Power Soak

[RandomRedLetters]

I was wonder where to start when developing a powersoak (reduces volume) for a 50w amp with a 16 ohm speaker cabinet. If anyone could point me in the right direction, let me know.

[The Tone God]

I was wonder where to start when developing a powersoak (reduces volume) for a 50w amp with a 16 ohm speaker cabinet. If anyone could point me in the right direction, let me know.

:arrow: Search

The search function is your friend.

Andrew

[RandomRedLetters]

the search function came up with nothing relevant. Thats why I posted.

I saw the powersoak on blueguitar.org but it looks like its for 8ohm 25w max.

[The Tone God]

Try "power attenuator" and "dummy load"

Andrew

[sir_modulus]

Here's some good things to look for on the internet:

Briged T attenuator
L Pad Attenuator
Weber Mass (they used to sell just the mass, but not n'more)

or, if you wanna just buy one...
Marshall powerbrake
THD HotPlate
Weber Mass (/mini mass etc..)

Cheers,

Nish

[Dave_B]

How about this?
http://www.lalena.com/audio/calculator/lpad/
http://www.lalena.com/audio/calculator/lpad/help.shtml

If you go this route, buy the appropriate wattage resistors and keep in mind that at least one of those buggers will get hot.  Enough to burn you badly if you accidently touch it.

There are apparently better ways of doing power attenuation with regard to sound and maybe even amp life (the previously mentioned Weber Mass), but I don't know how to make them.  

[diydude]

Hello:

I read an article once about EVH...when he was just starting out...he supposedly went to a hardware store and bought a varistat (a device that is used to charge up large capacitors - used mostly by electicians).  He somehow linked it between the AC outlet and his Marshal amp.  I have also heard of guitar players using a ceiling fan rheostat (kind of a variable on/off swith) to control the AC before it gets to their amp.

I have never tried it though...it is most likely very dangerous.  Could also damage your equipment IMO.

diydude

[Dave_B]

Hello:
I read an article once about EVH...when he was just starting out...he supposedly went to a hardware store and bought a varistat

I read that also.  He used a Variac.  Variacs have an AC jack on them that you plug things into.  They're sort of like a great big light dimmer.  They have a knob on them that typically allows you to vary the output voltage from 0-110%.   Lowering the voltage on an amp can have the short term effect of glorious distortion, but the long term effect of blowing your amp.  I don't recall the specifics because it's been too long, but I think it does a number on output transformer.  It would also throw the bias voltages off on the tubes.  

There are uses for them though.  If you have a really old amp that was designed for 110, you can use a Variac to reduce the 117-120 of modern mains.  Still, that's not what Eddie was doing.  

[petemoore]

Foam padding cabinet damper...Letting the speakers move some but blocking say 8/10ths of the speaker facea.
 We used to see this band that had a great cranked stack sound at low volume...Real Nice, I asked the guitar player what those things that looked like 12'' cardboard cutouts were in front of his cabinet's speakers, he said 'they are cardboard', .. about 2'' or 3'' in front of the soundboard there were cardboard 'speaker covers'.

[Karmasound]

I've read he was using it at 90v on his 60's Marshall.

According to Gerald Weber it won't hurt the am to go down in voltage, just not up.


Or you can check out Kevin O'Connors method of power scaling.

[lovekraft0]

According to Gerald Weber it won't hurt the am to go down in voltage, just not up.

Well, yes, but you're also turning down the heater filament voltage by about 25%, which can't be really good for the tube - I'm not sure how low it can be before you start getting excess noise and cathode poisoning, but the rule of thumb has always been +/-10%. The chart (on Tone Lizard's Marshall Myths page) from Tremaine's Audio Cyclopedia appears to confirm that, so I always took it for gospel.

Then again, I might be overly concerned by what may be a second or even third order consideration - maybe RG, puretube, or one of the other tube mages will chime in with better info than my limited education can furnish (hint, hint!).

[Dave_B]

I've read he was using it at 90v on his 60's Marshall.
According to Gerald Weber it won't hurt the am to go down in voltage, just not up.
Or you can check out Kevin O'Connors method of power scaling.

Far be it for me to argue with Weber, but I'm pretty sure there's a point where that isn't correct.  The tubes are biased for an amps' stock voltage.  When you change the B+ without re-biasing, you're underbiasing the tubes.  I don't remember much, but I know that underbiasing can cause tubes to short out, possibly taking the output tranny with them.  Not trying to be arguementative, but I'm pretty sure that's the way it works.  Maybe we're all correct, since I don't know where the point of no return would be with a Variac and whatever Marshall Eddie started out with.  

[d95err]

Hello:

I read an article once about EVH...when he was just starting out...he supposedly went to a hardware store and bought a varistat (a device that is used to charge up large capacitors - used mostly by electicians).  He somehow linked it between the AC outlet and his Marshal amp.  I have also heard of guitar players using a ceiling fan rheostat (kind of a variable on/off swith) to control the AC before it gets to their amp.

I have never tried it though...it is most likely very dangerous.  Could also damage your equipment IMO.

diydude

AFAIK, varying the supply to the amp using a Variac has nothing to do with attenuating the volume of the amp. It's about changing the plate voltage for the tubes to change the sound (more distortion).

For attenuation, EVH supposedly used a simple high wattage resistor as a dummy load of his Marshall 100W Super Lead, tapping a small line out signal from the speaker out. At the end, a speaker simulator was used.

[d95err]

About attenuators, the cheapest solution is probably to buy a Weber MiniMASS or Load Dump. A 50W load dump is only $75, a 50W MiniMASS is $100.

[aron]

These might help too:

http://blueguitar.org/new/schem/misc_mod/power_sk.jpg

http://blueguitar.org/new/schem/misc_mod/volreduc.gif

http://www.geocities.com/SunsetStrip/Studio/2987/speaker.html

[cab42]

I'm planning to build on of these (great link):

http://amps.zugster.net/articles/attenuation/


Regards

Carsten

[WGTP]

Aren't we talking about 2 different things?  The Variac might reduce the volume some and has been credited with the BROWN sound, but isn't the same as an attenuator between the amp and the speakers.  Or did I miss something?  

[cd]

Aren't we talking about 2 different things?  The Variac might reduce the volume some and has been credited with the BROWN sound, but isn't the same as an attenuator between the amp and the speakers.  Or did I miss something?  

Nope.  A variac is completely different from an attenuator.  A variac will vary the supply voltage to the ENTIRE amp - i.e. 120VAC from your wall can be adjusted from say, 90-130V with a variac.  Now, the reason you DON'T want to do this, despite what your guitar god hero may say or do - your amp is designed to run on a certain voltage, in North America, typically 120VAC.  Most vintage amps were designed around 117VAC, but 120VAC is close enough.  The power transformer in your amp (assuming it's a tube amp) takes that voltage and knocks it down to the 6.3VAC required for the tubes' heaters.  The heaters themselves have an approx. +/-10% tolerance; any more/less than that, you're pushing the tube into a region where it's dangerous to run.  At worst, you could blow the tube, and hopefully your amp's fuse will save the amp... but it may not.

[bass_econo]

I'm planning to build on of these (great link):

http://amps.zugster.net/articles/attenuation/


Regards

Carsten

L-Pads are not that expensive really -

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=260-255

[stankyfish]

I'm planning to build on of these (great link):

http://amps.zugster.net/articles/attenuation/


Regards

Carsten

Purely resistive loads don't present a varying impedance to the amplifier the way a real speaker does.  This is supposed to have an adverse effect on sound and possibly on the output transformer.  I don't know if I'd bother with a purely resistive load.