Attenuator circuit tone alteration?

[Howlin' Mad Mac]

Found this circuit scribbled down somewhere or other & interested in trying it but I've a question for all my mighty tube amp guru friends on here... will this thing squash my highs & could it be improved with a "bright" bypass cap incorporated somewhere? Many thanks y'all for looking!

25 Watt Power Attenuator pg 1 with Values.pdf

[kleuck]

Found this circuit scribbled down somewhere or other & interested in trying it but I've a question for all my mighty tube amp guru friends on here... will this thing squash my highs & could it be improved with a "bright" bypass cap incorporated somewhere? Many thanks y'all for looking!

[ATTACH]14992[/ATTACH]

It will
Here is one of my own attenuators wich is "tone-friendly"
http://farm6.static.flickr.com/5219/...9092a65c_b.jpg
As you can see, it's meant for low volume use, as the minimal attenuation is about 12 db.
Looks like that : http://farm6.static.flickr.com/5096/...7115b560_b.jpg
You can of course build a more powerful one :
http://farm6.static.flickr.com/5052/...9ab4dcb7_b.jpg
http://farm6.static.flickr.com/5133/...02b838aa_b.jpg
Not exactly the same, this one is a 16 ohms one.

[Howlin' Mad Mac]

Thanks kleuch, I'd like to see your values for the larger version. Seems like it works almost like a passive crossover in which case it would also be helpful to see the math so I could play around with slopes & frequencies.

[kleuck]

More like that :

[kleuck]

There’s not a lot of maths.
Resistors are here to help dissipate the whole power, and to limit the bright cap's efficiency -if you find the right cap you don't even need a switch to turn it off- you can calculate the cap, but with an 8 or 16 ohms SPKR, good values are around 5 - 10 µf, best is to try and choose the best for you use.
Chokes are here to help maintain an inductance seen by the amp, speaker are between 200 and 600 µH.

[kleuck]

Another one :

[imaradiostar]

I've built a few that are roughly based on the TW Airbrake. I use the large Ohmite wirewound resistors and add taps as needed. I use generic L-pad calculators on the web to calculate 3dB steps and usually end up with 0, -3, -6, -9, -12 and -15 steps while keeping the load reflected to the amp exactly at 4, 8 or 16 ohms depending on the build. Sometimes I'll tack a non-polar cap from one terminal to another to make it brighter as you increase the attenuation. I've found the "bedroom" setting to be pretty useless in the past. Everyone I've built one for really likes them and thinks they sound really natural. I have a THD hotplate and I'd say each one has their strengths. The hotplate gives more tonal control but it doesn't sound quite as natural as the airbrake to my ear. On the other hand the airbrake type designs tend to get overly dark sounding.

I have several l-pads like those shown above but I haven't tried them. Any small low powered amp should be pretty forgiving of impedance mismatch so all of the above designs look usable to me!

Last winter I built a tiny single ended amp and I intended to mount a pad inside the chassis as a "master volume" but I never finished it. I really need to though- should be a lot of fun once it's working. All of my amps are really too loud for indoor practice and this would help.

jamie

[kleuck]

Update : http://farm7.static.flickr.com/6072/...34b76504_b.jpg