Blue magic hiss

Bagge · March 29, 2005, 06:07:15 AM

Hi

I just finished a combined Sparkle boost/ Blue magic stompbox. The sparkle boost really sounds great. I do believe there are some great sounds in the Blue magic as well, but I seem to be getting a lot of hiss. Is it normal for Blue magic to be this noisy? It seems that when I turn up the volume pot with drive low, the noise gets far worser than high drive/low volume.
I read somewhere that mosfets could add a lot of hiss. I would like some comments from others before I start to rewire the whole thing.

hilbi · March 29, 2005, 06:12:20 AM

My Blue Magic is really quiet, no hiss and noise.

Bagge · March 29, 2005, 06:24:31 AM

okay

I'll try to look into the different parts to see if I can find the hiss source.
I just didn't wanna rip it apart if it was noisy.

Bagge · March 29, 2005, 09:40:27 AM

So I finally located the hiss origin to drain of bs170. It is a very audible. I turned down the volume of my guitar to isolate the hiss. But I can't find the source. I tried to change to another bs170, but no change. Could it be the 4,7K resistor? Or is it possible that the power rail cap C3 10uF causes it?

Paul Marossy · March 29, 2005, 10:58:02 AM

Are you sure that all of you solder joints are good? Sometimes a less than perfect solder joint can introduce a hiss into a circuit.

EDIT: I forgot to mention that carbon comp resistors can cause a hiss. What type of resistors did you use?

Bagge · March 29, 2005, 12:14:38 PM

I used carbon film for the 4,7K and have not used any carbon comp resistors. I'll have to check the solder joints as well as some more testing tonight. It's not that bs170 in general adds hiss?

Paul Marossy · March 29, 2005, 12:39:04 PM

My Blue Magic is very quiet. I have no hiss at all. I used a BS170 in it, too.

Bagge · March 29, 2005, 02:19:26 PM

I really don't get this. I changed 4,7K res. to metal film. I also changed a couple of Electrolytic caps and checked and redid some solder joints. It is pretty obvious that the hiss comes from drain of BS170, and move on from there. I might double check on the tran socket.

Bagge · March 29, 2005, 05:09:44 PM

I found out that there is an amount of noise from drain of both J201 in the sparkleboost and J201 in Blue Magic. So the problem must be that the hiss isn't cut away in Blue Magic in a proper way. Could this be C10 o,1 uF?

Paul Marossy · March 29, 2005, 05:35:29 PM

I am not sure what is going on in your case. I built mine exactly per the schematic, and I have zero hiss.

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Blue magic hiss