2 tube micro head

[tedmich]

well I know I'm getting old but that sounded horrible to me.

[PeanutNore]

I swapped the PT and the plate voltage is now 285 and it sounds so much better, and it's a whole lot louder than it was this morning, with a lot more bass. I think I'm done tinkering around inside this thing for a while. I'm really surprised at how good it sounds and I don't want to mess it up. Before I screwed the bottom plate back on though I did take a few minutes to plot out what I actually built, so I can share the schematic. B+1 tests at 285v and B+2 at 233.

I have a few solid state pedal ideas that I need to experiment with before I build anymore amps but damn it's fun. I think I got bit by the bug.

Just noticed the schematic is missing a .022uF cap on the input jack to block any DC from effects or what not.

[Chuck H]

well I know I'm getting old but that sounded horrible to me.

I still identify with contemporary metal... Some. But less and less every year. I gave a like on that basis. I think the playing is right but the tone is wrong. Modern metal tones all seem to be blatty and exceedingly low in dynamics, favoring harmonics. IMHO high gain tone peaked with the SLO/Dual recto/5150 type amps. Taking it further than that hasn't really done much for me.

I recently demoed one of my amps for a metal guy. This model could be compared to a Trainwreck Liverpool/Express for gain and I had it cranked through a 2x12 sealed cab. The guy said "Sounds great for what it is. Let me know if you ever build a high gain amp." No $h!t!?! I went straight home to change my Grampers, had some prune juice and took a nap. I'm clearly a dinosaur.

[Gregg]

I've played with those low power amps and subminuature tubes a lot and my general impression is there was always something missing. Using a dual preamp triode as power amp is possible but it's just not it. Most guitar amps are class AB push pull pentodes or tetrodes so if you're going to simulate a big amp you should try to stick closer to the original concept because class A triode amp doesn't sound anywhere near. For me these amps are nice toys but nothing more.

[PeanutNore]

It's triodes, but it is push pull and should be class AB most of the time. They aren't going to sound like pentodes but it is going to display the characteristic harmonic cancellation of push pull that single ended amps are missing. You might be thinking of those designs that use a fender reverb driver transformer as an OT with parallel single ended triodes.

[Gregg]

They aren't going to sound like pentodes but it is going to display the characteristic harmonic cancellation of push pull that single ended amps are missing.

That's in theory and in Hi-Fi... Depending on the type of music you play you might not want to cancel even harmonics content completely.

You might be thinking of those designs that use a fender reverb driver transformer as an OT with parallel single ended triodes.

These sounded worst of all I tried. That OT produces a rather dull and thin sound but that's normal because it was intended for other purposes.

[g1]

it is going to display the characteristic harmonic cancellation of push pull that single ended amps are missing.

Depending on the type of music you play you might not want to cancel even harmonics content completely.

It would be interesting to see how a dual triode of dissimilar types (ex.12DW7) would affect this.

[Gregg]

You don't need to go that far - if you change one of the PI resistors in value up or down you'll get plenty of even harmonics.
I don't remember testing a PP amp that didn't have second harmonic content. Sometimes it's less than the 3d one sometimes more but it's always there so cancelling the even harmonics sounds good only in theory and in Hi-Fi where you'll need special extra measures to prevent that from happening. In guitar amps just forget about it and even if it happens by accident most probably you're not going to like it.

[PeanutNore]

Here's a quick demo I made messing around with a fuzz pedal. I clipped the .0022uF cap between the plates from the Firefly design because I couldn't figure out what it would be doing other than cutting treble and the amp sounds a lot better now.

youtube link

[Chuck H]

I can honestly say that it sounds like a loud amp, but less loud

[leadfootdriver]

well I know I'm getting old but that sounded horrible to me.

LOL It's a metal mix. I think the raw tone from 2:00-2:15 is pretty good. Even still you could EQ it to your liking. That's the caveat with any recording because mic placement, mic type, EQ, the guys ears doing the mix blah blah... all influence the final product. That said, I think the basic tone in that 15 seconds is pretty good for a little 12AU7.