Using Kalamazoo Model One as a preamp.

[Boy Howdy]

I have a Model One that has lost any hope of originality long ago (for starters the particle board cabinet literally disintegrated on a cross-country move).

I now have just the chassis and associated electronics, which have been the victim of many an experiment over the years. I've configured a base to hold it upright and so the tubes are protected, exposing the electronics to my deviousness.

Okay, enough with the prelims.

I've added a piece of metal to my wooden base to hold the speaker output jack, a master volume and preamp out jack. I often use the Kalamazoo as a booster preamp for larger amps. The master volume and preamp out jack are essential for this, of course.

In order to use the amp this way though it is necessary to remove the power tube (unless I want to use it to power a speaker, which I don't). I would like to add a switch of some sort to make removal of the tube unnecessary. Possibly it could even be part of a switching jack arrangement in conjunction with the preamp out jack.

What would be the best way to disable the power tube without having to remove it? Obviously, I don't want to blow the OT. Can I switch off the heater/filaments, for example? How would I go about that? I'm a bit clueless with this one (Hey, what else is new?).

I'll be offline till Thursday, but will return. Thanks in advance for any help.

[Chuck H]

Why not use the power tube as well??? It's only a three watt amp (maybe five on peaks)! I would just strap a 25W, 10 ohm resistor across the speaker jacks and use a typical "line out" circuit. The kind that is powered at the speaker jack. The "one" will be happy, you'll have more options for the input tonality (clipped or clean), and the output impedance will likely be reduced. Which minimizes loading at the input of the host amp.

The site is currently having a time with downloads. So bear with me. Just put a 25W 10R resistor across the +/- connections for a speaker. Then, from the + terminal, a 1.5k resistor to the #1 lug of a 500 ohm pot. Ground the #3 lug and take the signal from the center (#2) lug. That's it. Now you can run the "one" clean or dirty, enjoy the tonality of the whole amp, and adjust the output to suit whatever your plugging into. Be it a mixing board or another guitar amp.

Hope this helps.

[Mick Bailey]

I have a harp-playing customer with one of these amps and I've done exactly that. Because the 'cabinet' was still intact I mounted the resistor inside a diecast box along with the pot and socket, wired to cut off the internal speaker when a plug is inserted. It barely gets warm, though his amp is largely original and the output is severely limited by the absence of a cathode bypass cap on the EL84.

See also the Garnet Herzog schematic - pretty much the same thing.

[mac dillard]

Give the Firezog a try. I have it on a 5 watt amp that is used as a pre amp. Works pretty good.

Line Out and Attenuator Designs

[Boy Howdy]

Thanks for all the replies!

Yeah, I've been thinking about doing the line out thing for years. I've looked at all of these options. For some reason, I've never actually gotten around to trying it. I think I even have the resistors on hand. No excuses, I guess.

Funny thing though. The other night I was looking at the amp and suddenly it hit me that all I had to do was interrupt the line going to pin 2 on the el-34. And then another realization, I had already done it when I wired up the preamp out jack (which is a switching jack)! BUT, when I tested it, it doesn't completely stop the signal from passing to the el-34. I haven't got that figured out yet.

I think I'm going to have to put a bass control in the amp. It's just too muddy when I crank it. I rarely even use the treble roll off control, I just keep it full up. I'm wondering if can have just a bass control without a treble control at all. Any thoughts? And yes, I realize I could use a concentric pot deally. I may have to give that some thought, even though I hate those things. I'd rather not drill a new hole for a second tone control, but I doubt that it would affect the value much (in any sense) at this point.

[Chuck H]

If you build the dummy load/line out in an aluminum box you can add a bass cut control there. Or you could run the preamp out to an EQ pedal. Or, since you only seem to use the little amp as a preamp, you could modify it to make the tone more to your liking for this purpose.

[Leo_Gnardo]

I think I'm going to have to put a bass control in the amp. It's just too muddy when I crank it. I rarely even use the treble roll off control, I just keep it full up. I'm wondering if can have just a bass control without a treble control at all. Any thoughts? And yes, I realize I could use a concentric pot deally. I may have to give that some thought, even though I hate those things. I'd rather not drill a new hole for a second tone control, but I doubt that it would affect the value much (in any sense) at this point.

EL84 I think you mean... And to cut muddy bass reponse overall you can chisel away at the "usual" places, reduce values of preamp cathode bypass caps, reduce value of interstage caps. Could boost top end by adding a small value cathode bypass cap in output tube circuit, say half a uF up to 2 or 3. I'd encourage you to use the "whole amp", as others have noted it's only a couple of watts, easy to dissipate with a load resistor.

When you get your sound dialed in join the crowd of rockers who have done similar. Randy Bachman and his Garnet "Herzog" - you've heard it on "American Woman", Robin Trower who used a champ-like Selmer to get gut-wrenching overdrive on early Procol Harum albums, John Platania (with Van Morrison) who has used a Champ and Peavey Rage as overdrive boosts, and I'm sure many others. Oh and Lou Reed who claims he linked 13 Marshalls in series to create the industrial accident he called "Metal Machine Music."

[Boy Howdy]

Well, you're just full of ... good ideas, Chuck.

I have a lot to think about here. I do like the idea of the Herzog/Firefly line out and will almost certainly implement it, but I'm also thinking the preamp out could come in handy for some things. No reason I can't have both. I just have to figure out how to configure it, what with the space constraints and all. I almost put the Herzog/Firefly thing in last night, but thought I'd better decide about the preamp out first.

There are times when I use a stage or two from the Kalamazoo in conjunction with a one tube (high voltage) preamp that I built. The one tube alone don't cut it. But with the additional stage or two from the Kalamazoo, it sounds so amazingly good! And the Kalamazoo alone couldn't match that with its one preamp tube. So I either have to accommodate the preamp out or build myself a two tube preamp ... which I've actually started but it may be a thousand years before I get around to finishing it.

[Boy Howdy]

Wow, that's some hellacious history there, Leo!

Yeah, I've done some of what you suggest. And yes, I meant EL-84. .005 - .01 is my preferred coupling cap range, so I probably want to leave that be. But I did add a couple of 1mf caps on the cathodes. I tried bigger, but even a 2mf was too muddy for me. I changed the input resistor to 20k for more highs, and added a treble bypass on the volume control, and on the master volume as well. Still it just gets too muddy when cranked. It's just like with a big amp, you want the bass turned up when playing clean, but then want to cut it way back when cranked. I think I gotta get myself a bass control.

[Leo_Gnardo]

Wow, that's some hellacious history there, Leo!

Yeah, I've done some of what you suggest. And yes, I meant EL-84. .005 - .01 is my preferred coupling cap range, so I probably want to leave that be. But I did add a couple of 1mf caps on the cathodes. I tried bigger, but even a 2mf was too muddy for me.

Thanks Boy Howdy & good experimentation on your part too. I'd try shaving down the coupling cap selection in spite of "favorite values." 0.0022 - 0.001 - heck a lot of Fenders use only a 500 pF to join preamp to power amp & still have plenty of low end. I used to like large values but discovered the advantages of smaller caps in cutting "mud". Your ears will know when it's right. You might have to put in a switch to mute input to the power amp when using preamp line out. As you noticed a little signal leaks through.

If youi haven't already had a look, here's a link to "history of the Herzog"

"Gar" Gillies' HerzogŪ - All Tube Guitar Effect - garnetamps.com - Home of the Garnet™ Amplifier Company

Thanx to LeftyStrat over at our friends The Amp Garage.

[Boy Howdy]

You know, even as I was typing that last thing I was thinking that maybe I should try a smaller coupling cap. Just cause I didn't like a .002 in my Traynor doesn't mean it wouldn't be right in the K.

I'm pretty familiar with the Herzog (though I've never played one). I own a Garnet tube PA head that I modded to make it more guitar friendly (with input from Gar himself). That thing sounds amazing. I have Gar's book too. That book has all kinds of ideas in it. More than I can ever even hope to understand, let alone use.