Jim Kelley Attenuator

[Runaway J]

Jim Kelley now sells his attenuator again and has soundclips on his page.

http://www.jimkelleyamplifiers.com/JimK ... atorMK.htm

(Scroll down to the links).

I’m really impressed, so I thought maybe this could be interesting for folks here.

Gut shots anyone ?

[paulster]

There's definitely an attenuator renaissance going on right now.

I wonder how this compares with the leading bunch (Alex, Aracom, Faustine).

[David Root]

I didn't know he was back in business. Some classic stuff in there, including two of the three schematics I had not seen before.

Interesting that he recommended Sylvania 6V6GTAs about the same time Dumble was specifying Sylvania 6L6GCs in his amps. Probably for the same reason, flat, clean, extended response.

[jaysg]

I think he's hit retirement and is a bit bored. All the better for musicians.

[Reeltarded]

I should have bought all the FACS amps they were throwing away at GIT when I left

[Dr-Joned]

"throwing away" ????????????

Why would anyone in their right mind throw away a tube amp?

[Runaway J]

Bump.
I'd like to know a bit more about the JK attenuator. The sound examples on his page are impressive IMO.
Jim states that it's just a standard L-pad design, using two 100W ohmite rheostats.
Does anyone here have a gutshot or a schematic or can tell the values of the rheos ?

[selloutrr]

Seems pricey for 100watts max power.
I'd worry about burning it up using it with a true 100 watt amp - usually the ones I want to tame the volume on.

since the device only offers 1 knob yet two rheostats are operating. I assume it uses a dual stacked rheostat?

i.e. - i know the example is only 50watts per but it shows the stacked rheostats.

http://cgi.ebay.com/OHMITE-DUAL-20-20-O ... 5ad5b9b568

You would need to do the L-pad calculations to determine the value of the rheostats. you already know they are 100watt per, wirewound, and made by ohmite. from here it's just sourcing the correct part, or closest match based on a product catalog.

the product page almost tells you how to build.

[selloutrr]

http://www.sengpielaudio.com/calculator-Lpad.htm

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

http://www.diyaudioandvideo.com/Calculator/LPad/

[Runaway J]

Thanks for answering selloutrr,
what makes me wonder is that when I do the calculation I get special combinations of resistor values for each step of attenuation,
but those rheostats are linear taper and when staggered would never exactly match that values. Should only result in a tolerable
impedance mismatch though (and maybe in an uneven pot scale).
Think I should go for 8 Ohm R1 and 25 Ohm R2 ?
More info appreciated.

[vibratoking]

All of the resistive designs that I have seen on the market result in an impedance mismatch. It is a VERY costly and cumbersome design that results in zero mismatch at all settings. It gets even worse if you start to consider reactive designs that mimic the impedance of an actual speaker. I wouldn't recommend going down this path. I have and concluded that the results were not desirable. VVR

[selloutrr]

if you look at the face plate silk screening the numbers do not line up in exact spacing. That is how he gets around the majority of the miss matching, But yes - it will almost always be mismatched, though your speaker impedance will also shift... so it's not really a battle you can win.

I guess someone could create a digital Attenuator that reads the speakers actual impedance and auto adjust to give the correct load, but the price would put it in the hi fi market.

If you want to mimic the speaker - weber sells "motors" that are basically a speaker minus the speaker.

[paulster]

Or you could pay the money and get a Phantom, an Alex, an Aracom or the new Rivera Rockcrusher.

All in a different league from attenuators we've seen before.

[selloutrr]

IMHO even those have flaw's... and not just the $1K price tag

I've demo'd the Rivera it's 8ohm / 16ohm is a lot more limiting then it sounds. hopefully the mass production sounds better, but when I dimed it was not as smooth as the ultimate attenuator. I ended up pulling all attenuation and loading the room and using and SPL meter to place the microphone.

These companies market them as a studio piece of gear???

The best part of a real studio is not having to choke back an amp the room is tuned and being able to capture the natural breathing of the room as you tune up the amp... it is gold.

Use any of those with a well tuned Orange or Hiwatt that's dimed and it's a door stop, or at least on the tech bench getting rebuilt.

Wattage is very limiting.

With the advances of PA systems - stage volume is no longer needed/wanted. They do have a use but again it's live so most of the suddle sweetness is lost in the crowd and bleeding drums... or the lead singer's monitor.

What needs to happen is a product for the cost of a foot pedal ($200) that handles 200watts and gives 2-4-8-16 in and out - mix and match.

[Amberden]

personally its all a huge waste of money.

all you want is to lower output volume so you can drive the tubes harder and get that epic power tube tone.

some of them have little tweaks like boost to bass or treble but even that is a gimmick that can be fond in what I'll share with you.

go to google search, press on "shopping" and type in "wall mono volume control" omg power attenuators for $20.

you can find these for up to 1000 watts and most are auto impedance protection meaning they will match the impedance with out worry of having to switch it. some have treble or bass boost too.

why would you shell out near $500 for a rock crusher? its seriously nothing new and is 16x over priced.