Out Damn Hiss!

[CrocMule]

I have a '66 Danelectro DS50 (wait, don't go...) with a stubborn hiss that I have traced all the way to nowhere.  I know Danelectros are trashy, but it's an interesting project.  Schematics attached. 

I left the cab plugged into the head throughout my testing, and the hiss has remained unchanged in volume or timbre -- depending on the test, it's either there or the amp is silent.

All the voltages were reasonable when I last checked.

It's a pronounced steady hiss, like a blank D-90 cassette turned up loud.  No crackles or pops, hardly any buzz or hum.

None of the pots affect it, volume, EQ, reverb.  (Can't remember if trem does)

Tubes V1 (reverb), V2 (1st stage), and V5 (tremolo) can be pulled without causing a change to the hiss.

Unplugging the pre-amp from the power-amp cuts all hiss -- silence.  So the source must be in the pre-amp.

Pulling either V3 or V4 in the pre-amp cuts all hiss -- silence.

I've swapped in several tubes in both V3 and V4 positions with no change in hiss, so it's not the tubes.

I figure the source has to be between V3 and V4.  If the source of the hiss came after V4, I'd expect to be able to pull V3 as well and still hear hiss.

The 2 filter caps in the pre-amp section are new F&T 16uF@475V -- tested good before installation, ESR good in circuit.  (Hiss was present before and after all new e-caps.)

I disconnected the leads (330k, 330k, and 2.2M) going to V3 P2 and grounded P2 -- no change in hiss (still loud).  So it's definitely not coming from before V3 -- not the tone stack or reverb.

I tested and swapped in known good components for every cap and resistor between V3 and V4, and in the preamp B+, with no change in hiss.  I did this one or two components at a time, lifting one lead and jumpering known good ones into the circuit -- and I noticed no changes.

The thought occurred to me that, since Danelectro used bottom quality components, the SUM of the hisses from all the carbon comps could be creating a whole that doesn't seem to be affected by swapping in a couple new components at a time (metal film resistors and Mallory 150 caps).  I didn't leave the new ones in place if they didn't seem to make a difference, so it's (mostly) all still original components with some new solder.

I did replace the .01uF cap coming off V3 P7, because the leads spun in the original (I think I manhandled it a little too much when unsoldering it to test).  I also replaced the .02 coupling caps coming off V4 P1 and P6, because it seemed like a good idea (the coupling caps in front of the 6L6s). 

If the SUM of all hisses theory were true then I'd expect the entire wad of CCs in the tone stack to contribute some hiss too -- but disconnecting the signal path after the tone stack and reverb and grounding the V3 input didn't make a bit of difference. 

I'm stumped.  Anybody have any ideas?

I've cleaned the sockets.  There are no bad noises when gently wiggling the tubes.  I don't see any bad solder joints. 

Unlike the single ground bus shown on the schematic, the grounds are all secured to the chassis with machine screws (center tabs of tag strips all over the place).  Only one is accessible to a nut driver to tighten -- the others are obstructed by the PTP wiring.  Could a sketchy ground connection cause an ocean of hiss? 

Thanks in advance for any help!

[PRR]

Does it hiss on-stage with an audience??

It IS a cheap piece of chit. Sensitivity at the volume pots is like 60mV, which is on the low side. So it is going to hiss. It may be quite noticeable at home.

[HotBluePlates]

Pulling ... V3 ... cuts all hiss -- silence.

I've swapped in several tubes in ... V3 ... with no change in hiss, so it's not the tubes. ...

The hiss is at or before V3.  Hiss with V2 pulled means only that the hiss is after V2.

That means every pot & resistor from the 330kΩ late loads of V2 through to the 220kΩ & 68kΩ plate loads and 68kΩ cathode load of V3 are suspect.  Highest priority for replacement goes to any resistor with significant voltage (over 20v) across it.  However, any of those tone circuit pots, or 100-220kΩ resistors could be the noise-maker, too.

Below is a video that shows how voltage across a resistor results in noise (skip to 1:45:50 and watch for a couple minutes):

&t=6345s

[CrocMule]

Thanks PRR.  This thing wouldn't hold up to being gigged -- not once.  Besides, I'm not a performer -- I don't get near audiences anymore.  I'm an at-home "recording artist" so hiss like this would be noticeable in the mic. 

The bulk of the hiss isn't coming from the inputs.  It seems to be coming from something between V3 and V4.  I just reconfirmed my test of grounding P2 (the input) of V3 (thus removing the inputs, tone stack, and reverb from the circuit), and there was a very slight reduction of hiss when grounded, so there is some hiss coming from the inputs, tone stack, and reverb, but very little. 

[CrocMule]

The hiss is at or before V3.  Hiss with V2 pulled means only that the hiss is after V2.

That means every pot & resistor from the 330kΩ late loads of V2 through to the 220kΩ & 68kΩ plate loads and 68kΩ cathode load of V3 are suspect.  Highest priority for replacement goes to any resistor with significant voltage (over 20v) across it.  However, any of those tone circuit pots, or 100-220kΩ resistors could be the noise-maker, too.

I disconnected the tone stack and reverb, so there's no connection to the circuit upstream, and grounded P2 (the input) of V3, and the majority of the hiss is still present.  It can't be coming from the tone stack

[CrocMule]

Below is a video that shows how voltage across a resistor results in noise (skip to 1:45:50 and watch for a couple minutes):

&t=6345s

Thanks for the link.

The crux of the problem is that I've swapped in known good resistors for all the ones that could be the hiss source, and none of them are. 

I might have to go through them all again.  I hate to load up the chassis with bright blue metal films

[CrocMule]

I know my problem with this amp doesn't make sense, that's why I'm stumped.  That's why I put the question to the group.  I was hoping for some help figuring it out.

HBP, you didn't even read my whole OP before you started telling me how I was wrong.  (PRR, you didn't read it all before you started typing either.)  You guys fly off the handle when others don't do their due diligence by posting schematics, gut shots, voltages, yet you didn't do your own basic due diligence by reading my whole OP before responding.  I know it's long, but i was trying to be thorough and include all the relevant info -- I thought you guys would give me hell if I didn't.

I'd rather you didn't respond at all than respond after reading just the first few paragraphs.  That was a waste of my time and yours.  If you're going to respond, then do your due diligence -- read the post your responding to.

We hear...
We hear...
We hear...

What's the purpose of that comment?  The mocking tone is clear to everybody.  You just trying to make a newbie look like an idiot in public again?  You do that a lot -- seems to be a hobby of yours, shooting people down, making them feel stupid.

Your response above is nothing as far as the severity of your comments in the past -- you've slammed me much harder on TGP.  Maybe your snide response here triggered me.  Maybe I'm just fed up with your abrasive negativity and the effect it has on everybody around you.  My criticism goes way beyond what you said above -- it's a much bigger issue than just one snide comment to me in this thread.

I've read the tongue lashings you've given to numerous others -- you do it on a regular basis.  You're smart, you know how to use language as a weapon, and you use it to cut people to shreds.  I've seen you lay into people like a complete a-hole for almost nothing.  I've watched you chase countless newbies off for asking honest newbie questions, time after time after time -- they usually don't even get to their 10th post before tucking tail and slinking away. 

So you're perfect?  You never had a newbie question?

[CrocMule]

How many noobs do you think you've run off over the years?  Hundreds?  You think ridiculing everyone who dares to ask a noob question is healthy for this community?  It certainly isn't for the people asking those questions.  You probably justify it to yourself as some kind of tough love -- did your teachers do the same to you?  But I'm sure some of those noobs you chased off gave up amp-building entirely after running into you, after you made them feel like garbage -- how helpful is that?  You seem to be intentionally making people feel bad about themselves.  Is that fun for you?  Are you a bully at heart?  Were you picked on as a kid, is that it?

Did it ever occur to you that you could simply not reply to the posts of those you find annoying?  Or is the urge to belittle those you deem beneath you irresistible?

There's no need for your caustic rudeness.  It's destructive.  Your knowledge is a boon to us all here, and I sincerely thank you for sharing (when you're nice), but your attitude toward those of us not in the IN crowd is very often toxic. 

I realize you deal with a good number of boneheads who don't do their homework and that you're jaded -- I understand -- but I put a lot of time and research into my OP, and I'm not a bonehead.  Don't treat me like one. 

It's clear, for whatever reason, that you feel the need to boost your ego by putting others down.  You have created a hostile air, here and at TGP.  I think there are probably a good number of people on both forums who are afraid to post questions because of you.  You may be the smartest guy in the world, but you act like a real jerk to a lot of people, and that's not cool.

There's nothing wrong with being respectful and nice.  It makes one feel good.  You might try it.

I know you're a moderator and that you can kick me right off this forum, and TGP for that matter, but somebody needs to call you out.  Your verbal abuse is hurtful to a lot of people.  Stop being such a jerk.

If all you can think of saying in response to this is something snarky and disparaging, then please just keep it to yourself.  If you can't at least be respectful to me, if you can't respond without condescension and mockery, then I really don't need it.  Seriously -- just don't.

In fact, I'm really not interested in anything you have to say to me.  So just drop it and leave me alone.  Put me on your ignore list.

There are plenty of other knowledgeable members on this board with friendlier attitudes who I'd rather talk to, so if you'd kindly just get out of the way, please -- you're obstructing my pursuit of knowledge.
 
Does anybody else have helpful advice, insights, ideas?

Back to the OP:

Could a sketchy ground connection cause an ocean of hiss? 

[HotBluePlates]

Let's assume I am wrong about the resistors being the noise source.

The Tone Stack of this amp is over-complicated compared to a Fender 2- or 3-knob tone stack (lots of extra resistors/caps).  The output of the Treble control feeds a 50pF cap at the wiper of the Volume pot.  That seems like it could leave a bunch of hiss while chopping out all the meat of the sound.  The effect would be worst when the Volume is very low (which could be partially the source of PRR's question, "Does it hiss on-stage with an audience??").

Let's guess the Dano tone circuit holds no magic, and rebuild with the tone stack of a Deluxe Reverb.  Be especially sure to copy how the output of the DR's Treble pot goes straight to the outer-lug of the Volume and not the wiper.

How's the hiss now?

How many noobs do you think you've run off over the years?  Hundreds?  You think ridiculing everyone who dares to ask a noob question is healthy for this community?

I am sorry for my comment.

It was intended in the spirit of, "all evidence is contradictory, the problem seems like it couldn't occur, therefore something is being overlooked."

I have to apply the same self-criticism when I try to troubleshoot something I'm working on or built:  if it's not working properly and "I've checked and everything is okay," then the only possibility remaining is that I am overlooking something.  I have to ask, "how did I screw this up," or the problem never gets fixed.

HBP, you didn't even read my whole OP before you started telling me how I was wrong.

... doesn't seem to be affected by swapping in a couple new components at a time (metal film resistors and Mallory 150 caps).  I didn't leave the new ones in place if they didn't seem to make a difference, so it's (mostly) all still original components with some new solder. ...

Hiss usually comes from resistors, and I interpreted your statement above to mean a few resistors were replaced but the originals were put back in before moving on to trying a few other resistors.  So what happens if 5 or 10 or 20 noisy resistors are present?

If the amp is worth keeping, the tone-stack re-dux above doesn't solve the issue, and there is no scope or other tool to isolate the source of the noise then it may be easiest to replace all the resistors and pots.

... Could a sketchy ground connection cause an ocean of hiss? ...

Normally, no.  See the tube amp debugging page.

An exception might be 60+ year old Fender amps with the brass grounding plate.  Because it and the chassis are dissimilar metals, they develop corrosion over time.  Techs solve all manner of noise problems by not-diagnosing and skipping straight to removing the pots & brass plate, then throughly cleaning the chassis & brass plate with an abrasive before reassembling & re-evaluating the amp's noise.

I don't know that your Dano has a comparable connection anywhere.  If it doesn't and the resistors are excluded as a source, then that seems like more support for the tone stack being the cause of hiss.

[PRR]

...PRR, you didn't read it all before you started typing either....

I did read every word, thus wasting your time and mine. It won't happen again.

[CrocMule]

I did read every word

I made an assumption, based on your initial response (about the inputs), that you hadn't read the part of my OP where I said I had disconnected everything upstream from V3 (which includes the inputs).  After re-reading your response, I now see how I misinterpreted what you wrote.  I didn't read what YOU wrote closely enough -- the opposite of my assumption.  I was wrong, and I apologize.

[bmccowan]

I hate it when this chit happens on the Forum. People make mistakes, people misinterpret, people misread, people are sarcastic (me in particular) and sometimes people are just tired. But in the end, everyone is here to share information. That's a great gift that the internet facilitates. Enjoy it. Happy New Year all.

[Platefire]

I have read through this once. And yes I see the problem seems to have been isolated around V2 and V3.This problem reminds me so much of the irritating hiss I experienced in my Silvertone 1482/Danelectro.
So I know this probably won't apply but my ugly hiss was from V1 Cathode resistor R5 and R6(both 2.2K). Never had a cathode resistor hiss-ed like in this amp before. I changed them to a 1 watt Metal film and there has been perfect silence every since. This is probably not the solution in your case, but it might be something out of the blue to try. After all they are both Danelectro:>)
 

[bmccowan]

A listening probe/amp is a great tool for finding the location of the noise source. The methodology is detailed in many Forum threads. It's simple to set up and will save much time and aggravation chasing the gremlin. When the problem is an audible hiss, a signal generator is not even needed, as the hiss is the signal being monitored - just probe the signal chain from one end to the other. Good luck.

[HotBluePlates]

A listening probe/amp is a great tool for finding the location of the noise source. The methodology is detailed in many Forum threads. ...

The Listening Amp has been on the bottom third of this page for ~20 years now.

[bmccowan]

The Listening Amp has been on the bottom third of this page for ~20 years now.

And it still has not lost it's Mojo.

[CrocMule]

I am sorry for my comment.

Thank you for your apology, and thank you for going ahead and offering help after I let you have it.  What you pointed out is very helpful, and I appreciate it.  I'll have to read through it more thoroughly when I get a chance to get back into the amp.

I owe you an apology as well, HBP.  I got all butt-hurt, lost my head, and crossed the line.  Even though you've made me feel stupid on a few occasions in the past, you've helped me out way more than that.  I lost sight of that fact.  I'm sorry.

[CrocMule]

I have read through this once. And yes I see the problem seems to have been isolated around V2 and V3.This problem reminds me so much of the irritating hiss I experienced in my Silvertone 1482/Danelectro.
So I know this probably won't apply but my ugly hiss was from V1 Cathode resistor R5 and R6(both 2.2K). Never had a cathode resistor hiss-ed like in this amp before. I changed them to a 1 watt Metal film and there has been perfect silence every since. This is probably not the solution in your case, but it might be something out of the blue to try. After all they are both Danelectro:>)

Hey Platefire.  I didn't know cathode resistors could cause hiss.  I will definitely look into that more closely.
 Thanks for the tip!

[CrocMule]

A listening probe/amp is a great tool for finding the location of the noise source. The methodology is detailed in many Forum threads. It's simple to set up and will save much time and aggravation chasing the gremlin. When the problem is an audible hiss, a signal generator is not even needed, as the hiss is the signal being monitored - just probe the signal chain from one end to the other. Good luck.

Thanks.  I made a listening probe for this (according to the plans below), but I guess I need more practice probing a signal chain with it to know how to really use it properly.  The results of my tests with it were confusing, and thus inconclusive.  Maybe I should give it another shot.  I'll search for threads where people explain its use.

[Platefire]

I've been told the same thing, that cathode resistor couldn't cause hiss. All I know is when I replacedthe original carbon resistor one channel V1A it quit.  Sometime later on the other side V1b started hissing and I changed it with another 1 watt Metal film 2.2K and that one hushed up. I never had a cathode resistor cause hisss in no other amp????? 

[sluckey]

I made a listening probe for this (according to the plans below)

I highly recommend replacing that green cap with a .1µF @ 630V.

[CrocMule]

I highly recommend replacing that green cap with a .1µF @ 630V.

Doh! That seems so obvious now that you pointed it out.  I completely missed that.  I think I used a 200V that I had laying around.  I'll have to test it after I replace it -- I may have fried it with the first touch.  Thank you!

[bmccowan]

I made a listening probe for this (according to the plans below), but I guess I need more practice probing a signal chain with it to know how to really use it properly.  The results of my tests with it were confusing, and thus inconclusive.  Maybe I should give it another shot.  I'll search for threads where people explain its use.

I do not find those instructions for using the tool to be all that clear. The link that HBP provided for Doug's instructions are clearer.
For finding a noisy component or assembly, this is what I do:
 - attach the ground clip to the chassis of the noisy amp
 - set a guitar in a stand and plug it into the noisy amp
 - plug the probe into the input jack of the listening amp - I just use a cheap mini-amp, but any amp will do. An amp with headphones works well if you are careful with volume.
 - with the listening amp off, turn on the noisy amp and set it to generate the hiss, but not too loud
 - turn on the listening amp and set the volume fairly low at first
 - hit the guitar strings and touch the probe to the input jack of the noisy amp, adjusting the volume of the listening amp until the signal can be easily heard
 - carefully work your way down through the signal chain - best to sketch out your signal chain if you are not sure
 - at some point you will pick up the hiss in the listening amp
 - now you know which component or assembly is generating or amplifying the hiss
 - before replacing components I take another look to make sure the components in that location are correct and are properly soldered.
I've never written this down before, so hopefully my memory is clear.
Worth repeating - take the standard precautions and do not forget that the amp is live and waiting to shock you - be careful.

Edit - I forgot to mention that I am not too keen on the idea of using a piece of wire attached to an alligator clip to probe around in a live amp. At a minimum I would strip the ends of an insulated piece of wire, so as to avoid making unwanted contacts or shorting something. I made my probe by soldering an axial cap, like a Mallory 150 to a lead, and inserting it into the body of a plastic ballpoint pen with the other end of the cap sticking out of the pen tip about 1/2 inch.

[HotBluePlates]

Thank you for your apology, and thank you for going ahead and offering help after I let you have it.  ...
I owe you an apology as well, HBP.  I got all butt-hurt, lost my head, and crossed the line.  ...

Regardless of my intent, the words I chose were snarky and you would have reacted differently if I was more tactful.  I'm sorry for contributing to the problem.

Being over at TGP has made me more combative overall.  Mainly because there's a lot more rude people over there.  But I shouldn't drift down to their Norm.  Maybe a good resolution would be to emulate Tubenit more, who is always very tactful & considerate with his wording.

[66Strat]

It is very difficult to interpret "tone" in writing. I have considerable professional (technical) writing experience. The goal is to understand the audience, and adjust the tone of your writing to the audience. This can be very difficult to do, especially when writing in factual terms. The reader does not have the inflection of the spoken voice to assist them in interpreting the tone of the writer. Even so, spoken verbiage can often be taken the wrong way when the audience does not understand the subject matter. I offended an assistant Scout Master when I corrected her regarding one of the Boy Scout guidelines to safe scouting. It was a big stink. It wasn't resolved until I sat down with the Assistant Scout Master and showed her the specific written rule. It's one thing to get all butt hurt that someone doesn't like your response on a geetar amp forum and a whole different ball of wax when the safety of children under your care is involved.

[g-man]

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[bmccowan]

For the signal tracer, the value of the cap is not all that important right? I have a 0.68uF/630V with beefy leads that I think would work well. And the resistors shown in the diagram above aren’t needed if you’re using another amp with a volume control as the listening amp?

Yes and yes, as far as I am aware. The cap is to block DC from coming back through the probe. So the voltage rating is the important thing. And with a separate listening amp all the probe is doing is intersecting the signal and sending it to the input of the listening amp. Without headphones, its a bit of a trick to adjust the volume of the two amps, in order to hear the noise through the second amp. A dummy load on the suspect amp is ideal, but not necessary. I sometimes damp that speaker with a few rags. With headphones, the trick is not let your ears get blasted. A bit of practice with the setup helps.

[HotBluePlates]

For the signal tracer, the value of the cap is not all that important right? ...

The cap interacts with the Input Impedance of the listening amp to set the low frequency limit of what gets passed, in proportion to RxC.  So going a little higher is preferable to going lower on the cap value.

... And the resistors shown in the diagram above aren’t needed if you’re using another amp with a volume control as the listening amp?

The diagram's resistors, and this diagram's pot, are used to keep the probed signal from being too large for the listening amp (blowing your ears, or blowing a speaker, or blowing up parts in the listening amp).

You don't "need them" to get started.  But eventually you'll encounter a situation where you need them.  And a pot is preferable to any fixed voltage-divider made of resistors.

[g-man]

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