DIY Attenuator

[Vince]

I've been looking into making an attenuator and it seems the 'best' option is an L-Pad based one. I've seen ones that are basically a volume knob in the effects loop too. I've heard that the L-pad ones can get pretty hot too. So I'm a bit nervous as I don't want to blow a £600 amp!

Any info is appreciated.

Cheers

[Beaker]

Kind of like this?






Here's a schem:




Dead easy to build, but trust me, boy do they get hot. BIG heatsinks and steel mesh enclosure for maximum ventilation required.

Have a look here:


http://archive.ampage.org/threads/4/gadc/235045/power_attenuator_schematics-1.html

A friend of mine uses a Marshall Power Brake, so I am familiar with these beasties. I'm not a fan really, they really suck the top end off your tone.

[Vince]

Yeah, something like that. I was looking at this one.

http://guitarprojects.weebly.com/diy-attenuator.html

Someone suggested using a 100w L-pad to reduce the heat but it's the tone suck that concerns me too. I may have a go at one as it would be fairly cheap to do

[Beaker]

As a matter of interest, what amp are going to use this with?

[induction]

If you are looking for cranked tube tone at lower volume, you might have better luck with a re-amping approach (a resistive dummy load and lineout box followed by a clean SS power amp). Depending on your volume needs, you can use a simple LM386 circuit (like a ROG Ruby, though I'd increase the coupling cap for more bass), or something bigger. I find this approach has less negative impact on the tone, and you can EQ after the power tubes to adjust the response. You can also put any reverb, delay, etc. after the power tubes, where they usually sound best.

This approach essentially turns your amp into a pedal or preamp, and the signal can then be effected and then amplified to any volume you like, so tone and volume become decoupled. Clean SS poweramps are cheap and easy to make.

The Garnet Herzog is exactly this. It turns a Fender Champ into a preamp. Gordie Johnson from Big Sugar uses this and he has one of the best hard rock tones I've ever heard. He goes the other direction though, amplifying a small single ended amp to high volumes with a huge power amp.

Just an idea.

[Beaker]

Great suggestion Induction, one I've used myself before when my bass amp failed on me just before a gig.

It's that old problem - small low watt amp cranked up sounds amazing, 100 watt "stadium" rig forced to be quiet sounds weedy and lifeless.

[Vince]

Another good suggestion, induction. Thanks to both of you. I was looking at a Webber minimass too, A lot of info about the ear perceiving tone etc, to do with the speaker not being pushed etc.

I'm using a Laney L5T-112 Lionheart, Beaker.

Only 5w but I use it at home. I'm not really after cranking it full, just enough to not have to microscopically nudge the master volume and cause a huge volume boost. So i'd probably just push it up about 25-50% and attentuate it back down to a neighbour happy volume.

[Beaker]

Ah! a very fine choice indeed.

The easiest, quickest, and cheapest is the simple volume pot in the effects loop, but thinking about your description of the problem, I don't think it's going to solve much.

Back in the old days Fender used Log taper pots on the volume controls of their amps for a smooth transition up from 1 to 10. When Marshall came along and wiped the floor with Fender in terms of sheer VOLUME, and sales stated to suffer, they hit on a sneaky sales ploy.

They swapped out the log pots for linear taper pots. This had the effect of making the amp come on monstrously loud with the volume on 1, but not get an awful lot louder as you cranked it up to 10. Salesmen in guitar shops were able to yell at customers "Yes mate, it is really loud, and you've only got it turned up to 3!"

Fender have stuck with this ever since, as have many "Fenderlike" brands. As a result THE most common mod on Fender amps is to replace the linear taper volume pots for log ones.

I've not seen seen a schematic or parts list for the Lionheart, but I have played one, and I would bet my shirt on it having a linear pot.

Something to consider?

[IvIark]

I've got a 100W L-pad hiding somewhere in my man cave.  Not built it up yet but I thought it looked like nice easy option to try.  I think at 100 watts it's rated maybe 5 times the level I ever play my amp at so I was hoping the extra capacity would stop it getting too hot

[induction]

Here's the setup I use with my Vox AC4TV, in case you want to try it.

Dummy load/lineout (based on the Weber Loadline, but with a better tonestack):





Power amp:

[Vince]

Some great info there,

I'll have a bit of a think further but many thanks, there is a lot to consider there...

[IvIark]

Yes excellent info, thanks for sharing

[Beaker]

Looks like I owe you guys a shirt - found a parts list - 1 Meg Log.

[moda]

Ok, so im reviving this thread as ive been asked to build one for a friend.
I do have a schematic of a tube town attenuator but not sure whether i should post as we dont generally post schematics.
So the linky thing.
https://www.tube-town.net/cms/?DIY/Amp-Tools/PoS_%28engl%29

Looks simple enough...... My friend wants one for a Boogie 100w so im assuming 150w power resistors at a minimum?
Thoughts and feedback welcomed.

[traktop]

I´m really done with L-pads attenuators. Is not only about tone but about lost dinamics in the way.
I built the airbrake and it wasn´t too bad for knocking 3 or 4 dbs, from there, you could really feel the speaker and amp loosing its interaction in a really bad way.
Then you got the speaker power issue. If you attenuate a tube amp, please, find a lower rate speaker to play with it, so you can feel the cone moving.
For me, the best aproach is solid state reamping, but first try to find something that cheats your amp believing that it really has a speaker connected to it. The goal is getting a similar speaker impedance curve through frequency spectrum; You will need 3 elements: The resistive, (covered by l-pads), the inductive ,(covered by some attenuators), and the capacitive, (basically a bass cap).
A couple of years ago I found a very interesting "bedroom attenuator project" for big amps ,(16ohms load), on a spanish forum that basically did that.
The way it´s designed, it always starts with about 9dbs of attenuation, then you go down from there to zero with a rheostat. That´s perfect for me to open my 100watts hiwatt on rehearsals or playing it at home with a 10watts speaker. You could even install a line out plug for computer recording or reamping tasks. The great thing about it, is that I can´t perceive any loss in sound or dinamics.
This is the impedance curve you get with this thing, (very similar to a guitar amp speaker):

This is my build, (biggest cap ever...:

And this is the schematic:

This is a recording I uploaded to soundcloud:
https://soundcloudx.com/thrashtop/1973-hiwatt-dr-103-wgs-et90-speakers-american-stratocaster-stug-decimator-attenuator-1
This is the spanish thread, (photobucket linked pictures  )
http://www.guitarrista.com/phpbbforum/viewtopic.php?f=90&t=112369
And this is a thegearpage thread talking about the same concept:
https://www.thegearpage.net/board/index.php?threads/aikens-reactive-dummy-load.1072793/