Help reducing hiss from amplifier???

[suprleed]

I just finished my ROG Ruby project and I am very impressed.  I've been running it thru different settings of the vol and gain pots, guitar pickup configurations, pedals in front of it, etc. trying to get a feel for the various sounds produced by the circuit.  So far so good.  I did notice that on high gain settings that I can hear a constant hiss thru my speaker cab.  Using the headphone output the hiss is noticeable even at low gain settings.  My headphone output has a Zoebel network per the GGG layout using a 47uf cap and 10R resistor (I read somewhere that this can help reduce hiss).  My 20 watt commercial SS amp also has constant hiss at high gain/volume settings and it drives me nuts!!!  I'm not sure if this is specific to SS or if the same is true with tube amps as well at high gain settings (I don't own a tube amp)?

Is it possible to completely eliminate hiss from an amplifier or am I doomed to live with hiss whenever I use high gain/volume settings?  Maybe you have to go hi-fi before hiss is noticeably reduced?  Any thoughts?

Thx

[armstrom]

It should be said that a little hiss at full gain is to be expected. In my case I'm feeding the output into a 15W power amp and even then I barely hear the hiss at full volume and full gain, but it's still there.

You can do some testing to find out where the noise is coming from.
Here are my suggestions in easiest to hardest order.

-Try a different power supply. IF you're using a battery then this won't make any difference but if you're using a wall-wart you may be getting noise from there. Either try a different wall wart or switch to a battery.

-Swap out the buffer JFET. Assuming you socketed the JFET just try another one. I've had problems with MPF102 FETS being noisy in the past. Using a different batch or a different manufacturer cleared up the problem.

-Swap the LM386 chip. I've never encountered a bad one, but if you socketed the chip it will be super easy to try another (assuming you have a spare).

-Double-check all your solder joints. You may have a cold joint or a small solder bridge causing interference from another part of the circuit.

-Remove the input wire coming from the jack (desolder it at the board, not at the jack). If the noise goes away then your input wire is acting like an antenna picking up RF interference that then gets amplified by the ruby. Either make the wire shorter or use shielded wire.

-Remove the wires leading to and from the volume pot (again, at the board). Same story here as the input wires.. shorten or shield if they're picking up RF

-Change out the power supply filter CAP (100uF on a Ruby) Either try a different cap or increase it to a 220uF like the Noisy Cricket has. Again, not likely, but who knows.

-If all else fails, rebuild the circuit. This is what I ultimately did.  I was trying to eliminate RF interference in my ruby and somehow "broke" it. Probaby created a solder bridge or something but I have no idea what caused it. Since the ruby is such a simple circuit I decide to just build a new one. It took me all of 30 minutes and it works like a champ.

I hope you find your issue.. the Ruby is a great little circuit.

-Matt

[Jack1962]

I have not built this amp myself( not enough time) however , I will say all of armstrom's suggestions are a good start , however , looking at the diagram of this little amp , I would think it would a small amount of hiss , I would start with changing the 100uf cap (which is recommended on the web page) also I would increase the supply voltage to 12 volts as recommended ( more headroom less hiss).
Also the FET sometimes you get a noisy one , the 386 what can ya say maybe , but I doubt it. there's just not a lot that can go wrong with this little amp. Good Luck

                                              Rock On

[suprleed]

Thanks for the excellent suggestions.  I am running this at 12v with a regulated power supply.  I suppose all circuits will have some degree of hiss, but I'll give your suggestions a try and see what happens.  Thanks again.   :tu:

[suprleed]

I found the source of my hiss.  Turns out it was coming from my pedal chain.  One of my high gain pedals was the culprit.  I had my pedal chain hooked up to the Ruby in my initial tests.  The other night I plugged directly from the guitar to the Ruby and presto, silent as could be even at high gain!  I re-routed my power wires closer to the chassis and fiddled with my pedal chain and got things under control. 

The Ruby is sweet!  Love this thing.

Thanks all.