ShakaTube under construction (built, audio sample available)

[transient]

Well, as the title suggests, i started building it. I learned a lot about it using the search function (yes it's my friend ) but i still have a few questions:

1) Do i leave the pins 5,6,7 of the opamp unconnected? Or should they be grounded or something? I remember (though not clearly) reading something about grounding the unused half of an opamp to prevent oscillations, but i'm not sure if i should do it for Shaka Tube.

2) I have an AC 14V 0.8A Boss adaptor. Its output voltage without a load measures 15.6 V. I've read that it isn't good for tube life to use more than 12V for the heaters, but can i at least use it for testing purposes until i get a 12V adaptor, or would it destroy the tube pretty quickly? (I have a no-name tube that i wouldn't mind hurting a little ) Or would adding 1W resistors drop the voltage to safe levels?

Thanks...

...
emre

[aron]

>1) Do i leave the pins 5,6,7 of the opamp unconnected?

I left them unconnected but you could tie the inputs to ground.

2) I have an AC 14V 0.8A Boss adaptor. Its output voltage without a load measures 15.6 V.

I used a regulated 12V adaptor from Radio Shack. I'm not sure that that higher voltage would do to the tube.

[transient]

Thanks Aron

Can i use zener diodes to drop the voltage? Or should they only be used with DC?

.
e

[petemoore]

I'd try Si, like 2n4007 or 4001's, seriesing them 'till it drops to  V<13v .
 Using a voltage regulator is another option, as long as it meets the current requirements...

[aron]

I don't know. If I had to guess and I am guessing, I would think you might need a transformer to reduce AC like this:

http://www.geofex.com/Article_Folders/vintvolt/vintvolt.htm

[transient]

Thanks guys. Well, i decided to make it right, so i'm going out to get a 12V adaptor

By the way, the build is finished. How do i set the trimpot? Does it have to be set to a specific voltage, or do i set it by ear?

.
e

[Merlin81]

From what I've heard Aron tell others, Just set it where it sounds right. Paul M. set his hard to the side, all the way up. More gai nthat way, I suppose.

[transient]

Ok, thanks : )

One more question, i used 16V capacitors for the power section, and a few 25V caps are used in the main circuit. Would it be a problem? V+, V- and B voltages all measure below 16V with the bias not set. Would setting the bias trimmer to min or max result in higher voltages?

...
emre

[transient]

I got impatient and measured the voltages while adjusting the trimpot. Luckily none of them goes above 13V, so i guess i'm safe.

[transient]

I got it working!



It's pretty much at the testing stage, so there are cables and electrical tapes everywhere. In addition to that, i've run out of enclosures, so it will have to wait 'till my next small bear order, to get boxed up.

I adjusted the bias roughly, as it's hard to find the proper bias point with the current trimpot. I'll try replacing it with a lower value trimpot and a fixed resistor to fine-adjust the bias.

One thing that surprised me, is the amount of gain this circuit has. It pretty much becomes a high gain pedal when the drive knob gets past 8 o'clock. I guess it's the result of the lowered headroom caused by running the tube at low voltage. I'll get lower gain tubes to see if it helps.

By the way, where's the distortion generated, in the opamp or the tube?

As it's been stated before, it becomes a little too bright when the tone knob is set above 9-10 o'clock. And i guess there's a HP filter somewhere, it has less bass than unity. Both these could be modified for a better sound.

Anyway, my first impression is that it sounds good. I'll try modding it to my taste (mainly to make it a bit fatter and lower gain). Thanks a lot Aron, both for the circuit and your help

(I may post a sound sample soon)

...
emre

[Paul Marossy]

Rock on!  It's still one of my favorite pedals.

[transient]

I know Paul. In fact, i might not have built it if you had not advertised it so often

...
emre

[transient]

Here's a short recording with my ShakaTube.

The rhythm guitars are recorded with the drive pot at its minimum setting, the solo has a little more drive (but it's still pretty close to 0). The tone pot is all the way down for both rhythm and lead.

There's a little hissing, but it's not related to ShakaTube. I couldn't crank my amp, so i had to crank the mic pre which added the hissing. ShakaTube is pretty quiet, it's sitting right in front of the computer monitor, and it's not boxed up yet, but there's no hum whatsoever

Anyway, enjoy

...
emre

EDIT: The mp3 link does not work anymore, but you can get the mp3 file from here:
http://diystompboxes.com/pedals/sounds/transient_shakatube.mp3

[Paul Marossy]

I know Paul. In fact, i might not have built it if you had not advertised it so often

...
emre

LOL.  :lol:

Nice soundclip. It is amazing how quiet mine is, too.

[MartyMart]

Great work transient, I'm starting mine tomorrow
I just need a "tube base" to hold in/wire up as I have a spare 12AX7
my CV4070's would work, but require a different "bias" .... so I may try
one of those too.
Cheers,
Marty

[markr04]

I wanted it to work so badly, but my build was a failure. Gated farts with the bias not set correctly and screaming oscillation 10x louder than the input when biased.

Your clip and build report have inspired me to rebuild the pedal. Thank you.

[transient]

Thanks

Good luck with your build Marty.

And Markr04, i hope your re-build works fine. One thing to keep in mind though, is that i have tried 3 tubes (all 12AX7), and i couldn't bias the circuit with one of them. The other two tubes work fine. So you might want to try a few tubes.

...
emre

[MartyMart]

Thanks transient, both boards are done and I get the tube socket tomorrow
I guess tubes are like transistors ---- NOT all the same eh !!
That sucks, as I only have 1 12AX7 .....  :shock:

Marty.

[barret77]

the sound clip sounds really good...

[GreenEye]

Wow - great sound clip!!  I'm lazy - could you post a link to the schematic?