But a variable Lpad would bleed the excess power to ground, right? In my case, it is supoosed to instead go to the main (sub) speaker that will be connected in parallel to the two JC120 guitar speakers. So we are more talking about a passive balance pot between the guitar and sub speakers.
Adding something like a 4ohm resistor in series to the JC120 speakers would drastically alter the crossover/HPF point I assume, correct?
As would running the two guitar speakers in series vs. parallel?
An L-pad will consume more power than a single series resistor, sometimes that's not a problem. The L-pad has the benefit of being more consistent when you vary it to change the level of the speaker output. Another benefit is that it reduces the variations of impedance vs frequency.
A single resistor can be done. You may want to change the crossover along with it to keep it working as it should. However you should really adjust your crossover when using an L-pad as well.
The point is it's easier to work with the L-pad, and it's easier to vary the level with an L-pad when not wanting to make crossover adjustments, however there's nothing wrong with using just one resistor.
As far as your sub is concerned, it's more typical to leave the quietest driver alone and reduce the loud ones. Typically the higher frequency ones.
A single resistor can be done. You may want to change the crossover along with it to keep it working as it should. However you should really adjust your crossover when using an L-pad as well.
The point is it's easier to work with the L-pad, and it's easier to vary the level with an L-pad when not wanting to make crossover adjustments, however there's nothing wrong with using just one resistor.
As far as your sub is concerned, it's more typical to leave the quietest driver alone and reduce the loud ones. Typically the higher frequency ones.
Could this inductor at the speaker output potentially interefere with the high pass filter network?
Sorry for these noob questions but I am a bit surprised by the general 'dimensions'/scale of the required elements.
First of all, I didn't realize how huge and expensive the required inductors would be. From my calculations I would need ~30mH per speaker. The largest inductors I can find here in Germany are 15mH and they cost 50 bucks a piece.
Then in contrast to that, the 25V 140uF electrolytics are such tiny elements.
Is this right or am I fundamentally misunderstanding something here?
Regarding the capacitors: I don't actually have a 140uF cap but I have 50V 47uF ones. Can I just combine them in parallel or would this result in the voltage rating no longer being applicable?
First of all, I didn't realize how huge and expensive the required inductors would be. From my calculations I would need ~30mH per speaker. The largest inductors I can find here in Germany are 15mH and they cost 50 bucks a piece.
Then in contrast to that, the 25V 140uF electrolytics are such tiny elements.
Is this right or am I fundamentally misunderstanding something here?
Regarding the capacitors: I don't actually have a 140uF cap but I have 50V 47uF ones. Can I just combine them in parallel or would this result in the voltage rating no longer being applicable?
Could your mids run together with the subs or do they need to be high passed?
Are you sure 80Hz is the right place?
Are you sure 80Hz is the right place?
Well, I have scrapped this idea with the subs for now since I am beginning to question the practicality for live gigging because the PA systems I have encountered so far have been quite good.
So for now it is just about being able to run my electric bass through the Roland JC120 without ruining the speakers (also just for home practice).
It is perfect as a mid monitor, which is essential for fretless to hear your intonation properly on stage. For small bar gigs it's even loud enough on its own (without bi-amping a proper bass amp or routing the Roland's lineout to the house PA).
And no, I am not sure about the 80Hz. This is just what I assumed based on the fact that the amp was designed for guitar.
So for now it is just about being able to run my electric bass through the Roland JC120 without ruining the speakers (also just for home practice).
It is perfect as a mid monitor, which is essential for fretless to hear your intonation properly on stage. For small bar gigs it's even loud enough on its own (without bi-amping a proper bass amp or routing the Roland's lineout to the house PA).
And no, I am not sure about the 80Hz. This is just what I assumed based on the fact that the amp was designed for guitar.
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Re:'going like this: PowerAmp->HPF1->Sp1->HPF2->Sp2 (in series)' - won't work on a JC120, it has separate power amps for each speaker.
However, The JC120 has a effects loop, which makes 6thplanets solution viable.
Degailen, do you have a graphic equalizer pedal? - put one in the effects loop & problem solved
However, The JC120 has a effects loop, which makes 6thplanets solution viable.
Degailen, do you have a graphic equalizer pedal? - put one in the effects loop & problem solved
High power low frequency passive crossovers are big, heavy and expensive.
Capacitance adds in paralel, but the voltage remains the same as the capacitor rating.
As mentioned before, you could insert a line level high pass filter/eq/crossover in the effects loop, it's level can be set to +4dBm or -20dBm.
That said, you will hear gross distortion from the JC 120 speakers without ruining them, simply turn down the bass tone control if you hear them distort, let the PA do the bottom octave.
Yes I know. This series wiring idea belongs to the disgarded idea of running the speakers together with a sub off a separate external power amp.
I have a 1976 JC120. There is no effects loop. I even had to mod it just to get a stereo lineout.
All the suggestions about doing it at line level simply don't work for me because the final signal at the amp's lineout CANNOT be high-pass-filtered since it will go the the house PA. Since the amp is voiced for guitar it is already somewhat filtered, especially with the analog chorus engaged.
I know I am probably overreacting but since they are still the original aluminium speakers from the 70s I want to remove all risk of damaging them. And by playing through headphones I noticed that the amp itself begins to distort earlier than expected which means I won't be able to tell if it is the amp or the speakers when going through them.
Ah right, so for the capacitors going by the voltage rating is not enough? I was wondering how such tiny caps are supposed to handle 60W even though it says they are good for 25/50V.
Quick side question: Would it be ok to leave the HPF circuit permanently connected to the power amp even if the speakers are not plugged in or could this overload the circuit?
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A second order filter at the output of the amp could cause a problem if there is no speaker to damp it's resonance.
Ok.
So I guess I will have to bite the bullet and spend some cash on those inductors. Well, in the end it's better than potentially damaging the speakers. Plus I only payed 350 for the JC in the first place.
I am still confused about the capacitors, though. I only ever see voltage ratings so how do I know if they can handle the power or not?
Also, what cutoff frequency would you suggest as an alternative?
Because I might have misunderstood the HPF calculation. Essentially, I want the signal above 80Hz to remain unaltered.
So I guess I will have to bite the bullet and spend some cash on those inductors. Well, in the end it's better than potentially damaging the speakers. Plus I only payed 350 for the JC in the first place.
I am still confused about the capacitors, though. I only ever see voltage ratings so how do I know if they can handle the power or not?
Also, what cutoff frequency would you suggest as an alternative?
Because I might have misunderstood the HPF calculation. Essentially, I want the signal above 80Hz to remain unaltered.
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Just use the "Bass" knob on the Roland knob and turn it down - that will protect your speakers and still let your hear the overtones...?
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I checked the frequency spectrum of the lineout and there is still a significant amount of the bottom octave present even with the bass all the way down (and you can hear/feel it, too).
Ahhh, I see. In that case, I'd grab a DI box to send your bass to the board. Then out of the DI to a HP filter, then into the amp. Most FOH people have the DI box to use anyway.
Not an option. The whole point is to give the PA that delicious analog stereo chorus signal (I separated the two channels and removed R60).
The DI will come after the lineout.
The DI will come after the lineout.