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Ohm help please

6Tones

Member
Messages
4,983
My VHT amp internal speaker is 8ohm,and I want to run a 16ohm extension cab with it,the amps selector switch is 4,8,16 ohms, what should I set it too?
Also what if I used a 8ohm extension cab,would I set the ohm selector switch rating to 4?
Thanks in advance!
 

John Phillips

Member
Messages
13,038
If the internal speaker is 8-ohm, and the extension is 16, the total impedance is 5.33 ohms - assuming the sockets are in parallel, which in most amps they are.

This is a safe mismatch from either the 4 or 8 ohm settings (it 'sounds' closer to 4, but actually it's a 33% mismatch from either if you work it out!). Try both and see which sounds better. If you can't tell any difference, it probably doesn't matter at all either way. If I had to pick, I'd probably go for 4 since mismatching fractionally upward is a little less hard on the tubes than downward. Also, it may be worth mentioning that 2/3 of the power will go to the 8-ohm speaker and only 1/3 to the 16-ohm extension cab.

If you're using an 8-ohm extension cab, set the amp to 4, yes. The power is divided equally between the internal and external speakers.
 

6Tones

Member
Messages
4,983
Ok Ill go with the 4ohm setting.
Thanks John!
Originally posted by John Phillips
If the internal speaker is 8-ohm, and the extension is 16, the total impedance is 5.33 ohms - assuming the sockets are in parallel, which in most amps they are.

This is a safe mismatch from either the 4 or 8 ohm settings (it 'sounds' closer to 4, but actually it's a 33% mismatch from either if you work it out!). Try both and see which sounds better. If you can't tell any difference, it probably doesn't matter at all either way. If I had to pick, I'd probably go for 4 since mismatching fractionally upward is a little less hard on the tubes than downward. Also, it may be worth mentioning that 2/3 of the power will go to the 8-ohm speaker and only 1/3 to the 16-ohm extension cab.

If you're using an 8-ohm extension cab, set the amp to 4, yes. The power is divided equally between the internal and external speakers.
 

J.T.

Silver Supporting Member
Messages
2,393
Is the 16 ohm cab a 2x12 ? It might be easier to re-wire the 2x12 for 8ohms that paired with the internal 8 ohms will give you 4 ohms total with out a mismatch
 

6Tones

Member
Messages
4,983
Originally posted by J.T.
Is the 16 ohm cab a 2x12 ? It might be easier to re-wire the 2x12 for 8ohms that paired with the internal 8 ohms will give you 4 ohms total with out a mismatch

No its a 1x12 16 ohm extension cab:p
 




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