HT20H Cab out put: 1x8 ohm + 1x16ohm at the same time?

Discussion - HT Venue amplifiers. Inspiration from Studio to Stage.
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El_Sisto
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Joined: Tue Jul 05, 2016 1:55 pm
Location: UK

Tue Jul 05, 2016 2:35 pm

Hey Guys,

I am tempted to run 2 cabs from my HT20H. Can I plug my HTV212 (8ohm mono) and a Marshall 412 (16ohm) at the same time using both side output of the amp?

In the picture:
HTV212 8ohm MONO into the left output
412 Marshall 16 ohm MONO into the right output

Image

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thephantum
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Location: Virginia, United States

Tue Jul 05, 2016 6:57 pm

If you are asking can you run both the 8 ohm and 16 ohm tap off the amp at the same time, the answer is no. The output transformer (OT) is not designed to drive both sets of winding's simultaneously. So you have to pick one or the other.

Having said that, you can run both cabs with a couple of caveats
  • You will have to mismatch impedance.
    The OT can take up to a 2x mismatch and with tube amps it's better to mismatch low than high. An 8 ohm and 16 ohm cabs together will result in around 5.33 ohms. So if you run them off the 8 ohm tap you are under the 2x limit (which would be 4 ohms).

    Power will not be evenly distributed between the cabs.
    Because the impedances aren't the same, the cabs will receive uneven power. Specifically, the 8 ohm cab will draw around 66.7% of the power with the other 33.3% going to the 16 ohm cab.

thenewbruno
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Joined: Fri Jul 08, 2016 2:33 pm
Location: Mississauga Ontario

Sat Jul 16, 2016 6:19 am

Ok on a similar topic, what if I want to use an HTV212 with my club 40? In my head its just not working. How can I plug the combo's 16ohm and the cab's mono 8ohm at the same time with proper impedance everywhere? Surely we're not expected to not use the combo's on board speaker when we get an extension cabinet.


thenewbruno
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Location: Mississauga Ontario

Sat Jul 16, 2016 7:28 pm

Really appreciate the links, but they don't address what we're addressing here. These Blackstar extension cabinets are 8 ohm not 16, and that's fouling up the works. The options off the combo amps are one 16, one 8, or two 16s. Not a 16 and an 8. The proposition of a 16 and an 8 doesn't make any sense in the interest of amp life expentancy and sound quality. What's the deal??

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thephantum
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Sat Jul 16, 2016 8:24 pm

You can do it, but there's a catch:

Most tube amps, (specifically the Output Transformers) can take up to a 2x +/- impedance mismatch with no issues whatsoever. Blackstars are no different. What that means is you can run both the internal 16 ohm speaker and an 8 ohm extension cabinet safely off the 8 ohm tap on the head. The total load will be 5.3 ohms, which is less then the 2x limit and thus perfectly safe.

The catch is that the majority of the power (26.6 watts in this case) will go to the 8 ohm load (the cab). The remaining power (13.3 watts) will go to the 16 ohm load (the combo speaker).

Or, you can change the speakers and rewire the cab to get it to 16 ohms. This is the route I went, but it was more because I personally think that 70/80's suck...so it was more about the speaker swap.

thenewbruno
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Joined: Fri Jul 08, 2016 2:33 pm
Location: Mississauga Ontario

Sun Jul 17, 2016 5:46 pm

thephantum wrote:You can do it, but there's a catch:

Most tube amps, (specifically the Output Transformers) can take up to a 2x +/- impedance mismatch with no issues whatsoever. Blackstars are no different. What that means is you can run both the internal 16 ohm speaker and an 8 ohm extension cabinet safely off the 8 ohm tap on the head. The total load will be 5.3 ohms, which is less then the 2x limit and thus perfectly safe.

The catch is that the majority of the power (26.6 watts in this case) will go to the 8 ohm load (the cab). The remaining power (13.3 watts) will go to the 16 ohm load (the combo speaker).

Or, you can change the speakers and rewire the cab to get it to 16 ohms. This is the route I went, but it was more because I personally think that 70/80's suck...so it was more about the speaker swap.
So it's just not right then and that's about the extent of it. Either have a mismatch or change speakers out. Makes no sense at all that Blackstar makes extension cabinets that provide an impedance mismatch with the combo amp they extend from. lol.

But yeah swapping a pair of 8ohm V30s for the seventy eightys isn't the worst situation. ;)

dsmmrm
Posts: 23
Joined: Tue Mar 24, 2015 12:46 pm

Mon Jul 18, 2016 3:44 pm

Or just plug into a 16ohm extension cabinet. I use one from "another company" that has 4 g12t-75s in it and along with the stock 70/80 sounds huge.

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