DIY Project - preamp-gain causes noise - diyAudio
Go Back   Home > Forums > Live Sound > Instruments and Amps
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Instruments and Amps Everything that makes music, Especially including instrument amps.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools Search this Thread
Old 24th May 2012, 12:41 PM   #1
diyAudio Member
Join Date: May 2012
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,
Attached Files
File Type: zip (259.4 KB, 65 views)
  Reply With Quote
Old 24th May 2012, 02:47 PM   #2
DF96 is offline DF96  England
diyAudio Member
Join Date: May 2007
Should be in Instruments and Amps forum? I'm sure a Mod will oblige.
  Reply With Quote
Old 31st May 2012, 01:03 PM   #3
diyAudio Member
Join Date: May 2012
Well... no answers or action. Guess I'll try it by myself.
  Reply With Quote
Old 31st May 2012, 01:07 PM   #4
SY is offline SY  United States
On Hiatus
SY's Avatar
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 2
Originally Posted by DF96 View Post
Should be in Instruments and Amps forum? I'm sure a Mod will oblige.
I've moved it.
"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
  Reply With Quote
Old 31st May 2012, 03:33 PM   #5
Join Date: Apr 2012
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, 175 views)
File Type: jpg 234d4722d3cff30.jpg (201.1 KB, 166 views)
  Reply With Quote
Old 31st May 2012, 10:48 PM   #6
diyAudio Member
Join Date: May 2012
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.
  Reply With Quote
Old 1st June 2012, 02:00 AM   #7
diyAudio Member
Join Date: Apr 2010
I would say you have a high frequency oscillation going on. Try some chop sticks and move some wires around.
  Reply With Quote
Old 1st June 2012, 02:08 AM   #8
Join Date: Apr 2012
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.
  Reply With Quote
Old 1st June 2012, 09:47 AM   #9
diyAudio Member
Join Date: May 2012
You serious? The first thing i did was moving the wires around.

Here's some pics of my amp:




Last edited by Cypheron; 1st June 2012 at 10:09 AM.
  Reply With Quote
Old 1st June 2012, 06:22 PM   #10
diyAudio Member
Join Date: May 2012
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.
  Reply With Quote


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
New DIY Project for measuring noise : 10Hz..100kHz LNA // 1MHz RMS-DC converter Frex Equipment & Tools 96 26th January 2016 04:25 PM
Minimalist diy preamp project Mywing Pass Labs 21 4th May 2007 01:24 PM
DIY preamp design - gain topology, IC vs. discrete, OPA627 vs. Zen... ? dorkus Pass Labs 18 10th July 2001 05:26 AM

New To Site? Need Help?

All times are GMT. The time now is 07:14 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2