skrm experiments /etap2hw clicking noise?

[idy]

I have been experimenting with experimental noize's SKRM modules (FV-1 daughter boards.)
I first made a mono version (copying from the data sheet) and used this with the guitar fx (G01) module. This was fine, although I wasn't really excited with the effects. Well done little multi-effects unit but on the generic side.

I then built a stereo version for the R02 unit (also from the data sheet.) This I really like, several usable reverbs, nice double delay with separate time for R and L. By having the "mix" function happen in the analog domain you have three parameters to adjust, nice. And separate mix for each channel makes good.

The problem is when I plug their Etap2hw module in to this new stereo pedal (or the mono one.) There are a series of audible "clicks" after you play a note, cycling through the delays. Happens on all 8 programs. Not related to input level (clipping LED works fine.)

Any ideas?

[octfrank]

So the clicks exist only with signal? Silent when no signal? Is the rate the same no matter the program selected?

Just noticed you said you used the example SKRM schematics for the eTap, that may not be correct. Piet wrote the code around his schematic so you may want to try building the full eTap circuit rather than the example for the G01/R01/R02.

[idy]

The clicks accompany the notes I play. A note causes a click regardless of volume/level/program. I am not playing near the clipping level.

You're probably right that I should try Piet's circuit. It seems weird to have to build stereo inputs though... I do see his circuit does mixing in the digital domain, and that he has put frequency shaping in the feedback loops of the opaamps. 

Thanks

[idy]

So I ordered the PCB and kit for the Etap2hw from Newtone Winkel. Price was a little lower than advertised because no VAT. Shipping from Holland to US was only $6 and the package arrived in less than 1 week. Very thoughtfully put together kit.

I assembled it yesterday and... same problem as when the module was in the other pedals:

a click that follows some notes and cycles through the delay. It only happens when I play. Not every note, put when I begin playing sooner or later (like avery few seconds) a note will "catch" and I will get a series of echoed clicks. Not subtle.

Any ideas? Could I have harmed the module by putting it into a data sheet circuit for the SKRM modules? Since the other builds sound fine with the other modules, and the problem is the same in the new PCB, I am doubtful that "its my soldering" or something.

I read the available Bulletins on Echotapper, did the suggested mods: removing the 2 100k resistors from the opamp inverting inputs to ground, changing the two feedback loop low pass ceramics to 220p, changing the two resistors that "pad" the inputs of the opamps. Used the suggested method of choosing S and D resistors for the FETs (the alternate values supplied with the kit worked fine.)

[Ice-9]

This sounds more like the issue lies in the SKRM module rather than the external circuits. What happens if you turn down the volume of the guitar a bit, do the clicks still occur ? When you are hearing the clicks does the clipping LED light up at all ?

I would also check for the correct voltage on the FV-1 chip from the 3.3v regulator.

[idy]

All voltages normal; the daughter board is turning out 3.3v.
The clicks also come when hitting the bypass switch.

When I use the input volume pot (an input trim, 1m with a 220p cap between 1 and 3, 33k padding resistor to 2,) down around 10 o'clock I can get no clicks... at a level way below unity when compared to bypass. When the volume comes up to say 2 o'clock I have unity. I then can turn my strat down to about 5 before click come back. This is no where near where the LED would light (same as the other perfectly working pedals). In fact, if I turn the input and guitar up to where the LED lights, I can play a chord and sometimes clicks, sometimes no.
Its intermittent, I can play maybe 5 seconds without and then it starts. And the amount is pretty much the same with the guitar on 6 and on 10. It doesn't become more or less frequent changing the input level until I get way below unity.

You can change the resistor on the LED and this will not make it light more easily: just dimmer. The clipping LED is either on or off.

It seems to be more like one single click for a group of notes that the echo then repeats. On the reverb setting it is a static sound.

[octfrank]

It seems to be more like one single click for a group of notes that the echo then repeats. On the reverb setting it is a static sound.

This is very odd, if it were a problem on the SKRM board I would expect it to happen with no signal or at the very least have multiple clicks at a non-regular rate with a signal.

What do you mean by "On the reverb setting it is a static sound." ? There is no reverb program on the eTap2.

[idy]

program no. 7 is "reverb and/or tremolo."

Because a reverb is a lot of very tiny delays, the click becomes smeared into static noise.

[octfrank]

Forgot he put that in there. On the reverb, does it make the noise right from the start or only after playing something into it?

[idy]

Only when you play. Same as with the delays, but the multiple tight delays that make a reverb transform the click into static.

[slacker]

Any ideas? Could I have harmed the module by putting it into a data sheet circuit for the SKRM modules?

The only way you could harm the module by putting it in correctly working G01 or R01 circuits is if the etap module doesn't have input capacitors. Piet's support circuit includes caps to remove the 4.5 Volt bias from opamp buffers (C10 and C3 on his schematic) the G01 and R02 schematics lack these, so I assume they must be included on the modules. I'd imagine the etap module also has them but if not connecting 4.5 Volts to the input could have damaged the FV-1.
I don't know if schematics are available for the modules but I guess Frank can confirm if they all have input caps or not.

http://www.echotapper.nl/wp/wp-content/uploads/2011/10/eTAP2hw_1_5b.jpg Piet's circuit
http://www.experimentalnoize.com/wp-content/uploads/2013/04/SKRM-C8-G01.pdf G01 circuit
http://www.experimentalnoize.com/wp-content/uploads/2013/04/SKRM-C8-R02.pdf R02 circuit

[Ice-9]

Any ideas? Could I have harmed the module by putting it into a data sheet circuit for the SKRM modules?

The only way you could harm the module by putting it in correctly working G01 or R01 circuits is if the etap module doesn't have input capacitors. Piet's support circuit includes caps to remove the 4.5 Volt bias from opamp buffers (C10 and C3 on his schematic) the G01 and R02 schematics lack these, so I assume they must be included on the modules. I'd imagine the etap module also has them but if not connecting 4.5 Volts to the input could have damaged the FV-1.
I don't know if schematics are available for the modules but I guess Frank can confirm if they all have input caps or not.

http://www.echotapper.nl/wp/wp-content/uploads/2011/10/eTAP2hw_1_5b.jpg Piet's circuit
http://www.experimentalnoize.com/wp-content/uploads/2013/04/SKRM-C8-G01.pdf G01 circuit
http://www.experimentalnoize.com/wp-content/uploads/2013/04/SKRM-C8-R02.pdf R02 circuit

Yeah Ian you are correct, all the SKRM modules include input and output capacitors, including the eTap module.

[idy]

Any ideas beyond buying a second etap2hw module and seeing if it works?

[octfrank]

Email me at Experimental Noize

[Ice-9]

Any ideas beyond buying a second etap2hw module and seeing if it works?

Have you got the equipment to read and re-program the Eeprom, if so read and save the contents of the Eeprom to keep the eTap2HW code safe, and the write a program that will read the input and write it to the output. This will just pass the dry signal directly through the FV-1. Check for audible clicking.

[eagleaudio]

How exactly do you use the module? Do you mix the signal from two channels into mono signal? There are two known problems with etap2hw and circuits designed by Piet. The first one is incorrect biasing of the input transistor (I hope you don't use the circuit, or you corrected it). The second is the fact that etap2hw is mono effect but FV-1 processes two channels. As far as I can remember, the change of effect parameters affect only one channel (in etap2hw). In the second channel the signal is at maximum values of the parameters (resulting in a very poor sound). If you mix the correct channel with the other you get a very bad sound. Maybe it's the reason why you get clicking. Make sure that you use one channel only. I think that this should be corrected by Piet (maybe it's already done).

PS: you can listen to etap2hw here: http://eagle-audio.eu/gallery/ but of course this is not SKRM module but rather a board designed by me. There is no clicking as you can hear. I'd like to test SKRM modules. I don't think that there is a problem in the design.

Eagleaudio

[idy]

Sorry, forgot about this thread. It was an issue with the module. New module= no problems, works as advertised.
Thanks all.