Hearthrob. Can I ramp between two speeds?

[Chris S]

I have a Hearthrob tremolo with two speeds that I can switch between. The speed change is instant, is there a way to make a slow ramped change between the two? Thanks!

[PRR]

No.

[Chris S]

Dang... Can I swap that reply for a "why don't you use the search function here's a link answering you question in detail" reply? 

[Rob Strand]

Dang... Can I swap that reply for a "why don't you use the search function here's a link answering you question in detail" reply?

You might be able to do it by replacing the frequency pot with a vactrol/resistive opto coupler.
The frequency is set using DC voltages or currents.

It's not clear how you want to get between the two rates: oscillating up and down, or a single ramp up which will
need a a switch to start it.   From a circuit point of view it's probably better with an ramp rate control and a depth control.  You also need to set how quickly it goes between the two and the trajectory between the two (maybe linear).

It's going to be a bit fiddly (I suspect if you knew how to get all that working you probably wouldn't be posting.)
Using a digital LFO using a micro controller would be much neater and compact.

[ElectricDruid]

Using a digital LFO using a micro controller would be much neater and compact.

Exactly what I was thinking. I actually programmed such a thing once upon a time for someone who was developing a Leslie speaker emulation. In that case, there are two Leslie speeds, and it takes a short while to get from one to another since you have to wait for the rotating speaker to accelerate. I think it slows down faster than it speeds up too, which adds another twist.

Tom

[PRR]

> Can I swap that reply for a "why don't you use the search function...

Heartthrob with two Tees would search a bit better?

And show/link what you are talking about. https://postimg.org/image/abiztiq3v/

The rate is set with fixed parts. In a scheme like this, there's no "easy" way to make fixed part vary slowly from one value to another.

Similar to the problem of making a semitone glissando on a highly fretted instrument. Easy on violin, rough on frets/finger guitar, "impossible" on piano. (OK, slide-guitar glisses fine, and I have worked with pianists who applied a tuning-wrench in performance, much like some banjo-players twist their tuners for emphasis.)

An additional, personal, problem is that I do not see how that oscillator works. It seems to have two very different paths and modes for slow and fast. Maybe I'm not looking at it right.

If we can identify a single resistor with a large influence on rate, without much effect to anything else (loop gain, limiting amplitude), we could replace it with a photo-resistor, an LED, and a current source rigged to slide slowly from, say, 0.5mA to 2mA, and back. Photoresistors are getting hard to get. There may be no good way to control rate with one resistor. (Two is possible but tracking may more than double your headaches.)

"THE" way is to scrap the semi-fixed oscillator and build a voltage control oscillator. Switch two control voltages at it, through a filter to smooth the transition. There's a bajillion VCO plans. The problem is finding one with good wave-shape AND output level and bias which suits this crude amplitude controller (a near-naked BJT).

At this point you start to think about a "better" VCA (voltage controller attenuator/amplifier), to simplify interfacing with the VCO (and maybe gain signal quality). Now you've thrown-out the whole baby and the bathwater.

So... no. Keep this one for what it is and explore other trem plans for the sound you want.

[PRR]

OK, before Rob gets back and points out what a git I am....

This is a Phase Shift oscillator. Just way more added parts than my little mind could stand.

And DUH! That 1Meg "Speed" pot begs to be an opto-resistor. Clearly this does not give wide range of rate (otherwise the fast/slow switch would not be needed). Probably under an octave. But maybe enough.

[Rob Strand]

OK, before Rob gets back and points out what a git I am....

LOL - you make me sound like the bad guy.  I wasn't going to do that anyway. 
When I read you post I thought maybe the OP wanted to go between the two - which *is* going to be difficult.
I don't know the motivation behind the different slow and fast ckts.

Clearly this does not give wide range of rate (otherwise the fast/slow switch would not be needed).

Maybe that's it.

[PRR]

No.... at the 4th cup of coffee _I_ "saw it" and felt dumb.

No idea if this is really what the OP wants. IMHO, once you get beyond what the dead-simple(?) circuit does naturally, it may be best to go over to "near ideal" plans, essentially Operational Computing.

BTW: sine oscillators don't shift frequency well. They may overload or crap-out until they come back to normal. With the large fat/slo change this may not matter. For a gliss, it may.

[Rob Strand]

BTW: sine oscillators don't shift frequency well.

I suppose if you can adjust the pot manually to get what you want it will probably work in automatic mode.

[Chris S]

Thanks for the responses guys. I was hoping I might have missed something and it wouldn't be too tricky a mod.

[JustinFun]

Thinking laterally, why not add an expression pedal output which when plugged in bypasses and replaces the speed knob?

*edit* though I suppose that wouldn't give you the range of speed that the switch does. Never mind.

[R.G.]

Leslie Effect Rotor Adapter (LERA), 1999.
http://www.geofex.com/article_folders/lera/lera.htm