The amp seems to work fine. Although, it appears that the longer it is switched on, the louder a buzzing noise gets over time.
Wondering if one of the resistors or caps is on it's way out?
I can't find a Schematic on the Sunn Amps site and the model isn't listed there either.
As a general question, what could be causing this slowly rising buzzing sound in the amp?
I can post a video if necessary.
Wondering if one of the resistors or caps is on it's way out?
I can't find a Schematic on the Sunn Amps site and the model isn't listed there either.
As a general question, what could be causing this slowly rising buzzing sound in the amp?
I can post a video if necessary.
Last edited:
Many of the smaller combo Sunn by Fender amps have an identical Fender branded model. Try looking for a Fender model with the same features as your Sunn.
If it is over 15 years old, the main power supply rectifier caps get higher resistance the hotter they get. If they are dried up, which is very likely. Once some noise like this happens, and the calender says the rubber cap sealant is tired & likely broken, I replace all the electrolytic caps in an amp, ordering all at once. But I put them in 2 at a time so if I make a mistake I know right where the fault is: worked before but hummed, doesn't work after, Duh, must be my fault. Order caps with service life over 3000 hours so you don't have to do it again in 5 years. Off the shelf at a store caps are 1000 hours or even 500. Farnell & digikey have the hours service life in the selector table, mouser makes you download the datasheet. alliedelec only stocked 1000 hour ones when I tried to order some yesterday & save freight from another vendor.(they had something nobody else had).
Hum can also be dirty contacts, brass or tin oxidized by time or covered in cigarette ash if your band is typical. Spray out the latter with contact cleaner, the former can be removed by unplugging and replugging. Any connector anywhere inside or outside can be the fault, even the ground star washer on the case. But getting worse as it warms up is a signature of dried up e-caps.
Warning proper contact cleaner is flammable, no smoking open flame or electricity turned on or off within 10 m of spray. The non-flammable kind of contact cleaner from the electrical supply house (brominated hydrocarbon) dissolves PVC & styrene plastics used in consumer products so don't pay the $25 a can to get it.
Hum can also be dirty contacts, brass or tin oxidized by time or covered in cigarette ash if your band is typical. Spray out the latter with contact cleaner, the former can be removed by unplugging and replugging. Any connector anywhere inside or outside can be the fault, even the ground star washer on the case. But getting worse as it warms up is a signature of dried up e-caps.
Warning proper contact cleaner is flammable, no smoking open flame or electricity turned on or off within 10 m of spray. The non-flammable kind of contact cleaner from the electrical supply house (brominated hydrocarbon) dissolves PVC & styrene plastics used in consumer products so don't pay the $25 a can to get it.
Last edited:
CALL Fender and ask for the drawings, they don't remotely have their whole collection on the web site. And LT is right, it is often the case that a Sunn model is identical to some Fender model.
Your amp MAY need new caps, but please don't just start swapping out lots of parts, we call that "guessing". Once you find the actual problem and can make the amp work right, THEN you can upgrade caps or whatever.
FIND OUT what your loud buzzing is. A failed filter cap will put large ripple on a power supply rail. So, when it buzzes, are the supplies ripply? DC on the output of an amp translates into a loud buzz, so when it starts, is there a large and growing DC offset on the speaker leads?
DC on the speaker also pushes the speaker cone one direction where it stays. Does your speaker start to move off center when teh buzz starts?
DO ANY of the controls affect the hum in ANY way? VOlume, tone?
When it happens, ball up your fist and whack the amp on top. Does that affect the hum in ANY way?
Your amp MAY need new caps, but please don't just start swapping out lots of parts, we call that "guessing". Once you find the actual problem and can make the amp work right, THEN you can upgrade caps or whatever.
FIND OUT what your loud buzzing is. A failed filter cap will put large ripple on a power supply rail. So, when it buzzes, are the supplies ripply? DC on the output of an amp translates into a loud buzz, so when it starts, is there a large and growing DC offset on the speaker leads?
DC on the speaker also pushes the speaker cone one direction where it stays. Does your speaker start to move off center when teh buzz starts?
DO ANY of the controls affect the hum in ANY way? VOlume, tone?
When it happens, ball up your fist and whack the amp on top. Does that affect the hum in ANY way?
- Status
- Not open for further replies.