passive attenuators??

[rightintheface]

http://cgi.ebay.com.au/ATTENUATOR-FOR-FENDER-HOT-ROD-BLUES-DELUXE-DEVILLE-TWIN_W0QQitemZ200434614405QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item2eaad58085#ht_2962wt_788

i've just stumbled across this concept. surely this is better for an amp than a power soak/attenuator that goes between the head/speakers? my local tech hates power soak attenuators. said something about putting a giant resistor in front of all that signal and then going max vol on your amp can be damaging. said it was like a car: just because it says it can do 240km on the speedo, doesn't mean it's DESIGNED to run that fast. eventually things wear down and break. said it was a similar concept for amps. just because they CAN go to ten, doesn't mean they should.

anybody got any expert advice on this? i imagine alot of people will say "i use an attentuator and it's no problem", but from a purely engineering side, is it not potentially damaging? i honestly don't know enough about amps to comment IMO.  :tard:

surely the passive volume attentuator in the fx loop would work just as well, and heappppppps cheaper? or would you run into tonal problems?

 

[Death by Uberschall]

It's not the same application of the attenuator concept. Attenuators allow you to push the power tubes to get the cranked power tube tone at lower volume levels. Basically you crank up the amp, your power tubes and output tranny are moving some high output wattage, making the amp/speakers screaming loud and producing that great tube tone. An attenuator gets between the output tranny and the speaker, reducing the volume coming from the speaker.

What this device does is the same as a master volume control on an amp. You crank the preamp up, then this device reduces the volume before the power tubes to reduce the volume of the amp. So your pre-amp is cooking along well, then this device lowers the volume and your power tubes/output tranny are just idling along and not being driven hard.

Insert a volume pedal into your effects loop and you'll get the same effect if you want to try it out first.

 

[-CB-]

my local tech hates power soak attenuators. said something about putting a giant resistor in front of all that signal and then going max vol on your amp can be damaging

a - you can build your own little box for the effects loop, its not hard and takes a box, pot, cap, two jacks and a little wire.  Use a 1m pot and a 250pf or so across it.  Better yet, go whole hog... and put in a 50pf, 100pf, a 250pf, a 500pf and a .001uf cap on a rotary switch, so you can dial in any one ya like for "just the right" amount of sparkle at any setting.

b - your tech is right, but only to a point, and a minor one at that.  You crank an amp up to max and play it through anything, its gonna wear out the output tubes faster, preamp tubes a little faster, create more heat, maybe make the screen grid resistor go south a little sooner.  Using his car analogy - listen bro, the road is a terrible place at times.  Dangerous it is!  So you gotta decide to keep yer car parked in the garage, or face life. 

Tone has a price.  The tone you get from your effects loop being hammered by the preamp is not the same as output tube distortion.  Thats because the output section of your amp draws big power and that power "sags" by design.  You get a natural compression as the power level cannot keep up with the demand.  The notes blossom, the top end is creamy.  You dont get that with preamp tube distortion.  Some preamps sound great when driven hard... most dont.

But if you build that box, I also suggest you get an EH LPB-1 to drive your preamp tubes harder.  Using that method, you'll wear the preamp a little faster, but not much.  It will still last years and  years between tube changes, or maybe forever if you dont keep it maxed out all the time.  Preamp tubes are almost unaffected by being driven hard - they're class A amps anyway, so always run at the full amperage (low).

To muddy up the works, I designed some years ago, a working prototype of a box which would combine resistive and inductive elements, in order to make a 100w rated 2/4/8 ohm speaker eliminator.  What you did, was crank up your amp into this heat sinked device (after setting the correct impedance), then it had a separate output control to vary its output - which fed another amp's input, or a line level device's input.  It worked GREAT, still does.  I never got it into production, but use the box all the time.  Using that, you can get output tube distortion, power sag, and some of the response of a speaker actually being driven by the load - which imparts energy back into the output of the amp.  We could get started on "damping factor" but... not here.

 

[rightintheface]

ahhhhhhhhhh of course i didn't even think of the fact that the fx loop is before the power amp stage  :doh:

so CB, i'm a little confused... you designed a SPEAKER eliminator? and i'm not sure if i read into this correctly, but you need two amps to do this? i think i may have read a thread on this awhile back.. can't remember. they all blend in after a while.

 

[Death by Uberschall]

ahhhhhhhhhh of course i didn't even think of the fact that the fx loop is before the power amp stage  :doh:

so CB, i'm a little confused... you designed a SPEAKER eliminator? and i'm not sure if i read into this correctly, but you need two amps to do this? i think i may have read a thread on this awhile back.. can't remember. they all blend in after a while.

Basically what =CB= is describing is using one whole amp (pre and power sections) as a pre-amp to feed into another amp for sound. Think of the first complete amp as an overdrive pedal in front of a second, clean amp. You use the dummy load/line out box in place of the speakers for the first amp.

If you go through the "Rack Gear" thread in the Rig Forums, you'll see I did basically the same thing in my Mesa rack using the Palmer load/line out unit.

 

[-CB-]

Dunno how theirs works, but thats what mine does.  With rows and rows of inductors... and two BIG 100w resistors.

Keep in mind that there is really too much dynamic happening to get an absolutely perfecto emulation or elimination.  Speakers drive air, they feedback into the output section differently depending on the note and volume and attack of the note, all sorts of things happen since coils in motion not only use, but produce electricity.  Weber and Weber both tried to do this with speaker voice coils, and it was admirable, but its just not the same as cones flexing and surrounds farting out and such.

 

[tfarny]

I have a Weber mini mass which uses inductors and a speaker voice coil - it does a good job helping you go from "Holy Mother" loud to just loud-for-an-apartment, and when you turn it down it of course doesn't sound quite the same. Last thing I'm worried about is wearing out the tubes - I only have three of them anyhow and they're not NOS cork-sniffer tubes.

You know, the actual "new thing on the block" is VVR attenuators, which do something or other to the voltage post-power stage ( right?) and by all accounts beat every inductor based attenuator or MV hands down but require actual amp modification to do so. London Power is the company in question. I would love to hear from CB, Mayfly, or the other gurus around here about VVR, pro or con.

 

[ironeddie]

http://cgi.ebay.com.au/ATTENUATOR-FOR-FENDER-HOT-ROD-BLUES-DELUXE-DEVILLE-TWIN_W0QQitemZ200434614405QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item2eaad58085#ht_2962wt_788

i've just stumbled across this concept. surely this is better for an amp than a power soak/attenuator that goes between the head/speakers? my local tech hates power soak attenuators. said something about putting a giant resistor in front of all that signal and then going max vol on your amp can be damaging. said it was like a car: just because it says it can do 240km on the speedo, doesn't mean it's DESIGNED to run that fast. eventually things wear down and break. said it was a similar concept for amps. just because they CAN go to ten, doesn't mean they should.

anybody got any expert advice on this? i imagine alot of people will say "i use an attentuator and it's no problem", but from a purely engineering side, is it not potentially damaging? i honestly don't know enough about amps to comment IMO.  :tard:

surely the passive volume attentuator in the fx loop would work just as well, and heappppppps cheaper? or would you run into tonal problems?

I live in a basement suite and I have a 150 watt all tube half stack.  In order for me to even turn it on, i have to run through an effects loop with a volume pedal in the middle.  It won't give me the tone of an amp at 7 but at least its quieter.  When nobody is home upstairs.... then there is no need!