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Old 24th May 2012, 12:41 PM   #1
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Default DIY Project - preamp-gain causes noise

Hello everyone,
I'm new to this board. The main reason is because I encountered a noise problem with my DIY JCM 800 2204.

It plays well on low master levels. If I turn up the gain or play the strings very hard, I get a buzzing sound out of it. However, the main volume does not cause a noise.

Now I'm wondering, where the problem may lie. I'm sure you experts can help me out. Is it wiring, the tubes or caps? I don't know.

I've attached a sound file where you can hear the noise. I'm turning the master knob up and down.

Once the amp runs smoothly I'm willing to share my documented building process.

With regards,
Cypher
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File Type: zip DIYJCM800_Noise.zip (259.4 KB, 58 views)
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Old 24th May 2012, 02:47 PM   #2
DF96 is offline DF96  England
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Should be in Instruments and Amps forum? I'm sure a Mod will oblige.
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Old 31st May 2012, 01:03 PM   #3
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Well... no answers or action. Guess I'll try it by myself.
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Old 31st May 2012, 01:07 PM   #4
SY is offline SY  United States
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Quote:
Originally Posted by DF96 View Post
Should be in Instruments and Amps forum? I'm sure a Mod will oblige.
I've moved it.
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Old 31st May 2012, 03:33 PM   #5
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Maybe share a bit of your progress now, at least the schematic for those not familiar with the JCM.

Is it like one of these layouts?
Have you compromised or omitted any parts?
Is it point to point or PCB, if PCB did you do the layout?
Attached Images
File Type: jpg JCM800_2204Ceriatone.jpg (266.2 KB, 165 views)
File Type: jpg 234d4722d3cff30.jpg (201.1 KB, 156 views)
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Old 31st May 2012, 10:48 PM   #6
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I used the layout you posted - Ceriatone. I exactly rebuild the amp, using only the best parts on a turret board. Only difference for me: no resistors on big cap & standby. And no voltage selector & impedance selector, but instead hardwiring to 230v and 8ohm. 4ohm line is connected to board directly.

I realised my poor heater wiring and completly redid it the proper way - twisting, angles, etc. The amp sounds different, but anything from normal. I still get a high pitched noise when strumming hard or turning off. Even if gain goes up more now, its a similiar effect then before. If I turn up volume and gain as much as it is possible without getting buzz, the guitar still plays pretty silent. It's supposed to blow me away on that level.

Biasing tubes is not really possible, as I don't have any voltage on the 1ohm resistors on standby. Turning standby off sometimes gives me a voltage and sometimes its zero. Weird.

I'm really frustrated and I'm beginning to think that I should have invested the 300 bucks in a real amp... Well, but now as someone answered, I dont wanna lose hope.
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Old 1st June 2012, 02:00 AM   #7
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I would say you have a high frequency oscillation going on. Try some chop sticks and move some wires around.
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Old 1st June 2012, 02:08 AM   #8
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You will get it sorted, I agree it sounds like some sort of oscillation.

It will work, others have succeeded, then you will have a great amp you could not buy for $300.

If your really frustrated, put it down for a day or so, come back with fresh patience.
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Old 1st June 2012, 09:47 AM   #9
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You serious? The first thing i did was moving the wires around.

Here's some pics of my amp:
heater.jpg

overview.jpg

board.jpg

top.jpg

Last edited by Cypheron; 1st June 2012 at 10:09 AM.
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Old 1st June 2012, 06:22 PM   #10
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Update: I rewired input/output by placing input closer to the volume pot and preamp tube 1. Also output wires run accross the side to the power side of the amp, where there is the jacks and on the way the power tubes.

Result: 1. on low gain, hi input - lots of volume that blows you away. No hum, but tube distortion when chording sounds bad.
2. High gain, hi input - same result as in the beginning. Pig squeel which wont go away easily, even after turning gain down. Distortion sounds awful.
3. Low gain, low input - when strumming hard i get the same results as in the beginning. A harsh, hi hat kinda hiss is included on every loud note.
4. Low gain, low input - same as 2. But worse.

When going to standby or turning the amp off, it goes silent much more pleasingly. No more blobb or mega loud hiss ( just a little hiss).

I'm on my way. If anyone has suggestions besides chopsticks, I'd appreciate that.
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