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Insufficent ampage with new cab and other factors...


Ajoten
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Hmm, something's not right here.

  • I could gig with my Trace 1x15" 150W combo, 4 ohm speaker. Loads of oomph.
  • I removed the amp and put it in MDF box to use as separate head.
  • For lightweight solution am putting it through a shiny new 300W 2x10 8 ohm cab.

This cunning strategy hasn't worked, as at rehearsal last night it really struggled. I was told that although an 8 ohm cab is only going to get half the power the difference in volume wouldn't really be noticeable. So - given it's not a powerful amp, could it be that there's a bigger difference between 150W split between 4 or 8 ohms, compared with doing the same to a 500W amp?

Or have I sh@gged the amp with my faffing about? I can't believe there's much drop in quality between an entry level 90s Trace and a 2018 300W Laney.

I'm hoping it's all about the ohms, otherwise I've been stupid.

 

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An amp rated at 150 watts @ 4 ohms will be putting out about 75 watts at 8 ohms. Sorry, IMO your problem is not enough watts. 

I'd get a 500 watt amp so that you'll have 250 watts available for your 210. Then you can add another 210 if you need more volume. A second 210 will improve your tone as well.

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Add to Chris's comment the fact that your old Trace 15" speaker will have been very thoroughly worn-in and probably be capable of a great deal of excursion, whereas your brand-new 2x10 will be (temporarily) very stiff and reluctant to move as much as it will in due course. You're changing too many things at once.

Do you have a separate power amp somewhere, or a friend with one?

Try taking a feed from the FX Send on the Trace head to an external power amp (preferably 500W or greater), then use that power amp to drive the new 2x10 cab. That should tell you where the problem lies.

 

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27 minutes ago, la bam said:

Your laney is a 300w 8ohm cab.

To get that at 8ohm, youd be looking at a 500w amp to achieve it.

What you are actually doing is putting around 75w into a 300w cab. Hence the big drop in volume.

You need to check the output at 8 ohms. The output of SS amps is usually stated at 4 Ohms and it may well be that a 500Watts amp can output 300 watt and more in to 8ohms. However That would be unusual as generally the 8 ohm output is half the 4 ohm output.

 

Boring techie stuff. The power output of an amplifier is usually constrained by both the amplifier design and the power supply design.  If we look atb the power supply it will have both current and voltage limitations. Given that you are likely to be driving 4 or 8 ohms, the maths are simple. The power output into 4 Ohms  is double that into 8 ohms. However IF for some reason the power supply cannot supply enough current into 4 ohms, then the power output will be restricted and the 8 ohm power would be greater than half the 4 ohm power. Most manufacturers would not design this way as it adds cost to the amp without improving the headline power output.  An example of this is the Ampeg PF350. It outputs 350W into 4 ohms and 250 into 8 ohms.

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24 minutes ago, Chienmortbb said:

...An example of this is the Ampeg PF350. It outputs 350W into 4 ohms and 250 into 8 ohms...

This is where I get in a tangle thinking about a Wattier replacement. For any given amp sold as (i.e. @ 4 ohms) 350W how much discernible difference would there be between the expected 175W in 8 ohm and Ampeg 250W? Or for that matter between 175 Ampeg Watts vs the expected 150W from a 300W like the Ashdown Original HD-1?

(To which everyone will say "no, go for 500W" I bet, although my intention at the mo is simply to not be quieter than the combo I'm replacing 🙂.)

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I always think of buying gear as 'choose two from three' - you can only have two of the following - light, cheap & good sound. 

So, if you want it to sound good and be light, it's going to cost you. If you want light weight and cheap. it ain't going to sound so good, and if you want good sound and cheap, it's going to be heavy.

The only exception would be if you were lucky enough to find someone selling on a modern lightweight high quality cab for less than it's worth. Otherwise either your back, your ears, or your wallet is going to suffer!

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3 hours ago, Ajoten said:

I was told that although an 8 ohm cab is only going to get half the power the difference in volume wouldn't really be noticeable.

That's mostly correct. Doubling the impedance load reduces the maximum power delivery by about 40%, not 50%, with a reduction in maximum output of perhaps 2dB, a negligible amount, assuming no change in speaker sensitivity and/or frequency response. That last bit is the key factor. What you're experiencing indicates that the sensitivity and/or frequency response of the 210 is not equal to that of the 115. 

I'm hoping it's all about the ohms,

It's all about sensitivity and frequency response.

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56 minutes ago, Ajoten said:

This is where I get in a tangle thinking about a Wattier replacement. For any given amp sold as (i.e. @ 4 ohms) 350W how much discernible difference would there be between the expected 175W in 8 ohm and Ampeg 250W? Or for that matter between 175 Ampeg Watts vs the expected 150W from a 300W like the Ashdown Original HD-1?

(To which everyone will say "no, go for 500W" I bet, although my intention at the mo is simply to not be quieter than the combo I'm replacing 🙂.)

I think you know the answer. The difference between 175 Watts and 250 Watts is negligible to your ears assuming you are using the same speaker. I suspect you would be happy with the Ashdown Original but I would probably suggest something with a bit more power. After all Volume controls go down as well as up. If I started were in your position (and this is only my opinion) I would try the Ashdown RM500 EVO II.

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6 hours ago, Ajoten said:

I'm hoping it's all about the ohms, otherwise I've been stupid.

Not stupid, you just haven't thought about all of the factors. Your problem is assuming that it's all about the impedance when it isn't. In moving from one cab to another you've done more than change the nominal impedance, you've also changed:

the number of drivers
the maximum excursion of those drivers
the sensitivity of the drivers and, as a result, the total sensitivity of the cabs
the frequency response
several 'non-textbook' factors such as the age, quality. lifespan and general condition of the cabinets and speakers

If you changed between two otherwise identical Trace 1x15" cabs in the same condition from the same year, one 4R and one 8R then you'd be unlikely to notice a difference. That's not the case here though.

 

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Watts do matter and so does sensitivity. Let's imagine your 2x10 has a sensitivity of 96dB for 1W and your old 15 is 98dB/W. If you ran 100W into your old 15" Trace, that gives you 20dB of amplification (20dB louder than if you only give it 1W) It's max volume will be 118dB.

Now replace that with your 2x10. Because it's 8ohms and you aren't running it flat out the power will be almost exactly halved. 50W gives you 3dB less gain so 17dB of amplification. That means you will get 96+17dB or 113dB. That's 5dB you've lost probably the difference in turning down from 10 to about 8 on the dial and that you will notice. Both the amp and the speaker will have contributed.

I'll make another guess too. I reckon that Trace has a nice lively 'smiley face' frequency response which punches out bass boom and a nice middy punch, a lot of old fashioned shouty sound. The Laney is probably better balanced but expects plenty of power to do it's thing. The trace speaker only ever had to handle 150W so it could be made shorter throw with a nice light cone and hence more efficient. 

I'd put the Trace amp back with the speaker it was made for and look for an amp to get the best out of the Laney.

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Your old combo may have a low mid hump whereas the more modern Laney may have a flatter response? The volume might be similar but the baked in sound might give more perceived volume.

If it has the mid pre shape switched in then disengage that.

Edited by lemmywinks
poor spelling!
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3 hours ago, FinnDave said:

I always think of buying gear as 'choose two from three' - you can only have two of the following - light, cheap & good sound. 

 

Presumably Hoffman's Iron Law, Dave, which i thought was Bass extension,  Small cab,  Efficiency. 

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12 minutes ago, fleabag said:

Presumably Hoffman's Iron Law, Dave, which i thought was Bass extension,  Small cab,  Efficiency. 

Far too technical for me, I just think wallet, ears, back - one of them's going to suffer! These days the wallet takes the hit, my back's already knackered!

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4 minutes ago, FinnDave said:

Far too technical for me, I just think wallet, ears, back - one of them's going to suffer! These days the wallet takes the hit, my back's already knackered!

Just quoting Yoda Fitz from years ago.  Cheap should have been Hoffmans 4th choice.  :)

I'm with you - small and bass extension. I'd just get a bigger amp for the  3rd one.

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