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Hiss

Started by XinTX, July 06, 2007, 02:50:44 PM

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XinTX

Just finished my starter project.  The Noisy Cricket from the Beavis Audio site.  Finished debugging it and it works okay.  But I have a hiss in the sound.  And this circuit has a 'grit' switch, but the switch seems to make little difference other than upping the overall volume and hiss levels.  Any ideas on where to start? 

teemuk

#1
I have no experience with this one but looking at the schematic I see a high value input resistor (will generate some hiss), JFET (hissy), buffer and volume control (signal-amplitude-wise this is only an attenuating configuration) and finally the LM386 with variable gain from value x (gain control at full resistance) to about 200 (gain control bypassed). The power amp pretty much amplifies all the hissing originating from the preamp, which is essentially just attenuating your guitar signal and decreasing SNR. It also seems that the circuit will introduce pretty much low low frequency cut therefore enhancing the high frequency noise in relation to rest of the signal. I'd say the circuit is inherently pretty hissy. Try JFET that has better noise figures or alternatively make it have some gain (to improve SNR) and backup the gain a little in the LM386 circuit.

I never experienced any hiss with similar circuits but then again I have only built LM386 amps with some preamp gain or completely without any preamps. Never got them work OK with the full gain of 200 either. There must be plenty of people on this forum who built Rubys and stuff like this. What's your opininion, are they hissy?

joecool85

I never built a noisy cricket, but I've built a couple little gems.  One ran on 9v the other on 4.5v and both of them were hiss free and quite loud for their size.  I'm not sure what would cause the hissing, but I would check for a bad solder somewhere as that was my issue one time (I had a squealing though).
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

LJ King


Not having a circuit diagram posted, not knowing what a noisy cricket might even be, I can only ask one question:

Did you use carbon comp resistors anywhere in the circuit?

And this may seem sarcastic, but it really is out of my ignorance - does the Beavis audio site have any relationship to the butthole site?

XinTX

Schematic of the Cricket is here:

http://www.beavisaudio.com/Projects/NoisyCricket/DIY/

Don't know about Beavis' friend though.  Maybe he has an FX site now? 

XinTX

Well I think my issues may be due to my desire to use this amp stricly with headphones.  I didn't do anything to reduce the output, just made the circuit like it's on the page in my previous post.  I pulled out an old set of headphones I had laying around that has an inline volume control and turned the volume up on the amp with the 'grit' circuit on.  By upping the gain and volume I was able to make the amp start to distort.  And there was no hiss. 

So my question, how can I add something to cool the output to the headphones without using this ancient set I have (it is kind of cheesy).  Would the addition of a resistor in the circuit just before the phone plug do the trick?