NOISE

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Leevi
Junior tube assistant
Posts: 82
(2/2/04 2:47 pm)
 NOISE
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 Hi,
I would like to proceed with this topic because the noise is still my problem #1. I have changed resistor to better ones (i.e. more wattage), replaced capacitors, switched tubes, renewed cables etc. without any remarkable progress so far. The noise, very load and sharp, can be heard when the guitar is unplugged and volume/tone are in their highest position. The noise is the hardest in the channel 1 which has more gain. If you have interest please check the schematics in the following location (click Rikstone C15).
All ideas are welcome.
/Leevi

www.kolumbus.fi/risto.kiv...stoneAmps/

 
bluesbear
Hey get your own solder
Posts: 322
(2/2/04 3:06 pm)
 Re: NOISE
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 Does the noise get better (quieter) when you bypass the master volume?
Dave
 
sfsorrow01
Junior tube assistant
Posts: 7
(2/2/04 3:07 pm)
 Re: NOISE
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 please ignore if you've already done this but have you tried in a completely different room?

 
jc
I only work on Fender's
Posts: 669
(2/2/04 6:54 pm)
 Re: NOISE
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 Leevi,
Is that picture on your c15 page the amplifer?

Pull all of the pre-amp tubes. Is there still a noise?
put the PI back in.
put the PI and EF86 in.
put the PT, EF86, and 2nd 12ax7 in.

When do you have the noise and when is it gone? This will let us know the general area of the noise.

Do you have a bigger picture of the inside of the amp?

Edited by: jc at: 2/2/04 7:06 pm
 
Leevi
Junior tube assistant
Posts: 83
(2/3/04 1:32 am)
 Re: NOISE
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 Answers to ýour questions:

- There are no difference if I bypass the master vol and turn it to the highest position

- I have tried it in other rooms, no differences

- I'll try to locate the problem area according to the way jc proposed (in the evening after I'm back from my job)
The picture is on the C15, I can fix a better picture in the evening (noon in U.S).

/Leevi
 
Leevi
Junior tube assistant
Posts: 84
(2/3/04 2:09 pm)
 results
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 hi,
I tested the amp as jc proposed and here are the results:

power tubes only: quiet even with high master vol
power tubes+PI: quiet
power tubes+PI+EF86: acceptable noise
power tubes+PI+EF86+2nd 12AX7: very low noise, little bit hum
All tubes installed: loud noise in the 1st channel

The noise is probably generated before the 2nd stage. The amplification is maybe too high in the first stage. If I set the gain to 10-11 a clock, the amp starts to overdrive.

Unfortunately I don't have a better picture, It has been taken with a digital camcorder and that's why the bad resolution.

www.kolumbus.fi/risto.kiv...inside.jpg

Leevi
 
jc
I only work on Fender's
Posts: 670
(2/3/04 5:26 pm)
 Re: results
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 Is the noise acceptable at 10 oclock (and the gain)? The thing that you don't have in your circuit is the voltage divider from channel one going into the PI. There is a 220k and a 100k resistor before the PI. On your schematic you would take the 220k from the tone control to the PI. At the junction where the 220k meets the .01uf you would put a 100k going to ground. This voltage divider will reduce the gain of that channel. Check out the matchless lightning schematic at www.schematicheaven.com

matchless lightning
 
Leevi
Junior tube assistant
Posts: 85
(2/4/04 1:30 am)
 Re: results
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 jc,
Actually I have a voltage divider before the tone stack 22K/82K which is purposed to reduce amplification in the 1st channel. Should it be placed just before the PI ?

No noise can be noticed at gain postition 10 oclock when master vol is by-passed and guitar unplugged.

/Leevi


 
jc
I only work on Fender's
Posts: 671
(2/4/04 6:49 pm)
 Re: results
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 Leevi,
You could always try to put another voltage divider right before the PI. It should be pretty easy to wire up. Where did the tone control in the first channel come from?
One other thing is to bypass the cathode follower. Take the output of the volume straight into the PI. That will rule out one more thing. If we don't have noise we know it is the cathode follower and tone circuit.
 
Leevi
Junior tube assistant
Posts: 86
(2/5/04 1:07 am)
 Re: results
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 Thank you for the tip jc. I'm gonna try that. The tone stack
has been copied from Duncan pages, where the circuit is presented under the "Tone stack calculator" application with the name "Big muff". I have changed the component values from the default configuration.

www.duncanamps.com/software.html

/Leevi
 
gammelnalle
Junior tube assistant
Posts: 1
(2/5/04 7:51 am)
 Re: results
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 Terve!!

If you still get the noise, try to short the input grids of each tube with a capasitor to ground. Any cap over 10nF will probably do the trick. Work from PI-and towards the input When the noise stops .... You got it...

Greetings from Sweden
 
Leevi
Junior tube assistant
Posts: 87
(2/6/04 1:26 am)
 Re: results
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 Tjanare gammelnalle,

I'm gonna try that. Thanks for the advise.
/Leevi
 
Leevi
Junior tube assistant
Posts: 88
(2/7/04 1:00 pm)
 results
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 The capacitors from input grids to ground decrease the noise but they "eat" the sound as well.
/Leevi
 
gammelnalle
Junior tube assistant
Posts: 4
(2/8/04 4:05 am)
 Re: results
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 I see now that I may have expressed my self a little bit strange.
Use just one cap ! and try one grid at the time. And see where the noise stops most.

(Sorry if my english needs a little refreshing... but my finish is even worse...)

Kahru Virtavouri (?)
 
Leevi
Junior tube assistant
Posts: 89
(2/8/04 6:32 am)
 results
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 Gammelnalle,
I understood exactly what you mentioned and I tried it both in the first stage and PI. I was more satisfied with the PI connection but the sound changed too much so I thought to find another solution. Thanks, Leevi
 
Leevi
Junior tube assistant
Posts: 90
(2/8/04 10:08 am)
 Re: results
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 I'm now quite satisfied with the noise level of the amp after last changes. I added a voltage dividers also after tone stack just before the PI (220K on the signal wire and 100K to the ground). The power measurement shows that the power has dropped about 4Watts but I'm now under 15W which is optimal for the Celestion Blue. Thanks for help guys.
/Leevi
 
 
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