Simple stratoblaster problem.

[Buzz]

Hi, I decided to put a stratoblaster in my strat.

I made this vero layout, but so far it won't work, I don't know why.

What happens: When the switch is on bypass it's fine. When I turn the booster on the volume drops drastically. The pot "works" insofar as it turns the volume down from quiet to nothing. There is no static, buzz or any unwanted noises. Just a massive volume cut, instead of boost.

I have substituted a 2N5484 for the original 2N5457 transistor. At C1 I have used a 1uf cap instead of 1.5uf. ( this is fine according to GGG ).

I first put tantalum caps in. When the booster didn't work I replaced them with electrolytics, and put a fresh transistor in the board. The results were identical.

I have checked on the datasheets for the 2N5484 and I believe I've done the pinout right. ( as it is in the layout ).

Nice fresh battery. Measures 9.08v unplugged.  Pos is 8.90v on the board end when the effect is active.

Q1 is D 6.21v
        S  2.86v
        G 0v

[Buzz]

Original schematic was from GGG.

[brett]

Hi
pinout looks right. And the drain voltage indicates that the JFET is 'on'.
If you have a meter, check that the signal makes it to the Gate.
cheers
ps
The Gate connection to ground is via the pickups or pots. I'd add a 1M tie-down resistor between the Gate and Gnd.

[Buzz]

Hi Brett.

Thanks for your reply.

The ground ( in this situation ) is via the pots

How would I test that the signal is making it to the gate? ( sorry, newb )

[Buzz]

....and put the 1M resisor in like this?



If the layout is OK I think I'll bin what I've got and start fresh.

[brett]

Hi again
RE: testing the signal gets to the gate
Turn up the volume, hit a couple of strings and you should be able to measure an AC voltage at the input and hopefully at the Gate. It'll be about 0.1 volts for a second.
(the link to the graphic for the 1M resistor is broken. But if you look at buffers at amz or generalguitargadgets you'll see the large value "pull down" resistors)
good luck

[J0K3RX]

Hi again
RE: testing the signal gets to the gate
Turn up the volume, hit a couple of strings and you should be able to measure an AC voltage at the input and hopefully at the Gate. It'll be about 0.1 volts for a second.
(the link to the graphic for the 1M resistor is broken. But if you look at buffers at amz or generalguitargadgets you'll see the large value "pull down" resistors)
good luck

Should still work without the 1M resistor... Q1 drain may be too high @ 6.21v...? Try to get it lower, 50k trim pot would be your best bet..

[Buzz]

Hi all, thanks for your replies. Got it sorted. The problem was simple, and came down to me rushing the job.
I went to start over this morning, figuring I had all the components and it's easier to build a board than to fix one.
This time I measured the resistors before assembly. Pulled a 100k resistor out of the same bag I had used yesterday, tested it.... 100ohm.
Replaced the resistor in the original board and now all is fine.

I didn't bother adding the 1M resistor as the pop won't bother me, I just like the option of the bypass so the guitar isn't rendered useless by battery death.
It's more of a safety switch.

Well, lesson learned... This has taken me longer and been more of a pain than anything I have built so far.

[Paul Marossy]

This time I measured the resistors before assembly. Pulled a 100k resistor out of the same bag I had used yesterday, tested it.... 100ohm.

I'm sure we have all done that at least once. And we all pulled out our hair just the same until we figured out the dumb mistake we made.  

[duck_arse]

trying to read those blue-bodied resistors has made my hair just fall out, no tearing needed.

[Paul Marossy]

trying to read those blue-bodied resistors has made my hair just fall out, no tearing needed.

Yeah, I don't like those. I use the DMM on those.

[Buzz]

Yup, they're the blue metal film ones. Hair thin lines.

The carbon ones are easier.

But still, mistaking black for orange  must've been late at night....

Lol.

[Buzz]

Also JOK3RX mentions a 50k trimpot to alter the voltage at drain. ( replacing R2 on my layout ). How would this affect the booster?

I assume you could add clarity ( at the cost of volume ) by lowering the voltage. The opposite by raising it. Or would it just work / not work / burn out?

GGG rates the voltages as 6.9v at drain, 1.0v at source, 0v at gate so I'm close enough, but I'm intrigued by the possibility of set and forget tuning the booster to my taste.

I'm going to rebuild it anyway with room for the pulldown resistor. The pop doesn't matter except that it annoys me. Makes it feel like a rubbish job.

Trimpot worthwhile?

[duck_arse]

the trimpot means you can set your preffered drain voltage for a wide range of devices, for maximum unclipped output, or for minimum headroom and max clipping on one polarity of the signal. it's also one less blue resistor to read.