Echo Base - noise

[ACS]

Hey all,

Breadboarded an Echo Base a week or so ago, and was really enjoying mucking around with it.  Noticed that it was a bit noisy at the time, but figured this was just cos it was on the breadboard.  Finally transferred to a PCB yesterday and boxed it up tonight - it's much less noisy now, BUT is still a lot noisier than if 'true' bypassed. 

The noise is the same whether the effect is on or bypassed - best description is simply hiss...

Have tried it on battery with no difference.

Is this just the nature of the beast?  Or is this out of the ordinary?

Cheers
Aidan

[Taylor]

Hey all,

Breadboarded an Echo Base a week or so ago, and was really enjoying mucking around with it.  Noticed that it was a bit noisy at the time, but figured this was just cos it was on the breadboard.  Finally transferred to a PCB yesterday and boxed it up tonight - it's much less noisy now, BUT is still a lot noisier than if 'true' bypassed. 

The noise is the same whether the effect is on or bypassed - best description is simply hiss...

Have tried it on battery with no difference.

Is this just the nature of the beast?  Or is this out of the ordinary?

Cheers
Aidan

Is the noise worse on long delays, or the same always? The EB does get noisy on long times, but mine is not really hissy in other cases. Since there is a lot of off-board wiring, this can create noise in certain cases, with certain other pedals.

[ACS]

No, it's the same at all times.  Including whether bypassed or not.  Just this hiss - similar to what you get when you turn your amp up really loud 

Put it this way - with my Valve Jr, it sounds about the same with the Echo Base bypassed and the amp at about 11 o'clock as when I plug straight in and turn the amp all the way up...

[Taylor]

As with all debugging, it's just about impossible for someone to diagnose it over the internet, but it shouldn't be that noisy. If it's happening when using the tails bypass, you might try swapping the CMOS IC (4066? can't remember) for another one. I've heard people say that sometimes you get a bad one.

[ACS]

Hmmn, tried swapping both the 4066 and the TL072, with no change.  Does the 4066 actually play any part in the processing of the signal, or is it just routing the signal?  ie would it either work, or not work, with no shades of grey?

Got to admit, I'm actually struggling to understand this electronic switching, and can't actually figure out where the signal is going when it's bypassed.  Or am I over thinking things?  Is it just that the 4066 is 'stopping' the signal at pin 1 when bypassed, therefore forcing the signal up through the 10K resistor to the output?  If so, then that narrows down my source of noise considerably...

Schematic here if anyone's wondering what the heck I'm talking about!!

[doug deeper]

mine was also very hissy,
i just gave up on it.
not that you should though!
 

[slacker]

There shouldn't be any hiss when it's "bypassed" all that's in the signal chain at that point is a couple of buffers, they shouldn't add any noticeable noise. What I'd do to try and narrow down what's causing the the hiss is to remove the PT2399, the CD4066 and the LFO opamp.
That leaves just the input and output buffers connected so hopefully the hiss will now be gone. If it is then add the other ICs one at a time, starting with the CD4066, then the PT2399 and finally the LFO opamp, hopefully that will help pinpoint what is causing the hiss.

The electronic switching works like this. The dry signal passes through the first buffer (U3A) and through the 10k resistor to the output buffer/mixer (U3B), this happens whether or not the effect is bypassed. When the effect is "on" U4A and U4D are both closed so the signal can pass through them to and from the PT2399, the delayed signal then gets mixed with the dry signal by U3B. When the effect is "off" in Boss mode U4D is open so no signal can get from the PT2399 to the mixer stage, so you just hear the dry signal. When it's off in tails mode U4A is open so no signal gets to the PT2399, U4D is closed though so whatever signal is currently being processed by the PT2399 is still mixed with the dry signal, to give the tails effect. If you had a lot of noise coming from the PT2399 you would still hear this when bypassed in tails mode. This wouldn't affect Boss mode though and turning the level pot all the way down would stop it.
I wonder if there might be an issue with some CD4066s or more likely with my circuit, because a few people have mentioned problems with the delay signal bleeding through in bypass, mine doesn't have this problem though.

[slacker]

I did a bit of experimenting tonight and mine does indeed have some hiss. At low volumes it's not noticeable, but on my amp with the volume wound up it's there's quite a bit more hiss than either my guitar straight into the amp or running the guitar through a Boss pedal. I wouldn't say it makes the pedal unusable, at those volumes there's plenty of other hum and buzz from my guitar.
Some of the noise seems to be coming from the PT2399 even when bypassed, I'm not sure how this is getting into the signal path, I'll have to poke around with the scope and see if I can figure it out.
I think some of it is thermal noise caused by the 2M2 resistors in the input buffer, changing these to 470k reduces the hiss a lot, but unfortunately leads to some tone sucking. I suppose one option would be to change the input buffer to a non-inverting one, or lower the value of the resistors and stick a Jfet buffer on the front.
I'll have a play about and see what I can do.

[ACS]

Thanks Ian, you've been helping me a lot with this one

Glad that my build seems 'right ' - but I'd love to clean this up... Excluding this issue, this is hands down the best delay I've ever played with... I ended up putting a 100K resistor in instead of the 20K to tame the feedback, but also put a 100K trimmer in line as well.  I then put the feedback pot to maximum, and set the trimmer to just the right level to not quite hit osscilation.  Combined with the tails mode, this gives me a superb sample and hold, that tails off over 30-40 seconds.  Have you seen Dave Gilmour doing Shine by himself with just an acoustic?  Same thing - very cool...

[slacker]

No problem, it's really useful people raising issues they've found, especially if they can help improve the thing.
Glad you like it, apart form the noise yeah the "endless" repeats is cool, bit tricky to dial in on mine, but I like the madness you can get with the 20k resistor, 100k or so is probably more useful for most people though.

I did some more poking about and a lot of the hiss is crap from the PT2399 riding on the 5volt line which is then used to bias the opamps. I thought the regulator would give a solid enough voltage so that wouldn't be a problem, looks like I was wrong though. I breadboarded a new input buffer section, making it a non inverting buffer with some extra filtering on the bias voltage and the hiss is loads better. On my amp at any practical volume level it's now pretty much gone.
It should be easy to mod the vero version with the changes not too sure about the PCB version though.
I'll post a schematic if you want to give it a try.

[ACS]

No problem, it's really useful people raising issues they've found, especially if they can help improve the thing.
Glad you like it, apart form the noise yeah the "endless" repeats is cool, bit tricky to dial in on mine, but I like the madness you can get with the 20k resistor, 100k or so is probably more useful for most people though.

I did some more poking about and a lot of the hiss is crap from the PT2399 riding on the 5volt line which is then used to bias the opamps. I thought the regulator would give a solid enough voltage so that wouldn't be a problem, looks like I was wrong though. I breadboarded a new input buffer section, making it a non inverting buffer with some extra filtering on the bias voltage and the hiss is loads better. On my amp at any practical volume level it's now pretty much gone.
It should be easy to mod the vero version with the changes not too sure about the PCB version though.
I'll post a schematic if you want to give it a try.

Absolutely - do you reckon it might be possible to build the new input buffer section on vero, and just patch it in at the right point on the PCB perhaps?  Is the output buffer still the same?

Thanks mate, awesome work

[slacker]

Yeah if it works you could just build it on a bit of vero and connect it up to the PCB. If you want to give it a try here's the schematic as it stands at the minute.



It's the input and output buffers, I thought about just doing the input buffer but then you'd have half an opamp left on the PCB, so it made more sense to just do them both.

If you wouldn't mind breadboarding this up to see if it helps that would be great. To test it you can just remove the buffer opamp from the PCB and connect this straight up without having to remove anything else.
In and Out go to the in and out jacks, disconnect these from the PCB. Send goes to pin 7 of where the opamp was, you can just shove a wire in the socket. Return comes from the wiper of the level pot, you could disconnect this from the PCB but it works fine with it still connected. +5 volts can come from anywhere on the board you can get to 5 volts, you could just put a wire in pins 3 or 5 of the empty opamp socket.
It might be worth experimenting with a bigger cap for the 47u.

The only issue with this is that the phase of the dry signal is now inverted, personally that doesn't bother me, but if this seems to work I might look at making the output mixer non inverting as well. Then the dry signal wouldn't get inverted.

[slacker]

Send goes to pin 7 of where the opamp was, you can just shove a wire in the socket.

Make that pin 1 on the PCB layout.

[ACS]

Thanks mate, will give this a crack over the weekend...

[ACS]

Hey Ian, had a crack at building this, and have turned my Echo Base into a very impressive fuzz box - kinda cool, but not what I intended!  Need to sit down and debug this when I have a chance.  Am guessing some kind of short between pins 1&3, as the repeats don't sound as I'd expect if the output buffers was clipping...

Being something of neophyte with anything outside of discrete components, what's the purpose of the direct connection between pins 1 and 2?  I'm assuming this is the so-called 'negative feedback loop'...  I guess to my layman's eye I'd expect there to be some kind of control there, and in a roundabout way am asking if this is an error!!

Cheers
Aidan

[ACS]

Haha, ironically the connection between pins 1&2 was the error; ie it wasn't there!!

Added in the jumper and hey presto, all up and running.

Have built this up on to a small piece of perf, and wired it permanently in to the box.  Definitely less noise, so thanks loads for that!  Reckon there still might be some room for improvement, so will have a play with some different i/o buffers at some stage... 

Cheers for a great design Ian - I think that extra cap between the LFO and speed pot and the modified input buffer are both keepers. 

Aidan

[slacker]

Glad to hear it worked. I've got a few more things I want to try to see if I can make it even quieter, I'll let you know how it goes.

[Michael Allen]

Any other additions here for noise Ian?

[alparent]

OK I'm now ready to build an echo bass is there a final layout with all the changes and noise reducing updates Ian made?

I will be making my own PCB layout but would like to have the latest layout.

Thanks

[Subzero]

A small question.
Does the vero ver. posted on the gallery include the modded buffer ?

Thnx