Tweet
not sure what's causing this hum. owner said it started recently...before, all was normal and quiet. makes no difference if anything is plugged into the input jacks, and same hum present when plugged into effects return jack. volume/tone/reverb controls have no effect. no hum from effects send into another amp, and no hum from headphone jack. i wish i had a schematic...no response from hiwatt tech support yet. i might swap out the tda2050 just for fun. thanks for your help!
-
-
here's the schematic: HIWATT BULL30R.pdf
I replaced the TDA2050...no change. Hum is still present. Resoldered all the pots and jacks, and I tried a different speaker...no change. I metered the diodes and ICs, they all seem to be behaving normally. any ideas as to what could be going on? -
A bad ground connection? Is there no hum from the headphones or FX out? That pretty much eliminates most of the circuit.
Read the dc voltages on the inputs and outputs of the signal opamps. If you find anything over a few mV's might be a bad chip. Any of the ic's getting warm?Comment
-
First thing to check with a hum problem is the main Vdc power rails.
Are they holding up? Are the + & - voltages relatively the same?
Look for inapropriate amounts of Vac ripple.
A few 10's of mv AC is o/k.
The same goes for the power rails for the IC's.
In this case you would expect to see no ripple at all.Comment
-
-VCC = -15.9V
+VCC = 16.0V
no AC ripple on +/-VCC or B+/B-
this amp does not have .01uF caps C45-C46-C47-C48 installed across the rectifier diodes on page 4. would adding them help? I'll clip some in tonight and see.
Also, i think I might change out the 6 filter caps in the power amp section on page 4.Comment
Comment