Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: fuzz on January 17, 2013, 11:53:27 am

Title: Stand alone tube tremolo
Post by: fuzz on January 17, 2013, 11:53:27 am

Hi,

i've made a tube tremolo using a single 12AX7. The idea is a bias tremolo using triodes inspired by the Selmer Mercury 5 :
http://www.vintagehofner.co.uk/selmer/schematic/merc.jpeg (http://www.vintagehofner.co.uk/selmer/schematic/merc.jpeg)

I've only added a 470K resistor between the wipper of the depth pot and the ground .

I had to tweak few things to make it work good with triode (big signal coming from the LFO) but now it works as expected .

the only issue is that the speed control doesn't give a great amplitude . I've medium fast to fast only and I'd like to have something slower . I've tried to increase the pot value until 3M with resistors but didn't improve the circuit (and 3M pot are hard to get) , also tried to make cap bigger without success.  

 I know that the phase shift oscillators are limited but maybe some of you have work on similar circuit and could give some advices ?

the ideas was to put a hi/lo switch to set the speed of the tremolo and get a wider range.

here's the LFO schematic I used :
(http://www.valvewizard.co.uk/Trem3.jpg)

from : http://www.valvewizard.co.uk/trem1.html (http://www.valvewizard.co.uk/trem1.html)

thanks

best regards,

EDIT...fixed pic link... sluckey

Title: Re: Stand alone tube tremolo
Post by: kagliostro on January 17, 2013, 12:14:31 pm

Merlin has build a stand alone vibrato/tremolo unit based on the circuit of the Vox AC30 and called it Vibrotron

if you are interested you can find a bit about that here with Vibrato and Tremolo samples
(look to post # 24)

http://www.el34world.com/Forum/index.php?topic=14935.0 (http://www.el34world.com/Forum/index.php?topic=14935.0)

(http://www.el34world.com/Forum/index.php?action=dlattach;topic=14935.0;attach=34299;image)

K

Title: Re: Stand alone tube tremolo
Post by: sluckey on January 17, 2013, 12:59:05 pm

Tack solder a 10nF cap across the middle 10nF cap. If you like it put it on a switch. Look at the LFO on this schematic...

http://home.comcast.net/~seluckey/amps/warbler/warbler_rev1.pdf (http://home.comcast.net/~seluckey/amps/warbler/warbler_rev1.pdf)

Title: Re: Stand alone tube tremolo
Post by: fuzz on January 18, 2013, 07:48:58 am

hi guys !

thanks for your answers .

Sluckey , actually I just did that, I put a 10n cap with the middle one and works great. I also put a switch to change tail resistor with the speed pot and have two speed. Seems to work very good ! I've still have to work on it  find the right resistor tail on the low side (too low and trem is really subtle ) .

otherwise , I've to tame gain in the stage because it gives distortion really soon when plugged in the input of my tube amp (EF86 in V1) but it's a matter of divider network with the volume pot.