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Check out this silly vid of me demoing a guitar amp. I cannot play guitar, but demo it to show how the otl works as a guitar amp.
Hopefully I'll get a guitarist to come over for a real demo soon.
http://www.youtube.com/watch?v=3293JPYNOM8
Follow Ups:
Have you seen this?
It also drives 32 ohms, in the form of 4 8" speakers, but I think next time I will use 2 12" units.
I ran the B+ at about 200V and cut the current way back, so the amp is class AB2. The nice thing about that is there are no adjustments needed at all.
What sort of tone stack did you use?
I've also played with AB2, not at any higher voltages, but just to get more from what I got. Without grid drive, each triode puts out about 500mA into 8ohms, a little less the higher impedance I go since then we have more voltage over the load and less over the tube.
With grid drive I've got up to 1A! (That was using a MOSFET as a source follower on the grids, using a 6922 I got about 750mA since the 6922 couldn't supply as much grid current). The high current seems too high for comfort, and since three tubes is loud enough, I figure I'd play it safe.
It's tempting to use grid drive on combos with 4x16ohms in series b/c then I know the tubes always see an easy load. But on a head amp, I never know what load somebody puts on. Not sure the tubes would last long in AB2 into a 4ohm speaker...
Yes I have seen that and find it strange I haven't heard more about it.
Actually I dont find it strange anymore. I tried for a long time to make my amps and combos 100% original looking. I once believed guitarists were like artists where originality is strived for. But most are a conservative bunch of 'monkey see monkey dos' that simply want to look like the classic guitar hero with reliced guitars and classic combos. Musiscians are not performing artists, but merely performing entertainers. Too bad we dont have Zappa around anymore.
So if you make a combo with say 4x10" alnico powered Jensens or Webers and make it look like a Fender Bassman, I bet you'll get their attention.
I believe a 12" is the optimum speaker for guitar b/c you want the cone to break up. For a change I want to try 10" drivers in my next combo, a 'Bassman killer' and will use alnico types with small voice coils.
My OTLs are very dynamic (little compression) and a alnico magnet has some compression. So guitar speakers with alnico magnets are a good match, at least in my amps.
I use a simple bandaxal type tonestack, two controls, bass and treble.
I find most guitarists want a simple layout b/c they end up using pedals for their main sound. Again b/c they are dependent on sounding like each other. It's amazing the pedals I see in front of great amps like Matchless, DrZ, Vintage Fenders, and such. They end up using that green overdrive box (loaded with solid state chips), the funky looking fuzz box, some run of the mill sustainer, echoes, hoopla this and that.
It's strange how they can be crazy about the amps tone and how wonderfully it breaks up etc, and still they put this stuff in their signal chain.
I sound negative now, I actually do see the point. Effects are great tools and they are a necessary part of electric guitar. But it makes all those late nights spending hours and hours finding the right tone seem kinda a waste.
Me frustrated? Well, I keep making guitar amps, so I can't hide the fact that it is fun, and I do get a kick out of seeing my amps being used on stage.
Wow, I really am not the diplomat am I? I actually respect guitarists and musicians above most others and even within the little click of guitarists I know all of them are genuine artists.
I meant to drive home the fact about the image factor, and how looks can at times seem more important than anything else.
Ralph: Do you have clips of your otlcombo?
... comparable powered OPT amp. Is this typical of OTL amps? What kinda speakers are you using?
Thanks!
hmmm...well; the OTLs are very wideband since the transformer acts like a bandpass filter and cuts both low and high end. But guitars are really not that wideband, and even the cheapest output transformer will have bandwidth enough.
but I have actually placed a small capacitor over the driver stage's gain section to limit the high end. I found it too bright when the output tubes started crunching. Then again I often do that to my vintage type amps (the amps with OPTs) as well.
I use Jensen P12Q in 16ohm version. I want to find some louder type of speaker though, and plan to try out Weber for my next project.
I also have some Jensen NEO12 (16ohm) and they are much louder. I actually like them better, but they dont compress as much. I guess for jazz and metal that is ok, but for blues and classic rock the P12Q is probably better.
Not something one normally hears with, say, a 8-watt single ended amp that has a tiny OPT. Kinda nice to hear a low output amp with this kinda "headroom." And not the compression and saturation one hears with usual Champ-type amps.
Yes indeed the 'bite' is a good thing. The best advice I once got regarding the tone of an amp was: 'make it so bright it hurts'. However, sometimes the bite can sting a bit too much, and the art is finding just how much bite is good, and when it's too much. Thats where the high-end limiting comes in.
The OTLs are very dynamic, even the smallest, and it sure is nice to have an amp that follows your touch. Gently touch the strings, and the sound is soft, hit them hard and the volume really gets you. The dynamic range of instruments is pretty awesome. I've measured a few mV of signal when barely stroking the strings, and over 2volts when hitting them hard. (Using my O-scope at the guitar output). Typical pentode amps compress in a nice way to even out the dynamics a bit, and that has become the norm. A more dynamic amp allows you to play it more, but also lets all 'faults' come thru. A great way to explore both worlds is to use a good compressor that you switch in or out.
An amp that already compresses, will never be more dynamic than that, but a dynamic amp can be used with a compressor and allows wide range of dynamic to compressed sounds.
It might be good to have this option. Helps cut through bass/drums "mud." Then one could "tame" the beast a bit be twirling knobs and changing pickups & fingering techniques. But, you have the edge when you need it.
Sorta, the Telecaster approach to things.
8^)
The Telecaster separates the men from the boys.............. slop sounds like slop with that instrument.................Hello Roy Buchanan!
The Mind has No Firewall~ U.S. Army War College.
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