Stereo Ampifier?

[ViperDoc]

Can you give me an example of a TRUE STEREO guitar amplifier? Seems most are dual mono. Not an earth-shattering contemplation, but I have an idea bouncing around. Can you feed a speaker a half-wave signal?

[martin manning]

Magnatone 480? https://ampgarage.com/forum/viewtopic.p ... 45#p232545

[Stevem]

If your thinking of feeding two different speakers a true 1/2 of a sine wave then I think you will end up with the worlds worst case of crossover distortion .

Another concern is that for any amount of speakers I think you will end up with only 1/2 of the SPL that could have otherwise been had.

Along these same lines it would seem to me that the output state be it tube or SS will need to be sized twice as large to produce a given amount of wattage.

[didit]

Helo --

Gibson built stereo guitars, and to accompany also made the GA-83S Stereo-Vib and the GA-79RVT. Magnatone after the 480 etc., also built the M14, M15 and M15a in the mid '60s.

Curious, like others here, what you meant by "feed a speaker a half-wave signal".

Best .. Ian

[ViperDoc]

Curious, like others here, what you meant by "feed a speaker a half-wave signal".

Best .. Ian

I wondered if you could run two SE output transformers, with each power tube being fed by one plate of a phase inverter.

[cdemike]

Curious, like others here, what you meant by "feed a speaker a half-wave signal".

Best .. Ian

I wondered if you could run two SE output transformers, with each power tube being fed by one plate of a phase inverter.

Would the design goal be to simplify a stereo build by using the PI as a mixer? If so, I wonder if it'd be easier to use a common anode mixer ahead of the PI (depends what the broader design goals are -- in either case, it'd be really difficult to have meaningful dynamic differences between the sides if sharing a PI if you're planning on something with dramatically different input signals like a wet/dry rig or two separate players running into the same amp).

I built a two-in-one amp that has two completely separate preamps and power amps so that my wife and I would only need to bring the one head and one stereo-capable 2x12 to gigs. Each output section is an ECC99 running PP into separate OTs. One preamp is a Brown Princeton sans tremolo and the other is a top-boost channel of an AC15: https://ampgarage.com/forum/viewtopic.php?f=6&t=36398

I suppose in a sense that amp isn't stereo in the hi-fi sense of the word since the channels are voiced differently, but it'd be easy to make a version that has identical preamps. While that thread had a happy ending, I'm actually tearing that amp down sometime soon to redo grounding thanks to a 60hz hum that's only present on the Vox channel. I suspect there's a ground loop since I used un-insulated Switchcraft input jacks, so I'll be switching to Cliff jacks (would use insulating washers but I need to cannibalize the Switchcrafts for a pedal project where Cliff jacks are too big), but I suspect I'll need to eventually switch to a dual-star system (binary star? ). I mention it because it seems to me that, if one of the design goals is true separation of the channels, i.e., truly stereo operation, then I think reasonable separation of B+ rails, grounding, and output sections is important. That also likely means at least 2 speakers if any amount of speaker breakup is desired.

Obviously mine is not a commercial design. If you're looking for a commercial design, those Gibsons didt mentioned were my inspiration for the parallel output sections and will likely be the basis for the anticipated grounding rework.

Maybe it's because planning out an attenuator build, but it occurred to me that it'd be possible to build a truly stereo amp that only runs into one speaker using a built-in reamping device with each of the parallel output sections feeding load boxes, then sending each line-level signal to a mixer, and ultimately to a power section. In other words, something like:
Preamp > PI > Power tubes > OT > Load box | > Mixer > Reamping device > Speaker
Preamp > PI > Power tubes > OT > Load box |

That'd work fine with most setups where each channel is expected to see similar magnitudes of signal (e.g. each receiving the stereo out of an ES-345-type guitar), but for something like a wet-dry rig where better separation is desired I imagine you'd want the reamping portion and speaker to have such high headroom that the input signal cannot distort it (something like a SS class D output section driving an EVM12L).

Edit: fixed formatting issue on first draft of my pigeon block diagram.

[ViperDoc]

My understanding is a stereo signal required two outputs, one for "right" and one for "left". A single speaker cannot, by definition, deliver a stereo image. The half wave feed to a speaker seems impossible. Perhaps an alternative would be running two parallel PP output stages, but then how do I inject a stereo reverb signal???? There's an interesting amp in the 18Watt.com universe: the Tremolo TMB Reverb. It mixes the reverb signal into the opposite leg of the PI, so sort of a wet/dry approach using only half the signal? Not sure if that's right. See here: https://www.18watt.com/files/JMPGuitars ... ematic.pdf

Is there a way to use two PI tubes? Seems a guaranteed problem. Or would it be? At what point does it not just make sense to use two amps?

Because STEREO.

[didit]

No 'half-wave" -- Output of each PI triode is a full wave, just that they have inverted relationship; and it's the power stage that due to bias etc that divides the work into AB push-pull ..

[cdemike]

My understanding is a stereo signal required two outputs, one for "right" and one for "left". A single speaker cannot, by definition, deliver a stereo image. The half wave feed to a speaker seems impossible. Perhaps an alternative would be running two parallel PP output stages, but then how do I inject a stereo reverb signal???? There's an interesting amp in the 18Watt.com universe: the Tremolo TMB Reverb. It mixes the reverb signal into the opposite leg of the PI, so sort of a wet/dry approach using only half the signal? Not sure if that's right. See here: https://www.18watt.com/files/JMPGuitars ... ematic.pdf

Is there a way to use two PI tubes? Seems a guaranteed problem. Or would it be? At what point does it not just make sense to use two amps?

Because STEREO.

I'm not sure I understand the design goal. Are you after a wet/dry rig with one side doing reverb and the other dry signal? If the goal is reverb-only on one side rather than reverb mixed with the "original" guitar signal, I think that's only possible with two separate channels, whether that's using two amps or a stereo amp. If the goal is dispersion of sound over a physical space, a stereo head into two separate cabinets might be best to minimize headaches with needing several outlets, more cables, frustrations with levels/apparent volumes, etc.

Sorry if it's off-base, but it seems to me that based on the question about separate phase splitters you may be after a setup that takes a mono input and splits it into two separate outputs that can be fed to two separate cabinets placed apart from each other for a spatial stereo effect. If that's the case, I would approach it as one preamp feeding parallel output sections either with two phase inverters or two single-ended output sections. The PI mixer setup in the 18Watt.com schematic seems to me to work in reverse of what you're aiming for if you want two separate and different signals fed to different places.

[ViperDoc]

I'm not sure I understand the design goal. Are you after a wet/dry rig with one side doing reverb and the other dry signal? If the goal is reverb-only on one side rather than reverb mixed with the "original" guitar signal, I think that's only possible with two separate channels, whether that's using two amps or a stereo amp. If the goal is dispersion of sound over a physical space, a stereo head into two separate cabinets might be best to minimize headaches with needing several outlets, more cables, frustrations with levels/apparent volumes, etc.

Sorry if it's off-base, but it seems to me that based on the question about separate phase splitters you may be after a setup that takes a mono input and splits it into two separate outputs that can be fed to two separate cabinets placed apart from each other for a spatial stereo effect. If that's the case, I would approach it as one preamp feeding parallel output sections either with two phase inverters or two single-ended output sections. The PI mixer setup in the 18Watt.com schematic seems to me to work in reverse of what you're aiming for if you want two separate and different signals fed to different places.

Splitting a mono signal is a dual mono arrangement by definition until some sort of stereo field effect is introduced, like a stereo reverb or a stereo oscillator, like a tremolo or Leslie effect. If I just split a preamp output into parallel output stages with separate cabs, that's dual mono output, not stereo. Both cabs would be sending out the same signal, so a RIGHT/RIGHT output, or however you want to call it. The SPACE YOU"RE PLAYING IN AND HEARING would create a stereo impression, but not the ampifier itself. I was envisioning the use of FX loops in each channel to receive an actual stereo reverb effect so that each cab would then have a Right Wet and a Left Wet output signal respectively. The amp itself doesn't seem to be able to render a stereo image. Right? That's what I asked, is there such thing as a stereo guitar amp in the first place?

The idea of stereo guitars, for instance, seems to be a misnomer (no offense). It's like dual half mono output, right? Like I'm sending half the strings to one ring of a TRS jack, and the other strings to the tip. That's not stereo! Maybe I'm overthinking this. But do you get what I mean? Put any amp in a room and the ROOM is stereo. What makes the AMP stereo???? Just trying to proverbially shroom out the possibilities in my head.

[ViperDoc]

No 'half-wave" -- Output of each PI triode is a full wave, just that they have inverted relationship; and it's the power stage that due to bias etc that divides the work into AB push-pull ..

Good point. So then parallel SE output stages from each side of a PI tube would then cancel each other out. Right? Sh!tballs.

[Colossal]

Because STEREO.

Life's the same, I'm moving in stereo
Life's the same, except for my shoes


I play in whatever you call two amps and speaker cabs with my band. It's fantastic.

[timrobertson100]

Good point. So then parallel SE output stages from each side of a PI tube would then cancel each other out. Right? Sh!tballs.

Swap the phase of the speaker coming out of one?

[ViperDoc]

Good point. So then parallel SE output stages from each side of a PI tube would then cancel each other out. Right? Sh!tballs.

Swap the phase of the speaker coming out of one?

OH SH!T!

[TUBEDUDE]

Here's a stereo power amp I made as a final for a Magnatone clone. Each side is a single ended KT-88 driven by one side of a 12AU7. Stereo in, stereo out.

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