I recently acquired a pair of Solavox TK30 speakers and have been advised to replace the capacitor that provides the bass-roll of for tweeter protection. I also wanted to put proper terminal binding posts in each speaker to replace the captive wires.
I have acquired a pair of WEAH D222 crossovers which are integrated with the terminal block so seem to include the necessary components, sporting a hefty inductor as well as various capacitors and resistors. My guess is this is overproduction of a crossover aimed at car loudspeaker systems as there seem to be lots of ads on the internet for this.
I have included a photo and I have derived a circuit diagram based on continuity tests, but I'm puzzled by the 2 white components ( blue on my crossovers) and the yellow component. They appear to be in series with the larger tweeter roll-off capacitor at the top of the photo, but I don't understand the function - some sort of tweeter protection I imagine. Does anyone have an official circuit diagram for this crossover ? I'll post my attempt if required but it would be much easier if someone actually has the diagram, then I can decide if I want all these components modifying the signal to the tweeter.
.
I have acquired a pair of WEAH D222 crossovers which are integrated with the terminal block so seem to include the necessary components, sporting a hefty inductor as well as various capacitors and resistors. My guess is this is overproduction of a crossover aimed at car loudspeaker systems as there seem to be lots of ads on the internet for this.
I have included a photo and I have derived a circuit diagram based on continuity tests, but I'm puzzled by the 2 white components ( blue on my crossovers) and the yellow component. They appear to be in series with the larger tweeter roll-off capacitor at the top of the photo, but I don't understand the function - some sort of tweeter protection I imagine. Does anyone have an official circuit diagram for this crossover ? I'll post my attempt if required but it would be much easier if someone actually has the diagram, then I can decide if I want all these components modifying the signal to the tweeter.
To be clear, the Solavox TK 30 used nominally 6 ohm drivers. The mid/bass driver ran full range and the tweeter was protected by a 6 uF capacitor.
On the picture of the two-way crossover above, the white objects are resistors (used for attenuating the tweeter}, the blue objects are film capacitors and the mustard object will be a PTC tweeter protection device (resettable fuse): https://en.wikipedia.org/wiki/Resettable_fuse
On the picture of the two-way crossover above, the white objects are resistors (used for attenuating the tweeter}, the blue objects are film capacitors and the mustard object will be a PTC tweeter protection device (resettable fuse): https://en.wikipedia.org/wiki/Resettable_fuse
That does not seem to be commercially available.
To help you in drawing your own circuit diagram, the two tweeter attenuating resistors will be wired as shown below, forming what is known as an L-pad attenuator. The PTC component will no doubt be directly in line with the series resistor, R1.
If your TK30 tweeter is not loud enough with this crossover, you can lift one end of R2 from the circuit board (or remove it completely) and solder a shorting wire link across R1.
EDIT: I will have to attach the L-pad diagram.
Last edited by a moderator:
Thanks for both replies, both the one about the PTC thermal fuse ( I had heard of them but had no idea what one looked like - to me it looked like a ceramic capacitor used to suppress RF), and the L-Pad. I confirm that the markings on the PCB for two white (in my case blue) components adjacent to the PTC are R1 and R2. I might just bypass both of them as there is only a capacitor in tweeter leg in the actual speaker, whilst the inductor will give a steeper roll off for the bass unit, which may or may not be beneficial. I can't calculate the transfer function or plug them into a crossover programme without the values of the components, which is why I was hoping someone had the circuit diagram with values.
Before you "bypass" anything, it would be best to confirm the component layout.
Don't be shy in posting your version of the circuit diagram so that we may agree with, or modify, it.
Clear plan views of the both sides of the circuit board may enable a member with sharper eyes than mine to deduce the schematic.
Don't be shy in posting your version of the circuit diagram so that we may agree with, or modify, it.
Clear plan views of the both sides of the circuit board may enable a member with sharper eyes than mine to deduce the schematic.
Thank you for the responses.
Here are three photos - component side, pcb side and and edge-on view showing the large capacitor and one face of the two resistors. I also attach my guess at the circuit diagram BUT I have found the the inductor is open circuit between the two ends ( the diagonal contacts at 90 degrees to the cable ties). Unless someone has an idea why a properly installed inductor would be open circuit, I can only think that there was a problem with the soldering - perhaps the varnish on the wires wasn't scraped off before soldering. I'll have a look at that over the next few days, perhaps remove, clean up and resolder those contacts and check the continuity before I try to use the crossovers.
Here are three photos - component side, pcb side and and edge-on view showing the large capacitor and one face of the two resistors. I also attach my guess at the circuit diagram BUT I have found the the inductor is open circuit between the two ends ( the diagonal contacts at 90 degrees to the cable ties). Unless someone has an idea why a properly installed inductor would be open circuit, I can only think that there was a problem with the soldering - perhaps the varnish on the wires wasn't scraped off before soldering. I'll have a look at that over the next few days, perhaps remove, clean up and resolder those contacts and check the continuity before I try to use the crossovers.
Attachments
Am I correct in assuming that this is the case with both crossover boards?
The top solder joint doesn't look shiny. In fact, I would reflow all the solder joints.
Yes,both boards have the same continuity/open circuit readings between contacts, and specifically the inductors on both boards have continuity between the positive terminal and one end of the inductor, and the positive bass output terminal and the other side of the inductor....but the two ends of the inductor show open circuit.
It would be easier to trace the circuit if the top and bottom plan views were side by side (photograph both crossovers side by side).
My head just spins trying to correlate the two views. Let's face it, you are in the best position to follow the component layout,
However, I'm now wondering about the function of some of the components.
This is the best description of the crossover I have found:
"The treble is a 3.3 uF blue 100V Siemens capacitor, resistor and overcurrent protector. The bass is an oxygen-free copper core inductor."
(Is the black toroid in the middle of the inductor coil a ferrite core?)
The large blue capacitor coded 335 is indeed a 3.3 uF capacitor according to this calculator: https://kiloohm.info/3-digit-capacitor/335
In that case, the blue component next to the 3.3 uF capacitor is a 470 nF capacitor and NOT a resistor.
So, it seems we need a rethink and a clear photo of the markings on each of the other blue components.
I would have been inclined simply to change the ageing 6 uF electrolytic capacitor originally used as a high pass filter to a modern 5.6 uF film capacitor as that may have been sufficient to refresh the sound of the speaker. But there you go!
My head just spins trying to correlate the two views. Let's face it, you are in the best position to follow the component layout,
However, I'm now wondering about the function of some of the components.
This is the best description of the crossover I have found:
"The treble is a 3.3 uF blue 100V Siemens capacitor, resistor and overcurrent protector. The bass is an oxygen-free copper core inductor."
(Is the black toroid in the middle of the inductor coil a ferrite core?)
The large blue capacitor coded 335 is indeed a 3.3 uF capacitor according to this calculator: https://kiloohm.info/3-digit-capacitor/335
In that case, the blue component next to the 3.3 uF capacitor is a 470 nF capacitor and NOT a resistor.
So, it seems we need a rethink and a clear photo of the markings on each of the other blue components.
I would have been inclined simply to change the ageing 6 uF electrolytic capacitor originally used as a high pass filter to a modern 5.6 uF film capacitor as that may have been sufficient to refresh the sound of the speaker. But there you go!
Come to think of it, I'd be inclined to strip this circuit board down to the bare necessities.
That is, just the 3.3 uF capacitor in series with tweeter and the inductor in series with woofer.
This should be easy enough to do on the circuit board by removing all the unnecessary components and employing wire links where required.
That is, just the 3.3 uF capacitor in series with tweeter and the inductor in series with woofer.
This should be easy enough to do on the circuit board by removing all the unnecessary components and employing wire links where required.
Attachments
Hi Gaul,
Reducing the components to a capacitor and inductor was always sort of my ultimate plan, unless the crossover yielded something superior. I have now removed all the components from one crossover and this has enabled me to analyse the layers of the pcb, and hence work out the circuit diagram, which I attach.
I have been able to work out the values of all the capacitors from the calculator you provided, but I don't understand the benefit of the picofarad size capacitors in parallel with the thermal fuse, so I'm just going to use the larger value capacitors in their current positions and leave the thermal fuse in place.
I conclude that this crossover is a bitza assembly from available components, an example of Chines "Cabbaging" as the picofarad capacitors cannot do anything significant unless the designer thinks that VHF/UHF signals to the tweeter are a problem.
Oh, the inductor does have a tubular ferrite core !
Thanks for all the inputs.
Reducing the components to a capacitor and inductor was always sort of my ultimate plan, unless the crossover yielded something superior. I have now removed all the components from one crossover and this has enabled me to analyse the layers of the pcb, and hence work out the circuit diagram, which I attach.
I have been able to work out the values of all the capacitors from the calculator you provided, but I don't understand the benefit of the picofarad size capacitors in parallel with the thermal fuse, so I'm just going to use the larger value capacitors in their current positions and leave the thermal fuse in place.
I conclude that this crossover is a bitza assembly from available components, an example of Chines "Cabbaging" as the picofarad capacitors cannot do anything significant unless the designer thinks that VHF/UHF signals to the tweeter are a problem.
Oh, the inductor does have a tubular ferrite core !
Thanks for all the inputs.
Attachments
Thank you, and good work on your own behalf! Your circuit diagram now looks OK. I too don't deem it necessary to shunt very high frequencies around the PTC.
I await to find out if the new crossover produces a positive result. If not, try simply replacing the old 6 uF tweeter capacitor with a 5.6 uF film type as I mentioned earlier.
I await to find out if the new crossover produces a positive result. If not, try simply replacing the old 6 uF tweeter capacitor with a 5.6 uF film type as I mentioned earlier.
Well I have now rebuilt both crossovers with the inductor wiring cleaned of varnish an re-soldered, plus the additional low-value capacitors removed. I have installed the crossovers in the Solavox TK30s, disconnecting the original existing 6microfarad capcitors.
Everything works and the treble is significantly more noticable (without being excessive), despite the 3.3mF capacitor theoretically having less HF gain than the 6 mF item fitted originally. From that I conclude that the 6mF capacitors were on their way out, as initimated by Gaul, so now I'll have to investigate the characteristics of capacitor deterioration a bit more because the next job might be to replace the caps on my 20-year old Mission 773s !
Everything works and the treble is significantly more noticable (without being excessive), despite the 3.3mF capacitor theoretically having less HF gain than the 6 mF item fitted originally. From that I conclude that the 6mF capacitors were on their way out, as initimated by Gaul, so now I'll have to investigate the characteristics of capacitor deterioration a bit more because the next job might be to replace the caps on my 20-year old Mission 773s !
I'm glad you are satisfied with the results. Happy listening!
The 6 uF capacitor originally fitted in the TK30 was an ELCAP bipolar electrolytic capacitor.
If an electrolytic capacitor dries out over time, its capacitance decreases.
If it doesn't dry out and the applied voltage is too low for a long time, the capacitance increases.
Consequently, one really needs to check the condition of old electrolytic capacitors by measurement (or to simply replace them with modern equivalents as a matter of course).
