Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jeff on August 14, 2010, 07:35:26 pm

Title: tremolo circuit
Post by: jeff on August 14, 2010, 07:35:26 pm

Could someone please explain a tremolo circuit to me? I'm talking about the type that uses a "roach"

I assume the first half of the tube creates the ocsillation?

What exactally is the signal sent to the second half of the tube?

Please explain.

Thanks-Jeff

Title: Re: tremolo circuit
Post by: stingray_65 on August 14, 2010, 11:15:06 pm

I'm sure some one will chime in who is much more versed in such things than I am, but I'll give it  a go.

first off a  tremolo circuit (Fender) is actually a vibrato circuit, it modulates amplitude as if you run the volume knob on your guitar up and down quickly.

the first half of the dual triode does create the oscillator. this runs to the roach which is fed by the intensity pot. as the intensity is turned up the roach is "more sensitive".

the other side of the roach is connected to the plate of the second half of the tube which has the signal passing through it.

so as the oscillations on the plate varies up and down, so does the signal coming out of the second half of the tube.

Ray

Title: Re: tremolo circuit
Post by: Danskman on August 15, 2010, 12:53:35 am

Tremolo=amplitude change
Vibrato= frequency change

Fender always used the term "Vibrato" on their amps, but it's not correct.
On guitars, the whammy bar acts to change the height of the notes; it's a vibrato effect.

In a typical BF amp, the 1st half of the 12AX7 is used as a Low Frequency Generator, giving a sinusoidal waveform signal; the 2nd half is used to boost the signal and pilot a small neon bulb that faces a Light Dependent Resistor (named "The Roach", or The Bug, whatever else...). As the LFO signal varies in amplitude, this changes the value of the LDR, thus changing the "Vibrato" channel instrument signal amplitude.
HTH,
Danskman

Title: Re: tremolo circuit
Post by: jeff on August 15, 2010, 01:40:47 am

'On guitars, the whammy bar acts to change the height of the notes; it's a vibrato effect"

right but for some reason they called that a trem bar. wierd huh?

Guess Leo didn't know his tremolo from his vibrato

Title: Re: tremolo circuit
Post by: Fresh_Start on August 15, 2010, 10:52:12 am

Quote

I guess a 'whammy bar' is where they go to do those things......  :grin:

That could be scary with those pointy guitars like Doug Hoffman's in that recent video he posted :wink:

Chip

Title: Re: tremolo circuit
Post by: P Batty on August 15, 2010, 11:20:16 am

I read somewhere  that Lonnie Mack´s use of the vibrato tailpiece on his song Wham! was where that term came from. That may or may not be true, but is a possible answer.

Title: Re: tremolo circuit
Post by: tubeswell on August 15, 2010, 02:35:59 pm

Good explanation here

http://www.freewebs.com/valvewizard1/trem1.html

Title: Re: tremolo circuit
Post by: jeff on August 16, 2010, 12:34:04 pm

Thanks a million

      Jeff