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PostPosted: Mon Feb 26, 2018 10:55 pm 
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Mark III

Joined: Sun Feb 18, 2007 7:55 pm
Posts: 197
So I have a JP2C coming this weekend, very excited. I have a mark IV widebody combo, am a former IIc+ player (needed more on spot versatility at the time), and I can’t wait to plug in the new Mark. My question is, if I keep the IV powered off, can’t I use its speaker as the can for the JP, until I get a cab? I know the wattage is a bit different from JP to the c90, but I won’t be running it to that power...yet.
In theory, I could keep the IV off and go straight into the 8 ohm (or 4) speaker input from amp to combo.


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PostPosted: Thu Mar 01, 2018 7:47 am 
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Donating Member
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Joined: Wed Jun 26, 2013 3:56 pm
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Location: Norfolk, CT
Yes, you can do that.

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JP2C, Mark llC++ DG, Mark IV-A/B.


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PostPosted: Thu Mar 01, 2018 9:28 am 
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Mark III

Joined: Sun Feb 18, 2007 7:55 pm
Posts: 197
Thank you.


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PostPosted: Sat Mar 03, 2018 9:26 am 
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Triple Recto

Joined: Fri Feb 22, 2013 7:31 am
Posts: 3062
Location: North Carolina
I would not use the JP-2C at 100W with the MC90. the JP-2C will peak at 140W RMS as I have seen on the power attenuator I use. Also note that the MC90 will taint your tone, or color it with more midrange or honky sounds which is what I found with the Mark IV combo I had. I was happy when the speaker blew out so I could replace it with something else. Then again, if you have the Mark IVa with the EVM Black Shadow speaker then by all means run the JP-2C at full power. This is to assume you are connecting direct to the speaker and not using the speaker output jacks on the Mark IV to couple the JP to the speaker in the combo.

Best thing to do is use a speaker cable coupler (one end has male and the other is female ) to connect direct to the combo speaker. Never attempt to use the terminals on the amp as a means to connect to the speaker of a combo amp as the end result will not be 8 ohms. Instead the JP-2C will be connecting to a 0.8 ohm load as this is what I measured with the Mark V combo amp with the speaker plugged into one 8ohm jack and a speaker cable into the other 8ohm jack. I measured less than 1 ohm impedance. Do not use any amp as a terminal block to connect its speaker to another amp as the end result will be the OT impedance and not the speaker impedance. I am assuming this is what you meant to do, is that correct? This could result in undesireable effect even if it does work. Also once you push current into the OT of the unpowered amp, the end result will be high voltage on the high side of the OT. Since the OT is a step down transformer, when run in reverse as this will be the case it will operate as a step up transformer. I would not do it as this may damage both amps at the same time.

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Current amps: TC-100, TC-50, JP-2C, MK V, Roadster, RA100


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PostPosted: Sun Mar 04, 2018 9:20 pm 
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Mark III

Joined: Sun Feb 02, 2014 11:51 am
Posts: 175
Quote:
Never attempt to use the terminals on the amp as a means to connect to the speaker of a combo amp as the end result will not be 8 ohms.


Very good advice. When connecting a combo speaker to another amp head, just unplug the combo speaker cable from the back of the combo amp. Then, as you say, get an adapter (male one end, female on the other) and connect the external head directly to the combo speaker. The combo amp should be off and totally disconnected from everything!!


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