Howdy,
I posted a similar question in a guitar amp forum, but I have not had success in getting any answers and am wondering if anyone here might be able to help.
I have a Leslie guitar speaker cab from the early 70's - it is basically a speaker cab with a rotating drum that spreads the sound vertically and to the sides at either a slow or fast speed. You would hook a guitar amp up to this cab and also to another speaker. Highs and lows were passed to the "regular" speaker, while the rotating speaker got more of the mid range. This was done using a cable assembly that included an inductor and capacitor wired in parallel - effectively creating a notch filter for the "regular" speaker, and a capacitor in the Leslie cab which would act as a high pass filter. I have not been able to find pictures of the inside of the cable assembly, but based on its cylindrical shape (bottom left of the attached picture), I am inclined to think that the inductor was perhaps a cylinder shape with radial leads.
Anyway, the reason for my post is that I do not have the crossover cable assembly. I'd like to build the crossover into a metal enclosure (basically a guitar pedal), but I am struggling figuring out what type of inductor to use. Using an oscilloscope, I ran my guitar amp at my usual volume through a 4 Ohm dummy load and measured ~13Vrms at 400Hz which I believe thus implies ~13/4 = 3.25Amps were running through the load at this frequency. In looking at radial ferrite core inductors, it seems like their current handling specs are usually nowhere near 3 Amps for the inductance values I would need (see below). Air core inductors seem popular for use in stereos, but they seem somewhat impractical to mount inside a guitar pedal.
Is my reasoning with regards to the calculated current flowing through the circuit logical? Is it critical that the inductor be rated for this level of current, or is it unlikely that this much would flow through the inductor alone when in reality guitar signals will always have multiple frequencies (including harmonics) and thus the current would be split and also flow through the capacitors (one parallel to the inductor at the "regular" speaker, one high pass at the rotating speaker)?
I have an 8 Ohm speaker in the Leslie as well as in my amp, and I am looking to use a 100uF cap at the rotating speaker to act as a 200Hz high pass filter, and then a ~2.4mH inductor and 1uF cap in parallel for the notch filter going to the "regular" speaker.
Any thoughts as to what I should be considering for the inductor? Is air core the way to go, and I just need to get creative in terms of mounting it inside the enclosure, or are there options for ferrite core radial inductors at these values?
Thanks!
I posted a similar question in a guitar amp forum, but I have not had success in getting any answers and am wondering if anyone here might be able to help.
I have a Leslie guitar speaker cab from the early 70's - it is basically a speaker cab with a rotating drum that spreads the sound vertically and to the sides at either a slow or fast speed. You would hook a guitar amp up to this cab and also to another speaker. Highs and lows were passed to the "regular" speaker, while the rotating speaker got more of the mid range. This was done using a cable assembly that included an inductor and capacitor wired in parallel - effectively creating a notch filter for the "regular" speaker, and a capacitor in the Leslie cab which would act as a high pass filter. I have not been able to find pictures of the inside of the cable assembly, but based on its cylindrical shape (bottom left of the attached picture), I am inclined to think that the inductor was perhaps a cylinder shape with radial leads.
Anyway, the reason for my post is that I do not have the crossover cable assembly. I'd like to build the crossover into a metal enclosure (basically a guitar pedal), but I am struggling figuring out what type of inductor to use. Using an oscilloscope, I ran my guitar amp at my usual volume through a 4 Ohm dummy load and measured ~13Vrms at 400Hz which I believe thus implies ~13/4 = 3.25Amps were running through the load at this frequency. In looking at radial ferrite core inductors, it seems like their current handling specs are usually nowhere near 3 Amps for the inductance values I would need (see below). Air core inductors seem popular for use in stereos, but they seem somewhat impractical to mount inside a guitar pedal.
Is my reasoning with regards to the calculated current flowing through the circuit logical? Is it critical that the inductor be rated for this level of current, or is it unlikely that this much would flow through the inductor alone when in reality guitar signals will always have multiple frequencies (including harmonics) and thus the current would be split and also flow through the capacitors (one parallel to the inductor at the "regular" speaker, one high pass at the rotating speaker)?
I have an 8 Ohm speaker in the Leslie as well as in my amp, and I am looking to use a 100uF cap at the rotating speaker to act as a 200Hz high pass filter, and then a ~2.4mH inductor and 1uF cap in parallel for the notch filter going to the "regular" speaker.
Any thoughts as to what I should be considering for the inductor? Is air core the way to go, and I just need to get creative in terms of mounting it inside the enclosure, or are there options for ferrite core radial inductors at these values?
Thanks!
Attachments
The original crossover inductor must be a small ferrite core to fit into the can. It's possible that the resultant high series R and possibly premature core saturation is part of the characteristic Leslie sound.
Thanks guys. The Leslie cabs mentioned in the links above are a bit different as those were designed for organs and as far as I know do use physically larger inductors that were attached to a piece of wood or plywood.
If I were to try a ferrite core inductor such as one of the IHD-3's below from Vishay Dale, what is the worst that could happen? As an example, the 2.2mH (2200uH) spec indicates a max current rating of 0.5A. If the core saturates, is it basically no longer going to be effective as a low pass filter? Is there a real risk that a 3A current could cause the inductor to burn up?
https://www.mouser.com/datasheet/2/427/VISHS96175_1-2566416.pdf
Thoughts?
If I were to try a ferrite core inductor such as one of the IHD-3's below from Vishay Dale, what is the worst that could happen? As an example, the 2.2mH (2200uH) spec indicates a max current rating of 0.5A. If the core saturates, is it basically no longer going to be effective as a low pass filter? Is there a real risk that a 3A current could cause the inductor to burn up?
https://www.mouser.com/datasheet/2/427/VISHS96175_1-2566416.pdf
Thoughts?