Dumbloid  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
User avatar
rocklander
Old Solderhand
Information
Posts: 2726
Joined: 18 Apr 2008, 11:33
my favorite amplifier: my jansen bassman 50
Completed builds: rebote 2.5; supreaux; odie; heartthrob tremolo; ross phaser; dr. boogey; thor; baja black toast; slow gear attack, rebote, tri-vibe, small clone, little angel, magnus modulus, echo base, hex fuzz, big muff, 22/7.
Location: Rotorua, New Zealand
Has thanked: 1406 times
Been thanked: 231 times
Contact:

Post 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.
world's greatest tautologist ...in the world
Ronsonic wrote:...the lower the stakes the more vicious the combat.

User avatar
mmolteratx
Degoop Doctor
Information
Posts: 508
Joined: 19 Dec 2009, 01:50
Has thanked: 93 times
Been thanked: 619 times

Post 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.

User avatar
astrobass
Cap Cooler
Information
Posts: 548
Joined: 02 Mar 2013, 01:30
Has thanked: 42 times
Been thanked: 74 times

Post 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.

User avatar
Ripdivot
Resistor Ronker
Information
Posts: 316
Joined: 19 Jan 2008, 19:15
Location: Canada
Has thanked: 8 times
Been thanked: 78 times

Post 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.

User avatar
johnk
Resistor Ronker
Information
Posts: 282
Joined: 05 Apr 2010, 07:33
Has thanked: 36 times
Been thanked: 293 times

Post 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.

User avatar
astrobass
Cap Cooler
Information
Posts: 548
Joined: 02 Mar 2013, 01:30
Has thanked: 42 times
Been thanked: 74 times

Post 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+.

User avatar
tictac
Breadboard Brother
Information
Posts: 149
Joined: 27 Nov 2008, 07:30
Been thanked: 10 times

Post 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

User avatar
induction
Resistor Ronker
Information
Posts: 276
Joined: 07 Feb 2012, 20:47
Has thanked: 61 times
Been thanked: 116 times

Post by induction »

Isn't there already a 10K from both non-inverting inputs to Vref?

User avatar
astrobass
Cap Cooler
Information
Posts: 548
Joined: 02 Mar 2013, 01:30
Has thanked: 42 times
Been thanked: 74 times

Post 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.

User avatar
Ripdivot
Resistor Ronker
Information
Posts: 316
Joined: 19 Jan 2008, 19:15
Location: Canada
Has thanked: 8 times
Been thanked: 78 times

Post by Ripdivot »

Thanks for the suggestions Astrobass. I'll give them a try on the weekend.

User avatar
mmolteratx
Degoop Doctor
Information
Posts: 508
Joined: 19 Dec 2009, 01:50
Has thanked: 93 times
Been thanked: 619 times

Post 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?

User avatar
astrobass
Cap Cooler
Information
Posts: 548
Joined: 02 Mar 2013, 01:30
Has thanked: 42 times
Been thanked: 74 times

Post 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.

User avatar
mmolteratx
Degoop Doctor
Information
Posts: 508
Joined: 19 Dec 2009, 01:50
Has thanked: 93 times
Been thanked: 619 times

Post 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.

User avatar
Manfred
Tube Twister
Information
Posts: 1937
Joined: 04 Apr 2009, 23:42
Has thanked: 1671 times
Been thanked: 1344 times

Post by Manfred »

One more question.
Is the intensity of the decay fizz depend on the setting of "Accent" or "Drive", respectively.

User avatar
Ripdivot
Resistor Ronker
Information
Posts: 316
Joined: 19 Jan 2008, 19:15
Location: Canada
Has thanked: 8 times
Been thanked: 78 times

Post 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.

User avatar
1oldsidewinder
Information
Posts: 42
Joined: 01 Mar 2011, 14:37
Has thanked: 18 times
Been thanked: 6 times

Post 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.

User avatar
ipm
Information
Posts: 10
Joined: 06 Jun 2012, 22:23
Been thanked: 1 time

Post by ipm »

Hi Mr Amplifiednation,

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

User avatar
Manfred
Tube Twister
Information
Posts: 1937
Joined: 04 Apr 2009, 23:42
Has thanked: 1671 times
Been thanked: 1344 times

Post 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?

User avatar
Nocentelli
Tube Twister
Information
Posts: 2222
Joined: 09 Apr 2009, 07:06
Location: Leeds, UK
Has thanked: 1152 times
Been thanked: 954 times

Post 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
modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

User avatar
Ripdivot
Resistor Ronker
Information
Posts: 316
Joined: 19 Jan 2008, 19:15
Location: Canada
Has thanked: 8 times
Been thanked: 78 times

Post 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.

Post Reply