So I just did a full tube replacement and bias with JJ's in my Marshall DSL401 Amp along with swapping out the stock Celestion Goldback 100W speaker for a new Celestion G12-65W. I was surprised to find that I had to raise the volume 2/3 notches on my amp to play at the same level as I did before the change.

The only difference in changing the tubes was that I got a balanced P.I. tube for the V4 position as recommended. I would'nt think that would effect volume but I'm not that clued up on the ins and outs of amp circutry.

I realise that new speakers go through a break-in period but I would have thought that this effects the voicing of the speaker not the volume. Am I wrong?.

I would add that the amp is still very useable and I like the change of tone (not so much harsh mids) I just thought that this was a little strange. Anybody got any thoughts on this.
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different speakers may have different db ratings making them quieter or louder.

the G12-65 has a 97 db rating, and I believe the Goldback has a 99 db rating, although im not 100% positive

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Aye, these guys are right. Tube amps work on a logarithmic power to dB ratio where doubling the power gives only a 3 dB increase, so if you swap for a speaker that is even 3 dB lower in it's sensitivity rating, you are literally attenuating your amp by about half power.
He's right you know.

each 'notch' on your amp is roughly 1dB so 2-3 notches is the 2dB lower sesitivity of the new drive units.
This is a bad thing? You should be able to crank it more.
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Quote by sesstreets
This is a bad thing? You should be able to crank it more.

Indeed! I think it's a good thing, esp with a head that loud.

25 watt amp with a 100dB speaker = 50 watt amp with a 97dB speaker
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Yeah, I'm using vintage30 speakers, they are effin' loud. Enjoy the lower volume/more crankage.
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