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bradovka dropped over yesterday to pick-up parts to upgrade his TMB to a v6. It will be the first such conversion as far as I know since the kits are sIII /v6. This will be interesting to hear and I look forward to hearing his results.

But he brought over his home made attenuator and it was pretty impressive. So much so, I'm going to get one and do some tests on it.

It was a substantial and good looking beast he built, enclosed in a cast aluminum Hammond Box measuring 3.5" x 4.5" x 2.25" . It had some interesting graphics on it too!

He used the venereable Radio Shack http://www.thesourcecc.com/estore/Produ ... ct=4008983

The attenuator is meant as a wall mounted stereo volume control with 45 watts RMS / 90 watts max capacity. It had two transformers on a circuit board, one for each channel (L & R) and a step switch with many decks on it. It only works with 8 ohm speaker loads.

I'm always skeptical until I hear/see/try things for myself but I have to say, I was impressed because it worked very well.

I did notice a change in high end response on extreme attenuation
levels. bradovka agreed and suggested it was probably a combination of factors:
1) Our ears efficiency at low volumes
2) Speaker efficiency at low volumes,
3) Attenuators ability to evenly reduce volume across the spectrum.

bradovka said it sounds best when you set it at mid-range attenuation (-9 to -18db) and whatever 'loss' in high frequency can usually be dialed back in using the tone controls. You could switch it/out a 5/10uF cap to compensate for the loss in high end at low volumes.

So, if anyone else has used this, your input would be helpful. I was going to try power scaling but might now put that on the back burner [again]. Maybe bradovka can post some pictures and comment a bit more.

I plan to test this out & see what the frequency response is like and if it can be used safely without damaging an amp but so far, it looks pretty good and cost effective as an outboard attenuator!

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

http://www.radioshack.com/product/index ... age=search

I use the mono version. It works as well as my Altair from the mid seventies.

LeeMo

Cool, it can handle 25 Watts (RMS) or 50 Watts Maximum and has a 10-Position Control. Should do an 18 watt I think.

Sounds good?

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Yep. Sounds good for the first three or four "notches". I read somewhere that the reason heavy attenuation souns bad has something to do with the way we hear. The Fletcher-Munsen curve and all. However , as long as there is at least one watt driving the speaker, all is well.
I've thought of converting it to a modified powerbrake.
http://www.schematicheaven.com/marshall ... rbrake.pdf


LeeMo

I don't know about the 25 watt version. I guess it all depends on how you're going to be using it. If you're pretty well happy with the volume of an 18 watt and just want to shave it back a bit then it should be fine. But I live in a condo and would like to avoid one of those Aerosmith/RunDMC battles through the wall. Well... At least at night anyway.

So I have occation to really rope in my amp. The distortion can get pretty wild. I can see the power tubes really glowing bright. (not redplating or anything, but nice and healthy glow.) As far as being safe to use without damaging the amp. I can say I've used it for a good 15 or 20 hours and I don't see any problems yet.

As far as switching in capacitors I sure would like to try that. Where does it go? From the input (+) terminal to the output (-) terminal? I've also heard of smaller values such as 2.2uF. Adding a switch for 16ohm would also greatly increase versitillity.

Here's some shots of the one I've been using. Maybe I should shoot it with some clearcoat before that lettraset wears off!

Did anyone notice if their OT was heating up under high levels of attenuation / volume?

From 18 Watt site: One guy used switched non-polarized electrolytic caps in this configuration. You could dispense with the capacitor switch and just wire a 4.7uf cap straight from + to +Speaker. The "hotplate" inside the Univalve, BiValve is frequency compensated by a 2,2uF cap from input to wiper.


You could adapt it to yours.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Hey, thanks for the diagram. I remember seeing that before and I didn't really *get* it. But I do now.

My OT doesn't heat up when I use it. Maybe VERY slightly. But it could just be radiant heat from the tubes. That's how slight I'm talkin'.

Right now my tubes aren't even heating up! Ohhh, but when they do....... just you wait and see. I'll save that for another post.

Here's a nice 70W version. 12-step attenuation, Auto-Former Design, Frequency response of 20Hz-20kHz. 8 ohm

http://www.radioshack.com/product/index ... 2286101&cp

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

looks like the perfect model to do some tests with!

Very cool thread gang. I am kinda the poster child for hearing damage from low wattage amps. I have two attenuators but Neither is this cheap or simple.

Larry

Coco was telling me that power scaling is a cheaper option. I'm assuming it's more complicated, and might require some major amp surgury.

Best thing about these autotransformers is they are small enough to fit right inside the 18 watt chassis. I thought about drilling a hole and mounting it right inside, but since I don't know enough about noise issues I figured it would be best left as a standalone unit.

Does anyone know if these things could cause noise issues?

The PS is probably cheaper based on parts alone for a DIY, but it is more complicated to build & set up. I expect it would cost double the RS unit to professionally build & install in an amp.

When I get one, I will put it close to the inside as possible and see what noises appear. The nice thing about having an external unit is that it can be used with any amp you want, or you can take it over to your local amp company and show it off!!

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Holy magnetic flux field batman, this RS thing is good. It sounds much better at low volume than other both my mass and my UA. I used the RS attenuator mounted on a custom jig by coco, and clicked on level from off. It was freaking nice. Good bottom end, nice amp tone, pinch harmonix and very nice bass. Best of all there was no grainy skank tone that other attenuators will give you at high levels of gain reduction.

That's Right Robin. Not as elegant as electronic power scaling, but it really seems to do the job. No Muss. No Fuss.

To the Batmobile!!

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

The only thing that I have found so far that is negative is that it does indeed seem to add some distortion some how. I don't know if it is coming from the attenuator or what but it is there and seems like it is adding distortion to the mix. This is most appearant when you are dialing in the cleanest of clean tones. But boy does it sound good for crunch tones.

We'll just have to feed it with a pure sine wave and scope it out then.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Here is a link to an 80 watt speaker volume control. It has a selector switch for 4, 8, & 16 ohms!!!

Airmech has a friend who has two. One is set up to use both channels (it has left and right channels) so that you and a friend can plug in to your own attenuator (80 watts each). The other is set up for 160 watts single channel. They have a slide switch to select the ohm rating you want.
Apparently the off position has a continuous load applied so you will not blow the output transformer. [but check to be sure]

I hear it works great. I tried to get one but shipping to Canada was almost the price so I have to get one sent up by someone else.

http://www.smarthome.com/8262w.html

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps