Tremolo Effects Pedal - Page 1
Forum section: electronics / projects

author: 8163jb
author_rank: Contributor
timestamp: January 29, 2014, 05:36:25 pm
content: Just thought I'd show the project I'm currently working on: it's a tremolo effect pedal for a guitar. So it's just basic amplitude modulation of the signal. Everything is detailed in the blog post:http://doayee.co.uk/tremolo-effects-pedal/any additions and comments are welcomeI am still learning so feel free to point stuff out and correct things if they are wrong! Cheers!

author: fcb
author_rank: Super Contributor
timestamp: January 29, 2014, 06:17:45 pm
content: Build an actual prototype and try it.I think you might need to (at least) add a resistor from the synthetic ground to the C6/R9 junction (perhaps 270K) to bias the input, there might be some interesting asymmetric effects of the modulating FET also, but that's cool perhaps. Also, your PSO might not have quite the range you want.

author: 8163jb
author_rank: Contributor
timestamp: January 29, 2014, 10:26:30 pm
content: Cheers very much! I'll try that when I'm testing itQuoteWhat do you mean by PSO? I've not heard that term before? Is is what I call the sine wave generator? Thanks again

author: fcb
author_rank: Super Contributor
timestamp: January 29, 2014, 10:55:29 pm
content: PSO - phase shift oscillator

author: 8163jb
author_rank: Contributor
timestamp: January 30, 2014, 07:45:31 am
content: Ahhh rightmakes sense now! Never heard it called one of them before. Cheers!

author: t0m
author_rank: Regular Contributor
timestamp: January 31, 2014, 04:55:19 pm
content: I think tremelo circuits used a vactrol back in the day.

author: 8163jb
author_rank: Contributor
timestamp: January 31, 2014, 06:04:20 pm
content: QuoteA vactrol? What is one of those? I've never heard of that before?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 31, 2014, 07:46:25 pm
content: CdS photocell coupled to a source of illumination (an LED these days, but might've been an incandescent or neon light back in the day!).There are opto-FETs still available today (same thing, in silicon), though uncommon. Let's see... H11F1 and variants appears to be the only family on Digikey.The main downside is the low CTR (fractional mA output for 20mA input) and voltage range (under 0.1V; for low distortion, maybe only 10mV), since like JFETs, they are constant current devices for most voltages.The main downside of CdS is -- besides the low availability of prepackaged vactrols -- the poor repeatability, drift, and long time constants make precision isolation difficult at best (but, not something you'd notice for a tremolo circuit).Neat fact: lots of old circuits used the neon light type vactrols as isolated switches for gating chopper amplifiers. This was used in very sensitive and low drift circuits, as far back as the vacuum tube days, where an average tube had microamperes of grid leakage (how much, and which direction, depends on where it's biased -- obviously a bit of a problem!).Tim

author: t0m
author_rank: Regular Contributor
timestamp: January 31, 2014, 09:35:07 pm
content: It's like a current controlled resistor. They were also commonly used in compressors. You can get them from surplus electronics places.

author: kaindub
author_rank: Regular Contributor
timestamp: February 06, 2014, 12:24:28 am
content: I'll try and be delicateYour circuit will not work as intended.The fet you are using only conducts linearly in one direction. In the reverse direction there is the body diode. Your circuit will work as a sort of fuzz box.Secondly, where the fet is placed, the source is tied to the op amp output. The drive for the fet, (ie the gate to source voltage) will be modulated by the audio signal, in some cases with a high enough audio input, the fet will be cut off.A better way to do this is to use some enhancement mode fet ie J201.Connect your audio signal to a resistor in series with the fet. Fet to ground. Take the output from the junction of the resistor and fet. This is then just a voltage divider with a controlled resistance.You won't be able to get much dynamic range using fets.Also consider adding a depth ( of modulation) control.Hope this helpsRobert

author: fcb
author_rank: Super Contributor
timestamp: February 06, 2014, 08:34:15 am
content: Quote from: t0m on January 31, 2014, 04:55:19 pmIf your making a one off, then a vactrol is a great way to do it - and simple to.If your making a production unit, then forget it. A vactrol (which as someone already said) is just a CdS photocell (google ORP12, cadmium sulphide, etc..) being illuminated by an LED. CdS photocells are not, or ever will be RoHS compliant.

author: t0m
author_rank: Regular Contributor
timestamp: February 08, 2014, 03:03:12 pm
content: Absolutely true.Doesn't stop them being used in kid's toys in the USA - even expensive ones. Check out this video - the CdS photoresistors are clearly visible under the puzzle pieces.

author: 8163jb
author_rank: Contributor
timestamp: February 28, 2014, 08:51:00 pm
content: Hey everyone!Just thought I'd update you on the projectI built it! And it works!video here:

author: dentaku
author_rank: Frequent Contributor
timestamp: March 01, 2014, 04:22:09 pm
content: Quote from: 8163jb on February 28, 2014, 08:51:00 pmNice. I recently built a VCA with an LM13700 OTA and it can do roughly the same thing. You control the amplitude of the audio going into it with an LFO and you get a tremolo.I wonder what's the first effect Fran Blanche ever built?

author: 8163jb
author_rank: Contributor
timestamp: March 01, 2014, 06:15:32 pm
content: QuoteI wouldn't be surprised if it was a tremolo! These things are really easy to buildI might try a distortion next, they don't look too bad

author: 8163jb
author_rank: Contributor
timestamp: March 01, 2014, 07:39:15 pm
content: I wrote a second blog post about it, this one explains more about how it works and breaks it up into sectionsalso I've started using KiCad instead of Eagle, much prefer it!http://doayee.co.uk/tremolo-effects-pedal-part-2/