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Author Topic: debugging a small amp  (Read 24566 times)

kin0

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debugging a small amp
« on: May 11, 2011, 11:09:07 AM »

Hay, today I finished building my first ss amp. It's a 8w chipamp kit for the power amp and the barber ltd (silver fox clone) for preamp. The power amp worked great and made sounds but after I added the preamp I can just hear white noise (then I turn on the drive channel i hear more gain but still no sound). What places to check and how to debug?
Here is the topic with my project planning (in the end I put a barber ltd instead of the shredmaster and used only 1 drive pedal instead of 2)

http://www.ssguitar.com/index.php?topic=1834.msg12006#msg12006
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tonyharker

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Re: debugging a small amp
« Reply #1 on: May 11, 2011, 11:39:34 AM »

Sounds like the preamp is at fault.  Did you build it yourself from a kit or was it ready made?  Do you have the circuit for it? 
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kin0

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Re: debugging a small amp
« Reply #2 on: May 11, 2011, 01:04:09 PM »

I made the pcb myself. Here it is:
I can't find form where I downloaded it.

http://www.siz.co.il/my/mvjyyahzftwm.bmp
oh and this is the power amp kit.
http://www.vellemanusa.com/us/enu/product/view/?id=350529

Oh, im so stupid. I forgot in insert the ic in the preamp. But it still don't explains why it haven't made any sound in the clean channel and why it made so much noise.
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joecool85

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Re: debugging a small amp
« Reply #3 on: May 11, 2011, 01:39:45 PM »

Wait...no IC would mean no sound.  Have you tried it now that you have the IC in?
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Life is what you make it.
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kin0

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Re: debugging a small amp
« Reply #4 on: May 12, 2011, 12:04:23 AM »

the problem it haven't worked even then I bypassed the overdrive. By the way I used a dpdt switch. 1 Pole is switching out put and 1 is switching the led (the inputs are joined together). Is this a good switching?
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kin0

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Re: debugging a small amp
« Reply #5 on: May 16, 2011, 08:30:54 AM »

okay now I got the power amp working. A power wire got loose. I also put in the IC. the clean (staright to the power amp) works but the dist channel still just makes noise. Also I put a pot before the power amp (as it's said here in page 8:http://www.vellemanusa.com/downloads/0/illustrated/illustrated_assembly_manual_k4001.pdf -except I put it between a dpdt so it would work only with the clean) but it does nothing the volume stays the same.
Oh and there are some buzz then the volume is up. In my guitar amp there is no buzz at the same volume.
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joecool85

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Re: debugging a small amp
« Reply #6 on: May 16, 2011, 11:01:11 AM »

okay now I got the power amp working. A power wire got loose. I also put in the IC. the clean (staright to the power amp) works but the dist channel still just makes noise. Also I put a pot before the power amp (as it's said here in page 8:http://www.vellemanusa.com/downloads/0/illustrated/illustrated_assembly_manual_k4001.pdf -except I put it between a dpdt so it would work only with the clean) but it does nothing the volume stays the same.
Oh and there are some buzz then the volume is up. In my guitar amp there is no buzz at the same volume.

I would remove the pot and dpdt switch, sounds like they may be suspect in this case.  Let us know if that gets it working on the clean and OD sections.
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kin0

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Re: debugging a small amp
« Reply #7 on: May 18, 2011, 08:58:18 AM »

KK
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kin0

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Re: debugging a small amp
« Reply #8 on: May 21, 2011, 12:56:54 PM »

I tried to take out the pot the the switch. The clean works (straight to preamp) but the drive channel (through the pedal) don't work-just makes lots of noise.
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joecool85

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Re: debugging a small amp
« Reply #9 on: May 23, 2011, 08:28:11 AM »

When you say "drive channel (through the pedal)", do you mean you are running a pedal in front of the clean circuit?  Or is it it's own preamp entirely?

I ask this because I don't see two channels in the preamp schematic you showed us.
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Life is what you make it.
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kin0

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Re: debugging a small amp
« Reply #10 on: May 27, 2011, 08:13:21 AM »

Clean I mean directly to the power amp and by drive channel i mean when i put the stompbox circuit i posted before the power amp
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phatt

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Re: debugging a small amp
« Reply #11 on: May 27, 2011, 10:32:35 AM »

Hi Kin0,
           R11 does not look right and the bas/treb looks rather odd also?
i'd be checking that the schematic actually Valid and known to work.

Also your board has a earth traversing all the way round the outer edge.
that is a loop and can cause issues,, but should not stop it from working.

R11 normally goes through a Capacitor to ground not bias voltage.
Check on other circuit that are known to work to give you some ideas.
Personally I would not use this circuit as it would be prone to problems,,, but I've not built that exact circuit so who knows maybe it would.

I found tone circuits are always *After distortion circuits* and I've had far more success by implimenting tone stuff *Before Dist* my 2 cents :tu:
Phil.

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kin0

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Re: debugging a small amp
« Reply #12 on: May 27, 2011, 01:53:18 PM »

I don't think that there is a problem with the circuit. This is a barber LTD clone and it uses the exact schematic that is given in Barber site.
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joecool85

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Re: debugging a small amp
« Reply #13 on: May 27, 2011, 02:01:07 PM »

Have you tried running the OD circuit into a known working amp?
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Life is what you make it.
Still rockin' the Dean Markley K-20X
"New" amp: Fender Frontman 25 DSP (FM25DSP)
thatraymond.com

J M Fahey

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Re: debugging a small amp
« Reply #14 on: May 27, 2011, 05:02:39 PM »

Quote
This is a barber LTD clone and it uses the exact schematic that is given in Barber site.
Fine, congratulations, re-check it anyway.
Even after thousands of amplifiers, each new one I finish building goes through the series lamp first, no exceptions.
Most times, say  95% , it comes alive with no hitches; yet a few here and there do not.
There's always the very minor problem which rises its head at intervals.
Oh well.
That's why even monster robotized factories such as Fender, Marshall, etc, regularly pull some amps from the assembly line for special checking, and most serious ones check *all* (even if only for one minute) , at least by strumming a few chords through them.
I have somewhere the famous picture of a *very* plain looking Chinese girl, clad in blue worker's overalls, with spectacles and ponytail, playing a very evil looking Death Metal guitar through Bugera heads prior to packing and shipping.
So, in a nutshell, building something apparently "by the book" is no 100% guarantee that it will work as expected or not need any testing.
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