Tonestack help

[ODR]

Hi. I was wondering if anyone here could tell me what would be the "Tonestack" in this Fender Pro Junior setup. I need to tweak the treble/bass a bit.

[überfuzz]

Hi, and welcome!

You got a tone pot on that amp right? I think its' a simple highpass/lowpass pot. Are you familiar with highpass and low-pass filters? The so called cut-off frequency can be manipulated by altering the components according to f = 1/(2*pi*R*C).

[ODR]

Tonestack help

Hi, and welcome!

You got a tone pot on that amp right? I think its' a simple highpass/lowpass pot. Are you familiar with highpass and low-pass filters? The so called cut-off frequency can be manipulated by altering the components according to f = 1/(2*pi*R*C).

Thank you, if you could point out the parts that can be altered like resistor Cap values up or down to increase or decrease bass / treble?

[pdf64]

That image is too poor a resolution to be any use; and a schematic would be better.
Is it a pro jnr III http://support.fender.com/schematics...atic_Rev-F.pdf ?

[ODR]

Tonestack help

That image is too poor a resolution to be any use; and a schematic would be better.
Is it a pro jnr III http://support.fender.com/schematics...atic_Rev-F.pdf ?

Not, it's a tagboard build by Jellyfish Audio after a drawing on another website. It's not a Fender Pro Junior as Fender sells them.

Maybe this can help?

https://www.facebook.com/photo.php?f...type=3&theater

[pdf64]

I think that some technical detail regarding your amp's design may be required to make progress with this.
Unfortunately I can't see any at the linked facebook page.

[Chuck H]

Hi, and welcome!

You got a tone pot on that amp right? I think its' a simple highpass/lowpass pot. Are you familiar with highpass and low-pass filters? The so called cut-off frequency can be manipulated by altering the components according to f = 1/(2*pi*R*C).

Someone chose to be snarky!

[eschertron]

comparing the hand-drawn layout with the schematic, it looks as though C3 and C4 are still the tone caps (wired directly to the legs of the tone pot). To change the behavior of the tone pot, then change the values of the caps.

C4 goes to ground and should be the smaller of the two caps. this is the caps that bleeds treble off to ground (just like a guitar's tone control). Remember that the larger the value of the cap, the "more" frequencies will pass; for this cap, then, a bigger value will allow more treble (and ranging downward into the freq spectrum, per Mr Fuzz's equation) to be 'grounded out', lost from the signal. So it is the cap that controls how 'bassy' the signal appears when the tone is turned all the way to that side.
C3 goes around the volume pot, and acts as a bypass; sometimes called a treble bleed when found in a guitar. Here the larger the cap value, the more will be allowed to bypass the volume control and pass into the signal. It controls how 'treble-y' the signal will appear when the tone pot is turned all the way in that direction. Be advised that it has no effect when the volume is all the way up, just like on a guitar. You can play with those cap values, using values that are bigger or smaller by a factor of 2X will change the range of effect by 1 octave in the audio spectrum.

[Chuck H]

ODR, how do you wish to tweak the tone and how do you use the amp (cranked? clean?) What isn't it doing for you and when? Pointing you to the right components will require knowing what you want to achieve.

[überfuzz]

Someone chose to be snarky!

Naa... not really intended. Given that this was the first post from ODR I actually thought my comment would reveal, lets call it, the level of entry.

ODR - In your own words, how does the amplifier sound untempered? Given that you have a PRO JUNIOR circuit you need to find the capacitors connected to the tone pot (See the linked schematics and compare to your amp). These are the most apparent targets for a tweek on the tone control. However, it may be the case that the voice of you're amp can be altered to your liking with some other tinkering...

[ODR]

ODR, how do you wish to tweak the tone and how do you use the amp (cranked? clean?) What isn't it doing for you and when? Pointing you to the right components will require knowing what you want to achieve.

I have two Pro Juniors and I am trying to change different values to actually hear the differenc, if any. I have done this also to a Marshall Clone Plexi to great resilt. I find that the upper freq in the junior to be still a bit to much, allthough not at all like Fender. So I was interested in what values that influenced the sound of the amp the most.

[Chuck H]

I have two Pro Juniors and I am trying to change different values to actually hear the differenc, if any. I have done this also to a Marshall Clone Plexi to great resilt. I find that the upper freq in the junior to be still a bit to much, allthough not at all like Fender. So I was interested in what values that influenced the sound of the amp the most.

Wow.!.

Ok... Uber gets to jump my S for this (though I'm not trying to be snarky), but...

What you just said is about equal to "What makes a car go". And it also seems that you've been happy just changing things to see what happens and settling when it seems better to you with no idea what you did.

There are multiple gain stages in the amp. Each one and it's circuits have an influence on the sound. If the amp is flabby when overdriven, harsh when clean or buzzy in general, etc. What's wrong and under what circumstances it is wrong is paramount to isolating a solution. Simply affecting change or experimenting without a very clear direction won't usually get a positive result. There WILL be a result, but I don't generally place my food order at a restaurant by asking for "food". If you get my meaning.

The tone control is an adjustment and not exclusive to the response of the amp. If the amp is too bright you can turn it down. If the amp is too bright with the tone knob all the way down that would be unusual. Or perhaps you just don't like the sound with the tone knob down but the amp is too bright with the tone knob up? This is a different thing and has more to do with the frequency response of each gain stage rather than "amp is too bright". It's called a tone control but it's not the only thing shaping the tone of the amp. No more than a gas pedal makes a car go because it controls the speed. Would you expect extending the range of a gas pedal to be an effective means of hot rodding a car to go faster? Of course not.

If you just want to F with the amp and have fun seeing what happens, like an Easter egg hunt, go ahead. But there's no clear direction of help I can offer with that. If you're having a problem with the sound of the amp and can explain what you don't like in some detail we can probably tell you what to try and why.

[pdf64]

Consider disconnecting the presence boost capacitor, the left hand 0.1uF cap on the board photo.

[ODR]

Wow.!.

Ok... Uber gets to jump my S for this (though I'm not trying to be snarky), but...

What you just said is about equal to "What makes a car go". And it also seems that you've been happy just changing things to see what happens and settling when it seems better to you with no idea what you did.

There are multiple gain stages in the amp. Each one and it's circuits have an influence on the sound. If the amp is flabby when overdriven, harsh when clean or buzzy in general, etc. What's wrong and under what circumstances it is wrong is paramount to isolating a solution. Simply affecting change or experimenting without a very clear direction won't usually get a positive result. There WILL be a result, but I don't generally place my food order at a restaurant by asking for "food". If you get my meaning.

The tone control is an adjustment and not exclusive to the response of the amp. If the amp is too bright you can turn it down. If the amp is too bright with the tone knob all the way down that would be unusual. Or perhaps you just don't like the sound with the tone knob down but the amp is too bright with the tone knob up? This is a different thing and has more to do with the frequency response of each gain stage rather than "amp is too bright". It's called a tone control but it's not the only thing shaping the tone of the amp. No more than a gas pedal makes a car go because it controls the speed. Would you expect extending the range of a gas pedal to be an effective means of hot rodding a car to go faster? Of course not.

If you just want to F with the amp and have fun seeing what happens, like an Easter egg hunt, go ahead. But there's no clear direction of help I can offer with that. If you're having a problem with the sound of the amp and can explain what you don't like in some detail we can probably tell you what to try and why.

I see what you mean, but I am looking for a specific tone in the amp. I did this to my tagboard Marshall clone, in that amp there different parts with different values that clearly change the sound. I have two Juniors, and I did a Fromel mod to them as a starter. One of them I changed to turretboard. Then I bought lots of old / new caps and resistors to see / hear if there was any change in the overall tone. I heard f ex a rather big difference changing the the two 10 uf caps to Blag Gate ones, rounded of the overall audible. I changed some of the other caps to Orange drops, also better tone, but lesser audibility. I now have two Ajax Blues in there and som old Astrons and Bradelys. I also changed to Billm's output trafo, changed the cabinets and lots of speakers 10 inch and 12 inch.
This is basically a hobby, but I rarely get the chance to experience what differences actually makes a change in the sound. So no perticular plan, but to look for changes that gets closer to the sound I am looking for.

[Chuck H]

Most of the MO you're describing doesn't exactly fit with what I know most members of this forum to be about. That's about as civil as I can put it. I'm sure you'll learn something about what changes make differences, what those changes are actually doing to the circuits and what those circuits are doing in your own time. Until then...

You can change almost any value in the DC isolated signal chain of the amp without blowing anything up. Other things that will change the sound, gain of a tube stage include preamp cathode bypass capacitors. You can change the value of these, add them if their not there or remove them completely. A good starting point for the Easter egg hunt version of modding is to at least learn about what constitutes the DC isolated signal chain and what constitutes the power supplies. It may also help you to learn at least a little about some common tube gain stages used in guitar amps rather than just passively shaping the AC in between them. This can open up new possibilities to actually make the tubes clip more symmetrically or less so. And if less symmetrical on which end (cutoff or saturation) the clipping occurs. You seem to be at the stage where it's time to get a couple of books on the subject. There are many that are recommended. Most are pretty good.