SHO build with Problems ?

[HOTTUBES]

I have built a SHO circuit and installed it into a 1590B inclosure , my schematic & diagram is from IvIark with the Tiltle " ZVEX SHO TURRET "

I'am using the fallowing components etc .

BS170
5k rev log pot
10meg.  ohm resistors  x 2
5.1 k
100 k
10 uF cap
100 nF  cap
3PDT  switch
5 mm LED


Battery Voltage is 8.76 V
Note : i'm not running a internal battery in this build , its will be run on external DC only !
I have checked everythng several times , and still have not got it to work !!



Here's short description :

It will pass audio , but its all muddy / Farty & distorted  like when you put a diode in backwards etc .
Its also very quiet even at full volume . The pot is scratchy as it should be .....
When you switch the foot switch it goes back to full by pass , full volume and sounds right ! ( Effect off )

Also , the LED does not work at all , and the strange part is that it has only 1.68 volts at the led .
I have installed a 2.2 k resistor on the POS. + side of the Led , and checked & observed the proper
polarity . If i remove the resistor it will work , but blows my Led in a few short seconds ? I find this
kinda strange

I have wired the switch like this ......








Thanks for any help !
I must warn you ....i'm a noob !!  LOL !!

[LucifersTrip]

I have built a SHO circuit and installed it into a 1590B inclosure , my schematic & diagram is from IvIark with the Tiltle " ZVEX SHO TURRET "


Here's short description :

It will pass audio , but its all muddy / Farty & distorted  like when you put a diode in backwards etc .
Its also very quiet even at full volume . The pot is scratchy as it should be .....
When you switch the foot switch it goes back to full by pass , full volume and sounds right ! ( Effect off )

consider removing the switch from the circuit and wiring straight thru to simplify & eliminate that as a problem

Also , the LED does not work at all , and the strange part is that it has only 1.68 volts at the led .

What size led are you using?
I believe a 5mm needs at least 1.8v

I have installed a 2.2 k resistor on the POS. + side of the Led , and checked & observed the proper
polarity . If i remove the resistor it will work , but blows my Led in a few short seconds ? I find this
kinda strange

the obvious would be that you're letting the full battery voltage hit the led. you definitely need a resistor



good luck

[HOTTUBES]

Thanks , i will have a read ......

[Paul Marossy]

Sounds like a misbiased transistor to me.

[HOTTUBES]

I was working on this problem last and found that i some how installed the wrong resisitor that sits between the Drain & gate , it should have been a 10 MEG , but i installed a 1 K resisitor in its place . I have since replaced it with the proper value ( 10 Meg ) , but it still sounds way off imo ......

I have  checked my work on the board as well , as far as i can tell , it all checks out OK ! ( but i must be missing something !! )


Here is the measured voltages at the transistor with effected circuit ON .
These voltage values do not change when in by pass as well ..

D = 4.48 v
G = 2.23 v
S = .475 v




Could this have damaged the trasistor ( BS170) ( NTE490) ?
What resisitor controls the bias ?



Thanks for your help !!

[HOTTUBES]

I replaced the BS170 trasisitor with a new one - no change still sounds crappy !!
I'm still not sure what i have done wrong ......

[HOTTUBES]

any other thoughts on this matter .......




It sucks being a Noob !! 

[IvIark]

Are you sure you've connected DGS to the right tags as marked up?  When I did most of the tagboard layouts I just used the transistor symbol as a graphical representation to show a transistor rather than to show the specific orientation, which is why I mark up the tags with the required pins.  Failing that can you post a pic of the board to see if anything obvious pops out.

[Paul Marossy]

Are you sure you've connected DGS to the right tags as marked up?

Yeah, good point. The transistor might be in the circuit wrong. Always check those pinouts!!!!!

[HOTTUBES]

I have installed the BS170 as shown in your diagram , left to right   Drain - Gate - source .
with the drain connected to the  10uF cap and the source connected to the 3rd pin on the pot .etc

D G S


Thank you for you help !!!!

[IvIark]

Well that's as it should be then.  It is possible that the mosfet has blown because they are susceptible to static and so it's definitely worth trying a new one, or you could have a cold joint somewhere in the soldering perhaps?  The layout has been verified so we know it should work, so maybe if you could post a pic.  You can sort out these little glitches quite quickly sometimes with more than one pair of eyes on it.

[HOTTUBES]

Its possible that may have happened , but i replaced it with a second one , with the same results ....

Is it possible to have the diodes in backwards ?
One should be facing the transistor , and the other towards the 9 volt pos+ wire etc .

How does one test to see if the transistor is blown ?




Thanks again for your help !

I will take some pics of the board and post them later ....

[HOTTUBES]

Ok , here is some pics of the board , its not pretty i must warn you !!!!
Please keep in mind this is my first build ....
























The soldering looks nasty , but i have checked it out , and there's no bridges that i can see or can test with my DVOM ...

[IvIark]

Your layout looks fine to me at first glance, but that last resistor to ground from the output, I see that as brown, black, brown, gold, is that right?  If so you've used 100 ohm instead of 100K.

[HOTTUBES]

Ah !!     Just goes to show that even when you think you have checked it all , ya need to check it again !!!


I swapped out the 100 ohm for a 100 K , and BANG !!   IT WORKS !!!( Imagine that ! )


IvIark , Very Cool of you to help out on this SNAFU of mine !!
A tip of the hat  to you ....


Thanks to all who posted on this thread ........

[IvIark]

Excellent, glad you sorted it out.  An extra pair of eyes helps all of us from time to time

[Paul Marossy]

Ah !!     Just goes to show that even when you think you have checked it all , ya need to check it again !!!


I swapped out the 100 ohm for a 100 K , and BANG !!   IT WORKS !!!( Imagine that ! )

Yay!