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For those of you who can't get enough Tube Screamer I present the YATS Overdrive (Yet Another Tube Screamer). This project takes the CJOD mods and applies them to the Jack Orman Son Of Screamer circuit topology - CJOD Lite. I tested this project on a breadboard - it works and it sounds just like a CJOD. I've been over the layout a few times and the following documents appear to be free of error. I'll be building this one to perf-board tomorrow. I'll post any corrections if errors are discovered during the build.

Enjoy!







I used metal film resistors throughout. You can change the resistors in the audio signal path to carbon comp type for more 'mojo'.

Hey there Deaj, when the CJOD scheme came out I whipped this up on breadboard: http://revolutiondeux.blogspot.com/2008 ... drive.html

Looks just about the same, give or take a few cap values.

It is a nice sounding TS derivative. The input and output buffers do nothing for the sound!

Thanks for sharing, your layouts looks great!

briggs wrote:Hey there Deaj, when the CJOD scheme came out I whipped this up on breadboard: http://revolutiondeux.blogspot.com/2008 ... drive.html

Looks just about the same, give or take a few cap values.

It is a nice sounding TS derivative. The input and output buffers do nothing for the sound!

I remember seeing a post from you that you were playing with this as well.

I've been playing with the circuit on the breadboard this afternoon and the cap I have between the volume pot sweeper and the output doesn't really make any significant difference. Also the value of the input cap seems to make little difference. I'm going to tinker with it a little more before I build it.

Project files have been updated to reflect the circuit currently on my breadboard. More edits coming I'm sure.

Deaj,

Did you try dropping the OPA2134 into your Eternity build? Seems like it would have to get close to the CJOD with the switch set to LEDs.

I found the input and output caps only start to make a difference when you make them really small and their impedence increases to a noticable level for lower freq signals.

It is a lovely layout. I just need some more OPA2134's! Gah, I spend all of my cash on parts... Banzai must love me!

I'd be interested in trying the OPA2134 in a timmy circuit that has LED's instead of the 1N914 diodes. I prefer the sound of a stock timmy to a stock TS.

briggs wrote:I'd be interested in trying the OPA2134 in a timmy circuit that has LED's instead of the 1N914 diodes. I prefer the sound of a stock timmy to a stock TS.

Note the original Timmy tweak of making R2 = 12k, no other YATS has that.

Noob question:

I'm getting high frequency oscillation when the tone control is at full CW and the gain is set anywhere above 1 o'clock or so. Can a sloppy breadboard build cause this kind of a thing with a high gain circuit?

When I say sloppy I mean this:



Briggs - did you have this issue with your breadboard build?

Thanks!

Deaj wrote:Noob question:

I'm getting high frequency oscillation when the tone control is at full CW and the gain is set anywhere above 1 o'clock or so. Can a sloppy breadboard build cause this kind of a thing with a high gain circuit?

Briggs - did you have this issue with your breadboard build?

Thanks!

The oscillation was due to the sloppy layout. I decided to go ahead and build it assuming this was the case. The finished pedal is quiet and sounds great.

A few suggestions from me:

R4 - 1M
Insert some resistor between 1k-10k at the input and one at the output. 4k5 or 10k is OK.

OPA opamp is fast opamp. It's better to reduce high frequency oscillation to solder 100nf direct to pin 4 and 8 - power supply pins.

Use asymmetric clipping stage for even harmonics. I suggest schottky diode or schottky with fet as diode.
C8 must be larger. 10uF is better.

Ala tubescreamer overdrive sounds better with 500k gain pot.

modman wrote:

briggs wrote:I'd be interested in trying the OPA2134 in a timmy circuit that has LED's instead of the 1N914 diodes. I prefer the sound of a stock timmy to a stock TS.

Note the original Timmy tweak of making R2 = 12k, no other YATS has that.

OK. I've tried, oh, I've tried, but curiosity has finally gotten the better of me. Timmy? Timmy? TIMMY?

(I'm sure I'll have a forehead slapping moment when I find out... )

Thanks for sharing your excellent layouts!

How does the YATS sound compared to your Eternity build with LEDs.

erikm5150 wrote:Thanks for sharing your excellent layouts!

How does the YATS sound compared to your Eternity build with LEDs.

You're welcome!

The two sound quite different. I would say that this circuit sounds 'thicker' than the Eternity w/LED clippers. It has a lot more gain on tap. Both sound compressed (as any TS does) but in very different ways to my ears. The Eternity works better as a low gain overdrive I think. This one sounds more aggressive and less natural at low gain (as did the CJOD). It does work really well as a low gain boost in front of an overdriven amp!

Deaj wrote:

erikm5150 wrote:Thanks for sharing your excellent layouts!

How does the YATS sound compared to your Eternity build with LEDs.

You're welcome!

The two sound quite different. I would say that this circuit sounds 'thicker' than the Eternity w/LED clippers. It has a lot more gain on tap. Both sound compressed (as any TS does) but in very different ways to my ears. The Eternity works better as a low gain overdrive I think. This one sounds more aggressive and less natural at low gain (as did the CJOD). It does work really well as a low gain boost in front of an overdriven amp!

Thanks for the descriptions.
I already started an E build based on your layouts... I might just convert it to this one instead.
I'm looking for a TS-type OD, but I'm pretty sure I only want one of those.

modman wrote:

briggs wrote:I'd be interested in trying the OPA2134 in a timmy circuit that has LED's instead of the 1N914 diodes. I prefer the sound of a stock timmy to a stock TS.

Note the original Timmy tweak of making R2 = 12k, no other YATS has that.

Modman - not sure where you got your info from - it's incorrect. Tim/timmy never had any 12k resistors in them. Are you talking about a mod that some guy named "timmy" came up with, and not my pedals?? If so I'm sorry for saying you're incorrect

The voltage divider in the tim/timmy pedals is 8k2/10k. Unlike the "yats" designs tims don't have an active opamp EQ section. They use a flat responce opamp gain stage on the output to bump up the output level. The 8k2/10k values were used to allow max clean headroom out of that stage. A standard 50/50 divider would cause asym rail clipping. The values I used came from scoping out the design, and designing for max headroom.

Briggs - if you try LED's you'll have to change the output section. The larger signal coming from the LED's will cause the output amp to clip (ugly/splatty). You can make it a unity gain buffer, but even that can be clipped if the incoming signal get's to high. It's also easy for that stage to clip with low batt voltages. I've been messing around with droping that stage and going with a DC coupled source follower instead. With higher threashold clipping there's plenty of clean gain to still give a good amount of boost without needing the extra kick at the ouput.

Later, PaulC
Tim & timmy pedals

Hey there Paul - I was just about to come back with that conclusion! Lowering the gain sorts it right out. What I did like was placing a FET booster in the place of the opamp stage, that sounded pretty nice and avoided any nasty clipping at all.

The one thing I do like about the Timmy design is the nice smooth gain control. I've got a project coming up that I'm thinking about placing it in (Don't worry - it's a none profit project, charity based! Something that I'm not sure has ever been done with stompbox building )

briggs wrote:Hey there Paul - I was just about to come back with that conclusion! Lowering the gain sorts it right out. What I did like was placing a FET booster in the place of the opamp stage, that sounded pretty nice and avoided any nasty clipping at all.

The one thing I do like about the Timmy design is the nice smooth gain control. I've got a project coming up that I'm thinking about placing it in (Don't worry - it's a none profit project, charity based! Something that I'm not sure has ever been done with stompbox building )

Maybe I'm considered an ingnoramous or something, since I asked earlier- but since you and Paul C are discussing Timmy pedals, and I am not in the US or Europe, can you PLEASE explain what a timmy pedal is. I gather is is a SOTS-type design, but can you be a bit more specific.

There, I'll even say "please".

Not that I'm expecting a reply to this one either.

....can you PLEASE explain what a timmy pedal is.

Did you know that this forum has a search function ?

If you type in: "Timmy" you will get this:
viewtopic.php?f=7&t=140&hilit=timmy

Now maybe you will wonder if Paul Cochrane and PaulC are one and the same person: yes they are......

and if you read the thread you will be able to find guts, schematics etc.

Yes..... and I am sure, that if you ask PaulC friendly, he even will sell you such a pedal....

analogguru

analogguru wrote:

Yes..... and I am sure, that if you ask PaulC friendly, he even will sell you such a pedal....

analogguru

I know you roll your eyes at this AG, but I PM'd Paul and he sold me a "Timmy" at what I consider to be an EXTREMELY FAIR PRICE. Yeah, I could have certainly built one for less, but the price he asked was worth having the "real deal", at least to me.

Because of my surgery I havent had a chance to adequately test it out, but I did fire it up for a minute and was "quite" satisfied.

Remember people that "Paul" isnt the one charging $200 for these on Ebay.

Do you think that it could be possible that you misunderstood my rolling eyes a little bit?

analogguru