1980 Super Reverb recording line out noisy. Testing Electrolytics. Any Point?

[Toxophilite]

My 1980 Super Reverb has been a brick of an amp and has seen me though over a 1000 gigs over the past zillion years.
I've enjoyed that it has a recording line out but the line out has always been a little noisy
(I used it for writing mixes, and as a line out into a stereo amp)

It has a LOT of hiss now though, maybe more so lately
THis line out includes the reverb and tremelo and the preamp
Is that normal for this, and does anyone use this on their Fender amps?

What could I do to quiet it down a little?,
It seems to be part of the negative feedback circuit (??)though it has an additional 2.2K resistor and a 270ohm resistor to ground at the line out jack

[Raybob]

1980 filter caps?  If so, change them and the bias cap.

[stratele52]

Hiss is not like hum which need new filter caps .

Hiss can come from old plate resistors , replace them one each tube. And bad wiring dress.

Any picture from the wiring ?

[eleventeen]

Those 100K plate resistors. Nobody believes it until they they change their first set on an older Fender amp. Oh boy. Especially if the amp is well-well-well used, not just chronologically old. This is a near-religion for me. Doug's 3 watt metal film ones are perfect for this. By far, the cheapest thing you can do to an amp that has potentially the maximum effect.

[Toxophilite]

Maybe it's time to open up the chassis again and start measuring resistors etc
I'll report back with some photos etc

[eleventeen]

The tendency of those old carbon comp R's to inject noise is not something an ohms test will reveal. It is true that most will be "baked up" in value which is entirely common with old carbon comps. You could see 100K ohm R's measuring 115K ohms, even 120K. That in itself isn't what causes the noise. It is some kind of thermal effect which I will not try to describe. What I *can* tell you is if you ever get an older Fender amp on your bench which is generally working but making spitting, hissing noises and you just replace all the 100K 1 W plate R's with new ones, you will fall over when you hear the difference.

[Toxophilite]

I hope I don't fall into the amp!
I was wondering about that as they all measure between 101 and 104 k
Also I di notic the amp has some hum all by itself regardless of where controls are set..about low A# if that means anything...not really low
Maybe I should replace some of the electrolytics as well
Here's some photos

It's pretty messy in there..looks a little greasy!!..always has though ,I replaced the power tube sockets a wjile back and the master volume pot when the old one disintegrated.No silly volume boost now.

[Toxophilite]

Just to reiterate
The hiss/noise problem is largely coming from the recording line out
THough I'm proably going to replace those 100k resistors, For about $6 it's an easy experiment to try and I'm not attached to old worn out parts (except my own)

[stratele52]

Wow what a horrible wires dress . Sure you"ll have noise with this poor wiring .

[Toxophilite]

Wow what a horrible wires dress . Sure you"ll have noise with this poor wiring .

THanks! That's extremely helpful!
As this has been my main amp for 25 years now, with people constantly telling me what a lovely sound I have annnd it's always sounded great on recordings (about 7 or 8 albums with this amp)
I think I'll leave that part how it is.
I know it's the least desirable of the Silverfaces etc etc but for cleans, it sounds amazing and takes pedals quite well (when I use them)

The amp hasn't been very noisy by itself.

AS I said I'm talking about noise on the recording line out .
Not necessarily the whole amp (though I could see it contributing)which has more of a filter cap hum than anything else..and who can blame it, It's 34 years old, has been ridden hard and put away wet!

[Willabe]

Replace all electrolytic caps, including cathode bypass caps in the amp as their 34 years old.


            Brad     

[Toxophilite]

Thats the plan. I was just writing down what was needed earlier
Thanks for reminding me about the cathode bypass caps and other electrolytics

Nobody likes to be told their girlfriend is wearing an ugly dress!!

[Willabe]

Thanks for reminding me about the cathode bypass caps and other electrolytics

-bias caps too.


            Brad   

[Toxophilite]

Weeell, I'm going to replace all the electrolytics
Can you elaborate a little on which caps you're referring to as the bias caps?
I was trying to research it and couldn't find any info

[sluckey]

They're the filter caps in the bias supply. Looks like you have 2 in that amp. Your "line out" is just a simple voltage divider across the speaker output. It's hard to think of filter caps causing your hiss. I wonder if it's maybe the interface to your external equipment? Do you have "a LOT of hiss" through the speakers also?

I'd be very reluctant to do a wholesale replacement of all electrolytics based solely on a hissy line output jack. I'd need more symptoms. I think this is your schematic in case you don't have one. Gonna need to take this file to your 'good' computer.   

http://www.el34world.com/charts/Schematics/files/fender/cbs_70w_mstrvol_pullsw_super-pro-bmstr_rev.pdf

[Willabe]

I'd be very reluctant to do a wholesale replacement of all electrolytics based solely on a hissy line output jack.

I should have been more clear, I'm not saying it will cure any hiss, but they are 34 years old and he say's it's his main amp.

I'd say he got his money's worth out of them.


             Brad     

   

[Toxophilite]

I don't know how the grounding is here in my old building (well old for Vancouver) but my amp is humming by itself as well..I just noticed it. I can't play it here really, it's too loud, and when I'm in rehearsal , we pay for the space and my bandmates are there and I don't want to spend tooooo much time goofing around with my gear.(that was my excuse for just noticing it now)

The hum I'm hearing is around B# in tone, a fret up the A string if that gives you an idea, low but not super low, and I can have EVERYTHIng turned right down on both channels and still hear it the same volume.
That makes me think electrolytics but I could be wrong
I have certainly gotten my moneys worth out of them..The amount of gigs and road it's seen don't include the rehearsals and recording sessions!! I've probably got a few peoples moneys worth out of them.
I don't like to fix things that still work though as I'm not made of money and little lazy

It also starts to crap out on the bottom end much past 4 with the master all the way up

Back to the Hiss
I don't hear it out of the speakers much or at all

The sound out of the line out is quite bright and hifi-esque (maybe thinner)very very crisp, like an acoustic hi end

I run the line out straight into another amp

I go into a Space echo (after a tuner and Eq/volume boost) the space echo has separate dry and echo
The dry goes into the super, the echo goes into another amp, and I take a line out of the super into a 2nd channel on the other amp so when I turn off the echo I'm still stereo.
I could use a splitter but it's nice to have the tremelo and reverb in both amps

[HotBluePlates]

Back to the Hiss
I don't hear it out of the speakers much or at all

The sound out of the line out is quite bright and hifi-esque (maybe thinner)very very crisp, like an acoustic hi end

This is not a mystery... Look at the schematic Sluckey posted.

See the line out jack on the schematic, over by the output transformer? The line out taps signal off the negative feedback loop, which itself is fed from the speaker output of the output transformer. Whatever hiss is present at that line out jack is the hiss of the entire amp. Said another way, it is the sum of all the individual sources of hiss in the amp, and the exact same noise which is present at the speaker jack.

"I don't hear it out of the speakers much or at all

The sound out of the line out is quite bright ..."

It's not that the line out is bright... just that the speakers are dark.

Follow me here... The line out signal is exactly the same as the speaker out signal, just smaller. But you hear less treble (and hiss) from your speakers than you do from the line out. That's because your amp's speakers are rolling off treble (at a range of frequencies which are not helping your guitar sound anyway).

Hiss is a broadband noise, but you notice it more at high frequencies (in this case, and this type of hiss). Because noise is broadband, engineers speak of "noise bandwidth". Say you have a hiss which when measured with a spectrum analyzer shows energy from 100Hz to 50kHz and an average level of 100mV. You can reduce noise by reducing the average level of all the noise from 100mV to 50mV. But you can reduce the noise the same amount by reducing the bandwidth from 100Hz-50kHz to 100Hz-12.5kHz.

Said another way, rolling off unneeded treble reduces the noise bandwidth, which reduces the noise power and how much hiss you hear. Since your line out doesn't have the treble roll-off your speakers do, you're hearing more hiss from the line out. Solution: turn down the treble on whatever you're feeding this signal to, which also solves the brightness issue.

You're still hearing more hiss than you used to, and increased hiss (in the same amp with no changes) almost always comes from resistors which have gone noisy. Tubes with too high a supply voltage and/or too much gain (often the reverb circuit in Fender amps) can contribute hiss as well, but if that were the cause in this instance, you'd have always heard the hiss. Swapping for low-noise resistors (metal film) is probably the best best, as is rolling off treble in whatever the line out feeds.

The hum you describe sounds like 120Hz hum (out of tube A#/B-flat), and will likely be fixed when you replace all the electrolytic caps (which have probably served their useful life anyway).

[alerich]

+1 on replacing the filter caps. They behave somewhat like fluorescent lights to me in that they fade gradually... almost imperceptibly. 34 years is a long time for the stock caps. I would expect you to hear a noticeable improvement in tone if you replace them. Tone aside - that's a long time for filter caps. Particularly in an amp that has seen such heavy duty as yours. The unfortunate aspect of filter caps is that when they fail they almost never open up. They almost always short circuit. When they do they almost always take other stuff (often other expensive stuff) with them.

I wouldn't touch the lead dress. There are legions of players using those silverface Fender amps and they sound great. I'd be afraid of screwing up the tone. you love.

[Toxophilite]

That makes sense
I have the schematic and could see where it was coming from..could I understand it completely?...not quite, You (Hot Blue PLates)and Sluckey helped a lot
I wonder if if I could do something to the line out without affecting the whole sound (cap diverting extreme high frequencies to ground), It seems like that would be problematic, if not impossible unless that line out is isolated enough

On the super , for my rambunctious rock band, I usually have the bright switch on and the volume about 3-4, and the  treble mid and bass all set on about 3, maybe a bit more. Prior to the rock band I'd never really ever had the volume past 3
Without the bright switch off it's definitely more of a soft Jazz tone at those settings, which I use with my jazzy latin caberet band
My speakers might be getting a little tired too, they're orginal, one was reconed about 20 years ago when beer was spilt on it, that's it.
I've never compared it with another Super of similar vintage.

The two channel amp I was running the line out into had 2 channels (individual volume controls feeding one tone stack (actually the PA300 I'm reconverting in another thread) So currently I don't have the option for individual channel EQing and the main sound of that amp is the echo which is coming right out of the RE 150 space echo so I don;t want to roll off all the top end. I used to use a PA head and one CAb so I had more control.
maybe I have to make something/ redesign something for just this purpose...I could maybe make one of my channels a little darker on two channel unit.

I'll do the maintenance though, because it's never had much other than tubes and fixing/replacing anything that was outright broken.
It'll be fun and satisfying too
THanks Alerich for the Silverface support, not the most coveted of the fender amps, humourously I pulled all the black tolex off of mine about 20 years ago and finished it really nice. It's pretty beat now and in need of attention but people always think it's a really really old amp because of that, even other guitar players!
I wouldn't mess with the lead dress, as it's a big job, and as it's sounded fine for years it seems unnecessary
So my amp is wearing a tawdry old dress..it still has class and sounds pretty!

[Willabe]

It also starts to crap out on the bottom end much past 4 with the master all the way up

New information.   
   
   
      Brad

[Toxophilite]

I never turned it up past three really till about 7 years ago (up to 4!)and it did the same thing..it's pretty loud at that point.
I could be because I have my Eq turned down pretty low
Having no other experience with these amplifiers and having almost always played clean and never been one to overdrive my amp I've never looked into when they should start to break up.

[sluckey]

I'd be very reluctant to do a wholesale replacement of all electrolytics based solely on a hissy line output jack.

I should have been more clear, I'm not saying it will cure any hiss, but they are 34 years old and he say's it's his main amp.

I'd say he got his money's worth out of them.


             Brad     

   

I agree that the electrolytics should be replaced based on age, especially now that we know the amp hums too. My comment was not about that at all. And I'm not advocating to not replace them.

But, this thread is about a noisy/hissy line out and replacing electrolytics is not likely to fix that. I simply wanted Toxo to be aware of that. Replacing all plate load resistors with MF in the signal chain is much more likely to reduce hiss at the line out jack.

[Toxophilite]

Any confusion is likely my fault
When I went to have a good listen to the amp itself(not just the line out) I noticed the hum, which I hadn't noticed in the haste of recent rehearsals. So I brought it up, adding another unrelated symptom to the thread.
I got a little excited about giving the old reliable amp an overhaul!

The hiss from the line out I noticed anew when I was recording last week

[Toxophilite]

Hey
Should I be replacing all the plate resistors
I think I have 6 100 k and then ether's a 220K and the 2 47ks on the PI and the the 470 ohms on the powertubes,(though they look pretty new comparatively, shiny, clean and smooth, not rough and roasted)

[sluckey]

Replacing all plate load resistors with MF in the signal chain is much more likely to reduce hiss at the line out jack.

[eleventeen]

At 30 cents each....?

Wait til you get to replacing those electrolytics, especially if you want Sprague.

Your old 100Ks can look perfectly fine and hiss like angry cats!

[Toxophilite]

Okay okay!
All of them!
People were initially talking about the 100k ones so I got that in my thick head
And yes the electrolytics will cost me a bundle 220 mfd at 285..eek
I guess I paid $325 for my amp and have sunk very little into over the past 25 years (most of my tubes are free)

[eleventeen]

I know I'll take a whole pile of crap for this....but I generally recap Fenders with axial-mount (PC mount) electrolytics. They are profoundly cheaper than radials. You have to figure out a way to keep them secure against the cap board. What I do is to take a 4-5" piece of 1/2" PVC pipe and saw it in half the long way. I wire up the two little caps in series (for the first two) and place the half-pipe over them as a positioner, then place like a transformer on top to act as a weight. Then I can silicone them in place with a neat little fillet-bead instead of a giant blob. Sometimes you may want to place a plastic insulator between the head of one cap and the leads of the next one....remember that the can of such caps is "live"...usually the neg terminal. I allow space, but I also use a piece of credit card.

By the way, when you order the plate resistors, also order the 2 or 3 resistors that sit between the A-B-C-D nodes in your power supply. Sometimes they are 4700 or 5K, sometimes they are 10K, replace those with the 3 watt MFs also. That way if and when you decide to re-do your cap board, you can just tear the whole thing apart and start from new.

[HotBluePlates]

I know I'll take a whole pile of crap for this....but I generally recap Fenders with axial-mount (PC mount) electrolytics. They are profoundly cheaper than radials. ...

You mean "recap with radials, rather than the original axials."

I don't have a problem with that at all. Cheaper, higher quality caps are available in radial format because of the higher usage rate in pc boards.

[eleventeen]

Geez, I got that backwards. Good thing I got new tires on my car last week, I might have chosen axials!

[PRR]

> I run the line out straight into another amp

Another *guitar* amp?

The output is over 1V, perhaps 1.5V. That's WAY big to go to a guitar amp. It goes to a mix/PA console Line In, or to a standalone Power Amp.

To feed a guitar amp, the lower resistor of the divider should be more like 30 or 60 ohms.

To offer all options, hack another jack in, make the string (spk) 2.2K (line out) 220 (git out) 47 (gnd).

[Toxophilite]

Geez, I got that backwards. Good thing I got new tires on my car last week, I might have chosen axials!

Ahh jeez
I thought the radials went on the axials??
If I go with radials should I get steel belted,  or all season electrolytics??
I thought this was going to be relatively straightforward!!

I think I'll get whatever doesn't cost a zillion dollars and I can always make do with shrink wrap, zip ties and silicon blobs if need be to keep everything safe and secure.

Another line out might be a good idea..then when I die the new owner of the amp can come on the forum asking what ^%$%& this extra jack was all about!

Seriously though, it's a good idea and made me think another possibilty would be a power amp in with a volume pot on my second guitar amp.
I'll look into that after i do my maintenance
Off to the electronics store

[Toxophilite]

So I'm replacing the plate resistors in the signal path of my amp
i've notuced that it's waxy/greasy in their and soldering in the new resistors confirms that everything is coated in fine coat of wax.

I know my amp overheated once (20 years ago) and popped the thermal circuit breaker. I was on the road then and the tech at the L&M I took it too said that they would sometimes blow for whatever reason and he bypassed it. Being even more ignorant then, I let him do it and carried on. It seems to have worked for the past 20 or so years.
In retrospect I attributed the overheating to some JAN WGB tubes I put in, but that could be wrong.

Anywho is the wax a sign of past overheating and the power tranny losing some of it's goo?

Next: electrolytics!

[Willabe]

i've notuced that it's waxy/greasy in their and soldering in the new resistors confirms that everything is coated in fine coat of wax.

Fender was having a problem with the eyelet boards absorbing moisture and becoming conductive so they started dipping the eyelet boards in wax to seal the board.

Your amp is from that time period.


               Brad      

[Toxophilite]

Interesting, and somewhat of a relief Thanks!..they seemed to have dipped the lot in wax but it makes sense to solder everything on and then dip!

By the way when doing these sorts of things it's very cool to have people with a lot of experience and specific knowledge of guitar amplifiers
My experience with fender amps is confined to this one so it's much appreciated and I really enjoy learning about it all.

I think the new resistors sound better. The amp seems a little quieter overall, though I didn't fall over
which was probably a good thing!

And as I had to lengthen my speaker wires(something I'd meant to do for a long time) to bench test the amp I noticed that the ground wire going from speaker 1 to 2 to 3 was hanging on by a strand or two so I fixed that while I was at it which should help some and save me from future problems.

[jojokeo]

Toxo - I mostly scanned the thread but you need to know something here. These amps get corrosion and not like rust corrosion. It's the type from an oxide layer + dirt+ grime+ moisture, + who knows what sometimes? I've seen MANY bad connections - especially ones that aren't used often - be simply dirty old jacks. On amplifiers and guitars and effects boxes, etc...
Get yourself about 5 Q-Tips and some metal cleaning polish of your choice and just like waxing you car's rims or paint, clean the crap out of your jack(s)! Polish them up really well and while you're at it, check out any cables or other stuff that could use a good cleaning. This could be all that's required? It's the easiest, fastest, and cheapest thing you can do. Even if it's not the problem you can be sure you'll be "good to go" for a long while further with positive connections throughout from your guitar to your speaker, even your line out jack. :)

This would be step #1 in troubleshooting 101 per se and step #1 for this kind of troubleshooting (making absolutely sure your ground and signal tip connections are clean). Make sure all your jacks are nice and tight! NEVER attack a problem w/out following a systematic approach. And never troubleshoot a problem by skipping any steps - even the most obvious and basic ones like this. So, exhaust all "free" steps first. As sooner or later it'll kick you right in your butt costing you potentially many many hours of frustration and many hard earned dollars as well.

[Toxophilite]

A good point and well made!
I'll certainly do a bit of cleaning as well
Thanks

[jojokeo]

I just had this very problem w/ a JCM800 amp where I was getting sporadic signal through only while playing in the high gain input. Through the low gain jack it was fine and flawless. But through the high gain was where the issue was. I was poking around (chop sticking) all the components, re-soldering all contacts, changing tubes, etc... scratching my head & getting frustrated. I revisited the schematic wondering about a few things further and then   bingo! I saw & remembered that the high gain jack goes into a gain stage which it's output goes back through the low gain input jack's switching lug when nothing is inserted in this jack. I skipped the most basic of steps of not checking the input jacks (& contacts) themselves!   It makes you just want to kick you own self right in the butt - especially when you know better!

[Toxophilite]

So I bought some new electrolytics, I spent about $46 getting mostly less expensive ones
All axial expect the 220s which the only other choice was the $20 a pop Spragues so I got the $6 radials
I was asking the guy at the store what the difference was and he said the new ones were just made with better materials so they were smaller
He laughed when I commented on it and came out with a big box of large old yellow paper Atom 'lytics. I reached for one to look at the value and he jokingly yanked it away like they were precious..Hilarious!. ..I just yanked one out of amp the other day! He's going to test them and sell them I think

I'm not a big cap snob nor do I have dog ears, if they test good and are decently made I figure they're going to do the job..I feel the same way about tubes and I've had literally hundreds of the most coveted ones pass through my hands. My attitude is more practical than mystical you might say.

Anywho
And I was talking to my electrical engineer brother about Electrolytics
He grew up making ham radio sets and playing with tube gear some
He used a component tester..(LCD meter?? not sure) to test the ones I bought just out of interest and of course they all tested as they should but the cheaper looking IC ones had higher dissipation
He was saying that despite modern materials(and he's really savvy to the latest technology cause he works as a programmer) size matters with electrolytics due to the way in which they work. I think he was referring to longevity

I thought it'd be neat to get him to test the Mallorys in my Super Reverb
I drained the caps and desoldered all the plus sides and had him test them
He found one 70 mfd was bad and two of the 20 mfd ones were bad and we tested them twice
(I didn't test the bypass caps,I'm just going to replace them) the big 220 mfd ones tested fine

When they were bad they wouldn't stay on a value, jumping all over and he said they were leaking and behaving like variable resistors
Also with the bad ones the dissipation was over 1 ohm on all of them (that's what he said)
while the good ones were considerable lower

Anywho I was wondering if this is okay

[Toxophilite]

Is there any point in testing the old electrolytics as per my last post
I was talking to my brother-in-law(electrical engineer guy) again about testing electrolytics at high voltage and he said he would want to have a reason/symptom to do that before he would think it was necessary. He is obviously not an amp tech but he's very savvy about this sort of gear.
What's the concensus from those who do this on a regular basis?

[Toxophilite]

Got the electrolytics all replaced
and the plate resistors too
Found the 4.7k 1-2 watter carbon comp resistor feeding the last 20mfd filter cap and the preamp was measuring about 8K so I was probably loosing some voltage to my preamp. It looked a little burnt in the middle too on close inspection. the others measured okay so I left them for now as I didn't have big enough subs. i'll go back and get them later.

The amp sounds good, a little bit buzzy maybe, but the real test will be in rehearsal at volume with my hard hitting drummer.
We'll see if the bottom end holds together a bit better whe i crank it to 4!

By the testing my Brother-in-law did 3 of the filter caps were toast so it was good I got that done.

[stratele52]

Thanks for reminding me about the cathode bypass caps and other electrolytics

-bias caps too.


            Brad   

Good to reminder ,but it is a filter caps too and electrolytic

[stratele52]

Replace all electrolytic caps, including cathode bypass caps in the amp as their 34 years old.


            Brad     

This do not fix the hiss . In my opinion is waste of time ( and money ) for now . Hiss need to be fix first . In the  worst case filter cap do some hum , that is not what you said .

[Toxophilite]

THanks for your input
However the hiss was/is only from the recording line out and not coming out the speakers
As I said upon testing the filter capacitors, 3 of them very very definitely bad, as they were behaving like variable resitors. So it was very good to replace them. Also I found a burnt resitor in the power supply that had doubled it's value and fixed that as well.

I didn't get around to putting in a new lineoput Jack as suggested, as there wasn't much room. I'd have to put it way off on the preamp side. Still might do it though as I liked the idea

[stratele52]

THanks for your input
However the hiss was/is only from the recording line out and not coming out the speakers
 

The wiring is a real mess as I write few days ago . Only a clean up will probably remove hiss.  You must do that before anything .

[alerich]

Is there any point in testing the old electrolytics as per my last post

No. Testing 34 year old filter caps might tell you whether they are leaking DC but not much else. They might pass this test today and fail tomorrow and destroy other stuff along the way.

[jojokeo]

Is there any point in testing the old electrolytics as per my last post

No. Testing 34 year old filter caps might tell you whether they are leaking DC but not much else. They might pass this test today and fail tomorrow and destroy other stuff along the way.

Can't force people to do anything, just let them attend my favorite University (SHK) and maybe they'll learn from experience?

[birt]

Is there any point in testing the old electrolytics as per my last post

No. Testing 34 year old filter caps might tell you whether they are leaking DC but not much else. They might pass this test today and fail tomorrow and destroy other stuff along the way.

it does when your tester measures ESR.

[birt]

THanks for your input
However the hiss was/is only from the recording line out and not coming out the speakers
 

The wiring is a real mess as I write few days ago . Only a clean up will probably remove hiss.  You must do that before anything .

as you might have read even before that, the amp didn't always hiss that much and the wiring hasn't changed. changing the wiring might do more bad than good.