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Author Topic: 5e3 hiss  (Read 14941 times)
Ren
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« on: May 05, 2013, 05:55:34 AM »

Hi,

The instrument/bright channel of my ceriatone 5e3 hisses. The hiss becomes louder, as you turn the instrument volume pot and/or the tone pot. Hiss starts at about 2 (instrument volume) and 6 (tone pot). The amp sounds great, but i would not record the amp with a cranked tone pot, even at lower volumes because of the hiss. If you pull either V1 or V2, the hiss is gone.

I built the kit according to the ceriatone layout with few exceptions:
- I used another PT, which had no filament CT.
- did not ground the first filter cap to the input/tone-section, but near the PT.

What i tried:
- installed artificial filament CT (two parallel 100 ohm resistors to ground) --> got rid of some hum, but not the hiss
- changed all resistors in the preamp section and the B+ supply to 2W metal film resistors
- changed bypass and decoupling caps in the preaamp stage
- swapped V1 and rectifier tube with tubes that do not hiss
- shielded the wires which go to the grids of V1 and V2
- changed the two tone caps
- changed potentiometers

All this had no effect.

The only thing that killed the hiss was a second 5 nF cap bridging the complete tone pot (between the 2 already existing tone caps). But then the amp had a lack of highs of course.

Do you have any idea?
Or is a hissing 5e3 normal, if you crank the tone pot?

I would be deeply grateful, if you will tell me your opinion.
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Ren
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« Reply #1 on: May 21, 2013, 03:07:23 AM »

Maybe I should emphasize the 2 questions, that are most important to me.

1. Did you experience hiss, when you crank the tone pot of your 5e3? And when does it start?

2. When I pull V1, the hiss is completely gone. Does that really mean, that the source of the hiss has to be in front of the grid of V1? Or is it just very likely?

Thank's for reading!
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wyatt
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« Reply #2 on: May 21, 2013, 09:26:52 AM »

Well, "hiss" is a bit ambiguous. I could assume it is more benign than it is in person. So, take all of this with a grain of salt.

The noise floor is significantly raised when you turn up the Tone knob on a 5E3. Yes. Absolutely. But it shouldn't be unbearable.

Around 12 o'clock on the dial (neutral-ish position for the Tone knob), it should be relatively quiet (at a reasonable volume).  Below 12 o'clock, the Tone control shunts high-end signal to Ground via the .005uF Tone cap, above 12 o'clock, the Tone control steers signal through the 500pF Bright Cap, this is primarily on the Bright/Instrument Channel of the amp, but because the both Volume pots are tied together at their output, it also bleeds some high-end through for the Normal Channel.

The Volume and Tone controls are all between V1 and V2. So, if the Hiss goes away with V1 pulled it just means it's somewhere before the channels get mixed done for the second gain stage.

Since your Hiss starts as you exceed that 12 o'clock position, it's frequency is high enough that it needs that 500pF Bright cap to pass through. That's why it's in the Bright Channel and when the Tone is turned up. But what could cause excessive hiss? That's the troubleshooting issue. Important things to note is the lead dress and arrangement near the tubes, making sure the filament wire is parallel to itself (that's why we twist it) but also far enough away and perpendicular to the the plate, cathode and grid wires. Maybe you should consider shielded wiring for the inputs to V1 and/or from the Volume knob to V2. Or could you just be using single coils?
« Last Edit: May 21, 2013, 09:31:42 AM by wyatt » Logged
Ren
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« Reply #3 on: May 21, 2013, 10:42:58 AM »

Thank you very much for your reply, wyatt!

Yes, I use nothing but the single coils of my Fender Mustang. But there is no noise, when the volume of the guitar is muted or when no instrument is plugged in. So I think it is not the guitar that is hissing.

In the next few weeks I will rewire everything before V2 with new parts. I'am going to report of course.

Thanks again for reading.
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wyatt
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« Reply #4 on: May 21, 2013, 02:33:10 PM »


Yes, I use nothing but the single coils of my Fender Mustang. But there is no noise, when the volume of the guitar is muted or when no instrument is plugged in. So I think it is not the guitar that is hissing.

There may be a typo or a problem conveying your point above, but I fail to see how turning the guitar volume down or unplugging it negates single coil noise as a suspect.

If it is the single coils, the noise will decrease with everything else when reducing the volume (probably disproportionately fast since it's the high-end). And, well, obviously there is no pickup noise when not plugged in. The input jacks on the 5E3 are shorted to Ground when not used, so it should be pretty quiet with nothing plugged in. The is nothing to amplify since it's all sent to Ground instead.

Good luck. Right now I'm dealing with a ghost buzz on a 5E3 I'm looking at for a friend. The likely culprit is a cold solder joint, but haven't find it yet.
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Ren
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« Reply #5 on: June 06, 2013, 02:36:48 PM »

Today I finished the amp.

- rewired preamp stage
- new socket for V1
- new input jacks
- new grid stoppers and V1 cathode resistor (2w metal film)
- cleaned up the star grounding a bit

--> No difference at all. Probably this is the tonal character of a 5e3.
However I am very happy with it.

Thank's for reading!
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genthry
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« Reply #6 on: June 11, 2013, 05:04:14 AM »

This noise can be reduce slightly by adding rubber washers to each input and output jack - confirmed

I will try on separating 2 star grounds one for the OT and power cord to 1 star and the rest to another star ground. This should further help. Will report further on this.




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Ren
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« Reply #7 on: June 11, 2013, 12:01:24 PM »

Thank's for your comment, genthry.

I think you're right, that it's better to use isolated input jacks. I used those.

Basic knowledge about star grounding: http://www.aikenamps.com/StarGround.html
I followed those instructions.
Star 1: PT center tap, 1. filter cap, OT secondary ground
Star 2: 2. filter cap, preamp stage
Connected star 1 and star 2 at one point.
AC mains ground remains separated from all this.

But maybe I shouldn't give you any advice, because my amp is not that silent.  Grin
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wyatt
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« Reply #8 on: June 11, 2013, 03:56:14 PM »

As I said the beginning of this thread, it's hard to tell from an internet forum when a noise is just part of the amp's nature and when it is indicative of a problem. I can say all 5E3's are noisy when the Bright Volume and Tone are turned up, and it's true, or that the amp's EQ is enhancing a band of noise inherent to the pickups, which is possible, or whether the amp has a real problem. All we can do is assume.

But I trust that if you have decided it is just the "way the amp is" I trust that. Most problems result in an unbearable amount of hum, oscillation, or noise.

On a tangent, I hate star ground, almost every time I run into one it is the cause of a problem (including the very ground loops they are suppose to save). These days I use "zones"...



Except on a cathode-biased amp like a 5E3, I ground the artificial center-tap (two 100-ohm resistors, if there is no 6.3V center tap) to the cathodes of the power tubes. Thant said, this is a tangent, do not rewire your grounding scheme. I think you are "there."
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