Dual Channel Amp: Primer?

[Decko]

Just My two cents since I have been there and done that. The amp you want to build is not as easy as it seems. The Rocket and the Express have two preamps that when the signal hits the PI is 180 degrees out of phase. So combining them before the preamp would require a mixer stage or at least another inverter stage before the PI. Or you could insert each pream on oposite grids of the PI like a 18watt marshall. Only problem there is that the Express uses a Presence control whis is fed off ta negative feedback circuit. Problem here is that if you set your switching up so that only one preamp at a time is supplying the PI when you switch to the Rocket channel you will now have positive feedback which wouldn'd be good. The Rocket also has a Hi Cut control after the PI. You could leave this in for both channels but I didn'tersonally care for the HI cut on an Express Pream. There are other problems too like different resistor values on the PI tail for both the rcket and the Express so you will need to either switch those or settle for a happy median.

Here is a link to my project from a few years ago

https://tubeamparchive.com/viewtopic.ph ... ht=pegasus

Hi Dana, thanks for chiming in. I see a lot went into your design. That said I want to build it!

Decko

[LeftyStrat]

I haven't tried this, but I think it is worth investigating. Build a rocket, but take the unused triode (which is a travesty, btw) and switch it in and out with a relay, and do the third stage of the liverpool, with associated high pass filtering in front, i.e. cold biased, no cathode cap.

Now it's not going to be exactly like a liverpool, since the liverpool has NFB and the rocket doesn't, and the rocket has a tube rectifier and the liverpool doesn't.

You might be able to compensate by dumping the tube rectifier, and upping the filtering, to get tighter bottom with the lack of negative feedback. Perhaps some sort of compromise of the two power amps would get you into the right territory.

Which sort of explains Ken's philosophy (in an opposite sort of way). He built one purpose amps, so as not to have to compromise on the tone. Perhaps the ultimate recording amps, not so much for the gigging musician (unless you're willing to carry a couple of amps. And if you want post distortion fx, dummy loads and even another amp).

IMHO:

Versatile = Compromise

Obviously, it is possible to strike nice a balance, as HAD did. But it's the classic "Jack of all trades, master of none."

I've played quite a few of the three channel, Fender, Marshall, High Gain amps, and they give a reasonable approximation of a Fender and Marshall, but they're not a real Fender or Marshall.

But it's always up to the player. Certainly compromise is lighter

[Richie]

But Dana's amp when channels are switched change the feedback, or lifts it depending on what channel your using. So it not only switches channels, it switches circuits in the amp too.

[LeftyStrat]

But Dana's amp when channels are switched change the feedback, or lifts it depending on what channel your using. So it not only switches channels, it switches circuits in the amp too.

Oops, sorry, missed that.