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Re: Dumbloid

PostPosted: 29 May 2014, 02:17
by rocklander
IvIark wrote:Or do what they did in the Hot Cake and put an 8V2 zener between supply and ground.

my hotcake was still fizzy as hell.. did not like .. which is weird cos I like hot.. and I love cake.

Re: Dumbloid

PostPosted: 29 May 2014, 04:07
by mmolteratx
astrobass wrote:
Manfred wrote:
Ripdivot wrote:All those op-amps have been tried and they don't help the fizzy decay. I have had both Hotcakes and they have the same problem. :hmmm:


thanks, I see there is no quick fix to solve the fizzy decay problem.

Sure there is. Put a diode in.

The op amp rail is at 4.5V, right? Most of the tone you're getting from having one side diode clipped and the other rail clipped comes from the fact that you have asymmetric clipping.

So, use a diode with a 4V forward voltage drop. Anything up to 4.4V should be fine. You want a bit of margin as if you're using battery power, the rails will get closer as the battery decays. If you're using DC then you just need to use your multimeter to check how far the rails ACTUALLY are in your build to verify where the threshold should be. 4V is probably safe though.

Alternatively, if you put diodes in series, their voltage thresholds add up. LEDs clock in around 1.7V, 1N914s and 1N4001s are around 0.65V, so two LEDs and one common silicon diode should set you at about 4V.

This WILL change the sound slightly, but it should be quite close to what you have, minus the fizz. It's easy enough that it's worth trying. You could even use a switch to connect/disconnect just the 4V diode (or the cumulative 4V diodes) to hear the precise difference between the two.


Or two zeners for a lower parts count. I use two 3v6 back to back in a lot of my own designs where I want a decent bit of headroom but don't want the op amp to clip.

Re: Dumbloid

PostPosted: 29 May 2014, 04:17
by astrobass
Yeah, a 3.6V Zener would work as well. Anything in that range. There are also cheap 4V Zener diodes and probably a few others in the 3 to 4.2V range. But not everyone has those on hand, and most do have lower voltage diodes that could be connected in series. The closer you get to the same threshold as the rail, the more it'll sound like the rail.

Re: Dumbloid

PostPosted: 29 May 2014, 06:46
by Ripdivot
astrobass wrote:
Manfred wrote:
Ripdivot wrote:All those op-amps have been tried and they don't help the fizzy decay. I have had both Hotcakes and they have the same problem. :hmmm:


thanks, I see there is no quick fix to solve the fizzy decay problem.

Sure there is. Put a diode in.

The op amp rail is at 4.5V, right? Most of the tone you're getting from having one side diode clipped and the other rail clipped comes from the fact that you have asymmetric clipping.

So, use a diode with a 4V forward voltage drop. Anything up to 4.4V should be fine. You want a bit of margin as if you're using battery power, the rails will get closer as the battery decays. If you're using DC then you just need to use your multimeter to check how far the rails ACTUALLY are in your build to verify where the threshold should be. 4V is probably safe though.

Alternatively, if you put diodes in series, their voltage thresholds add up. LEDs clock in around 1.7V, 1N914s and 1N4001s are around 0.65V, so two LEDs and one common silicon diode should set you at about 4V.

This WILL change the sound slightly, but it should be quite close to what you have, minus the fizz. It's easy enough that it's worth trying. You could even use a switch to connect/disconnect just the 4V diode (or the cumulative 4V diodes) to hear the precise difference between the two.


I tried all sorts of diodes and no luck. I tried them in the first stage too. The one thing I didn't try is placing diodes in both stages at the same time.

Re: Dumbloid

PostPosted: 29 May 2014, 07:49
by johnk
I tried diodes too (to no avail) and the best I could get it to have the least fizz on the decay was to use the LM33172 chip.

Re: Dumbloid

PostPosted: 29 May 2014, 14:46
by astrobass
You'll need the diodes on every op amp that's currently being allowed to go to rails. You're trying to prevent the op amp from rail clipping, while still coming as close as possible to doing so.

If you're still getting fizz, you should check what Vref is in your build. That's the threshold* that you want to undershoot by just a little bit. If you've done so correctly, you're not rail clipping any more. If you're not rail clipping and you still have fizz, then the fizz you're hearing is not a result of rail clipping.

*assuming Vref is exactly or nearly exactly 1/2 V+.

Re: Dumbloid

PostPosted: 29 May 2014, 16:56
by tictac
Reading some engineer's comments on opamp "latch-up" one engineer suggested the following; "Try adding a 1M0 resistor from the non-inverting input (+) input of the opamp to ground. " Something about providing a DC path or something like that...

TT

Re: Dumbloid

PostPosted: 29 May 2014, 17:21
by induction
Isn't there already a 10K from both non-inverting inputs to Vref?

Re: Dumbloid

PostPosted: 29 May 2014, 19:20
by astrobass
induction wrote:Isn't there already a 10K from both non-inverting inputs to Vref?

Yes there would be. He said 1M to ground. I've never done that before. It would be creating a voltage divider with the bias setting resistor, but with it being 100 times the size of the 10K bias resistor, you shouldn't see too much of a reduction in Vref. It should definitely be substantially larger than the bias resistor though.

But I haven't seen it before so I have no idea if that will help.

Re: Dumbloid

PostPosted: 29 May 2014, 19:43
by Ripdivot
Thanks for the suggestions Astrobass. I'll give them a try on the weekend.

Re: Dumbloid

PostPosted: 29 May 2014, 23:29
by mmolteratx
astrobass wrote:
induction wrote:Isn't there already a 10K from both non-inverting inputs to Vref?

Yes there would be. He said 1M to ground. I've never done that before. It would be creating a voltage divider with the bias setting resistor, but with it being 100 times the size of the 10K bias resistor, you shouldn't see too much of a reduction in Vref. It should definitely be substantially larger than the bias resistor though.

But I haven't seen it before so I have no idea if that will help.


Are you sure he wasn't referencing a circuit with a bipolar supply?

Re: Dumbloid

PostPosted: 30 May 2014, 01:44
by astrobass
I have no idea. I was commenting to what the other poster said about a thing he remembered reading from some unnamed engineer at some point. It's highly possible that something's been glossed over.

Re: Dumbloid

PostPosted: 30 May 2014, 07:21
by mmolteratx
astrobass wrote:I have no idea. I was commenting to what the other poster said about a thing he remembered reading from some unnamed engineer at some point. It's highly possible that something's been glossed over.


Whoops. Quoted the wrong person. Searched the quote on Google, and he was definitely referring to a bipolar supply.

Re: Dumbloid

PostPosted: 01 Jun 2014, 10:23
by Manfred
One more question.
Is the intensity of the decay fizz depend on the setting of "Accent" or "Drive", respectively.

Re: Dumbloid

PostPosted: 01 Jun 2014, 17:52
by Ripdivot
Manfred wrote:One more question.
Is the intensity of the decay fizz depend on the setting of "Accent" or "Drive", respectively.


Sort of. The more drive you have the longer it takes for the fizzy decay to happen. The fizzy crackle sound always happens when the notes are transitioning from dirty to clean as they ring out.

Re: Dumbloid

PostPosted: 07 Jun 2014, 07:34
by 1oldsidewinder
I think I'm hearing something a little different. The 3mm LED seems to decay faster than the op-amp clipping, making a transition from fairly severe asymmetric clipping to the op-amp's more symmetric sound as the note fades away. If you look at the accent control, you can see how it's being put to cross-purposes. It not only boosts the gain but also forms a bypass across the LED, changing how the LED conducts as you vary the resistance by advancing it's setting. I've had some luck smoothing out my pedals by replacing the LED with diodes having a slightly lower forward voltage in order to prolong their decay. Haven't run through all the options yet but around 1200mV seems to be the magic number for me. Some diode combinations will change the character of the distortion more than others.

Re: Dumbloid

PostPosted: 09 Jun 2014, 14:03
by ipm
Hi Mr Amplifiednation,

What seems to cause fizzy decay? What is wrong in ivlark's layout?
Thanx.

Re: Dumbloid

PostPosted: 09 Jun 2014, 16:47
by Manfred
I am confused after reading through the pages.
Which have been as first the vero layout or the schematic?
Was the schematic draw separately from the layout or was the layout designed from the schematic?

Re: Dumbloid

PostPosted: 09 Jun 2014, 16:54
by Nocentelli
ipm wrote:Hi Mr Amplifiednation,

What seems to cause fizzy decay? What is wrong in ivlark's layout?
Thanx.


I think you have zero chance of a reply because AN has:
a) Too much respect for the designer
b) $300 clones for sale on his website

Re: Dumbloid

PostPosted: 09 Jun 2014, 17:33
by Ripdivot
I don't think there is anything wrong with Ivark's layout. A friend of mine owns the AN Big Bloom and it has the same crackling decay. I have spent a few hours with it and it is identical sounding to the one I have on the bread board. As far as I know all op-amps do this when clipped to some degree. At the end of the day I think there are better sounding "D" pedals. The dumbloid does have a nice voicing though.