EHX Small Clone mods?

[zachlovescoffee]

Howdy!

I ran across this awesome YouTube video and I'm wondering if anyone has any resources for how to perform these mods? The swapping of the depth to a variable resistors I can certainly handle but the rest seem like more research is needed. Hence this post! Any links would be greatly appreciated.

https://www.youtube.com/watch?v=WdLkcecRQJc

[idy]

I see three mods: depth (which you understand) rate LED, chorus/vibrato switch. That's it?

The chorus vibrato switch cuts out the dry signal from the mix. Do you have a schematic you like? The signal goes first into an opamp buffer and then splits, going both into the BBD (with transistor buffers before and after,) and straight through a 22k resistor to mix passively, and then an output opamp buffer. If you lifted that 22k you'd have vibrato.

The rate LED: The lm358 is the LFO. Pin 1 should be good. Add a CLR(2k-10k) to protect LED and control brightness. To ground... Some times you get clicking from this. There are various cures, bigger CLR, buffer....Try it. Also possible on pin 7. I've done it but don't have one around to check how I did it...

[zachlovescoffee]

I see three mods: depth (which you understand) rate LED, chorus/vibrato switch. That's it?

The chorus vibrato switch cuts out the dry signal from the mix. Do you have a schematic you like? The signal goes first into an opamp buffer and then splits, going both into the BBD (with transistor buffers before and after,) and straight through a 22k resistor to mix passively, and then an output opamp buffer. If you lifted that 22k you'd have vibrato.

The rate LED: The lm358 is the LFO. Pin 1 should be good. Add a CLR(2k-10k) to protect LED and control brightness. To ground... Some times you get clicking from this. There are various cures, bigger CLR, buffer....Try it. Also possible on pin 7. I've done it but don't have one around to check how I did it...

Thank you! What does “lift 22k resistors” mean? Like put it in a toggle switch and send it to ground?

[idy]

"Lifting" means literally pulling it out... really you just need to "lift" one end...but better to remove it.  In this case a switch will  allow you to toggle from chorus to vibrato.

It is a little awkward to have a component with one end on the pcb and the other going to a switch (it will break after a few "adjustments") so one finds a way to attach it to the switch. I often use a double pole switch so I have extra terminals to attach the resistor to.
The terminals are numbered
1  4
2  5
3  6

The resistor goes from 1 to 4. The wires to the holes where it came from go to 2 and 5. Or one of the wires can go to the resistor; wires to 1 and 5 or etc.

[zachlovescoffee]

"Lifting" means literally pulling it out... really you just need to "lift" one end...but better to remove it.  In this case a switch will  allow you to toggle from chorus to vibrato.

It is a little awkward to have a component with one end on the pcb and the other going to a switch (it will break after a few "adjustments") so one finds a way to attach it to the switch. I often use a double pole switch so I have extra terminals to attach the resistor to.
The terminals are numbered
1  4
2  5
3  6

The resistor goes from 1 to 4. The wires to the holes where it came from go to 2 and 5. Or one of the wires can go to the resistor; wires to 1 and 5 or etc.

Double Pole Single Throw (on/off?) or Double Throw (on/off/on?)?

So basically, when the switch is "on" or up then the resistor is in circuit and it's chorus but when it's off or down, then the resistor is out of circuit and it's vibrato?

[Govmnt_Lacky]

Double Pole Single Throw (on/off?) or Double Throw (on/off/on?)?

So basically, when the switch is "on" or up then the resistor is in circuit and it's chorus but when it's off or down, then the resistor is out of circuit and it's vibrato?

You need a DPDT ON/OFF toggle. The 22K resistor will be soldered between lugs 2 and 5. The wires where the resistor came from the PCB will be soldered (one each) onto lugs 3 and 6.

Typical toggles work opposite. When the baton is UP, then the middle lugs make contact with the BOTTOM lugs. Plenty of diagrams online to look at if clarification is needed.

[zachlovescoffee]

I see three mods: depth (which you understand) rate LED, chorus/vibrato switch. That's it?

The chorus vibrato switch cuts out the dry signal from the mix. Do you have a schematic you like? The signal goes first into an opamp buffer and then splits, going both into the BBD (with transistor buffers before and after,) and straight through a 22k resistor to mix passively, and then an output opamp buffer. If you lifted that 22k you'd have vibrato.

The rate LED: The lm358 is the LFO. Pin 1 should be good. Add a CLR(2k-10k) to protect LED and control brightness. To ground... Some times you get clicking from this. There are various cures, bigger CLR, buffer....Try it. Also possible on pin 7. I've done it but don't have one around to check how I did it...

Not certain on a schematic, there are many of them. If you have one you can recommend that is high resolution and maybe has a wiring diagram that would be awesome.

For the rate LED, when you say Pin 1 of the LFO -- what do you mean? You mean splicing into the IC at pin one? Assume this means under the board. And also, what is "CLR"? Say question for "pin 7" as pin 1. I'm guessing this LED would flicker with the speed rate selecting from the speed rate mod (below)?

Also, I'm unclear on how to do the "speed rate" mod to get more ring modulation like tones (https://www.youtube.com/watch?v=Pey0qAb4S6U @ 2:57).

Final stupid question for now I have a 3PDT on/on toggle switch (chorus, vibrato) is it possible to add two LEDs to this switch so show when chorus or vibrato are on?


Are we talking about R10 @ 22k? If so, check out these photos to see if I have it identified and have wired my 3PDT (on/off) switch correctly.

[idy]

 That is a lot of questions. Not stupid to ask. But go slow amigo. I strongly suggest you get these mods going one at a time and make sure they work before you tear everything up and wonder where it all went wrong! That said, the vibrato mod is a good place to start. And once it works, yes, with a 3pdt you can add two LEDs or a bi-color LED to show the status. First get the mod working though!

No part numbers on this schematic. But it looks like you have the correct resistor circled for the vibrato mod. You will see a 22k and 33k attached to pin one of the IC1 (a 4558.) That looks like the one you circled. Remove it carefully (how carefule are you? how sure are you about the temperature of your iron? Do you have delicate tools to pull it out? Have you looked at a video or 3 about removing components w/o lifting traces on the board?), and put it on a switch, as I said, using an unused terminal to hold one end. Try that out first before you get deeper.

CLR is "current limiting resistor." An Led hooked up to a 9v battery will flash and burn out pronto. There is a limit to how much current they can take. The long answer is spec sheets, ohms law, blah blah blah. The short answer is 1k us pretty safe for most LEDs with 9v. You are probably not getting that much from the LFO, but I would start there. With LEDs like you want to add to the vibrato mod, you will go to 9v and then you will need an R between 4.7k (the default value on old schematics with old fashioned LEDs and over 10k (a go to for modern super brights.)

But wait and think about all that. Maybe the whole project just needs one bi-color LED; it flashed with the LFO and changes color with the Vibrato/Chorus switch. Just a thought. Other wise you have a bypass LED, a LFO LED, and a mode LED.

I won't go into the depth pot mod yet. It involves removing two Rs and replacing with a pot. The Tonepad schematic shows that.

[zachlovescoffee]

 That is a lot of questions. Not stupid to ask. But go slow amigo. I strongly suggest you get these mods going one at a time and make sure they work before you tear everything up and wonder where it all went wrong! That said, the vibrato mod is a good place to start. And once it works, yes, with a 3pdt you can add two LEDs or a bi-color LED to show the status. First get the mod working though!

No part numbers on this schematic. But it looks like you have the correct resistor circled for the vibrato mod. You will see a 22k and 33k attached to pin one of the IC1 (a 4558.) That looks like the one you circled. Remove it carefully (how carefule are you? how sure are you about the temperature of your iron? Do you have delicate tools to pull it out? Have you looked at a video or 3 about removing components w/o lifting traces on the board?), and put it on a switch, as I said, using an unused terminal to hold one end. Try that out first before you get deeper.

CLR is "current limiting resistor." An Led hooked up to a 9v battery will flash and burn out pronto. There is a limit to how much current they can take. The long answer is spec sheets, ohms law, blah blah blah. The short answer is 1k us pretty safe for most LEDs with 9v. You are probably not getting that much from the LFO, but I would start there. With LEDs like you want to add to the vibrato mod, you will go to 9v and then you will need an R between 4.7k (the default value on old schematics with old fashioned LEDs and over 10k (a go to for modern super brights.)

But wait and think about all that. Maybe the whole project just needs one bi-color LED; it flashed with the LFO and changes color with the Vibrato/Chorus switch. Just a thought. Other wise you have a bypass LED, a LFO LED, and a mode LED.

I won't go into the depth pot mod yet. It involves removing two Rs and replacing with a pot. The Tonepad schematic shows that.

Awesome response and I owe you a beer! I have a few hundred hours soldering PCBs and and point to point amp boards. Variable temp iron, desoldering gun, a good meter and pretty much all of the amateur level tools. No oscilloscope yet but it’s on my Christmas list. Having said all that I am an amateur and I’m still getting used to reading schematics and understanding circuits and components outside of basic tube amps.

I’ll make these mods one at a time starting with the variable resistor on the depth switch swap and report back!

For the LEDs I definitely like the idea of a bi-color to switch between the vibrato and chorus (blue/red). An LED for unit power on/off and a rate change LED tied to the rate knob. For the bi-color is that common cathode or anode?

Thank you!!!

[idy]

You mean starting on the lifted resistor for the vibrato/chorus?
Depth is a different mod requiring replacing 2 Rs and a switch with a pot.
We haven't touched on the high speed mod; that will probably be switch swapping two caps.

For the bi-color, common K, common A, doesn't matter.

[zachlovescoffee]

You mean starting on the lifted resistor for the vibrato/chorus?
Depth is a different mod requiring replacing 2 Rs and a switch with a pot.
We haven't touched on the high speed mod; that will probably be switch swapping two caps.

For the bi-color, common K, common A, doesn't matter.

The simple depth mod where we replace the depth switch with an A100k pot. Cool on the LED!

I have tons of DPDT toggle switches so hopefully that works. I only have one 3PDT toggle at the moment.

[idy]

The "simple" depth mod you describe will not give you any more depth, only less, but maybe you know. The Tonepad (or guitar pcb or madden touchstone) show the depth control that gives more or less.

[zachlovescoffee]

The "simple" depth mod you describe will not give you any more depth, only less, but maybe you know. The Tonepad (or guitar pcb or madden touchstone) show the depth control that gives more or less.

I looked around tonepad and I think I found the schematic. Looks like a B10k wired into two different resistors on the pcb. 39k and 68k? One resistors seems to be removed though I can’t tell which value it is. I’ll keep digging.

[idy]

The depth control involves removing a 4.7k and 2.7k. The 4.7k goes to pin 1 of the lm358 and the 2.7 goes to the switch. When the depth switch is engaged, there is a path to ground and those two Rs make a "voltage divider", reducing the output of the LFO by about two thirds. 2.7/2.7+4.7... =.36, it divides the LFO signal down to about a third.
The pot that takes their place has pin 3 going to the hole for the 4.7k that goes to the Lm358, pin 1 goes to ground, and pin 2 (the wiper) going to the 39k and 10uf cap to ground (that would be the other hole for the 4.7k. Capiche? This method will however give you no depth at all at minimum.

The 68k doesn't figure in, the line we are interested in has a little "loop" where it crosses near that R. The little loop is one way of showing, in a schematic, that two paths don't connect, but cross for the convenience of putting the schematic neatly on paper. Some schematics don't do that little courtesy, but put dots where two "crossing" paths really do connect. The tonepad does both. The one I posted uses loops but no dots...

[zachlovescoffee]

The depth control involves removing a 4.7k and 2.7k. The 4.7k goes to pin 1 of the lm358 and the 2.7 goes to the switch. When the depth switch is engaged, there is a path to ground and those two Rs make a "voltage divider", reducing the output of the LFO by about two thirds. 2.7/2.7+4.7... =.36, it divides the LFO signal down to about a third.
The pot that takes their place has pin 3 going to the hole for the 4.7k that goes to the Lm358, pin 1 goes to ground, and pin 2 (the wiper) going to the 39k and 10uf cap to ground (that would be the other hole for the 4.7k. Capiche? This method will however give you no depth at all at minimum.

Got it. So if it gives no depth at all what's the point? Or are you saying that when the pot is at it's lowest value it proves no depth and as you turn it the depth goes up to maximum?

The 68k doesn't figure in, the line we are interested in has a little "loop" where it crosses near that R. The little loop is one way of showing, in a schematic, that two paths don't connect, but cross for the convenience of putting the schematic neatly on paper. Some schematics don't do that little courtesy, but put dots where two "crossing" paths really do connect. The tonepad does both. The one I posted uses loops but no dots...

This makes sense. It reminds me I need to revisit the beavisaudio tutorials on schematics!

So, in a sense, find those resistors, lift them, wire in the lugs of the pot and test for zero to maximum depth for the depth mod? Or am I missing something? So excited! Once you confirm, in an abundance of caution I will take photos on my board of the offending resistors and draw a little diagram for review to ensure I don't bugger anything up!

Also, I ordered some bi-color (red/blue) common anode LEDs

[idy]

Yes, when there pot is all the way CCW, no depth. When at CW, you will get more than you can now. There is a way to avoid the CCW no depth, you have to add a small value R on the leg to ground, where the 2.7k is now. maybe 1k or less.

[zachlovescoffee]

Yes, when there pot is all the way CCW, no depth. When at CW, you will get more than you can now. There is a way to avoid the CCW no depth, you have to add a small value R on the leg to ground, where the 2.7k is now. maybe 1k or less.

I think I’m catching up. Check out this image. I was able to find the 4.7k resistor that is close to pin 1 of the lm3005 but I’m not sure it’s the right one. On my board is don’t see how they are connected. So, presuming that’s it, lift it, lug 3 and lug 2 get wired in and lug 1 I’ll take to ground.

I’m not sure how the 2.7k fits in? And how it interacts with lug 1 of the depth pot (b10k). If I removed the 2.7k what goes there?

[idy]

You have found the only 4.7k that goes to pin 1 of there LM358, it is the right one.
The 2.7k goes to the depth switch, its just dangling there dong nothing until that switch closes, then it provides a path to ground and "voltage divides.".

So: You remove the 4.7k.
the side of the 4.7k that went to pin one of the 358 goes to pot pin 3 (your "hot" lfo signal).
The other side of the 4.7k goes to pot pin 2. The wiper, the output of your depth pot going on to wiggle the clock (CD4047) speed.
Pot pin 1 goes to ground.
You can leave the 2.7k in place, but remove the switch. It will be isolated.  If you want to remove it, it will provide a handy grounding spot. I think you can use a meter or eyes to determine which side of the 2.7k went to ground.

In short, your little yellow lines are mixed up.

[zachlovescoffee]

You have found the only 4.7k that goes to pin 1 of there LM358, it is the right one.
The 2.7k goes to the depth switch, its just dangling there dong nothing until that switch closes, then it provides a path to ground and "voltage divides.".

So: You remove the 4.7k.
the side of the 4.7k that went to pin one of the 358 goes to pot pin 3 (your "hot" lfo signal).
The other side of the 4.7k goes to pot pin 2. The wiper, the output of your depth pot going on to wiggle the clock (CD4047) speed.
Pot pin 1 goes to ground.
You can leave the 2.7k in place, but remove the switch. It will be isolated.  If you want to remove it, it will provide a handy grounding spot. I think you can use a meter or eyes to determine which side of the 2.7k went to ground.

In short, your little yellow lines are mixed up.

Got it! So what if I run a 1k resistor from pot one to ground to get that CCW tweak you were talking about? One leg of the resistor to lug 1 and the other side to the ground pad of the 2k7 resistor?

Check out the pic. I think I have the wiring correctly. I’ve enumerated the pot lugs and wires. I drew a fake orange wire coming off the 2k7 since I removed it. I added a question mark there and one to a white wire. I believe they were both hooked up to the depth switch. Safe to remove now?

Thank you so much btw! I know it takes your time and effort to read and analyze my work and I really appreciate it.

[idy]

the side of the 4.7k that went to pin one of the 358 goes to pot pin 3 (your "hot" lfo signal).

Are you sure you have right end? I cold have sworn I could see in previous photo that the end near the 358 was connected to pin 1, and that big cap there...no?