Mark Hammer's Forty Niner sounds gated...

gigimarga · July 15, 2008, 10:59:57 AM

Thx gez...i'd tried what you said and still i have some oscillation.

gez · July 15, 2008, 11:39:05 AM

So you always get oscillation when SW2 is engaged, regardless of how the other knobs are set?

gigimarga · July 15, 2008, 04:26:03 PM

I've tried 49er again this afternoon and i observed the next two aspects:

1. if i roll down a little the boost pot (10k) then the oscillation disappear
2. the boost pot have almost no effect.

Thx a lot gez!

gez · July 15, 2008, 05:24:39 PM

The filter looks like an 'activated' bridged-T. The leg of the filter with the caps is bootstrapped from the output of the op-amp via the boost pot and its stop resistor. When SW2 is engaged the amp goes from unity gain to a gain of 2, so it wouldn't be hard to create a +ve feedback loop that is causing oscillation.

When gain is set above unity to create a resonant peak, it's not usually as high as 2 (well, not in my limited experience). Obviously someone has got it to work with that gain, though! I think a lot would depend on layout. It could also be that the wires to your boost pot are too long and are picking up stray capacitance (shielded wire would help here), but more likely that your problem is too much gain in this stage. Try reducing R8 (the 10k resistor from output to - input). You'll probably find that oscillation stops somewhere in the 2k2 - 4k7 range, but see what you can get away with (make the resistor as high as possible). Alternatively, make the stop resistor (R6) bigger. This might be the better option if you want a little more kick to drive the inverters.

As far as the boost pot having no effect goes, perhaps the frequency boost is in the wrong range for the pickups you use? Play around with cap values.

spud · July 15, 2008, 05:47:18 PM

Hi - been following this thread and I was interested in knowing which of the 4049 pedals you've built and which one sounds the best? I've built a DD (twice) and both times I've had problems. First was on Perf and I could never quite get the Bounce channel to work - Jiggle was ok. On the second try I built it on bread board and again the Jiggle is fine but the Bounce is not working right - this time it produces sound but tends to oscilate like crazy even at very low settings of gain (drive?) and volume. I'm still poking around and trying to get it quite down but no luck. I was interested in the 22/7ths as well (on breadboard first)- what modifications did you make to it - also, you said the UBEScreamer was good, I'm going to do that one too (on breadboard first). My plan is that if I can get it to work well on breadboard I'll build it into a perf or IC perf type board (I haven't tried etching yet) - ultimately, I'd like to get a decent sounding one to use as a SS amp pre-amp for like the TDA series or LM3886 chips.

Thanks for the great info -

SPUD

gigimarga · July 16, 2008, 02:10:37 AM

Thx gez...i will try to change the resistors as you wrote.
The boost pot seems to act strange because when i switch the caps using SW1 i hear a boost on mids or highs (so the caps have right values IMHO), but i can't control the boost level.

Anyway, my great mystery is why the demo of Mark Hammer sounds so good and mine no???

gez · July 16, 2008, 02:44:34 AM

Quote from: gigimarga on July 16, 2008, 02:10:37 AM
The boost pot seems to act strange because when i switch the caps using SW1 i hear a boost on mids or highs (so the caps have right values IMHO), but i can't control the boost level.

The boost pot isn't meant to increase volume, it accentuates a certain band of frequencies to varying degrees. All the pot does is subdue the effect as its resistance increases (I'm assuming this - I've never breadboarded the forty niner or played around with this filter). If the effect is still pronounced when the boost control is at its lowest setting, then perhaps a larger value pot would help so that you can hear more of a contrast between the max and min settings. It's also likely that you'll hear more contrast once gain is reduced (or the value of the stop resistor is increased).

Spud, presumably your question was directed at gigimarga? (the only CMOS circuit I've ever breadboarded was Craig Anderton's guitar player one; everything else I've played around with has been of my own invention).

spud · July 16, 2008, 10:50:26 AM

Yes - I'm sorry I wasn't clear - but of course if anyone has any insight or opinions on 4049/4069 circuits that they have built and sound good please comment and share your experience.

gigimara I'm sorry if this is going off topic - maybe I should start a new thread or is there one already out there somewhere on this topic??? Anyone have a link?

spud

gigimarga · July 16, 2008, 11:27:52 AM

you can do as you wish...no problem from me...

another very well sounding 4049 circuit (for me) it's UBEscreamer...i like it a lot!

Mark Hammer · July 16, 2008, 01:05:32 PM

How about we start from the proper starting point?

Has anyone built this project successfuly using the GM layout? I'm certainly not questioning the quality or reliability of the good doctor's work or Radu's etching skills. I just want to be able to start with a correct assumption that a) the layout itself has no corrections needed and does not itself generate any of the symptoms Radu notes, and b) none of the symptoms reported are a result of the wiring or PCB.

As for the booster portion, it should not produce any oscillation. The combination of a 5k6 fixed resistor and 10k pot should provide a minimum and maximum amount of boost that should not break into oscillation. Is it possible that one of the resistances is not the proper value?

As for the sound clip I posted, I did not do anythng very different, except that I built mine using perfboard.

gez · July 16, 2008, 02:06:39 PM

Quote from: Mark Hammer on July 16, 2008, 01:05:32 PM
How about we start from the proper starting point?

Has anyone built this project successfuly using the GM layout? I'm certainly not questioning the quality or reliability of the good doctor's work or Radu's etching skills. I just want to be able to start with a correct assumption that a) the layout itself has no corrections needed and does not itself generate any of the symptoms Radu notes, and b) none of the symptoms reported are a result of the wiring or PCB.

As for the booster portion, it should not produce any oscillation. The combination of a 5k6 fixed resistor and 10k pot should provide a minimum and maximum amount of boost that should not break into oscillation. Is it possible that one of the resistances is not the proper value?

As for the sound clip I posted, I did not do anythng very different, except that I built mine using perfboard.

As well as layout, Mark, op-amp choice might have something to do with it. Input capacitance and stability of an amp at low closed-loop gain could both be a factor here. I know from personal experience of cranking up the Q in SV filters that some chips behave impeccably, whilst others whistle like a kettle on boil, even at moderate Q settings.

gigimarga · July 17, 2008, 02:49:31 AM

Thx all!

Mark, in the post http://www.diystompboxes.com/smfforum/index.php?topic=68652.msg552532#msg552532 awitee seems to have the same problems as me...i've made the mods that you indicated there...so it's strange to me.

lokki · June 24, 2014, 07:15:31 PM

zombifying this thread...

had exactly the issues described by others with the gaussmarkov layout. solved it with sw2 connected to ground and a cap. i too have oscillation at high boost settings when the switch is set to low mode. changed power supply to match mark's original schematic.

but the sound is very nice!!!

Strat68 · January 14, 2015, 08:44:02 PM

Quote from: Mark Hammer on July 16, 2008, 01:05:32 PM
How about we start from the proper starting point?

Has anyone built this project successfuly using the GM layout? I'm certainly not questioning the quality or reliability of the good doctor's work or Radu's etching skills. I just want to be able to start with a correct assumption that a) the layout itself has no corrections needed and does not itself generate any of the symptoms Radu notes, and b) none of the symptoms reported are a result of the wiring or PCB.

As for the booster portion, it should not produce any oscillation. The combination of a 5k6 fixed resistor and 10k pot should provide a minimum and maximum amount of boost that should not break into oscillation. Is it possible that one of the resistances is not the proper value?

As for the sound clip I posted, I did not do anythng very different, except that I built mine using perfboard.

As I raise this from the dead again. I finished it today from the GM layout. But the only control that has any noticeable affect is the volume. Gain, maybe a touch. I'll try it on a different amp/guitar combo to see what happens.

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Mark Hammer's Forty Niner sounds gated...