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Post subject: Very loud hissing with gain turned on in a fender twin.
Posted: Mon Oct 25, 2010 11:53 am
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this Twin is a superb tube amp, and the gain distortion is excellent, with one major flaw: very loud hissing when the gain is turned up to 4 or 5--gets louder and louder up to 10. Makes it unuseable in a studio. In practice, the other guys constantly complain about the loud hiss.

i just had it in for a tune-up--I got all new tubes, bias adjustments, cleaned the pots, etc etc. He also repaired all the buttons on the foot switch, which activates the gain channel. But: the hiss is still just as bad when the gain is turned on.

i have a PRS hollow-body, a great guitar. I also just had it cleaned up, including the electronics.

any solutions out there?

Thx,
Jeff


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Posted: Mon Oct 25, 2010 1:00 pm
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Welcome Jeff,

(Are we talking about 65 Twin reverb?)

Hissing is can come from 2 origines : Electronics or mechanical (or electromechanical)

First, try to remove V3 and V4. Only the normal channel will work. Let me know if hiss is still present.

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Posted: Mon Oct 25, 2010 3:05 pm
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I assume you are talking about the red knob Twin or just plain Twin and not the '65 Twin Reverb reissue since you have a gain knob. It's normal. Every tube amp I've had that has a master volume gets hissier as the gain is turned up. Adding more gain adds more noise. Just like when you stomp on a cranked distortion pedal it's gonna add hiss.

It's not so bad live, but in the studio I can imagine it's annoying. Luckily in the studio you can use a noisegate and/or just mute the channel that your amp is on until you start playing.

Now if your Twin is noisier than other Twins at the same setting, then you got a problem with the amp.

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Posted: Tue Oct 26, 2010 5:58 am
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tissan: Help me out here please: what are the V3 and V4?

yes, my Twin is not the 65--i bought it new about 5 years ago. it has only 1 input, with 2 channels.

jeff


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Posted: Tue Oct 26, 2010 6:07 am
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Gosh ! I've to investigate on this Twin's schematic.

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Posted: Tue Oct 26, 2010 6:22 am
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Tissan wrote:
Gosh ! I've to investigate on this Twin's schematic.


I think it's the modern-era "Twin Amp", Tissan (sometimes referred to as the "Evil Twin").

HTH

Arjay

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Posted: Tue Oct 26, 2010 7:04 am
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Was it always this hissy since you got it, or did it just start after the tune-up?

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Posted: Tue Oct 26, 2010 9:23 am
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no, it's not any worse since the tune-up. It's always been present somewhat, but it has gotten louder over the last few years.
jeff


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Posted: Tue Oct 26, 2010 12:12 pm
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As Retro pointed, tell me if it's the right one:
http://support.fender.com/schematics/gu ... SchE45.pdf

If it's the right one, the first test is:
Put your guitar in "PWR Amp In" and let me know if you still have the hiss (note that there is no vol/tone control).

The goal is to identify if the hiss is located in preamp or amp.
8)

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Posted: Tue Oct 26, 2010 12:31 pm
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Tissan: Yes, that schematic does appear to be my Twin--all the knobs, inputs, etc match up exactly. I'm guessing that on the schematic, PWR Amp In is the input labelled PA In. I'll try it out this evening and reply.
Thx!
Jeff


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Posted: Tue Oct 26, 2010 1:41 pm
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Tissan: I just tried plugging guitar into Power Amp In. There was no hiss/hum at all.
Jeff


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Posted: Tue Oct 26, 2010 2:03 pm
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Good; The amp seems OK (Phase inverter and Push-pull = 6 valves OK)
:)
Second test:
Try to connect "preamp out" to an other amp (even Hifi, just take care of volume). Do you hear the hiss?

Using boolean method, the purpose is to confirm that the hiss is coming from the preamp?

Let me know.

(by the way if you have another preamp, you can connect it on your twin in oder to have pleasure to play)

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Posted: Tue Oct 26, 2010 5:16 pm
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Tissan: Yes, i can do that tomorrow, probably about 3pmCST. There's a fender twin reverb in the practice room--so i will cable from my Twin to the Twin Reverb. But (sorry for my lack of technical expertise) what input do i plug this cable into in the Twin Reverb?

i see that you are in France. We were in Paris for 2 weeks this summer, where my daughter was married, in Monet Gardens. A great trip, and the best coffee (cafe creme, and of course expresso) i've ever had (not to mention the terrific beer!).

thx,
jeff


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Posted: Wed Oct 27, 2010 12:08 am
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Great that you have appreciated Paris, as french people is taste sensitive they import knowledge for expresso and biere from Italia and Belgium/Germany. Did you try frogs or snails with Chablis?

By the way, connect the preamp out of your amp on Power amp of the other.

8)

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Posted: Wed Oct 27, 2010 4:29 am
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I think those amps have often bad wiring routing ( is that rigth words ? ) And wires are too long on the preamp section, they are like an antenna = hiss.

Can you show us a picture of preamp section, I tell you if it the case ?


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