Micro Dark Head 2x PPC108 cabs

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Jocraig
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Micro Dark Head 2x PPC108 cabs

Post by Jocraig » Sun Jan 01, 2017 9:10 pm

Hi I have a Micro Dark Head and two PPC108 cabs my problem is I cant connect them together iv heard its possible but no one seems to know how I'm using 2x Fender Custom Shop cables for the cabs and one for the guitar does anyone know what to do to make it work as I'm new to this and have no idea what I'm doing
Many Thanks

Ruptor
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Re: Micro Dark Head 2x PPC108 cabs

Post by Ruptor » Mon Jan 02, 2017 9:39 am

IF it is this combo
https://www.amazon.com/Orange-Micro-Hyb ... B0161KSGSU" onclick="window.open(this.href);return false;
then the amplifier is designed for one speaker not two. The amplifier has a minimum 8R output impedance and the speaker has 8R input impedance so they are matched for maximum power. If you fudge a parallel connection to add a second cabinet the total speaker impedance would be 4R and that would increase the power taken from the amplifier by four times and damage the amplifier. Fudging a series connection of speakers would give 16R and reduce the output power by four times so there is no point in adding a second speaker.

jontheid
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Re: Micro Dark Head 2x PPC108 cabs

Post by jontheid » Tue Jan 03, 2017 6:23 pm

. . . the amplifier is designed for one speaker not two
It is a good idea to differentiate between 'speakers' and 'cabinets/cabs'.
You can't say an amp is only designed to work with one speaker! Or indeed only one cab for that matter.
The amp is designed it to work over a range of output impedances - from 8 ohms to 16 ohms.
So long as you are in this range you will be ok - you can do this with one cab, two cabs, three cabs etc.

You can have 2x12" cabs that are rated at 8 ohms - you could use one of these with the Micro Dark without issue.

You could also use 2 4x12" 16 Ohm cabs in parallel (total overkill with a Micro Dark but it won't hurt the amp).

Also doubling the output impedance doesn't reduce the output power by 4 times. It will roughly halve it.
Similarly halving the output impedance won't increase the power by 4 times. It will roughly double it.

There is no harm at all in using a proper series adaptor box to connect 2 PPC108s to a Micro Dark.
However it will reduce the output power. It may sound better. It may sound worse.
There are a few reports of the PPC108s sounding quite 'boxy'.
If you really want to get a bigger sound out of the Micro Dark you would be better off getting a cab with bigger speakers that is rated at 8 Ohms.

Cheers,
Jon

Ruptor
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Re: Micro Dark Head 2x PPC108 cabs

Post by Ruptor » Tue Jan 03, 2017 7:04 pm

jontheid wrote:Also doubling the output impedance doesn't reduce the output power by 4 times. It will roughly halve it. Similarly halving the output impedance won't increase the power by 4 times. It will roughly double it.
Yes you are right I forgot the impedance is half or double that opposes the increased current and was thinking of the condition of a fixed load. The figures may be wrong but the principle of matching the cabinet load to the amplifier for maximum power transfer is still correct. I guess if guitar players want distortion from unmatched loads it is another story so long as it doesn't destroy the amp. :roll:

jontheid
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Re: Micro Dark Head 2x PPC108 cabs

Post by jontheid » Tue Jan 03, 2017 10:08 pm

the principle of matching the cabinet load to the amplifier for maximum power transfer is still correct.
No, it isn't. Not with a solid-state amp output section anyway.

Maximum power transfer occurs when source impedance (impedance of output section) is the same as the load impedance (speaker impedance).
When this occurs there is as much power dissipated in the output section as there is in the speaker.

However the output impedance of a solid-state amp is low. Much lower than typical speaker impedances. Less than an ohm.
If you tried to match speaker impedance to this very low level you would get too much power dissipated in the output stage and it would blow.

Solid-state amplifiers are efficient because of this low output impedance. They don't achieve 'maximum power transfer' because they aren't trying to.

Image

The graph above has load impedance divided by source impedance on the x-axis. The two curves represent power transfer and efficiency.

Note that when 'impedance matching' occurs the power transfer is 100% but efficiency is only 50%.

If the load impedance is increased to 5 times the source impedance power transfer falls to about 50% of maximum but efficiency increases to over 80%.

Hope this makes sense,
Jon

PBA
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Re: Micro Dark Head 2x PPC108 cabs

Post by PBA » Wed Jan 04, 2017 8:31 am

The OP wants to connect two PPC108, 8 ohm cabs to his MD which has a single 8 to 16 ohm connection? I don't have one, but the general advice here previously has been to not bother but look to get a PPC112 as that will sound better than two PPC108s.

As the advice above says, if the OP really wants to connect two PPC108s a series (not parallel) connection is needed. This would require a "special" cable.

When cabs are normally connected together to a single amp, the connection is usually made either via a SECOND jack socket on the cabs or via a second jack socket on the amp. I believe these are not available on the MD or PPC108.

Most worrying to me is the OP's description of the connecting cables. I am not sure if guitar cables are being used. The cable used to connect a guitar to an amplifier should not be used to connect the amp to any kind of speaker. To connect speakers, you need a speaker cables. They look the same in that there will be 1/4" jack plugs at each end but the cable is different. Before going any further with experimenting on connecting cabs, please ensure that the correct cables are being used.

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