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Re: Let's do something fun

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4/10/1998 12:27 PM
Don Symes	Re: Let's do something fun What about a full amp, with 12AX7 output tubes? <2 watts output, but pre-clip and/or power-clip.

4/16/1998 4:27 AM

What about a full amp, with 12AX7 output tubes? <2 watts output, but pre-clip and/or power-clip.

Because this should be a SS circuit. Have you guys actually tried any of those tube amp emulating solid state amps? I've tried Roland's Bluescube, and it was definitely more tube-like than a Marshall's Valvestate. It had even a switch for diode/tube power supply emulation. The sound was more convincing when cranked, I couldn't get good smooth bluesy overdrive from it. Another excellent amp which sounded exactly like a tube amp even with clean tone was a german manufactured Rath-Amp (model Retro 50/115+, see http://www.solton.com/rathamp.htm). They have some tube-amp & speaker simulators, too,worth looking into if you ever happend to find a one.

-Mikko

4/16/1998 10:10 AM
R.G.	That's actually one of the things in my to-do queue. I have conceptual plans to combine my two-tube, two channel preamp with a 12AT7 power amp with a reverb driver transformer. It all fits in a 1 rack-unit cabinet, probably about 1-2 Watts at maximum warp.

4/16/1998 10:53 AM

All right, R.G., here's my latest Krazy Idea
(I found a cheapo tube receiver chassis with a good power transformer, some tube sockets, and a pair of small OP transformers) :

I want to build the Fender two-band tremolo preamp circuit and send the output to a pair of 12AT7 outputs in stereo. (I have to see if there is a way to tap into each band seperately - I do NOT understand how this circuit works terribly well, basically I am lost past the oscillator.)

Whaddaya think?

-j

4/16/1998 12:45 PM

It's a GREAT idea. I have this list of fun stuff to do that I can't even write down fast enough. I always wanted to do the Concert tremolo (I think that's the two band job) as a standalone, but using two small power amps is as good, even better if you drive two separated speakers.

What the circuit does is provide out-of-phase LFO outputs to two bias-voltage type amplitude modulators, the two sections of a tube. The highs are split from the lows with an RC high/low pass crossover and one of each routed to the two modulators. The outputs are summed back together. The summing cancels out the two out-of-phase LFO signals, and leaves the alternately tremolo'ed highs and lows. It started as a trick to get rid of LFO thump, but sounds a bit like a phaser.

4/17/1998 8:22 AM

>The Concert tremolo<

In the Weber book it shows up in the Twin and the Bandmaster, G*-A schematic numbers. It maybe in the same series Concert as well - I'm not sure I checked that section of the book.

>The summing cancels out the two out-of-phase LFO signals<

So if I was to tap into these signals prior to the mixing point, would I have an oscillation superimposed on each output? Could I filter this out with intentionally poor LF response, a too-small value cathode bypass cap perhaps? (Way too small on the high band, a little too small on the lows, maybe.)

I guess another approach might be wet out one channel and dry out the other for stereo?

Sounds like Step One : Build As Drawn!

-j

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