shaka tube build problems...

[changes]

well i breadboarded it
i used tl082 didn't have any tl072
it sounded like....misbiased
i checked the voltage coming out from the 230V-12V transformer
said 11V AC

here are the voltage ratings on the circuit

V+  11.5
V-  8.8
B   9.1


tube:

1  7.6
2  8.5
3  8.2

6  7.4
7  9.2
8  9

i tried to raise the V+,V- voltage by reducing the 1k,470Ohm resistors but i had no sound at all
so i returned to their original ratings...
what is wrong???isn't the grid voltage too high?how can i lower that???
pleaz help

[Thomas P.]

Do you bias with B? When yes then it is truly misbiased. In my version I fixed the bias at V- . Same is done in the Chandler Tubedriver.
So try getting the bias to V- and report again.
You should also note that it is highly sensitive to the opamp used. Mine sounded good only with a NJM4558.

[changes]

i biased with the 10k all the way down
anyway i think i fixed all problems (except from one)
i raised the supply with success
V+ 15V
V-  12V

tube:
1    4V
2    13.4V
3    13V
6    almost same as 1
7    almost same as 2
8    almost same as 3


i couldn't find NJM4558 so i tested it with an MC4558CN
it sounded awful ofcourse...So i kept the TL082 until i get a TL072 or a NJM4558
At low gain sounds good but at higher gain settings there is an annoying thin noise and it doesn't clip tubish...
any way to get rid of that noise?

should i use a 12AU7 i heard that it will sound milder and better than with 12AX7

[Paul Marossy]

In my latest Shaka Tube build, number 3, http://www.diyguitarist.com/DIYStompboxes/ST1590BB.htm
I used a TL072 and a NOS German manufactured RSD brand 12AT7, and it sounds awesome. I have felt that the Shaka Tube can sound pretty harsh with the tone control too much towards the treble end, but I have found that installing a 0.1uF cap on the output helps quite a bit to make it sound smoother. I actually made this into a bright switch on my Shaka Tube. Your V+/V- voltages look like the what I have measured on my latest build.

A 12AU7 will sound somewhat milder than a 12AT7 or a 12AX7, but the distortion really comes mostly from the opamp. In my 2nd build of this circuit, I used a JRC4558D and I thought that sounded the best of the ones that I tried, but the TL072 seems to break up better. They are also two different kinds of opamps - the JRC4558D is a BJT opamp and the TL072 is a JFET type. They do have a little bit different sound to my ears...  

[Paul Marossy]

I didn't notice this last night, but if you are only measuring 11VAC, that sounds a little low - but it's only just a little bit more than 10% less than 12.6V. In mine, I measured 12.8VAC which is pretty close to right on target. So, what does all that mean? The tube might not last quite as long because it's running on something less than 12.6V, but, preamp tubes don't cost that much, and they can last quite a while compared to power tubes...

[aron]

>I have felt that the Shaka Tube can sound pretty harsh with the tone control too much towards the treble end,

Yes, that tone control used on lots of my pedals needs to be limited in scope. I will have an example of this soon.

[petemoore]

Isn't the circuit side of the Tube supposed to be at a higher voltage?
 Mine's running at 30VDC on the tube bais rails. I only read that tubes run under a certain voltage don't act the 'same'.
 The heater voltage is supposed to be within + or - 10% of the voltage indicated on the data sheet.

[Thomas P.]

I felt that mine sounds best at really low gain settings. The gain pot in my unit is always within the first 25%. I think it would be usefull to limit the gain adjustment with a fixed resistor and a smaller pot value or something like that...

[changes]

the filament gets AC right
can i supply it with DC for less hum
if yes how much volts?

[aron]

The Shaka Tube is pretty quiet. No need to put 12VDC on the heaters. At least the one I have.

[Paul Marossy]

I haven't had any problems with hum in mine. Are you using a wall wart? Perhaps your heater wires are running too close to other wires? Did you twist the heater wires tightly? How old is your tube? I have had some tubes that hum like an son of a gun, probably because they were old...

[changes]

the tube is a brand new Sovtek 12AX7WB
i haven't put the circuit in a box yet
like i said above at low gain level everythin is fine
at high gain there is lots of noise that comes straight into your head killing your eardrums
probably some power supply wire is to close to another one
or i have to use extra shielded wires....

[Paul Marossy]

I did use shielded wire for the connections from the jacks to the bypass switch and from the circuit board to the bypass switch. That might possibly help in your case. What kind of caps did you use? (the ones in the signal path)

[changes]

i used ceramic caps
couldn't get metal film...
i want to make it clip a lot smoother
i lowered the pot but it still cliup a little harsh even at low gain

[changes]

hey aron how can i make my pedal sound as good as in your demo???
help me pleazzzzzzz

[Thomas P.]

i used ceramic caps
couldn't get metal film...
i want to make it clip a lot smoother
i lowered the pot but it still cliup a little harsh even at low gain

Maybe you could try cutting the highs by tweaking the highpass rolloff-frequenzy of the opamp.

edit 1: I should have done some math before :oops:
If I did it right I get folowing roll-offs for high freq. :
gainpot @ 100k: f=6.4kHz
gainpot @ 5k: f=12.7kHz

So high frequenzies shouldn't be the problem here. I guess I'll have to think some more...

[changes]

you mean to replace the 250pF with another value??
will this make it sound softer and smoother???
any suggestions

[Thomas P.]

I made a simulation of the pedal and found out that with the gainpot at 100k, the tonepot at 50% and the level at max. I get a strange frequenzy response. It looks like a bandpass with its peak at 1000Hz and 70(!)dB. At 16kHz it is still somewhere at 40dB. Maybe this could explain the "harshness" described?

[Paul Marossy]

I think in this case, the ceramic caps could be contributing to the lack of tone that you seem to be describing, especially if they are low voltage types. I am pretty sure that Aron used film caps in his, as I did in mine.
As I said before, adding a 0.1uF cap to ground on the output really seems to help it to sound a lot less harsh.

[aron]

The tone pot on any of these Shaka HV tone controls should be at about 9'o clock.