Anyone have knowledge of valve amp technology?

Sweetloaf

Sweetloaf

Sweetloaf

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I''ve recently bought a valve amp with a numer of output options, Speaker out 8 and 4 Ohm and a dedicated speaker emulated line out.

I want to record stuff late at night via the speaker emulated line out the only problem being that it doesn't mute the speaker. The speaker itself can be unplugged which I have tried and it works very well, however it advises against operating the amp without the speaker plugged in. Anyone know why this might be?
 
becuase theres no where for the current to flow so your tubes are outputting high voltages with low current draw, in thoery mate, as long as the speaker output doesnt touch anything conductable than you *should* be okay but im no expert on tubes.

A better idea would be to get some power resistors to act as your speaker :)

rapid have a wide range and should cost you less than a tenner, again, this is all thoery but I dont see why it wouldnt work.
 
m3csl2004 said:
A better idea would be to get some power resistors to act as your speaker :)
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Ok, do what with a what from where was that? :)

I take it plugging a guitar lead into it an then into a second amp and turning the volume down on that one won't work then? :D

m3csl2004 said:
in thoery mate, as long as the speaker output doesnt touch anything conductable than you *should* be okay but im no expert on tubes.
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The speaker output is female so there is little chance of that.
 
You really need a speaker attenuator but I don't know if they can fully mute the amp (not that familiar with them), just know that it's a very bad idea to run a valve amp without some sort of load. All that energy which would be creating sound will instead dissipate as heat which is bad news for the amp.

Something like a THD Hot Plate would be ideal I expect but never used one myself.
 
hot plates are designed to attenuate *some* of the energy, so you can saturate the power stage of the amp at low volumes, wouldnt really be suited for this situation.

power resistors are cheap electrical components, designed to dissipate large amounts of power into heat (instead of noise, like a speaker), for example, say you had an 8 ohm speaker, which makes a lot of noise, you could connect an array of power resistors to dissipate the energy, with an effective resistance of 8 ohms (you would need to use several at once, to make sure they wernt running near there peak value)

however, giving your reply, it seems your not quite as happy with electronics as I would recomend when dealing with high power applications, as mess it up and very bad things can happen to your amp and you...
 
m3csl2004 said:
however, giving your reply, it seems your not quite as happy with electronics as I would recomend when dealing with high power applications, as mess it up and very bad things can happen to your amp and you...
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Sound advice :D

You're right, I would have a clue where to start, nevermind, I'm sure I'll find a way around it without frying me or the amp. :)

Thanks.
 
actually having Done a bit of reading I may owe an apoligy to one more solo, the hotplate may be able to be used as a full dummy load, but without looking into how it works I wouldnt like to say. and there website is very unclear.


edit: if im not mistaken its the 40w ashdown you got in the other thread?
 
m3csl2004 said:
actually having Done a bit of reading I may owe an apoligy to one more solo, the hotplate may be able to be used as a full dummy load, but without looking into how it works I wouldnt like to say. and there website is very unclear.


edit: if im not mistaken its the 40w ashdown you got in the other thread?
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I was thinking the same thing about their website, I *think* you can use it as a dummy load but their description is awful.

The simplest thing would be two 4 ohm 25W rated resistors wired in series with some thick wire and a male jack on one end to connect to the speaker out.
 
Wait wait.

I just had a great idea. I tried turning the master volume down and the independant channels still sound through the output.

Problem solved, thanks for your time and effort guys :)







(yes I'm a little embarassed but I'm not going to admit it) :D
 
Some rules (probably have been mentioned before in the thread but didnt read that carefully)

Do NOT disconnect the speaker as the power will have nowhere to go

The THD hotplate is a great idea but expensive

My dad and I created a similar (but looking much more home made) thing with power resistors (definitely mentioned above) which works well

Does your amp have an effects loop? If so then just plug in a cable to the return part (from what would be the output of the effects loop). This will effectively disconnect the preamp from the power amp silencing the main input but not destroying your output section.

The idea of attenuation is meant to get the power amp working at reasonable levels which gives a nice creamy distortion. When using our home-made attenuator, it definitely reduced the volume without breaking anything, but it is my belief that part of the "feel" of a valve amp is from the volume you need to get power-amp distortion and how it affects your bones which is lacking if you reduce the volume.

Anyway my 2 cents...
 
youve also got to remember what your speaker brings to the party :)


I found quite a nice diagram for an reactance modelling power sponge which emulates a speakers current draw more accuratly, but I'm solidstate so I dont need it. seems like a cool thing to build if you actually have a decent amp though lol.
 
Sweetloaf said:
I take it plugging a guitar lead into it an then into a second amp and turning the volume down on that one won't work then? :D
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I hope you are joking? Please don't do this. Putting the speaker output of your amp into the input of another amp would be a very bad idea. Not quite 'DON'T CROSS THE STREAMS' bad, but not good. :)
 
Personally i would be very, very surprised if the emulated output produces anything near a passable tone. You would be better of using a mic, but each to their own
 
Clinkz said:
Personally i would be very, very surprised if the emulated output produces anything near a passable tone. You would be better of using a mic, but each to their own
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Of course but it isn't always possible, I was actually very suprised at the quality to be honest, it doesn't sound half bad :)
 
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