Tremolo questions

[mountainhick]

Bias tremolos, I am not experienced with them, never had an amp or pedal with tremolo in 55 years of playing. So I don't know boo about sound differences between different trem circuits.

My new effects loop reverb is working pretty well, and I have room in the chassis to expand, so thinking about adding a simple tremolo circuit, and gain stage. The only problem with the reverb is a little loss in the passive FX loop, so a bump should help.

Looks like the most basic is something like the "rick tone" that uncle doug shows with one triode configured as LFO coupled to the cathode of a gain stage.

I do want to keep it simple and use on the cathode of an input gain stage in my stand alone FX loop box, so the concept of this circuit as starting point is appealing. But I don't like his demo of it. A lot of his demos don't sound good to me. I think it is because of the settings he he chooses, and crappy audio recording, but I am not sure.

Does this kind of simple term circuit actually just sound crappy? I could choose to add another tube, but for what benefit? and I still won't be hooking it up to the PI or power tubes. They are in a different chassis.

 

[Phrygian77]

If you're wanting to add gain with an extra stage, you might want to consider doing it like a VC, but since you only have two triodes, use a IRF820 mosfet for the CF.

 

[mountainhick]

If you're wanting to add gain with an extra stage, you might want to consider doing it like a VC, but since you only have two triodes, use a IRF820 mosfet for the CF.

Thanks,

But why? Doesn't the first triode already function as a gain/input stage which just happens to have the trem function on its cathode?

I don't even know yet if there something undersirable about this circuit essentially as shown?

Re: Mosfet, not interested in buying more stuff. I have all the tubes and parts for using tubes. I have space in the chassis for 2 or 3 tubes so up to 6 triodes, but if there is no good reason for the third tube, I'd rather keep it simple.

 

[Phrygian77]

@mountainhick I guess I misunderstood. You said:

My new effects loop reverb is working pretty well, and I have room in the chassis to expand, so thinking about adding a simple tremolo circuit, and gain stage. The only problem with the reverb is a little loss in the passive FX loop, so a bump should help.

Use a triode as a cathode follower if you don't want to use a mosfet. I was just suggesting it so you could add a gain stage without an extra triode.

 

[mountainhick]

@mountainhick I guess I misunderstood. You said:

My new effects loop reverb is working pretty well, and I have room in the chassis to expand, so thinking about adding a simple tremolo circuit, and gain stage. The only problem with the reverb is a little loss in the passive FX loop, so a bump should help.

Thanks, sorry, I guess my wording must be confusing.

I am referring to the schematic I posted above which is a gain stage acted on by an LFO.

The most basic question is: Is there any reason to make it any more complicated than that?

And if so, why?

 

[Phrygian77]

I don't even know yet if there something undersirable about this circuit essentially as shown?

The gain stage in the circuit posted is unbypassed. The gain of the stage is going to drop significantly as the depth is turned up because feedback at the cathode increases.

Also, because of that feedback, the output impedance of the stage increases, which will affect the frequency response and overall signal attenuation in the following circuit. A typical bypassed stage with a 100k plate load has an output impedance around 38k. That unbypassed stage with a 220k plate load will be around 93k with the depth full down, and 185k full up.

Edit: I clearly didn't look closely at the schematic.

 

[Phrygian77]

I should have added that all of that may be okay. I'm just pointing out potential negatives that you may not expect.

 

[Wally]

There is no benefit, imho, in creating a bias vary tremolo in the tube domain. Since you have an effects loop, why not get a pedal to work there. The are pedals with various types of tremolo(amplitude modulation) plus vibrato(frequency modulation). The reverb is what I would want in the tube domain….but you have a pedal for that.

 

[mountainhick]

The gain stage in the circuit posted is unbypassed. The gain of the stage is going to drop significantly as the depth is turned up because feedback at the cathode increases.

Also, because of that feedback, the output impedance of the stage increases, which will affect the frequency response and overall signal attenuation in the following circuit. A typical bypassed stage with a 100k plate load has an output impedance around 38k. That unbypassed stage with a 220k plate load will be around 93k with the depth full down, and 185k full up.

Hmm, So the 0.22uf from V1A cathode doesn't count as bypass because of its smaller?

I do see what you are saying about the gain being affected by the pot.

Would it be OK to configure the gain stage like a typical Fender with 100K plate, 1.5K cathode 22uf bypass instead?

Hmm, that 220K also is in series with the 100K, so it's 320K on the V1A plate.

There is no benefit, imho, in creating a bias vary tremolo in the tube domain. Since you have an effects loop, why not get a pedal to work there. The are pedals with various types of tremolo(amplitude modulation) plus vibrato(frequency modulation). The reverb is what I would want in the tube domain….but you have a pedal for that.

Thanks, Point taken!

Why not get a pedal? Because I already have too much stuff and don't need the expense! Because I already have the tubes and parts to build something. Because the reverb pedal is not a reverb pedal and I have room to build in here. So maybe bad idea... shrug. I like projects.

Tube reverb build project

A little different experiment, a simple point to point tube reverb to use on any amp with FX loop. I was playing around with a smaller chassis, but with the power transformer cutout, things were tight. I just freed this chassis from an old magnavox hifi amp, it is too small for my intended...

www.tdpri.com

 

[Wally]

Okay…so you are wanting something like the Revibe unit that Jeff Gehring designed and Weber made available in kit form?

 

[mountainhick]

Okay…so you are wanting something like the Revibe unit that Jeff Gehring designed and Weber made available in kit form?

Same concept in the box, but ideally a simpler circuit. The reverb itself is a single tube job and works fine for my needs. If I can use one more dual triode for gain and tremolo I'd be tickled. The whole reason for my questions is for feedback whether that compliment will work well.

 

[mountainhick]

@Phrygian77

Would it be reasonable to reconfigure the gain triode like a typical fender style 100K plate (straight to B+), 1.5K cathode, 22uf bypass?

 

[Wally]

Okay..interesting. Subscribed and following.

 

[bottlenecker]

There is no benefit, imho, in creating a bias vary tremolo in the tube domain. Since you have an effects loop, why not get a pedal to work there. The are pedals with various types of tremolo(amplitude modulation) plus vibrato(frequency modulation). The reverb is what I would want in the tube domain….but you have a pedal for that.

One advantage of a tube bias tremolo is that the attack of each note can "sneak through", making it a dynamic effect that gets out of the way when playing harder, and most importantly, it doesn't disrupt the sound of the player's rhythm, even with a strong depth setting.
Pedal tremolos don't do this (even when they claim to), and I have almost no use for them. They're either set so shallow they're barely there, or they're cutting off a bunch of what the player is doing and the sound gets annoying quick.
My opinion is tube bias trem = magic, pedal trem = annoying.

Thank you for indulging my selfish mission to get people to build more amps with tube bias tremolo.

 

[Phrygian77]

Hmm, So the 0.22uf from V1A cathode doesn't count as bypass because of its smaller?

I do see what you are saying about the gain being affected by the pot.

Duh! Yes, so just ignore what I said.

@Phrygian77

Would it be reasonable to reconfigure the gain triode like a typical fender style 100K plate (straight to B+), 1.5K cathode, 22uf bypass?

If you increase the .22uF, it can potentially affect the tremolo signal. The reason it works is because the bypass frequency is above the tremolo frequency.

 

[mountainhick]

Duh! Yes, so just ignore what I said.



If you increase the .22uF, it can potentially affect the tremolo signal. The reason it works is because the bypass frequency is above the tremolo frequency.

No problem,

Got it! since the LFO signal is coming through the IK resistor, is it as simple as the cutoff being determined by the 1K/0.22uf RC filter, so 3db slope? That's 732 hz. Seems like room to move?

Oops, I think was looking at it backwards. You're talking bypass frequency, I ran with 2.2uf and 22uf on this calculator https://www.ampbooks.com/mobile/amplifier-calculators/cathode-capacitor/calculator/ and its pretty visible how the curve increases down near 10-20hz. Might get away with some increase in bypass value.

I am not sure why though the VC V1B where the Trem connects is indeed the 100K 22uf/1.5K configuration, and apparently no consequences. It dies have the extra triode cathode follower to push it more.

 

[Phrygian77]

I am not sure why though the VC V1B where the Trem connects is indeed the 100K 22uf/1.5K configuration, and apparently no consequences. It dies have the extra triode cathode follower to push it more.

The Vibro Champ has a 10uF.

 

[King Fan]

@mountainhick, this may not help, but have you seen Merlin's note on a simple LED to replace the LFO cathode resistor *and* cap? He points out this can also be a visual rate indicator, but if you don't want that, many people just leave it inside the chassis. IME simple, smooth, quiet, effective, very natural tube trem. It cured my stubborn trem thump, too, which had tried to live through a couple conventional fixes. Last paragraph here:

The Valve Wizard- Tremolo Oscillator

www.valvewizard.co.uk

 

[mountainhick]

@mountainhick, this may not help, but have you seen Merlin's note on a simple LED to replace the LFO cathode resistor *and* cap? He points out this can also be a visual rate indicator, but if you don't want that, many people just leave it inside the chassis. IME simple, smooth, quiet, effective, very natural tube trem. It cured my stubborn trem thump, too, which had tried to live through a couple conventional fixes. Last paragraph here:

The Valve Wizard- Tremolo Oscillator

www.valvewizard.co.uk

I have not, thanks! I'll read this after breakfast.

 

[joulupukki]

On my latest builds I used an LED on the cathode and it helped give it a much deeper trem. On the beating side of things, lead dress is still important. In one of these amps if the B side of the reverb recovery was too close to the wires / terminals of the trem circuit it I could hear a faint beating/ticking.