I mean "what would the amp sound like if there were no EQ settings". Flat EQ, not flat frequency response.
Besides, your graphs seems too smooth to be real :mrgreen:

bluesky636 wrote:
There is no "intended" way to set the tone controls. You can use any method you like to get the sound you want. I start with all controls at 6 and adjust from there. Buddy Guy sets his Presence, Treble, and Middle controls to 12 and Bass to 0. he also uses the Bright channel. :shock:

I'm a musician and of course I know there's a lot of ways of setting an amplifier...
My question is about the process of setting the amplifier (as you understood at the beginning of your sentence, but the following videos don't show any process)

The thing is that I tend to believe that a control at 12 (= no EQ) gives a "cleaner", unaffected sound that one at -10 dB... Maybe it's negligible, or not...

bluesky636 wrote:
Yes, I am an engineer (BSEE by degree, Systems Engineer by profession).

I meant *Fender* engineers, sorry :mrgreen:
(anyway anyone can answer)


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Post subject: Re: How to set a Passive EQ ?
Posted: Thu May 02, 2013 5:36 pm
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theredled wrote:
Thanks a lot for your detailed answer.
bluesky636 wrote:
Wrong.

Here is the frequency response of the original 1959 5F6A Bassman:

By "flat", I don't mean flat frequency response, I mean "what would the amp sound like if there were no EQ settings". Flat EQ, not flat frequency response.
Besides, your graphs seems too smooth to be real :mrgreen:

bluesky636 wrote:
There is no "intended" way to set the tone controls. You can use any method you like to get the sound you want. I start with all controls at 6 and adjust from there. Buddy Guy sets his Presence, Treble, and Middle controls to 12 and Bass to 0. he also uses the Bright channel. :shock:

I'm a musician and of course I know there's a lot of ways of setting an amplifier...
My question is about the process of setting the amplifier (as you understood at the beginning of your sentence, but the following videos don't show any process)

The thing is that I tend to believe that a control at 12 (= no EQ) gives a "cleaner", unaffected sound that one at -10 dB... Maybe it's negligible, or not...

bluesky636 wrote:
Yes, I am an engineer (BSEE by degree, Systems Engineer by profession).

I meant *Fender* engineers, sorry :mrgreen:
(anyway anyone can answer)


Those graphs are an accurate depiction of the frequency response of the tone stack.

"12" does not equal "no EQ".

You clearly have no clue how the tone stack of a guitar amplifier operates, and I'm not going to waste any more time trying to explain it to you. Maybe someone else here will, but I would not hold my breath. :roll:

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Post subject: Re: How to set a Passive EQ ?
Posted: Fri May 03, 2013 5:15 am
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In a typical amp, such as most all Fenders, all volume, gain and tone pots and their associated capacitors and resistors, can only be "attenuators", there is no "boost" from a potentiometer and/or capacitor. You start with a signal from a guitar and any tone or volume pots that are encountered by the signal can only attenuate, or take away from the signal, they can not boost or add to the signal. Any gain in the signal is done by tubes/transistors, and the volume and tone controls can only limit, or cut any boost.

In other words, there isn't a pot made that can boost a signal, so yes, setting the tone/volume pots at full CW is a fully unattenuated signal. Capacitors are called "filters" because that's what they do, filter out or "pass" certain frequencies, they can not boost the signal either.

Note the graphs posted by bluesky636, none of the signal is above zero, so it clearly shows no boost, only cut or attenuation.

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Post subject: Re: How to set a Passive EQ ?
Posted: Fri May 03, 2013 5:48 am
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shimmilou wrote:
In a typical amp, such as most all Fenders, all volume, gain and tone pots and their associated capacitors and resistors, can only be "attenuators", there is no "boost" from a potentiometer and/or capacitor. You start with a signal from a guitar and any tone or volume pots that are encountered by the signal can only attenuate, or take away from the signal, they can not boost or add to the signal. Any gain in the signal is done by tubes/transistors, and the volume and tone controls can only limit, or cut any boost.

In other words, there isn't a pot made that can boost a signal, so yes, setting the tone/volume pots at full CW is a fully unattenuated signal. Capacitors are called "filters" because that's what they do, filter out or "pass" certain frequencies, they can not boost the signal either.

Note the graphs posted by bluesky636, none of the signal is above zero, so it clearly shows no boost, only cut or attenuation.


And none of them are "flat" or no eq either. The only way that will happen would be to remove the tone stack completely, although B=0, T=0, and M=12 is close it still shows a loss of 10 dB.

But then neither one of us is a "Fender" engineer, so we're probably not qualified to answer the OP's question. :roll:

Oh, and as far as the graphs looking "too smooth", the OP is welcome to read "Circuit Analysis of a Legendary Tube Amplifier: The Fender Bassman 5F6-A, Third Edition" by Richard Kuehnel. There the derivaton of these graphs is presented in great detail. Of course, the OP will have to understand a little bit of math. :lol:

Regarding the "process" used to set the tone controls, ever guitarist I have ever met has their own "process" and they are equally vaild as long as the desired result is achieved.

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Post subject: Re: How to set a Passive EQ ?
Posted: Fri May 03, 2013 6:06 am
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shimmilou wrote:
In a typical amp, such as most all Fenders, all volume, gain and tone pots and their associated capacitors and resistors, can only be "attenuators", there is no "boost" from a potentiometer and/or capacitor. You start with a signal from a guitar and any tone or volume pots that are encountered by the signal can only attenuate, or take away from the signal, they can not boost or add to the signal. Any gain in the signal is done by tubes/transistors, and the volume and tone controls can only limit, or cut any boost.

In other words, there isn't a pot made that can boost a signal, so yes, setting the tone/volume pots at full CW is a fully unattenuated signal. Capacitors are called "filters" because that's what they do, filter out or "pass" certain frequencies, they can not boost the signal either.

Note the graphs posted by bluesky636, none of the signal is above zero, so it clearly shows no boost, only cut or attenuation.

Very clear, thanks !
bluesky636 wrote:
And none of them are "flat" or no eq either. The only way that will happen would be to remove the tone stack completely, although B=0, T=0, and M=12 is close it still shows a loss of 10 dB.

But then neither one of us is a "Fender" engineer, so we're probably not qualified to answer the OP's question. :roll:

Oh, and as far as the graphs looking "too smooth", the OP is welcome to read "Circuit Analysis of a Legendary Tube Amplifier: The Fender Bassman 5F6-A, Third Edition" by Richard Kuehnel. There the derivaton of these graphs is presented in great detail. Of course, the OP will have to understand a little bit of math. :lol:

Regarding the "process" used to set the tone controls, ever guitarist I have ever met has their own "process" and they are equally vaild as long as the desired result is achieved.

No reason to get ironic. I'm sorry if you feel offended, I have few knowledge in electronics, and I admit my "too smooth" bit was stupid.

bluesky636 wrote:
And none of them are "flat" or no eq either. The only way that will happen would be to remove the tone stack completely, although B=0, T=0, and M=12 is close it still shows a loss of 10 dB.

Seems like you're not an engineer in understanding people: I've never meant "flat" as "flat frequency response".

Thanks again Shimmilou.


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Post subject: Re: How to set a Passive EQ ?
Posted: Fri May 03, 2013 6:15 am
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theredled wrote:
Seems like you're not an engineer in understanding people: I've never meant "flat" as "flat frequency response".


What part of the concept that setting all controls to 12 still results in EQ being applied to the amp do you not understand?

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Post subject: Re: How to set a Passive EQ ?
Posted: Fri May 03, 2013 9:04 am
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Yeah, the capacitors and resistors in the tone stack would still be there in the signal path, so there is some EQ action going on, even with the pots at full CW. Being as how the pots are only part of an RC network for the tone stack, and the only part that can be dialed out of the equation, it's still an equation nonetheless. You could jumper out the whole tone stack with a clip lead and check the sound then. Could be interesting, vely intelesting. :lol:

BTW, the only acceptable way to set the tone controls for any amp is the way that I do it, with scooped mids. :shock: :lol:

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Post subject: Re: How to set a Passive EQ ?
Posted: Fri May 03, 2013 10:42 am
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And to further muddle the picture, I'd say about 99% of all tone & volume pots are logarithmic (or audio taper). This is to compensate for how the human ear and brain "hears" things.

Very difficult to relate a linear desired result to a logarithmic funcion, without some calculus. Prolly beyond the scope (sorry for pun) of this topic. :D :lol:

BTW... I really love that tone stack calculator software. Nice when building or tweaking tone sections. :D


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Post subject: Re: How to set a Passive EQ ?
Posted: Fri May 03, 2013 12:11 pm
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I think this is a good question. I understand what the OP is asking, I think. I sometimes set my amps tone controls at zero and bring them up to the desired result, instead of setting everything at noon and adding or subtracting to get what I want. I don't know if that's the best way to go about the process or not. I would appreciate some CONSTRUCTIVE advice or opinions on the subject. My particular amps are a 68 Super, and a Reissue Twin. I find the Super is a real breeze to EQ, it's a challenge to get a bad tone from it. The Twin is a little more of a challenge. I find if I turn the bass up too high it almost stifles the low end if that makes sense. In other words, the bass control adds low end up to about 6 then it seems to offer less bass from 6-10. Does that make sense?

One more thing. I have only been on this forum for a few months and just about everyone on here is very helpful, considerate, and seems to like to help people who have questions. That's the thing about forums, people exchange information on them. I think that is the idea.
Bill aka Bluesky...I'm sure you are a nice guy but you sure do come across as a crotchety, mean bastard. You reply in every single thread in this forum, often just to throw jabs or insult people for asking questions. What's up with that man?


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Post subject: Re: How to set a Passive EQ ?
Posted: Fri May 03, 2013 12:25 pm
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thenedster wrote:
Bill aka Bluesky...I'm sure you are a nice guy but you sure do come across as a crotchety, mean bastard. You reply in every single thread in this forum, often just to throw jabs or insult people for asking questions. What's up with that man?


Really? You think my first response was insulting and a jab? Every single thread? Wow. Did you count them all and read through all 7000+ of them? I'm impressed.

On that note, so I don't insult any one else, I'm done with this thread. Have fun.

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Post subject: Re: How to set a Passive EQ ?
Posted: Fri May 03, 2013 5:37 pm
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thenedster, going back to Bluesky's original reply, use the Tone Stack Calculator to simulate the frequency response wrt tone stack of your particular amp. Then, you can see the result of each tone control position by sliding the pot values.

Unless you have a signal generator and a mike hooked to a scope, it'll be hard to find the resultant tone curve. The human ear does not hear in linear fashion. And is more sensitive to midrange to moderate highs, than bass. So amps need to be designed accordingly.

http://www.duncanamps.com/tsc/


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Post subject: Re: How to set a Passive EQ ?
Posted: Fri May 03, 2013 6:38 pm
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I like to take the "less is more" approach. Meaning, if I want more bass, I will cut the treble and maybe a little mids instead of adding more bass. It used to bother me if the controls weren't set as I thought they should be, but it doesn't matter if the knobs look "out of whack" as long as it sounds good. :idea:

I also usually add a jumper on the mid pot if necessary, so that when all three tone controls are set to zero, there is no sound from the amp.

Of course if you switch guitars, often a few tweaks to the tone controls might be needed.

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Post subject: Re: How to set a Passive EQ ? He
Posted: Sat Sep 16, 2017 8:50 pm
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bluesky636 wrote:
theredled wrote:
Hello,

I know that most Fender amplifiers have passive EQs - at least mine, Hot Rod and Bassman.
That means that "flat" sound is obtained by setting all EQs to 12 (max).


Wrong.

Here is the frequency response of the original 1959 5F6A Bassman:

Image

The green trace is B/M/T all set to 6.5.

The yellow trace is B/M/T set to 12.

The red trace is B/M/T set to 0.

The blue trace is B set to 0, M set to 12, and T set to 0.

theredled wrote:
That leads me to a question:

What is the intended way to adjust EQ settings :
- set everything on 12 (flat) and then cut what's too much
- OR set everything on the middle position and "boost" what's missing and cut what's too much, as most people do?

Does the amp sound best with all EQs on 6.5 or on 12 ? is it the same (that would be surprising)?

Any engineers here maybe?

Many thanks!


There is no "intended" way to set the tone controls. You can use any method you like to get the sound you want. I start with all controls at 6 and adjust from there. Buddy Guy sets his Presence, Treble, and Middle controls to 12 and Bass to 0. he also uses the Bright channel. :shock:

Here are some You Tube examples of other settings:













Yes, I am an engineer (BSEE by degree, Systems Engineer by profession).


Hello bluesy

Very interesting post. Don't you know where can I find the same graphic but for the hot rod Deville? Does the same principle apply for the hot rod Deville. I think is different to other fender amps since when you put all the eq pots to 0 still there is sound.


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