If you can't easily get a 15W R1 10 Ohm resistor try for the 10W to be held proud on the board for air to can circulate and keep it away from insulation materials inside the cabinet. Or use two 20 Ohm 10W in parallel resulting to one 10 Ohm 20W equivalent.
The supplier I've been using can supply 10W 22 Ohm Resistors.
2 in parallel would make it 20W 11 Ohm.
10 Ohm is specified.
Will 11 Ohm do the job without a negative impact?
They have 18Ω which will provide 9Ω when in parallel.
As indicated, It's closer, but will I experience compromise in sound and performance?
Also, when paralleling Resistors should I keep them apart from each other to reduce heat build up?
Nice adjustment.
You're very good at thinking outside of the box.
Can I summarize my shopping cart to make sure I understood?
Tweeter circuit.
2 x 6uF Caps
2 x 0.25mH 18AWG Air Core Inductors
Woofer Circuit:
2 x 10uF Caps
2 x .633mH 18AWG Air Core Inductors
2 x 10W 33Ω Resistors
If result, high end unacceptably sharp fit Rp1 & Rp2 Resistors to Tweeter Circuits (1Ω & 10Ω), and replace 33Ω Resistors in Woofer Circuits with 10W 18Ω & 22Ω Resistors in parallel to yield 20Watts.
Correct.
By the way, industrial type relatively economic polypropylene capacitors like the CDE 930C should do fine in this project.
By the way, industrial type relatively economic polypropylene capacitors like the CDE 930C should do fine in this project.
Thanks Salas.
A quick search but couldn't find outlets in Australia.
Also CDE 930C caps appear to be -+ 10% which seems general purpose??
Mouser carries them. Digikey also. If 10% is unacceptable there should be a 5% variation too. J suffix. But its not standard issue.
Wima MKP4 could also be used. These come in 5% stock more often. Anyway, as parts are hard to locate in good variety during this period, get some decent economic polypropylene series you trust and you can easily find.
Anything like that will be miles ahead from the decades tired high loss and high tolerance tiny sized BP electrolytics of the standard crossover.
Wima MKP4 could also be used. These come in 5% stock more often. Anyway, as parts are hard to locate in good variety during this period, get some decent economic polypropylene series you trust and you can easily find.
Anything like that will be miles ahead from the decades tired high loss and high tolerance tiny sized BP electrolytics of the standard crossover.
While the parts are on their way, I started dismantling and cleaning up one of the crossovers in preparation.
The existing resistor was 12ohms.
Attached is a photo of the heat damage it caused.
One thing which isn't intuitive to me is the requirement to connect +ve Amp to the -ve on the Tweeter terminal (reverse polarity).
Why would this be required?
Also, as this speaker has by wire terminals (2 x +ve & 2 x -ve) at rear, which of the 2 relate to the tweeter.
I'll try to keep positions factory standard.
thanks
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Hi Cliff,
Well it's not really intuitive but some 12db filters will imply that voltage and current are out of phase once summed ( this is caused by capacitor and inductance). If you let them run without inverting polarity on one of the way you'll have some canceling within the xover passband and as a result a 'notch' filter.
In other word a 12db hp will be +90° and your lp will be -90° at fc. This will make them 180° appart, so inversed polarity ( out of phase).
This may or may not be clearly audible ( it depends of the frequency range where it happens as we are more sensitive within some range than others).
One way to figure out what happen is to experiment with a simulation software and see what happens when you tweak things with 'perfect' ( idealized) drivers ( vituix cad comes to mind but other exists too). .
It was not intuitive for me neither but once you experimented it, it become a fact you'll agree with. Even less intuitive once you factor in the fact that the driver center to center distance may induce some variation to this too... as well as the driver physical depth which comes into play too.
I think you'll have to trace signal path (follow the physical realisation) to define which goes where.
It's strange the resistor got this hot it melted the plastic! It must have seen some abuse for extended period of time!
Well it's not really intuitive but some 12db filters will imply that voltage and current are out of phase once summed ( this is caused by capacitor and inductance). If you let them run without inverting polarity on one of the way you'll have some canceling within the xover passband and as a result a 'notch' filter.
In other word a 12db hp will be +90° and your lp will be -90° at fc. This will make them 180° appart, so inversed polarity ( out of phase).
This may or may not be clearly audible ( it depends of the frequency range where it happens as we are more sensitive within some range than others).
One way to figure out what happen is to experiment with a simulation software and see what happens when you tweak things with 'perfect' ( idealized) drivers ( vituix cad comes to mind but other exists too). .
It was not intuitive for me neither but once you experimented it, it become a fact you'll agree with. Even less intuitive once you factor in the fact that the driver center to center distance may induce some variation to this too... as well as the driver physical depth which comes into play too.
I think you'll have to trace signal path (follow the physical realisation) to define which goes where.
It's strange the resistor got this hot it melted the plastic! It must have seen some abuse for extended period of time!
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Its not too strange when you think that a 10W resistor was resting on plastic as it was shunt to the woofers thus dissipating 12/4=1/3 the amplifier's power
The top red and black posts pair. In other words the ones towards the RTL3 print at the back of the cup.
Their counterparts near the Made In England print are for the woofers.
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Yes you are right about the resistor Salas.
I'm surprised it wasn't anticipated by designers and they didn't leave a gap or something to allow some passive cooling or at least not to put an heating part in contact to plastic.
I'm surprised it wasn't anticipated by designers and they didn't leave a gap or something to allow some passive cooling or at least not to put an heating part in contact to plastic.
Unfortunately they were doing many overlooks and afterthoughts back in the day. Usually some smaller specialist companies. Remember the beautiful sounding popular Musical Fidelity slim Class A integrated amps and their thermal design "margins"?
Tbh, no. I've never really been into audiophile stuff. 🙄
I suppose i've spent too much time here... and i'm now used to a high degree of attention to this kind of details.
I suppose i've spent too much time here... and i'm now used to a high degree of attention to this kind of details.
@ Cliff
By the way what DCR those coils show on the Ohm meter? Also what DCR each woofer shows? Zero the meter first if it has a REL or Δ button.
By the way what DCR those coils show on the Ohm meter? Also what DCR each woofer shows? Zero the meter first if it has a REL or Δ button.
I tested the coils (several times to look for variations).
Meter doesn't have a zeroing function/button but if I short the terminals I get reading 0.2Ω
Larger coil = 7Ω 0.53mH
Smaller coil = tested either 6Ω 0.20mH or often faulty/unknown
I'll work on the woofers.
The replacement air core inductors on order are rated @ 0.65mH 18awg 0.38Ω & 0.25mH 18awg .22Ω
Vikash used 0.633mH & 0.243mH
It appears the original iron core Inductors are considerably out.
The DCR readings on the original coils form post#50 seem way too high. The woofers inductor should have been getting very hot if so. Its bobbin size does not imply that high a DCR. Also the small coil appears close in DCR to the big one and that's fishy too. See alike coils typical DCR
How you got their mH? You have a DMM that reads inductance too? By the way since you are a speakers hobbyist maybe get a DATS V3 interface at a point. Measures not only the drivers T/S parameters but inductors and capacitors too in a proper way for audio band use.
There are no off the shelf such nominal inductance values for air core inductors. But there are tolerances. Being thorough, Vikash either noted down the replacement air core exact unit values or the original coils unit values. Most possibly by using an LCR meter set at 1kHz. 0.65mH vs 0.633mH is 2.7% tolerance. Not critical.
Last but not least we don't know what Vikash found for original coils DCR but we know that he used air core replacement coils similar to your order and he ended up with a correct loudspeaker response result.
How you got their mH? You have a DMM that reads inductance too? By the way since you are a speakers hobbyist maybe get a DATS V3 interface at a point. Measures not only the drivers T/S parameters but inductors and capacitors too in a proper way for audio band use.
There are no off the shelf such nominal inductance values for air core inductors. But there are tolerances. Being thorough, Vikash either noted down the replacement air core exact unit values or the original coils unit values. Most possibly by using an LCR meter set at 1kHz. 0.65mH vs 0.633mH is 2.7% tolerance. Not critical.
Last but not least we don't know what Vikash found for original coils DCR but we know that he used air core replacement coils similar to your order and he ended up with a correct loudspeaker response result.