Amp Help(Electronics problem)

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Permalink Reply by Ron "Oily" Sprague on September 15, 2012 at 10:54am

You yourself, with your bod, have been taking the place of a multimeter. You touch bare metal on the speaker chassis, vol comes up, you grounded something. You touch both chassis and cable jack shaft, everything's hunky dory, you grounded something correctly. My guess would be to check your wiring, solder joints, and make sure that all your grounds tie to the back of the vol pot before the single ground to the jack. If you left out the Tone pot on the Noisy Cricket schematic, then it's possible your wiring ain't zackly kosher.

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Permalink Reply by Ross Porter on September 15, 2012 at 11:19am

Thanks for the reply Oily,

Grounding was my first thought but I tried running a ground wire and I couldn't duplicate "my touch". 

From my limited understanding of the LM386 the volume/tone circuit in the NC should be a stand alone thing. My  thinking (and my bench test) would be that changing it to a simple volume circuit shouldn't effect the rest of the amp. Perhaps my thinking is wrong and I need to just study more and start from a basic amp in the datasheet and work out to get what I want.

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Permalink Reply by Ross Porter on September 15, 2012 at 11:26am

I should add I have been rechecking everything and continue to. Don't want you to think that part fell on deaf ears.

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Permalink Reply by Ron "Oily" Sprague on September 15, 2012 at 11:37am

Ross,

Hmm. The NC uses an LM386...somewhere in the back of my mind, there's something niggling me about reading what happens if you just run a simple vol pot on the NC circuit...I can't access runoffgroove.com from here at the moment to check. Or was it ax84.com?

The Tone pot also helps with noise reduction on that circuit; I believe it has either a .022 or .043 microFarad cap across it. What's bugging me is that I think I remember reading you can jump a cap across the Vol pot in the same fashion, and that also helps with noise.

IIRC, there's a Builder's forum at runoffgroove...

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Permalink Reply by Ross Porter on September 15, 2012 at 11:43am

I found it from beavisaudio, I'll do some looking at both of those in a bit and see if anything pops up. Thanks again.

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Permalink Reply by Ron "Oily" Sprague on September 15, 2012 at 11:40am

Bah. It was beavisaudio.com

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Permalink Reply by RTZGUITARS on September 15, 2012 at 1:25pm

At the very least you need the speaker output to go through a cap and then another cap to ground. This will get a lm386 working and at the right temp. Listen to Oily it sound like a lose ground somewhere best to ground eveything you can. It takes a few chips and boards to get what you want cause we ain't electrical engineers. I don't use the tone on my amps mostly not enough room or i'm lazy if I want to shape the sound i use my pedals. GOOD LUCK

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Permalink Reply by Jim Woods on September 15, 2012 at 2:35pm

I use the LM386 - Noisy Cricket plan for my amps.  I have to jump a ground to the speaker chassis from the negative lead of the speaker.  

I also could not get mine to work with ceramic caps for the small ones (100nf,  22nf,  47nf, etc).  The worked when I used mylar (gumdrops)  not sure why?

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Permalink Reply by Ross Porter on September 16, 2012 at 7:01pm

Thanks for the replies guys

RTZ - I ask as I haven't noticed any ground side caps in schematics, where do you put the cap on the ground side?

Jim - I find it interesting that you have trouble with the ceramic ones as that's all I've used (size and application) and have had no problems.

Well I haven't had much time to fiddle with it but here's where I'm at.

I'm starting to think my problem lies in the fact that I'm trying to use two 2.25x4 speakers. As I messed with my test amp and breadboard I did accidently stumble across the fact that putting an extra cap (47 or 100 tried both) in before the vol pot helped but didn't solve the problem.

I may tinker with it some more but after looking at runoff (Thanks for pointing me there Oily) I'm starting to think about starting over and going w/ a litle gem2. When I had this one working it has a nice clean sound that I was using the 2 speakers to achieve but I think they are a bit much for the cricket. <-- Possibly part of my overall problem?

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Permalink Reply by RTZGUITARS on September 17, 2012 at 2:43am

The circle is the cap to ground the line going up is a way I have done them for some reason but don't take my word cause I just wire them tell they sound good. I think this is the Ti. schematics thats the site to go to. I only wire volume and gain and don't do anything that cut volume. Watch the polarity of the caps.

 

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Permalink Reply by Ross Porter on September 17, 2012 at 7:18am

Thanks RTZ, that's way different than what I had pictured when I read above. I think that would would act like a treble bleed for tone but it gives me something else to try. 

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Permalink Reply by Jim Woods on September 17, 2012 at 7:08pm

Ross,

That circled cap is listed as a .047uf in the little cricket.  It needs to be there to make mine work - I messed with one for way too long trying to toubleshoot before I realized a 10 M ohm resistor is definitley different than a 10 ohm ( the one in series with the circled Cap)

A cap ( .022u , .047u or .1u ) in series with the input going to the Vol pot does help considerably.

The Little Cricket has a .1u cap from 7 to ground that helps a lot if you are getting imperfect voltage input.  I noticed a huge difference whan using a 9v adapter.

 

I assume you are looking a a schematic like:

  

 

Attachments:

• lil cricket.jpg, 11 KB

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