[Paul Running]

Interesting circuit, here's Gibbo's version...early 60s ES-345:

It would be cool to compare the dynamics with the Yammy.

 

[mhammer]

Note that the 10meg resistors effectively bump the corresponding capacitor out-of-circuit. The rotary switch bridges/bypasses the 10meg resistor of the capacitor you want to use, without inducing any switch-popping (as it would if the capacitors were all "hanging", with one end unconnected).

 

[Paul Running]

Gibson has drawn the inductor as a simple, single 1.5H inductor whereas, if the schematic of the Revstar is accurate then, the transformer could be configured as a parallel-aiding or a parallel-opposing inductor...depending upon the phasing connections of the primary and secondary windings of the TFM so, the total inductance will differ in each config.

 

[sjp]

On balance, do you think the schematic of the revstar that angellahash posted in the other forum is correct? Does it at least make sense?

 

[Mark Brown]

The schematic Paul shows indicates an LCR filter - a variable resistance in series with a capacitor and inductor. The typical result of that is a bleeding of spectral content above some point and below some other point. This is precisely what the old Varitone circuit did/does, except that in this instance, there is only one capacitor value, in tandem with a way to vary the resistor. The Varitone has a fixed amount of cut, but switches between different capacitor values to move the focal point and width of the mid-cut around.

Here's Craig Anderton's "Passive Tone Circuit" - an adaptation of the Varitone as a single passive pedal, from his 1980 book, Electronic Projects for Musicians. He uses one side of a small interstage transformer as an inductor, with a switch to double/halve the inductance, a rotary switch to select between capacitor values, and moves the variable resistance after the inductor, instead of before the capacitor as in the Revstar circuit. I built one into a pedal, in conjunction with a single FET booster stage, to compensate for the passive loss. I realized that by bypassing the inductor, it would become a treble cut, by bypassing the capacitors become a bass cut, and by bypassing both the caps and inductor, a simple attenuator. So I made that all switchable, turning it into a very flexible tool.

In an older document I got from Dan Torres, he also has a circuit for a bidirectional tone control. One side from the midpoint is normal treble-cut, and the other direction of rotation has a cap in series with an inductor to ground, providing a variable mid-cut. I can credit Yamaha for including such a circuit, in order to make an otherwise standard 2-pickup/two-knob guitar a little more flexible. But credit for the circuit itself has to go to many people before Yamaha.
View attachment 431361

Holy shit I understood that!!!

 

[mhammer]

On balance, do you think the schematic of the revstar that angellahash posted in the other forum is correct? Does it at least make sense?

Is that schematic the one that Paul posted here, incorporating the 5-way switch?
If the perceived "boost" IS simply a change in overall level resulting from the spectral content removed or added, then yes. Since the drawing indicates that engaging the transformer/inductor removes/bleeds-off content, however, that implies that engaging the transformer when one pulls the knob "up" is actually the lower output, and not the higher output one.

I'll add, since it appears it wasn't commented on, that the #2 and #4 positions of the 5-way switch, cut out the bass of one, and the other, pickups via the series capacitor introduced. That, plus the "varitone" mid-cut would offer a pleasingly wide range of tones, with little fuss. Clever.

That would be my understanding if the drawing is accurate.

 

[Paul Running]

On balance, do you think the schematic of the revstar that angellahash posted in the other forum is correct? Does it at least make sense?

Yes, it makes sense. I have not been able to locate an official datasheet for the transformer used in the Revstar...a slight twist to the Varitone config, with the option to switch the inductor in or out of circuit.

 

[sjp]

@mhammer, yes I was referring to the schematic that Paul posted. You noted that "engaging the transformer when one pulls the knob "up" is actually the lower output". That is definitely not how the revstar works. Could the wiring diagram have the switch in backwards?

 

[mhammer]

I can't tell which switch position is up or down from the diagram, and wouldn't necessarily assume that the drawing of the connections directly reflects the position of the knob (up or down). It just shows component connections. But looking at it just now, I realized the transformer is always connected. The push-pull switch either bridges the transformer to provide a straight-wire path to ground, or makes the path to ground through the transformer.

 

[Paul Running]

In the early 60s, Epiphone introduced their very limited EA-Professional series (only one was made in 1966). It was a guitar/amp combo in which the Varitone circuit was in the guitar, interfaced to the amp through a 6-conductor cable. Here's the schematic of the EA8-P model:

Publicly, it never caught on.

 

[Paul Running]

After doing a bit of searching, I located a spec sheet for that TFM in the Revstar. Alternative sources indicate an audio line-transformer with an impedance ratio of 6.67:1, centered for 4KΩ to 600Ω-line. It does have a voltage ratio of near triple. however, it would require an active circuit to prevent severe loading of the guitar PUs if it's wired as a conventional TFM...last nail for inductor.

Product : Signal line-transformer
Primary Impedance: 4KΩ. secondary impedance: 600Ω. impedance ratio: 6.6°:1. voltage ratio: 2.58:1
DCRprimary : 148 Ω. DCR secondary: 64Ω. frequency range: 300Hz - 3.4KHz.

 

[AngelLaHash]

The circuit that i drew was from what I could see from the colour wires

I don't think it's a Booster but more set hi and then brought down low.

IE like what car makers are doing now.. selling you add-on. Heated seats just pay so much a month. It was always a part of the car so isn't really an add-on.

We can't creat power we can only transform it from one state to another.
I did wonder if I could boost a single pickup with the power from the second one, I am thinking I would have to bring the second pickup more in phase with the first to sound like a boost or I would just get Neck+Bridge.

 

[Paul Running]

We can't creat power we can only transform it from one state to another.
I did wonder if I could boost a single pickup with the power from the second one, I am thinking I would have to bring the second pickup more in phase with the first to sound like a boost or I would just get Neck+Bridge.

An active circuit would produce more effective results...DC power in, to produce more dynamic power out.

 

[AngelLaHash]

An active circuit would produce more effective results...DC power in, to produce more dynamic power out.

I only said that to call it a boost when there isn't any power being added is untrue.

Its feels more like a con.

1) this is the sound of the guitar
2) this is the boost

2)this is the true sound of the guitar
1)this is a cut down sound

Car terms. If you push on the accelerate we can go fast. But if we push harder we get a boost. If you just push harder you get the same speed as the boost. Guess more electric car feel to it.


But if you can suggest a replacement transformer as I didn't have a clue on its values just the name . I we recheck the circuit from the images I can see. As the colours make it so nice