More tremolo?

[sluckey]

This is an idea I've been sitting on since I began putting LEDs in my tremolo oscillators. I finally took it to the bench and tested it today. It works much better than I had hoped. This produces a very strong, smooth tremolo without the hassles of power tube bias modulation or neon bulb optocoupler ticking. And only one triode!

[Swampertech]

Steve, would your circuit be a good candidate to modulate the cathode bias of this V4A pre-PI 12AX7?

[sluckey]

This circuit is not meant to bias modulate anything. It simply ties into the signal path and shunts the signal to ground. If I were gonna put this circuit in your circuit I would connect R_x to the right side of C15. The PI would also need an input cap.

[Toxophilite]

ooooo cool!
Thanks very much for putting this up!
I almost want to swap this into the princeton deluxe thingy I made.
I like  the sound of bias vary but it always seems to be a bit of a balancing act. Sometimes it gets weaker when it gets faster and can distort in an ugly way at higher volumes and intensity settings.


Does it insert where a standard fender optibug tremelo would insert and is it closer in sound to that tremelo




and can you explain the 'swamp' switch. Does that emulate the bias vary sound?


Now I have to build something to try this, and or dod a version on a tiny board and try hooking i into my princeton deluxe build to hear how it sounds.

[sluckey]

You could insert at the same point as an AB763, or at the volume pot, or you could insert at the junction of the two 220K mixing resistors and the PI input cap if you want tremolo on both channels. I think it has a much smoother and deeper sound than the neon roach used by Fender. The swamp switch just gives you a slower speed range.

I tried this in my supro amp. I just replaced the cathode resistor for the oscillator triode with the opto and connected the output to the #2 volume pot. This way I still had stock preamp bias tremolo on Channel 1 and new trem on Channel 2. Very easy to compare. Sounded very close but the new trem was capable of much more intensity.

     http://sluckeyamps.com/supro/supro.pdf

You could do a similar test in your DR or PR. Only takes a few minutes to do a temporary mockup. And you would still have your original tremolo circuit. Compare the two simply by turning one intensity to zero. You could even run both trems at the same time!

Experiment by connecting the trem output to different places in the signal chain. The only caution is don't connect it to any place that has dc voltage present, such as tube plate or PI grid.

[Toxophilite]

Where do you get your Vactrol VTL 5C1 ?
I see antique electronics has it. I can't seem to find it on the Hoffman site.


What about 'Trem - U - Later'

[sluckey]

I bought some 10 years ago when I was working on my Sunn tremolo. I've already renamed it Tremo-Nator. Not really locked in on anything. This may just fade away.

[vampwizzard]

This may just fade away.

.. then come back.. you know.. then repeat cyclically. 

[Slimtim]

i bought the last vtl5c1 doug had in stock last week.sorry bout that.are the xvive not as good?

[tony321owen]

what is th usable b+ range for this circuit?

[sluckey]

Wide range. I have nine amps with tube tremolo. The B+ for the oscillator ranges from 210V up to 440V.

[DummyLoad]

I bought some 10 years ago when I was working on my Sunn tremolo. I've already renamed it Tremo-Nator. Not really locked in on anything. This may just fade away.

tremotrol? 


--pete

[Tapsnap]

What is the triode you are using?

[sluckey]

12AX7

[2deaf]

Not really locked in on anything. This may just fade away.

Attached is a different way to do the footswitch.  It puts the photocell at maximum resistance when the tremolo is switched off.  It also kills the LFO when switched off.

I don't think this idea is going to fade away as long as these photcell optocouplers are available.

[Toxophilite]

Does this dispense with the need for a bias voltage as per the previous modification?

[sluckey]

Yes it does. I like that idea. Have you tried it? Did the oscillator start quickly.

My dead was similar but without the 10K. The tube would be completely off. I was concerned that may be slow to start up though. I haven't had any time to tinker lately.

[2deaf]

I only built it by itself on the bench.  I haven't tried it in an actual amp.  The oscillator started immediately, but it took it a couple of seconds to stop completely.  Doesn't seem to matter because the optocoupler cuts the signal immediately.  I couldn't detect any transients, but you just never know until it is actually in an amp.

I have noticed that VTL5C1's have wildly different output performances.  The only thing that is of concern to me is the minimum resistance, but that can be altered somewhat by changing the plate resistor.   

[PRR]

> Attached is a different way to do the footswitch.

I think with plate resistors as high as 470k, the cathode resistor may need to be more than 10k to get for-sure oscillator quit. (The trem of course will stop when the LED is cut out.)

[2deaf]

> Attached is a different way to do the footswitch.

I think with plate resistors as high as 470k, the cathode resistor may need to be more than 10k to get for-sure oscillator quit. (The trem of course will stop when the LED is cut out.)

Peters out pretty fast with 430V, 470K plate, and 10K cathode.  The thing loses its motivation with a 4.7K cathode resistor when the bypass capacitor is removed, although it takes a lot longer.  If other people are not getting satisfactory results, then by all means increase the cathode resistor.

You can also switch the speed pot off of ground with the same switch and take the middle 1M resistor off of the cathode and switch it off of ground, also.  I did this with an LND150 design and it worked pretty good.

[kagliostro]

I've read only now the thread and ....


Beautiful idea


Franco

[PRR]

> with a 4.7K cathode resistor ... it takes a lot longer.

The oscillator needs a gain of 27 to work. With 220k and 10k the no-LED gain is 22, minus other losses, so should fade quick. At 470k:10k the apparent gain is 47; won't be that high but if it comes to gain of say 25 the oscillation will fade slow.

I'm not sure that there is any "upper limit" on the "10k". 100k may idle fine and fade quick.

Obviously you know what you are looking at, but for benefit of others with less insight it might be interesting to know if the "10k" may be large and die more reliably/quickly.

[sluckey]

Actually it would be better to keep the oscillator running. The FS is gonna kill the LED immediately  and if the osc remains running the LED will immediately start flashing when the FS is kicked on.

[PRR]

> better to keep the oscillator running

Agreed, as long as leakage doesn't throw thumps when trem is off.

Thinking over many systems: sometimes the osc is left on for instant action, sometimes shut-down for for-sure no interference. While 5Hz is not going to go far, in a compact chassis with marginal filtering it can sneak around.

A side effect: osc left running the trem will start at "any" point on the wave. Osc stalled but self-kick-starting, it always comes up from the same point (zero), less and more predictable turn-on transient.

But I may be over-thinking because I don't want to go out and chip any more ice.......

[sluckey]

ICE! Sorry to hear that. My azaleas and daffodils and peach trees are in bloom. Bees are a buzzin.

[2deaf]

The oscillator needs a gain of 27 to work. With 220k and 10k the no-LED gain is 22, minus other losses, so should fade quick. At 470k:10k the apparent gain is 47; won't be that high but if it comes to gain of say 25 the oscillation will fade slow.

I'm not sure that there is any "upper limit" on the "10k". 100k may idle fine and fade quick.

Obviously you know what you are looking at, but for benefit of others with less insight it might be interesting to know if the "10k" may be large and die more reliably/quickly.

I must be calculating the gain for the 470K/10K combo wrong because I keep getting 30.  I tried a couple of tubes in real life and observed a gain of 20.

I don't have any particular 10K fetish, it's just that it worked well in a source-follower design.  I have noticed that the 10K shunts enough current to adversely increase the minimum VTL5C1 output resistance with wimpy VTL5C1's.  A 47K cathode resistor seems to be acceptable as far as output resistance goes and it stops the oscillation quite rapidly when the LED is disconnected. 

It has crossed my mind that the sudden change in current might cause a pop when the pedal is toggled on and off.  If this is a legitimate concern, it would argue for the smallest cathode resistor feasible to keep the current difference as small as possible.  I would have to install this in an actual amplifier to see if any problem really  exists.

If you are really, really concerned about shutting down the oscillation, you could also switch out one or two of the RC phase shifters.

[punkykatt]

Thanks Steve for sharing the Tremor-lator circuit. I finally got around to install it in my 7591A cathode biased 6G16 style amp and works great. Finally got rid of that thumping that was in the other circuit. Takes about  a second and a half to start the trem once the Ft Sw is pressed, shuts off quick. I can live with that.   Punky

[sluckey]

Look at some of the simple mods 2deaf offered. Should give a fast startup.

[shooter]

trees are in bloom

rub it in, still artic blast here, but yours is coming, when my trees bloom, you'll be sweating you azaleas off 

[sluckey]

Hey it's been cold down here the last couple days. I may have to fire up the pool heater! 

[shooter]

again with full disclosure, I spent 90days enjoying every second of "your" southern weather, I just came back early enough that I could whine about the 20days I've had to endure the cold 

[sluckey]

June, July, and August are tough. High 90s, temp and humidity! We have to turn the pool heater off during the day! 

[shooter]

I've found I "acclimate" within a day to large swings, but can't seem to regulate with small swings  , 40's by the weekend, PRR by Wed. 

[DummyLoad]

going to be in the 70's here tomorrow    it got down to 28deg. last night. we'll get about 2 weeks of spring and then it'll be hot and humid with continued hot and humid for 6 months.


--pete 

[punkykatt]

Did 2deaf`s mod#2 with the 10k cathode resistor and moved the foot switch location. Trem works flawlessly.   Instant start and stop.  Thanks Guys.

[sluckey]

That's good to hear. Thanks

[Backwoods Joe]

Added the original, highly acclaimed, "patented" TREMOR-LATOR to a Martin 112/ 5E3 build. Very happy, Thanks Mr. Sluckey.

[mwelch55]

Do you think a MOSFET can be used instead of a triode? 

I have seen LND150 used in place of a triode.  If you could get the LND150 to work in this circuit, it would be smaller and there would be a lot less heat.  It shouldn't affect the tone since the signal is being shunted to ground and the MOSFET is not in the signal path.

[sluckey]

I think it would work. If I had a breadboard I'd try it.

[2deaf]

Do you think a MOSFET can be used instead of a triode?

I'm not sure I can get that LND150 to oscillate with a bias that cold.  Could put the VTL5C1 in the drain circuit and I bet it would work.  I put the VTL5C1 into a source follower circuit where I could control the current and it worked. 

[2deaf]

I think it would work. If I had a breadboard I'd try it.

It never occurred to me to try it in your configuration.  If I can free up some time this afternoon, I will play with it a little.

[JB]

How critical is the VTL5C1 to the design?  They're pretty scarce=expensive.  There are Chinese made ones on eBay but would they work the same in this circuit or are they junk?

[Swampertech]

Hey Steve, 2deaf. Does the 220K resistor in series with the VTL5C1 resistance provide the proper load for V4A, and also act as a mixing resistor for the "Tremor-lator" and the ac signal at the plate of V4A? Would this be the proper implementation of the "Tremor-lator" in the circuit? Thanks

[sluckey]

Try and see.

[Swampertech]

This is how the BF DR mixes. This must work, huh?

[sluckey]

Where did R37 come from?

[Swampertech]

Hey Steve, R37 is one of the feedback resistors, along with R38. I was adding a selectable FB range, or no feedback, to the LTPPI. Is that bad?

[2deaf]

Hey Steve, 2deaf. Does the 220K resistor in series with the VTL5C1 resistance provide the proper load for V4A, and also act as a mixing resistor for the "Tremor-lator" and the ac signal at the plate of V4A? Would this be the proper implementation of the "Tremor-lator" in the circuit? Thanks

The Fender roach tremolo works by varying the load on the output of a 12AX7.  The varying load causes the gain to vary.  The gain only changes a little if the load is from 470K to 100K and a tremolo working in that range would be too light.  The gain changes a whole lot if the load is from 50K to 5K and a tremolo working in that range would be heavy.  Another one of those exponential things.  You wouldn't want a 220K resistor in series with the 50K pot because that would put you in a load range that isn't conducive to tremolo.

[Swampertech]

2deaf, the VTL5C1 resistor varies from 50M (dark resistance -OFF) to 20k with 1mA through the LED, to 600 ohms with 10mA through the LED, and 200 ohms with 40 mA through the LED. If the Tremor-lator resistor is connected as a varying load for the output 12AX7(past the plate CC), would the swing from 50M down to 600 ohms provide the wobble needed for good tremolo? Or assuming that the tube is drawing 1mA, would the variation from 20k to 600 ohms be enough for good tremolo without loading the 12AX7?

[sluckey]

Hey Steve, R37 is one of the feedback resistors, along with R38. I was adding a selectable FB range, or no feedback, to the LTPPI. Is that bad?

Say what! I'm asking about the schematic you posted in this thread.