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Thread: Throwing metal film resistors in Fender amps

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    Throwing metal film resistors in Fender amps

    Hi everyone,

    Despite the fact that English is not my mothertongue, I try to read as many articles as I can in English in order to improve my modest knowledge in guitar amps and lead my experiments in a better way. But I still get a little confused with all the specific component names.

    I currently own a DRRI which is a amp I truly love (even more since I put a WGS G12C in it, such a perfect match) and which as been modded a little :
    Middle pot, Bright switch, NFB resistor on-off switch, all Mallory 150s caps, ... very versatile and great sounding amp.
    But I experiment some hiss (which is louder with the less efficient G12C) that I want to reduce as much as I can.
    From what I've read, the easiest solutions seem to lean toward a smart wiring and metal film resistors.
    That's where I need your tremendous help.
    For the first one, the inside of my DRRI is quite a mess and might cause some unwanted noises, if anyone has a guide or link to how to properly place the wires in a Fender amp, that'd be great.

    For the second one, I'm a little confused in all the resistors name but I mainly understood that high-wattage metal films were the quietest and that they're very useful for reducing noise in the input stages and power stages (complete this if it's wrong). For the moment my amp is running on stock carbon film resistors (it's a 1999 DRRI, for a 22 year-old dude like me, I consider it vintage piece, haha!). Resistors that drifted have been replaced. I'm now looking to replace the ones who are prone to make indesirable noises.

    Based on this schematic, can you please point out the resistors or various components I should replace to minimise noises (Hiss in particular) without loosing the "Mojo" factor of carbon comp and carbon film resistors which for unknown reasons affects me quite a lot ...
    And if you have the time, that would be great if you could write the specific names (fonction) of these components so I can improve my knowledge and impress my mom who thinks I'm crafting bombs in the cellar... haha

    Click image for larger version. 

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    Thank you very very very much !
    Wil from Belgium.

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    Quote Originally Posted by Wil View Post
    Despite the fact that English is not my mothertongue, I try to read as many articles as I can in English in order to improve my modest knowledge in guitar amps and lead my experiments in a better way. But I still get a little confused with all the specific component names.
    Hi, Wil. I admire how very well you do in English. I wish my abilities in any other language were as good.

    Resistors that drifted have been replaced. I'm now looking to replace the ones who are prone to make indesirable noises.

    Based on this schematic, can you please point out the resistors or various components I should replace to minimise noises (Hiss in particular)
    All of them, with only two exceptions, those two being R54 and R55. But there is a middle ground that works almost as well and is less work.

    The nature of noise is that the noise/hiss of the first amplifier stage almost totally determines the hiss. So the other middle ground way is to start with the resistors at the input jack of the amplifier, and replace those first. In your schematic, this approach would start with R1, 2, 3, 4, 13, 14, 15, 16, 28 and 29. These resistors are all involved in amplifying up a quite-small voltage, so any hiss from them gets amplified with the signal.
    without loosing the "Mojo" factor of carbon comp and carbon film resistors
    Read http://www.geofex.com/article_folder...carboncomp.htm
    which for unknown reasons affects me quite a lot ...
    It's human physiology and psychology. Humans simply like soft even-order distortion.

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    Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

    Oh, wait! That sounds familiar, somehow.

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    Quote Originally Posted by R.G. View Post
    Hi, Wil. I admire how very well you do in English. I wish my abilities in any other language were as good.


    All of them, with only two exceptions, those two being R54 and R55. But there is a middle ground that works almost as well and is less work.

    The nature of noise is that the noise/hiss of the first amplifier stage almost totally determines the hiss. So the other middle ground way is to start with the resistors at the input jack of the amplifier, and replace those first. In your schematic, this approach would start with R1, 2, 3, 4, 13, 14, 15, 16, 28 and 29. These resistors are all involved in amplifying up a quite-small voltage, so any hiss from them gets amplified with the signal.

    Read http://www.geofex.com/article_folder...carboncomp.htm

    It's human physiology and psychology. Humans simply like soft even-order distortion.
    Thank you for the flash fast answer ! One off-topic question remains in my head : Are you R.G. Keen, webmaster of Geofex.com ??

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    It's a good idea to narrow down where any hiss is coming from to save unnecessary work.

    Firstly, does it hiss with no guitar plugged in and the volume and tone controls set to where you'd usually have them? (reverb off) If it does, do either (or both) of the volume controls affect the hiss?

    Is it worse with your guitar plugged in?

    Does the reverb control affect it?

    One thing to make sure of is that the preamp tubes are as quiet as they can be. A surprising amount of noise can be attributed to a good-but-noisy tube. Auditioning different tubes, or installing ones which have been tested for noise is a good bet. Out of any batch of preamp tubes there will be a small number that are quieter than the rest, given that other characteristics remain the same.

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    Quote Originally Posted by Mick Bailey View Post
    It's a good idea to narrow down where any hiss is coming from to save unnecessary work.

    Firstly, does it hiss with no guitar plugged in and the volume and tone controls set to where you'd usually have them? (reverb off) If it does, do either (or both) of the volume controls affect the hiss?

    Is it worse with your guitar plugged in?

    Does the reverb control affect it?

    One thing to make sure of is that the preamp tubes are as quiet as they can be. A surprising amount of noise can be attributed to a good-but-noisy tube. Auditioning different tubes, or installing ones which have been tested for noise is a good bet. Out of any batch of preamp tubes there will be a small number that are quieter than the rest, given that other characteristics remain the same.
    Thanks for the answer.
    Well, actually, that amp is magical. I played it 2hours ago and it was hissy but very open and articulate.
    Now, to experiment what you just wrote, I lit it up and it was kind of silent.
    Volume on 10, all other controls on 0, very low noise, near no noise at all.
    Volume on 10, Treble only on 10, hissy as hell, horrible. (Middle control does the same thing in a less loud way)
    Volume on 10, Bass only on 10 adds a noise that sounds like a big industrial fan.
    Volume on 10, Reverb on 10 adds some sort of 60 cycle hum.

    It's noisier with my guitar plugged it. It adds a low background noise and low 60 cycle hum which I assume is produced by the P90s on my guitar. (I have no humbucker at all actually).

    I believe I already replaced R18 with a Metal film equivalent. I might go with a higher wattage like 1-2watts.

    EDIT : The magical thing I'm talking about is actually real. I wanted to check the controls again and this time, the amp made an extra constant white noise... I did not open the amp, just turn it off and light it up an hour later... Defective switches ? But with the hiss, the amp sounds more open and clear. Funny.

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    Last edited by Wil; 01-09-2014 at 06:37 PM.

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    It is normal to have more noise when volume is up even without guitar. Check the reverb dial, see how much noise it goes up when you crank the reverb high. R.G got most of the resistors already. The preamp tubes V1 and V2 also can be problem as Mick Bailey said.

    There is no difference in Thermal noise between MF and carbon comp resistors. The main difference is the 1/f noise at low frequency. Carbon comp resistor may have more low frequency noise ( not necessary all of them, you can even hand pick ones that don't). MF resistors have no 1/f noise.

    Before you do anything, I would get a lower noise 12AX7 ( or 7025 of Fender) and try that first, because it's the easiest to do. Then worry about the resistors. I would isolate exactly where the noise is from before blanket replacing all the resistors. It's a big job to change all those resistors on a pcb.

    Let me raise another question to the knowledgeable people here. Does it make a difference in sound between MF and carbon comp resistors? If so, how much and why. I never A/B compare as it is hard because of all the other variables. But I personally do not believe it makes a difference. I understand carbon comp has voltage coef that it's not totally linear with voltage. But I feel the curve ( distortion) of the triode way dominates the linearity. Please correct me if I am wrong.

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    The Fender tone stack will cut out most of your signal when the three controls are turned down, that's why the hiss almost disappears, even with the volume on 10. Because the volume control for each channel is connected off the tone stack, there's not much difference between all tone controls on zero/volume on 10, or all tone controls on 10/volume on zero.

    From what you describe the hiss is mainly coming from V1a and V2a, certainly prior to the tone stacks, and you need to get the right tubes in those early positions before deciding to replace resistors. Don't forget that even if you replaced all the resistors with MF, the pots will be left. Each time you work on the PCB you risk lifting a track or pad.

    A few years back I built two amps and I still have both of them. The first was with carbon film built as a head. I liked it so much I built another as a combo with metal film. No difference at all with hiss or any other noise, which leads me to consider that resistor type isn't the major contributor to hiss in a tube amp, but preamp tube quality is.

    Plenty of amps have wires all over the place and nothing special in terms of components - just industry standard stuff at the time they were built, and they're as quiet as you could ever want.

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    Quote Originally Posted by Wil View Post
    One off-topic question remains in my head : Are you R.G. Keen, webmaster of Geofex.com ??
    Yep, that's me.

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    Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

    Oh, wait! That sounds familiar, somehow.

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    Quote Originally Posted by Wil View Post
    Hi everyone,

    Despite the fact that English is not my mothertongue, I try to read as many articles as I can in English in order to improve my modest knowledge in guitar amps and lead my experiments in a better way. But I still get a little confused with all the specific component names.

    I currently own a DRRI which is a amp I truly love (even more since I put a WGS G12C in it, such a perfect match) and which as been modded a little :
    Middle pot, Bright switch, NFB resistor on-off switch, all Mallory 150s caps, ... very versatile and great sounding amp.
    But I experiment some hiss (which is louder with the less efficient G12C) that I want to reduce as much as I can.
    From what I've read, the easiest solutions seem to lean toward a smart wiring and metal film resistors.
    That's where I need your tremendous help.
    For the first one, the inside of my DRRI is quite a mess and might cause some unwanted noises, if anyone has a guide or link to how to properly place the wires in a Fender amp, that'd be great.

    For the second one, I'm a little confused in all the resistors name but I mainly understood that high-wattage metal films were the quietest and that they're very useful for reducing noise in the input stages and power stages (complete this if it's wrong). For the moment my amp is running on stock carbon film resistors (it's a 1999 DRRI, for a 22 year-old dude like me, I consider it vintage piece, haha!). Resistors that drifted have been replaced. I'm now looking to replace the ones who are prone to make indesirable noises.

    Based on this schematic, can you please point out the resistors or various components I should replace to minimise noises (Hiss in particular) without loosing the "Mojo" factor of carbon comp and carbon film resistors which for unknown reasons affects me quite a lot ...
    And if you have the time, that would be great if you could write the specific names (fonction) of these components so I can improve my knowledge and impress my mom who thinks I'm crafting bombs in the cellar... haha

    Click image for larger version. 

Name:	DRRIschem.jpg 
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ID:	26898

    Thank you very very very much !
    Wil from Belgium.
    Yes metal film resistor is less noisy. That is proven fact.
    Even better is Bulk Metal Foil Resistor. That is well documented.

    And you can see that many manufacturers have started using Metal Film in production amp / audio equipment.

    BUT in tube amp, you can also use snubber capacitor to reduce the noise. This is used widely.
    3-7 pf between grid and plate is my preferred method. It works very well.
    There are several other accepted methods also.
    Click image for larger version. 

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    Last edited by soundguruman; 01-09-2014 at 08:23 PM.

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    Far as I know there are three type of noise:

    1) current noise ( shot noise) where it generates as current passed through a device.
    2) Thermal noise where it only depends on the resistance.
    3) 1/f noise that is device dependent. It is mainly lower frequency noise. You can hand pick carbon resistor that don't have this noise.

    Of cause all of them depends on the BW in their definition. MF resistor don't have 1/f noise, only the other two type.

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    Quote Originally Posted by Mick Bailey View Post
    The Fender tone stack will cut out most of your signal when the three controls are turned down, that's why the hiss almost disappears, even with the volume on 10. Because the volume control for each channel is connected off the tone stack, there's not much difference between all tone controls on zero/volume on 10, or all tone controls on 10/volume on zero.

    From what you describe the hiss is mainly coming from V1a and V2a, certainly prior to the tone stacks, and you need to get the right tubes in those early positions before deciding to replace resistors. Don't forget that even if you replaced all the resistors with MF, the pots will be left. Each time you work on the PCB you risk lifting a track or pad.

    A few years back I built two amps and I still have both of them. The first was with carbon film built as a head. I liked it so much I built another as a combo with metal film. No difference at all with hiss or any other noise, which leads me to consider that resistor type isn't the major contributor to hiss in a tube amp, but preamp tube quality is.

    Plenty of amps have wires all over the place and nothing special in terms of components - just industry standard stuff at the time they were built, and they're as quiet as you could ever want.
    Can you hear any difference in sound quality between the MF and carbon in the two amps?

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    What do you mean by 1/f noise ?

    Regarding the tubes, I tried swapping with no improvment, unfortunately.

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    Quote Originally Posted by R.G. View Post
    Yep, that's me.
    Wow. Actually, you were basically the brain of my wah build and I was the sloppy hands. I simply experiment relying on what was written on your site.
    I really admire your knowledge and am thankful for your tremendous contribution to building my own.

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    Supporting Member Jazz P Bass's Avatar
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    I Googled '1/f' noise & it came with Wiki: pink noise.

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    Alan presented a short list of self-noise sources for the component. But a carbon comp resistor has a granular interior, which can become mechanically unsound, and that will cause noise due to vibration and even thermal expansion of the body. Also the wire leads have to bond to the resistive part, and that can become loose.

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    Education is what you're left with after you have forgotten what you have learned.

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    Quote Originally Posted by Enzo View Post
    Alan presented a short list of self-noise sources for the component. But a carbon comp resistor has a granular interior, which can become mechanically unsound, and that will cause noise due to vibration and even thermal expansion of the body. Also the wire leads have to bond to the resistive part, and that can become loose.
    Well, I just assume things are in good condition, no mechanical problem. Or else, the source is endless!!!

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    Quote Originally Posted by Wil View Post
    What do you mean by 1/f noise ?

    Regarding the tubes, I tried swapping with no improvment, unfortunately.
    What make you think the tubes are all good? Try pulling out V1, v2 and V3 one at a time, see which one affect the noise. V1 is Normal channel ( no reverb), V2 is Vibrato channel and V3 is reverb. Then concentrate on the one that gives you problem.

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    Or else, the source is endless!!!
    But that was exactly the point. For a resistor to have a mechanical defect or weakness, it doesn't have to be beat up or in "bad shape." One can never know by looking what the inside of a resistor is doing. Your list was for theoretical noise sources in a component, but they are not the only way a part can be noisy.

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    Quote Originally Posted by Enzo View Post
    But that was exactly the point. For a resistor to have a mechanical defect or weakness, it doesn't have to be beat up or in "bad shape." One can never know by looking what the inside of a resistor is doing. Your list was for theoretical noise sources in a component, but they are not the only way a part can be noisy.
    So you think the defect resistor is making noise sitting by itself with no vibration. I assume OP had the amp on and heard the noise without touching it or playing through it. If you are right, then it can happen to all different types of resistors, capacitors, transformers, diodes......................... You have to eliminate things one at a time.

    Theoretical noise works very good. I might not be working with guitar amp as much, but I did design ultra low noise circuit and had to deal with noise problem all the time.

    To me, I am not even convinced totally that OP's amp has a problem. All amp hiss when cranked up, just how much. That's the reason I suggested pulling the preamp tube and reverb tube and try to narrow down the source first. Even if it's a defect resistor, narrow down the possibility before changing everything. Replacing all the components is a dangerous game for a cheaply made pcb. From pictures I saw before, it seemed to be a single sided board with no plate through holes. It would be very easy to pull the traces during soldering and de-soldering.

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    Quote Originally Posted by Alan0354 View Post
    Far as I know there are three type of noise:

    1) current noise ( shot noise) where it generates as current passed through a device.
    2) Thermal noise where it only depends on the resistance.
    3) 1/f noise that is device dependent. It is mainly lower frequency noise. You can hand pick carbon resistor that don't have this noise.
    there is more info on types of noise here:

    https://web.archive.org/web/20080304...istorNoise.htm

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    Quote Originally Posted by frus View Post
    there is more info on types of noise here:

    https://web.archive.org/web/20080304...istorNoise.htm
    Seems like the article call 1/f as contact noise. It did say it's 1/f. The main issue of carbon comp resistors is 1/f noise.

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    Quote Originally Posted by soundguruman View Post
    Yes metal film resistor is less noisy. That is proven fact.
    Even better is Bulk Metal Foil Resistor. That is well documented.

    And you can see that many manufacturers have started using Metal Film in production amp / audio equipment.

    BUT in tube amp, you can also use snubber capacitor to reduce the noise. This is used widely.
    3-7 pf between grid and plate is my preferred method. It works very well.
    There are several other accepted methods also.
    Click image for larger version. 

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    Metal Film has been around for a long time now, but manufacturers have persisted with CF because they're cheap and in a well designed amp don't contribute enough noise to warrant the (then) extra cost, other than in certain strategic locations. I can see that stocks of CF are being reduced (in the UK anyhow) by component suppliers in preference to MF. Eventually I can see CF drying up as it makes more economic sense for a manufacturer to rationalise component stocks.

    Amp manufacture is a tiny fraction of electronics production and in a world of increasingly more complex circuits the stability and tolerance of MF is a better choice.

    The DRRI isn't a high gain amp and every one I've worked on has been pretty quiet, other than the annoying vibrato tick. A more efficient speaker will emphasize hiss and the speaker characteristics are an important factor, particularly if the upper-end is better represented. I can't agree that taking an established, proven design and changing the resistor technology is a good move. There must either be a fault or less-than-perfect valve choice.

    Adding snubber caps to an existing design shouldn't be necessary in low-gain triode audio stages - it may offer a 'fix' by masking symptoms, but I'd rather find the cause and fix that.

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    Old Timer J M Fahey's Avatar
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    Agree.
    Killing highs sure will mask hiss, but I wouldn't call that a proper repair.

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    Juan Manuel Fahey

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    Quote Originally Posted by Alan0354 View Post
    Seems like the article call 1/f as contact noise. It did say it's 1/f. The main issue of carbon comp resistors is 1/f noise.
    By contact noise, should I understand cold solder ?

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    Contact noise is inherent to the resistor.

    The boundry between the actual carbon grains can produce a voltage when a current is running through it.
    There is also a temperature reliance.
    The higher the temp, the more voltage is produced.

    In reality, we are talking about nano volts!

    If every amplifier that Leo or Jim made (all used carbon comp resistors) had a 'real' issue, they would not have been as successful as they became.

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    In this amp, you will find the quieter operation by adding a capacitor between plate and grid of the first input stage.
    This kills the "white noise."
    This is the method used by Fender and Marshall in factory production. Either in the layout or the actual PARTS design.
    This is by far, the best compromise.
    No matter what design, It's ALWAYS a compromise. There is NO perfect noiseless design.

    As has been said by me and others, the noise of the first stage is more important because it is amplified by all the following stages.
    That "ALONE" is probably the most important consideration of all.
    Resistor noise, guitar pickup noise, filament noise, power supply noise.....it's ALL there in the first stage, and then amplified. (garbage in, garbage out)
    So it's a very good practice to reduce the noise of the first stage to as low as possible.

    The plate and the grid wire located next to each other FORMS a capacitor.
    Any time you locate two wires in close proximity, you are also making a capacitor between them.

    Example

    is layout of Boogie amp. (as much as you may hate it)
    The circuit tracks are laid out very close to each other, on purpose. Almost too close for my taste...
    This forms capacitor between the circuit tracks, and kills noise and oscillation.
    Whether you install an actual capacitor or locate the plate and grid layout next to each other, to FORM a capacitor...
    or twist the plate and grid wires together...

    In Fender amps, the grid wire is routed right under the plate circuit, to FORM a capacitor. It's ALL absolutely deliberate.

    You separate this layout, and the noise is going to increase. The ringing and tendency to oscillate will also increase.

    FIRST stage, Metal film resistors, plate to grid capacitance, DC heaters, Humbucking pickup, etc... will all lower the
    noise of the first stage and produce a quieter result in the end.

    Reducing the high frequency response? It's a necessity. It's a requirement.
    The guitar does not go to 1,000,000 Hz. But the amplifier WILL unless you deliberately limit it by design and components used.

    In ALL well designed high gain guitar amps, the high frequency is deliberately limited.
    If it was not, you would have major irritating noise, ringing and oscillations. The amplifier would be UN-useable.

    SEE, you START with a p-90 pickup.
    That's the noisiest pickup on planet earth.
    Then you amplify it. Then you get NOISE. Of course you do. NOISE IN, NOISE OUT.

    Please don't insist on using the noisiest pickup, and then complain about the noise.
    and don't blame the amplifier, it's only amplifying the noise, that YOU present to it. It OBEYS.

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    Last edited by soundguruman; 01-10-2014 at 04:00 PM.

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    I would not put any cap from grid to plate just yet, that has a miller effect of multiplying the cap by the gain. If the cap can reduce audible hiss, it will reduce the audible highs of the guitar signal. This is particular bad in Mesa. But I think they did that because of the uncontrollable feedback when cranked. To me, Mesa amps do not sound good, you use their cascade channel and roll down the volume of the guitar, it is all muffled because of the filter caps in the signal path.

    More important is as Bailey and Fahey said about using a P90 and complain about noise and masking a real problem.

    To me, amps do hiss a little, it is not important in real life situation compare to other noise. If it is excessive, something is wrong. That's the reason I suggested removing V1, V2 and V3 one at a time to pin point the noise path. If all three are the same, chances are the amp is ok. You don't have 3 sources going back at the same time. If one one gives you the problem, then chase it down.

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    Quote Originally Posted by Alan0354 View Post
    Can you hear any difference in sound quality between the MF and carbon in the two amps?
    Not really, I switch between them and think I hear something different but then ask myself if I'm trying to convince myself of something that isn't really there.

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    Senior Member Mars Amp Repair's Avatar
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    I would only add that if a carbon resistor is 'noisey' and not necessarily 'intermittent' as a result of the glued in leads being loose, dropping freeze spray on them can help locate the ones area actually adding 'noise' to the system. BTW, if you do have an old amp that actually has the bad glue carbon resistors, freeze spray is excellent for ferretting them out.

    Also you can limit the upper frequency response of the stage (only recommended if you're stage is oscillating) by adding a 'Snubber' capacitor across the plate load resistor. This is not to limit the audible frequencies ie; limit noise, but to remedy undesirable oscillation.

    BTW the reason for placing the cap across the load resistor & not to ground is that the cap would need to be rated at the plate voltage plus a safety margin & the power supply on the other side of the plate load resistor is ground to AC signals by virtue of its heavy filtering. So a lower voltage cap is sufficient. glen

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    FWIW, 1/f noise is so called because it is inversely proportional to frequency (less noise is produced the higher the frequency, and vice-versa).

    I have a mid-90s DRRI and it's pretty quiet. I did add the vibrato-ticking-reduction capacitor.

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    Snubber resistors crept in on audio equipment in designs where they previously weren't used. Possibly this was to compensate for tube specs slackening off. Removing them from (for instance) a Twin Reverb has a beneficial effect on tone, so long as the tubes are good quality. Putting snubbers in means that pretty much any quality tube will work and in production line amp builds this matters, but it isn't good for sound quality.

    Consideration has to be given to the fact that suppressing frequencies marginally above the hearing range, or upper frequency response of the speaker, has a detrimental effect on frequencies within the hearing range due to sum and difference components. Removing those frequencies early on can result in a very dull-sounding amp.

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    Quote Originally Posted by Mick Bailey View Post
    Snubber resistors crept in on audio equipment in designs where they previously weren't used. Possibly this was to compensate for tube specs slackening off. Removing them from (for instance) a Twin Reverb has a beneficial effect on tone, so long as the tubes are good quality. Putting snubbers in means that pretty much any quality tube will work and in production line amp builds this matters, but it isn't good for sound quality.

    Consideration has to be given to the fact that suppressing frequencies marginally above the hearing range, or upper frequency response of the speaker, has a detrimental effect on frequencies within the hearing range due to sum and difference components. Removing those frequencies early on can result in a very dull-sounding amp.
    Are you referring to the 2200pF caps from the grid of the power tubes to ground in all the newer Silver Face Fender in the 70s? I am just doing this experiment using a switch it in and out and listen. I can definitely hear the difference. You get more chime, not obvious as the presence control, it just give that bit more transparency.

    I would avoid putting any caps from signal path to ground or miller caps if all possible. The only time I encounter oscillation is in the cascade gain preamp that you put a lot of gain. I still try to divide the gain down after the over driven stage to avoid adding caps.

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    Here comes my two cents worth. Hisses for me are just about as bad as hums to figure out. I've used carbon film for years and never heard complaints about noise afterwards. Finding the source of the hiss is the key. I would probably look at the plate resistors on V1 and V2 first. I'm sure it's been mentioned before but pull your PI tube. Turn the amp on and see if it still hisses. If it does then check your screen resistors on your output tubes.. If not then it may be the plate resistors. I used to blame coupling caps for being noisy but have since found it's most likely a resistor. But tubes can get noisy as well. Make sure the socket contacts are clean and well tensioned. Clean all your pots and make sure everything is well grounded. Hope this helps a little.

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    Removing V1 and V2 reduces the hiss but adds a sort of "boiling teapot" noise (see famous movies with boiling teapots). Removing V4 makes the amp dead silent.
    Would the main hiss be located between the input stage and the reverb and tremolo recovery stage ?
    I did not try removing the phase inverter tube (V6).
    I have to mention that the vibrato is very very weak, almost dead. I don't use it. The intensity pot is a SPST 50k which allows me to disconnect the vibrato by virtually cutting the wire from R35 to R48 (aka intensity pot). I changed the roach and various component with no positive effect. But I have a great tremolo pedal I made that I use instead so it doesn't matter.

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    Last edited by Wil; 01-11-2014 at 03:20 PM.

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    If the amount of noise reduced by pulling V1 alone is same as pulling V2 alone, I don't think the problem is V1 and V2 section. You pull the V4, you cut off the Vibrato channel all together. So normal channel (V1) is not your problem for sure.

    I suspect reverb circuit is your problem. Put everything back together, unplug the reverb tank and see whether that reduces the noise. If it does not, your problem is V4 circuit. Take the tube from V1 and replace V4 to make sure it's the the tube.

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