I want to connect my Polytone MiniBrute IV combo to a Polytone Pro Series Cabinet I found.
My question is, is my plan good, how to improve my plan? Thank you.
MY PLAN:
cut and resolder/shrinktube the 4 wires that make up the existing parallel circuit to the internal 15" and the EXT OUT jack, from that junction add a new pair of leads for the SERIES loop to the internal 15" and a NEW JACK w/SHUNT (1/4" switchcraft w/shunt). I will leave the HEADPHONE jack wired, but will stow it securely inside the box. The NEW JACK will go in the hole labeled HEADPHONE. I will add a label that says SERIES OUT.
I don't know why, move more air, fill out the tone, or just because it seems like these two old PTs belong together and there are some funk parties on the horizon
Some calculations (courtesy geoffthegreygeek) show the most effecient (and safe) way to plug them all in would be to connect in:
Is this a good idea?
Thank you
My question is, is my plan good, how to improve my plan? Thank you.
MY PLAN:
cut and resolder/shrinktube the 4 wires that make up the existing parallel circuit to the internal 15" and the EXT OUT jack, from that junction add a new pair of leads for the SERIES loop to the internal 15" and a NEW JACK w/SHUNT (1/4" switchcraft w/shunt). I will leave the HEADPHONE jack wired, but will stow it securely inside the box. The NEW JACK will go in the hole labeled HEADPHONE. I will add a label that says SERIES OUT.
I don't know why, move more air, fill out the tone, or just because it seems like these two old PTs belong together and there are some funk parties on the horizon
AMP:
Polytone 100w 3ohm
there's a single 15" 3ohm speaker in the combo.
"EXTENSION SPEAKER" jack [parallel to the 15" internal speaker] and some other jacks, I'm thinking of highjacking the HEADPHONES jack for an additional extension in SERIES (see below)
CABINET:
2 jacks
1st reads 8ohms - connected to a 8ohm 12" Eminence
2nd reads 4ohms - connected to a 4ohm 8" + 2x 8ohms tweeters
Polytone 100w 3ohm
there's a single 15" 3ohm speaker in the combo.
"EXTENSION SPEAKER" jack [parallel to the 15" internal speaker] and some other jacks, I'm thinking of highjacking the HEADPHONES jack for an additional extension in SERIES (see below)
CABINET:
2 jacks
1st reads 8ohms - connected to a 8ohm 12" Eminence
2nd reads 4ohms - connected to a 4ohm 8" + 2x 8ohms tweeters
Some calculations (courtesy geoffthegreygeek) show the most effecient (and safe) way to plug them all in would be to connect in:
SERIES the 15" 3ohm and Jack1 cluster (8" 4ohm +2tweeters in parallel 8ohm each = 4ohm) For 7ohms
and
PARALLEL the 12" 8ohm, 8ohms
My logic: this arrangement evenly distributs the power of the amp across all speakers, and the output Imp is 3.73 - only .73 over optimal
and
PARALLEL the 12" 8ohm, 8ohms
My logic: this arrangement evenly distributs the power of the amp across all speakers, and the output Imp is 3.73 - only .73 over optimal
Is this a good idea?
Thank you
Attachments
Probably not.
Just because you have a reading of the DC resistance of your drivers doesn't mean you have a complete impedance plot. At certain frequencies, drivers can draw much more current than the DC resistance would indicate. If this is an instrument amp, as the moderators have decided, then a single frequency may be the intended load.
It appears is if your device has 4 output transistors, this may not be 2 ohm capable. So you might damage them.
You need to find the line level point in the amp, put a jack on that, and run to another amplifier for the extension speaker. Line level is about 2 volts maximum at about 600 ohms drive. This is usually after the input transistor.
Also, usually, tweeters & 15" speakers are separated in frequency by a "crossover" device. These devices are not cheap, and are frequently left out of inexpensive units. Read the multi-way speaker threads, but usually the crossover unit separates at a frequency somewhere between 800 hz and 2500 hz.
The one thing certain about your extension speaker is that it would move more air.
Your user name lists no location, so I will not recommend a speaker parts company, as export of these products from one consumer country to another involves multiple customs charges. The direct market in the producer country confronts one with 99.9% snake oil merchants and slimeballs. So reputable agent in your country to sort through the trash to access real products is useful.
Just because you have a reading of the DC resistance of your drivers doesn't mean you have a complete impedance plot. At certain frequencies, drivers can draw much more current than the DC resistance would indicate. If this is an instrument amp, as the moderators have decided, then a single frequency may be the intended load.
It appears is if your device has 4 output transistors, this may not be 2 ohm capable. So you might damage them.
You need to find the line level point in the amp, put a jack on that, and run to another amplifier for the extension speaker. Line level is about 2 volts maximum at about 600 ohms drive. This is usually after the input transistor.
Also, usually, tweeters & 15" speakers are separated in frequency by a "crossover" device. These devices are not cheap, and are frequently left out of inexpensive units. Read the multi-way speaker threads, but usually the crossover unit separates at a frequency somewhere between 800 hz and 2500 hz.
The one thing certain about your extension speaker is that it would move more air.
Your user name lists no location, so I will not recommend a speaker parts company, as export of these products from one consumer country to another involves multiple customs charges. The direct market in the producer country confronts one with 99.9% snake oil merchants and slimeballs. So reputable agent in your country to sort through the trash to access real products is useful.
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Guitar doesn't play high enough to gain any value from the tweeters.
See the manual -
http://www.modernguitarist.com/wp-content/uploads/2015/05/mini-brute.pdf
It can use an external speaker >4ohms.
Connect the 12" driver to the external speaker jack on the amp through a suitable lead.
Ignore the tweeters.
Simples.
See the manual -
http://www.modernguitarist.com/wp-content/uploads/2015/05/mini-brute.pdf
It can use an external speaker >4ohms.
Connect the 12" driver to the external speaker jack on the amp through a suitable lead.
Ignore the tweeters.
Simples.
The Polytone Combo has a MAIN OUT (I think it's a preamp out),
I can use this as you suggest to another amplifier?
This rig is for electric guitar w/ effects. The 15" is very directional and lacks highs/mids, I want to utilize the Cabs 12" and 8" drivers (maybe the tweeters are pointless, but why does Polytone Pro Series cab include them?)
If I only add the 12" 8ohm I get a Total Imp = 2.18ohms
72% internal speaker, and only 27.3% power going to the 12" extension
If I add plug in the 12" 8ohm in parallel AND ADD the 4ohm 8" in series I calculate a Total Imp = 3.73ohms
and the drivers get 22, 30, 46% power respectively, seems more even.
Is this safe to try and experiment with?
Will I damage the fabric of the universe with too good of tone?
No, only your own output transistors. Only $5 apiece, plus all the upstream components they can blow with rail voltage released from the base terminal.
If you want to know actual impedance instead of resistance, sweep the drivers with a tone from 30-7000 and plot AC current at all frequencies. AC current meters are not cheap, and the $30 DVM measure AC voltage & current accurately only at 50 or 60 hz.
Some 15" drivers perform well to 4000 hz. Some stop at 800 hz. Perhaps such is the reason the designers used a tweeter.
A crossover puts higher impedance in front of a driver at frequencies it is not useful at. For example, I'm putting a 5 mH coil in front of my 15" Eminence driver, to stop flow of current above 1200 hz. A 20 uf film capacitor series the 22XT tweeter blocks current below 1200 hz.
If I was going to experiment, I'd try to see if the main out doesn't go over 2 vac at full volume. Then if that is true, is there current drive sufficient to charge the capacitance of a cable over to another amplifier? To measure AC music cheaply, I use an analog Volt meter with 20 vac & 2 vac scales.
My CS800s amp that is capable of 2 ohm loads, two parallel 4 ohm speakers, has 5 pairs of output TO3 MJ15024/25 transistors, per channel. How many pairs of output transistor do you have? One? Two? TO3, TO247, or TO220?
Designers add up the DC soa rating at rail voltage to estimate how much current each transistor can safely put out, if the heat sink doesn't heat up.
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> SERIES the 15" 3ohm and Jack1 cluster (8" 4ohm +2tweeters in parallel 8ohm each = 4ohm)
In this string, the beefy Fifteen is getting 3/7 or less than half of the power. Actually since the tweeters *must* have series caps, over most of the range the mighty Fifteen takes 1/3rd of power, the small Eight gets 2/3rd. The Eight will melt before the Fifteen speaks well.
In this string, the beefy Fifteen is getting 3/7 or less than half of the power. Actually since the tweeters *must* have series caps, over most of the range the mighty Fifteen takes 1/3rd of power, the small Eight gets 2/3rd. The Eight will melt before the Fifteen speaks well.