Ampeg SS-150 Head Issues... Sound cuts in and out...

[johnboypitt]

I have had this gem for almost 20 years now, and am in no way ready to let it die... Over the past year or so, for the second, maybe third time now, when I'm playing through channel A (crunch), The sound will fade out till it was very faint, sometimes completely, and then fade back in here and there, sometimes back to full volume, sometimes not.  If I turned up the gain to almost 9 or 10, it would blast back in and work for a few minutes and do it again.  I play it through an Ampeg 4x12 celestion cab (bought the head/cab together), and it has been flawless since day 1.  I have a Jackson Dinky and a Fender Strat that I kinda rotate between, and a Zoom 505 effects pedal, all of which I wouldn't think are causing this.  I treat the amp with the utmost care, so it's not that.  The local music shop where I bought it is still around, and have had it repaired these times through them, and apparently it was a capacitor issue.  Anyway, this is becoming too repetitive, and would do mostly anything to not have to replace it.  So, I just dropped it off today for analysis, but if this is occurrence #3, am I just throwing away money to fix it and will only have it happen again?  Is it simply time to look for a new (and inferior for metal) head?  Has anyone experienced this issue before?  Are the guys repairing it maybe morons?  They are an authorized Ampeg dealer/repair facility, so I have faith in them.  Any info or tips would be appreciated, if I pay to fix it this time and it ends up happening again, I think I'll loose my mind!  Save my SS-150!!!    Thanks...

[phatt]

 Hello johnboypitt,

You are obviously going through a shop ,, Ask if you can get the phone num of the repair guy and talk directly to him.
Explain what you just stated here and you might get much better service/advice.
If the Amp is not really worth fixing he will probably tell you straight up.
Remember Unless you talk direct your Amp is just another job number from the shop.
Hope it pans out for you,, Phil.

[Jack1962]

If you really like this amp , and don't feel that you can replace this cap( no part goes out repeatedly without there being another problem) then have the guy replace it( I nave ran a shop for many many years, if a customer ask I will tell them whatever they want to know). Also make sure he shows you what cap it is , in case you want to replace it yourself. However , this cap has something that is making it go out and if not dealt with  you will eventually have a bigger problem.

                                                  Rock On
                                                Jack Latham

[johnboypitt]

Yea, that's a good idea... It's almost frickin $75 each time they work on it, and who knows what they actually did/might do to it, if anything... I guess I just trusted them the first couple times... Maybe this one should be a freebie, since they haven't gotten it right yet...

[J M Fahey]

Hi JohnBoyPitt.
I think you have a point there, stick to it, make them repair it for good, you have already paid for it to be done properly, as you say "this is becoming too repetitive".
That said, I think their "technical explanation" sucks. A capacitor may fail, as any other component, but doing so repeatedly means it either is an electrolytic installed backwards or underrated or simply there is "some other" problem which they fix poorly.
Ask them to fix it again (not for "free", but you already paid for it .... twice) and give you the old capacitor, showing you where on the board it sits.
You may even draw a circle on the board with Sharpie around it.
Next time, if it repeats and you dare, change it yourself to see what gives, but I already suspect the real problem is elsewhere.
And yes, that head is well worth keeping, they don´t make it anymore (don´t know why) and the sound is impressive.

[johnboypitt]

Thanks, that's great advice.  I have never found a head that I like more than this one, or sounds like this one... The sound is so exactly what I want from a head, it's like it was made for me.  I haven't seen another one since as long as I could remember, so it's not like I could run out and get another ss-150 from somewhere, and if I could, the person selling it would probably be asking a good amount for it.  Anyway, I will be much more diligent with the Ampeg folks to make sure I get quality service and a good understanding of what part is going bad and why.  It's worth it.    I'll let ya know how it goes if you're interested...

[J M Fahey]

I´m all ears, and I´m sure *many* others too.
Besides, it´s something of a pride issue: in the midst of a Tube-crazy world, appears our Paladin, the mighty SS150 (or its brother, the Crate/Ampeg 140) to defend the colors of SS lovers.
We won´t let it go easily !!
Good luck.

[Enzo]

Geez, my first reaction was that this sounds like the classic FX loop return jack problem, or a power amp in jack problem.  Electrically dirty cutout contact on one of those jacks can cause exactly this symptom.

[J M Fahey]

Hi Enzo, I fully agree with you, I didn´t want to flame a fellow Technician, but I stated "I think their "technical explanation" sucks. ".
I guess the amp isn´t even being sent to a Technician proper but some odd-job kid at the back of the shop messes somewhat with it until it sort of works ... for a while.....
I guess that when they spot our friend approaching the shop they order some Pizza and Beer, and I wonder ... who´s paying for it?.

[limpdogskip]

hey johnboypitt.  I don't know if you're still looking for answers, but here's my thoughts on your problem if you're interested:

I'm an electrical engineering student, and I'm pretty much in love with this amp.  I actually just built my own modified version of it for a school project, so I know a little bit about it to say the least.  If you have no electronics background, you could perhaps present some of this advice to a repairman.

Here's my logic flow from the problem which you described:

(Before all of this excessive technical explaination I'm assuming that the problem is not because of some dirty pots or because of a backwards capacitor.)

I'm assuming that your clean channel works because you said that the problem only occurs when you're on the gain/distorted channel.  This implies that your power amp is working just fine, which is good because that's the hardest part to fix due to the high voltages/currents and the much greater complexity compared to the pre-amp.  Also, the fact that one of your pre-amp channels works implies that the problem must lie in circuitry specific to channel A of the pre-amp.  This is good because you could replace the entire channel A for about 15 bucks (so it's definitely worth it for you to keep this gem).  If I am correct in assuming that the sound coming from the amp is the same, but the volume is the only change, then that means the signal is being passed through the EQ and distortion stages (because these stages contribute the most to how the signal will actually sound).  This leads me to say that the problem must exist at the last gain stage of channel A.  There are two parts that would be of concern here: an op-amp and a JFET.  The problem is most likely in active parts because these can be damaged non-visibly unlike resistors for example.  Also, depending on what damage has been incurred either of these parts could cause the problem you're describing.

If I had to guess, I would say to replace that last op-amp in channel A's signal path.  The part number is AC4558P.  There are 3 of these on the pre-amp board (if you decide to open up the amp, the pre-amp is the board with the control knobs); the middle one is the one that you want to replace.  You prrobably won't be able to find that specific part anymore, but any op-amp with the 4558 number in it would do the trick.  The JFET part number is J112.   

As for the capacitor being the problem, I would say that if it failed multiple times, the capacitor blowing is because of one of the active components failing, not because of the capacitor itself.

If getting it repaired causes too many issues, I have seen these on ebay several times periodically.  You just have to check it occationally and within a month or two one should come up.  It's tough to say how much I'd pay for one of these.  I got mine for 150, but that was because it was broken.  How much did you pay for it 20 years ago?  I can't find an original price for this thing, and I'd be interested to know what the original design went for.

Hoped this helps,

Rob

[J M Fahey]

Hi Rob/Limpdog . Excellent analysis, very likely that´s the problem, although, of course, only actual testing will tell.

[Enzo]

Watch out with those assumptions.  he said the problem occurs in the A channel.  Unless he also says the other channel works fine, I can't assume that it does.  A lot of guys only use one channel all the time and will simply report the one used without ever checking the other.  I don;t know that that is the case here, but believe me, I hear it all the time.

"Uh, my lead channel cuts out."  "does the clean channel cut out too?"  "I don't know, I never use it, dude."

Problems are not always bad parts.  The connections between them can cause trouble too.  Electrically dirty switch or relay contacts, cracked solder joints, broken traces, and jack contacts all routinely cause trouble.

To me the large clue is that he can crank the amp up to 9 or 10 and it will pop back into play.  This is the classic description of dirty shunt contacts in an effects loop return jack, and if not that, any of a number of other contact issues.  The increase in signal level is enough to overcome the resistive contact and the circuit comes alive.  That doesn't sound like a bad semiconductor to me.

And be wary of "multiple cap failures."  If the problem still occurs after that cap change, chances are the amp was never really repaired in the first place.  They went inside, changed out a cap, the amp woke up at that time, they assumed the correlation meant causality, and closed it up.  Then a little later the same unrepaired problem resurfaces, and they noodle around some more and solder another cap, etc.

Of course, whatever it is, we'd like to hear the results.

[J M Fahey]

"If the problem still occurs after that cap change, chances are the amp was never really repaired in the first place. " [2]
I agree fully, that´s why, among other things, I suggested marking it with Sharpie.
As Enzo suggests, it may well be a cracked track (the peskiest problem possible) which gets re-soldered when changing a perfectly working capacitor.
I often get dead or faulty amps, which work when opened and even continue to do so after re-mounted ito their cabinet, where I can´t find nothing wrong.
Usually I don´t charge for them (although I always get some tasty pizza , a bottle of good wine or something similar) for the *very* good reasons that: a) It´s going to fail again, gess who´s going to get this and other jobs; and b) Don´t know there, but here in Argentina most Rock musicians know each other and word-of-mouth is very important. As in most human societies, "bad news" travel fast, and "good news" travel slowly. I´d rather be well considered than have a few extra bucks for a poorly done job.

[DA25or624]

Was just reading about the problem you encountered with your Ampeg head.  I am having the exact same problem with mine and was wondering if you ever diagnosed the problem?  Thanks.