MagnaTone? Anyone?

[The Ballzz]

Hey Folks,

Just spit ballin' here. I've become enamored with the concept of the Magnatone stereo amps with selectable frequency/amplitude modulation. These would be the "Twilighter Stereo" at 22 watts per side and the "Panoramic Stereo" at 12 watts per side. I'm thinking that in today's "volume limited" venues, even a stereo 12 watt amp may be a bit too loud to get away with. Does anyone here have much experience with these types of circuits? If so, how difficult are they to get right?

I'm thinking it would be very cool to develop a similar amp, but instead utilize two single ended (6V6 or 6L6) power amps. Of course I'm not sure if the actual Magnatone circuits are dependent upon the "push/pull" design of each ouput section for their effective tremolo/vibrato? I'd also like to think about incorporating a stereo return effects loop, for "echo junkies" like me.

Any Experience/Thoughts Around Here?
Gene

[R.G.]

Let's start with the disclaimer: I'm not familiar with those particular models. I could get familiar with them if you will post a link to the schematics.

I have looked at some Magnatones. The modulation was done by varying the voltage across varistors, varying their resistance, and using that as part of a modulated all-pass filter - a phaser stage. Don't know about those particular models, but...

[TUBEDUDE]

You had me at stereo effects return for echo junkies.. I'm in.

[R.G.]

If I found the right schematic, the Twilighter uses a one-stage allpass/phaser stage, not bias modulation.

[TUBEDUDE]

Is it like the M15 circuit, or something newer?

[didit]

If I found the right schematic, the Twilighter uses a one-stage allpass/phaser stage, not bias modulation.

Curious which schematic you referenced. The Magnatone "memorial" site describes it as switchable from phaser to what is likely bias modulation --

https://www.magnatoneusa.com/panoramic-stereo

Best .. Ian

[R.G.]

They do, don't they? I didn't see "bias" describing the tremolo, though.

I'll go look it up again. If it's bias tremolo, it will be obvious.

[R.G.]

I'm having real problems finding it again. The simple search for Magnatone Panoramic Stereo Schematic turns up only the rising tide of suckerbait web sites, and any images that turn up are either to suckerbait sites or Magnatone.com, and I can't get to the actual schematic.

So... give me a link to the schematic you're talking about, or better yet, put it some place I can get a look at it. The inspection isn't all that difficult.

[trobbins]

There is a Panoramic 1210 schematic with stereo input socket, but it only has one output stage - same for the 450, 460, M9, and M10A.

Th 280A and 480 have two input channels through to 2 output stages.

[didit]

So... give me a link to the schematic you're talking about, or better yet, put it some place I can get a look at it. The inspection isn't all that difficult.

I'd no luck either, which is why the ask to post to yours -- so will poke around more.

Best .. Ian

[didit]

Hello -

After another fruitless 20 minutes or so I give up. Suspect it's just alternate-universe contemporary "memorial" confection. Suggest it's in the spirit of 480 - https://www.magnatoneamps.com/schematic ... ne_480.pdf, perhaps with idea cribbed from https://www.magnatoneamps.com/schematic ... one_M2.pdf.

Best .. Ian

[R.G.]

For those two schematics, the 480 looks like just the allpass phaser style. I can't find any path from the oscillator to a tube that would do bias-modulation. The oscillator seems to only wind up on the phase inverters that run the varistor phase shift stages.

On the M2... maybe. The LFO oscillator does twiddle the bias conditions on the tube section that feeds the two varistors out of phase, I think that it's set up so that all of that wobbling happens well into the linear operation range of the plate curves, but some of it might traverse into the variable gain region. So that one might have some amplitude modulation as well as phase modulation. In this one, the designers seem to have economized on the usual varistor phase shift stage, possibly for lower tube count. I think in this variant of varistor wobbling, there might be some amplitude modulation as well as phase shifting. It would probably depend on the DC bias point, and serves as a counter example to my blithe "oh, I can easily tell by a look at the schematic" statement.

[didit]

Hmmm -

Check out 2nd page M2 schematic for modernized tidyness including optional switched-to bias wiggler, added by Steve Luckey when crafted modern tidyness.

Best .. Ian

[TUBEDUDE]

So Gene,
We're you thinking of keeping the reverb circuit? If we can cobble a schematic up, I'll likely save a tube and pass on the reverb. I like my Avalanche Run or Afterneath better than sproings. Not a surf fan and the extra tube will come in handy with a stereo efx loop being added.
Has anyone found a suitable opto for the Vibrato circuit?

[trobbins]

Opto ? Or did you mean varistor?