My Shaka tube works great in multisim9 but fartgates in reality...

[frickecello]

Hi, I have read a lot of similar posts about the shaka tube "fartgate" issue....

I captured the circuit (multisim9) with the original schematic component values, but as soon as I clicked siumlate, it crashed..... and crashed and crashed....

So I studied the circuit...... maybe that 220 ohm resistor is the problem (from the inverting output)...... and changed it for a 1.7k...... also I calculated the value for the cap...

Voila! it worked but... just in the simulator I recorded 10 secs with my guitar and ran the simulation !!!! it didnt crashed this time  and distorted!

Then returning to reality.... I changed the resistor and the cap from my pcb..... and all I can hear is a loud eerie (like eee!) sound..... and the fartgating is not gone yet...

Any advice?

[aron]

If the op amp is biased properly it will not "gate". 220 vs. 1K vs. 1.7 will not affect the biasing of the op amp.

>Any advice?

Yes, perhaps you have a mis-wiring problem and/or oscillation as well?

[R.G.]

When a new doctor gets out of med school and into internship, they teach them the following aphorism: If you hear hoofbeats in the hallway, look for horses, not zebras.

Meaning obviously, if something is wrong, check the simple, obvious things first before you go looking for rare, unusual causes.

The beginner wants to believe that their circuit doesn't work because something like the gain-bandwidth of the opamp is resonating with the barium titianate plating on the leads and causing electrochemical noise pulses in response to ambient light, when in fact there's a bad solder joint, backwards transistor, or misplaced wire.

That doesn't mean you'll never find a zebra (especially if your internship is in sub-Saharan Africa) but it does mean that you should look for the simplest possible explanation. Occam's Razor still applies. I think that Mother Nature must have written Occam's Razor into some of her Rules.

[Paul Marossy]

Three questions:

1. How did you build it? Perfboard or a PCB layout?
2. How do you have the bias set? (referring to V+/V-)
3. Are you sure that you have your bias network wired up properly?

[frickecello]

First of all thanks for your reply, my V+ is 14.8 volts and V- is -10 volts, B voltage is set to 1.6 volts...

When I set the bias pot to half I cant hear any sound just a loud popping when I strum hard... and when I make B voltage more negative the thing starts to sound only when I "strum hard" but it fartgates to zero, also when I move the tone pot a loud eeeeeeee sound is heard that varies in pitch as I move this pot...

Its not a pcb layout issue because Im not using Paul's layout, I did one myself, I read a similar post from a guy that had or has, EXACTLY the same problem, the post is called "opamp weirdness"...

I tested the input of the circuit with the audio probe the weird thing is that the signal is lost at the input every 30 seconds of so, the same thing that happened to mark04 the guy that started the "opamp weirdness" topic...

[Paul Marossy]

Well, you must have a wiring mistake somehwere then. I can assure that the circuit works great as per the schematic. 

[fikri]

I can assure that the circuit works great as per the schematic. 

I made my own layout, with separate PCB for the tube and the opamp section http://fikri_ilyas.blogs.friendster.com/photos/new_project/img_4082.html and had no problem with it.

[frickecello]

I finally finished it, I expected a lot more from it  but Im going high voltage now.... I will try one of those Marshall 2203 preamp stompbox clones.... (Hotbox, Hoffman, High octane, etc etc)

[Paul Marossy]

It's got a "starved tube" sound. It's not going to sound like a Hot Box or similar pedal... 

[aron]

I finally finished it, I expected a lot more from it  Tongue but Im going high voltage now.... I will try one of those Marshall 2203 preamp stompbox clones.... (Hotbox, Hoffman, High octane, etc etc)

Who knows if your pedal even sounds correct. It had problems from the beginning. Don't you love DIY?

Please read about safety procedures before starting. Wiring mistakes with high voltage can be deadly.

[aron]

Does yours sound like this?

http://diystompboxes.com/pedals/sounds/shakaTubeDemo.mp3

[frickecello]

Im sorry if I offended you Aron, it was not my intention,  yes I finally finished it, it is really quiet and it is working ok, I dont like it because it didnt gave an audible valve character to the sound, but it is just my opinion, and I know it is a starved plate topology... dont get mad with me, you probably prefer fender amps and dislike vox amps for example, everyone has its personal likes and dislikes....  I have tested it with an ecc83 (12ax7) and ecc82 (12au7), I think it sounds better (to me) with the ecc82 
Well 220 volts can be as deadly as 12-15v, how about a car battery?? 

Best regards!