Jim Kelley Attenuator

[Alexo]

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

Not to speak ill of one who's passed, but those don't really cut the mustard either, jmho.

There are other ways to skin a cat. VVR, or even a hardwired switch to lower power taps on the PT or switch in some high wattage zeners. ...but of course these are no good for those who don't build or mod their own amps.

[paulster]

I would surmise that you've never compared an L-Pad to one of the new generation of attenuators!

Believe me, I wouldn't have shelled out the money for a Phantom if it didn't live up to the claims. I've had L-pads and all sorts before but this is a whole new ball game. And as I build amps rather than buy them I could have built something for myself, but it was going to be cheaper to buy the Phantom than to have the custom metalwork and everything done it would have taken to build an equivalent quality of product, so in this case it was cost-effective.

It means that my 100 watters are genuinely usable at home and sound the same as when fully cranked, and this holds true for all my amps.

And, for me, that's the key - sounding the same at the reduced volume, not having to dial in the amps differently so that when you get to open them up you've it doesn't sound anything like you were expecting.

[vibratoking]

I can buy and install alot of VVRs for a thousand bucks. And I can then use them together in a multi amp setup. With the attenuators, I basically multiply the number of amps I want to use by the cost of each attenuator. The sound is better and the investment is much less.

[paulster]

I can buy and install alot of VVRs for a thousand bucks. And I can then use them together in a multi amp setup. With the attenuators, I basically multiply the number of amps I want to use by the cost of each attenuator.

All true, but VVR isn't a universal panacea either, needs to be beefed up to work in a 100W amp because the MOSFET's going to have to dissipate a massive amount of heat, particularly at -6dB. And you're unlikely to want to retro-fit it to anything vintage for fear of affecting its value.

The sound is better and the investment is much less.

I'm going to wholeheartedly disagree on the sound front. If you've got a circuit that has power supply compression caused by the limitations of the power transformer regulation (and we know that most have pretty poor regulation because the original specifications were all about making them cheap) then you'll lose this part of the equation as you turn down the volume.

Now, whether the tonal alteration of any given attenuator is more or less significant than this is open to debate, but VVR is not completely transparent as it can't defy basic electronic theory.

Don't get me wrong; I like VVR. But I also appreciate its practical limitations. And if these limitations didn't exist every manufacturer would be putting it in their products to get round the problem of wanting 'that tone' at all volumes.

[statorvane]

I have to say the Phantom attenuator clips sound really good. Slight tone shift, but nothing beyond a seemingly reasonable tweak of a tone pot. The cost of admission is however prohibitive for me.

IMHO, the attenuator, VVR / power scaling, Mojave-like limiter, and LarMar PPIMV all provide some degree of volume reduction coupled with a progressive tone shift. However, I have yet to find a sure-fire method of:

- power attenuation
- voltage reduction
- PI bias adjustment
- master volume / grid leak adjuster

that will provide a reasonable palm-mute thump at low volume, like a JMP50 / JCM800 cranked through a 4 x 12" cab. Besides the sound generally getting raspy at the lower volumes, the palm-mute "thump" gets lost really quick. I was thinking this just may not be possible.

OTOH, my old SS audio amp has a loudness switch. At lower volumes the human ear isn't as responsive to low freq, as it is at higher volume, so the various audio companies added this "loudness" button that would boost the low freqs. Anybody know how that is done? I think it could be useful to sort of bring back the palm-mute thump at lower volumes for a guitar amplifier - that's what I really miss at low volumes.

[Runaway J]

Hi guys,
thanks for your opinions.
I'm sure that VVR has it's advantages and there are lots of nice attanuators on the market. But ... did you listen to JK's recordings ?
OK, it's hard to compare, but from what i've seen and heard on youtube the JK-attenuator is better than most of that stuff + it is switchable.
If I could achieve similar results with a homebrew L-pad (the most simple designs of all), I'd be absolutely fine.
I'd love to buy the original from Jim, but 449 $ is a bit over my limit.
Any further info appreciated.

Cheers, Juergen

[selloutrr]

you could easily make a few switchable presets using adjustable resistors
i.e. -3 -6 -9 -12db using an output impedance switch.

You can use the L-Pad calculator to figure out the correct Ohm's

Make sure you give it plenty of air flow to help with heat above and below the chassis they get hot enough to melt tolex.

It would be very easy to make a bypass switch.

[vibratoking]

I'm going to wholeheartedly disagree on the sound front. If you've got a circuit that has power supply compression caused by the limitations of the power transformer regulation (and we know that most have pretty poor regulation because the original specifications were all about making them cheap) then you'll lose this part of the equation as you turn down the volume.

Now, whether the tonal alteration of any given attenuator is more or less significant than this is open to debate, but VVR is not completely transparent as it can't defy basic electronic theory.

I agree that there are drawbacks with every type of attenuation. I've tried several types of attenuation on a 5E3 and Express. The tone of both circuits is influenced by power supply sag, but VVR is the best solution that I have heard for both.

I'm sure that VVR has it's advantages and there are lots of nice attanuators on the market. But ... did you listen to JK's recordings ?

I listened to the recordings. Have you tried JK's attenuator in-person with a real guitar and amp? When and if you do, I suspect that you will no longer be as impressed by the recording. This has been my experience, FWIW.

[Runaway J]

I listened to the recordings. Have you tried JK's attenuator in-person with a real guitar and amp? When and if you do, I suspect that you will no longer be as impressed by the recording. This has been my experience, FWIW.[/quote]

Never had a chance to try one. That's why I'm asking stupid questions here.
I've got nothing against VVR at all and if you're telling from first hand experience that VVR is the way to go, I appreciate the info and may give it a try.
Thanks vibratoking.

[d95err]

OTOH, my old SS audio amp has a loudness switch. At lower volumes the human ear isn't as responsive to low freq, as it is at higher volume, so the various audio companies added this "loudness" button that would boost the low freqs. Anybody know how that is done? I think it could be useful to sort of bring back the palm-mute thump at lower volumes for a guitar amplifier - that's what I really miss at low volumes.

The loudness feature is usually just a shelving lowpass filter that reduces mid and treble a bit. Sometimes more advanced filters are used to decrease just the mid range. Some solutions use a tapped pot to cause a gradual "loudness" increase as the volume is turned down.

It should be possible to add a similar shelving lowpass filter to a simple attenuator. It's just a matter of finding the right R/C combo and inserting it paralell to the attenuator.

[d95err]

I think in general, people seem to approach the amp volume reduction problem from the wrong end. They start out with the amp at full volume and then compare it to the tone with the volume turned down (using an attenuator/powerscsaling/master volume). This kind of comparison is usually pointless.

What you need to do is to start out with the volume limit. What volume is appropriate for this club/bar/outdoor stage/rehershal room/studio? What volume can I use while keeping my hearing safe?

Then ask yourself - how can I achieve the best possible tone at that volume level? Is it using an attenuator? Powerscaling? Master volume turned down? Smaller amp? Smaller speaker? It is pointless to compare with anything louder, because you can't use it.

[paulster]

I think in general, people seem to approach the amp volume reduction problem from the wrong end. They start out with the amp at full volume and then compare it to the tone with the volume turned down (using an attenuator/powerscsaling/master volume). This kind of comparison is usually pointless.

What you need to do is to start out with the volume limit. What volume is appropriate for this club/bar/outdoor stage/rehershal room/studio? What volume can I use while keeping my hearing safe?

Then ask yourself - how can I achieve the best possible tone at that volume level? Is it using an attenuator? Powerscaling? Master volume turned down? Smaller amp? Smaller speaker? It is pointless to compare with anything louder, because you can't use it.

I'm going to mostly agree with you.

It's very rare that I've had the chance to run my 100W amps flat out, or een my 50W amps for that matter, but other NMV amps like the Express/Liverpool/Rocket you do get the opportunity to use unattenuated sometimes, so these comparisons are valid in certain circumstances.

And that's why I chose an attenuator that has absolutely minimal effect on tone.

It's almost irrelevant what it does to the big amps because they won't be used unattenuated and so you will dial them in attenuated for tone, but smaller amps this argument doesn't apply to. IMO.

[selloutrr]

I guess i'm using the attenuators the wrong way... I've never been in a position where while I'm playing I've used an attenuator and then turned it off giving the amp full power. If I have a need to use a means of volume control it's for a reason so I'm sure not going to run the amp with it out of the circuit.

Like pointed out - you dial the tone of the amp for the application which usually removes any concern of tone sucking since the amp is voiced with the attenuation already injected into the circuit.

From a mixing stand point it would be a nightmare to level match a guitarist switching the attenuator on and off all night live or in the studio. as soon as you get a sweet stop the switch would get pushed and you would loose the mix. the guitar would over power the vocals or get lost in the back ground. both are not exceptable = major limiting compression and sucking any last bit of dynamics out of the performance to ensure a stable presentation of the music - Talk about tone sucking!

If you wanted to have a volume increase / decrease during a performance use your guitars volume knob - It's easy and you already paid for it when you bought the guitar.

I'll be the first to say I like to run an amp wide open.. But I'm not sure how much the actual output tube compression adds to most amps tone. my reason is more for how the microphone reacts to the full signal strength and the combination of natural tube compression (mainly preamp) and loading the room along with the microphone running at the optimal lowest noise floor makes for a very large in your face, clean, 3 dimensional performance that needs little to no compression from the outboard gear.

If you are any good at listening to your amp and dial it in for "it's" sweet spot. ( keep in mind you can't make an amp do something it can't i.e. fender champ isn't going to give you 80's solid state metal ) You can get just as great of a tone out of a Power Soak or Marshall Powerbrake as any of these $$$ botique units. The best tool is your ear.

I feel like the quest for pure tone or non tone sucking gear is an excuse for people who brick walled and need an excuse for not playing as good as they could be. Great players make great tone, even on not so great gear.

[drz400]

I listened to the recordings. Have you tried JK's attenuator in-person with a real guitar and amp? When and if you do, I suspect that you will no longer be as impressed by the recording. This has been my experience, FWIW.

The JK attenuater actually sounds very good, I have heard the Faustine which I ordered and the JK. The JK is great for knocking off some volume and balancing the second channel in his FACS amp which is what the intention was. Just not as good at Bedroom volumes as the Faustine. Plus the Faustine recording out is very nice. There is a significant cost difference though and yes the JK does sound like his clips. I also like VVR or Power scaling but it is very different and really isn't the same.

[awardsjake]

Hi Guys,
I played on those clips for Jim on his web site. I've been using these since back in the 80's on Jim's FACS amps. I used to run a pair in stereo....those were the days. When he started making them to work on other tube amps I got the prototype and played it with a JCM 800,
the 50 watt JMP bass amp on the clips, a bunch of Fenders, and a Divided by 13 FRT37. This is the real deal. He made a few adjustments before putting them out and those clips are legit. There were no tricks done...just the raw tracks. The only amp that seemed to not like the attenuator was the FTR37. It lost some high end where the others very
unscathed. I think (guessing a little) that the problem with the attenuator and the FTR37 had to do with the amp having no negative feedback.
Other than that it's a beautiful safe piece of gear. As a lot of you know
the FACS amps were very hard on tubes. Using Kelley amps and
attenuators for over 25 years, I've never thrown a tube.
Best wishes,
Jake Hill
jakeh@tustinawards.com